CN112557824A - Fault full-sensing terminal and small-current single-phase grounding accurate positioning method thereof - Google Patents

Abstract

The invention provides a fault full-sensing terminal and a small-current single-phase grounding accurate positioning method thereof, which are characterized by comprising the following steps: the system comprises an electronic voltage transformer, an electronic current transformer, a protection line loss board and a main board; the electronic voltage transformer is used for collecting phase voltages of an A phase, a B phase and a C phase of the ring main unit; the electronic current transformer is used for collecting phase A, phase B and phase C currents at intervals of the ring main unit; the electronic voltage transformer and the electronic current transformer are respectively connected with the main board through the protection line loss board; an integrator and a filter are integrated in the electronic voltage and electronic current transformer and are resistance-capacitance transformers; the protection line loss board is used for carrying out analog-to-digital conversion on voltage and current signals. The real-time depiction of the running state of the cable is realized through various signal acquisition, the early warning is carried out in advance to eliminate fault equipment, and meanwhile, the accurate positioning of various faults can be realized in a short time during the fault.

Description

Fault full-sensing terminal and small-current single-phase grounding accurate positioning method thereof

Technical Field

The invention belongs to the technical field of operation and maintenance of power distribution networks, and particularly relates to a fault full-sensing terminal and a small-current single-phase grounding accurate positioning method thereof.

Background

In the power industry, the existing DTU lacks the diagnosis capability for the low-current ground fault and does not describe the hidden danger characteristics of the old cable. Especially under the scenes that the cabling rate is high and the cable fault ratio is relatively high, the 10kV distribution network system adopts an arc suppression coil grounding mode, and the following difficult problems exist in the actual operation and maintenance process:

1. and the cable fault point is difficult to find. The cable is buried underground, and unable direct observation, in addition lack ground fault and study and judge the means, cable network fault location is inaccurate, leads to cable fault point to look for the difficulty to cause the long overlength of trouble-shooting, cause great influence to the power failure user, can't satisfy the requirement that promotes power supply service quality.

2. The distribution network is easy to cause secondary faults. Due to the lack of a cable operation monitoring means, when a distribution network is in ground fault, phase voltage is raised to line voltage, and old cable hidden dangers cannot be found and eliminated in time, so that weak links (such as cable heads and the like) of the line are easy to break down, and multiple secondary faults are caused in recent years. The generation of secondary faults also shows that the cable network in the stone lion area really has weak points, and the realization of real-time monitoring of cable operation is an urgent problem to be solved at the present stage.

By 3 months in 2020, 11661 primary and secondary complete sets of equipment are put into operation in a certain province, lines 5018 are covered, 288 standard automatic feeders are formed, and the ground fault judging accuracy of the primary and secondary complete sets of equipment in 2 months in the whole province is only 11.74%.

By analyzing waveform characteristics, only 9 waveforms which can be actually used for research and judgment are found, and the other 120 waveforms (accounting for 93.02%) have the phenomena of serious clutter, no zero-sequence current, no zero-sequence voltage, unbalanced phase current and the like, which are main reasons for misjudgment.

In conclusion, the characteristics of deep analysis of old fault cables by taking a small-current grounding fault positioning key technology of a medium-voltage distribution network as a warp and non-electric quantity monitoring such as partial discharge and temperature as a weft are researched, the single-phase grounding fault is accurately positioned, and the early warning and elimination of the hidden danger cables and the full-sensing terminal are required to be urgently needed.

Disclosure of Invention

Aiming at the defects and shortcomings of the existing scheme, the invention provides a fault full-sensing terminal and a small-current single-phase grounding accurate positioning method thereof, which specifically adopt the following technical scheme:

a fault fully-aware terminal, comprising: the system comprises an electronic voltage transformer, an electronic current transformer, a protection line loss board and a main board; the electronic voltage transformer is used for collecting phase voltages of an A phase, a B phase and a C phase of the ring main unit; the electronic current transformer is used for collecting phase A, phase B and phase C currents at intervals of the ring main unit; the electronic voltage transformer and the electronic current transformer are respectively connected with the main board through the protection line loss board; an integrator and a filter are integrated in the electronic voltage and electronic current transformer and are resistance-capacitance transformers; the protection line loss board is used for carrying out analog-to-digital conversion on voltage and current signals.

Preferably, the main board and the protection line loss board are arranged in the terminal cabinet.

