CN109507519B - Low-current ground fault line selection method, device and system - Google Patents
Low-current ground fault line selection method, device and system Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
Abstract
The application discloses a small current ground fault line selection method, a device and a system, wherein the method comprises the following steps: acquiring voltages at two ends of an arc suppression coil in the power distribution network, and setting delay time when the voltages at the two ends of the arc suppression coil are both larger than half of phase voltage; after the delay time is reached, acquiring a low-frequency constant current signal injected into the power distribution network by the inverter, wherein the low-frequency constant current signal is generated by controlling the inverter by an inverter controller; respectively calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network; determining the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate of each line as a fault line; respectively calculating the current oscillation change rate of each phase in the fault line; and determining the phase corresponding to the maximum value of the oscillation change rate of each phase current as a fault phase. By adopting the method, the fault line and the corresponding fault phase can be simply and accurately selected, and the measurement precision of the voltage transformer cannot be influenced.
Description
Technical Field
The present application relates to the field of fault detection in power systems, and in particular, to a method, an apparatus, and a system for selecting a low-current ground fault line.
Background
With the rapid development of electric utilities, more and more transmission lines are arranged in a power distribution network, so that more and more faults of the transmission lines are caused. If the faults of the power transmission line are not checked and repaired in time, huge economic loss can be brought to people, and meanwhile, great inconvenience can be brought to the life of people.
The current 6KV-35KV power distribution network generally adopts a low-current grounding operation mode, and the low-current grounding operation mode adopts a neutral ungrounded mode or a mode of grounding through an arc suppression coil. However, in the operating mode in which the neutral is not grounded or is grounded via the arc suppression coil, the probability of occurrence of a single-phase ground fault is large, and is about 80% or more. When a single-phase earth fault occurs in a power distribution network, the voltage and the phase of each phase are usually kept unchanged at the initial stage of the fault, and the balance of a three-phase system is not damaged, so that the power distribution network can operate for more than 2 hours with a fault line. However, as the operation time of the belt fault is prolonged, the belt fault line may cause phase-to-phase short circuit and even lead to the breakdown of the whole system. Therefore, it is necessary to select a fault line in the low-current grounding operation mode for timely maintenance, wherein the process of selecting the fault line in the low-current grounding operation mode is the low-current grounding fault line selection.
The existing small current ground fault line selection method adopts a signal injection-based method, in the method, phase voltage and zero sequence voltage of a fault line can change after a single-phase ground fault occurs in a small current ground system, and the approximate region of the fault line can be preliminarily determined according to the change condition of the phase voltage and the zero sequence voltage; and then starting an injection signal source, enabling the injection signal source to generate a sinusoidal current signal (such as 120Hz, the amplitude is about 5A) different from the inherent frequency of the power distribution network, short-circuiting the injection signal source to a fault phase on the secondary side of the voltage transformer, injecting the sinusoidal current signal generated by the injection signal source into the approximate region of a fault line, coupling the signal into a primary system from the secondary side, and calculating to obtain a final fault distance according to relational expressions between the voltage and the current of the head end of the line and the voltage and the current of the injection signal at the fault point and the fault distance to determine the fault point.
However, in the research process of the present application, the inventor finds that, in the existing low-current ground fault line selection method, the accuracy of the voltage transformer is affected by injecting a signal to the voltage transformer side, which affects the power distribution network, and meanwhile, the amplitude of the injected signal at the secondary side of the voltage transformer is reduced to hundreds or even tens of milliamperes, so that the current transformer is difficult to detect the amplitude of the signal, which causes inaccurate ground fault line selection.
Disclosure of Invention
The embodiment of the application provides a current ground fault line selection method, a current ground fault line selection device and a current ground fault line selection system, and aims to solve the problems that in the prior art, signals are injected to the side of a voltage transformer, the precision of the voltage transformer can be influenced, and a power distribution network is influenced, meanwhile, the amplitude of the injected signals on the secondary side of the voltage transformer can be reduced to hundreds or even dozens of milliamperes, the amplitude of the signals is difficult to detect by the current transformer, and the ground fault line selection is inaccurate.
