阅读说明：本技术 小电流接地系统单相接地故障定位方法及系统 (single-phase earth fault positioning method and system for small current earthing system ) 是由 荆平 任西周 李大鹏 李猷民 于 2019-09-11 设计创作，主要内容包括：一种小电流接地系统单相接地故障定位方法及系统。本发明利用小电流接地系统或不接地系统发生单相接地故障后,在变电站接地系统中性点注入零序电流,通过判断接地系统各出线电流在中性点注入零序电流后分布以及变化状况确定接地故障点。本发明通过对比接地系统注入零序电流前后接地线路两次采集获得线路电流及其变化状况判断接地点,因而无需在控制主站合成线路零序电流。为了进一步提高定位精度,本发明对采集数据进行了归一化处理,从而完全克服现有故障指示系统的缺点,并且装置构成简单,不需要GPS校时以及高速数据采集,不需要大容量数据通讯,不受采集器CT变比误差影响,不受环境因素影响,可以准确识别、定位特殊类型接地故障。(A single-phase earth fault positioning method and system for a low-current earth system. According to the method, after a single-phase ground fault occurs in a small-current grounding system or an ungrounded system, zero-sequence current is injected into a neutral point of a grounding system of a transformer substation, and a ground fault point is determined by judging distribution and change conditions of outgoing line currents of the grounding system after the zero-sequence current is injected into the neutral point. The invention judges the grounding point by comparing the two acquisition of the grounding line before and after the zero sequence current is injected into the grounding system to obtain the line current and the change condition thereof, thereby the zero sequence current of the line does not need to be synthesized in a control main station. In order to further improve the positioning precision, the invention carries out normalization processing on the acquired data, thereby completely overcoming the defects of the existing fault indication system, having simple device structure, not needing GPS timing and high-speed data acquisition, not needing large-capacity data communication, not being influenced by CT (computed tomography) transformation ratio error of the acquisition device and environmental factors, and being capable of accurately identifying and positioning the special type ground fault.)

1. A method for locating a ground fault of a low-current grounding system, the method comprising:

The method comprises the following steps that firstly, a background is controlled to send acquisition commands to collectors in a low-current grounding system, so that each collector controls a collector arranged on each line connected with the collector to acquire the current value of the line arranged on the collector;

secondly, after issuing an acquisition command by the control background, injecting zero-sequence current into the low-current grounding system with the grounding fault at a first time interval;

Thirdly, the control background sends out a command of quitting the injection of the zero-sequence current at a second time interval after sending out the command of injecting the zero-sequence current;

Fourthly, the control background sends a data calling command to a collector of each line grounding phase of the grounding system, so that the collector controls a collector connected with the collector to upload the collected current value;

And fifthly, calculating the current value and the variable quantity of each line before and after the zero-sequence current is injected according to the acquired current value, and positioning the current change abnormal position point according to the current value and the variable quantity of each line, wherein the abnormal position is a grounding point.

2. the small current grounding system ground fault location method of claim 1, wherein the zero sequence current is injected into the small current grounding system by the steps of:

And putting arc suppression coil parallel resistors into the small current grounding system or sending a putting command to a zero sequence current injection device in the small current grounding system.

3. The small-current grounding system ground fault location method according to any one of claims 1-2, characterized in that locating the current change abnormal location point according to the current value of each line and its variation is determined by any one of the following ways:

Longitudinal comparison mode: calculating difference value delta I of outgoing line current values obtained by acquiring each collector of the line twice before and after zero-sequence current injection respectively for each outgoing line_jWherein j is 1,2, ┄, m, m +1, ┄, n is a collector S arranged on a certain line₁To collector S_nThe number of (2); if collector S₁To collector S_mCurrent difference Δ I of_jGreater than or equal to a first threshold value, and collector S_m+1To collector S_nIs less than a second threshold value, it is determined that the abnormal position is located at the collector S_mTo collector S_m+1The grounding point is positioned at the collector S_mTo collector S_m+1To (c) to (d); if the current difference value delta I of the line collector_jIf the grounding point is smaller than the third threshold value, the grounding point is not on the line; if all lines are judged to have no grounding points, the grounding points are located on the bus, wherein the first threshold value is larger than the second threshold value and larger than the third threshold value;

