CN210572464U - Current measuring device for neutral point direct current magnetic bias of power transformer - Google Patents
Current measuring device for neutral point direct current magnetic bias of power transformer Download PDFInfo
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- CN210572464U CN210572464U CN201920903714.1U CN201920903714U CN210572464U CN 210572464 U CN210572464 U CN 210572464U CN 201920903714 U CN201920903714 U CN 201920903714U CN 210572464 U CN210572464 U CN 210572464U
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Abstract
The utility model relates to a current measuring device for power transformer neutral point direct current magnetic biasing, which comprises a power transformer, wherein two grounding flat steels are led out from the power transformer neutral point on the power transformer and are connected into a transformer substation ground grid by the two grounding flat steels; each grounding flat steel led out from the neutral point of the power transformer is provided with a set of flat steel voltage clamping pieces and a set of flat steel current clamping pieces, each set of flat steel voltage clamping pieces is connected with a voltage measurement and control module through a voltage signal wire, each set of flat steel current clamping pieces is connected with a current source measurement and control module, and the voltage measurement and control module and the current source measurement and control module are electrically connected with a main controller module; each grounding flat steel is also provided with a flat steel temperature measuring module, and each flat steel temperature measuring module is electrically connected with the main controller module. The utility model discloses realize wide temperature range, compatible two flat steel condition that connects to ground, high accuracy, wide dynamic range measure transformer neutral point direct current magnetic biasing current.
Description
Technical Field
The utility model relates to an electric power measurement field relates to power transformer neutral point direct current magnetic biasing current measurement technique, and specific saying so relates to a current measurement device for power transformer neutral point direct current magnetic biasing.
Background
At present, when a direct current transmission system operates in an earth return mode (including a single-pole earth return mode and a double-pole unbalanced mode), or a direct current supply rail transit system or an earth magnetic field changes, a direct current magnetic bias problem of a partial neutral point grounding transformer in an alternating current power grid may be caused, so that harmonic waves are generated, problems of noise, vibration, overheating and the like are caused, and a large influence is caused on the normal operation of the transformer.
Neutral point dc bias negatively interferes with the operation of the transformer. The power personnel need to adopt a scientific and reasonable method to strictly control the direct current flowing into the neutral point of the transformer and reduce the interference of the direct current on the transformer to the minimum. The method is characterized in that an electric power enterprise selects a grounding pole address by combining a specific engineering background, reasonably demonstrates the magnetic saturation influence of direct current pole-to-ground current on an alternating current power transformer, and adopts specific inhibition measures to limit the direct current level of a neutral point of the transformer, so that an electric power system is always in a good operating environment, and the rapid development of the electric power enterprise in China is promoted.
At present, the measurement requirement of a power system on direct current in an alternating current and direct current hybrid power grid is quite wide, particularly when a direct current transmission line is in single-pole operation, the direct current condition of a neutral point of a main transformer of an alternating current transformer substation around a direct current grounding electrode needs to be mastered in real time, the operation state of the main transformer is evaluated, and reference and guidance are provided for construction of a direct current magnetic bias defense system and site selection of a newly-built transformer substation.
The power transformer neutral point current measurement can utilize a flat steel clamping piece to sample a direct current signal at a transformer neutral point flat steel, but because the flat steel material is influenced by the environmental temperature, the impedance change of a section of sampled flat steel is large, and the accuracy of direct current measurement is directly influenced; meanwhile, the neutral point of the on-site main transformer has the condition that two flat steels are grounded simultaneously, and the current of the neutral point of the main transformer can be shunted to the ground from the two grounded flat steels.
SUMMERY OF THE UTILITY MODEL
In order to solve the problems of the background art, the present invention provides a current measuring device for dc bias of a neutral point of a power transformer.
In order to achieve the purpose, the invention adopts the technical scheme that:
the utility model provides a current measuring device for power transformer neutral point direct current magnetic biasing, which comprises a power transformer, wherein two grounding flat steels are led out from the power transformer neutral point on the power transformer and are connected into a transformer substation ground grid by the two grounding flat steels; the device also comprises two sets of flat steel voltage clamping pieces, a voltage measurement and control module, two voltage signal wires, two sets of flat steel current clamping pieces, a current source measurement and control module, two flat steel temperature measurement modules and a main controller module;
each grounding flat steel led out from the neutral point of the power transformer is provided with a set of flat steel voltage clamping pieces and a set of flat steel current clamping pieces, each set of flat steel voltage clamping pieces is connected with a voltage measurement and control module through a voltage signal wire correspondingly arranged with the flat steel voltage clamping piece, each set of flat steel current clamping pieces is connected with a current source measurement and control module, and the voltage measurement and control module and the current source measurement and control module are electrically connected with the main controller module;
each grounding flat steel is also provided with one flat steel temperature measuring module, and each flat steel temperature measuring module is electrically connected with the main controller module.
