CN114725914A - High-sensitivity neutral point flexible grounding power distribution network fault handling method and system - Google Patents

High-sensitivity neutral point flexible grounding power distribution network fault handling method and system Download PDF

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CN114725914A
CN114725914A CN202210375175.5A CN202210375175A CN114725914A CN 114725914 A CN114725914 A CN 114725914A CN 202210375175 A CN202210375175 A CN 202210375175A CN 114725914 A CN114725914 A CN 114725914A
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fault
phase
line
neutral point
voltage
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CN114725914B (en
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梁睿
孔令昌
刘心瑜
王全金
彭楠
靳维
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China University of Mining and Technology CUMT
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/08—Limitation or suppression of earth fault currents, e.g. Petersen coil
    • 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
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

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  • Engineering & Computer Science (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
  • Emergency Protection Circuit Devices (AREA)
  • Locating Faults (AREA)

Abstract

The invention discloses a high-sensitivity neutral point flexible grounding power distribution network fault handling method and system. The method comprises the following steps: step S1, monitoring the zero sequence voltage and neutral point current of the bus on line, and judging whether a ground fault occurs; if a ground fault occurs, the process proceeds to step S2; step S2, judging whether the ground fault disappears according to the arc suppression coil; if arc extinction does not occur, the process proceeds to step S3; step S3, estimating the ground fault resistance RfAnd comparing the magnitude with a set threshold epsilon; if R isfIf yes, the process goes to step S4; if R isfIf the value is more than epsilon, sending out warning information; step S4, putting in a small resistor in parallel connection to promote the zero sequence current protection action of the circuit; if not, starting the line selection method of the flexible grounding system; if so, the flow proceeds to step S5; step S5, removing the fault line, and exiting the parallel connectionAnd (4) resistance. The invention is simple and easy to operate, does not need to change the original protection device of the circuit, not only retains the advantages of a flexible grounding system, but also can ensure reliable tripping when a human body is subjected to electric shock and high resistance grounding fault.

