WO2019086917A1 - Method and apparatus for determining the insulation resistance of dc network, and for potential reduction and increase of battery systems using functional earthing - Google Patents
Method and apparatus for determining the insulation resistance of dc network, and for potential reduction and increase of battery systems using functional earthing Download PDFInfo
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- WO2019086917A1 WO2019086917A1 PCT/HU2018/000046 HU2018000046W WO2019086917A1 WO 2019086917 A1 WO2019086917 A1 WO 2019086917A1 HU 2018000046 W HU2018000046 W HU 2018000046W WO 2019086917 A1 WO2019086917 A1 WO 2019086917A1
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- 238000009413 insulation Methods 0.000 title claims abstract description 165
- 238000000034 method Methods 0.000 title claims abstract description 48
- 230000009467 reduction Effects 0.000 title claims description 43
- 238000002347 injection Methods 0.000 claims abstract description 67
- 239000007924 injection Substances 0.000 claims abstract description 67
- 238000005259 measurement Methods 0.000 claims abstract description 52
- 230000001603 reducing effect Effects 0.000 claims abstract description 30
- 238000001514 detection method Methods 0.000 claims description 26
- 230000006866 deterioration Effects 0.000 claims description 4
- 230000005355 Hall effect Effects 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 abstract description 2
- 230000003247 decreasing effect Effects 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 47
- 238000004146 energy storage Methods 0.000 description 13
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
- H02S50/10—Testing of PV devices, e.g. of PV modules or single PV cells
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the object of the invention relates to a method for
- a current injection resistance meter may be used to implement the method, which preferably operates without switching off the equipment or device used to detect earth leakage, and fix, raise or decrease potential, and switching arrangement and apparatus for reducing or increasing the potential of battery systems.
- the value of the insulation resistance of the network compared to earth is desired to be maintained in the Riso 0 -200 kO range, and potential decrease or potential increase is understood to mean the reduction or increasing of the electric potential of the system as compared to earth.
- the main advantage is that an earth leakage does not involve a consumer power cut as a consequence of the interruption of the energy pathway. However, it is necessary to correct the fault occurring in the network, because if one more fault occurs in the network at another location, a short circuit will develop through it, which the short circuit protection facilities terminate by switching off the system.
- the determination of the insulation resistance of the network in direct current networks operating in this way causes problems in the case of symmetrical double earth leakages, as the method currently in use are based on voltage asymmetry measurement, and differential current measurement, and none of these are used in the case of a symmetrical double earth leakage occurring in one branch.
- the invention provides a solution for this.
- PV solar cells from the term photovoltaic
- PVM modules which provide a voltage of approximately 50 V.
- PV generators By connecting the strings in parallel high output, 20 kVA to several VA, units are created, which in accordance with international practices are hereinafter called PV generators.
- inverters supply current transformers (hereinafter: inverters), which by transforming the direct current of the PV generators to alternating current are connected to the alternating voltage network.
- One operation mode is the earth-independent insulated network operation method, in the case of which no single point of the solar cell system is fixed to earth potential, surge arresters provide protection against extreme
- the other operation mode is that the network is operated by creating a potential connection to earth with either the positive or negative pole via a resistance, a so-called "functional earth".
- the method according to the invention provides a solution for how to determine the insulation resistance (Riso) of networks with functional earth in the 0 to 200 kQ range without disconnecting the earth, even if the insulation fault occurs on a functionally earthed pole or point of the network.
- the potential increasing apparatus used for implementing the method reduces the risk of the PID effect to a minimum.
- the object of the invention also relates to a circuit arrangement implementing potential reduction or increasing of battery-based energy storage networks.
- the energy is then stored, then in the interest of better utilisation it is fed into the alternating current network at the necessary time.
- An example of such a system provided with a photovoltaic- supplied battery storage device is the Tesla Powerpack at the Mira Loma substation manufactured by Tesla and Southern California Edison (California) .
- This 20 MW/80 M h energy storage network facility is constructed from 396 Tesla Powerpacks and 48 Inverters.
- the Powerpack energy stores are established from hundreds of thousands of 73x13 mm small cylindrical batteries of a similar size to the
- BEES Battery Energy Storage System
- the measurement of insulation is carried out by performing insulation measurement in disconnected state. It is not necessary to disconnect the connection in order to perform the insulation measurement according to the invention.
- the invention elaborates a circuit arrangement that reduces or increase potential for use in battery systems, which by using the insulation resistance measurement method
- the battery facility on the one part, makes it possible to for the battery facility to operate at a lower voltage as compared to earth than in the case of the earthing of either of the poles, and, on the other part, determines the insulation resistance without interrupting the connection between the battery and the alternating current network, therefore, in this way more constant operation and availability can be provided.
- the voltage of the battery poles drops as compared to earth, the lower voltage places less demand on the insulations of the battery and the network,
- One of the modes of operation of insulated direct current networks is the mode when the network is insulated
- Insulation monitoring devices operate by injecting current through this.
- insulation monitoring devices are known as IMDs.
- IMDs Insulation monitoring devices for IT systems
- insulation monitoring devices must operate for both symmetrical and asymmetrical faults.
- earth leakage relays detect voltage asymmetry and according to this criterion, in the sense of this section of the IEC61557 these are not insulation monitoring devices.
- the network is not independent of earth, instead the positive or negative pole of the network, or the mid-point of two series resistors connected between the positive and negative poles, as a neutral point, is
- a mode of operation also exists that limits the range of the potential of the network as compared to earth, i.e. the operating voltage range of the network, for example by using 2 diodes connected in series from the negative pole in the direction of the positive pole, the common point of which is connected to earth.
- point 6.4.1.2. of the IEC 62548 standard determines the minimum insulation value of the system according to system size category. For example, in the case of a system with an output of ⁇ 20 kW the minimum insulation resistance value is 30 kQ, or, in the case of a system with an output of ⁇ 500 kW the minimum insulation resistance value for detection is 1 kQ.
- Such devices are known of, such as the ABB PV800 type inverter,
- the built in current detecting device is unable to measure the insulation resistance of, for example, 1 kQ -30 kQ. Therefore both the AEG Protect PV600/800, and the SMA SC1000CPXT devices switch off the functional earth every day, and then measure the insulation resistance of the network in switched-off state.
- FE functional earth resistance or GFDI
- FE or HRG functional earth resistance the earth connection of the potential increasing or reduction device
- Figures 1 to 3 present the earth status of the network, the network voltage conditions, and the deficiencies of the functional earthing solutions according to the state of the art and used in practice, where figure 1 shows potential fixing, figure 2a, 2b and 2c present potential increasing versions, and figure 3 presents potential reducing:
- FIG. 14 represents the individual units of the batty installation.
- Reference number 15 represents consumers interposed between the positive PI and the negative Nl poles.
- the figure also displays the connection resulting in the realisation of the functional earth Y-PK, the Rcsat connected resistances with reference numbers 17 and 18 and the functional earth resistance R F E « Also depicted is an insulation measuring device 19, and its injected current I inj , such as a Bender IRDH275, ABB CM-I S- IWN or similar known type.
- the Riso resistance represents the resultant of the
- the voltage U is represented on the vertical axis, and the various fault statuses are indicated on the horizontal axis .
- the figures IF represents a PV generator, which is created through the series and parallel connection of the PVM modules.
- the solar cell figures display an inverter 2 (insulated DC/AC transformer), alternating voltage network system 24, GFDI ground fault detection and interruption unit 3, which contains a current sensor 30 and interrupter 31 and
- FIG. 2B displays a current sensor and interrupter 3B, which contains a current sensor 30 and interrupter 31.
- the connections 10, 11 are the connectors of 3 and 3B, 90 represents a direct current potential shifting device, and 91 and 92 its connections.
- Reference number 21 represents the DC/AC inverter switch, and 22, 23 represent the connection points of the inverter.
- the earth potential has been indicated with an
- connection 13 shows the potential fixing in the figures.
- Daylight hours are shown in the figures using a sun symbol and nigh time hours are indicated with a moon symbol.
- the voltage of the non- fixed pole as compared to earth may vary and fluctuate significantly depending on the time of day and the amount of sunlight. This fluctuating voltage is indicated with a wavy line. The voltage during the day may rise to a maximum of as much as even 1500 V, and during night-time hours it is close to zero.
- the figures also show a fault R F occurring at a critical position representing an earth short circuit of 1 kQ to 30 kQ, which insulation resistance value needs to be
- connection point 11 which is connected to the earth potential point 13. It is also characteristic of solar cell solutions that the current is measured in the functional earthing circuit 3, 3B connected to the point 11 in order to show deterioration in the condition of the insulation and if the current reaches a certain value, then it is interrupted.
- connection Y-PK shown in figure 1 the electrical mid-point of the network is offset in the positive direction in the case of a fault affecting the negative side and in the negative direction in the case of a fault affecting the positive side to an extent depending on the magnitude of the insulation resistance.
- the extent of the displacement is smaller than if there were no Y-PK earth, therefore this operation mode is preferable than the isolated operation mode from the point of view of
- Figure 1 shows that in the case of the Y-PK functional earthing, in the case of faultless and simultaneous double earth leakage the asymmetrical voltage U AS z between earth and the poles does not occur, therefore voltage sensing earth leakage detectors are unsuitable for determining these .
- the insulation measuring device will measure the resultant of the Riso and of the R FE , which deviates from the real value of the Riso.
- the voltages of the network at PI and Nl as compared to earth, and the pathway Ii nj of the current flowing from the insulation measuring device have been indicated in figure 1.
- the earthing resistance R FE earths the common point of the connected resistances interposed between the positive and negative poles of the network. If the star connection is transformed into an equivalent delta connection using a method known from the basic techniques of electro-technology it is apparent that both the positive pole and the negative pole of the network are each earthed through a resistance of the order of lkQ to 30kQ, in this way the network operates with a practically limited current, double earth fault that does not result in interruption.
- the operation of the generally used insulation measuring instruments, which are connected between the positive and negative poles and to earth, is influenced by the interposed functional earthing Y-PK and as a result they do not display the real insulation
- Solutions are also known of that serve for interrupting earth leakages with a device interposed between the mutual, so-called neutral electrical midpoint of the resistances interposed between the positive pole and the negative pole of the network and earth, such as the Littelfuse SE-601 DC ground fault relay,
- the solar cell network IF feeds an insulated inverter 2 through the points PI and Nl via the switch 21 and the connection points 22, 23, which on transforming the direct voltage to alternating voltage it then feeds an alternating current network 24 or consumers.
- the resultant insulation resistance of the entire network is formed by the Riso.
- the negative pole Nl of the network IF is earthed with the GFDI relay 3 via the connections 10, 11.
- the disadvantage of the solution is this it is not suitable for detecting greater faults, e.g. 1 kQ - 30 kQ. It is also unsuitable for determining the insulation resistance of the system as compared to earth.
- the current between the IF (PV generator) and the earth potential 13 is monitored by a current detector 30, and when it reaches a specified value a switch 31 disconnects the potential increasing device from the solar cell network.
- R F 1 kQ -30 kQ in the figure, due to there being the same voltage at both points of the fault location resistance R F no current flows through it. Therefore, the installed current detector will not detect it and it will remain unnoticed. A second fault will result in short circuit current, which will even remain after the voltage increasing equipment has been switched off.
- the example presents the solution in patent registration number DE 202006008936 Ul (published: 17.08.2006), which raises the voltage of the negative pole Nl to approximately 50 V according to claim 3, and makes use of the current detection according to claim 5 to identify the earth fault.
- DE102015102310 Al (published: 18.08.2016) is also known, which connected in series with a potential increasing device provides a unit serving to measure insulation, which contains voltage inserted between the positive pole point of the PV generator and the potential increasing device. It measures the change to the voltage of the positive pole of the PV generator and the current flowing through the series-connected potential increasing device. It calculates the insulation resistance as the ratio of the voltage change and the current change.