In the technical scheme, the voltage measurement and control module comprises a voltage channel switching circuit, an overvoltage protection circuit, a sensor zero calibration circuit, a program control amplifying circuit, a whole-period integrating circuit, a voltage signal acquisition circuit and a communication isolation circuit; the voltage channel switching circuit is electrically connected with the output end of the main controller module and is controlled by the main controller module;
analog voltage signals sampled from two pieces of grounded flat steel are accessed into a voltage channel switching circuit in a time-sharing manner through voltage signal lines corresponding to the analog voltage signals, the voltage channel switching circuit is electrically connected with an overvoltage protection circuit, the overvoltage protection circuit is electrically connected with a sensor zero calibration circuit, the sensor zero calibration circuit is electrically connected with a program control amplification circuit, the program control amplification circuit is electrically connected with a whole-period integration circuit, the whole-period integration circuit is electrically connected with a signal acquisition circuit, the signal acquisition circuit is electrically connected with a communication isolation circuit, and the communication isolation circuit is electrically connected with an input end of a main controller module;
the voltage channel switching circuit is used for accessing a two-way analog voltage signal; the overvoltage protection circuit is used for EMC protection; the program-controlled amplifying circuit and the whole-period integrating circuit are used for signal conditioning to realize tiny signal amplification and inhibit alternating current signals; the sensor zero calibration circuit is used for eliminating measurement errors introduced when the program control amplification circuit and the whole-period integrating circuit carry out signal conditioning; the signal acquisition circuit is used for converting analog signals into digital signals, and the communication isolation circuit is used for outputting the digital signals to the main controller module.
In the technical scheme, the voltage measurement and control module is powered by an isolation power supply.
In the technical scheme, the current source measurement and control module comprises a controllable current source, a current channel switching circuit and a current signal acquisition circuit;
the output end of the controllable current source is connected to two sets of flat steel current clamping pieces in a time-sharing manner through a current channel switching circuit; the current channel switching circuit is also electrically connected with the current signal acquisition circuit and the output end of the main controller module respectively, and the current signal acquisition circuit is also electrically connected with the input end of the main controller module and is used for converting the acquired current analog signals into digital signals and connecting the digital signals into the main controller module.
In the above technical scheme, each set of the flat steel voltage clamping pieces comprises a positive voltage clamping piece and a negative voltage clamping piece; each set of flat steel current clamp comprises a positive current clamp and a negative current clamp;
the positive voltage clamping piece corresponding to each set of flat steel voltage clamping piece and the positive current clamping piece corresponding to each set of flat steel current clamping piece are both arranged at one end, close to the neutral point of the power transformer, of the grounding flat steel corresponding to the positive voltage clamping piece, and the positive current clamping piece corresponding to each grounding flat steel is correspondingly arranged on the outer side of the positive voltage clamping piece corresponding to the grounding flat steel, namely the positive current clamping piece is closer to the neutral point of the power transformer than the positive voltage clamping piece;
the negative voltage clamp corresponding to each set of flat steel voltage clamp and the negative current clamp corresponding to each set of flat steel current clamp are both arranged at one end, close to a transformer substation ground grid, of the corresponding grounding flat steel; the cathode current clamp corresponding to each grounding flat steel is correspondingly arranged on the outer side of the corresponding cathode voltage clamp, namely the cathode current clamp is closer to a transformer substation ground grid than the corresponding cathode voltage clamp;
when current is injected into the two grounding flat steels led out from the neutral point of the power transformer in a time-sharing manner, the voltage drop of the two grounding flat steels under the condition of current injection is measured through the two sets of flat steel voltage clamping pieces respectively, so that the resistance of the power transformer neutral point double grounding flat steel is calculated.
In the technical scheme, each voltage signal wire is wound in a twisted-pair manner by two single-core shielding wires, one end of each of the two single-core shielding wires is correspondingly connected to a positive voltage clamp and a negative voltage clamp of a flat steel voltage clamp corresponding to the single-core shielding wire, and the other end of each of the two single-core shielding wires is connected to the input end of a voltage measurement and control module;
the shielding layer on one side of each voltage signal wire close to the flat steel voltage clamping piece is suspended, and the shielding layer on the other side of each voltage signal wire is connected to the power supply ground end of the voltage measurement and control module isolation power supply.
In the technical scheme, each flat steel temperature measurement module is a temperature sensor, is respectively installed on the corresponding grounding flat steel and is used for monitoring the real-time temperature value of the surface of each grounding flat steel.
