Power distribution network single-phase earth fault degree tracking method based on hybrid arc extinction process

Abstract

The invention discloses a power distribution network single-phase earth fault degree tracking method based on a hybrid arc extinction process. In a mixed arc extinguishing process, accurate measurement of grounding resistance and real-time tracking of grounding fault degree are realized based on transient zero sequence voltage waveform characteristics of an arc extinguishing coil arc extinguishing stage and an active arc extinguishing stage. Fault arc extinction and fault tracking can be performed synchronously, and the problem that power distribution equipment is subjected to secondary impact of short-circuit current due to the fact that an arc extinction device needs to be quitted when grounding resistance is measured in a traditional fault tracking method is solved. The method is easy to implement and high in reliability.

Description

Technical Field

[0001] The present invention relates to the field of single-phase grounding fault detection and protection in a distribution network, and in particular to a single-phase grounding fault degree tracking technology in a distribution network based on a hybrid arc extinguishing process. Background Art

[0002] The distribution network is the main battlefield for the construction of new power systems under the background of the "dual carbon" strategic goal. The transformation of the distribution network side has become the focus of power system construction. Grounding is the most important type of fault in the distribution network, which endangers system operation and personal safety. Rapid arc extinguishing is the key to curbing the development of faults and achieving self-healing of faults. At present, the State Grid Corporation requires "rapid isolation of permanent faults and safe arc extinguishing of transient faults", which puts higher requirements on fault type identification and rapid arc extinguishing capabilities. From a safety perspective, the arc extinguishing device should be put into operation immediately after the fault occurs to quickly self-heal the fault, but rapid arc extinguishing will cover up the fault information and interfere with fault detection, which brings about a new problem that the time between fault detection and fault arc extinguishing cannot be coordinated. The synchronous fault development tracking and identification under the arc extinguishing state is the key to solving the problem.

[0003] 80% of single-phase grounding faults are instantaneous faults. When the grounding current is suppressed to less than 10 A or the fault phase voltage is reduced to less than the arcing voltage, the grounding arc is difficult to sustain and extinguishes. The transition resistance of faults such as tree collision is unstable, causing fluctuations in the transition resistance. Therefore, the arc extinguishing process is often accompanied by changes in the fault degree. Fuzhou University and Changsha University of Science and Technology in my country proposed to observe the change law of zero-sequence voltage and line zero-sequence current by delaying the exit of the arc extinguishing device to determine the occurrence of instantaneous or permanent faults. Scholars from Harbin Institute of Technology and others proposed to predict the nature of the fault by using the volt-ampere curve constructed by the zero-sequence component of the fault feeder, and further determine the nature of the fault by the change of the amplitude and phase of the zero-sequence current after the arc extinguishing device is put into use. However, most of the existing transition resistance identification methods are independent of the arc extinguishing process, and it is necessary to exit the arc extinguishing device after a delay to determine the nature of the fault. For more than 80% of transient faults and when there are multiple development stages, the arc extinguishing device exits lagging under transient faults, the distribution equipment is subjected to secondary short-circuit current shocks, and the real-time tracking of fault development is poor.

[0004] After searching the prior art field, it was found that the Chinese patent application number is 202410650784.6, the application publication number is CN118566639A, and the patent name is: Ground fault line selection method for resonant grounded distribution network based on phase similarity. This patent measures the value of grounding resistance by calculating the similarity of the zero-sequence voltage and the zero-sequence current phase of the fault line. The interference of the zero-sequence signal in the tuning process of the arc suppression coil is not considered, and the measurement error is large.

[0005] The Chinese patent application number is 202110408920.7, the application publication number is CN113097989A, and the patent name is: A composite arc extinguishing method for faults in a flexible grounded distribution network. The patent proposes a hybrid arc extinguishing strategy, but does not consider the impact of asymmetric distribution parameters of the distribution network on the arc extinguishing effect. Therefore, the grounding current cannot be completely compensated, resulting in poor measurement of grounding resistance. Summary of the invention

[0006] Technical problem: The technical problem to be solved by the present invention is to provide a method for tracking the degree of single-phase grounding fault in a distribution network based on a hybrid arc extinguishing process. The method should be able to solve the problems that the traditional grounding fault resistance measurement effect is easily affected by the arc extinguishing process and the fault tracking method has poor real-time performance.