- the method performs measurement sequentially at several time points due to the gradual charging up of the capacity of the network. In addition to this it also takes into consideration the momentary the pole voltages Ul and Nl, to which it assigns correction factors.
- connection 4 used for measuring the insulation uses active insulation measurement to determine the
- connection 4 is connected to the positive pole of the PV generator with connector 11, and to the negative pole of the PV generator with connector 19, and is
- the electrical mid-point of the network in these cases is close to earth potential, therefore in the case there is no fault no current flows through the measuring resistance connected in series with the additional voltage source interposed between earth and the common point of the connected resistances creating the electrical midpoint, but current flows in the case of a single or double fault.
- the insulation resistance may be calculated from the voltage of the measuring resistance and its current. If the measuring method according to EP 0654673B1 is to be used by patent number DE102015102310 in an offset potential network, current will flow through the measuring resistance even in the case of there being no fault, because there is a voltage of 500-1000 V between the electrical midpoint of the network and earth, which will drive a current even in the case of there being no fault.
- the method is not suitable for measuring the Riso insulation resistance of the network. If the measuring device is connected between the pole earthed through the above devices and earth, the Riso insulation resistance cannot be measured, instead the resistance of the earthing device is measured. Connection to the positive pole cannot be realised, because, on the one hand in the case of a 1500 V PV generator network the injection device must also have at least this level of voltage in order for current to flow through the injecting diode, and, on the other hand, with a current that makes it possible to measure the difference between the voltages without injection and the voltages measured in the course of injection. Such capacity would be required for this that could change to a measureable extent the voltage earthed through the GFDI, or the voltage measured between earth and the poles of a direct voltage system operating with
- the IMD device is able to measure symmetrical double earth faults at all on a network with potential increasing functional earthing, such as according to figure 2b.
- the potential increasing device raises the PI pole to 1000 V and during the night-time the Nl pole is at a voltage of around 900 V, assuming a symmetrical 30 kQ double earth fault, it is difficult to imaging that it can be measured.
- the potential increasing device and the double earth fault maintain the electrical midpoint of the network on about 950 V.
- the IMD device needs to inject current to this 950 V point, which is doubtful.
- the IMD device must have such resolution that is able to reliably distinguish the measured R G ES values, 2.982107 kQ and 2.727272 kQ, even in this low resistance range, the feasibility of which is also doubtful with an IMD device connected to the poles and earth.
- the difference between fault-free and faulty cases is just 0.25 kQ and within 10%.
- the current obtained from solar cell equipment is used to charge battery facilities directly or via an alternating current network, the energy is stored, then in the interest of putting it to better use it is returned to the alternating current network at the required time. It is of prime importance for the connection between the battery and the alternating current network to be available constantly and without interruption to assist the alternating current network to maintain its frequency. In the case of
- DC-coupled system In the case of these systems the battery system is also connected to the alternating current network via the solar cell system's central DC-AC inverter, in the case of which the battery storage system is connected to the central DC-AC inverter directly or via the rectifier.
- Patent registration number US 9,685,852 B2 (published:
- the object of the invention also relates to a switching arrangement implementing potential reducing or increasing in battery energy storage networks and a potential reducing and potential increasing device that has not been used to date in battery systems, which by using the insulation resistance measurement method according to the invention, on the one hand, makes it possible for the battery
- the task to be solved is the elaboration of a method and device for the determination of the value of the insulation resistance of insulated direct current network system using functional earthing, with which the insulation resistance of direct current networks operating with Y-PK functional earthing, potential fixing, increasing or reducing, as well as the value of the insulation resistance of symmetrical double earth faults can be determined. This is necessary in order to be able to correct faults in the case of
- the method should implement potential fixing, increasing or reducing, and with the exception of start-up it should not demand measurement of the voltages of the poles of the network, there should be no need for the measurement of the occasional very small current flowing through the potential increasing or reduction device, it should not significantly influence the normal operating conditions of the battery network, the earth fault current detection, or the
- the task also includes the elaboration of a circuit
- the task may be solved by creating a single functional earth that realises the earth connection of the potential fixing, increasing or reduction device with two series- connected functional earth resistances of the order of 1 kQ -30 kQ, and the value of the Riso insulation resistance of the network is calculated from the resistance measurement result (Rmert) of the earth-connected element of the functional earthing device with a current injection
- figure 5 indicates the current injection resistance measuring device 5 for measuring the resistance of the functional earth and determining the Riso.
- the reference numbers in the figures correspond to the reference numbers appearing in the figures presented in the case of the state of the art, the reference numbers of the new elements are presented in the description of the figures.
- the Y-PK connection shown in figure 4 is taken as an example in the case of battery networks.
- the functional earthing resistance R FE connected to the common point of the connected resistances 17, 18 installed at the poles is established from two series-connected resistances R, R2, such as from two 1.5 kO resistors.
- the insulation resistance of the network can be calculated from the measured value, because the Riso insulation resistance is connected in parallel to the resistance Rl via the 1.5 kQ resistance R2 and the
- FIG. 4a A second example is given in figure 4a, a solar cell network with GFDI relay earth fault detection and
- resistance measuring device 5 is connected between the earth connection point 11 of the GFDI relay functional earth according to figure 2a and earth 13 according to the connection in figure 4a.
- Figure 6 illustrates the connection arrangement serving for reducing the voltage as compared to earth of the battery network 6 and serving from determining the insulation resistance.
- Figure 7 illustrates the connection of the direct voltage source potential reducing and potential increasing device 7 appearing in the figure.
- GFDI relay Round Fault Detector, Interrupter
- New elements include the connection 4, the series
- Figure 5 presents the inclusion of the current injection resistance measuring device 5 and its internal connections.
- the current injection resistance measuring device 5 is connected to the two connections of the resistance Rl, with the interposing of the indicated current meter 9 and voltage meter 8.
- the current injection resistance measuring device 5 has a limiting resistance 54 and load resistance 57 series connected between its first connector 52 and second
- the determination of the insulation resistance as compared to earth of the insulated direct current network is carried out by creating a functional earth, continuous operation is maintained, in the event of voltage asymmetry occurring in the case of a single earth fault in the operating network or when current is started, and in the lack of asymmetry or current, in the interest of determining symmetrical faults, at the desired times or at regular intervals, such as every hour, the Rpot resultant of the series resistance Rl interposed between the connection 11 of the network and earth 13 and the parallel connected R2 resistance and the Rcsat connected resistances 17, 18 of the Y-PK connection and the value of the resultant of the Riso insulation resistances are measured (Rmert) using the current
- injection resistance measuring device 5 connected to the connections 12 and 13 of the resistance Rl, and the Riso insulation resistance of the network is calculated from the measured value.
- the measured value of the resistance Rl is calculated with the following formula:
- Riso (Rmert (Rl+R2+Rpot ) -Rl (R2+Rpot) ) / (Rl-Rmert) where Riso is the resultant insulation resistance of the network
- Rmert is the value of resistance Rl determined by
- Rl is the known actual value of the resistance Rl
- R2 is the known actual value of the resistance R2
- Rpot is the resultant of the Rcsat connected resistances If, for example in the case of a Y-PK connection, the value of the resistances Rl and R2 used is 1.5 kQ,
- the same method may be used in the case of a solar cell network, for example in the case of the solution used in the ABB PVS800 inverter
- Earth-independent battery networks frequently do not have current injection insulation measurement suitable for determining double earth faults. In the case of these networks it is preferable to establish the Y-PK functional earth for the duration of the measurement using the
- the direct voltage source for the current injection is the direct voltage source for the current injection
- resistance measuring device may be preferably established using a DC/DC or AC/DC voltage rectifier.
- the method may be used in both the case of direct voltage potential increasing and in the case of potential
- connection arrangement realising potential reduction or increase in battery energy storage networks 6 and a potential reduction device not yet used to date in battery system will be presented, (figure 6) , which may also be used connected in parallel in solar cell direct current network systems IF.
- the internal connections of the direct voltage source potential reducing or potential increasing device inserted in the figure are shown in figure 7, the elements and connection of which correspond to those in the direct voltage current source of the current injection resistance measuring device presented in figure 5, but in the interest of differentiation it is presented in a separate figure with different reference number and has the reference number 7.
- the potential reduction device makes it possible for the battery facility to operate at a lower voltage as compared to earth than an earthed or earth-independent insulated network, however, the insulation resistance of the system may also be determined. This lower voltages place less demand on the battery and on the insulation of the network.
- the device 7 is connected swapping the connections 71 and 72, in the case of which the negative pole Nl is raised to a positive voltage that equals the voltage of the internal direct voltage source 80 of the device 7.
- the reference number 6 represents the battery network system.
- the positive pole of the battery established by connecting the battery units 64 in series is designated API, and the negative pole AN1.
- the positive pole API is connected to the positive input 22 of the inverter 2 via the switch 62 and the connector 66, via the switch 21.
- the negative pole AN1 is connected to the negative input 23 of the inverter 2 through the switch 62 and the connector 67 via the switch 21.
- the battery network system 6 is also connected to the points PI and Nl of the solar cell network via the connectors 66, 67 and the switch 62, from which both systems supply the alternating current network 24 via the insulated central inverter 2.
- the direct voltage source device serves for reducing potential, which is connected between the negative pole 67 of the network system and the connector 10 of the current sensor and interrupter unit 3 via the connections 71 and 72.
- the internal voltage source 80 is set to the value of 500 V.
- the direct voltage source device 7 also serves for
- the voltage of the internal voltage source 80 is set to the value of 50 V.
- measuring method indicated in figures 4, 4a and 5 is used for the determination of the Riso insulation resistance of the battery network.
- Figure 7 shows the schematic connection of the direct voltage source potential reducing or potential increasing device 7.
- a limiting resistance 74 and a load resistance 77 is series connected between the first connection 72 and the second connection 71 of the direct voltage source device 7, and a diode 76 is connected in parallel to the load
- the measure may be taken that corresponds to the demands of the network use, such as alarm or disconnection.
- the insulation resistance of direct current networks operating with Y-PK functional earthing, with potential fixing, potential reducing and potential increasing, including the value of the insulation resistance of symmetrical double earth faults may be determined by using the method serving for determining the insulation
- the method realises the Y-PK functional earthing in battery systems, as well as the functional earthing in solar cell direct current networks, and realises potential fixing, increasing or reduction.
- faults may be resolved even in the case of symmetrical earth faults without the risk of false disconnection when the one earth fault occurs on the input of a microprocessor or other digital element.
- detecting instruments can be preferably used for fault detection by creating the Y-PK functional earth using the method for the duration of the measurement and performing the current injection resistance measurement.
- the advantage of this is that the Riso insulation resistance of networks with either a single or symmetrical double earth fault can be determined and the position of the fault can be located without the risk of false disconnection.
- the current injection resistance measuring device used contrary to other methods, does not increase but reduces the risk of false interruption, and it performs this at a voltage not resulting in under-voltage tripping.
- the measurement can be performed even by switching off certain network branches, which makes it possible to select the faulty branch with the potential increasing or potential reduction device, without switching off the functional earthing.
- connection arrangement realising potential reduction and the potential reduction device make it possible for the battery system to operated while placing a lower demand on the insulation, which increases the lifetime of the equipment as it slows down ageing of the insulation.
- the use of the method is also preferable in the case of PV systems constructed from solar cell types that are less sensitive to the PID effect, because there the insulation resistance can be determined and the faults branch selected even in networks with the commonly used GFDI (Ground Fault Detector, Interrupter) device, but without over-current protection on the earthed side or elements that can be disconnected, even if a single or even symmetrical earth fault occurs in parallel with the point of the network earthed with a GFDI, for example on the pole to which the GFDI (Ground Fault Detector, Interrupter) device is connected.
- GFDI Round Fault Detector, Interrupter
- the insulation resistance of solar cell systems operating with functional earth cannot be measured, therefore the standard states that if with functional earthing the insulation resistance cannot be measured, then the insulation of the solar cell network must be measured once a day by disconnecting the functional earth. As opposed to this, using the functional earth according to the invention the insulation resistance can be measured without disconnecting the earth.