Preferably, the voltage of the A phase, the B phase and the C phase of the ring main unit is acquired by arranging two electronic voltage transformers with spaced incoming lines, and leads of a direct voltage sensor are fixed on an ABC three-phase copper bar of the ring main unit and electrically connected with the copper bar.

Preferably, the electronic current transformer is used for collecting phase A, phase B and phase C currents at intervals of the ring main unit according to a 600A/1V transformation ratio and is installed on a cable in a buckling mode; the electronic voltage transformer converts the 10kV voltage of the line into 3.25V voltage.

Preferably, the electronic voltage transformer and the electronic current transformer are integrated into a cable-controlled connection protection line loss board through a secondary line.

Preferably, the method further comprises the following steps: install in the perception sensor is put in the trinity cable office of supersound/TEV/UHF of cabinet inner wall under the looped netowrk cabinet, install in the temperature sensor of cable head and install in the harmful gas detection device of cabinet lower part under the looped netowrk cabinet to wireless receiving module through wireless communication connection mainboard.

Preferably, the method further comprises the following steps: the leakage current transformer is arranged at the cable grounding wire of the ring main unit; the leakage current transformer is connected with the main board through the protection line loss board.

And according to the accurate positioning method of the small current single-phase grounding of the fault full sensing terminal, the method is characterized in that:

secondary clutter is suppressed and formed through an integrator and a filter which are integrated in the electronic voltage and electronic current transformer, and the protection line loss board converts and transmits voltage and current signals to a main board; the main board realizes the accurate positioning of the small-current single-phase grounding according to the voltage and current signals and a preset small-current single-phase grounding criterion.

Preferably, the preset criterion of low-current single-phase grounding is as follows:

when a line ground fault occurs, if a certain path meets the following conditions, the line ground fault is positioned as a low-current single-phase ground fault:

the zero sequence voltage leads the zero sequence current by 60 degrees to 120 degrees and the zero sequence voltage under the on-off state is all larger than 0;

the ratio of the two-phase voltage increase to the one-phase voltage decrease is larger than a first set value, and the zero-sequence voltage is larger than a second set value, at least one of the two-phase voltage increase and the one-phase voltage decrease is satisfied;

zero sequence current is larger than a third set value;

the voltage of at least two phases is greater than 4 kV.

Preferably, when the preset low-current single-phase grounding fault is located, whether the grounding alarm enable is started is judged, and if the grounding alarm enable is started, the grounding alarm is started.

Compared with the prior art, the invention and the preferred scheme thereof have the following main characteristics and advantages:

1. the method has the advantages that an advanced ground fault research and judgment technology is adopted, the selected voltage and current sensors are higher in precision and safer, and the resistance-capacitance type electronic sensor is adopted, so that the method is not saturated, wide in frequency response range, large in measurement range, good in linearity, free of ferromagnetic resonance and free of short-circuit overvoltage risk; thus, an advanced algorithm comprehensively researched and judged through transient steady state and direction can be used.

2. Installing a cable running state monitoring and sensing sensor additionally: adopt advanced trinity cable office to put perception sensor, need not follow-up fortune dimension and charge, cable joint department installs temperature sensor additional simultaneously, installs gas monitoring device additional simultaneously, puts through the office and temperature measurement and harmful gas detection device and leakage current monitoring, early warning cable insulation hidden danger and latent fault in advance, improve old cable operational environment, reduce secondary fault and take place.

3. The existing terminal is free from operation and maintenance: the terminal has low power consumption, and can adopt a high-performance maintenance-free backup power supply to reduce the operation and maintenance quantity of the terminal. The lithium iron phosphate battery with the quality guaranteed for 8 years can be used as a backup power supply, the power consumption is low, the heat dissipation is small, the lithium iron phosphate battery can stably run at 0-70 ℃, the service life is not less than 8 years, the capacity is not less than 25Ah, and the capacity decay rate is not more than 10%/year.

4. The network distribution operation and maintenance service such as supporting the synchronous line loss is realized: the method has the advantages that the electric quantity data are automatically acquired, the data such as three-phase voltage, three-phase current, zero-sequence voltage, zero-sequence current, active/reactive power, electric quantity and the like are acquired according to the metering precision, and the line loss assessment is facilitated. Meanwhile, the automatic phase checking function is achieved, the manual operation burden is reduced, the forced locking phase sequence loop closing of the circuit which does not correspond to the phase sequence is realized, and the intrinsic safety is improved.

