A method for locating single-phase grounding fault in 10kV line of small current grounding system

Abstract

The present invention discloses a method for locating single-phase grounding faults of 10kV lines in a small current grounding system, which overcomes the problems that the method for judging the fault point based on the transient current direction in the prior art needs to install high-precision voltage and current acquisition devices, which is costly; the amount of information transmission is large, and the actual engineering application value is low. The method comprises the following steps: S1: analyzing the existing fault circuit K and non-fault circuit N to obtain the phase current variation characteristics of the fault circuit K and non-fault circuit N; S2: collecting the real-time current of the switch on the distribution network and sending it to the distribution automation master station; S3: analyzing the phase current of the collected switch, and locating the fault according to the phase current variation characteristics. The method can quickly and accurately locate the grounding fault point of the 10kV line and avoid power outages in non-fault areas.

Description

Technical Field

[0001] The invention relates to the technical field of small current grounding fault positioning in a distribution network, and in particular to a method for positioning a single-phase grounding fault of a 10kV line in a small current grounding system. Background Art

[0002] At present, the neutral point of my country's 10kV distribution network generally adopts the method of grounding through arc suppression coils, that is, a small current grounding system. When a grounding fault occurs, the transient line selection device in the substation can analyze the transient components of all lines under the same 10kV busbar and select the grounding line with high accuracy. However, the transient line selection device cannot accurately determine the grounding point. Pulling and stopping the substation line switch will cause power outages in non-fault areas. Power operators must find the fault point and isolate it within 2 hours. Due to the large number of distribution network line branches and tight time, it is necessary to study a method for quickly handling 10kV line grounding faults.

[0003] At present, the commonly used ground fault location methods in distribution networks are based on zero-sequence voltage, current transient components, etc. Common implementation methods include the first half-wave method, the traveling wave method, etc., which compare whether the directions of the three-phase transient currents are the same to determine the fault point. However, there are the following disadvantages:

[0004] 1) The information within the coverage of distribution automation is obtained by ordinary voltage and current acquisition devices, while the existing technical criteria require the installation of high-precision voltage and current acquisition devices. There are many distribution network switchgear, the investment cost is high, and the installation of the device requires power outage, which is difficult to achieve;

[0005] 2) The existing method based on transient current direction is not suitable for low-current grounding systems where the neutral point is grounded through an arc suppression coil. It is prone to misjudgment and has low practical engineering application value.

[0006] 3) In actual application, all information needs to be uploaded to the main station for judgment. The network communication of the main station is under great pressure during the information transmission process. The calculation logic is relatively complex during the comprehensive judgment process. The entire positioning process is susceptible to external interference, which affects the accuracy and real-time performance of the results.

[0007] For example, the Chinese Patent Office disclosed an invention entitled "A method for locating a small current grounding fault section in a distribution network based on transient energy analysis" on July 6, 2018, with the publication number CN108254657B. The method includes the following steps: first, determine the passband range of the digital filter, and configure a micro PMU at each node of the distribution network; use the micro PMU to obtain the zero-sequence voltage phasor and zero-sequence current phasor of each node of the distribution network, and determine whether the system has a fault according to the zero-sequence voltage phasor and zero-sequence current phasor of each node. If a fault occurs, start fault location, read the three-phase current signals recorded by each micro PMU, calculate the transient zero-sequence current of each node using the three-phase current signal, process the transient zero-sequence current, calculate the transient energy of each section, and determine the fault section according to the transient energy of each section. The physical meaning of the fault characteristics used in this invention is clear, and the fault section positioning accuracy and reliability of multi-branch lines are high, and there is no need to invest in a middle resistor in parallel with the arc suppression coil or install a signal injection device. This invention solves the problem described in the above-mentioned shortcoming 1, and does not require the installation of additional equipment, but still uses transient current and needs to upload information to the main station. Summary of the invention

[0008] The purpose of the present invention is to overcome the problems existing in the prior art and provide a method for locating single-phase grounding faults in a 10kV line of a small current grounding system, which can quickly and accurately locate the grounding fault point of the 10kV line and avoid power outages in non-fault areas.

[0009] In order to achieve the above object, the present invention adopts the following technical scheme: a method for locating single-phase grounding fault of 10kV line in a small current grounding system, characterized in that it comprises the following steps:

[0010] S1: Analyze the existing fault circuit K and non-fault circuit N to obtain the phase current variation characteristics of the fault circuit K and non-fault circuit N;

[0011] S2: collects the real-time current of switches on the distribution network and sends it to the distribution automation master station;

[0012] S3: Analyze the collected phase current of the switch and locate the fault according to the characteristics of the phase current change.