- the Riso insulation resistance of a battery network can also be determined with the solution.
- the battery energy storage system can be connected to the alternating voltage network using the inverter of the solar cell network as well, which increases its use and does not require the installation of another inverter between the battery energy storage system and the alternating current network.
- the connection between the direct current battery and the alternating current network it is important for the connection between the direct current battery and the alternating current network to be constant, only in this way can it help maintain the frequency of the alternating current network.
- connection between a battery network containing batteries connected in series, as well as other types of DC-connected energy storage battery systems, and the alternating current network may be made more reliable and constant, even in a network supplied with GFDI earth fault protection, because in order to perform the insulation measurement of the direct voltage network it is not necessary to disconnect the DC/AC inverter.
- the measurement of insulation takes place with the functional earth and the connection in disconnected state. With the insulation measurement according to the invention it is not necessary to disconnect the connection. This provides the opportunity for the connection between the storage battery on the DC-connected battery network and the alternating current network to be continuous even when the insulation measuring process is being performed.
- the method according to the invention only measures the resistance of the approximately 1 kQ element connected to earth of the functional earth of the magnitude of 1 kQ-30 kQ whilst maintaining continuous operation.
- the current is determined by the voltage of the injecting device, its internal voltage and the value of the series- connected resistance Rl to be measured. This can be set to a range that can be easily measured (e.g. of the order of 10 mA) , and only changes to a small degree, and even flows, if there is an earth fault on the point (pole) of the network at earth potential, which is not true of the other solutions.
- the determination of the Riso insulation resistance does not significantly influence the normal operating conditions of the battery network, the earth fault current detection, or the operation of the solar cell network operating with potential increasing or potential reduction.
- the internal direct voltage current source 60 of the current injection resistance measuring device, and the internal direct voltage source 80 of the potential increasing or potential reduction device are established with a DC/DC or AC/DC voltage converter.
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Abstract
The invention relates to determining the value of the insulation resistance of battery and/or solar cell direct current network systems through functional earthing, and to decreasing or increasing the potential of battery systems. During the method according to the invention functionally earthed operation is created with two resistances (R1) and (R2) of the order of 1 kΩ -30 kΩ and the resultant of the earth-connected resistance (R1), the parallel-connected resistance (R2), the connected resistances (Rpot) of the potential fixing, increasing or reducing device and the network insulation resistance (Riso) is measured using a current injection resistance measuring device (5). During the measurement the value (Rmért), Rmért = (Uki-Ube) / (Iki-Ibe), is determined with the current injection resistance measuring device (5) connected to the resistance (R1) with the device in switched off and switched on states as the ratio of the voltage difference and current difference measured by the voltage meter (8) and current meter (9), and from the measured value (Rmért), the value of the insulation resistance of the network (Riso) is determined by calculation, using the following formula: Riso=(Rmért (R1+R2+Rpot ) -R1 (R2+Rpot) ) / (R1-Rmért). The subject of the invention also relates to a connection arrangement for reducing or increasing the voltage as compared to earth of battery network systems (6), and for the arrangement a direct voltage source device (7) for realising the voltage decrease or increase, which is installed between the negative pole (AN1) of the battery network and earth (13) via the GFDI earth fault current sensor and interrupter unit (3), the resistances R2 and R1 and current injection resistance measuring device (5).
Description
Method and apparatus for determining the insulation
resistance of a DC network, and for potential reduction and increase of battery systems using functional earthing The object of the invention relates to a method for
determining the value of the insulation resistance of battery and/or solar cell direct current network systems through functional earthing, a current injection resistance meter may be used to implement the method, which preferably operates without switching off the equipment or device used to detect earth leakage, and fix, raise or decrease potential, and switching arrangement and apparatus for reducing or increasing the potential of battery systems. In the present specification the value of the insulation resistance of the network compared to earth is desired to be maintained in the Riso 0 -200 kO range, and potential decrease or potential increase is understood to mean the reduction or increasing of the electric potential of the system as compared to earth.
The main technical areas of application are the following: - The direct current auxiliary facilities of electricity production:
In the field of electricity production and distribution the constancy of supply to the auxiliary facilities of the main equipment is essential, generally these are earth- insulated, earth isolated direct current networks, in these networks tripping does not occur in the case of the first earth fault. The main advantage is that an earth leakage does not involve a consumer power cut as a consequence of the interruption of the energy pathway. However, it is necessary to correct the fault occurring in the network,
because if one more fault occurs in the network at another location, a short circuit will develop through it, which the short circuit protection facilities terminate by switching off the system.
In the course of correcting an earth leakage fault, on the one hand, it is difficult to detect very small currents, and, on the other hand, the measuring voltages created in order to find the faulty branch may cause faulty operation at the inputs of the microprocessor devices supplied from the network.
Consequentially, according to a wide-spread solution the isolated direct current network supplying the main
equipment of the electricity networks are established so that two series impedances, usually resistances are
interposed between the positive and negative poles of the network, the common point of which is on the electric potential representing the electric centre point of the voltage of the network and the battery pack supplying it. This electrical centre point is fixed to the earth
potential via impedance. This circuit representing
functional earthing is called a Y-PK or T circuit in
Russian systems, (where Y or T refers to the switching of the connected three resistances) . This is called a Y-PK circuit in the specification.
However, the determination of the insulation resistance of the network in direct current networks operating in this way causes problems in the case of symmetrical double earth leakages, as the method currently in use are based on voltage asymmetry measurement, and differential current measurement, and none of these are used in the case of a
symmetrical double earth leakage occurring in one branch. The invention provides a solution for this.
- The other area of application of the solution are the networks of photovoltaic solar power plants. According to the general structure of solar cell equipment (PV solar cells from the term photovoltaic) photovoltaic solar cells are connected in series to create solar panels or modules (hereinafter referred to as PVM modules, which provide a voltage of approximately 50 V. By connecting these in series PV strings are established that provide a direct current voltage of 800-1000 V. By connecting the strings in parallel high output, 20 kVA to several VA, units are created, which in accordance with international practices are hereinafter called PV generators. These supply current transformers (hereinafter: inverters), which by transforming the direct current of the PV generators to alternating current are connected to the alternating voltage network. In the case of the operation of solar power plant systems established in this way endeavours are made to terminate the first fault by switching.
Many types of solution have been established for the operation of solar cell networks:
One operation mode is the earth-independent insulated network operation method, in the case of which no single point of the solar cell system is fixed to earth potential, surge arresters provide protection against extreme
voltages, and constant insulation measuring is performed on the network.
The other operation mode is that the network is operated by creating a potential connection to earth with either the positive or negative pole via a resistance, a so-called "functional earth".
In the case of solar cell networks these operation modes were established for the following reasons:
- Simple use with smaller (in the order of ohms) resistance using a (GFDI) Ground Fault Detector, Interrupter device, or with a higher resistance of 1 kQ - 30 kQ for the
following reasons:
- In the interest of avoiding PID (Potential Induced
Degradation) (output reduction) and TCO (Transparent
Conducting Oxides) corrosion risk.
- Reduction of the insulation level of solar cell networks by reducing the voltage of the network as compared to the earth.
The method according to the invention provides a solution for how to determine the insulation resistance (Riso) of networks with functional earth in the 0 to 200 kQ range without disconnecting the earth, even if the insulation fault occurs on a functionally earthed pole or point of the network. The potential increasing apparatus used for implementing the method reduces the risk of the PID effect to a minimum. The object of the invention also relates to a circuit arrangement implementing potential reduction or increasing of battery-based energy storage networks.
According to solutions becoming widespread today the current gained from solar cell equipment is used to charge battery installations either directly or by interposing an
2018/000046
- 5 - alternating voltage network, the energy is then stored, then in the interest of better utilisation it is fed into the alternating current network at the necessary time.
An example of such a system provided with a photovoltaic- supplied battery storage device is the Tesla Powerpack at the Mira Loma substation manufactured by Tesla and Southern California Edison (California) . This 20 MW/80 M h energy storage network facility is constructed from 396 Tesla Powerpacks and 48 Inverters. The Powerpack energy stores are established from hundreds of thousands of 73x13 mm small cylindrical batteries of a similar size to the
Lithium-ion batteries used in electric cars connected in series and parallel. This may be a Grid-Connected Solar System and Battery Energy Storage System (BEES) .
In the case of the operation of battery storage systems it is important for the connection between the direct current battery and the alternating current network to be
uninterruptible, because only in this way is it possible to maintain the frequency of the alternating current network. In the case of the present DC-connected solutions, the measurement of insulation is carried out by performing insulation measurement in disconnected state. It is not necessary to disconnect the connection in order to perform the insulation measurement according to the invention.
The invention elaborates a circuit arrangement that reduces or increase potential for use in battery systems, which by using the insulation resistance measurement method
according to the invention, on the one part, makes it possible to for the battery facility to operate at a lower voltage as compared to earth than in the case of the earthing of either of the poles, and, on the other part,
determines the insulation resistance without interrupting the connection between the battery and the alternating current network, therefore, in this way more constant operation and availability can be provided. In the case of reducing potential the voltage of the battery poles drops as compared to earth, the lower voltage places less demand on the insulations of the battery and the network,
therefore it is preferable from the point of view of the ageing of the insulation. In the case of increasing
potential in the case that the battery system is connected to the solar cell network in parallel the risk of TCO corrosion and of PID (Potential-Induced Degradation) output reduction can be minimised while operation may be carried out constantly, without interruption. It is important to note that this solution does not extend to those insulated direct current networks in which
operation with leakage to earth is not permitted, such as the high voltage equipment in motor vehicles, because they are covered by different prescriptions for life safety considerations.
The state of the art:
One of the modes of operation of insulated direct current networks is the mode when the network is insulated
independent of earth, in the case of which no single point of the battery network or the solar cell network is connected to earth potential, and continuous insulation measurement is performed on the network.
In the case of IT systems according to point 411.6.1 of the IEC 60364-4-41, according to the IEC 60364-4-41 point
411.3.2.1- notes 1 to 3 automatic fault correction is not generally necessary in the case of the occurrence of a first fault in electricity distribution, electricity production and transmission systems.
According to the IEC 61557-8-3.13 the international symbol of functional earthing is FE (Functional Earthing) , and according to the note this is the measuring connection to earth in the case of insulation monitoring devices.
Insulation monitoring devices operate by injecting current through this.
The requirements for insulation measuring are contained in the IEC 61557-8 (Insulation monitoring devices for IT systems) standard, insulation monitoring devices are known as IMDs. According to the IEC 61557-8 point 4.1, insulation monitoring devices must operate for both symmetrical and asymmetrical faults. According to remark 2 of the standard, the so-called earth leakage relays detect voltage asymmetry and according to this criterion, in the sense of this section of the IEC61557 these are not insulation monitoring devices.
According to another mode of operation of isolated direct current networks, the network is not independent of earth, instead the positive or negative pole of the network, or the mid-point of two series resistors connected between the positive and negative poles, as a neutral point, is
connected to earth via some sort of impedance with so- called "functional earthing", with the latter being called a Y-PK connection in this specification.
A mode of operation also exists that limits the range of the potential of the network as compared to earth, i.e. the operating voltage range of the network, for example by
using 2 diodes connected in series from the negative pole in the direction of the positive pole, the common point of which is connected to earth.
In the case of use with solar cells, it is important that disconnection take place when the first short circuit occurs .
In the case of solar cell systems point 6.4.1.2. of the IEC 62548 standard determines the minimum insulation value of the system according to system size category. For example, in the case of a system with an output of ≤20 kW the minimum insulation resistance value is 30 kQ, or, in the case of a system with an output of ≥500 kW the minimum insulation resistance value for detection is 1 kQ.