The invention and the optimized scheme realize real-time depiction of the running state of the cable through various signal acquisition, early warning and elimination of fault equipment, and simultaneously can realize accurate positioning (particularly low-current grounding) of various faults in a short time when the faults occur, thereby reducing the time length of power failure of the faults and greatly advancing to zero power failure perception.

Drawings

The invention is described in further detail below with reference to the following figures and detailed description:

fig. 1 is a schematic view of an installation position of each sensor in a ring main unit according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a protection line loss board and a main board in a terminal cabinet according to an embodiment of the present invention;

FIG. 3 is a schematic diagram illustrating a low current single-phase grounding criterion according to an embodiment of the present invention;

FIG. 4 is a schematic illustration of an in-bound fault;

FIG. 5 is a schematic of an out-of-range fault;

FIG. 6 is a schematic diagram of a single-phase ground out-of-bound waveform;

FIG. 7 is a schematic diagram of a single-phase line break waveform;

FIG. 8 is a schematic diagram of a three-phase line break waveform;

FIG. 9 is a schematic view of a bad contact waveform of an aerospace joint;

FIG. 10 is a schematic diagram of a device start-up process according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of an active analog integrator in accordance with embodiments of the present invention;

in the figure: 1-an electronic voltage transformer; 2-an electronic current transformer; 3-protecting the line loss board; 4, a main board; 5-three-in-one cable partial discharge sensing sensor; 6-temperature sensor; 7-harmful gas detection device; 8-leakage current transformer.

Detailed Description

In order to make the features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail as follows:

as shown in fig. 1 and fig. 2, in order to implement the function of accurately positioning the low-current single-phase ground, the fault fully-sensing terminal provided by the apparatus of the present embodiment includes: the system comprises an electronic voltage transformer 1, an electronic current transformer 2, a protection line loss board 3 and a main board 4.

The electronic voltage transformer 1 is used for collecting phase A, phase B and phase C voltages of the ring main unit and converting 10kV voltage of a line into 3.25V voltage available for a terminal. Because the looped network cabinet is the same as a bus, and a transfer path is not determined, two transformers with interval incoming lines are additionally arranged, and the three-phase voltage of the line can be acquired and the corresponding voltage is shared with other outgoing line intervals (two interval voltages are acquired according to the requirements of functionality and cost) no matter which side is supplied with power. Therefore, in this embodiment, the electronic voltage transformer 1 with two spaced incoming lines is used to collect the voltages of the a phase, the B phase and the C phase of the ring main unit, and the lead of the direct voltage sensor is fixed on the ABC three-phase copper bar of the ring main unit and electrically connected to the copper bar. In the aspect of installation, can loosen the copper nose screw of ABC three-phase copper bar earlier after having a power failure, lock direct voltage sensor lead wire on the copper bar that corresponds, the base is fixed on cabinet body bottom plate with the self tapping screw to go up the earth connection.

In this embodiment, the electronic current transformer 2 is used for collecting phase currents of a phase, a phase B and a phase C at intervals of the ring main unit according to a 600A/1V transformation ratio, and is installed on the cable in a snap-in manner after power failure.

The electronic voltage transformer 1 and the electronic current transformer 2 are respectively connected with a main board 4 through a protection line loss board 3; an integrator and a filter are integrated in the electronic voltage and electronic current transformer 2, and the electronic voltage and electronic current transformer is a resistance-capacitance type transformer; the protection line loss plate 3 is used for carrying out analog-to-digital conversion on voltage and current signals. Mainboard 4 and protection line damage board 3 set up in the terminal cabinet.

The integrator and the filter integrated in the electronic voltage transformer 1 and the electronic current transformer 2 are used for inhibiting secondary clutter from forming, secondary lines of corresponding current and voltage are integrated into a control cable to transmit corresponding voltage and current signals to the protection line loss board 3 in a centralized manner, analog-to-digital conversion is realized as shown in figure 2, corresponding digital signals are transmitted to the main board 4 through J1, the collected current and voltage are processed in the main board 4, according to the optimized traditional one-secondary complete switch algorithm logic shown in figure 3, current starting criteria and power research criteria are added, clutter interference intervals are avoided, and accurate positioning of small current single-phase grounding is realized.

