A protection method and system for single-phase ground fault of power distribution network

Abstract

The application belongs to the field of power distribution network fault operation and maintenance, and particularly relates to a protection method and system for single-phase grounding fault of a power distribution network. The method comprises the following steps: step 1: obtaining the working state of the power distribution network, and judging whether a fault occurs in the power distribution network; when a fault occurs in the power distribution network, starting protection; step 2: recording the period in which the protection is started as the tth period, and recording the zero-sequence current amplitudes I i,t of each line in the tth period; step 3: judging whether the fault disappears in the t+1th period; if the fault does not disappear, recording the zero-sequence current amplitudes I i,t+1 of each line in the t+1th period; step 4: performing calculation and analysis by using the zero-sequence current amplitudes of each line in the tth and t+1th periods, locating a fault line, identifying a system state, and taking protection measures. Through the application, the situation that the auxiliary contact of a small-resistance switching switch cannot be used in sectionalization protection and branch line protection can be effectively handled.

Description

Technical Field

[0001] This application belongs to the field of distribution network fault operation and maintenance, and in particular relates to a protection method and system for single-phase grounding faults in distribution networks. Background Technology

[0002] A power distribution network refers to a power grid that receives electrical energy from the transmission network or regional power plants and distributes it locally or tiered according to voltage to various users through distribution facilities. In the current production context, the normal transportation and distribution of power resources is particularly important for social economic and labor production. Therefore, a series of operation and maintenance tasks for the distribution network must be given due attention. For line faults, the faulty line must be selected and corresponding protection measures must be taken. To improve the reliability and security of power supply in the distribution network and effectively handle single-phase grounding faults, a flexible grounding method with a small resistor connected in parallel to the neutral point via an arc suppression coil has been proposed. The basic idea of ​​the flexible grounding method is to rely on the arc suppression coil to compensate for the fault current in the early stages of a grounding fault, extinguishing the transient fault; when the fault persists for a certain period of time and is determined to be a permanent fault, a small resistor is connected through a switching device to amplify the fault characteristics, thereby activating the zero-sequence protection of the line to disconnect the faulty line or faulty section. However, protection measures often have the possibility of maloperation before the small resistor is connected, so it is necessary to select the faulty line and confirm that the parallel small resistor is connected before operation. Currently, the operating status of the system is usually determined based on the auxiliary contacts of the low-resistance switching switch. However, in actual operation and maintenance, the auxiliary contact information of the low-resistance switching switch cannot be used to effectively handle grounding faults for sectional protection, branch line protection, etc.

[0003] Therefore, there is an urgent need for a method and system for protecting distribution network fault lines without relying on auxiliary switch contacts. Summary of the Invention

[0004] To address or improve the aforementioned problems, this invention provides a protection method and system for single-phase grounding faults in power distribution networks, the specific technical solution of which is as follows:

[0005] This invention provides a protection method for single-phase ground faults in distribution networks, comprising:

[0006] Step 1: Obtain the operating status of the distribution network and determine whether a fault has occurred. If no fault has occurred, do not activate the protection and do not execute any further steps. If a fault has occurred, activate the protection. Step 2: Record the period in which the protection is activated as period t, and record the zero-sequence current amplitude I of each line within period t. i,t i = 1, 2, ..., n; Step 3: Determine whether the fault has disappeared in the (t+1)th period; if the fault has disappeared, no further steps are performed; if the fault has not disappeared, record the zero-sequence current amplitude I of each line in the (t+1)th period. i,t+1, i = 1, 2 ... n; Step 4: Calculate and analyze the zero-sequence current amplitude of each line in the t-th period and the zero-sequence current amplitude of each line in the t+1-th period to locate the faulty line in the distribution network and identify the system status, and take protective measures.

[0007] Preferably, step 4 includes: using the ratio of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period to locate the faulty line in the distribution network and identify the system status, and taking protective measures.

[0008] Preferably, step 4 further includes: calculating the ratio T of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period. i =I i,t+1 / I i,t Take the largest ratio among the stated ratios, T j =max[T1, T2, ..., T] n ];when When, execute step 3; when Furthermore, if the phase difference between the zero-sequence current of this line and any other line is not less than β, the line is determined to be a faulty line, the system is identified as being in a state of arc suppression coil and low resistance, and the protective measures taken are: tripping to clear the fault; when there is only one T j When the line is determined to be faulty, the system status is not identified. The protection measures taken are: to issue a fault prompt and wait for manual instructions; where i = 1, 2...n, j = 1, 2...n, K is the preset fault threshold, and β is the preset phase difference threshold.