If in a network operating in the above operation modes (with standard functional earthing) it is not possible to measure the insulation, then it is prescribed that the insulation resistance of the network be measured every 24 hours by disconnecting the earth (usually by switching off the potential increasing or reduction device built into the inverter) .
Such devices are known of, such as the ABB PV800 type inverter,
DE_PVS800_57_HW_H_A4_screen . pdf,
the AEG Protect PV600/800 type inverter, and according to page 40 of
ahttps: //www. aegps.com/...PDFs... /BAL_PV.710_910_KOR_DE.pdf the active earth is switched off during the night when insulation measurement is performed.
This is how the SMA SCIOOOCPXT type inverters operate as well.
In the case of these devices, if there is an earth leakage
18 000046
fault on the earthed pole, the built in current detecting device is unable to measure the insulation resistance of, for example, 1 kQ -30 kQ. Therefore both the AEG Protect PV600/800, and the SMA SC1000CPXT devices switch off the functional earth every day, and then measure the insulation resistance of the network in switched-off state.
Each of the functionally earthed solutions according to the state of the art and presented in detail have a number of disadvantageous characteristics, which may be avoided with the present solution.
The disadvantages are as follows:
If an earth leakage occurs on a pole of the network that is connected to earth potential or at a point at earth
potential, its detection is uncertain using the techniques according to the state of the art, and in the case of a symmetrical double earth fault, the value of the insulation resistance cannot be measured.
If in this mode of operation traditional insulation
measurement methods are to be used in the case of unearthed networks, the measured result is false because the
functional earth (FE) resistance or GFDI, and the earth connection of the potential increasing or reduction device (FE or HRG functional earth resistance) is installed in parallel to the network's Riso insulation resistance, which falsifies the measurements.
For this reason, in the case of these networks earth leakage detection methods based on current measurement are frequently used, with which, however, the objective cannot always be achieved.
Figures 1 to 3 present the earth status of the network, the network voltage conditions, and the deficiencies of the functional earthing solutions according to the state of the art and used in practice, where figure 1 shows potential fixing, figure 2a, 2b and 2c present potential increasing versions, and figure 3 presents potential reducing:
The figures are as follows:
1. Battery network with Y-PK functional earthing
2a. Solar cell network with GFDI relay functional earthing and disconnection.
2b. Solar cell network with potential increasing connected to direct current Pi, with earth leakage detection and disconnection.
2c. Solar cell network with potential increasing connected to direct current Nl, with earth leakage detection and disconnection.
3. Solar cell network with direct current potential
reduction, with earth leakage detection and disconnection.
Uniformly in the figures the positive pole is marked with PI and the negative pole with Nl. Figure 1 shows a
schematic view of the battery network 1A. Reference number 14 indicated in the figure represents the individual units of the batty installation. Reference number 15 represents consumers interposed between the positive PI and the negative Nl poles. The figure also displays the connection resulting in the realisation of the functional earth Y-PK, the Rcsat connected resistances with reference numbers 17 and 18 and the functional earth resistance RFE« Also depicted is an insulation measuring device 19, and its injected current Iinj, such as a Bender IRDH275, ABB CM-I S-
IWN or similar known type.
The Riso resistance represents the resultant of the
insulation resistance of the network as compared to earth. The solutions realising potential fixing, potential increasing or potential reducing fix a point or pole of the network to a fixed voltage value as compared to earth, which has been indicated with a horizontal line in the figures .
The voltage U is represented on the vertical axis, and the various fault statuses are indicated on the horizontal axis .
In figure 1 in the case of the Y-PK connection the voltages of the poles of the network, in the case of fault-free and simultaneous double earth leakage, are nearly symmetrical as compared to earth, in the case of single faults the magnitudes of the pole voltages differ and asymmetrical voltage UAsz occurs. This shows the potential of the electrical mid-point of the network as compared to earth.
In the case of solar cell networks, in the figures IF represents a PV generator, which is created through the series and parallel connection of the PVM modules. The solar cell figures display an inverter 2 (insulated DC/AC transformer), alternating voltage network system 24, GFDI ground fault detection and interruption unit 3, which contains a current sensor 30 and interrupter 31 and
switches off the inverter 3. Figure 2B displays a current sensor and interrupter 3B, which contains a current sensor 30 and interrupter 31. The connections 10, 11 are the connectors of 3 and 3B, 90 represents a direct current potential shifting device, and 91 and 92 its connections.
Reference number 21 represents the DC/AC inverter switch, and 22, 23 represent the connection points of the inverter. The earth potential has been indicated with an
international earth symbol and the reference number 13. The connection between the connection 11 of the GFDI 3 and the current sensor and interrupter 3B and the earth
connection 13 shows the potential fixing in the figures. Daylight hours are shown in the figures using a sun symbol and nigh time hours are indicated with a moon symbol. In the case of the individual versions the voltage of the non- fixed pole as compared to earth may vary and fluctuate significantly depending on the time of day and the amount of sunlight. This fluctuating voltage is indicated with a wavy line. The voltage during the day may rise to a maximum of as much as even 1500 V, and during night-time hours it is close to zero.
The figures also show a fault RF occurring at a critical position representing an earth short circuit of 1 kQ to 30 kQ, which insulation resistance value needs to be
specified, because if this is not performed, and a second fault occurs, this may cause a high-current double earth fault within the system, which involve an increased risk of fire.
Each figure includes a connection point 11, which is connected to the earth potential point 13. It is also characteristic of solar cell solutions that the current is measured in the functional earthing circuit 3, 3B connected to the point 11 in order to show deterioration in the condition of the insulation and if the current reaches a certain value, then it is interrupted.
Presentation of the individual solutions:
1. Battery network with functional earthing Y-PK.
In the case of the connection Y-PK shown in figure 1 the electrical mid-point of the network is offset in the positive direction in the case of a fault affecting the negative side and in the negative direction in the case of a fault affecting the positive side to an extent depending on the magnitude of the insulation resistance. The extent of the displacement is smaller than if there were no Y-PK earth, therefore this operation mode is preferable than the isolated operation mode from the point of view of
disturbance resulting in false interruption.
Figure 1 shows that in the case of the Y-PK functional earthing, in the case of faultless and simultaneous double earth leakage the asymmetrical voltage UASz between earth and the poles does not occur, therefore voltage sensing earth leakage detectors are unsuitable for determining these .
It can also be seen from the figure that in addition to the Riso earth connection, it also has another two earth connections. The one is the functional earthing RFE, the other is the current injection insulation measuring device used. In this way the insulation measuring device will measure the resultant of the Riso and of the RFE, which deviates from the real value of the Riso. The voltages of the network at PI and Nl as compared to earth, and the pathway Iinj of the current flowing from the insulation measuring device have been indicated in figure 1.
In the case of the functional earthing Y-PK the earthing resistance RFE earths the common point of the connected resistances interposed between the positive and negative poles of the network. If the star connection is transformed
into an equivalent delta connection using a method known from the basic techniques of electro-technology it is apparent that both the positive pole and the negative pole of the network are each earthed through a resistance of the order of lkQ to 30kQ, in this way the network operates with a practically limited current, double earth fault that does not result in interruption. The operation of the generally used insulation measuring instruments, which are connected between the positive and negative poles and to earth, is influenced by the interposed functional earthing Y-PK and as a result they do not display the real insulation
resistance of the network. Therefore, in the case of these networks current or current difference evaluation is used: e.g. the Russian EKRA (www.ekra.ru) EKRA-SKI device,
Magnit' s (www.magnit-nsk. ru) CEHCOP device,
Elektrocbit' s (www.relpro.ru/kontakty) PK-31 devices.
Solutions are also known of that serve for interrupting earth leakages with a device interposed between the mutual, so-called neutral electrical midpoint of the resistances interposed between the positive pole and the negative pole of the network and earth, such as the Littelfuse SE-601 DC ground fault relay,
Littelfuse Protection Relays TN-GF06_SE-601-DC-Ground-
Fault-Protection.pdf
The latter, on the one hand, do not make continued
operation without interruption possible by maintaining the earth fault, and, on the other hand, they do not work in the case of a symmetrical double earth fault, because current does not flow through them.
The disadvantage of the known solutions is that in the case of a symmetrical double earth fault it is not possible to
measure the insulation resistance with these devices, because no current difference occurs in the case of a symmetrical double earth fault in a branch.
The insulation measuring method and device operating on the basis of Hungarian patent registration number
230628 (published: 28.08.2015) is also known. When using it the current injection device must be interposed according to claim 1 either between the connection of the negative pole Nl of the network and earth, or between the positive pole PI of the network and earth, and the voltage of the device and the current flowing through the device must be measured. The insulation resistance is calculated from the ratio of these. If the method is to be used in a network with Y-PK functional earthing, a bad insulation measurement result is obtained even in the case when there are no faults, because instead of the Riso insulation resistance, the value of the functional earthing resistance RFE is measured.
2a. Solar cell network with GFDI relay functional earth and interruption.
The solar cell network IF feeds an insulated inverter 2 through the points PI and Nl via the switch 21 and the connection points 22, 23, which on transforming the direct voltage to alternating voltage it then feeds an alternating current network 24 or consumers. The resultant insulation resistance of the entire network is formed by the Riso. The negative pole Nl of the network IF is earthed with the GFDI relay 3 via the connections 10, 11. The GFDI relay 3 switches off with switches 31, 21 above a certain threshold value. In the figure the critical position is the negative
pole Nl, if an RF fault occurs there no current flows through the GFDI relay, therefore the RF fault (RF = 1 kQ - 30 kQ in the figure) cannot be measured, and remains undetected. See so-called Blind-Spot fire events (e.g. 5 April 2009, Bakersfield, California, 16 April 2011, Mont Holly, North Carolina) .
Certain solutions, such as the solution described in the US patent number US 2015/0054523A1 (published: 26.02.2015) endeavour to reduce this risk. This makes use of reference impedance connected in series with the current detector and serving for detecting faults, which is for determining whether there is a low resistance earth fault on the earthed pole in solar cell systems. By using voltages at various frequencies and by measuring the current of the current detector, it determines the impedance of the earthing current path, which it then compares to the reference impedance.
The disadvantage of the solution is this it is not suitable for detecting greater faults, e.g. 1 kQ - 30 kQ. It is also unsuitable for determining the insulation resistance of the system as compared to earth.
2b. Solar cell network with potential increasing connected to direct voltage PI, with earth leakage detection and interruption.
The solution is presented by patent number EP 2086020B1
(published: 05.08.2009). According to claim 1 of the patent the positive pole is raised as compared to the earth potential with a direct voltage current source 90.
According to claim 15 of the patent the current between the IF (PV generator) and the earth potential 13 is monitored by a current detector 30, and when it reaches a specified
value a switch 31 disconnects the potential increasing device from the solar cell network.
If an earth fault occurs in the intermediate part of the network (PV generator) , such as near to the earth
potential, RF = 1 kQ -30 kQ in the figure, due to there being the same voltage at both points of the fault location resistance RF no current flows through it. Therefore, the installed current detector will not detect it and it will remain unnoticed. A second fault will result in short circuit current, which will even remain after the voltage increasing equipment has been switched off.
The devices distributed by PADCON GmbH (Germany) also operate according to this same principle according to their catalogues, e.g.
2759Flyer_PID_KILLER_DE_web_3.pdf
2755Float_Controller_CI_30_DE.pdf
2c. Solar cell network with potential increasing connected to direct voltage Nl, with earth leakage detection and interruption.
The example presents the solution in patent registration number DE 202006008936 Ul (published: 17.08.2006), which raises the voltage of the negative pole Nl to approximately 50 V according to claim 3, and makes use of the current detection according to claim 5 to identify the earth fault. The figure presents that in the case of a negative-side Nl RF = 30 kQ earth fault, or in the case of a 30 kQ earth fault affecting any pole in the night-time period only a current of 1.666 mA flows. Current significantly greater than this can flow during normal operation, or in the case of a 300 kQ positive side earth fault that does not yet count as a fault. Information on the above earth fault
cannot be obtained by measuring the currents, nor can the value of the insulation resistance be determined.