[0013] The present invention proposes a method for quickly locating 10kV line faults in a small current grounding system based on steady-state current. It does not require additional voltage and current acquisition devices. The grounding fault point can be quickly and accurately located by uploading information from the master station using the existing current acquisition device. The method has strong practicality, small calculation amount, fast calculation speed, and reduced analysis and judgment time. The method can be mutually verified with the line selection results of the grounding line selection device of the substation to improve the line selection accuracy.

[0014] Preferably, in step S1, the existing fault circuit K and the non-fault circuit N are analyzed to obtain the phase current variation characteristics of the fault circuit K and the non-fault circuit N, which are specifically manifested as follows:

[0015] S1.1: The outgoing lines of the same busbar are 1, 2, ..., N in sequence. Assume that the fault occurs at any point f on line K, and the fault phase is phase A. Apply the symmetrical component method to perform a steady-state analysis on the single-phase grounding fault of fault phase A on the fault line K. Only the fault line K and the non-fault line N are retained to obtain the sequence network equivalent circuit;

[0016] S1.2: Calculate the three-phase current change values ​​on the non-fault line N and the three-phase current change values ​​on the fault line K respectively;

[0017] S1.3: Determine the phase current variation characteristics of the fault circuit and the non-fault circuit based on the calculated results.

[0018] The method of symmetrical components is a basic method for analyzing the asymmetrical operating state of a symmetrical system in electrical engineering. It is widely used in the calculation of electrical quantities in three-phase AC systems with symmetrical parameters and asymmetrical operating conditions. Its purpose is to transform a set of asymmetrical ABC quantities into three sets of symmetrical three-phase phase quantities, which are called positive sequence, negative sequence and zero sequence quantities. Corresponding to each sequence voltage and current quantity, the power system is also divided into positive sequence, negative sequence and zero sequence networks. In each sequence network, the sequence voltage and current are analyzed in a symmetrical manner, and then synthesized into the actual ABC quantity, which greatly simplifies the calculation of asymmetrical faults.

[0019] Preferably, the sequence network equivalent circuit in step S1.1 includes:

[0020] Zero-sequence network: It is a passive network, a computational network determined by the zero-sequence network topology of the power system and the zero-sequence parameters of the components; the zero-sequence potential at the fault point is not zero; under the action of the zero-sequence potential, zero-sequence current flows through the three-phase zero-sequence network, the reactance of the corresponding line component is the zero-sequence reactance, and the current passes through three times the grounding impedance.

[0021] Negative sequence network: It is a passive network, a calculation network determined by the negative sequence network topology of the power system and the negative sequence parameters of the components. The negative sequence potential at the fault point is not zero.

[0022] Positive sequence network: It is an active network. The positive sequence potential at the fault point of the calculated network is not zero, which is determined by the positive sequence network topology of the power system and the positive sequence parameters of the components.

[0023] Preferably, in step S1.2, the three-phase current change value on the non-fault line N is:

[0024]

[0025] in:

[0026]

[0027]

[0028] In the formula, ΔI NA Indicates the change in current of phase A of the non-fault line N, ΔI NB Indicates the change in the B-phase current of the non-fault line N, ΔI NC Indicates the change in phase C current of the non-fault line N; I A1 ,I A2 ,I A0 Respectively represent the positive, negative and zero sequence current of the fault component at the fault point; Z 1∑ , Z 2∑ , Z 0∑ They represent the equivalent impedance of positive, negative and zero sequence respectively, with both sides of the fault point as ports. From this, the current variation characteristics on the non-fault line can be obtained.

[0029] Preferably, it is characterized in that, in the step S1.2, for the faulty line, there are:

[0030]

[0031] In the formula, ΔI KA Indicates the change in phase A current of fault line K, ΔI KB Indicates the change in the B-phase current of the fault line K, ΔI KC Indicates the change in phase C current of fault line K.

[0032] Thus, the current change characteristics on the fault line can be obtained. When a single-phase grounding occurs at a 10kV substation, the grounding line can be determined by the imbalance of the three-phase current of the substation line in the distribution automation system, and can also be verified with the small current grounding line selection device in the substation to determine the grounding line. The specific verification method is: 1. When the substation grounding line selection device selects the line correctly, the precise positioning device can be used to locate the fault point and confirm the correctness of the substation grounding line selection device; 2. When the substation grounding line selection device has more than one line selection result, the device can be used to confirm the grounding line and locate the fault point; 3. When the substation grounding line selection device selects the line incorrectly, since the device is different from the substation line selection device in principle, the device can provide the correct line selection result and locate it.

