CN111398871A - Device and method for checking polarity of zero sequence current transformer - Google Patents
Device and method for checking polarity of zero sequence current transformer Download PDFInfo
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- CN111398871A CN111398871A CN202010266159.3A CN202010266159A CN111398871A CN 111398871 A CN111398871 A CN 111398871A CN 202010266159 A CN202010266159 A CN 202010266159A CN 111398871 A CN111398871 A CN 111398871A
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Abstract
The invention discloses a device and a method for checking the wiring polarity of a zero sequence current transformer. The device comprises: the bus three-phase voltage transformer is used for obtaining a zero sequence voltage transformer of bus zero sequence voltage, the zero sequence current transformer used for obtaining zero sequence current of each outgoing line, and the bus three-phase voltage transformer further comprises a measurement amplification module, a data acquisition module and a data processing module which are sequentially connected, wherein the input end of the measurement amplification module is respectively connected with the output ends of the bus three-phase voltage transformer, the zero sequence voltage transformer and the zero sequence current transformer. The invention judges whether the earth fault occurs or not based on the amplitude and the variable quantity of the output signal of the zero sequence voltage transformer, identifies whether the wiring polarity of the zero sequence current transformer is correct or not based on the phase difference of the phase of the output signal of the zero sequence current transformer relative to the reference phase, can automatically detect whether the wiring polarity of each outgoing line zero sequence current transformer is correct or not on line, and has the advantages of simple hardware structure, reliable work, high identification precision and the like.
Description
Technical Field
The invention belongs to the technical field of power systems, and particularly relates to a device and a method for checking whether the wiring polarity of a zero sequence current transformer of a small current grounding system outgoing line is correct.
Background
The power system is divided into two types according to the operation mode of a neutral point: a neutral point active grounding system and a neutral point inactive grounding system. A system in which the neutral point is grounded directly or through low-value impedance is called a neutral point effective grounding system or a large-current grounding system; systems in which the neutral point is not grounded or grounded via a high-value impedance or grounded (resonance-grounded) via an arc suppression coil (arc suppression reactor) are referred to as neutral point non-active grounding systems or low-current grounding systems.
In a 6-66 kV power distribution network, a low-current grounding system is widely adopted. The power distribution network adopts a low-current grounding system, and has the advantages that: when a single-phase earth fault occurs, the fault point cannot generate large short-circuit current due to the fact that a neutral point is not effectively grounded, line voltage between phases is still symmetrical, power supply to a load is not affected, and therefore fault operation of the system in a short time is allowed. This is very significant to reduce the power outage time of users and improve the power supply reliability. The most essential idea of the existing grounding line selection algorithm, whether a transient method or a steady state method is to judge the direction of transient state or steady state derivative characteristic variables between a grounding line and a non-grounding line, and the line selection methods are easily influenced by the wiring polarity of an outgoing zero sequence current transformer; on the other hand, for 6-66 kV lines, zero sequence direction protection is rarely matched, so that operation and maintenance personnel pay less attention to the polarity of the outgoing line of the zero sequence current transformer.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides an apparatus and a method for checking the polarity of a zero sequence current transformer.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a device for checking the wiring polarity of a zero sequence current transformer, which is characterized by comprising the following components: the bus three-phase voltage transformer, the zero sequence voltage transformer used for obtaining the bus zero sequence voltage, the zero sequence current transformer used for obtaining the zero sequence current of each outgoing line, the measuring and amplifying module, the data acquisition module and the data processing module which are sequentially connected, wherein the input end of the measuring and amplifying module is respectively connected with the output ends of the bus three-phase voltage transformer, the zero sequence voltage transformer and the zero sequence current transformer; the data processing module judges whether the ground fault occurs or not based on the amplitude and the variable quantity of the output signal of the zero-sequence voltage transformer, and identifies whether the wiring polarity of the zero-sequence current transformer is correct or not based on the phase difference of the phase of the output signal of the zero-sequence current transformer relative to the reference phase, wherein the reference phase is obtained by calculating the phase of the sum of three-phase voltages output by the bus three-phase voltage transformer.