Figure 3 Potential decrease with direct voltage.
The solution is disclosed by patent registration number US 8,729,444 B2 (published: 29.09.2011) and by patent
registration number DE 102010012294 (published:
29.09.2011). Claims 8, 9 and 10 of these patents also describe interruption and fault alarm devices operating with current detection.
However, a problem occurs if during the day the PV
generator operates at about 1000 V, and an RF earth fault occurs at the PI pole or at the intermediate part of the PV generator in the proximity of the earth potential. In these cases there is almost no voltage difference on the fault location resistance RF, therefore no current flows through it. The detectors according to claims 8, 9, and 10 do not detect current either, therefore the fault can remain for an extended period. In the case of a fault occurring elsewhere short circuit current flows and then even if the current detector 3B switches off the voltage reducing voltage source 90, the double earth fault results in short circuit current within the PV generator.
The solution included in patent registration number
DE102015102310 Al (published: 18.08.2016) is also known, which connected in series with a potential increasing device provides a unit serving to measure insulation, which contains voltage inserted between the positive pole point of the PV generator and the potential increasing device. It measures the change to the voltage of the positive pole of the PV generator and the current flowing through the
series-connected potential increasing device. It calculates the insulation resistance as the ratio of the voltage change and the current change.
Riso= U1-U3/I1-I3
The method performs measurement sequentially at several time points due to the gradual charging up of the capacity of the network. In addition to this it also takes into consideration the momentary the pole voltages Ul and Nl, to which it assigns correction factors.
According to point (0019) of the specification and the figures, the connection 4 used for measuring the insulation uses active insulation measurement to determine the
condition of the insulation according to that described in patent registration number EP 0654673B1, for example, and for this the connection 4 is connected to the positive pole of the PV generator with connector 11, and to the negative pole of the PV generator with connector 19, and is
connected to earth 13 through the unit 3. It is doubtful that the solution can be used for determining an RF = 1 kQ -30 kQ earth fault close to earth potential shown in figure 2b. In the case of a 30 kQ earth fault, assuming Ul= 1000 V and a supplementary voltage of 50 V, this results in U3= 950 V. In the case of potential increase Ul no current will flow at the location of the fault, because the fault position is at earth potential.
11= 0 mA, 13 = 1.666 mA
Riso= U1-U3/I1-I3 = (1000 -950) / (0-1.666) mA = 30 kQ, the result may be correct, but it is doubtful how the current range of 0 -1.666 mA can be differentiated from the operating currents in the potential increasing device that are possible of an order greater than this (of a magnitude
of 30-100 mA according to point 0018 of the specification) . In the case of earth-independent networks the active insulation measurement methods referred to are suitable even for measuring simultaneous double insulations faults. The electrical mid-point of the network in these cases is close to earth potential, therefore in the case there is no fault no current flows through the measuring resistance connected in series with the additional voltage source interposed between earth and the common point of the connected resistances creating the electrical midpoint, but current flows in the case of a single or double fault. The insulation resistance may be calculated from the voltage of the measuring resistance and its current. If the measuring method according to EP 0654673B1 is to be used by patent number DE102015102310 in an offset potential network, current will flow through the measuring resistance even in the case of there being no fault, because there is a voltage of 500-1000 V between the electrical midpoint of the network and earth, which will drive a current even in the case of there being no fault.
If the Rr = 1 kQ fault indicated in figure 2b occurs at the positive pole of the solar cell network, the current of the potential increasing device reaches the critical current value set for disconnection, it disconnects and due to this the insulation resistance cannot be measured without switching off the potential increasing device.
The insulation measuring method and device operating on the basis of Hungarian patent registration number 230628
(published: 28.08.2015) is also known of. In the course of using it the current injection device must be interposed either between the negative pole connection Nl of the
network and earth, or between the positive pole connection PI of the network and earth according to claim 1, and the voltage of the device and the current flowing through the device must be measured. The insulation resistance is calculated from the ratio of these.
In the case of a solar cell network operating with a potential increasing or reduction device the method is not suitable for measuring the Riso insulation resistance of the network. If the measuring device is connected between the pole earthed through the above devices and earth, the Riso insulation resistance cannot be measured, instead the resistance of the earthing device is measured. Connection to the positive pole cannot be realised, because, on the one hand in the case of a 1500 V PV generator network the injection device must also have at least this level of voltage in order for current to flow through the injecting diode, and, on the other hand, with a current that makes it possible to measure the difference between the voltages without injection and the voltages measured in the course of injection. Such capacity would be required for this that could change to a measureable extent the voltage earthed through the GFDI, or the voltage measured between earth and the poles of a direct voltage system operating with
potential increase or potential decrease. Neither condition can be realised from a technical point of view.
A method is known of from patents with registration numbers DE 102011084219 and US20130088240A1 (published: 11.04.2013) that takes into consideration the distorting effect of measuring functional earthing resistance (designated high resistance grounding RHRG in the specification) so that the value measured with a current injection IMD insulation
measuring device is divided between the RHRG resistances connected in parallel with the Riso insulation resistance in correspondence with the parallel connected resistances. Riso = (RGESXRHRG) / (¾RG~RGES)
According to the specification and figure 1 of the patent it wishes to determine the RGES resultant insulation
resistance using an IMD device connected to the positive and negative poles and to the PE conductor, including, according to claim 3, the symmetrically falling insulation resistance.
If the method is to be used in the case of the Y-PK
connected functional earthing according to figure 1, in the case of symmetrical double earth faults occurring in the Riso 0-200 kQ range, it is difficult to imagine that the value of the 200 kQ double earth fault could be measured using the IMD device. In a fault-free case the IMD device measures the value of the artificial double earth fault created with the functional earth. The double earth fault occurring in parallel with this falling in the Riso = 0-200 kQ range to be measured only changes the RGES resultant insulation resistance value by a few %, which cannot be distinguished with the IMD device.
It is doubtful that the IMD device is able to measure symmetrical double earth faults at all on a network with potential increasing functional earthing, such as according to figure 2b.
In this case if the potential increasing device raises the PI pole to 1000 V and during the night-time the Nl pole is at a voltage of around 900 V, assuming a symmetrical 30 kQ double earth fault, it is difficult to imaging that it can be measured. The potential increasing device and the double
earth fault maintain the electrical midpoint of the network on about 950 V. The IMD device needs to inject current to this 950 V point, which is doubtful.
If the GFDI relay according to figure 2a with RHGR = 3 kQ functional earthing is examined, the measureable resultant insulation resistance is
from the formula RGES - l/(l/Riso +1/RHRG) in a fault-free case, if Riso+= 1ΜΩ, Riso-= 1ΜΩ
RGES = 2.982107 kQ.
In a network with a 20 k inverter it is necessary to measure a 30 kQ fault even if the fault is on the negative pole, because the GFDI in this case is ineffective. In this case
RGES = 2.727272 kQ
The IMD device must have such resolution that is able to reliably distinguish the measured RGES values, 2.982107 kQ and 2.727272 kQ, even in this low resistance range, the feasibility of which is also doubtful with an IMD device connected to the poles and earth. The difference between fault-free and faulty cases is just 0.25 kQ and within 10%.
According to recently emerging solutions the current obtained from solar cell equipment is used to charge battery facilities directly or via an alternating current network, the energy is stored, then in the interest of putting it to better use it is returned to the alternating current network at the required time. It is of prime importance for the connection between the battery and the alternating current network to be available constantly and without interruption to assist the alternating current network to maintain its frequency. In the case of
facilities charged with current obtained from solar cell
equipment, an economic solution is the so-called DC-coupled system. In the case of these systems the battery system is also connected to the alternating current network via the solar cell system's central DC-AC inverter, in the case of which the battery storage system is connected to the central DC-AC inverter directly or via the rectifier.
Patent registration number US 9,685,852 B2 (published:
05.01.2017) also contains such a DC-coupled uninterruptible system control. According to the current state of the art, as already presented on page 8 of this specification, the measurement of the insulation of a solar cell system takes place with the inverted switched off and changed from GFDI relay mode to insulated mode, with this the connection between the battery and the alternating current network is also disconnected, therefore, periodically the uninterrupted operation according to the patent and the possibility of connecting the battery to the alternating current network is lost. It is known that AC-connected battery systems operate in earth-independent isolated operation mode.
The method serving for measuring the insulation resistance of battery systems presented in patent specification registration number US 2013/0027049 Al (published:
31.01*2013) is known of, which inserts resistance
alternately between the pole voltages of the battery system and earth and calculates the value of the insulation resistance of the system from the pole voltages compared to earth. This may be used in earth-independent operation
mode, but not in potential increase or potential increase operation modes.
Also known of are the solutions presented in patent
applications registration number US 2017/0093156 Al
(published: 30.03.2017) and registration number US
2017/0093157 (published: 30.03.2017), which relate to possible structural solutions of an interacting solar cell network system and battery installation system. With respect to the battery installations these contain an earth-connected solution with differential current
detection with a GFCI type B device (GFCI ground fault circuit interrupter) , (elements number 122 and 210 in figure IB and figure 2), and an earth-independent solution. In the case of the earth-connected solution the detection of high-resistance symmetrical double earth faults is not possible by using GFCI differential current, because there is no discernable difference between the faulty and fault- free states. The specification does not contain a GFDI solution. The object of the invention also relates to a switching arrangement implementing potential reducing or increasing in battery energy storage networks and a potential reducing and potential increasing device that has not been used to date in battery systems, which by using the insulation resistance measurement method according to the invention, on the one hand, makes it possible for the battery
installation to operate at a lower voltage as compared to earth than in the case one of the poles is earthed, and, on the other hand, makes it possible to determine the
insulation resistance without interrupting the connection
between the battery and the alternating current network. In this way more constant operation and availability can be ensured. In the case of potential reduction the voltage of the battery poles as compared to earth falls, the lower voltage places a lower demand on the insulation of the battery and the network, therefore it is preferable from the point of view of the ageing of the insulation.
In the case of an increase in voltage with the battery system connected in parallel with the solar cell network it may operate with the risk of TCO corrosion and PID
(Potential Induced Degradation) being minimised.
With consideration to the state of the art the tasks to be solved are as follows:
The task to be solved is the elaboration of a method and device for the determination of the value of the insulation resistance of insulated direct current network system using functional earthing, with which the insulation resistance of direct current networks operating with Y-PK functional earthing, potential fixing, increasing or reducing, as well as the value of the insulation resistance of symmetrical double earth faults can be determined. This is necessary in order to be able to correct faults in the case of
symmetrical earth faults whilst maintaining the advantages of Y-PK functional earthing without the risk of false disconnection, when the one earth fault occurs on the input of a microprocessor or digital element.
The method should implement potential fixing, increasing or reducing, and with the exception of start-up it should not demand measurement of the voltages of the poles of the network, there should be no need for the measurement of the
occasional very small current flowing through the potential increasing or reduction device, it should not significantly influence the normal operating conditions of the battery network, the earth fault current detection, or the
operation of a solar cell network operating with potential increasing or potential reduction, at the same time it should also make it possible to measure the Riso insulation resistance compared to earth of the battery or solar cell network systems without disconnecting the potential fixing, potential increasing or potential reduction device or equipment realising the functional earthing. Viewing the regular determination of the Riso insulation resistance, e.g. every hour, as quasi-continuous it should be possible to react to faults that cannot be identified with the present solutions in good time.
With the use of the method the output reducing effect of PID (Potential-Induced Degradation) is minimised.