[0009] Preferably, determining whether a fault has occurred in the distribution network in step 1 includes: zero-sequence voltage U0 > zero-sequence starting voltage U act When the fault occurs, the power distribution network is faulty; otherwise, no fault occurs.

[0010] Preferably, determining whether the fault has disappeared in step 3 includes: if the amplitude of the zero-sequence current in the (t+1)th cycle is greater than the minimum operating current value I. act If the fault persists, it is determined that the fault has not disappeared; otherwise, the fault has disappeared.

[0011] Preferably, K is a preset fault threshold and β is a preset phase difference threshold, including: the preset fault threshold K = 10 and the preset phase difference threshold β = 60°.

[0012] Preferably, the zero-sequence start-up voltage U act This includes: the zero-sequence start-up voltage U act =15V.

[0013] Preferably, the minimum operating current value I act This includes: the minimum operating current value Iact = 0.5A.

[0014] Based on the same inventive concept, this application proposes a protection system for single-phase grounding faults in distribution networks, specifically for distribution networks where the neutral point is grounded via an arc-suppression coil and a small resistance. The system includes: a first state judgment unit: used to acquire the operating state of the distribution network and determine whether a fault has occurred; when no fault has occurred, protection is not activated and no further steps are executed; when a fault has occurred, protection is activated; and a first data unit: used to record the period in which the activation occurs as period t, and to record the zero-sequence current amplitude I of each line within period t. i,t i = 1, 2, ..., n; Second data unit: used to determine whether the fault has disappeared in the (t+1)th period; if the fault has disappeared, no further steps are executed; if the fault has not disappeared, the zero-sequence current amplitude I of each line in the (t+1)th period is recorded. i,t+1 , i = 1, 2 ... n; Fault protection unit: Calculates and analyzes the zero-sequence current amplitude of each line in the t-th period and the zero-sequence current amplitude of each line in the t+1-th period to locate the faulty line in the distribution network and identify the system status, and takes protective measures.

[0015] Preferably, the fault protection unit includes: a calculation module: used to calculate the ratio T of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period. i =I i,t+1 / I i,t Take the largest ratio among the stated ratios, T j =max[T1, T2, ..., T] n ]; Judgment module: used when When, execute step 3; when Furthermore, if the phase difference between the zero-sequence current of this line and any other line is not less than β, the line is determined to be a faulty line, the system is identified as being in a state of arc suppression coil and low resistance, and the protective measures taken are: tripping to clear the fault; when there is only one T j When the line is determined to be faulty, the system status is not identified. The protection measures taken are: to issue a fault prompt and wait for manual instructions; where i = 1, 2...n, j = 1, 2...n, K is the preset fault threshold, and β is the preset phase difference threshold.

[0016] The beneficial effects of this invention are as follows: This application utilizes the ratio of the zero-sequence current amplitude of each line within different periods for analysis to locate the faulty line and identify the system status. Then, based on the system status, corresponding protective measures are taken for the selected faulty line. This overcomes the deficiency of not being able to utilize auxiliary switch contacts and eliminates the need to reinstall the line selection device, saving economic costs. Attached Figure Description

[0017] Figure 1 This is a flowchart of a protection method for single-phase grounding faults in a distribution network according to an embodiment of the present invention.

[0018] Figure 2 This is a block diagram of a protection system for single-phase grounding faults in a distribution network, provided according to an embodiment of the present invention.

[0019] Figure 3 This is a block diagram of a fault protection unit according to an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0022] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0023] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0024] See Figure 1 , Figure 1 A flowchart of a protection method for single-phase ground faults in a distribution network proposed in this application includes:

[0025] Step 1: Obtain the operating status of the distribution network and determine whether a fault has occurred in the distribution network.

[0026] When there is no fault in the distribution network, the protection is not activated and no further steps are performed.

[0027] When a fault occurs in the distribution network, the protection is activated.

[0028] Specifically, zero-sequence voltage U0 > zero-sequence start-up voltage U act When the fault occurs, the power distribution network is faulty; otherwise, no fault occurs.

[0029] In practical applications, the zero-sequence start-up voltage U act =15V.

[0030] Step 2: Record the zero-sequence current amplitude of each line within the t-th period.

[0031] Specifically, the period in which the protection is initiated is denoted as period t, and the zero-sequence current amplitude I of each line within period t is recorded. i,t , i = 1, 2, ..., n.

[0032] Step 3: Determine whether the fault has disappeared in the (t+1)th period.

[0033] If the fault disappears, no further steps will be performed.

[0034] If the fault does not disappear, record the zero-sequence current amplitude I of each line within the (t+1)th cycle. i,t+1 , i = 1, 2, ..., n.