The working principle is as follows: firstly, arranging two sets of flat steel voltage clamping pieces and flat steel current clamping pieces on two pieces of grounding flat steel according to a certain sequence, injecting calibration current in a time-sharing mode, and measuring the direct current resistance of each of the two pieces of grounding flat steel which are connected in parallel (namely the initial resistance between the flat steel voltage clamping pieces on each piece of grounding flat steel at the initial temperature); then calculating the resistance values of the two flat steels at the current temperature according to the resistance temperature coefficient of the grounding flat steel material; and then collecting the voltage drop on the two grounded flat steels in real time, calculating to obtain the direct current flowing through the two grounded flat steels according to ohm's law, and finally adding the direct currents flowing through the two grounded flat steels to obtain the total current of the grounded flat steels, namely the neutral point direct current of the transformer.
Compared with the prior art, the beneficial effects of the utility model are that:
1. inhibiting power frequency and higher harmonics in the signal by a signal integral period integration method; and the gain of the direct current signal is automatically conditioned by applying a dynamic gear shifting technology. The method realizes the measurement of high precision and wide dynamic range of tiny direct current signals in alternating current and direct current mixed signals flowing on the power transformer neutral point double-grounded flat steel;
2. a loop circuit parameter equation is obtained through theoretical derivation, and the resistance of the two sections of grounded flat steel is measured according to a certain flow under the operating state of the power transformer, so that the self-calibration function of the resistance parameter of the flat steel is realized, and the accuracy of long-term monitoring data of the device is ensured;
3. the invention collects the surface temperature value of the flat steel in real time for dynamically correcting the resistance of the flat steel, and ensures that the device can normally work in a wide temperature range.
Drawings
FIG. 1 is a schematic diagram of the principles of the present invention;
FIG. 2 is a schematic layout of a flat voltage clamp and a flat current clamp;
FIG. 3 is a schematic diagram of the derivation process of equation (1);
the reference numbers illustrate:
100. a power transformer; 101. a power transformer neutral point; 200. grounding flat steel; 300. a transformer substation ground grid;
1. a flat steel voltage clamp; 11. a positive voltage clamp; 12. a negative voltage clamp; 2. a voltage measurement and control module; 20. a voltage channel switching circuit; 21. an overvoltage protection circuit; 22. a sensor zero calibration circuit; 23. a program-controlled amplifying circuit; 24. a full-period integration circuit; 25. a signal acquisition circuit; 26. a communication isolation circuit; 3. a voltage signal line; 4. a flat steel current clamp; 41. a positive current clamp; 42. a negative current clamp; 5. a current source measurement and control module; 50. a controllable current source; 51. a current channel switching circuit; 52. a current signal acquisition circuit; 6. a flat steel temperature measuring module; 7. a main controller module.
Detailed Description
In order to make the technical means, the creation features, the achievement purposes and the functions of the present invention easy to understand and understand, how to implement the present invention is further explained below with reference to the accompanying drawings and the detailed description.
As shown in fig. 1 and fig. 2, the present invention provides a current measuring device for dc magnetic biasing of a neutral point of a power transformer, which includes a power transformer 100, wherein two grounding flat steels 200 are led out from a neutral point 101 of the power transformer 100, and the two grounding flat steels 200 are connected to a transformer substation ground grid 300; the device also comprises two sets of flat steel voltage clamping pieces 1, a voltage measurement and control module 2, two voltage signal wires 3, two sets of flat steel current clamping pieces 4, a current source measurement and control module 5, two flat steel temperature measurement modules 6 and a main controller module 7; the main controller module 7 adopts an ARM processor, and the model is STM32F103RCT 6.
Each grounding flat steel 200 led out from a neutral point 101 of the power transformer is provided with a set of flat steel voltage clamping pieces 1 and a set of flat steel current clamping pieces 4, each set of flat steel voltage clamping pieces 1 is connected with a voltage measurement and control module 2 through a voltage signal wire 3 correspondingly arranged with the flat steel voltage clamping piece, each set of flat steel current clamping pieces 4 is connected with a current source measurement and control module 5 through a current source signal wire (not shown in the figure) correspondingly arranged with the flat steel voltage clamping pieces, and the voltage measurement and control module 2 and the current source measurement and control module 5 are electrically connected with a main controller module 7;
each grounding flat steel 200 is also provided with a flat steel temperature measuring module 6, and each flat steel temperature measuring module 6 is electrically connected with the main controller module 7.