With the method, in the case of solar cell types that are less sensitive to the PID effect, even in the case of networks that, in many cases, are earthed with a GFDI, it should be possible to determine the insulation resistance even in the case a fault occurs on the earthed pole, if a single or even symmetrical earth fault occurs in parallel with it . The task also includes the elaboration of a circuit
arrangement that realises potential reduction or increasing in battery energy storage networks and a potential reducing and potential increasing device that in the case of potential reduction makes it possible for the battery facility to operate at a lower voltage as compared to earth, as either an earthed or earth-independent insulated
network. This lower voltage places a smaller demand on the insulation of the battery and the network. In the case of operation in parallel with a solar cell system sensitive to the PID effect, it should realised an increase in voltage as compared to earth in the interest of reducing the PID effect, in which case it should raise the negative pole Nl of the system to a positive voltage as compared to earth. At the same time it should be possible to determine the insulation resistance of the system in both cases, and the battery system should be able to connect to the alternating voltage network with the inverter of the solar cell system.
The basic idea behind solving the tasks detailed above is that the task may be solved by creating a single functional earth that realises the earth connection of the potential fixing, increasing or reduction device with two series- connected functional earth resistances of the order of 1 kQ -30 kQ, and the value of the Riso insulation resistance of the network is calculated from the resistance measurement result (Rmert) of the earth-connected element of the functional earthing device with a current injection
resistance measuring device.
The solutions of the task are shown in figures 4, 4a, 5, 6 and 7. The figures are as follows:
4. Measurement of the Y-PK functional earth resistance of a battery network in order to determine the Riso.
4a. Solar cell network with GFDI relay earth fault
detection and interruption, as well as with potential increasing and functional earthing resistance measurement in order to determine the Riso.
5. Current injection resistance measuring device with the
measurement of the functional earth resistance in order to determine the Riso.
6. Circuit arrangement for reducing or increasing the voltage as compared to earth of battery network systems and the connection of a functional earth resistance measuring device.
7. Direct voltage source potential reducing or increasing device connection.
The connection of the device is indicated in figures 4 and 4a, and figure 5 indicates the current injection resistance measuring device 5 for measuring the resistance of the functional earth and determining the Riso. The reference numbers in the figures correspond to the reference numbers appearing in the figures presented in the case of the state of the art, the reference numbers of the new elements are presented in the description of the figures.
The Y-PK connection shown in figure 4 is taken as an example in the case of battery networks.
The functional earthing resistance RFE connected to the common point of the connected resistances 17, 18 installed at the poles is established from two series-connected resistances R, R2, such as from two 1.5 kO resistors.
If from between the two resistors the value of the
resistance Rl connected to earth is measured during operation, the insulation resistance of the network can be calculated from the measured value, because the Riso insulation resistance is connected in parallel to the resistance Rl via the 1.5 kQ resistance R2 and the
connected resistances 17, 18. As the insulation resistance changes the measureable resultant resistance also changes, from which the value of the insulation resistance can be
calculated.
A second example is given in figure 4a, a solar cell network with GFDI relay earth fault detection and
interruption, as well as with potential increasing and functional earthing resistance measurement in order to determine the Riso.
In the case of this solution the current injection
resistance measuring device 5 is connected between the earth connection point 11 of the GFDI relay functional earth according to figure 2a and earth 13 according to the connection in figure 4a.
Figure 6 illustrates the connection arrangement serving for reducing the voltage as compared to earth of the battery network 6 and serving from determining the insulation resistance. Figure 7 illustrates the connection of the direct voltage source potential reducing and potential increasing device 7 appearing in the figure.
List of figures:
1. Battery network with Y-PK functional earthing.
2a. Solar cell network with GFDI relay functional earthing and interruption.
2b. Solar cell network with potential increasing, earth fault detection and disconnection connected to direct voltage PI.
2c. Solar cell network with potential increasing, earth fault detection and disconnection connected to direct voltage Nl.
3. Solar cell network with direct voltage potential reduction, earth fault detection and disconnection.
4. The measurement of the Y-PK functional earth resistance
of a battery network in order to determine the Riso.
4a. Solar cell network with GFDI relay earth fault
detection and disconnection, as well as with potential increase and functional earth resistance measuring in order to determine the Riso.
5. Current injection resistance measuring device with the measurement of the functional earth resistance in order to determine the Riso.
6. Connection arrangement for the reduction or increasing of the voltage as compared to earth of battery network systems and the connection of a functional earth resistance measuring device.
7. Connection of a direct voltage source potential reducing or potential increasing device.
Explanation of the more important reference numbers
appearing in the figures:
1A. Battery network.
IF. Solar cell network.
2. Insulated DC/AC inverter.
3. GFDI relay (Ground Fault Detector, Interrupter) .
3B. Earth fault current detector and interrupter.
4. Current injection resistance measuring device
connection.
5. Current injection resistance measuring device for measuring functional earth resistance.
6. Solar cell battery network.
7. Direct voltage source device.
8. Voltage meter.
9. Current meter.
The methods of implementation of the invention are detailed with the help of figures 4, 4a, 5, 6 and 7:
The reference numbers in the figures are uniform, and correspond to the reference numbers used in the figures presenting the state of the art.
New elements include the connection 4, the series
resistances Rl and R2 interposed between its connection 11 and earth 13, the common point of the two resistances 12, the current injection resistance measuring device 5, which serves for measuring the resistance Rl and the parallel connected resistance R2, and the Rcsat resistances 17, 18 as well as the resultant of the Riso (Rmert) , the direct voltage measuring device 8 serving for measuring the voltage and current of the current injection resistance measuring device 5, and the direct current measuring device 9, the connection points 51, 52 of the current injection resistance measuring device 5. The elements 54, 55, 56, 57, 58, 59, and 60 that were presented in the connection figure 5.
The elements 6, 7, 66, 67, 63, 64, 65, API, AN1, 71, 72, 74, 75, 76, 77, 78, 79 and 80 included in figures 6 and 7 were also detailed in figures 6 and 7.
In the following an example of the essence of the solution according to the invention will be presented in the case of battery systems and Y-PK functional earthing for the determination of the Riso insulation resistance. The connection is indicated in figure 4, and the current injection resistance measuring device 5 for the measurement of the functional earth resistance and the Riso is
presented in figure 5.
The connection of the current injection resistance
measuring device serving for measuring the resultant Rpot of the resistance Rl and the parallel connected resistance
R2 and of the Rcsat resistances 17, 18 and the resultant of the Riso (Rmert) and the device are presented in detail through the presentation of preferable embodiment with reference to the attached schematic figures, where in figure 4 the interposing of the resistance Rl and R2 required for measurement, the connections 51, 52 of the current injection resistance measuring device 5, as well as the connection U= of the voltage meter 8 and connection 1= of the current meter 9 required for determining the
resistance Rl, and the connection possibilities 10 to the networks indicated in figures 1, 2a, 2b, 2c, 3, 4, 4a and 6 and the connection to earth 13 are shown.
Figure 5 presents the inclusion of the current injection resistance measuring device 5 and its internal connections. The current injection resistance measuring device 5 is connected to the two connections of the resistance Rl, with the interposing of the indicated current meter 9 and voltage meter 8.
The current injection resistance measuring device 5 has a limiting resistance 54 and load resistance 57 series connected between its first connector 52 and second
connector 51, and a diode 56 is connected in parallel with the load resistance 57, furthermore it also has a direct voltage source 60, the positive pole connection of which voltage source 60 is connected to the common connection 55 of the restricting resistance 54, the diode 56 and the load resistance 57 through the Kl switch 59 and rectifying diode 58, and its negative pole connection is connected to the second connector 51 of the current injection resistance measuring device 5.
The determination of the insulation resistance as compared to earth of the insulated direct current network is carried out by creating a functional earth, continuous operation is maintained, in the event of voltage asymmetry occurring in the case of a single earth fault in the operating network or when current is started, and in the lack of asymmetry or current, in the interest of determining symmetrical faults, at the desired times or at regular intervals, such as every hour, the Rpot resultant of the series resistance Rl interposed between the connection 11 of the network and earth 13 and the parallel connected R2 resistance and the Rcsat connected resistances 17, 18 of the Y-PK connection and the value of the resultant of the Riso insulation resistances are measured (Rmert) using the current
injection resistance measuring device 5 connected to the connections 12 and 13 of the resistance Rl, and the Riso insulation resistance of the network is calculated from the measured value.
In the course of the method using the current injection resistance measuring device 5 the value of the resultant Rmert resistance of the resistance Rl, the parallel
connected R2 resistance, and the Rpot resistances and Riso is measured in such a way that, with the (Kl) switch 59 of the current injection resistance measuring device 5 in switched-off state, the voltage Uki between the connections
51 and 52 of the current injection resistance measuring device 5, and the direct current Iki between the connection
52 of the current injection resistance measuring device 5 and the connection 12 of the current injection resistance measuring device 5 are measured.
The same values are measured with the (Kl) switch 59 of the
current injection resistance measuring device 5 in switched on state, the Ube voltage between the connections 51 and 52 of the current injection resistance measuring device 5, and the direct current Ibe between the connection 52 of the current injection resistance measuring device 5 and the resistance Rl.
The measured value of the resistance Rl is calculated with the following formula:
Rmert= (Uki-Ube) / (Iki-Ibe)
where the values are calculated in the following units Uki and Ube (V)
Iki and Ibe (mA) and
Rmert (kQ) .
In order to calculate the Riso insulation resistance of the network from the Rmert value, the formula corresponding to parallel connected resistances known of from electro- technology is taken into consideration
1/Rmert=l/ (Riso+Rpot+R2) +1/R1
from which
Riso= (Rmert (Rl+R2+Rpot ) -Rl (R2+Rpot) ) / (Rl-Rmert) where Riso is the resultant insulation resistance of the network,
Rmert is the value of resistance Rl determined by
measurement,
Rl is the known actual value of the resistance Rl,
R2 is the known actual value of the resistance R2,
Rpot is the resultant of the Rcsat connected resistances If, for example in the case of a Y-PK connection, the value of the resistances Rl and R2 used is 1.5 kQ,
the resultant of the Rcsat=10kQ connected resistances
Rpot=5 kQ then
Riso=(8Rmert-9.75) / (1.5-Rmert) (kQ)
or in the case of the solar cell GFDI solution according to figure 4a if the value of the resistances Rl and R2 is 1.5 kQ, Rcsat=0, Rpot=0
Riso=(3Rmert-2.25) / (1.5-Rmert) (kQ)
The same method may be used in the case of a solar cell network, for example in the case of the solution used in the ABB PVS800 inverter
or in the SMA SC1000CPXT inverter operating with current detection. In the catalogues of the devices in order to create the functional earth there are two 1.5 kQ
resistances, a total of 3 kQ connected in series with the GFDI relay.
DE_PVS800_57_HW_H_A4_screen.pdf (Hardware-Handbuch page 107) and
PV-Kraftwerkel-Wechselrichter_DE-123710_web.pdf
(Wechselrichter in PV-Grossanlagen page 59)
If the network's Riso insulation resistance is near
infinity, the measured value of the resistance Rl
corresponds to the rated value of resistance Rl: Rmert= Rl . If the network's Riso insulation resistance is zero, the measured value of the resistance Rl equals a half of the rated value of the resistance Rl : Rmert= Rl/2.
Earth-independent battery networks frequently do not have current injection insulation measurement suitable for determining double earth faults. In the case of these networks it is preferable to establish the Y-PK functional earth for the duration of the measurement using the
insulation resistance measurement unit of a fault-finding
portable earth fault detection instrument using the method in order to determine the insulation resistance and then perform the current injection resistance measurement. With this the Riso insulation resistance of networks with both single and symmetrical double earth faults can be
determined with the risk of false interruption.
In the case of the deterioration of insulation measurement can be performed while certain network branches are
switched off, which makes it possible to select the faults branch without switching off the potential increasing or potential reduction device.
A Hall effect sensor can also be used for measuring
resistance in the case of the solution, which ensures that the current measurement is isolated from high voltage equipment .
The direct voltage source for the current injection
resistance measuring device may be preferably established using a DC/DC or AC/DC voltage rectifier.