As shown in fig. 3, the criterion of the low-current single-phase grounding adopted in this embodiment is as follows:

when a line ground fault occurs, if a certain path meets the following conditions, the line ground fault is positioned as a low-current single-phase ground fault:

the zero sequence voltage leads the zero sequence current by 60 degrees to 120 degrees and the zero sequence voltage under the on-off state is all larger than 0;

the ratio of the two-phase voltage increase to the one-phase voltage decrease is larger than a first set value, and the zero-sequence voltage is larger than a second set value, at least one of the two-phase voltage increase and the one-phase voltage decrease is satisfied;

zero sequence current is larger than a third set value;

the voltage of at least two phases is greater than 4 kV.

When the preset small-current single-phase grounding positioning small-current single-phase grounding fault occurs, whether the grounding alarm enable is started or not is judged, and if the grounding alarm enable is started, the grounding alarm is started.

In addition, as shown in fig. 1 and fig. 2, in order to realize the function of monitoring the running state of the cable, a three-in-one cable partial discharge perception sensor 5 of ultrasound/TEV/UHF is adopted and is installed on the inner wall of the lower cabinet of the ring main unit; mounting the temperature sensor 6 on the cable head; considering factors such as high gas density of SF6 and the like, the harmful gas detection device 7 is installed at the lower part of the ring main unit, and the running state of the cable is monitored; the sensor module adopts a wireless communication mode to carry out matched communication with a wireless receiving module of a full sensing terminal mainboard 4 shown in figure 2, and then the wireless receiving module is transmitted to the mainboard 4 through analog-digital processing.

Simultaneously still installed leakage current transformer 8 of accurate measurement undercurrent additional in cable earth connection department and monitored leakage current, adopt the hard-wired mode to gather corresponding current signal and pass to protection line damage board 3 as figure 2, set for transfinite alarm function at mainboard 4 finally, pass corresponding fault signal and give the main website on, so that formulate relevant maintenance plan, change old cable and branch case, realize analyzing the characteristic state before old cable trouble, realize that the early warning eliminates old hidden danger cable.

The following provides a specific principle analysis of the scheme design of this embodiment:

reason analysis for low ground fault judging accuracy rate of 1-secondary complete equipment

1.1 one-time and two-time fusion complete switch small current grounding research and judgment logic

The traditional steady-state zero-sequence overcurrent needs to set each protection quantity offline, and when a multi-loop in-phase complex ground fault occurs in a small-resistance grounding system, the traditional zero-sequence current protection is easily rejected or mistakenly operated due to unreasonable set protection quantity, so that the requirement of a power grid on the selectivity of a protection device cannot be met.

As shown in fig. 4, is an in-bound fault, and as shown in fig. 5, is an out-of-bound fault.

Because clutter on the circuit is more complicated, in order to prevent the wrong report condition of the fault outside the boundary, the voltage starting threshold is recommended to be set by more than 20 percent of rated value, and the specific reason is as follows:

the conventional small current determination method is as follows:

the Nth effective sampling point of the zero-sequence voltage is larger than the zero crossing point:

the (N + 1) th effective sampling point of the zero sequence voltage is larger than the Nth effective sampling point and returns to 1, the trend is upward, otherwise, the zero sequence voltage returns to 0

The Nth effective sampling point of the zero-sequence voltage is smaller than the zero crossing point:

the (N + 1) th effective sampling point of the zero sequence voltage is smaller than the Nth effective sampling point and returns to-1, the trend is downward, otherwise, the zero sequence voltage returns to 0

The Nth effective sampling point of the zero-sequence current is larger than the zero crossing point:

the (N + 1) th effective sampling point of the zero-sequence current is larger than the Nth effective sampling point and returns to 1, the trend is upward, otherwise, the zero-sequence current returns to 0

The Nth effective sampling point of the zero-sequence current is smaller than the zero crossing point:

the N +1 effective sampling point of the zero sequence current is smaller than the Nth effective sampling point and returns to-1, the trend is downward, otherwise, the zero sequence current returns to 0

C = iN (return value) uN (return value) (N =0,1,2,3,4, …)

The small current grounding fault interval is judged by zero voltage starting and zero voltage and zero current included angle.

1.2 one-time and two-time fusion complete switch small current grounding misjudgment analysis

The pre-field fault waveform is a single phase earth out-of-bound waveform as shown in fig. 6. It can be seen that at around 78ms, when one voltage has reached the voltage threshold, the later change characteristics have met the above logic requirements.