As shown in fig. 1, the voltage measurement and control module 2 includes a voltage channel switching circuit 20, an overvoltage protection circuit 21, a sensor zero calibration circuit 22, a program control amplification circuit 23, a whole period integration circuit 24, a voltage signal acquisition circuit 25 and a communication isolation circuit 26; specifically, the voltage channel switching circuit 20, the overvoltage protection circuit 21, the sensor zero calibration circuit 22, the program control amplification circuit 23, the whole period integration circuit 24, the voltage signal acquisition circuit 25 and the communication isolation circuit 26 are all existing circuits in the market; the voltage channel switching circuit 20 utilizes the switching of a small signal relay to realize channel control; the signal input of the overvoltage protection circuit 21 is pulled up to a positive power supply by using a diode, and pulled down to a negative power supply by using a reverse phase to realize input signal clamping; the sensor zero calibration circuit 22 inputs the conditioning circuit into short circuit, and measures the output signal of the conditioning circuit to obtain the zero drift value of the conditioning circuit; the program-controlled amplifying circuit 23 realizes 1-time, 10-time, 100-time and 1000-time program-controlled amplification by utilizing AD 8253; the whole-period integrating circuit 24 uses an operational amplifier to build a circuit with the integration time equal to 20 mS; the voltage signal acquisition circuit 25 completes the conversion from analog to digital signals by using an ADC 7135; the communication isolation circuit 26 utilizes ADUM1201 magnetic optocoupler to achieve communication signal isolation.
The voltage channel switching circuit 20 is electrically connected with the output end of the main controller module 7 and is controlled by the main controller module 7;
analog voltage signals sampled from two pieces of grounded flat steel 200 are accessed to a voltage channel switching circuit 20 in a time-sharing manner through voltage signal lines 3 corresponding to the analog voltage signals, the voltage channel switching circuit 20 is electrically connected with an overvoltage protection circuit 21, the overvoltage protection circuit 21 is electrically connected with a sensor zero calibration circuit 22, the sensor zero calibration circuit 22 is electrically connected with a program control amplification circuit 23, the program control amplification circuit 23 is electrically connected with a whole-period integration circuit 24, the whole-period integration circuit 24 is electrically connected with a signal acquisition circuit 25, the signal acquisition circuit 25 is electrically connected with a communication isolation circuit 26, and the communication isolation circuit 26 is electrically connected with an input end of a main controller module 7;
the voltage channel switching circuit 20 is used for accessing two paths of analog voltage signals; the overvoltage protection circuit 21 is used for EMC protection; the program control amplifying circuit 23 and the whole-period integrating circuit 24 are used for signal conditioning to realize tiny signal amplification and inhibit alternating current signals; the sensor zero calibration circuit 22 is used for eliminating measurement errors introduced when the program control amplifying circuit 23 and the whole period integrating circuit 24 perform signal conditioning; the signal acquisition circuit 25 is used for converting an analog signal into a digital signal, and the communication isolation circuit 26 is used for outputting the digital signal to the main controller module 7. The voltage measurement and control module 2 adopts an isolated power supply for power supply; after isolation, the earth potential of the voltage measurement and control module 2 can be connected with the equipotential of the negative voltage clamp on the grounding flat steel, and the effect of effectively sampling signals between two points of the positive voltage clamp and the negative voltage clamp is achieved.
The high-precision and wide-dynamic-range measurement of the tiny direct current signals in the alternating current and direct current mixed signals flowing through the power transformer neutral point grounding flat steel is realized through the circuit combination of the sensor zero calibration circuit 22, the program control amplifying circuit 23 and the whole-period integrating circuit 24 in the voltage measurement and control module 2 and the combination of the program control amplifying circuit and other functional circuits.
In the invention, the current source measurement and control module 5 comprises a controllable current source 50, a current channel switching circuit 51 and a current signal acquisition circuit 52; the controllable current source 50, the current channel switching circuit 51 and the current signal acquisition circuit 52 are all modules existing in the market, and the current channel switching circuit 51 is realized by adopting a power relay; the current signal acquisition circuit 52 adopts an ADC7135 to complete the conversion from analog to digital signals; the controllable current source 50 realizes direct current output of various magnitudes through program control, and the types of the controllable current source on the market are various according to the output power and the brand of the current source.
The output end of the controllable current source 50 is connected to two sets of flat steel current clamping pieces 4 in a time-sharing manner through a current channel switching circuit 51; the current channel switching circuit 51 is further electrically connected to the current signal collecting circuit 52 and the output end of the main controller module 7, respectively, and the current signal collecting circuit 52 is electrically connected to the input end of the main controller module 7, and is configured to convert the collected current analog signal into a digital signal and access the digital signal into the main controller module 7.