[0007] Technical solution: In order to solve the above technical problems, the present invention proposes a method for tracking the degree of single-phase grounding fault in distribution network based on hybrid arc extinguishing process. Through the cooperation of arc extinguishing coil and active arc extinguishing device, the grounding resistance measurement and fault degree tracking based on multi-stage hybrid arc extinguishing process are realized.

[0008] A method for tracking the degree of single-phase grounding fault in a distribution network based on a hybrid arc extinguishing process comprises the following steps:

[0009] S1: When the distribution network is operating normally, monitor the steady-state zero-sequence voltage U 0, if the following equation is established, then go to step S2; if the following equation is not established, then the system is judged to be normal and the steady-state zero-sequence voltage continues to be monitored; Formula 1 In the above formula, ν is the detuning degree of the distribution network, is the phase voltage of the distribution network;

[0010] S2: Connect a hybrid arc extinguishing device at the neutral point of the distribution network, where the hybrid arc extinguishing device is composed of an arc extinguishing coil and an active arc extinguishing device in parallel; put the arc extinguishing coil into operation and record the zero-sequence voltage when the arc extinguishing coil is running alone u 0 waveform, and extract the transient component in the waveform; when the transient component decays according to the DC law, enter step S3; when the transient component decays according to the AC law, enter step S4;

[0011] S3: Read the horizontal and vertical coordinates of a point on the transient component waveform, denoted as t, u a_tra , then during the arc extinguishing stage of the arc extinguishing coil, the grounding resistance can be measured R E1 for:

[0012] Formula 2

[0013] In the above formula,L is the equivalent inductance of the arc suppression coil, C Σ is the total insulation capacitance of the system to ground, G Σ is the total insulation conductance of the system to ground, t 0 is the time when the arc suppression coil is put into operation. X , Y satisfy:

[0014] Formula 3 Formula 4

[0015] In the above two formulas, T y for t The current value on the arc extinguishing coil at time 0, V y for t The voltage value on the arc extinguishing coil at time 0, E A is the power supply A phase voltage, Y A , Y B , Y C are the relative admittances of A, B, and C respectively. p , θ are u af The amplitude and phase of

[0016] S4: Extract the upper envelope of the transient component waveform and read two points on the envelope Q 1( x 1, h 1) Q 2( x 2, h 2) When the difference between the ordinates of two points satisfies When, the difference between the horizontal coordinates Equal to the time constant , then during the arc extinguishing stage of the arc extinguishing coil, the grounding resistance can be measured R E1 for:

[0017] Formula 5

[0018] S5: When the arc extinguishing coil is put into operation for d When the arc extinguishing coil is fully compensated, the active arc extinguishing device is put into operation to fully compensate for the active component of the grounding current. The zero-sequence voltage is recorded after the arc extinguishing coil and the active arc extinguishing device are operated simultaneously. u 0 waveform, measured ground resistance R E2, including the following steps:

[0019] S5-1: Extract zero-sequence voltage u 0 The decaying DC component in the waveform;

[0020] S5-2: Read two points on the decaying DC component Q 3( x 3, h 3) Q 4( x 4, h 4), and the difference in ordinates satisfies , the difference between the horizontal coordinates Equal to the time constant ;

[0021] S5-3: Measured ground resistance R E2 for:

[0022] Formula 6

[0023] S6: Ground resistance measured at the arc extinguishing coil stage and the active arc extinguishing stage R E1 and R E2 The size is compared to track the degree of ground fault, including the following steps:

[0024] S6-1: When R E1 equal R E2 When , it indicates that the ground fault level has not changed during the mixed arc extinguishing process, and the mixed arc extinguishing device continues to operate;