As shown in fig. 7-9, respectively: single-phase broken line waveform, three-phase broken line waveform and aviation connector poor contact waveform

Samples of 129 complete switch false alarms were extracted. By analyzing waveform characteristics, only 9 waveforms which can be actually used for research and judgment are found, and the other 120 waveforms (accounting for 93.02%) have the phenomena of serious clutter, no zero-sequence current, no zero-sequence voltage, unbalanced phase current and the like, which are main reasons for misjudgment.

1.3 the reason for the misjudgment of the small current grounding of the first-second fusion switch set

The abnormal waveform has the following characteristics: 1. the amplitude (effective value) of the clutter is relatively small, with an approximate rate below 1A. 2. The positive and negative of the clutter are relatively symmetrical, and the change frequency is relatively fast.

According to the characteristics, three main attack directions are determined: 1. according to the characteristic that the amplitude of the clutter is small, but the simple current criterion is interfered by unbalanced current, the voltage criterion is more reliable in representing the low current grounding, so that the current starting logic can be considered to be corrected to be the voltage and current combined starting criterion, and the clutter influence interval is avoided. 2. The influence 3 of noise waves is filtered by adopting a high-precision voltage current transformer, a filtering loop, an integrator and the like, the power increasing criterion is adopted, and the effect of software filtering for counteracting the influence of high-frequency noise waves is achieved through the integral effect.

The embodiment is based on the fact that the traditional one-time and two-time fusion complete switch depends on a fixed installation mode to realize research and judgment of small current grounding consideration, optimize algorithm logic and related hardware, and realize development of a self-adaptive fault full-sensing terminal.

2 research of voltage and current combined starting criterion of fault full-sensing terminal

2.1 theoretical analysis of current starting criterion

Comparing the sampling signal with a starting threshold value, and starting and recording fault data by the device when the amplitude of two sampling points in three continuous sampling points is greater than the starting threshold value of the device in all the sampling points of the sampling window; otherwise, the device does not upload data to the master station and continues to sample the zero-mode current signals in the system. The specific implementation flow is shown in fig. 10.

2.2 summary of Voltage-Current Joint Start criteria

Because the low-current ground fault steady-state characteristic boundary switch at the boundary switch is generally installed at the tail end of a branch line or a line, the length of a downstream (user side) line of the boundary switch is far less than the sum of the lengths of other lines in the system, correspondingly, the distributed capacitance to the ground of the downstream line is far less than that of other lines, and the distributed capacitance current to the ground of the downstream line is also far less than that of an upstream (system side) line.

If the grounding point is positioned at the upstream of the demarcation switch, no matter the system is in a non-grounding or arc suppression coil grounding mode, the fault power frequency zero sequence current detected by the demarcation switch is the grounding distribution capacitance current of the downstream circuit. The amplitude is calculated according to the capacitance current to the ground of 30 mA of the overhead line with the length of 1 km and 10kV and the capacitance current to the ground of 600 mA of the cable line with the length of 1 km and 10kV, and is generally not more than 1A.

In summary, the steady-state current 1A is added to form the voltage-current combined starting criterion, so that the correctness of the action of the boundary switch can be effectively ensured, and the interference of high-frequency noise waves and low-amplitude noise waves can be inhibited.

3 research of fault full-sensing terminal voltage current transformer

3.1 research background and significance of RC mutual inductor

The traditional electromagnetic PT power supply mode is a power supply mode adopted by most of the existing automation equipment and switch operating mechanisms, due to the limitation of the technical principle, the failure rate of an electromagnetic PT device is very high, the electromagnetic PT device is a component with the highest failure rate on site at present, and the safety problems of overcurrent, electromagnetic resonance and the like caused by voltage secondary side short circuit exist, in addition, the secondary rated voltage of a voltage sensor is 100V or 100/3V, the secondary rated voltage of the voltage sensor is not convenient to be directly interfaced with modern microcomputer protection and measurement equipment, and the requirements of automation and digitization of an electric power system are difficult to adapt. The resistance-capacitance voltage division type voltage sensor has the advantages of high measurement accuracy, large linear range, wide frequency band and the like, eliminates potential safety hazards caused by ferromagnetic resonance and secondary side short circuit, and better overcomes various problems of electromagnetic PT in the working principle.