In the invention, each set of flat steel voltage clamp 1 comprises a positive voltage clamp 11 and a negative voltage clamp 12; each set of the flat steel current clamp 4 comprises a positive current clamp 41 and a negative current clamp 42;
as shown in fig. 2, the positive voltage clip 11 corresponding to each set of the flat steel voltage clip 1 and the positive current clip 41 corresponding to each set of the flat steel current clip 4 are both disposed at one end of the corresponding grounding flat steel 200 close to the neutral point 101 of the power transformer, and the positive current clip 41 corresponding to each grounding flat steel 200 is correspondingly mounted at the outer side of the corresponding positive voltage clip 11, i.e. the positive current clip 41 is closer to the neutral point 101 of the power transformer than the positive voltage clip 11;
the negative voltage clamp 12 corresponding to each set of the flat steel voltage clamp 1 and the negative current clamp 42 corresponding to each set of the flat steel current clamp 4 are both arranged at one end, close to a transformer substation grounding grid, of the corresponding grounding flat steel 200; the negative current clamp 42 corresponding to each grounding flat steel 200 is correspondingly installed on the outer side of the corresponding negative voltage clamp 12, that is, the negative current clamp 42 is closer to the substation grounding grid 300 than the corresponding negative voltage clamp 12;
the positive current clamps 41 corresponding to the two grounding flat steels are connected with the positive output of the controllable current source 50, and the negative current clamps 42 corresponding to the two grounding flat steels are connected with the negative output of the controllable current source 50.
When current is injected into the two grounding flat steels 200 connected and led out from the neutral point 101 of the power transformer in a time-sharing manner, the voltage drop of the two grounding flat steels 200 under the condition of current injection is measured through the two sets of flat steel voltage clamping pieces 1, so that the double grounding flat steel resistance of the neutral point 101 of the power transformer is calculated.
In the invention, each voltage signal wire 3 is wound by two single-core shielding wires in a twisted-pair manner, one end of each single-core shielding wire is correspondingly connected to a positive voltage clamp 11 and a negative voltage clamp 12 of a flat steel voltage clamp 1 corresponding to the single-core shielding wire, and the other end of each single-core shielding wire is connected to the input end of a voltage measurement and control module 2;
every voltage signal line 3 is close to the shielding layer unsettled of band steel voltage folder 1 one side, and the shielding layer of opposite side is received the power supply ground terminal that voltage measurement and control module 2 kept apart the power.
In the invention, each flat steel temperature measuring module 6 is a temperature sensor, and each temperature sensor is respectively arranged on the corresponding grounding flat steel 200 and is used for monitoring the real-time temperature value of the surface of each grounding flat steel 200.
The working principle is as follows:
according to the invention, current is injected into two grounding flat steels 200 in time-sharing mode through two sets of flat steel current clamping pieces 4, and initial resistance values R1 and R2 of the two grounding flat steels are obtained through calculation according to a double-flat steel resistance calibration method (at an initial temperature, the resistance value of each grounding flat steel is the initial resistance between a set of flat steel voltage clamping pieces 1 which are arranged correspondingly to the resistance value of each grounding flat steel); calculating the resistance values of the two flat steels at the current temperature according to a resistance temperature coefficient formula of the grounding flat steel material; collecting voltage drops on the two grounding flat steels in real time, calculating according to ohm's law to obtain direct currents flowing through the two grounding flat steels, and adding the direct currents flowing through the two grounding flat steels to obtain total current of the grounding flat steels, namely the neutral point direct current of the transformer.
The specific method comprises the following steps:
initial resistance of (I) grounded flat steel resistor
The double-flat-steel resistance calibration method comprises the following steps: the arrangement of the flat steel voltage clamps and the flat steel current clamps on the two grounded flat steels is shown in fig. 2, and the loop circuit parameters satisfy the following relations:
R1＝(V1*R2)/(I*R2-V2) (1)
wherein R1 and R2 are the initial resistance values of the two pieces of grounding flat steel; i is the injection current of the controllable current source; v1 and V2 are the pressure drop of the ground flat at the initial temperature.
At the initial temperature T0 of two pieces of grounding flat steel, firstly injecting current I between a positive current clamp and a negative current clamp on one piece of grounding flat steel, and measuring the voltage drop V1 'and V2' of the grounding flat steel and the other piece of grounding flat steel at the initial temperature T0; substituting into (1) to obtain a first relational expression between two unknowns of R1 and R2;
then inputting a current I between the positive current clamp and the negative current clamp on the other grounding flat steel, measuring to obtain the voltage drop V1 'and V2' of one grounding flat steel and the grounding flat steel at the initial temperature T0, and substituting the voltage drop V1 'and the voltage drop V2' into the formula (1) to obtain a second relational expression between two unknown quantities of R1 and R2;
and solving a linear equation of two variables, and calculating to obtain the initial resistance values R1 and R2 of the two ground flat steels.
