A method for identifying and locating high-resistance grounding faults based on composite factors

Abstract

The present invention discloses a method for identifying and locating high-resistance grounding faults based on composite factors. The method comprises the following steps: collecting the zero-sequence voltage of the busbar and the zero-sequence current data of each feeder in the distribution network; judging whether the change in the zero-sequence voltage of the busbar meets the starting criterion; if the starting criterion is not met, updating the collected data; if the starting criterion is met, calculating the magnitude of the composite factor of each feeder according to the zero-sequence voltage of the busbar and the zero-sequence current data of each feeder; comparing the calculated composite factor of each feeder with the preset value of the protection criterion to identify the feeder with high-resistance grounding faults; and calculating the fault location index of each node of the faulty feeder according to the zero-sequence voltage of the busbar and the zero-sequence current data of the identified faulty feeder to locate the high-resistance grounding fault. The present invention can effectively identify the feeder with high-resistance grounding faults, realize the section location of the high-resistance fault point, effectively narrow the power outage range, and the inventive method is simple and efficient, with a certain practicality.

Description

Technical Field

[0001] The present invention relates to the technical field of grounding faults, and particularly to a method for identifying and locating high-resistance grounding faults based on composite factors. Background Art

[0002] With the gradual replacement of urban overhead lines by cables, the capacitive current to the ground in the system increases, and the single-phase grounding fault current increases, making it difficult for the traditional neutral grounding through an arc suppression coil and non-grounding methods to meet the development needs. Since the 1980s, cities such as Beijing, Shanghai, and Shenzhen have changed the non-grounding or arc suppression coil grounding system to a small-resistance grounding system, and the small-resistance grounding method has been applied in more and more large urban distribution networks.

[0003] Currently, zero-sequence overcurrent protection is mainly used to identify single-phase grounding faults in the distribution network. Although the traditional zero-sequence overcurrent protection can reliably operate when a single-phase low-resistance grounding fault occurs in the system and cut off the faulty line, due to the need to avoid the capacitive current to the ground flowing through the line within the zone when a metallic grounding fault occurs in the external line, the setting value is relatively high. Therefore, when a high-resistance grounding fault occurs, the change in the zero-sequence current of the line is weak, and the fault current is very likely to be lower than the setting value of the traditional zero-sequence overcurrent protection, resulting in the refusal of the zero-sequence overcurrent protection to operate.

[0004] At the same time, for the existing grounding fault section location methods, such as the transient method that locates faults based on the principles of transient signal amplitude comparison, polarity comparison, power direction, etc. during the grounding fault transient process, although the cost is relatively low and the implementation is relatively convenient, it is mainly applicable to low-resistance grounding faults and cannot effectively target high-resistance grounding faults. Although some researchers have introduced the double-ended traveling wave ranging method into the distribution network, this method has high requirements for synchronous sampling and sampling frequency at both ends of the line, requires a large investment in equipment, and there are many branches in the distribution network. If double-ended traveling wave fault location is to be realized in the distribution network, the capital cost is relatively high. Summary of the Invention

[0005] In view of this, in order to solve the problem that the existing traditional protection methods cannot effectively identify and locate high-resistance grounding faults, the present invention proposes a method for identifying and locating high-resistance grounding faults based on composite factors. This method has good high-resistance tolerance, can not only effectively identify the feeder with a high-resistance grounding fault, but also efficiently locate the fault section and reduce the power outage range.

[0006] The present invention solves the above problems through the following technical means:

[0007] A method for identifying and locating high-resistance grounding faults based on composite factors, comprising the following steps:

[0008] Collect the zero-sequence voltage of the busbar and the zero-sequence current data of each feeder in the distribution network;

[0009] Judge whether the change of zero-sequence voltage of the busbar meets the starting criterion; if the starting criterion is not met, retain the voltage and current data of the current cycle and clear the voltage and current data of the previous cycle; if the starting criterion is met, calculate the magnitude of the complex factor of each feeder according to the zero-sequence voltage of the busbar and the zero-sequence current data of each feeder.