The invention also provides a method for checking the wiring polarity of the zero sequence current transformer by applying the device, which is characterized by comprising the following steps executed by a data processing module:
and 3, performing FFT (fast Fourier transform) on the output signal of each zero sequence current transformer to obtain the amplitude value and the phase value of the zero sequence current, calculating the sum of three-phase voltage signals output by the bus three-phase voltage transformer, performing FFT on the sum signal to obtain a reference phase value, calculating the difference between the phase value of the zero sequence current and the reference phase value to obtain a phase difference, and if the phase difference is greater than a set third threshold value and less than a set fourth threshold value and the amplitude value of the zero sequence current is greater than a set fifth threshold value, determining that the polarity of the zero sequence current transformer is connected reversely.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a device for checking the wiring polarity of a zero sequence current transformer, which comprises a bus three-phase voltage transformer, a zero sequence voltage transformer for obtaining bus zero sequence voltage, a zero sequence current transformer for obtaining each outgoing line zero sequence current, and a measurement amplification module, a data acquisition module and a data processing module which are sequentially connected, wherein the input end of the measurement amplification module is respectively connected with the output ends of the bus three-phase voltage transformer, the zero sequence voltage transformer and the zero sequence current transformer. The invention judges whether the earth fault occurs or not based on the amplitude and the variable quantity of the output signal of the zero sequence voltage transformer, identifies whether the wiring polarity of the zero sequence current transformer is correct or not based on the phase difference of the phase of the output signal of the zero sequence current transformer relative to the reference phase, can automatically detect whether the wiring polarity of each outgoing line zero sequence current transformer is correct or not on line, and has the advantages of simple hardware structure, reliable work, high identification precision and the like.
Drawings
Fig. 1 is a block diagram of a device for checking a wiring polarity of a zero sequence current transformer according to an embodiment of the present invention.
In the figure, 1-bus three-phase voltage transformer, 2-zero sequence voltage transformer, 3-zero sequence current transformer, 4-measurement amplification module, 5-data acquisition module and 6-data processing module.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The invention embodiment of a device for checking the wiring polarity of a zero sequence current transformer, the composition block diagram of which is shown in figure 1, the device comprises: the bus three-phase voltage transformer comprises a bus three-phase voltage transformer 1, a zero-sequence voltage transformer 2 for obtaining bus zero-sequence voltage, a zero-sequence current transformer 3 for obtaining zero-sequence current of each outgoing line, a measurement amplification module 4, a data acquisition module 5 and a data processing module 6 which are sequentially connected, wherein the input end of the measurement amplification module 4 is respectively connected with the output ends of the bus three-phase voltage transformer 1, the zero-sequence voltage transformer 2 and the zero-sequence current transformer 3; the data processing module 6 judges whether a ground fault occurs or not based on the amplitude and the variable quantity of the output signal of the zero sequence voltage transformer 2, and identifies whether the wiring polarity of the zero sequence current transformer 3 is correct or not based on the phase difference of the phase of the output signal of the zero sequence current transformer 3 relative to the reference phase, wherein the reference phase is obtained by calculating the phase of the sum of three-phase voltages output by the bus three-phase voltage transformer 1.
In this embodiment, the device mainly comprises a bus three-phase voltage transformer 1, a zero sequence voltage transformer 2, a zero sequence current transformer 3, a measurement amplification module 4, a data acquisition module 5 and a data processing module 6. The bus three-phase voltage transformer 1 is used for carrying out U-phase voltage on a busA、UB、UCSampling to obtain Ua、Ub、UcU is calculated by the data processing module 6a+Ub+UcAnd obtaining a self-generated zero sequence voltage, wherein the phase position of the self-generated zero sequence voltage is used as a phase position reference for subsequent data processing. The zero sequence voltage transformer 2 adopts an open triangle structure, is used for obtaining the zero sequence voltage of a bus and is mainly used for detecting whether a ground fault occurs. The zero sequence current transformer 3 generally adopts a single-turn straight-through current transformer, so that three-phase wires of outgoing wires can pass through the zero sequence current transformer at the same time, and only a neutral wire can pass through the zero sequence current transformer. Each outgoing line is provided with a zero sequence current transformer 3 for obtaining the zero sequence current of each outgoing line. The zero sequence current of the outgoing line is mainly used for carrying out polarity identification (whether the zero sequence current transformer 3 is connected reversely). The input end of the measurement amplifying module 4 is respectively connected with the output ends of the bus three-phase voltage transformer 1, the zero sequence voltage transformer 2 and the zero sequence current transformer 3, and the measurement amplifying module is used for amplifying and converting output signals of the 3 transformers and outputting the output signals to the data acquisition module 5. The data acquisition module 5 is used for converting the analog signals into digital signals according to a certain acquisition rate and then sending the digital signals to the data processing module 6. The data processing module 6 is mainly used for identifying the polarity of the zero sequence current transformer 3 according to the amplitude and the phase of the 3 signals and a certain algorithm. The identification principle is as follows: under normal conditions, the three-phase voltage is balanced, and the outputs of the zero-sequence voltage transformer 2 and the zero-sequence current transformer 3 are both very small and are approximately 0; when the outgoing line has a ground fault, the three-phase voltage is not balanced any more, and the outputs of the two transformers are all provided with oneAnd a larger value is output by the jump, so that fault detection is facilitated. Whether the ground fault occurs can be judged according to the amplitude and the variable quantity of the zero-sequence voltage transformer 2; and if the judgment result is that the ground fault occurs, judging whether the wiring polarity of the zero sequence current transformer 3 is correct or not according to the amplitude and the phase (phase difference relative to the reference phase) of the output signal of the zero sequence current transformer 3.