[0025] S6-2: When R E1 Greater than R E2 When , it indicates that the ground fault level becomes serious during the mixed arc extinguishing process, then the mixed arc extinguishing device is exited;

[0026] S6-3: When R E1 Less than R E2 When , it indicates that the ground fault level is reduced during the mixed arc extinguishing process, then the mixed arc extinguishing device is exited;

[0027] S6-4: When R E1 Less than R E2 and R E2When it is equal to positive infinity, it indicates that the single-phase grounding fault in the distribution network disappears, and the hybrid arc extinguishing device is exited.

[0028] Furthermore, the method for calculating the detuning degree of the distribution network in step S1 is: Formula 7

[0029] In the above formula, I C is the capacitive current of the grid, I L It is the active compensation current of the power grid.

[0030] Furthermore, in step S3, the arc extinguishing coil is in a fully compensated state, and the arc extinguishing coil has an equivalent inductance of L Satisfy the following formula:

[0031] Formula 8

[0032] In the above formula, ω is the power angular frequency.

[0033] Furthermore, in step S4 .

[0034] Furthermore, in step S5 d is equal to five times the time constant, that is .

[0035] Beneficial effects: The present invention proposes a method for tracking the degree of single-phase grounding fault in a distribution network based on a hybrid arc extinguishing process, which can achieve accurate measurement of grounding resistance and real-time tracking of the degree of grounding fault while fully compensating the grounding current after a single-phase grounding fault occurs in the distribution network. The method ensures that fault arc extinguishing and fault degree tracking can be performed synchronously, and can reliably determine the occurrence of transient and permanent grounding faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the operation diagram of the hybrid arc extinguishing device for the distribution network;

[0037] Figure 2 This is the principle diagram of ground resistance measurement during the arc extinguishing stage of the arc extinguishing coil;

[0038] Figure 3 This is the principle diagram of ground resistance measurement in the active arc extinguishing stage;

[0039] Figure 4 It is the topological structure diagram of the simulation system;

[0040] Figure 5 This is the simulation result diagram when the ground resistance is set to 20 ohms;

[0041] Figure 6This is the simulation result diagram when the ground resistance is set to 2000 ohms. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Attached Figure 1 This is a schematic diagram of the operation of the hybrid arc extinguishing device in the distribution network. n Lines, C nA , C nB , C nC The lines are n The distributed capacitance of phases A, B, and C to ground; G nA , G nB , G nC The lines are n The distributed conductance of phases A, B, and C to ground, R E is the grounding resistance. n Taking the A-phase grounding fault of a line as an example, a single-phase grounding fault degree tracking method of distribution network based on hybrid arc extinguishing process is specifically introduced.

[0044] Step S1: When the distribution network is operating normally, monitor the steady-state zero-sequence voltage U 0, if the following equation is established, then go to step S2; if the following equation is not established, then it is determined that the system is normal and the steady-state zero-sequence voltage continues to be monitored; Formula 9

[0045] In the above formula, ν is the detuning degree of the distribution network, is the phase voltage of the distribution network; ν The calculation method is:

[0046] Formula 10

[0047] In the above formula, I C is the capacitive current of the grid, I L It is the active compensation current of the power grid.

[0048] Step S2: Connect a hybrid arc extinguishing device to the neutral point of the distribution network, as shown in the attached Figure 1 As shown. The hybrid arc extinguishing device is composed of an arc extinguishing coil and an active arc extinguishing device in parallel. The active arc extinguishing device can be equivalent to a current source. Put the arc extinguishing coil into operation (i.e. close switch K1 and open switch K2), and record the zero-sequence voltage when the arc extinguishing coil is running alone. u 0 waveform, and extract the transient component in the waveform; as shown in the attached Figure 2 As shown in the figure, when the transient component decays according to the DC law, the process goes to step S3; Figure 3 As shown, when the transient component decays according to the AC law, the process proceeds to step S4.