[0010] Compare the calculated complex factor of each feeder with the preset value of the protection criterion to identify the feeder with high-resistance grounding fault.

[0011] Calculate the fault location index of each node of the faulty feeder according to the zero-sequence voltage of the busbar and the zero-sequence current data of the identified faulty feeder to locate the high-resistance grounding fault.

[0012] Preferably, judge whether the change of zero-sequence voltage of the busbar meets the starting criterion as follows:

[0013] If the change of zero-sequence voltage of the busbar meets Equation (1), it is considered to meet the starting criterion; if the change of zero-sequence voltage does not meet Equation (1), it is considered not to meet the starting criterion:

[0014]

[0015] In the formula: T is a power frequency cycle; u0(t) is the sampled value of zero-sequence voltage at time t; u0(t - T) is the sampled value of zero-sequence voltage at time t - T; △u0(t) is the magnitude of the change of zero-sequence voltage at time t; U N is the rated phase voltage of the system; K re is the reliability coefficient.

[0016] Preferably, considering the unbalanced voltage caused by unbalanced load and asymmetric feeder parameters, K re takes 1%.

[0017] Preferably, calculate the magnitude of the complex factor of each feeder according to the collected zero-sequence voltage of the busbar and the zero-sequence current data of each feeder, as shown in Equation (2):

[0018]

[0019] In the formula: S k represents the magnitude of the complex factor of feeder k, Re(*) and Im(*) respectively represent the real part and the imaginary part of *, i 0k represents the zero-sequence current of feeder k, u0 * represents the conjugate of the zero-sequence voltage of the busbar.

[0020] Preferably, compare the calculated complex factor of each feeder with the preset value of the protection criterion to identify the feeder with high-resistance grounding fault, as follows:

[0021] Preset the identification range of the composite factor for the normal feeder and the faulty feeder;

[0022] Compare the composite factor of each feeder with the preset identification range. If the magnitude of the composite factor of the feeder is within the identification range of the faulty feeder, then the feeder is a faulty feeder; otherwise, it is a normal feeder.

[0023] Preferably, the zero-sequence current flowing through the faulty line is the opposite of the vector sum of the zero-sequence currents of all healthy lines and the zero-sequence current flowing through the neutral point. And in the faulty line, the zero-sequence capacitive reactance is much greater than the zero-sequence resistance and zero-sequence inductive reactance. When calculating the composite factor of each feeder based on Equation (2), the composite factor of the faulty feeder will stabilize to the negative half-axis, and the composite factor of the normal feeder will stabilize to the non-negative half-axis; therefore, after the starting criterion is satisfied, calculate the magnitude of the composite factor of each feeder. The feeder with the composite factor stably maintained on the negative half-axis is the faulty feeder, and the feeder with the composite factor stably maintained on the non-negative half-axis is the normal feeder.

[0024] Preferably, calculate the fault location index of each node of the faulty feeder to achieve high-resistance grounding fault location, which specifically includes the following steps:

[0025] Calculate the fault location index of each node of the faulty feeder, as specifically shown in Equation (3):

[0026]

[0027] In the formula: S loc-j is the fault location index of node j on the faulty feeder, i 0j represents the zero-sequence current of the line flowing through node j, and u0 * represents the conjugate of the zero-sequence voltage of the busbar;

[0028] Compare the fault location index S of each node loc-j , and locate the high-resistance grounding fault section.

[0029] Preferably, compare the fault location index S of each node loc-j , and locate the high-resistance grounding fault section, specifically as follows:

[0030] The direction of the zero-sequence current flowing through the protection upstream of the fault point is exactly opposite to the direction of the zero-sequence current flowing through the protection downstream of the fault point. When calculating the fault location index of each node based on Equation (3), the fault location index of the node upstream of the high-resistance fault will be on the negative half-axis, while the fault location index of the node downstream of the high-resistance fault will be on the positive half-axis. Therefore, by comparing the S of each node of the faulty feeder loc-j , the high-resistance fault point can be located in the smallest section where S loc-j changes from negative to positive.