In a first aspect, an embodiment of the present application provides a small-current ground fault line selection method, including:
acquiring voltages at two ends of an arc suppression coil in the power distribution network, and setting delay time when the voltages at the two ends of the arc suppression coil are both larger than half of phase voltage;
after the delay time is reached, acquiring a low-frequency constant current signal injected into the power distribution network by the inverter, wherein the low-frequency constant current signal is generated by controlling the inverter by an inverter controller;
respectively calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network, wherein the zero sequence current oscillation change rate is the superposition value of the low-frequency constant current signal and the zero sequence current of the power transmission line;
determining the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate as a fault line;
respectively calculating the current oscillation change rate of each phase in the fault line, wherein the current oscillation change rate is the superposed value of the low-frequency constant-current signal and the phase current;
and determining the phase corresponding to the maximum value in the current oscillation change rate as a fault phase.
With reference to the first aspect, in an implementation manner, the low-current ground fault line selection method further includes:
and sending a request trigger pulse signal to the inverter controller to acquire a low-frequency constant current signal which is injected into the power distribution network again by the inverter.
With reference to the first aspect, in an implementation manner, the injecting, by the inverter, the low-frequency constant current signal is: i.e. iInverse direction＝Idmsin(2πfdt)；
Wherein, IdmIs the amplitude of the low-frequency constant-current signal, fdThe frequency of the low-frequency constant current signal is shown, and t is the duration of the low-frequency constant current signal.
With reference to the first aspect, in an implementation manner, the method for calculating the oscillation change rate of the zero-sequence current includes:
obtaining the magnitude of zero sequence current of every 20ms in an oscillation period on the kth line, which is respectively expressed as:
the zero-sequence current low-frequency oscillation amplitude of the line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows:
the zero sequence current low-frequency oscillation amplitude change rate of the kth line is:
with reference to the first aspect, in an implementation manner, the method for calculating the current oscillation change rate includes:
setting the three phases on the kth line as A, B, C three phases respectively, and obtaining the magnitude of zero sequence current of each 20ms in an oscillation period of the phase a, wherein the magnitudes are respectively expressed as: i isA1、IA2...IANAnd then the amplitude of the low-frequency oscillation of the phase A current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isAThen, the current low-frequency oscillation amplitude change rate of the phase a is:
obtaining the magnitude of zero sequence current of every 20ms in an oscillation period of the phase B, and respectively representing as: i isB1、IB2...IBNAnd then the amplitude of the low-frequency oscillation of the phase B current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isBAnd then the current low-frequency oscillation amplitude change rate of the B phase is as follows:
obtaining the magnitude of zero sequence current of each 20ms in an oscillation period of the C phase, and respectively representing the magnitudes as follows: i isC1、IC2...ICNAnd then, the low-frequency oscillation amplitude of the C-phase current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isCAnd then the current low-frequency oscillation amplitude change rate of the C phase is as follows:
with reference to the first aspect, in one implementation, the delay time is greater than or equal to 20 s.
In a second aspect, an embodiment of the present application provides a low-current ground fault line selection apparatus, including:
the voltage acquisition module is used for acquiring voltages at two ends of an arc suppression coil in the power distribution network, and setting delay time when the voltages at the two ends of the arc suppression coil are both larger than half of phase voltage;
the low-frequency constant current signal injection module is used for acquiring a low-frequency constant current signal injected into the power distribution network by the inverter after the delay time is reached, wherein the low-frequency constant current signal is generated by the inverter controller controlling the inverter;
the zero sequence current oscillation change rate calculation module is used for calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network respectively, wherein the zero sequence current oscillation change rate is the superposition value of the low-frequency constant current signal and the zero sequence current of the power transmission line;
the fault line determining module is used for determining that the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate is a fault line;
the current oscillation change rate calculation module is used for calculating the current oscillation change rate of each phase in the fault line respectively, wherein the current oscillation change rate is the superposition value of the low-frequency constant-current signal and the phase current;
and the fault phase determination module is used for determining that the phase corresponding to the maximum value in the current oscillation change rate is the fault phase.