(II) resistance value of two flat steels at current temperature
Two resistors R0 at the initial temperature of the grounding flat steel are stored in the main controller module 7, and the real-time temperature value of the surface of the flat steel monitored by the flat steel temperature measuring module 6 is received in real time; the main controller module 7 calculates the resistance value R of the two flat steels at the current temperature according to the resistance temperature coefficient of the grounding flat steel material and the conversion formula (2).
Temperature coefficient of resistance [ (R-R0)/(T-T0) ]/R0 (2)
In the formula, R is the flat steel resistance at the current temperature T, R0 is the flat steel resistance (namely R1 or R2) at the initial temperature T0, and T is the real-time temperature value of the flat steel surface; the material temperature coefficient can be calculated according to a table look-up or an experimental method.
Neutral point DC current of transformer
Collecting voltage drops on the two grounding flat steels in real time, calculating according to ohm's law to obtain direct currents flowing through the two grounding flat steels, and adding the direct currents flowing through the two grounding flat steels to obtain total current of the grounding flat steels, namely the neutral point direct current of the transformer.
The operation process comprises the following steps:
the two grounding flat steels are named as 1# flat steel and 2# flat steel respectively.
1. Firstly, arranging two sets of flat steel voltage clamping pieces and flat steel current clamping pieces on two pieces of grounding flat steel (namely 1# flat steel and 2# flat steel) according to a certain sequence, and respectively installing each flat steel temperature measuring module on the grounding flat steel corresponding to the flat steel temperature measuring module; the main controller module 7 receives the initial temperature T0 of the surface of the two pieces of grounding flat steel monitored by the flat steel temperature measuring module 6;
2. at an initial temperature T0, the main controller module 7 sends an instruction to the current channel switching circuit 51, so that the current channel switching circuit 51 is connected to the corresponding flat steel current clamp 1 on the 1# flat steel, and at this time, the output current I of the controllable current source 50 is connected between the corresponding positive current clamp and the corresponding negative current clamp on the 1# flat steel through the current channel switching circuit 51; meanwhile, the main controller module 7 sends an instruction to the voltage channel switching circuit 20, so that the voltage channel switching circuit 20 is connected to the corresponding flat steel voltage clamping pieces 1 on the 1# flat steel and the 2# flat steel in a time-sharing manner, and the corresponding flat steel voltage clamping pieces 1 on the 1# flat steel and the 2# flat steel respectively receive voltage analog signals through the voltage signal lines corresponding to the voltage signal clamping pieces 1, and are converted into digital signals through the voltage signal acquisition circuit 26 and then output to the main controller module 7;
when the initial temperature of the two grounding flat steels is T0 and the No. 1 flat steel is injected with the current I, the main controller module 7 obtains the voltage drop of the two grounding flat steels;
3. at an initial temperature T0, the main controller module 7 sends an instruction to the current channel switching circuit 51, so that the current channel switching circuit 51 is connected to the corresponding flat steel current clamp 1 on the # 2 flat steel, and at this time, the output current I of the controllable current source 50 is connected between the corresponding positive current clamp and the corresponding negative current clamp on the # 2 flat steel through the current channel switching circuit 51; meanwhile, the main controller module 7 sends an instruction to the voltage channel switching circuit 20, so that the voltage channel switching circuit 20 is connected to the corresponding flat steel voltage clamping pieces 1 on the 1# flat steel and the 2# flat steel in a time-sharing manner, and the corresponding flat steel voltage clamping pieces 1 on the 1# flat steel and the 2# flat steel respectively receive voltage analog signals through the voltage signal lines corresponding to the voltage signal clamping pieces 1, convert the voltage analog signals into digital signals and output the digital signals to the main controller module 7 through the voltage signal acquisition circuit 26;
when the 2# flat steel is injected with current I at the initial temperature of the two grounded flat steels, the main controller module 7 obtains the voltage drop of the two grounded flat steels;
4. the main controller module 7 substitutes the data obtained in the steps 2 and 3 into a formula (1) to calculate the initial resistance values of the two pieces of grounding flat steel;
5. the main controller module 7 receives the real-time temperature value T of the surfaces of the two pieces of grounding flat steel from the flat steel temperature measuring module 6 in real time;
6. under the real-time temperature value T, the main controller module 7 sends an instruction to the voltage channel switching circuit 20, so that the voltage channel switching circuit 20 is accessed to the corresponding flat steel voltage clamping pieces 1 on the 1# flat steel and the 2# flat steel in a time-sharing mode, voltage analog signals on the 1# flat steel and the 2# flat steel are collected and converted into digital signals to be output to the main controller module 7, and the main controller module 7 obtains the voltage drop of the two grounding flat steels at the current temperature;
7. the main controller module 7 calculates the resistance values of the two grounding flat steels at the current temperature through a resistance temperature coefficient formula according to the data obtained in the steps 4 and 5; and (3) calculating the magnitude and direction of the direct current flowing through the two flat steels by using the ohm law according to the voltage drop of the two grounded flat steels at the current temperature obtained in the step (6) by the main controller module (7), and adding the direct currents flowing through the two flat steels to obtain the total current flowing through the grounded flat steels.