As an alternative embodiment, the measurement and amplification module 4 mainly includes a voltage transmitter, a current transmitter and an operational amplifier connected to their outputs.
The embodiment provides a technical scheme of the measurement amplification module 4. In this embodiment, the measurement amplifying module 4 mainly includes a voltage transmitter, a current transmitter, and an operational amplifier. The voltage transmitter is respectively connected with the output ends of the bus three-phase voltage transformer 1 and the zero sequence voltage transformer 2, and the current transmitter is connected with the output end of the zero sequence current transformer 3 to play a role in isolation and amplification. The operational amplifier further amplifies the output signals of the voltage transmitter and the current transmitter to meet the amplitude requirement.
As an optional embodiment, the data acquisition module 5 mainly includes an AD conversion chip and an FPGA sampling control chip connected thereto.
The embodiment provides a technical scheme of the data acquisition module 5. In this embodiment, the data acquisition module 5 mainly includes an AD conversion chip and an FPGA sampling control chip. The AD conversion chip is used for converting the analog signal into a digital signal; the FPGA sampling control chip is used for outputting a sampling control signal to the control end of the AD conversion chip by the FPGA chip so as to realize the real-time acquisition of the signal.
As an alternative embodiment, the data processing module 6 mainly comprises an embedded processor.
This embodiment provides a technical solution of the data processing module 6. The data processing module 6 mainly comprises an embedded processor and a peripheral circuit. There are many optional embedded processor chips, such as ARM processors, and this embodiment is not limited in particular.
The method for detecting the wiring polarity of the zero sequence current transformer by using the device comprises the following steps executed by a data processing module 6:
s101, acquiring output signals of a bus three-phase voltage transformer 1, a zero sequence voltage transformer 2 and a zero sequence current transformer 3 in real time;
s102, if the amplitude of an output signal of the zero-sequence voltage transformer 2 in the current data acquisition cycle is larger than a set first threshold value and the variation of the amplitude of the output signal relative to the previous data acquisition cycle is larger than a set second threshold value, judging that a ground fault occurs, and executing the next step;
s103, performing FFT (fast Fourier transform) on the output signal of each zero sequence current transformer 3 to obtain the amplitude value and the phase value of the zero sequence current, calculating the sum of the three-phase voltage signals output by the bus three-phase voltage transformer 1, performing FFT on the sum signal to obtain a reference phase value, calculating the difference between the phase value of the zero sequence current and the reference phase value to obtain a phase difference, and if the phase difference is greater than a set third threshold value and less than a set fourth threshold value and the amplitude value of the zero sequence current is greater than a set fifth threshold value, determining that the polarity of the zero sequence current transformer 3 is connected reversely.
This embodiment provides a specific polarity identification method, which is implemented by the data processing module 6 executing steps S101 to S103.
In this embodiment, step S101 is mainly used to collect, in real time, bus three-phase voltage signals, bus zero-sequence voltage signals, and outgoing zero-sequence current signals output by the 3 kinds of transformers respectively. These 3 kinds of signal data are the basis of the data processing performed in the present embodiment.