3.2 selection of Filter and integrator of Fault fully-sensing terminal Voltage-Current Transformer

1) Design of low-pass filter

In order to improve the measurement accuracy, the input signal to be measured needs to pass through a low-pass anti-aliasing filter to filter the influence of noise. The most common types of low-pass filters are the Butterworth (Butterworth), Chebychev (Chebychev) and Bessel (Bessel) filters. The amplitude-frequency response of the Butterworth filter has the maximum flatness in the pass band, but the attenuation from the pass band to the stop band is slow, the Chebychev filter can quickly attenuate, but the error value in the pass band can be subjected to equal ripple variation. The Bessel filter only satisfies the phase-frequency characteristic and does not concern the amplitude-frequency characteristic, and the waveform with small phase distortion can be obtained. Meanwhile, the order of the selected filter is not too high, otherwise, the phase shift error of the voltage current channel is easy to increase. The filter is selected to meet certain bandwidth characteristics, and the phase offset value of the filter is ensured to be within the accuracy range conforming to the measurement error, and both the Chebychev or Butterworth second-order low-pass filters are common choices in practical processing.

2) Principle and design of an integrator

The integrator is a key part of a sensor signal processing link, and the integration precision of the integrator is directly related to the accuracy of the sensor output. From the foregoing analysis, it can be seen that analog integration and digital integration have advantages and disadvantages as two common integration methods. The analog integrator has the advantages of simple structure, response speed block, large input dynamic range and the like, and the technology is mature. When the integrating process is realized by using an analog device, the performance and the temperature stability of the integrating process are determined by analog elements. However, because the actual operational amplifier is not an ideal device, operational amplifier imbalance, leakage and loss of a capacitor, time drift and temperature drift of the operational amplifier and other analog devices all affect the integration result, and integration errors are caused. Furthermore, the design of the feedback and compensation of the analog integrator is not flexible enough and the compensation stage may introduce new errors. For an electronic transformer, the integrator needs to operate stably for a long time, and it is difficult to completely overcome errors caused by these factors.

The digital integrator has the advantages of simple hardware circuit, good temperature stability, flexible design, high reliability, high repeatability and the like. The amplitude and phase data of the original signal are calculated by using an integral algorithm, and the accuracy is only influenced by the A/D conversion accuracy, the number of sampling points and the calculation accuracy. However, the digital integrator needs to solve the problem of the algorithm of digital integration after high-speed a/D conversion, and the process must be as short as possible to achieve the purpose of fast sampling integration, so that the requirement on the operation speed of the microprocessor is very high, and meanwhile, factors such as speed, precision and the like need to be comprehensively considered in practice, and a proper number of sampling points is selected. In addition, in the design of the digital integrator, the influence factors of direct current offset, an initial integration value, input saturation and the like need to be solved, and the precision and the stability of the digital integrator are ensured by adding a compensation link.

An active analog integration device is selected to realize the integration function. The integrator circuit was fabricated as shown in fig. 11, combining the two improved integration circuits. Besides reasonable selection of parameters of the capacitor and the resistor, a fine tuning device is added in the circuit to ensure the precision of the transmission signal.

In summary, the fault full-sensing terminal voltage current transformer adopts a resistance-capacitance transformer to ensure the precision and simultaneously can inhibit the formation of secondary noise.

3.3 Fault fully-sensing terminal transient reactive power direction method

Because the transient current amplitude is generally several times to tens of times of the power frequency, the transient current amplitude is not influenced by arc suppression coil compensation and unstable arcs, a reliable judgment basis is provided for distribution network fault location, and the transient current amplitude is widely applied to distribution networks in China.

The transient reactive power is defined as the Hilbert transform value of the transient voltage signal and the average power of the transient current signal in the transient period. The calculation formula is as follows:

(1-5)

in the formula:

is a hilbert transform of the transient voltage signal.

After the small current grounding system has single-phase grounding fault, the zero sequence network of the system can be regarded as a simple uniform circuit with an open circuit at the tail end at the downstream of the fault point and a sound circuit, and the input impedance of the simple uniform circuit is not influenced by the arc suppression coil and is capacitive before the first series resonance. The input impedance of the measuring point from the upstream of the fault point to the bus is equal to the impedance of each sound line which is connected in parallel and then connected in series with the impedance between each measuring point and the bus, the input impedance is capacitive in the first series resonance, when the frequency is more than 150Hz, the compensation function of the arc suppression coil can be ignored, therefore, the input impedance is equivalent capacitive from 3 times of power frequency to the first series resonance, the low frequency band where each line is capacitive is selected as a characteristic frequency band, in the characteristic frequency band, the transient reactive power of all the measuring points at the upstream of the fault point of the fault line is less than 0, the transient reactive power of all the measuring points at the downstream of the fault point and the sound line is more than 0, and the positioning is carried out by utilizing.