In a third aspect, an embodiment of the present application provides a low-current ground fault line selection system, including:
the system comprises an inverter, an inversion controller, a grounding line selection fault device, an arc suppression coil voltage transformer, a zero sequence current transformer and a current transformer;
the inverter is connected with the arc suppression coil through an inductor, when a fault occurs, the arc suppression coil charges the inverter to a fixed voltage, the inverter is started, and the inverter is used for injecting a low-frequency constant-current signal into a power distribution network;
the inversion controller is connected with the inverter and the grounding line selection fault device and is used for controlling the inverter to generate a low-frequency constant current signal;
the voltage transformer of the arc suppression coil is connected with the grounding line selection fault device, and is used for measuring the voltage on the arc suppression coil and transmitting the voltage to the grounding line selection fault device;
the zero sequence current transformer is arranged on each line of the power distribution network, is connected with the grounding line selection fault device and is used for measuring the zero sequence current of each line of the power distribution network and transmitting the zero sequence current to the grounding line selection fault device;
the current transformers are arranged on all phases in the circuit and connected with the grounding line selection fault device, and the current transformers are used for measuring currents on all phases and transmitting the currents to the grounding line selection fault device.
With reference to the third aspect, in one implementation, the inverter includes:
four IGBT elements, four diodes and parallel capacitance, wherein the diodes are fast recovery diodes.
The embodiment of the application discloses a low-current ground fault line selection method, a low-current ground fault line selection device and a low-current ground fault line selection system, wherein the method comprises the following steps: acquiring voltages at two ends of an arc suppression coil in the power distribution network, and setting delay time when the voltages at the two ends of the arc suppression coil are both larger than half of phase voltage; after the delay time is reached, acquiring a low-frequency constant current signal injected into the power distribution network by the inverter, wherein the low-frequency constant current signal is generated by controlling the inverter by an inverter controller; respectively calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network, wherein the zero sequence current oscillation change rate is the superposition value of the low-frequency constant current signal and the zero sequence current of the power transmission line; determining the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate as a fault line; respectively calculating the current oscillation change rate of each phase in the fault line, wherein the current oscillation change rate is the superposed value of the low-frequency constant-current signal and the phase current; and determining the phase corresponding to the maximum value in the current oscillation change rate as a fault phase.
According to the small-current ground fault line selection method, device and system, the zero sequence current oscillation change rate and the current oscillation change rate are calculated, the fault line and the corresponding fault phase can be simply and accurately selected, and the measurement precision of the voltage transformer cannot be influenced.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic flowchart of a current-ground fault line selection method according to an embodiment of the present disclosure;
fig. 2 is a schematic structural diagram of a current ground fault line selection apparatus according to an embodiment of the present application;
fig. 3 is a schematic structural diagram of a current-ground fault line selection system according to an embodiment of the present application;
fig. 4 is a schematic structural diagram of an inverter in a current ground fault line selection system according to an embodiment of the present application.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.
The embodiment of the application provides a current ground fault line selection method, a current ground fault line selection device and a current ground fault line selection system, and aims to solve the problems that in the prior art, signals are injected to the side of a voltage transformer, the precision of the voltage transformer can be influenced, and a power distribution network is influenced, meanwhile, the amplitude of the injected signals on the secondary side of the voltage transformer can be reduced to hundreds or even dozens of milliamperes, the amplitude of the signals is difficult to detect by the current transformer, and the ground fault line selection is inaccurate.