Description

High-sensitivity neutral point flexible grounding power distribution network fault handling method and system
Technical Field
The invention relates to the technical field of distribution network automation, in particular to a high-sensitivity neutral point flexible grounding distribution network fault handling method and system.
Background
The topological structure of the power distribution network is gradually complicated, the cable rate is gradually improved, and the low-resistance grounding mode is gradually widely applied to large power distribution networks in cities. The neutral point can rapidly cut off the fault current and reduce the overvoltage level through a small-resistance grounding system, but the small-resistance grounding mode cannot distinguish the types of instantaneous grounding faults and permanent grounding faults, so that the tripping times are increased, the power supply reliability is reduced, and the flexible grounding mode can effectively ensure that the power supply for users is not interrupted when the instantaneous grounding faults occur, so that the flexible grounding mode of connecting the arc suppression coil in parallel with the small resistance is widely popularized and applied in China.
At present, most flexible grounding systems still adopt zero sequence overcurrent protection of small-resistance grounding systems, grounding resistance of about 150 ohms can be detected to the maximum extent, high-resistance grounding faults such as conductor falling on a grassland occur in the flexible grounding systems, and transition resistance during the high-resistance grounding faults is generally over 100 ohms; meanwhile, when a human body is in an electric shock fault, the normal human body resistance is 1k omega-1.5 k omega, the human body resistance after electric shock damage can be reduced to about 500 omega, and the zero sequence current is probably smaller than a setting value, so that passive protection is caused. If the fault line cannot be cut off for a long time, the fault range is possibly expanded, and the power supply reliability is influenced; in addition, when an electric shock accident happens to the actual 10kV line, the line is powered off after a dispatcher receives an alarm call, and personal safety is seriously threatened. Therefore, on the premise of ensuring personal safety, the problem of how to reasonably apply the flexible grounding system to solve the power distribution network fault needs to be solved.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides the high-sensitivity fault handling method and system for the neutral point flexible grounding power distribution network, the original protection device of the line is not required to be changed, and the problem of the power distribution network fault can be effectively solved by adopting the flexible grounding system.
In order to achieve the purpose, the invention adopts the following technical scheme:
according to one aspect of the invention, a high-sensitivity neutral point flexible grounding power distribution network fault handling method is provided, and comprises the following steps:
step S1, monitoring the zero sequence voltage and neutral point current of the bus on line, and judging whether a ground fault occurs; if a ground fault occurs, the process proceeds to step S2, and if no ground fault occurs, the process continues to step S1;
step S2, judging whether the ground fault disappears according to the arc suppression coil; if arc extinction occurs, the fault is eliminated; if arc extinction does not occur, the process proceeds to step S3;
step S3, estimating the ground fault resistance RfAnd comparing the magnitude with a set threshold epsilon; if R isfIf the value is less than epsilon, the step S4 is entered; if R isfIf the value is more than epsilon, sending out warning information;
step S4, putting in a small resistor in parallel connection to promote the zero sequence current protection action of the circuit; if not, starting the flexible grounding system line selection method, and then entering step S5; if so, go to step S5;
and step S5, cutting off the fault line, and exiting the parallel small resistor.
Further, in step S1, when the zero sequence voltage or the neutral point current exceeds the set threshold value, a ground fault occurs.
Further, when the arc suppression coil is extinguished and delayed for 2S in step S2, the fault is eliminated.
Further, in step S3, the ground fault resistor RfThe estimation steps are as follows:
s3.1, determining a fault phase according to the amplitude of the three-phase voltage of the bus, wherein the fault phase i is determined as the phase with the minimum amplitude of the three-phase voltage;
s3.2, calculating the resistance R of the ground faultf：
Figure BDA0003590447660000031
In the formula of UNiThe rated voltage amplitude of the fault phase i; j is the number of the feeder line of the distribution network, I0jThe zero sequence current amplitude of the jth feeder line is obtained; u shapeiThe voltage amplitude of the failed phase i; delta IijThe current amplitude variation before and after the fault phase i fault of the jth feeder line is obtained; delta Ii'jAnd (4) averaging the current amplitude variation before and after the fault of the other two phases of the jth feeder except the fault phase i.
Further, in S3, the threshold value ∈ is 3000 Ω.
Further, the line selection method in S4 is as follows:
s4.1, obtaining the voltage of the non-fault phase line according to the fault phase i determined in the S3
Figure BDA0003590447660000032
S4.2, calculating the phase difference variable quantity of the non-fault phase line voltage before and after the parallel small resistor and the zero sequence current of each line