[0031] Compared with the prior art, the beneficial effects of the present invention at least include:

[0032] 1) The calculation formula of the feeder composite factor is defined. When analyzing the high-resistance grounding fault, the amplitude polarity differences of the composite factors of the normal feeder and the faulty feeder are analyzed. According to the significant differences between the composite factors of the normal feeder and the faulty feeder, a high-resistance grounding fault identification method based on the composite factor is proposed. This method has strong high-resistance tolerance, can effectively identify high-resistance grounding faults, and is not affected by the weak change of zero-sequence current during high-resistance grounding faults.

[0033] 2) The calculation formula of the node fault index is defined. Only by using the data collected during the identification process of the faulty feeder, the section location of the high-resistance grounding fault can be realized, effectively reducing the power outage range. Description of the Drawings

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0035] Figure 1 It is the flowchart of the high-resistance grounding fault identification and location method based on the composite factor in Embodiment 1;

[0036] Figure 2 It is the topology diagram of the 10kV distribution network system in Embodiment 1;

[0037] Figure 3 It is the change curve of the composite factor magnitude of feeder F1;

[0038] Figure 4 It is the change curve of the composite factor magnitude of feeder F2;

[0039] Figure 5 It is the fault location index of each node of feeder F2. Detailed Embodiments

[0040] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the technical solutions of the present invention will be described in detail below with reference to the drawings and specific embodiments. It should be noted that the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0041] The present invention provides a high-resistance grounding fault identification and location method based on the composite factor, including the following steps:

[0042] S1. Collect the zero-sequence voltage of the busbar and the zero-sequence current data of each feeder in the distribution network;

[0043] S2. Determine whether the change in the zero-sequence voltage of the bus meets the starting criterion; if it does not meet the starting criterion, retain the voltage and current data of the current cycle and clear the voltage and current data of the previous cycle; if it meets the starting criterion, calculate the magnitude of the composite factor of each feeder according to the zero-sequence voltage of the bus and the zero-sequence current data of each feeder.

[0044] S3. Compare the calculated composite factor of each feeder with the preset value of the protection criterion to identify the feeder with high-resistance grounding fault.

[0045] S4. Calculate the fault location index of each node of the faulty feeder according to the zero-sequence voltage of the bus and the zero-sequence current data of the identified faulty feeder to locate the high-resistance grounding fault.

[0046] Specifically, in step S2, to determine whether the change in the zero-sequence voltage of the bus meets the starting criterion, it is as follows:

[0047] If the change in the zero-sequence voltage of the bus meets Equation (1), it is considered to meet the starting criterion; if the change in the zero-sequence voltage does not meet Equation (1), it is considered not to meet the starting criterion:

[0048]

[0049] In the formula: T is a power frequency cycle; u0(t) is the sampled value of the zero-sequence voltage at time t; u0(t - T) is the sampled value of the zero-sequence voltage at time t - T; △u0(t) is the magnitude of the change in the zero-sequence voltage at time t; U N is the rated phase voltage of the system; K re is the reliability coefficient, considering the unbalanced voltage caused by unbalanced loads, asymmetric feeder parameters, etc., K re is taken as 1%.

[0050] Specifically, in step S2, according to the collected zero-sequence voltage of the bus and the zero-sequence current data of each feeder, calculate the magnitude of the composite factor of each feeder, as shown in Equation (2) specifically:

[0051]

[0052] In the formula: S k represents the magnitude of the composite factor of feeder k, Re(*) and Im(*) respectively represent the real part and the imaginary part of *, i 0k represents the zero-sequence current of feeder k, u0 * represents the conjugate of the zero-sequence voltage of the bus.