In this embodiment, step S102 is mainly used to determine whether a ground fault occurs. Under normal conditions, the three-phase voltage is approximately balanced, the amplitude of the parent zero-sequence voltage signal is very small, and the change is slow and stable. When an earth fault occurs, the zero sequence voltage of the bus has a large jump, and the output amplitude is suddenly increased to a larger value. According to the characteristic, whether the ground fault occurs can be detected, and the detection method comprises the following steps: and calculating the difference value between the bus zero-sequence voltage amplitude of the current acquisition period and the bus zero-sequence voltage amplitude of the last acquisition period, comparing the bus zero-sequence voltage amplitude of the current acquisition period and the difference value with a set first threshold value and a set second threshold value respectively, and if the bus zero-sequence voltage amplitude of the current acquisition period and the difference value exceed the set threshold values, determining that an outgoing line has a ground fault. The magnitudes of the first threshold and the second threshold may be obtained empirically or through repeated experimentation.
In this embodiment, step S103 is mainly used to identify the zero sequence current transformer 3 with reversed polarity. Under the condition that the polarity of the zero sequence current transformer 3 is correct, the phase difference between the phase of the output zero sequence current and the reference phase is small; when the polarity of the zero sequence current transformer 3 is connected reversely, the phase difference is obviously increased. Polarity identification can be carried out based on the phase difference between the zero sequence current and the reference phase according to the characteristic. And obtaining a phase value of the zero-sequence current signal by performing FFT (fast Fourier transform) conversion on the zero-sequence current signal, calculating the phase difference between the zero-sequence current signal and a reference phase, and if the phase difference is within a set threshold range and the amplitude of the zero-sequence current signal is greater than a set threshold, determining that the polarity of the zero-sequence current transformer 3 is reverse. The minimum amplitude of the zero-sequence current signal is limited (larger than the fifth threshold) because when the signal is weak, the influence of the interference signal is large, the error of the obtained phase value is large, and the identification precision is low.
As an alternative embodiment, the method further comprises: establishing a set A1 consisting of all zero-sequence current transformers 3 judged to have reverse polarity after the current ground fault, calculating the intersection of the set A1 and a set A0 established after the last ground fault to obtain a set B, and if A1 is not equal to A0 and B is not an empty set, determining that the zero-sequence current transformers in B have reverse polarity; and after the polarity of the zero sequence current transformer 3 in the B is corrected, waiting for the next ground fault.
The embodiment provides a technical scheme for improving the identification precision. In this embodiment, each time a new ground fault occurs, identification is performed once, and after each time a ground fault occurs, all the zero sequence current transformers 3 determined to have the opposite polarities at this time form a set a1, and an intersection is obtained with the previous set a0 to obtain a set B. The element in the set B is the zero sequence current transformer 3 whose polarity is indeed opposite. Because the probability that the same zero sequence current transformer 3 is wrongly judged to be reversely connected twice is very small, the zero sequence current transformer 3 wrongly judged to be reversely connected can be filtered by solving the intersection, and the identification precision is improved. Since the polarity of the zero sequence current transformer 3 in B is corrected each time, a1 is not equal to a0 in general; when B is an empty set last time (no polarity correction is performed on the zero sequence current transformer 3 in a 0), and no new zero sequence current transformer 3 with reversed polarity appears this time, the element in a1 is not increased or decreased relative to a0, where a1 is a0, and B is a1 is a 0.
As an alternative embodiment, the method further includes the step of identifying whether the wiring polarity of the zero sequence voltage transformer 2 is correct: and performing FFT (fast Fourier transform) on the output signal of the zero sequence voltage transformer 2 to obtain a phase value of the output signal, calculating the difference between the phase value and the reference phase value to obtain a phase difference, and if the phase difference is smaller than a set sixth threshold value, correcting the wiring polarity of the zero sequence voltage transformer 2.
The embodiment provides a technical scheme for identifying whether the wiring polarity of the zero sequence voltage transformer 2 is correct. The output voltage of the zero sequence voltage transformer 2 is used for detecting the ground fault, when the polarity of the output voltage is reversed, the amplitude and the phase of the output voltage signal are changed, which may affect the normal detection of the ground fault, so that the polarity connection should be ensured to be correct. Under the condition that the polarity of the zero sequence voltage transformer 2 is correct, the phase difference between the phase of the zero sequence voltage signal and the reference phase is very small; when the polarity is reversed, the phase difference is obviously increased. Therefore, whether the wiring polarity of the zero sequence voltage transformer 2 is correct or not can be judged by comparing the phase difference with the set sixth threshold value. The phase of the zero sequence voltage signal can be obtained by performing FFT transformation on the zero sequence voltage signal. The sixth threshold is a small angle value, the magnitude of which is also empirically or experimentally obtained.