Referring to fig. 1, a low current ground fault line selection method is shown, the method comprising the steps of:
the phase voltage refers to the voltage between a phase line and a neutral line (zero line) in the power distribution network; by detecting the voltage across the arc suppression coil when the voltage is greater than
After the phase voltage is multiplied, the single-phase earth fault can be considered to occur, and delay time (generally more than 20s, so as to avoid the turn adjustment of the arc suppression coil and the current fluctuation in the transient process) is passed at the moment.
In this application, when the distribution network does not take place single-phase earth fault, the voltage of arc suppression coil both ends that causes because the unbalanced factor of distribution network is very low, usually between zero to tens volts, can be approximately think that there is not voltage on the inverter capacitance. After single-phase earth fault occurs, the voltage at two ends of arc suppression coil is quickly raised to system phase voltage, and after the voltage of arc suppression coil is stabilized, the charging of inverter capacitor is also quickly completed, so that it can be made into a stable direct-current voltage (for example Udc600V), since the arc suppression coil performs the turn adjustment operation, which is usually performed within a period of time, for example, 20s, after the capacitor is charged, a certain delay time is usually set to ensure that the arc suppression coil completes the turn adjustment operation and reaches a stable state.
In addition, the charging function is to ensure that the capacitors of the inverter are able to build up a voltage, while providing an ac voltage source to the inverter to ensure that the inverter is able to inject its desired current signal well.
Preferably, the delay time is 20s or more.
the inverter can be a single-phase inverter and a single-phase inverter bridge comprising IGBTs.
In this step, the reason for selecting the low-frequency constant current signal is as follows: first, since the reactor is connected to the inverter, the reactor attenuates a high frequency current more and attenuates a low frequency current less, and thus a large injection current can be obtained when outputting a low frequency current. Secondly, because the current and the zero sequence current in the power distribution network usually contain harmonic components, and the harmonic is usually higher harmonic of integral multiple of the fundamental wave, the injection of the low-frequency constant current can reduce the influence of the zero sequence higher harmonic current.
In this step, after the set delay time is reached, the inverter control module in the inverter controller controls the IGBT of the single-phase inverter bridge to be turned on, so that a low-frequency alternating current signal is injected into the power distribution network, for example: an alternating current of 10Hz is injected into the distribution network and flows as an additional zero-sequence current of the distribution network through the arc suppression coil via (for example 10KV) bus lines through the distribution network transmission lines. The duration of the low frequency AC current signal is usually set to be between 0.5 and 1 s.
103, respectively calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network, wherein the zero sequence current oscillation change rate is the superposition value of the low-frequency constant current signal and the zero sequence current of the power transmission line;
in this step, since the frequency of the low-frequency zero-sequence current transmitted from the inverter to the power distribution line through the arc suppression coil is different from the frequency of the zero-sequence current generated when the fault occurs in the power distribution network, the superposition of the two zero-sequence currents inevitably generates a frequency oscillation phenomenon of the magnitude of the zero-sequence current, that is, the low-frequency constant current signal injected in step 102 superposes the zero-sequence current generated due to the fault.
The zero sequence current oscillation change rate is the ratio of the oscillation change amount of each low-frequency zero sequence current within a certain oscillation period and the zero sequence current under the condition that the inverter module does not send out the low-frequency zero sequence current.
And 104, determining the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate as a fault line.
In this step, the maximum zero sequence oscillation change rate indicates that the fault current is more obvious, so that the maximum value in the zero sequence oscillation change rates of all lines can be used for judging the fault line.
in this step, since the frequency of the low-frequency zero-sequence current transmitted from the inverter to the power distribution line through the arc suppression coil is different from the frequency of each phase current generated during a fault in the power distribution network, the superposition of the two currents inevitably generates a frequency oscillation phenomenon of the magnitude of the current, that is, the low-frequency constant current signal injected in step 102 superposes each phase current generated due to the fault.