Figure BDA0003590447660000033
Figure BDA0003590447660000034
In the formula (I), the compound is shown in the specification,
Figure BDA0003590447660000035
the phase difference between the voltage of the front and rear non-fault phase lines of the parallel small resistor and the zero-sequence current of the jth line is respectively obtained;
Figure BDA0003590447660000036
the phase of the non-faulted phase line voltage;
Figure BDA0003590447660000037
the phases of the zero-sequence current of the j-th line before and after the small resistor are connected in parallel respectively;
s4.3, comparing the phase difference variation
Figure BDA0003590447660000038
And determining the fault line according to the magnitude of the reference value theta:
Figure BDA0003590447660000039
a further reference value theta is 45 deg..
According to another aspect of the present invention, there is provided a high-sensitivity neutral point flexible grounding power distribution network fault handling system, including:
the measuring unit is used for acquiring data signals of neutral point current, bus three-phase voltage and zero-sequence voltage, and line three-phase current and zero-sequence current;
the data processing unit is used for filtering and FFT conversion processing on the acquired data signals to obtain amplitude values and phase information of related voltage and current;
the judging unit is used for judging the direction of the fault handling strategy flow according to the set conditions;
the calculating unit is used for calculating the resistance value of the ground fault resistor, the voltage of the non-fault phase line before and after the small resistor is connected in parallel and the phase difference variable quantity of the zero-sequence current of each line;
the control unit is used for controlling the input and the exit of the small parallel resistors;
and the execution unit is used for executing the tripping action of the line protection and sending out an early warning signal.
Compared with the prior art, the invention has the beneficial effects that:
the high-sensitivity neutral point flexible grounding power distribution network fault handling method and system disclosed by the invention have the advantages that the principle is simple and feasible, the original protection device of a line is not required to be changed, meanwhile, the existing measuring device is utilized to provide the line selection method of the flexible grounding system, the advantages of the flexible grounding system are reserved, the reliable tripping operation when a human body is subjected to electric shock and high-resistance grounding fault can be ensured, and the high-sensitivity neutral point flexible grounding power distribution network fault handling method and system have higher practicability.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a block diagram of the present invention;
FIG. 3 is a 10kV neutral point flexible grounding power distribution network simulation model topological diagram.
Detailed Description
In order to better understand the technical scheme of the invention, the invention is further explained by combining the drawings and the specific embodiments in the specification.
Example 1
As shown in fig. 1, a method for handling a fault of a high-sensitivity neutral point flexible grounding distribution network includes the following steps:
step S1, monitoring the zero sequence voltage and neutral point current of the bus on line, and judging whether a ground fault occurs;
when the zero sequence voltage or the neutral point current exceeds the set threshold value, a ground fault occurs. If a ground fault occurs, the process proceeds to step S2, and if no ground fault occurs, the process continues to step S1; and meanwhile, the zero sequence voltage and the neutral point current of the bus of the power distribution network can be monitored to effectively ensure the accuracy of high-resistance ground fault detection, and the threshold values of the zero sequence voltage and the neutral point current are set to avoid the influence caused by 10% of three-phase unbalance of the system.
Step S2, judging whether the ground fault disappears according to the arc suppression coil; if arc extinction occurs, the fault is eliminated; if arc extinction does not occur, the process proceeds to step S3; and as optimization, when the arc suppression coil suppresses the arc and delays for 2s, the fault is eliminated, the arc burning duration time of the transient fault of the small-current grounding system is generally less than 200ms, and the arc suppression coil suppresses the arc and delays for 2s, so that the intermittent arc grounding fault and the permanent grounding fault can be effectively detected while the transient arc is suppressed.
Step S3, estimating the ground fault resistance RfAnd comparing the magnitude with a set threshold epsilon; if R isfIf yes, the process goes to step S4; if R isfIf the value is more than epsilon, sending out warning information;
wherein, the ground fault resistor RfThe estimation steps are as follows:
s3.1, determining a fault phase according to the amplitude of the three-phase voltage of the bus, wherein the fault phase i is determined as the phase with the minimum amplitude of the three-phase voltage;
s3.2, calculating the resistance R of the ground faultf：
Figure BDA0003590447660000051
In the formula of UNiThe rated voltage amplitude of the fault phase i; j is the number of the feeder line of the distribution network, I0jThe zero sequence current amplitude of the jth feeder line is obtained; u shapeiThe voltage amplitude of the failed phase i; delta IijThe current amplitude variation before and after the fault of the jth feeder fault phase i is obtained; delta Ii'jAnd (4) averaging the current amplitude variation before and after the fault of the other two phases of the jth feeder except the fault phase i.