[0053] Specifically, in step S3, compare the calculated composite factor of each feeder with the preset value of the protection criterion to identify the feeder with high-resistance grounding fault, as follows:

[0054] S3.1. Preset the recognition range of the composite factor for the normal feeder and the faulty feeder;

[0055] S3.2. Compare the composite factor of each feeder with the preset recognition range. If the magnitude of the composite factor of the feeder is within the recognition range of the faulty feeder, then the feeder is a faulty feeder; otherwise, it is a normal feeder.

[0056] The zero-sequence current flowing through the faulty line is the opposite of the vector sum of the zero-sequence currents of all healthy lines and the zero-sequence current flowing through the neutral point. Moreover, in the faulty line, the zero-sequence capacitive reactance is much larger than the zero-sequence resistance and zero-sequence inductive reactance. When calculating the composite factor of each feeder based on Equation (2), the composite factor of the faulty feeder will stabilize to the negative half-axis, and the composite factor of the normal feeder will stabilize to the non-negative half-axis. Therefore, after the startup criterion is satisfied, calculate the magnitude of the composite factor of each feeder. The feeder whose composite factor is stably maintained on the negative half-axis is the faulty feeder, and the feeder whose composite factor is stably maintained on the non-negative half-axis is the normal feeder.

[0057] Specifically, in step S4, calculate the fault location index of each node of the faulty feeder to achieve high-resistance grounding fault location, which specifically includes the following steps:

[0058] Calculate the fault location index of each node of the faulty feeder, as specifically shown in Equation (3):

[0059]

[0060] In the formula: S loc-j is the fault location index of node j on the faulty feeder, and i 0j represents the zero-sequence current of the line flowing through node j, and u0 * represents the conjugate of the zero-sequence voltage of the bus;

[0061] Compare the fault location index S of each node loc-j , and locate the high-resistance grounding fault section.

[0062] Among them, comparing the fault location index S of each node loc-j , and locating the high-resistance grounding fault section is specifically as follows:

[0063] The direction of the zero-sequence current flowing through the protection upstream of the fault point is exactly opposite to the direction of the zero-sequence current flowing through the protection downstream of the fault point. When calculating the fault location index of each node based on Equation (3), the fault location index of the node upstream of the high-resistance fault will be on the negative half-axis, while the fault location index of the node downstream of the high-resistance fault will be on the positive half-axis. Therefore, by comparing the S of each node of the faulty feeder loc-j , the high-resistance fault point can be located in the smallest section where S loc-j changes from negative to positive.

[0064] Compare the fault location index S of each node of the faulty feeder loc-j, find S loc-j The smallest section where the value changes from negative to positive can be used to locate that the high-resistance grounding fault occurs in this section.

[0065] The following uses specific experimental data to illustrate the present invention.

[0066] Embodiment 1

[0067] The flowchart of the high-resistance grounding fault identification and location method based on composite factors provided in this embodiment is as Figure 1 shown. The embodiment is a 10 kV distribution network as Figure 2 shown, where the system base capacity is 100 MVA and the base voltage is 10 kV. The lengths of lines AB, BC, CD, DE, AF, and FG are 5 km, 6 km, 10 km, 6 km, 5 km, and 5 km respectively. The zero-sequence parameters of the line are R0 = 2.7 Ω / km, L0 = 1.109 mH / km, C0 = 0.28 μF / km; the positive-sequence parameters of the line are R1 = 0.27 Ω / km, L1 = 0.255 mH / km, C1 = 0.339 μF / km; the feeder is connected with a load with a total rated power of 20 MVA and a power factor of 0.95.