[0035] Specifically, determining whether the fault has disappeared includes: if the amplitude of the zero-sequence current in the (t+1)th cycle is greater than the minimum operating current value I. act If the fault persists, it is determined that the fault has not disappeared; otherwise, the fault has disappeared.

[0036] In practical applications, the minimum operating current value Iact = 0.5A.

[0037] Step 4: Calculate and analyze the zero-sequence current amplitude of each line to locate the faulty line in the distribution network.

[0038] Specifically, by using the zero-sequence current amplitude of each line in the t-th period and the zero-sequence current amplitude of each line in the t+1-th period to perform calculations and analysis, the faulty lines in the distribution network are located and the system status is identified, and protective measures are taken.

[0039] In practical applications, the ratio of the zero-sequence current amplitude of each line in period t to the zero-sequence current amplitude of each line in period t+1 is used to locate faulty lines in the distribution network and identify the system status, and then protective measures are taken, including:

[0040] Calculate the ratio T of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period. i =I i,t+1 / I i,t Take the largest ratio among the stated ratios, T j =max[T1, T2, ..., T] n ].

[0041] when Then, proceed to step 3.

[0042] when If the phase difference between the zero-sequence current of the line and any other line is not less than β, the line is determined to be a faulty line, the system is identified as being in an arc suppression coil and low resistance state, and the protection measure taken is: tripping to clear the fault.

[0043] In one embodiment of this application, a time threshold for automatically issuing a trip command is preset. During the waiting period for the trip command, if the waiting time exceeds the time threshold and the faulty line does not receive the trip command during the waiting period, a trip command will be automatically issued to clear the fault.

[0044] When there is only one T j If the line is identified as faulty, a fault warning is issued. At this point, no system status is assessed, and the protective measure is to wait for manual intervention.

[0045] Where i = 1, 2, ..., n, j = 1, 2, ..., n, K is the preset fault threshold, K = 10, β is the preset phase difference threshold, β = 60°.

[0046] This application, based on the same inventive concept, proposes a protection system for single-phase ground faults in distribution networks. See also... Figure 2 , Figure 2 This is a block diagram of a protection system for single-phase grounding faults in a distribution network according to an embodiment of the present invention, comprising:

[0047] The first state determination unit is used to obtain the operating status of the distribution network and determine whether a fault has occurred in the distribution network. When no fault has occurred in the distribution network, protection is not activated and no further steps are executed; when a fault has occurred in the distribution network, protection is activated.

[0048] First data unit: used to record the period in which the positioning start occurs as period t, and to record the zero-sequence current amplitude I of each line within period t. i,t , i = 1, 2, ..., n.

[0049] The second data unit is used to determine whether the fault has disappeared in the (t+1)th period. If the fault has disappeared, no further steps are executed; if the fault has not disappeared, the zero-sequence current amplitude I of each line in the (t+1)th period is recorded. i,t+1 , i = 1, 2, ..., n.

[0050] Fault protection unit: Calculates and analyzes the zero-sequence current amplitude of each line in the t-th period and the zero-sequence current amplitude of each line in the t+1-th period to locate the faulty line in the distribution network and identify the system status, and takes protective measures.

[0051] See Figure 3 , Figure 3 The fault protection unit schematic diagram includes:

[0052] Calculation module: used to calculate the ratio T of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period. i =I i,t+1 / I i,t Take the largest ratio among the stated ratios, T j =max[T1, T2, ..., T] n ].

[0053] Judgment module: used when When, execute step 3 Furthermore, if the phase difference between the zero-sequence current of this line and any other line is not less than β, the line is determined to be a faulty line, the system is identified as being in an arc suppression coil and low resistance state, and the protection measure taken is: tripping to clear the fault.

[0054] This application utilizes the ratio of zero-sequence current amplitudes of various lines within different periods for analysis to locate faulty lines and identify system states. Based on the system state, corresponding protection measures are then implemented for the selected faulty lines. This overcomes the limitation of not being able to utilize auxiliary switch contacts and eliminates the need to reinstall the fault location device, thus saving economic costs.