The principle for setting the threshold epsilon is: considering the technical scheme of primary and secondary fusion of national power grid distribution equipment, the minimum measurement values of the zero-sequence current and the primary side of a zero-sequence voltage transformer of a 10kV distribution system are about 1A and 120V, and epsilon is set to 3000 omega. In S3, the threshold value ∈ is 3000 Ω.
Step S4, putting in a small resistor in parallel connection to promote the zero sequence current protection action of the circuit; if not, starting the flexible grounding system line selection method, and then entering step S5; if so, the flow proceeds to step S5;
the line selection method in the S4 comprises the following steps:
s4.1, obtaining the voltage of the non-fault phase line according to the fault phase i determined in the S3
Figure BDA0003590447660000061
S4.2, calculating the phase difference variable quantity of the non-fault phase line voltage before and after the parallel small resistor and the zero sequence current of each line
Figure BDA0003590447660000062
Figure BDA0003590447660000063
In the formula (I), the compound is shown in the specification,
Figure BDA0003590447660000064
the phase difference between the voltage of the front and rear non-fault phase lines of the parallel small resistor and the zero-sequence current of the jth line is respectively obtained;
Figure BDA0003590447660000065
a phase that is a non-faulted phase line voltage;
Figure BDA0003590447660000066
the phases of the zero-sequence current of the j-th line before and after the small resistor are connected in parallel respectively;
s4.3, comparing the phase difference variation
Figure BDA0003590447660000067
And determining the fault line according to the magnitude of the reference value theta:
Figure BDA0003590447660000068
the sensitivity of the actual field zero sequence current protection action is about 150 omega, when the ground fault resistance is overlarge, the zero sequence current protection is disabled, at the moment, the flexible grounding system line selection method is started, and the basic principle of line selection is as follows: when a line has a single-phase earth fault with a higher resistance, the phase difference variation of the non-fault phase line voltage and the fault line zero-sequence current before and after the parallel small resistance is about 0 degree, and the phase difference variation of the non-fault phase line voltage and the healthy line zero-sequence current is about 90 degrees. Considering the influence of other uncertain factors such as measurement errors of voltage and current transformers, line impedance angles, parameter errors and the like, in order to ensure the reliability of a line selection result, 0-degree and 90-degree angle bisectors are taken as boundary lines of two criterion intervals, so that the theta is set to be 45 degrees.
And step S5, cutting off the fault line, and exiting the parallel small resistor.
Example 2
The present embodiment provides a high-sensitivity fault handling system for a neutral point flexible grounding power distribution network, as shown in fig. 2, including:
the measuring unit is used for acquiring data signals of neutral point current, bus three-phase voltage and zero-sequence voltage, and line three-phase current and zero-sequence current;
the data processing unit is used for filtering and FFT conversion processing on the acquired data signals to obtain amplitude values and phase information of related voltage and current;
the judging unit is used for judging the direction of the fault handling strategy flow according to the set conditions;
the calculating unit is used for calculating the resistance value of the ground fault resistor, the voltage of the non-fault phase line before and after the small resistor is connected in parallel and the phase difference variable quantity of the zero-sequence current of each line;
the control unit is used for controlling the input and the exit of the small parallel resistors;
and the execution unit is used for executing the tripping action of the line protection and sending out an early warning signal.
Simulation verification
In order to verify the reliability and effectiveness of the invention, a 10kV neutral point flexible grounding power distribution network simulation model topological graph shown in figure 3 is constructed based on PSCAD/EMTDC. The simulation system comprises 5 outgoing lines l1～l5E is the main network voltage source, and is regarded as an infinite power source, and the impedance of the main network voltage source is approximately 0, RNThe neutral point is connected with a small resistor in parallel and is set to a field common value of 10 omega, S is a switch for switching in and out the small resistor in parallel, L is a neutral point grounded arc suppression coil, f is a fault point, RfIs a ground fault resistor. In l1A phase A grounding fault is set on the circuit, and the fault handling results under different grounding fault resistances are simulated. The simulated sampling frequency was set to 2kHz, and the fault handling results are shown in table 1 below. The result shows that the fault handling strategy applicable to the flexible grounding system can work correctly under different grounding fault resistances, and has higher practicability.
TABLE 1 Fault handling results at different ground fault resistances
Figure BDA0003590447660000081
It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the present application.