[0049] Step S3: As shown in the attached Figure 2 As shown in the figure, when the system is in an overdamped state, there is a decaying DC component in the zero-sequence voltage. The method for extracting this component is to use the Hilbert transform method to obtain the upper and lower envelopes of the zero-sequence voltage. The vertical bisectors of the upper and lower envelopes are the transient components to be extracted. Q The horizontal and vertical coordinates of the point are denoted as t and u a_tra , which is substituted into the following formula, the grounding resistance of the arc extinguishing coil in the arc extinguishing stage can be obtained R E1 for:

[0050] Formula 11

[0051] In the above formula, L is the equivalent inductance of the arc suppression coil, C Σ is the total insulation capacitance of the system to ground, G Σ is the total insulation conductance of the system to ground, t 0 is the time when the arc suppression coil is put into operation. X , Y satisfy:

[0052] Formula 12

[0053] Formula 13

[0054] In the above two formulas, T y for t The current value on the arc extinguishing coil at time 0, V y for t The voltage value on the arc extinguishing coil at time 0, E A is the power supply A phase voltage, Y A , YB , Y C are the relative admittances of A, B, and C respectively. p , θ are u af The amplitude and phase of the arc extinguishing coil; in this stage, the arc extinguishing coil is in a fully compensated state, and the equivalent inductance of the arc extinguishing coil L satisfy:

[0055] Type 14

[0056] In the above formula, ω is the power angular frequency.

[0057] Step S4: As shown in the attached Figure 3 (a) Attachment Figure 3 As shown in (b), when the system is in an overdamped state, there is an attenuated AC component in the zero-sequence voltage. Extract the upper envelope of the transient component waveform and read the two points on the upper envelope. Q 1( x 1, h 1) Q 2( x 2, h 2) When the difference between the ordinates of two points satisfies When, the difference between the horizontal coordinates Equal to the time constant , then during the arc extinguishing stage of the arc extinguishing coil, the grounding resistance can be measured R E1 for:

[0058] Formula 15

[0059] Step S5: When the arc extinguishing coil is put into operation for When the arc suppression coil is fully compensated, the active arc suppression device is operated and put into operation to fully compensate the active component of the grounding current. Figure 1 The middle switch K1 and switch K2 are both closed, and the zero-sequence voltage is recorded after the arc extinguishing coil and the active arc extinguishing device are operated simultaneously. u 0 waveform, the ground resistance is measured R E2 , including the following steps:

[0060] Step S5-1: Extract zero-sequence voltage u 0 The decaying DC component in the waveform;

[0061] Step S5-2: As shown in the attached Figure 3 As shown in (c), read two points on the attenuated DC component Q 3( x 3, h 3) Q4( x 4, h 4), and the difference in ordinates satisfies , the difference between the horizontal coordinates Equal to the time constant ;

[0062] Step S5-3: Measure the ground resistance R E2 for:

[0063] Formula 16

[0064] Step S6: Measure the grounding resistance of the arc extinguishing coil stage and the active arc extinguishing stage respectively R E1 and R E2 The size is compared to track the degree of ground fault, including the following steps:

[0065] Step S6-1: When R E1 equal R E2 When , it indicates that the ground fault level has not changed during the mixed arc extinguishing process, and the mixed arc extinguishing device continues to operate;

[0066] Step S6-2: When R E1 Greater than R E2 When , it indicates that the ground fault level becomes serious during the mixed arc extinguishing process, then the mixed arc extinguishing device is exited;

[0067] Step S6-3: When R E1 Less than R E2 When , it indicates that the ground fault level is reduced during the mixed arc extinguishing process, then the mixed arc extinguishing device is exited;

[0068] Step S6-4: When R E1 Less than R E2 and R E2 When it is equal to positive infinity, it indicates that the single-phase grounding fault in the distribution network disappears, and the hybrid arc extinguishing device is exited.