The oscillation change rate of each phase current is the ratio of the oscillation change amount of each low-frequency current within a period of time in a certain oscillation period of the phase to the phase current under the condition that the inverter module does not send out the low-frequency zero-sequence current.
And 106, determining the phase corresponding to the maximum value in the current oscillation change rate as a fault phase.
In this step, the maximum oscillation change rate of each phase current indicates that the phase fault current becomes more significant, and therefore the fault phase can be determined by using the maximum oscillation change rate of each phase current.
The embodiment of the application discloses a low-current ground fault line selection method, which comprises the following steps: acquiring voltages at two ends of an arc suppression coil in the power distribution network, and setting delay time when the voltages at the two ends of the arc suppression coil are both larger than half of phase voltage; after the delay time is reached, acquiring a low-frequency constant current signal injected into the power distribution network by the inverter, wherein the low-frequency constant current signal is generated by controlling the inverter by an inverter controller; respectively calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network, wherein the zero sequence current oscillation change rate of the power transmission line is the superposition value of the low-frequency constant current signal and the zero sequence current of the power transmission line; determining the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate of each line as a fault line; respectively calculating the current oscillation change rate of each phase in the fault line, wherein the current oscillation change rate of each phase in the fault line is the superposition value of the low-frequency constant-current signal and the phase current; and determining the phase corresponding to the maximum value in the oscillation change rate of each phase current as a fault phase.
According to the small-current ground fault line selection method disclosed by the application, the zero-sequence current oscillation change rate and the current oscillation change rate are adopted, the fault line and the corresponding fault phase can be simply and accurately selected, and the measurement precision of the voltage transformer cannot be influenced.
Preferably, the low-current ground fault line selection method further includes: and sending a request trigger pulse signal to the inverter controller to acquire a low-frequency constant current signal which is injected into the power distribution network again by the inverter.
In this embodiment, the low-frequency constant current signal re-injected into the power distribution network may occur after step 103, that is, if the calculated value of the zero sequence current oscillation change rate of each power transmission line is abnormal, a trigger pulse signal is sent to the inverter by the inverter controller, so as to request the inverter to re-inject the low-frequency constant current signal into the power distribution network. It may also happen that after step 106, the low-frequency constant current signal is injected into the power distribution network again, and then step 103 to step 106 are executed again, so as to further increase the accuracy of the calculation result.
Preferably, the inverter injects a low-frequency constant current signal as: i.e. iInverse direction＝Idmsin(2πfdt)；
Wherein, IdmIs the amplitude of the low-frequency constant-current signal, fdThe frequency of the low-frequency constant current signal is shown, and t is the duration of the low-frequency constant current signal.
In this embodiment, the starting conditions of the inverter are:
Uarc extinctionIndicating the voltage of the arc-suppression coil, UPRepresenting the system phase voltage, at represents the delay time, τdRepresenting the duration of the low frequency constant current signal.
Preferably, the method for calculating the oscillation change rate of the zero-sequence current comprises the following steps:
obtaining the magnitude of zero sequence current of every 20ms in an oscillation period on the kth line, which is respectively expressed as:
the zero-sequence current low-frequency oscillation amplitude of the line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows:
the zero sequence current low-frequency oscillation amplitude change rate of the kth line is:
in the present embodiment, the first and second electrodes are,
the largest is the faulty line.
Preferably, the current oscillation change rate is calculated by:
setting the three phases on the kth line as A, B, C three phases respectively, and obtaining the magnitude of zero sequence current of each 20ms in an oscillation period of the phase a, wherein the magnitudes are respectively expressed as: i isA1、IA2...IANAnd then the amplitude of the low-frequency oscillation of the phase A current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isAThen, the current low-frequency oscillation amplitude change rate of the phase a is:
obtaining the magnitude of zero sequence current of every 20ms in an oscillation period of the phase B, and respectively representing as: i isB1、IB2...IBNAnd then the amplitude of the low-frequency oscillation of the phase B current in the fault line is as follows:
if the inverter module does not emit low frequencyThe zero-sequence current under the condition of the zero-sequence current is as follows: i isBAnd then the current low-frequency oscillation amplitude change rate of the B phase is as follows:
obtaining the magnitude of zero sequence current of each 20ms in an oscillation period of the C phase, and respectively representing the magnitudes as follows: i isC1、IC2...ICNAnd then, the low-frequency oscillation amplitude of the C-phase current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isCAnd then the current low-frequency oscillation amplitude change rate of the C phase is as follows:
in the present embodiment, the first and second electrodes are,
and
the phase corresponding to the maximum value of (1) is the failed phase.