[0068] Taking the occurrence of a phase A high-resistance grounding fault (transition resistance 2000 Ω) at 50% of the CD section of feeder F2 as an example, combined with Figure 1 、 Figure 2 to illustrate the method of the present invention in detail:

[0069] 1. Collect the zero-sequence voltage of the busbar and the zero-sequence current data of each feeder in the distribution network;

[0070] Specifically, in this embodiment, the zero-sequence voltage u0 of the busbar in the distribution network and the zero-sequence currents i 01 、i 02 of feeders F1 and F2 are collected;

[0071] 2. Determine whether the change in the zero-sequence voltage of the busbar satisfies the starting criterion; if the starting criterion is not satisfied, retain the voltage and current data of the current cycle and clear the voltage and current data of the previous cycle; if the starting criterion is satisfied, calculate the magnitude of the composite factor of each feeder according to the zero-sequence voltage of the busbar and the zero-sequence current data of each feeder;

[0072] 2.1 Specifically, in this embodiment, according to the collected u0 data and combined with Equation (1), it is determined that the starting criterion is satisfied at 0.05 s (the moment when the high-resistance grounding fault is applied), and then the composite factor values of each feeder are calculated;

[0073]

[0074] Where: T is a power frequency period; u0(t) is the sampled value of the zero-sequence voltage at time t; u0(t - T) is the sampled value of the zero-sequence voltage at time t - T; △u0(t) is the magnitude of the change in the zero-sequence voltage at time t; U N is the rated phase voltage of the system; K re is the reliability coefficient, considering the unbalanced voltage caused by unbalanced loads, asymmetric feeder parameters, etc., K re is taken as 1%.

[0075] 2.2 Specifically, in this embodiment, according to the collected zero-sequence voltage u0 of the bus and the zero-sequence currents i 01 、i 02 data of the feeders F1 and F2, combined with Equation (2), calculate the magnitudes of the complex factors of the feeders F1 and F2 respectively as Figure 3 、 Figure 4 shown.

[0076]

[0077] Where: S k represents the magnitude of the complex factor of feeder k, Re(*) and Im(*) respectively represent the real part and the imaginary part of *, i 0k represents the zero-sequence current of feeder k, u0 * represents the conjugate of the zero-sequence voltage of the bus.

[0078] 3. Compare the calculated complex factors of each feeder with the preset values of the protection criterion to identify the feeder with high-resistance grounding fault;

[0079] 3.1 Specifically, in this embodiment, the protection criterion value is preset as: 0 < S k < 0.8 (normal line), -2 < S k < -1.5 (normal line).

[0080] 3.2 Specifically, in this embodiment, compare the complex factor S1 = 0.621 (after stabilization) of feeder F1 and the complex factor S2 = -1.997 (after stabilization) of feeder F2 with the preset protection criterion, and identify feeder F2 as the faulty line and feeder F1 as the normal line.

[0081] 4. According to the zero-sequence voltage of the bus and the zero-sequence current data of the identified faulty feeder, calculate the fault location index of each node of the faulty feeder to achieve high-resistance grounding fault location.

[0082] 4.1 Specifically, in this embodiment, according to the collected zero-sequence voltage u0 of the bus and the zero-sequence current data i 0A 、i 0B …i 0E, the fault location index of each node is calculated by combining formula (3) as Figure 5 shown, specifically: S loc-A =-1, S loc-B =-1, S loc-C =-1, S loc-D =1, S loc-E =1;

[0083]

[0084] In the formula: S loc-j is the fault location index of node j on the fault feeder, i 0j represents the zero-sequence current of the line flowing through node j, and u0 * represents the conjugate of the zero-sequence voltage of the bus.

[0085] 4.2. Specifically, in this embodiment, combining Figure 2 and Figure 5 , it is determined that the CD section of feeder F2 satisfies that S loc-j changes from negative to positive in the smallest section, so the high-resistance grounding fault point is located in the CD section of feeder F2