In the invention, the derivation process of the formula (1) is as follows:
two pieces of grounding flat steel are named as 1# flat steel and 2# flat steel respectively, the total resistance of a flat steel loop is set to be R, the resistance of the flat steel between flat steel voltage clamping pieces on the 1# flat steel is set to be R1, the resistance of the flat steel between flat steel voltage clamping pieces on the 2# flat steel is set to be R2, the resistance of the flat steel between flat steel current clamping pieces on the 1# flat steel is set to be R3, and the resistance of the parallel flat steel between two points of the 1# flat steel current clamping pieces is set to be RAnd are。
Step 1: i1 was injected into a No. 1 flat steel current clamp and measured to yield U1 and U2.
RAnd are＝R3*(R-R3)/(R3+(R-R3))＝R3(R-R3)/R
The current flowing through R1 is: U1/R1 ═ I1RAnd are/R3＝I1*(R-R3)/R (1-1)
The current flowing through R2 is: U2/R2 ═ I1RAnd are/(R-R3)＝I1*R3/R (1-2)
From the formula (1-2): r3 ═ U2R/(I1 ═ R2) (1-3)
Substituting equation (1-3) into (1-1) can obtain:
U1/R1＝I1*(R-U2*R/(I1*R2))/R＝(I1*R2-U2)/R2
the derivation yields: r1 ═ U1 × R2/(I1 × R2-U2) (1-4)
Step 2: i2 was injected into the No. 2 flat steel current clamp, and U1 'and U2' were measured.
Substituting into the formula (1-4) yields:
R1＝U1'*R2/(I2*R2-U2') (1-5)
and step 3: solving the equation of once two to obtain R1 and R2.
Finally, it is noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (7)
1. A current measuring device for power transformer neutral point direct current magnetic biasing comprises a power transformer (100), wherein two grounding flat steels (200) are led out from a power transformer neutral point (101) on the power transformer (100), and the two grounding flat steels (200) are connected to a transformer substation grounding grid (300); the device is characterized by also comprising two sets of flat steel voltage clamping pieces (1), two voltage signal wires (3), a voltage measurement and control module (2), two sets of flat steel current clamping pieces (4), a current source measurement and control module (5), two flat steel temperature measurement modules (6) and a main controller module (7);
each grounding flat steel (200) led out from the neutral point (101) of the power transformer is provided with a set of flat steel voltage clamping pieces (1) and a set of flat steel current clamping pieces (4), each set of flat steel voltage clamping pieces (1) is connected with a voltage measurement and control module (2) through a voltage signal wire (3) correspondingly arranged with the flat steel voltage clamping pieces, each set of flat steel current clamping piece (4) is connected with a current source measurement and control module (5), and the voltage measurement and control module (2) and the current source measurement and control module (5) are electrically connected with a main controller module (7);
every all still be equipped with one on ground connection band steel (200) band steel temperature measurement module (6), every band steel temperature measurement module (6) all with main control unit module (7) electricity is connected.
2. The current measuring device for neutral point direct current magnetic biasing of the power transformer according to claim 1, wherein the voltage measurement and control module (2) comprises a voltage channel switching circuit (20), an overvoltage protection circuit (21), a sensor zero calibration circuit (22), a program control amplifying circuit (23), a full-period integrating circuit (24), a voltage signal acquisition circuit (25) and a communication isolation circuit (26); the voltage channel switching circuit (20) is electrically connected with the output end of the main controller module (7) and is controlled by the main controller module (7);
analog voltage signals sampled from two pieces of grounded flat steel (200) are accessed to a voltage channel switching circuit (20) in a time-sharing mode through voltage signal lines (3) corresponding to the analog voltage signals, the voltage channel switching circuit (20) is electrically connected with an overvoltage protection circuit (21), the overvoltage protection circuit (21) is electrically connected with a sensor zero calibration circuit (22), the sensor zero calibration circuit (22) is electrically connected with a program control amplification circuit (23), the program control amplification circuit (23) is electrically connected with a whole-period integration circuit (24), the whole-period integration circuit (24) is electrically connected with a signal acquisition circuit (25), the signal acquisition circuit (25) is electrically connected with a communication isolation circuit (26), and the communication isolation circuit (26) is electrically connected with the input end of a main controller module (7);
the voltage channel switching circuit (20) is used for accessing a two-way analog voltage signal; the overvoltage protection circuit (21) is used for EMC protection; the program control amplifying circuit (23) and the whole-period integrating circuit (24) are used for signal conditioning to realize tiny signal amplification and inhibit alternating current signals; the sensor zero calibration circuit (22) is used for eliminating measurement errors introduced when the program control amplification circuit (23) and the whole-period integration circuit (24) perform signal conditioning; the signal acquisition circuit (25) is used for converting analog signals into digital signals, and the communication isolation circuit (26) is used for outputting the digital signals to the main controller module (7) and realizing ground potential isolation of the two functional modules.