Referring to fig. 2, there is shown a low current ground fault line selection apparatus, the apparatus comprising:
the voltage acquisition module 201 is configured to acquire voltages at two ends of an arc suppression coil in the power distribution network, and set a delay time when the voltages at the two ends of the arc suppression coil are both greater than half of a phase voltage;
the low-frequency constant current signal injection module 202 is configured to obtain a low-frequency constant current signal injected into the power distribution network by the inverter after the delay time is reached, where the low-frequency constant current signal is generated by the inverter controller controlling the inverter;
a zero sequence current oscillation change rate calculation module 203, configured to calculate a zero sequence current oscillation change rate of each power transmission line in the power distribution network, where the zero sequence current oscillation change rate is a superimposed value of the low-frequency constant current signal and a zero sequence current of the power transmission line;
and a fault line determining module 204, configured to determine that the power transmission line corresponding to the maximum value in the zero-sequence current oscillation change rate is a fault line.
A current oscillation change rate calculation module 205, configured to calculate a current oscillation change rate of each phase in the fault line, where the current oscillation change rate is a superimposed value of the low-frequency constant current signal and the phase current;
and a fault phase determination module 206, configured to determine that the phase corresponding to the maximum value of the current oscillation change rates is a fault phase.
Referring to fig. 3, there is shown a low current ground fault line selection system, the system comprising:
the system comprises an inverter 301, an inverter controller 302, a grounding line selection fault device 303, an arc suppression coil voltage transformer 304, a zero sequence current transformer 305 and a current transformer 306;
the inverter is connected with the arc suppression coil through an inductor, when a fault occurs, the arc suppression coil charges the inverter to a fixed voltage, the inverter is started, and the inverter is used for injecting a low-frequency constant-current signal into a power distribution network;
the inverter used in the application is connected between two taps of the arc suppression coil, and the arc suppression coil provides energy; the inverter can be charged only after the power distribution network has single-phase earth fault or three-phase imbalance, and energy supply and charging are not carried out on the capacitor of the inverter under the normal three-phase symmetry condition. The inverter is not only an inverter, and does not need an external power supply for supplying power, and the external power supply exists as long as a fault exists, and disappears after the fault disappears.
In addition, the injection signal source used in the application is realized by a part of variable voltage source between two taps of the inverter and the arc suppression coil.
The inversion controller is connected with the inverter and the grounding line selection fault device and is used for controlling the inverter to generate a low-frequency constant current signal;
the voltage transformer of the arc suppression coil is connected with the grounding line selection fault device, and is used for measuring the voltage on the arc suppression coil and transmitting the voltage to the grounding line selection fault device;
the zero sequence current transformer is arranged on each line of the power distribution network, is connected with the grounding line selection fault device and is used for measuring the zero sequence current of each line of the power distribution network and transmitting the zero sequence current to the grounding line selection fault device;
the current transformers are arranged on all phases in the circuit and connected with the grounding line selection fault device, and the current transformers are used for measuring currents on all phases and transmitting the currents to the grounding line selection fault device.
The inverter controller realizes the tracking control of the output low-frequency constant current signal of the inverter by measuring the terminal voltage of a parallel capacitor in the inverter and the output current of the inverter, and simultaneously keeps the voltage at two ends of the parallel capacitor in the inverter to reach the set tracking value, which is realized by controlling the trigger pulse of an inverter bridge IGBT in the inverter.