In conclusion, the power method realizes the integral effect of the voltage-current product, can realize the effect of algorithm filtering, can be used as the starting criterion of the self-adaptive judgment, automatically corrects the current included angle according to the positive and negative of the power and the self-power operation, and realizes the self-adaptive judgment of the small-current grounding.

The present invention is not limited to the above-mentioned preferred embodiments, and any other various types of fault sensing terminals and methods for accurately positioning a low-current single-phase ground can be derived from the teaching of the present invention.

Claims (10)

1. A fault fully-aware terminal, comprising: the system comprises an electronic voltage transformer, an electronic current transformer, a protection line loss board and a main board; the electronic voltage transformer is used for collecting phase voltages of an A phase, a B phase and a C phase of the ring main unit; the electronic current transformer is used for collecting phase A, phase B and phase C currents at intervals of the ring main unit; the electronic voltage transformer and the electronic current transformer are respectively connected with the main board through the protection line loss board; an integrator and a filter are integrated in the electronic voltage and electronic current transformer and are resistance-capacitance transformers; the protection line loss board is used for carrying out analog-to-digital conversion on voltage and current signals.

2. The fault fully-aware terminal of claim 1, wherein: the main board and the protection line loss board are arranged in the terminal cabinet.

3. The fault fully-aware terminal of claim 1, wherein: the electronic voltage transformer with two spaced incoming lines collects phase voltages of an A phase, a B phase and a C phase of the ring main unit, and leads of a direct voltage sensor are fixed on an ABC three-phase copper bar of the ring main unit and electrically connected with the copper bar.

4. The fault fully-aware terminal of claim 1, wherein: the electronic current transformer is used for collecting phase A, phase B and phase C currents at intervals of the ring main unit according to the 600A/1V transformation ratio and is installed on a cable in a buckling mode; the electronic voltage transformer converts the 10kV voltage of the line into 3.25V voltage.

5. The fault fully-aware terminal of claim 1, wherein: the electronic voltage transformer and the electronic current transformer are integrated into a control cable through a secondary line to be connected with the protection line loss board.

6. The fault fully-aware terminal of claim 1, further comprising: install in the perception sensor is put in the trinity cable office of supersound/TEV/UHF of cabinet inner wall under the looped netowrk cabinet, install in the temperature sensor of cable head and install in the harmful gas detection device of cabinet lower part under the looped netowrk cabinet to wireless receiving module through wireless communication connection mainboard.

7. The fault fully-aware terminal of claim 1, further comprising: the leakage current transformer is arranged at the cable grounding wire of the ring main unit; the leakage current transformer is connected with the main board through the protection line loss board.

8. The method for accurately positioning the small-current single-phase ground of the fault fully-sensing terminal according to claim 1, wherein the method comprises the following steps:

secondary clutter is suppressed and formed through an integrator and a filter which are integrated in the electronic voltage and electronic current transformer, and the protection line loss board converts and transmits voltage and current signals to a main board; the main board realizes the accurate positioning of the small-current single-phase grounding according to the voltage and current signals and a preset small-current single-phase grounding criterion.

9. The method for accurately positioning the small-current single-phase ground of the fault fully-sensing terminal according to claim 8, wherein the method comprises the following steps: the preset criterion of the small-current single-phase grounding is as follows:

when a line ground fault occurs, if a certain path meets the following conditions, the line ground fault is positioned as a low-current single-phase ground fault:

the zero sequence voltage leads the zero sequence current by 60 degrees to 120 degrees and the zero sequence voltage under the on-off state is all larger than 0;

the ratio of the two-phase voltage increase to the one-phase voltage decrease is larger than a first set value, and the zero-sequence voltage is larger than a second set value, at least one of the two-phase voltage increase and the one-phase voltage decrease is satisfied;

zero sequence current is larger than a third set value;

the voltage of at least two phases is greater than 4 kV.

10. The method for accurately positioning the small-current single-phase ground of the fault fully-sensing terminal according to claim 9, wherein the method comprises the following steps: and when the preset low-current single-phase grounding fault is positioned, judging whether the grounding alarm enable is started, and if so, starting the grounding alarm.

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