[0069] MATLAB / Simulink simulation is used to verify the method for tracking the degree of single-phase grounding fault in distribution network based on hybrid arc extinguishing process proposed by the present invention. Figure 4The topological structure diagram of the 10kV active distribution network simulation system is shown in Table 1 and Table 2 respectively. The parameters of each line of the distribution network and the parameter settings of the distributed power supply connected to the load side are shown in Table 1 and Table 2 respectively. L =0.2528H, equivalent output current of active arc extinguishing device I S = 72.430∠-92.002° A, the ground fault is set on phase A of line 3, t =0 seconds when the fault occurs. t =0.142 seconds, the arc extinguishing coil is put into operation. t =0.505s active arc extinguishing device is put into use. The grounding resistor is set with a small resistance ( R E = 20 ohms) and a large resistor ( R E =2000 ohms) two groups.

[0070] Table 1 Line parameters

[0071] (a) Line parameters per kilometer

[0072]

[0073] (b) Relative ground parameters of each line

[0074]

[0075] Table 2 Distributed power supply parameters

[0076]

[0077] When the grounding resistance is set to 20 ohms, the zero-sequence voltage and fault phase voltage waveforms of the arc extinguishing coil during the arc extinguishing stage are shown in the attached figure. Figure 5 As shown in the figure, it can be seen that a point on the transient component waveform Q The coordinates are (0.16, 385.76), substitute R E1 The measured value of the ground resistance obtained from the calculation formula is 19.987 ohms, and the error between it and the simulation setting value is 0.065%.

[0078] When the grounding resistance is set to 2000 ohms, the zero-sequence voltage and fault phase voltage waveforms of the arc extinguishing coil during the arc extinguishing stage are shown in the attached figure. Figure 6 (a) As shown in the figure, the coordinates of the two points on the upper envelope are: Q 1 (0.145, 8085.7), Q 2 (0.255, 6181.1), so the time constant is obtained , and further measured the ground resistance to be 1994.199 ohms, with an error of 0.290% from the simulation setting value.

[0079] When the grounding resistance is set to 2000 ohms, the zero-sequence voltage and fault phase voltage waveforms in the active arc extinguishing stage are shown in the attached figure. Figure 6 (b) As shown in the figure, the coordinates of the two points on the transient component are: Q 3 (0.550, 2253.5), Q 4 (0.604, 829.3), so the time constant is obtained , and further measured the ground resistance to be 1996.887 ohms, with an error of 0.157% from the simulation setting value.

[0080] In addition, multiple groups of grounding resistances of different sizes were set in the simulation to simulate the change of fault degree. The grounding resistance was measured using the arc extinguishing coil in the arc extinguishing stage and the active arc extinguishing stage, and the results shown in Table 3 were obtained.

[0081] Table 3 Ground resistance measurement and fault degree tracking results

[0082]

[0083] As shown in Table 3, no matter how the severity of the ground fault changes, the method proposed in the present invention can accurately measure the ground resistance at each stage and track the change of the fault severity. The measurement error of the ground resistance never exceeds 1.650%, which verifies the accuracy and reliability of the method proposed in the present invention.