In this embodiment, the ground fault line selection device obtains a voltage signal at two ends of the arc suppression coil, a current signal and a zero sequence current signal of each phase of the non-fault line, and a current signal and a zero sequence current signal of each phase of the fault line. And judging the grounding fault line and the fault phase through analysis and calculation. Meanwhile, a request trigger pulse signal is sent to the inverter controller to request the inverter to send a low-frequency constant current signal again, so that the judgment accuracy is improved.
Referring to fig. 4, there is shown a structure of an inverter including:
four IGBT elements, four diodes and parallel capacitance, wherein the diodes are fast recovery diodes.
As shown in FIG. 4, L1、L2For connecting two small inductors of an inverter, the function of the inductor is to convert a low-frequency voltage signal output by the inverter into a current signal, K1、K2、K3、K4To construct 4 IGBT (Insulated Gate Bipolar Transistor) elements of the inverter, D1、D2、D3、D44 fast recovery diodes. It is reacted with K1、K2、K3、K4Together form an inverter, CeThe value of the parallel capacitor of the inverter can be 104～105And muF. Wherein, K1And D1Are connected in parallel to form a first circuit, K2And D2Are connected in parallel to form a second loop, K3And D3Are connected in parallel to form a third circuit, K4And D4The first loop, the second loop, the third loop and the fourth loop are connected in series to form a fifth loop, and the fifth loop is connected with the CeThe inverter structure is formed by connecting in parallel; the arc suppression coil is a turn-adjusting coil, the number of the taps of the turn-adjusting coil is usually 9-24, and two connecting reactances L of the inverter1、L2Usually between two taps about 6% of the total voltage of the 10KV arc suppression coil. L is1、L2The value is usually between 1 and 10 mH.
The same and similar parts in the various embodiments in this specification may be referred to each other. In particular, as for the apparatus embodiment, since it is substantially similar to the method embodiment, the description is simple, and the relevant points can be referred to the description in the method embodiment.
The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.
Claims (9)
1. A small current ground fault line selection method is characterized by comprising the following steps:
acquiring voltages at two ends of an arc suppression coil in the power distribution network, and setting delay time when the voltages at the two ends of the arc suppression coil are both larger than half of phase voltage;
after the delay time is reached, acquiring a low-frequency constant current signal injected into the power distribution network by the inverter, wherein the low-frequency constant current signal is generated by controlling the inverter by an inverter controller;
respectively calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network, wherein the zero sequence current oscillation change rate is the superposition value of the low-frequency constant current signal and the zero sequence current of the power transmission line;
determining the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate as a fault line;
respectively calculating the current oscillation change rate of each phase in the fault line, wherein the current oscillation change rate is the superposed value of the low-frequency constant-current signal and the phase current;
and determining the phase corresponding to the maximum value in the current oscillation change rate as a fault phase.
2. The low current ground fault line selection method of claim 1, further comprising:
and sending a request trigger pulse signal to the inverter controller to acquire a low-frequency constant current signal which is injected into the power distribution network again by the inverter.
3. The small current ground fault line selection method of claim 1,
the low-frequency constant current signals injected into the inverter are as follows: i.e. iInverse direction＝Idm sin(2πfdt)；
Wherein, IdmIs the amplitude of the low-frequency constant-current signal, fdThe frequency of the low-frequency constant current signal is shown, and t is the duration of the low-frequency constant current signal.