[0086] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A high-resistance grounding fault identification and location method based on composite factors, characterized in that It includes the following steps: Collect the zero-sequence voltage of the bus and the zero-sequence current data of each feeder in the distribution network; Judge whether the change of the zero-sequence voltage of the bus meets the starting criterion; if the starting criterion is not met, retain the voltage and current data of the current cycle and clear the voltage and current data of the previous cycle; If the starting criterion is met, calculate the magnitude of the composite factor of each feeder according to the zero-sequence voltage of the bus and the zero-sequence current data of each feeder; specifically, as shown in Equation (2): Where: S k represents the magnitude of the complex factor of feeder k, Re(*) and Im(*) respectively represent the real part and the imaginary part of *, and i 0k represents the zero-sequence current of feeder k, and u0 * represents the conjugate of the zero-sequence voltage of the busbar; Compare the calculated composite factor of each feeder with the preset value of the protection criterion to realize the identification of the high-resistance grounded fault feeder; Calculate the fault location index of each node of the fault feeder according to the zero-sequence voltage of the bus and the zero-sequence current data of the identified fault feeder; specifically, as shown in Equation (3): Where: S loc-j is the fault location index of node j on the faulty feeder, i 0j represents the zero-sequence current of the line flowing through node j, u0 * represents the conjugate of the zero-sequence voltage of the busbar; Compare the fault location index S of each node loc-j to achieve high-resistance grounding fault location.

2. The high-resistance grounding fault identification and location method based on composite factors according to claim 1, characterized in that Judge whether the change of the zero-sequence voltage of the bus meets the starting criterion, specifically as follows: If the change of the zero-sequence voltage of the bus meets Equation (1), it is considered that the starting criterion is met; if the change of the zero-sequence voltage does not meet Equation (1), it is considered that the starting criterion is not met: Where: T is a power frequency period; u0(t) is the sampled value of the zero-sequence voltage at time t; u0(t - T) is the sampled value of the zero-sequence voltage at time t - T; Δu0 is the magnitude of the change in the zero-sequence voltage; U N is the rated phase voltage of the system; K re is the reliability coefficient.

3. The high-resistance grounding fault identification and location method based on composite factors according to claim 2, wherein Considering the unbalanced voltage caused by unbalanced load and asymmetric feeder parameters, K re Take 1%.

4. The high-resistance grounding fault identification and location method based on composite factors according to claim 1, wherein Compare the calculated composite factor of each feeder with the preset value of the protection criterion to realize the identification of the high-resistance grounded fault feeder, specifically as follows: Preset the identification range of the composite factor of the normal feeder and the fault feeder; Compare the composite factor of each feeder with the preset identification range. If the magnitude of the composite factor of the feeder is within the identification range of the fault feeder, then the feeder is the fault feeder; otherwise, it is the normal feeder.

5. The high-resistance grounding fault identification and location method based on composite factors according to claim 1, characterized in that The zero-sequence current flowing through the fault line is the opposite of the vector sum of the zero-sequence currents of all healthy lines and the zero-sequence current flowing through the neutral point. And in the fault line, the zero-sequence capacitive reactance is much larger than the zero-sequence resistance and the zero-sequence inductive reactance. When calculating the composite factor of each feeder based on Equation (2), the composite factor of the fault feeder will stabilize to the negative half-axis, and the composite factor of the normal feeder will stabilize to the non-negative half-axis; therefore, after the starting criterion is met, calculate the magnitude of the composite factor of each feeder. The feeder with the composite factor stably maintained on the negative half-axis is the fault feeder, and the feeder with the composite factor stably maintained on the non-negative half-axis is the normal feeder.

6. The high-resistance grounding fault identification and location method based on composite factors according to claim 1, characterized in that Compare the fault location index S of each node loc-j , and locate the high-resistance grounding fault section as follows: The zero-sequence current direction flowing through the protection upstream of the fault point is exactly opposite to the zero-sequence current direction flowing through the protection downstream of the fault point. When calculating the fault location index of each node based on Equation (3), the fault location index of the node upstream of the high-resistance fault will be on the negative half-axis, while the fault location index of the node downstream of the high-resistance fault will be on the positive half-axis. Therefore, by comparing each node S of the fault feeder loc-j , the high-resistance fault point can be located in the smallest section where S loc-j changes from negative to positive.

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