Claims (8)

1. A fault handling method for a high-sensitivity neutral point flexible grounding power distribution network is characterized by comprising the following steps:
step S1, monitoring the zero sequence voltage and neutral point current of the bus on line, and judging whether a ground fault occurs; if a ground fault occurs, the process proceeds to step S2, and if no ground fault occurs, the process continues to step S1;
step S2, judging whether the ground fault disappears according to the arc suppression coil; if arc extinction occurs, the fault is eliminated; if arc extinction does not occur, the process proceeds to step S3;
step S3, estimating the ground fault resistance RfAnd comparing the magnitude with a set threshold epsilon; if R isfIf the value is less than epsilon, the step S4 is entered; if R isfIf the value is more than epsilon, sending out warning information;
step S4, putting in a small resistor in parallel connection to promote the zero sequence current protection action of the circuit; if not, starting the flexible grounding system line selection method, and then entering step S5; if so, go to step S5;
and step S5, cutting off the fault line, and exiting the parallel small resistor.
2. The method for handling the fault of the high-sensitivity neutral point flexible grounding power distribution network according to claim 1, wherein: in step S1, when the zero sequence voltage or the neutral point current exceeds the set threshold, a ground fault occurs.
3. The method for handling the fault of the high-sensitivity neutral point flexible grounding power distribution network according to claim 1, wherein: and when the arc suppression coil performs arc suppression and delays for 2S in the step S2, the fault is eliminated.
4. The method for handling the fault of the high-sensitivity neutral point flexible grounding power distribution network according to claim 1, wherein: in step S3, the ground fault resistor RfThe estimation steps are as follows:
s3.1, determining a fault phase according to the amplitude of the three-phase voltage of the bus, wherein the fault phase i is determined as the phase with the minimum amplitude of the three-phase voltage;
s3.2, calculating the resistance R of the ground faultf：
Figure FDA0003590447650000021
In the formula of UNiIs the rated voltage amplitude of the fault phase i; j is the number of the feeder line of the distribution network, I0jThe zero sequence current amplitude of the jth feeder line is obtained; u shapeiThe voltage amplitude of the failed phase i; delta IijThe current amplitude variation before and after the fault phase i fault of the jth feeder line is obtained; delta l'ijAnd (4) averaging the current amplitude variation before and after the fault of the other two phases of the jth feeder except the fault phase i.
5. The method for handling the fault of the high-sensitivity neutral point flexible grounding power distribution network according to claim 1, wherein: in S3, the threshold value ∈ is 3000 Ω.
6. The method for handling the fault of the high-sensitivity neutral point flexible grounding power distribution network according to claim 4, wherein: the line selection method in the S4 comprises the following steps:
s4.1, obtaining the voltage of the non-fault phase line according to the fault phase i determined in the S3
Figure FDA0003590447650000022
S4.2, calculating the phase difference variable quantity of the non-fault phase line voltage before and after the parallel small resistor and the zero sequence current of each line
Figure FDA0003590447650000023
Figure FDA0003590447650000029
In the formula (I), the compound is shown in the specification,
Figure FDA0003590447650000024
the phase difference between the voltage of the non-fault phase line before and after the small resistor is connected in parallel and the zero-sequence current of the jth line is respectively obtained;
Figure FDA0003590447650000025
a phase that is a non-faulted phase line voltage;
Figure FDA0003590447650000026
the phases of the zero-sequence current of the j-th line before and after the small resistor are connected in parallel respectively;
s4.3, comparing the phase difference variation
Figure FDA0003590447650000027
And determining the fault line according to the magnitude of the reference value theta:
Figure FDA0003590447650000028
7. the method for handling the fault of the high-sensitivity neutral point flexible grounding power distribution network according to claim 6, wherein: the reference value θ is 45 °.
8. A fault handling method for a high-sensitivity neutral point flexible grounding power distribution network is characterized by comprising the following steps:
the measuring unit is used for acquiring data signals of neutral point current, bus three-phase voltage and zero-sequence voltage, and line three-phase current and zero-sequence current;
the data processing unit is used for filtering and FFT conversion processing on the acquired data signals to obtain amplitude values and phase information of related voltage and current;
the judging unit is used for judging the direction of the fault handling strategy flow according to the set conditions;
the calculating unit is used for calculating the resistance value of the ground fault resistor, the voltage of the non-fault phase line before and after the small resistor is connected in parallel and the phase difference variable quantity of the zero-sequence current of each line;
the control unit is used for controlling the input and the exit of the small parallel resistors;
and the execution unit is used for executing the tripping action of the line protection and sending out an early warning signal.
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109672164A (en) * 2019-02-22 2019-04-23 国网湖北省电力有限公司电力科学研究院 A kind of arc suppression coil parallel low resistance distribution net work earthing fault processing method
CN111693890A (en) * 2020-04-26 2020-09-22 国网浙江省电力有限公司 System and method for processing single-phase earth fault of power distribution network
CN112731047A (en) * 2020-12-03 2021-04-30 天津大学 Fault line selection method suitable for flexible grounding system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109672164A (en) * 2019-02-22 2019-04-23 国网湖北省电力有限公司电力科学研究院 A kind of arc suppression coil parallel low resistance distribution net work earthing fault processing method
CN111693890A (en) * 2020-04-26 2020-09-22 国网浙江省电力有限公司 System and method for processing single-phase earth fault of power distribution network
CN112731047A (en) * 2020-12-03 2021-04-30 天津大学 Fault line selection method suitable for flexible grounding system

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