Claims

1. A method for tracking the degree of single-phase grounding fault in a distribution network based on a hybrid arc extinguishing process, characterized in that: The transient zero-sequence voltage of the arc extinguishing coil in the mixed arc extinguishing process and the active arc extinguishing stage is used to measure and track the grounding resistance, including the following steps: S1: When the distribution network is operating normally, monitor the steady-state zero-sequence voltage U 0, if the following equation is established, then go to step S2; if the following equation is not established, then it is determined that the system is normal and the steady-state zero-sequence voltage continues to be monitored; Formula 1 In the above formula, ν is the detuning degree of the distribution network, is the phase voltage of the distribution network; S2: Connect a hybrid arc extinguishing device at the neutral point of the distribution network, where the hybrid arc extinguishing device is composed of an arc extinguishing coil and an active arc extinguishing device in parallel; put the arc extinguishing coil into operation and record the zero-sequence voltage when the arc extinguishing coil is running alone u 0, and extract the transient component in the waveform; when the transient component decays according to the DC law, enter step S3; when the transient component decays according to the AC law, enter step S4; S3: Read the horizontal and vertical coordinates of a point on the transient component waveform, denoted as t, u a_tra , then during the arc extinguishing stage of the arc extinguishing coil, the grounding resistance can be measured R E1 for: Formula 2 In the above formula, L is the equivalent inductance of the arc suppression coil, C Σ is the total insulation capacitance of the system to ground, G Σ is the total insulation conductance of the system to ground, t 0 is the time when the arc suppression coil is put into operation. X , Y satisfy: Formula 3 Formula 4 In the above two formulas, T y for t The current value on the arc extinguishing coil at time 0, V y for t The voltage value on the arc extinguishing coil at time 0, E A is the power supply A phase voltage, Y A , Y B , Y C are the relative admittances of A, B, and C respectively. p , θ are u af The amplitude and phase of S4: Extract the upper envelope of the transient component waveform and read two points on the envelope Q 1( x 1, h 1) Q 2( x 2, h 2) When the difference between the ordinates of two points satisfies When, the difference between the horizontal coordinates Equal to the time constant , then during the arc extinguishing stage of the arc extinguishing coil, the grounding resistance can be measured R E1 for: Formula 5 S5: When the arc extinguishing coil is put into operation for d When the arc extinguishing coil is fully compensated, the active arc extinguishing device is put into operation to fully compensate for the active component of the grounding current. The zero-sequence voltage is recorded after the arc extinguishing coil and the active arc extinguishing device are operated simultaneously. u 0 waveform, measured ground resistance R E2 , including the following steps: S5-1: Extract zero-sequence voltage u 0 The decaying DC component in the waveform; S5-2: Read two points on the decaying DC component Q 3( x 3, h 3) Q 4( x 4, h 4), and the difference in ordinates satisfies , the difference between the horizontal coordinates Equal to the time constant ; S5-3: Measured ground resistance R E2 for: Formula 6 S6: Ground resistance measured at the arc extinguishing coil stage and the active arc extinguishing stage R E1 and R E2 The size is compared to track the degree of ground fault, including the following steps: S6-1: When R E1 equal R E2 When , it indicates that the ground fault level has not changed during the mixed arc extinguishing process, and the mixed arc extinguishing device continues to operate; S6-2: When R E1 Greater than R E2 When , it indicates that the ground fault level becomes serious during the mixed arc extinguishing process, then the mixed arc extinguishing device is exited; S6-3: When R E1 Less than R E2 When , it indicates that the ground fault level is reduced during the mixed arc extinguishing process, then the mixed arc extinguishing device is exited; S6-4: When R E1 Less than R E2 and R E2 When it is equal to positive infinity, it indicates that the single-phase grounding fault in the distribution network disappears, and the hybrid arc extinguishing device is exited.

2. A method for tracking the degree of single-phase grounding fault in a distribution network based on a hybrid arc extinguishing process according to claim 1, characterized in that: The method for calculating the detuning degree of the distribution network in step S1 is: Formula 7 In the above formula, I C is the capacitive current of the grid, I L It is the active compensation current of the power grid.

3. The method for tracking the degree of single-phase grounding fault in distribution network based on hybrid arc extinguishing process according to claim 1 is characterized in that: In step S3, the arc extinguishing coil is in a fully compensated state, and the arc extinguishing coil has an equivalent inductance L Satisfy the following formula: Formula 8 In the above formula, ω is the power angular frequency.

4. The method for tracking the degree of single-phase grounding fault in distribution network based on hybrid arc extinguishing process according to claim 1 is characterized in that: In step S4 .

5. The method for tracking the degree of single-phase grounding fault in distribution network based on hybrid arc extinguishing process according to claim 1 is characterized in that: In step S5 d is equal to five times the time constant, that is .

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