3. The current measuring device for neutral point direct current magnetic bias of a power transformer according to claim 2, characterized in that the voltage measurement and control module (2) is powered by an isolated power supply.
4. The current measuring device for neutral point direct current magnetic bias of a power transformer according to claim 1, wherein the current source measurement and control module (5) comprises a controllable current source (50), a current channel switching circuit (51) and a current signal acquisition circuit (52);
the output end of the controllable current source (50) is connected to the two sets of flat steel current clamping pieces (4) in a time-sharing manner through a current channel switching circuit (51); the current channel switching circuit (51) is further respectively electrically connected with the current signal acquisition circuit (52) and the output end of the main controller module (7), and the current signal acquisition circuit (52) is further electrically connected with the input end of the main controller module (7) and used for converting acquired current analog signals into digital signals and connecting the digital signals into the main controller module (7).
5. A current measuring device for neutral point dc biasing of power transformers according to claim 1, characterized in that each set of said flat steel voltage clamps (1) comprises a positive voltage clamp (11) and a negative voltage clamp (12); each set of the flat steel current clamping pieces (4) comprises a positive current clamping piece (41) and a negative current clamping piece (42);
the positive voltage clamping pieces (11) corresponding to each set of the flat steel voltage clamping pieces (1) and the positive current clamping pieces (41) corresponding to each set of the flat steel current clamping pieces (4) are arranged at one ends, close to the neutral point (101), of the power transformer of the grounding flat steel (200) corresponding to the positive voltage clamping pieces, and the positive current clamping pieces (41) corresponding to each set of the grounding flat steel (200) are correspondingly arranged on the outer sides of the positive voltage clamping pieces (11) corresponding to the grounding flat steel, namely the positive current clamping pieces (41) are closer to the neutral point (101) of the power transformer than the positive voltage clamping pieces (11);
the negative voltage clamp (12) corresponding to each set of the flat steel voltage clamp (1) and the negative current clamp (42) corresponding to each set of the flat steel current clamp (4) are arranged at one end, close to a transformer substation ground grid, of the corresponding grounding flat steel (200); the negative current clamp (42) corresponding to each grounding flat steel (200) is correspondingly arranged on the outer side of the corresponding negative voltage clamp (12), namely the negative current clamp (42) is closer to the transformer substation grounding grid (300) than the corresponding negative voltage clamp (12);
when current is injected into two grounding flat steels (200) connected and led out from a neutral point (101) of the power transformer in a time-sharing manner, voltage drops on the two grounding flat steels (200) under the condition of current injection are measured through two sets of flat steel voltage clamping pieces (1), and therefore the double-grounding flat steel resistance of the neutral point (101) of the power transformer is calculated.
6. The current measuring device for the neutral point direct current magnetic bias of the power transformer according to claim 1, wherein each voltage signal wire (3) is wound in a twisted-pair manner by two single-core shielding wires, one end of each single-core shielding wire is correspondingly connected to a positive voltage clamp (11) and a negative voltage clamp (12) of a flat steel voltage clamp (1) corresponding to the single-core shielding wire, and the other end of each single-core shielding wire is connected to the input end of the voltage measurement and control module (2);
each voltage signal wire (3) is close to the shielding layer on one side of the flat steel voltage clamping piece (1) and is suspended, and the shielding layer on the other side is connected to the power supply ground end of the voltage measurement and control module (2) isolation power supply.
7. The current measuring device for neutral point direct current magnetic biasing of a power transformer according to claim 1, characterized in that each flat steel temperature measuring module (6) is a temperature sensor, which is respectively installed on the corresponding grounding flat steel (200) for monitoring the real-time temperature value of the surface of each grounding flat steel (200).
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114994443A (en) * | 2022-06-07 | 2022-09-02 | 国网江西省电力有限公司电力科学研究院 | Transformer neutral point direct current magnetic bias current measuring instrument |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114994443A (en) * | 2022-06-07 | 2022-09-02 | 国网江西省电力有限公司电力科学研究院 | Transformer neutral point direct current magnetic bias current measuring instrument |
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