For example, for uses with solar cell network applications, for the GFDI relay system according to figure 2a, the connections to determine the Riso insulation resistance are illustrated in figure 4a. While performing the measurement the steps to be taken are identical to those described in the Y-PK measurement described above.
The method may be used in both the case of direct voltage potential increasing and in the case of potential
reduction, in the case of which two resistances can be connected in series with the potential increasing or potential increasing device, among which the value of the resistance connected to earth is measured. The network insulation resistance can be calculated from the measured
value. When performing the calculation the Rpot resultant of the internal resistances of the potential increasing or potential reduction device are taken into consideration.
In the following the connection arrangement realising potential reduction or increase in battery energy storage networks 6 and a potential reduction device not yet used to date in battery system will be presented, (figure 6) , which may also be used connected in parallel in solar cell direct current network systems IF. The internal connections of the direct voltage source potential reducing or potential increasing device inserted in the figure are shown in figure 7, the elements and connection of which correspond to those in the direct voltage current source of the current injection resistance measuring device presented in figure 5, but in the interest of differentiation it is presented in a separate figure with different reference number and has the reference number 7. The potential reduction device makes it possible for the battery facility to operate at a lower voltage as compared to earth than an earthed or earth-independent insulated network, however, the insulation resistance of the system may also be determined. This lower voltages place less demand on the battery and on the insulation of the network.
If a solar cell system operated in parallel with the battery system requires an increase in voltage as compared to earth so as to reduce the PID effect, the device 7 is connected swapping the connections 71 and 72, in the case of which the negative pole Nl is raised to a positive voltage that equals the voltage of the internal direct voltage source 80 of the device 7.
In the figure the individual units have the same reference numbers as in the other figures. The reference number 6 represents the battery network system. The positive pole of the battery established by connecting the battery units 64 in series is designated API, and the negative pole AN1. The positive pole API is connected to the positive input 22 of the inverter 2 via the switch 62 and the connector 66, via the switch 21. The negative pole AN1 is connected to the negative input 23 of the inverter 2 through the switch 62 and the connector 67 via the switch 21. The battery network system 6 is also connected to the points PI and Nl of the solar cell network via the connectors 66, 67 and the switch 62, from which both systems supply the alternating current network 24 via the insulated central inverter 2. The charging of the battery units 64 with the switch 62 in its indicated position via the DC/DC rectifier 63 at the voltage corresponding to the components. In the course of charging the battery units 64 in earth-independent
operation mode they operate with a traditional insulation monitoring device 65. The current sensor and interrupter 3, the connection 4 serving for determining the Riso
insulation resistance, along with the current injection resistance measuring device 5, are identical to those used in the case of the GFDI relay solution described above (figure 4a) .
In potential reducing operation mode if the negative pole AN1 voltage of a 1000 V battery is offset in the negative direction by -500 V by the direct voltage source potential reduction device 7, the voltage between earth 13 and the negative pole AN1 will be -500 V, and the voltage between the positive pole API and earth 13 will be +500 V, neither
of them will reach 1000 V, the maximum voltage will be just 500 V. During charging in earth-independent operation mode the voltage between the positive pole and earth will also be +500 V, and the voltage between the negative pole and earth will be -500 V. This means a lower demand on the insulation.
The direct voltage source device serves for reducing potential, which is connected between the negative pole 67 of the network system and the connector 10 of the current sensor and interrupter unit 3 via the connections 71 and 72. In order to perform the 500 V offset the internal voltage source 80 is set to the value of 500 V.
The direct voltage source device 7 also serves for
increasing potential, which is connected to the negative pole 67 of the network system and the connector 10 of the current sensor and interrupter unit 3 via the connections 72 and 71. In order to raise the negative pole to +50 V the voltage of the internal voltage source 80 is set to the value of 50 V.
The already described current injection resistance
measuring method indicated in figures 4, 4a and 5 is used for the determination of the Riso insulation resistance of the battery network.
Figure 7 shows the schematic connection of the direct voltage source potential reducing or potential increasing device 7. A limiting resistance 74 and a load resistance 77 is series connected between the first connection 72 and the second connection 71 of the direct voltage source device 7, and a diode 76 is connected in parallel to the load
resistance, furthermore there is an internal direct voltage
source 80 of a size that corresponds to the potential reducing demand, and the positive polarity connection of the internal direct voltage source 80 is connected to the common connection 75 of the limiting resistance 74, the diode 76 and the load resistance 77 through the switch 79 and the rectifying diode 78, and its negative polarity connection is connected to the second connection 71 of the direct voltage source device 7.
Depending on the connection of the direct voltage source device the potential reducing or potential increasing operation modes are created by closing the switch 79.
In the formula used to calculate the Riso the resistance 74 is taken into consideration as the value of Rpot.
In the knowledge of the calculated Riso the measure may be taken that corresponds to the demands of the network use, such as alarm or disconnection.
The simple and reproducible steps of the method make the industrial application of the invention possible and enable the use of commercially available components for the manufacture of the devices.
The main advantages of the use of the invention:
The insulation resistance of direct current networks operating with Y-PK functional earthing, with potential fixing, potential reducing and potential increasing, including the value of the insulation resistance of symmetrical double earth faults may be determined by using the method serving for determining the insulation
resistance value of insulated direct current network systems with functional earthing.
The method realises the Y-PK functional earthing in battery systems, as well as the functional earthing in solar cell direct current networks, and realises potential fixing, increasing or reduction.
In auxiliary operation equipment, maintaining the
advantages of the Y-PK functional earthing, faults may be resolved even in the case of symmetrical earth faults without the risk of false disconnection when the one earth fault occurs on the input of a microprocessor or other digital element.
Earth-independent battery networks frequently do not have injection insulation measurement suitable for determining double earth faults. In the case of these networks the insulation measuring units of portable earth fault
detecting instruments can be preferably used for fault detection by creating the Y-PK functional earth using the method for the duration of the measurement and performing the current injection resistance measurement. The advantage of this is that the Riso insulation resistance of networks with either a single or symmetrical double earth fault can be determined and the position of the fault can be located without the risk of false disconnection. As the current injection resistance measuring device used, contrary to other methods, does not increase but reduces the risk of false interruption, and it performs this at a voltage not resulting in under-voltage tripping.
In the case of the deterioration of insulation, the measurement can be performed even by switching off certain network branches, which makes it possible to select the faulty branch with the potential increasing or potential reduction device, without switching off the functional
earthing.
In the case of battery energy storage network systems the connection arrangement realising potential reduction and the potential reduction device make it possible for the battery system to operated while placing a lower demand on the insulation, which increases the lifetime of the equipment as it slows down ageing of the insulation.
In addition to all this it determines the Riso insulation value of direct current network systems.
In the case of use in solar cell direct current systems the main advantage is that the output-reducing effect of PID (Potential-Induced Degradation) is minimised with the use of the method. According to the literature the PID effect is strongly influenced by the negative voltage as compared to earth of the PV generator. In the case of higher voltage, 1500 V, PV generators using the technology currently available even by raising the potential of the positive side by 1000 V the negative side of the PV
generator operates at negative voltage as compared to earth. By using the method even the negative side can be increased into the positive voltage range as compared to earth. In addition it is a significant advantage that the determination of the insulation resistance at short intervals without disconnecting the functional earth is almost equivalent to the continuous measurement of
insulation measurement. Using the technologies currently available the insulation measurement performed once a day, usually before the inverter is switched on at dawn, does not provide a realistic picture of the insulation
resistance values under natural operating conditions, and at maximum voltage and output, as well as in unfavourable
weather conditions. As opposed to this the determination of the insulation resistance every hour or thirty minutes can be viewed as almost constant. As a consequence of this faults may be reacted to in time that cannot be recognised using the present solutions.
The use of the method is also preferable in the case of PV systems constructed from solar cell types that are less sensitive to the PID effect, because there the insulation resistance can be determined and the faults branch selected even in networks with the commonly used GFDI (Ground Fault Detector, Interrupter) device, but without over-current protection on the earthed side or elements that can be disconnected, even if a single or even symmetrical earth fault occurs in parallel with the point of the network earthed with a GFDI, for example on the pole to which the GFDI (Ground Fault Detector, Interrupter) device is connected. According to the professional prejudice of the literature, the insulation resistance of solar cell systems operating with functional earth cannot be measured, therefore the standard states that if with functional earthing the insulation resistance cannot be measured, then the insulation of the solar cell network must be measured once a day by disconnecting the functional earth. As opposed to this, using the functional earth according to the invention the insulation resistance can be measured without disconnecting the earth.
The Riso insulation resistance of a battery network can also be determined with the solution.
In the case of use with energy storage batteries in solar cell systems there is the preferable possibility of charging the batteries with the energy provided by the
solar cells and not from the alternating voltage network. As it is economical to feed the energy stored in the battery into the energy systems at leak times when the solar cell systems are unable to provide sufficient capacity, by connecting the battery energy storage system in parallel with the solar cell system this missing
capacity can be replaced. In addition using the battery supply the amount of energy that can be taken out of the solar cell system can be increased if the voltage is raised in the morning and evening hours to such an extent that the solar cells can feed the system also. Using the parallel operation according to the invention the battery energy storage system can be connected to the alternating voltage network using the inverter of the solar cell network as well, which increases its use and does not require the installation of another inverter between the battery energy storage system and the alternating current network. In the case of battery storage systems it is important for the connection between the direct current battery and the alternating current network to be constant, only in this way can it help maintain the frequency of the alternating current network. According to the solution the connection between a battery network containing batteries connected in series, as well as other types of DC-connected energy storage battery systems, and the alternating current network may be made more reliable and constant, even in a network supplied with GFDI earth fault protection, because in order to perform the insulation measurement of the direct voltage network it is not necessary to disconnect the DC/AC inverter. In the case of the current solutions the measurement of insulation takes place with the
functional earth and the connection in disconnected state. With the insulation measurement according to the invention it is not necessary to disconnect the connection. This provides the opportunity for the connection between the storage battery on the DC-connected battery network and the alternating current network to be continuous even when the insulation measuring process is being performed.
The same is valid for networks operating with potential fixing, potential reduction or potential increasing, and also if the fault occurs on the earth potential point of the network.
Contrary to the traditional IMD insulation resistance measuring devices, which usually have an insulation
measuring range of 1 kQ-10 ΜΩ, the method according to the invention only measures the resistance of the approximately 1 kQ element connected to earth of the functional earth of the magnitude of 1 kQ-30 kQ whilst maintaining continuous operation.
The resistance measurement is performed with a current injection resistance measuring device, the injected current of which is almost independent of the magnitude of the Riso insulation resistance, whether the Riso=several hundred kQ, or if and the interim range can also be measured well. The current is determined by the voltage of the injecting device, its internal voltage and the value of the series- connected resistance Rl to be measured. This can be set to a range that can be easily measured (e.g. of the order of 10 mA) , and only changes to a small degree, and even flows, if there is an earth fault on the point (pole) of the network at earth potential, which is not true of the other solutions. In the case of the other solutions as both
points of the fault location resistance are at the same voltage, no current flows through it and so the resistance cannot be measured. It is also preferable that it is not necessary to measure the very small current flowing through the Riso resistance in the case there is no fault, nor the very small current occasionally flowing through the
potential increasing or potential reduction device, nor the voltage of the network as compared to earth, instead the stable current flowing through the resistance Rl that can be measured easily and only slightly depends on the fault to a small extent and the voltage on the resistance Rl are measured.
It is also preferable that the determination of the Riso insulation resistance does not significantly influence the normal operating conditions of the battery network, the earth fault current detection, or the operation of the solar cell network operating with potential increasing or potential reduction.
Another advantage is that by using the method the value of the Riso insulation resistance can be determined
independently of the network's voltage conditions, even in the case that the battery is disconnected with the network at zero potential, or, in the case of a solar cell network, when there is no solar radiation on a network at a voltage at a fraction of its rated voltage.