[0033] Preferably, in step S1.3, the phase current variation characteristics of the fault circuit and the non-fault circuit are:

[0034] 1. For the steady-state value of the three-phase current on the non-fault line N, we have:

[0035] ΔI NB =ΔI NC , ΔI NA ≈ΔI NB

[0036] It can be concluded that the phase current changes of the two non-fault phases are approximately equal, and are also approximately equal to the phase current change of the fault phase;

[0037] 2. For the steady-state value of the phase current on the fault line K, we have:

[0038] ΔI KB =ΔI KC , ΔI KA >ΔI KB

[0039] It can be concluded that the phase current changes of the two non-fault phases are approximately equal and smaller than the phase current change of the fault phase. Therefore, the fault location can be performed based on the two different characteristics of the phase current changes. Because there are multiple 10kV outgoing lines under the bus of the substation, when a line of a certain section of the bus is grounded in a single phase (assuming it is phase A), since other lines are connected to the line with the single-phase grounding fault through the substation bus, the A phase voltage of other lines will also decrease, which is called the fault phase.

[0040] Preferably, step S3 is specifically expressed as follows:

[0041] The real-time current of the switches on the distribution network will be sent to the distribution automation master station. By analyzing the phase current of the switches on the faulty line, the fault point can be determined. Specifically, the grounding of the distribution network line can be divided into two categories: trunk line grounding and branch line grounding:

[0042] 1. The distribution network line is trunk grounded: if the current amplitude of phase A of the switch of circuit 1 is greater than that of phases B and C, and the current amplitude of phase A of the switch of circuit 2 is basically equal to that of phases B and C, then it is judged that the grounding point is between the switch of circuit 1 and the switch of circuit 2;

[0043] 2. The distribution network is branch-line grounded: If the current amplitude of the circuit switch phase A is greater than that of phases B and C, the grounding point is determined to be located on the branch line where the circuit switch is located. There is no need to add voltage and current acquisition devices. The existing current acquisition device can be used to upload the information of the main station to achieve rapid and accurate positioning of the grounding fault point, which is highly practical.

[0044] Therefore, the present invention has the following beneficial effects: 1. There is no need to add voltage and current acquisition devices. The existing current acquisition device can be used to upload the information of the main station to realize the rapid and accurate positioning of the grounding fault point, which is highly practical; 2. The calculation amount is small, the calculation speed is fast, and the analysis time is reduced; 3. The line selection results of the grounding line selection device of the substation can be mutually verified to improve the accuracy of line selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a specific operation flow chart of the method of the present invention;

[0046] Figure 2 This is a schematic diagram of a single-phase grounding fault in a low current system;

[0047] Figure 3 It is the positive sequence network equivalent circuit diagram of the present invention;

[0048] Figure 4 It is the negative sequence network equivalent circuit diagram of the present invention;

[0049] Figure 5 It is the zero-sequence network equivalent circuit diagram of the present invention;

[0050] Figure 6 This is a schematic diagram of phase current changes when single-phase grounding occurs in a small current grounding system;

[0051] Figure 7 This is the connection diagram of the distribution network lines. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0053] like Figure 1 In the embodiment shown, a method for locating single-phase grounding faults in a 10kV line of a small current grounding system can be seen, and its operation process is as follows: Step 1, analyze the existing fault circuit K and non-fault circuit N to obtain the phase current variation characteristics of the fault circuit K and non-fault circuit N; Step 2, collect the real-time current of the switches on the distribution network and send it to the distribution automation master station; Step 3, analyze the collected phase current of the switches and locate the fault according to the phase current variation characteristics. The present invention does not require the addition of voltage and current acquisition devices. The information of the master station can be uploaded by the existing current acquisition device to realize the rapid and accurate positioning of the grounding fault point, which is highly practical; the calculation amount is small, the calculation speed is fast, and the judgment time is reduced; it can be mutually verified with the line selection results of the grounding line selection device of the substation to improve the line selection accuracy.

[0054] The following further illustrates the technical solution and technical effects of the present invention through specific examples.

[0055] The diagram of a single-phase grounding fault in a low-current system with a neutral point grounded via an arc suppression coil is as follows: Figure 2 As shown, the outgoing lines of the same bus are 1, 2, ..., N in sequence. Assume that a fault occurs at any point f on line K and the faulty phase is phase A.