4. The small current ground fault line selection method of claim 1,
the method for calculating the oscillation change rate of the zero-sequence current comprises the following steps:
acquiring the zero sequence current magnitude of every 20ms in an oscillation period on the kth line, and respectively representing the magnitude as：
The zero-sequence current low-frequency oscillation amplitude of the line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows:
the zero sequence current low-frequency oscillation amplitude change rate of the kth line is:
5. the small current ground fault line selection method of claim 4,
the calculation method of the current oscillation change rate comprises the following steps:
setting the three phases on the kth line as A, B, C three phases respectively, and obtaining the magnitude of zero sequence current of each 20ms in an oscillation period of the phase a, wherein the magnitudes are respectively expressed as: i isA1、IA2...IANAnd then the amplitude of the low-frequency oscillation of the phase A current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isAThen, the current low-frequency oscillation amplitude change rate of the phase a is:
obtaining the magnitude of zero sequence current of every 20ms in an oscillation period of the phase B, and respectively representing as: i isB1、IB2...IBNAnd then the amplitude of the low-frequency oscillation of the phase B current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isBAnd then the current low-frequency oscillation amplitude change rate of the B phase is as follows:
obtaining the magnitude of zero sequence current of each 20ms in an oscillation period of the C phase, and respectively representing the magnitudes as follows: i isC1、IC2...ICNAnd then, the low-frequency oscillation amplitude of the C-phase current in the fault line is as follows:
the zero-sequence current under the condition that the inverter module does not send the low-frequency zero-sequence current is set as follows: i isCAnd then the current low-frequency oscillation amplitude change rate of the C phase is as follows:
6. the small current ground fault line selection method of claim 1,
the delay time is 20s or more.
7. A low current ground fault line selection apparatus, comprising:
the voltage acquisition module is used for acquiring voltages at two ends of an arc suppression coil in the power distribution network, and setting delay time when the voltages at the two ends of the arc suppression coil are both larger than half of phase voltage;
the low-frequency constant current signal injection module is used for acquiring a low-frequency constant current signal injected into the power distribution network by the inverter after the delay time is reached, wherein the low-frequency constant current signal is generated by the inverter controller controlling the inverter;
the zero sequence current oscillation change rate calculation module is used for calculating the zero sequence current oscillation change rate of each power transmission line in the power distribution network respectively, wherein the zero sequence current oscillation change rate is the superposition value of the low-frequency constant current signal and the zero sequence current of the power transmission line;
the fault line determining module is used for determining that the power transmission line corresponding to the maximum value in the zero sequence current oscillation change rate is a fault line;
the current oscillation change rate calculation module is used for calculating the current oscillation change rate of each phase in the fault line respectively, wherein the current oscillation change rate is the superposition value of the low-frequency constant-current signal and the phase current;
and the fault phase determination module is used for determining that the phase corresponding to the maximum value in the current oscillation change rate is the fault phase.
8. A low current ground fault line selection system, wherein the system is configured to perform the method of any of claims 1-6, the system comprising:
the system comprises an inverter, an inversion controller, a grounding line selection fault device, an arc suppression coil voltage transformer, a zero sequence current transformer and a current transformer; the ground fault apparatus comprises the apparatus of claim 7;
the inverter is connected with the arc suppression coil through an inductor, when a fault occurs, the arc suppression coil charges the inverter to a fixed voltage, the inverter is started, and the inverter is used for injecting a low-frequency constant-current signal into a power distribution network;
the inversion controller is connected with the inverter and the grounding line selection fault device and is used for controlling the inverter to generate a low-frequency constant current signal;
the voltage transformer of the arc suppression coil is connected with the grounding line selection fault device, and is used for measuring the voltage on the arc suppression coil and transmitting the voltage to the grounding line selection fault device;
the zero sequence current transformer is arranged on each line of the power distribution network, is connected with the grounding line selection fault device and is used for measuring the zero sequence current of each line of the power distribution network and transmitting the zero sequence current to the grounding line selection fault device;
the current transformers are arranged on all phases in the circuit and connected with the grounding line selection fault device, and the current transformers are used for measuring currents on all phases and transmitting the currents to the grounding line selection fault device.
9. The low current ground fault line selection system of claim 8, wherein the inverter comprises:
four IGBT elements, four diodes and parallel capacitance, wherein the diodes are fast recovery diodes.
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