[0055] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0056] In the embodiments provided in this application, it should be understood that the division of units is only a logical functional division. In actual implementation, there may be other division methods, such as multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A protection method for single-phase grounding faults in distribution networks, used in distribution networks where the neutral point is grounded via an arc-suppression coil and a small resistance, characterized in that... include: Step 1: Obtain the operating status of the distribution network and determine whether a fault has occurred in the distribution network; When there is no fault in the distribution network, the protection is not activated and no further steps are performed; When a fault occurs in the distribution network, the protection system is activated. Step 2: Record the period in which the protection starts as period t, and record the zero-sequence current amplitude I of each line within period t. i,t i = 1, 2, ..., n; Step 3: Determine whether the fault has disappeared in the (t+1)th period; If the fault disappears, no further steps will be performed; If the fault does not disappear, record the zero-sequence current amplitude I of each line within the (t+1)th cycle. i,t＋1 i = 1, 2, ..., n; Step 4: Calculate and analyze the zero-sequence current amplitude of each line in the t-th period and the zero-sequence current amplitude of each line in the t+1-th period to locate the faulty line in the distribution network and identify the system status, and take protective measures. Step 4 includes: By using the ratio of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period, the faulty line in the distribution network can be located and the system status can be identified, and protective measures can be taken. Step 4 includes: Calculate the ratio T of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period. i =I i,t+1 / I i,t Take the largest ratio among the given ratios, 2-7; when When the time comes, proceed to step 3; when When the phase difference between the zero-sequence current of the line and any other line is not less than β, the line is judged to be a faulty line, the system is identified as being in an arc suppression coil and low resistance state, and the protection measure taken is: tripping to clear the fault. When there is only one T j If the line is determined to be faulty, no system status identification is performed. The protection measure taken is to issue a fault warning and wait for manual instructions. Where i = 1, 2...n, j = 1, 2...n, K is the preset fault threshold, and β is the preset phase difference threshold; Specifically, a time threshold for automatically issuing tripping commands is preset. If the waiting time exceeds the time threshold and the faulty line does not receive a tripping command during the waiting period, a tripping command will be automatically issued to isolate the fault.

2. The protection method for single-phase grounding faults in a distribution network according to claim 1, characterized in that, Step 1, determining whether a fault has occurred in the distribution network, includes: Zero-sequence voltage U0 > zero-sequence start-up voltage U act When the fault occurs, the power distribution network is faulty; otherwise, no fault occurs.

3. The protection method for single-phase grounding faults in a distribution network according to claim 1, characterized in that, Step 3, determining whether the fault has disappeared, includes: If the zero-sequence current amplitude in the (t+1)th period is greater than the minimum operating current value I act If the fault persists, it is determined that the fault has not disappeared; otherwise, the fault has disappeared.

4. The protection method for single-phase grounding faults in a distribution network according to claim 1, characterized in that, K is a preset fault threshold and β is a preset phase difference threshold, including: The preset fault threshold K=10, and the preset phase difference threshold β=60°.

5. A protection method for single-phase grounding faults in a distribution network according to claim 2, characterized in that, The zero-sequence start-up voltage U act This includes: the zero-sequence start-up voltage U act =15V.

6. A protection method for single-phase grounding faults in a distribution network according to claim 3, characterized in that, The minimum operating current value I act This includes: the minimum operating current value Iact = 0.5A.

7. A protection system for single-phase grounding faults in distribution networks, used in distribution networks where the neutral point is grounded via an arc-suppression coil and a small resistance, characterized in that, include: First state determination unit: used to obtain the working status of the distribution network and determine whether a fault has occurred in the distribution network; When there is no fault in the distribution network, the protection is not activated and no further steps are performed; When a fault occurs in the distribution network, the protection system is activated. First data unit: used to record the period in which the positioning start occurs as period t, and to record the zero-sequence current amplitude I of each line within period t. i,t i = 1, 2, ..., n; The second data unit is used to determine whether the fault has disappeared in the (t+1)th period. If the fault disappears, no further steps will be performed; If the fault does not disappear, record the zero-sequence current amplitude I of each line within the (t+1)th cycle. i,t＋1 i = 1, 2, ..., n; Fault protection unit: Calculates and analyzes the zero-sequence current amplitude of each line in the t-th period and the zero-sequence current amplitude of each line in the t+1-th period to locate the faulty line in the distribution network and identify the system status, and takes protective measures. The fault protection unit includes: Calculation module: used to calculate the ratio T of the zero-sequence current amplitude of each line in the t-th period to the zero-sequence current amplitude of each line in the (t+1)-th period. i =I i,t+1 / I i,t Take the largest ratio among the stated ratios, T j =max[T1, T2, ..., T n ]; Judgment module: used when When the time comes, proceed to step 3; when When the phase difference between the zero-sequence current of the line and any other line is not less than β, the line is judged to be a faulty line, the system is identified as being in an arc suppression coil and low resistance state, and the protection measure taken is: tripping to clear the fault. When there is only one T j If the line is determined to be faulty, no system status identification is performed. The protection measure taken is to issue a fault warning and wait for manual instructions. Where i = 1, 2...n, j = 1, 2...n, K is the preset fault threshold, and β is the preset phase difference threshold; Specifically, a time threshold for automatically issuing tripping commands is preset. If the waiting time exceeds the time threshold and the faulty line does not receive a tripping command during the waiting period, a tripping command will be automatically issued to isolate the fault.

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