[0056] Using the symmetrical component method, a steady-state analysis is performed on the A-phase single-phase grounding fault on line K. Only the faulty line K and the non-faulty line N are retained, and the sequence network equivalent circuit can be obtained, as shown in Figure 3 As shown, it is the equivalent circuit of the positive sequence network; Figure 4 As shown, it is the equivalent circuit of negative sequence network; Figure 5 The shown figure is the equivalent circuit of the zero-sequence network.

[0057] The changes of the three-phase currents of A, B, and C of the fault line K are ΔI KA , ΔI KB , ΔI KC , the positive sequence, negative sequence, and zero sequence currents are ΔI KA1 , ΔI KA2 , ΔI KA0 The current changes of the three phases A, B and C of the non-fault line N are ΔI NA , ΔI NB , ΔI NC , the positive sequence, negative sequence, and zero sequence currents are ΔI NA1 , ΔI NA2 , ΔI NA0 ; The positive, negative and zero sequence currents of the fault component at the fault point are I A1 ,I A2 ,I A0 ; Taking the two sides of the fault point as ports, the positive, negative and zero sequence equivalent impedances are Z 1∑ , Z 2∑ , Z 0∑ , the grounding resistance at the fault point is R f .

[0058] For the fault line, there are:

[0059]

[0060] in:

[0061]

[0062] It can be seen that: ΔI KB =ΔI KC , ΔI KA >ΔI KB .

[0063] For non-fault lines, we have:

[0064]

[0065] in:

[0066] Z eq ′=Z K0 -Z 0Σ (1+Z K0 JωC K0 )

[0067]

[0068] It can be seen that: ΔI NB =ΔI NC , ΔI NA ≈ΔI NB .

[0069] The following conclusions can be drawn from the above analysis: 1. For the steady-state value of the phase current on the non-fault path, the phase current changes of the two non-fault phases are approximately equal, and are also approximately equal to the phase current change of the fault phase. 2. For the steady-state value of the phase current on the fault path, the phase current changes of the two non-fault phases are approximately equal, and are smaller than the phase current change of the fault phase. Therefore, fault location can be performed based on the two different characteristics of the above phase current changes.

[0070] Taking the case of single-phase grounding of phase A on the 10kV busbar of a substation as an example, for a 10kV distribution network with three-phase load balance, the phase current changes between the fault path and the non-fault path are as follows: Figure 6 shown.

[0071] Therefore, when single-phase grounding occurs at a 10kV substation, the grounding line can be determined by the imbalance of the three-phase current of the substation line in the distribution automation system, and verified with the small current grounding line selection device in the substation to determine the grounding line.

[0072] Furthermore, the real-time current of the switches on the distribution network will be sent to the distribution automation master station. By analyzing the phase current of the switches on the faulty line, the fault point can be determined. The grounding of the distribution network line can be divided into two categories: trunk line grounding and branch line grounding. The connection relationship of the distribution network line is as follows: Figure 7 shown.

[0073] ① Main line grounding. When the 101 ring main unit 02 switch and the 102 ring main unit 01 switch are grounded, the A-phase current amplitude of the 101 ring main unit 02 switch is greater than that of the B and C phases, and the A-phase current amplitude of the 102 switch ring main unit 01 switch is basically equal to that of the B and C phases. It is judged that the grounding point is between the 101 ring main unit 02 switch and the 102 ring main unit 01 switch.

[0074] ② When the branch line where the switch 21 of the 102 ring main unit is located is grounded, the current amplitude of phase A of the switch 12 of the 102 ring main unit is greater than that of phases B and C, then it is judged that the grounding point is located on the branch line where the switch 21 of the 102 ring main unit is located.

[0075] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A method for locating single-phase grounding faults in a 10kV line of a small current grounding system, characterized in that: It includes the following steps: S1: Analyze the existing fault circuit K and non-fault circuit N to obtain the phase current variation characteristics of the fault circuit K and non-fault circuit N; Non-fault line: Calculate the ratio of the positive and negative sequence equivalent impedance of the fault line to the positive and negative sequence equivalent impedance of the non-fault line, M; calculate the ratio of the zero sequence equivalent impedance of the fault line to the zero sequence equivalent impedance of the non-fault line, N; the change of phase A current ΔI NA The product of the sum of the ratio N and the 2 times ratio M and the positive sequence current of the fault component, the change of the current of phase B ΔI NB and C phase current change ΔI NC They are the product of the difference between the ratio N and the ratio M and the positive sequence current of the fault component; Fault Line: Calculate the inverse of the ratio of the positive and negative sequence equivalent impedance of the fault line to the positive sequence current of the fault component and the equivalent impedance ratio of the power supply, P. The change in phase A current is -ΔI NA -2P, the change in current of phase B is -ΔI NB +P, C phase current change is -ΔI NC +P; S2: collects the real-time current of switches on the distribution network and sends it to the distribution automation master station; S3: Analyze the collected phase current of the switch and locate the fault according to the characteristics of the phase current change.