As an alternative, the first threshold is 30V, the second threshold is 10V, and the third threshold is 45V0Fourth threshold 1350The fifth threshold is 2mA, and the sixth threshold is 50。
This example shows a specific set of 6 thresholds for the previous example. This is a preferred embodiment, and specific values are given for a specific application scenario for reference only. Different application scenarios correspond to different thresholds, and thus the present embodiment does not limit or exclude other possible threshold data.
The above description is only for the purpose of illustrating a few embodiments of the present invention, and should not be taken as limiting the scope of the present invention, in which all equivalent changes, modifications, or equivalent scaling-up or down, etc. made in accordance with the spirit of the present invention should be considered as falling within the scope of the present invention.
Claims (8)
1. An apparatus for checking the wiring polarity of a zero sequence current transformer, comprising: the bus three-phase voltage transformer, the zero sequence voltage transformer used for obtaining the bus zero sequence voltage, the zero sequence current transformer used for obtaining the zero sequence current of each outgoing line, the measuring and amplifying module, the data acquisition module and the data processing module which are sequentially connected, wherein the input end of the measuring and amplifying module is respectively connected with the output ends of the bus three-phase voltage transformer, the zero sequence voltage transformer and the zero sequence current transformer; the data processing module judges whether the ground fault occurs or not based on the amplitude and the variable quantity of the output signal of the zero-sequence voltage transformer, and identifies whether the wiring polarity of the zero-sequence current transformer is correct or not based on the phase difference of the phase of the output signal of the zero-sequence current transformer relative to the reference phase, wherein the reference phase is obtained by calculating the phase of the sum of three-phase voltages output by the bus three-phase voltage transformer.
2. The apparatus for checking the wiring polarity of a zero sequence current transformer according to claim 1, wherein the measurement amplifying module mainly comprises a voltage transmitter, a current transmitter and an operational amplifier connected to their output terminals.
3. The apparatus for checking the wiring polarity of a zero sequence current transformer according to claim 1, wherein the data acquisition module mainly comprises an AD conversion chip and an FPGA sampling control chip connected thereto.
4. The apparatus for checking the wiring polarity of zero sequence current transformer according to claim 1, wherein the data processing module mainly comprises an embedded processor.
5. A method for checking the wiring polarity of a zero sequence current transformer by applying the apparatus of claim 1, comprising the following steps executed by the data processing module:
step 1, acquiring output signals of a bus three-phase voltage transformer, a zero sequence voltage transformer and a zero sequence current transformer in real time;
step 2, if the amplitude of the output signal of the zero-sequence voltage transformer in the current data acquisition cycle is larger than a set first threshold value and the variation of the amplitude of the output signal relative to the previous data acquisition cycle is larger than a set second threshold value, judging that a ground fault occurs, and executing the next step;
and 3, performing FFT (fast Fourier transform) on the output signal of each zero sequence current transformer to obtain the amplitude value and the phase value of the zero sequence current, calculating the sum of three-phase voltage signals output by the bus three-phase voltage transformer, performing FFT on the sum signal to obtain a reference phase value, calculating the difference between the phase value of the zero sequence current and the reference phase value to obtain a phase difference, and if the phase difference is greater than a set third threshold value and less than a set fourth threshold value and the amplitude value of the zero sequence current is greater than a set fifth threshold value, determining that the polarity of the zero sequence current transformer is connected reversely.
6. The method of claim 5, further comprising: establishing a set A1 consisting of all zero-sequence current transformers 3 judged to have reverse polarity after the current ground fault, calculating the intersection of the set A1 and a set A0 established after the last ground fault to obtain a set B, and if A1 is not equal to A0 and B is not an empty set, determining that the zero-sequence current transformers in B have reverse polarity; and after the polarity of the zero sequence current transformer 3 in the B is corrected, waiting for the next ground fault.
7. The method according to claim 6, characterized in that the method further comprises the step of identifying whether the wiring polarity of the zero sequence voltage transformer 2 is correct: and performing FFT (fast Fourier transform) on the output signal of the zero sequence voltage transformer to obtain a phase value of the output signal, calculating the difference between the phase value and the reference phase value to obtain a phase difference, and if the phase difference is greater than a set sixth threshold value, the wiring polarity of the zero sequence voltage transformer is incorrect.
8. The method of claim 7, wherein the first threshold is 30V, the second threshold is 10V, and the third threshold is 45V0Fourth threshold 1350The fifth threshold is 2mA, and the sixth threshold is 50。
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Application publication date: 20200710 |