To a certain extent it is a disadvantage and makes the dimensioning of the current injection resistance measuring device 5 of the insulation measuring method difficult in the case of use with solar cells that the R1/(R1+R2) proportion of the voltage of the system appears on the resistance Rl in the case of a positive earth fault.
In the case of the resistance measuring solution by using a Hall effect current sensor it can be ensured that the current measurement is isolated from the high-voltage equipment .
It is preferable if the internal direct voltage current source 60 of the current injection resistance measuring device, and the internal direct voltage source 80 of the potential increasing or potential reduction device are established with a DC/DC or AC/DC voltage converter.
METHOD AND APPARATUS FOR DETERMINING THE INSULATION RESI
AND FOR POTENTIAL REDUCTION AND INCREASE OF BATTERY SYSTEMS USING FUNCTIONAL
EARTHING
Explanation of the references appearing in the specification figures :
Figure 1
1A battery network
PI positive pole
Nl negative pole
14 individual units of the battery installation
15 consumers
17 Rcsat connected resistance
18 Rcsat connected resistance
Y-PK functional earth
Riso insulation resistance of the network as compared to earth RFE functional earth resistance
19 insulation measuring device
Iinj injected current
11 connection of the functional earth to earth
13 earth connection
Uasz asymmetrical voltage
RF earth fault resistance
Figure 2 a
IF PV generator
PVM module
2 insulated inverter
21 switch
22 inverter positive connection
23 inverter negative connection
24 alternating voltage network system
3 GFDI ground fault detection and interruption unit
30 current sensor
31 interrupter
10 connector of 3 and 3B
11 connector of 3 and 3B
sun symbol daytime
moon symbol night-time
Figures 2b , 2 c and 3
3B current sensor and interrupter
90 direct voltage current source
91 negative connector of potential increaser
92 positive connector of potential increaser
Figures 4 and 4a
4 connection of the current injection resistance measuring device
5 current injection resistance measuring device
10 connector of Y-PK functional earth
11 connector of functional earth
12 Rl and R2 common connector
13 connector of functional earth
R2 resistance
Rl resistance to be measured
8 direct voltage measuring device
9 direct current measuring device
51 second connection of the current injection resistance measuring device
52 first connection of the current injection resistance measuring device
Figure 5
54 limiting resistance
55 common connection of the diode 56 and the load resistance 57
56 diode
57 load resistance
58 rectifying diode
59 Kl switch
60 internal direct voltage source
Figure 6 and 7
6 battery energy storage network
API positive pole of battery system
AN1 negative pole of battery system
62 switch
63 DC/DC rectifier
64 battery units
65 traditional insulation monitoring device
66 positive connector of the battery system
67 negative connector of the battery system
7 direct voltage source potential reduction device
71 second connector of the direct voltage source potential reduction device
72 first connector of the direct voltage source potential reduction device
74 limiting resistance
75 common connection of the diode 76 and the load resistance 77
76 diode
77 load resistance
78 rectifying diode
79 switch
80 internal direct voltage source
Claims
1./ Method for determining the insulation resistance of direct current battery and/or solar cell network systems using functional earthing, during which two known value resistances (Rl) and (R2) of the order of 1 kQ -30 kQ are series connected and interposed between the earth
connection of a potential fixing, increasing or reducing equipment or device and earth, or in the case of a solar cell network it is solved through resistances interposed between a GFDI current detector and a disconnector, then using the interposed resistances (Rl) and (R2), the
resultant (Rmert) of the earth-connected resistance (Rl), the parallel-connected resistance (R2), the connected resistances (Rpot) of the potential fixing, increasing or reduction device and the network insulation resistance (Riso) is measured and from this the value of the network insulation resistance (Riso) is determined, characterised by that a functional earth is created, the operation of the network is continuously maintained, the measurement is performed on the operating network in the case of voltage asymmetry or current detection tripping occurring in the case of a single earth fault, and in the lack of asymmetry and current in the interest of determining the symmetrical faults using a current injection resistance measuring device (5) at the desired times or at determined intervals, where the measurement of the resultant (Rmert) of the resistance (Rl) , the parallel connected resistance (R2) and of the insulation resistance (Riso) of the direct current network is performed in the course of two consecutive measurements in such a way that a voltage (8) and current
i
- 50 - measurement (9) is performed on each occasion with the current injection resistance measuring device (5) is switched on and switched off states, and the resistance is determined as the ratio of the voltage difference on the connections of the device and the difference of the current flowing through the device according to the following formula,
Rmert = (Uki-Ube) / ( Iki-Ibe)
where
Rmert is the measured value of the resistance (Rl) ,
Uki is the direct voltage measured at the connections of the current injection resistance measuring device (5) with it in switched off state,
Ube is the direct voltage measured at the connections of the current injection resistance measuring device (5) with it in switched on state,
Iki is the direct current measured with the current
injection resistance measuring device (5) in switched off state between the resistance (Rl) and the current injection resistance measuring device (5) ,
Ibe is the direct current measured with the current injection resistance measuring device (5) in switched on state between the resistance (Rl) and the current injection resistance measuring device (5) , the insulation resistance (Riso) of the battery and/or solar cell network as compared to earth is determined from the measure value (Rmert) from the following formula corresponding to parallel connected resistances as follows,
1/Rmert=l/ (Riso+Rpot+R2) +1/R1
from which
Riso= (Rmert (Rl+R2+Rpot) -Rl (R2+Rpot) ) / (Rl-Rmert)
- 51 - where Riso is the resultant insulation resistance of the network,
Rmert is the value of the resistance Rl determined by measurement,
Rl is the known actual value of the resistance Rl,
R2 is the known actual value of the resistance R2,
Rpot is the resultant of the connected resistances Rcsat.
2. / Method according to claim 1, characterised by that in the case of earth independent networks a Y-PK functional earth is created using the insulation measuring unit of the fault finding earth fault detecting instrument for the duration of the measurement, and the insulation resistance (Riso) of the network is determined.
3. / Method according to claim 1, characterised by that in the case of insulation deterioration the selection of the faulty branch is performed with the potential fixing, increasing or reducing functional earthing device in switched on state with individual network branches being disconnected by determining the value of the insulation resistance (Riso) .
4. / Apparatus for the realisation of the method according to claim 1, which apparatus (5) has a restricting
resistance (54) and a load resistance (57) connected in series between a first connection (52) and a second
connection (51) , and a diode (56) is connected in parallel with the load resistance, furthermore it has an internal direct voltage source (60), the positive pole connection of which voltage source (60) is connected to the common connection (55) of the restricting resistance (54), the diode (56) and the load resistance (57) through the Kl
- 52 - switch (59) and rectifying diode (58), and its negative pole connection is connected to the second connector (51) of the apparatus, characterised by that as current
injection resistance measuring apparatus, the apparatus's (5) first connector (52) is connected to the common
connection (12) of the resistances (Rl) and (R2)
established as functional earth through a current meter (9), the other connection (51) of the current injection resistance measuring device is connected to the other connection (13) of the resistance (Rl) connected to earth and a direct current voltage meter (8) is connected to the connections of the resistance (Rl) .
5. / Apparatus according to claim 4 , characterised by that a Hall effect current meter (9) is used to measure the direct current.
6. / Apparatus according to claim 4, characterised by that the internal direct voltage current source (60) contains a DC/DC or AC/DC voltage rectifier.
7. / Electric circuit arrangement for reducing or increasing the voltage as compared to earth of battery network systems with the determination of insulation resistance according to claim 1, characterised by that in the case of voltage reduction a direct voltage source (7) is interposed between the negative pole (AN1) of the battery network system (6) and earth (13) via a switch (62), which offsets the
negative pole (71) in the negative direction as compared to earth, and the connector (10) of the current sensor and interrupter unit (3) is connected to the positive polarity connection (72) of the direct voltage source, and the current injection resistance measuring apparatus (5) is
- 53 - connected for determining the insulation resistance, in the case of voltage increasing a direct voltage source (7) is interposed between the negative pole (AN1) of the battery network system (6) and earth (13) via a switch (62), which offsets the negative pole (72) in the positive direction as compared to earth, and the connector (10) of the current sensor and interrupter unit (3) is connected to the
negative polarity connection (71) of the direct voltage source and the current injection resistance measuring device (5) is connected for determining the insulation resistance.
8. / Apparatus for the electric circuit arrangement
according to claim 7, which apparatus (7) has a restricting resistance (74) and a load resistance (77) connected in series between a first connection (72) and a second
connection (71) , and a diode (76) is connected in parallel with the load resistance, furthermore it has an internal direct voltage source (80) , the positive pole connection of which voltage source (80) is connected to the common connection (75) of the restricting resistance (74) , the diode (76) and the load resistance (77) through the Kl switch (79) and rectifying diode (78) , and its negative pole connection is connected to the second connector (71) of the apparatus, characterised by that as direct voltage source in the case of voltage reduction the apparatus's (7) first connector (72) is connected to earth (13) via the current injection resistance measuring device (5) and the current sensor and interrupter unit (3), its second
connector (71) is connected to the negative connection (ANl) of the direct current network (6), in the case of voltage increase the apparatus's first connector (72) is
connected to the negative connection (A 1) of the direct current network (6), its second connector (71) is connected to earth (13) via the connected current injection
resistance measuring device (5) and the current sensor and interrupter unit (3) and the voltage reduction or voltage increase is realise by closing the switch (79) of the internal direct voltage source (80) .
Applications Claiming Priority (2)
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HUP1700439 HUP1700439A1 (en) | 2017-10-31 | 2017-10-31 | Procedure and apparatus for determining the insulation resistance of dc networks and for potential reducing or potential increasing of battery systems, by functional earthing |
HUP1700439 | 2017-10-31 |
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WO2019086917A1 true WO2019086917A1 (en) | 2019-05-09 |
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Cited By (4)
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CN111257709A (en) * | 2020-02-11 | 2020-06-09 | 邢台钢铁有限责任公司 | Method for insulation detection of 24V power line of PLC system |
CN113156210A (en) * | 2021-03-12 | 2021-07-23 | 阳光电源股份有限公司 | Insulation detection method and application device thereof |
US20210382104A1 (en) * | 2020-06-04 | 2021-12-09 | Bender Gmbh & Co. Kg | Grounded socket and method for insulation fault location in an ungrounded power supply system including insulation monitoring |
CN117233532A (en) * | 2023-09-21 | 2023-12-15 | 中科智寰(北京)科技有限公司 | DC power grid ground fault on-line positioning and protecting system |
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EP3109647A1 (en) * | 2015-06-26 | 2016-12-28 | ABB Technology AG | Method and arrangement for measuring insulation resistance of photovoltaic system |
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EP1586910A1 (en) * | 2004-04-18 | 2005-10-19 | Deif A/S | Method of and device for insulation monitoring |
EP3109647A1 (en) * | 2015-06-26 | 2016-12-28 | ABB Technology AG | Method and arrangement for measuring insulation resistance of photovoltaic system |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
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CN111257709A (en) * | 2020-02-11 | 2020-06-09 | 邢台钢铁有限责任公司 | Method for insulation detection of 24V power line of PLC system |
US20210382104A1 (en) * | 2020-06-04 | 2021-12-09 | Bender Gmbh & Co. Kg | Grounded socket and method for insulation fault location in an ungrounded power supply system including insulation monitoring |
US11789060B2 (en) * | 2020-06-04 | 2023-10-17 | Bender Gmbh & Co. Kg | Grounded socket and method for insulation fault location in an ungrounded power supply system including insulation monitoring |
CN113156210A (en) * | 2021-03-12 | 2021-07-23 | 阳光电源股份有限公司 | Insulation detection method and application device thereof |
CN117233532A (en) * | 2023-09-21 | 2023-12-15 | 中科智寰(北京)科技有限公司 | DC power grid ground fault on-line positioning and protecting system |
CN117233532B (en) * | 2023-09-21 | 2024-02-09 | 中科智寰(北京)科技有限公司 | DC power grid ground fault on-line positioning and protecting system |
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