2. A method for locating single-phase grounding faults in a 10kV line of a small current grounding system according to claim 1, characterized in that: The step S1 is further expressed as: S1.1: Apply the symmetrical component method to perform steady-state analysis on the single-phase grounding fault of fault phase A on fault line K and obtain the sequence network equivalent circuit; S1.2: Calculate the three-phase current change values ​​on the non-fault line N and the three-phase current change values ​​on the fault line K respectively; S1.3: Determine the phase current variation characteristics of the fault circuit and the non-fault circuit based on the calculated results.

3. A method for locating single-phase grounding faults in a 10kV line of a small current grounding system according to claim 2, characterized in that: In the step S1.1, the sequence network equivalent circuit includes: a positive sequence network, a negative sequence network and a zero sequence network.

4. A method for locating single-phase grounding faults in a 10kV line of a small current grounding system according to claim 3, characterized in that: In step S1.2, the three-phase current change value on the non-fault line N is calculated: For non-fault lines, we have: A phase current change: Phase B current change: Phase C current change: in: WITH eq ′=Z K0 -WITH 0Σ (1+Z K0 jωC K0 ) In the formula, ΔI NA , ΔI NB , ΔI NC Respectively represent the A, B, and C three-phase current changes of the non-fault line N; I A1 ,I A2 ,I A0 Respectively represent the positive, negative and zero sequence current of the fault component at the fault point; Z 1∑ , Z 2∑ , Z 0∑ Respectively represent the equivalent impedance of positive, negative and zero sequence with both sides of the fault point as ports; Z eq Represents the positive-sequence and negative-sequence equivalent impedance of the fault line K; Z eq ′ represents the zero-sequence equivalent impedance of the fault line K; Z eqN Represents the positive-sequence and negative-sequence equivalent impedance of the non-fault line N; Z eqN ′ represents the zero-sequence equivalent impedance of the non-fault line N; Z N represents the positive sequence impedance of the non-fault line N; Z fN Represents the ground impedance of the non-fault line N; Z N0 represents the zero-sequence impedance of the non-fault line N; Z represents the equivalent impedance of the power supply; Z K represents the positive sequence impedance of the fault line K; Z K0 Represents the zero-sequence impedance of the fault line K; Z fK represents the grounding impedance of the fault line K; C N Represents the positive sequence capacitance of the non-fault line N to ground; C K Indicates the positive sequence capacitance of fault line K to ground; C N0 Indicates the zero-sequence capacitance of non-fault line N to ground; C K0 Represents the zero-sequence capacitance of the fault line K to ground.

5. A method for locating single-phase grounding faults in a 10kV line of a small current grounding system according to claim 3 or 4, characterized in that: In the step S1.2, the three-phase current change value on the fault line K is calculated: For the fault line, there are: A phase current change: Phase B current change: Phase C current change: In the formula, ΔI KA , ΔI KB , ΔI KC They respectively represent the changes in the three-phase currents of A, B, and C of the fault line K.

6. A method for locating single-phase grounding faults in a 10kV line of a small current grounding system according to claim 5, characterized in that: In step S1.3, the phase current variation characteristics of the fault circuit and the non-fault circuit are obtained as follows: For the steady-state value of the three-phase current on the non-fault line N, the changes in the phase currents of the two non-fault phases are approximately equal, and are also approximately equal to the changes in the phase currents of the fault phase; for the steady-state value of the phase current on the fault line K, the changes in the phase currents of the two non-fault phases are approximately equal, and are smaller than the changes in the phase currents of the fault phase.

7. A method for locating single-phase grounding faults in a 10kV line of a small current grounding system according to claim 1, characterized in that: The step S3 further comprises: The distribution network line is trunk grounded: if the current amplitude of phase A of the switch of circuit 1 is greater than that of phases B and C, and the current amplitude of phase A of the switch of circuit 2 is substantially equal to that of phases B and C, then it is determined that the grounding point is between the switch of circuit 1 and the switch of circuit 2; The distribution network is branch-line grounded: If the current amplitude of phase A of the circuit switch is greater than that of phases B and C, it is determined that the grounding point is located on the branch line where the circuit switch is located.

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