Transverse comparison mode: calculating two collectors S adjacent to the local line for each outgoing line_k,S_k+1Difference value I of current values acquired after zero sequence current is injected_k-I_k+1If S is₁To S_mThe difference between the current of two adjacent collectors is smaller than the first difference, and the collector S_mTo collector S_m+1The obtained current difference I is collected_m-I_m+1Greater than a second difference, and the current difference I_m-I_m+1If the maximum difference value of the line is obtained, the grounding point is determined to be positioned at the collector S_mand collector S_m+1To (c) to (d); if the current difference values of adjacent collectors of the line are smaller than the fourth threshold value, determining that the grounding point is not on the line; if all lines are judged to have no grounding points, the grounding points are located on the bus;

An increment comparison mode: for each outgoing line, firstly calculating the difference value delta I of the current values acquired by the collectors in two times before and after zero-sequence current injection_mThen calculating two adjacent collectors S_m,S_m+1The amount of change Δ I of the current difference therebetween_m-ΔI_m+1If the variation reaches a fifth threshold, determining that the grounding point is positioned at the collector S_mAnd collector S_m+1To (c) to (d); if the current difference variation of the adjacent collectors of the line is smaller than a fifth threshold, determining that the grounding point is not on the line; if all lines are judged to have no grounding points, determining that the grounding points are located on the bus;

The current values and the variation thereof adopted by the longitudinal comparison mode, the transverse comparison mode and the incremental comparison mode comprise scalars or vectors.

4. The method as claimed in claim 3, wherein the control background further normalizes the received current value collected by each collector of each outgoing line in the low-current grounding system, and determines the grounding point according to the abnormal position of the change of the current value of the outgoing line before and after injecting the zero-sequence current into the grounding system in at least one of a longitudinal comparison mode, a transverse comparison mode and an incremental comparison mode after the normalization.

5. The method for positioning the ground fault of the low-current grounding system according to claim 4, wherein the step of normalizing the outgoing line current values collected by the collectors uploaded by the collectors comprises the following steps:

Recording the outgoing line current values acquired by each acquisition device of the line before injecting the zero sequence current as follows:

I₁₁,I₂₁,…，I_m1，I_(m+1)1，…，I_n1；

The value of the outgoing line current acquired after the zero-sequence current is injected is as follows:

I₁₂,I₂₂,…，I_m2，I_(m+1)2，…，I_n2；

Wherein j is 1,2, …, m, m +1, …, N (N belongs to N) is the number of the collector arranged on the line; selecting a reference current I_baseLet the following hold:

I_base＝k_jI_j1，j∈n；

according to the reference current and the acquired current value, a group of normalization systems k of each line can be obtained through calculation₁,k₂,…,k_j，…,k_n(ii) a The normalization coefficient is real number or complex number; normalizing two groups of collected data before and after the injected zero-sequence current obtained by each collector of each line by using the normalization coefficient, and respectively recording as I'_j1＝k_jI_j1，I'_j2＝k_jI_j2J is 1,2,. n; normalizing each line of the grounding system one by one; wherein the reference current comprises a phase current of a grounding wire of the line or a measured value designated as one of collectors of the line.

6. A low current grounding system ground fault location system, comprising:

The control background is connected with the zero sequence current injection unit and each concentrator and/or collector in the low current grounding system and is used for issuing acquisition commands to each concentrator so that each concentrator controls the collector arranged on each line connected with the concentrator to acquire the current value of the line arranged on the collector; after the acquisition command is issued, the zero sequence current injection unit is controlled to inject zero sequence current into the small current grounding system with the grounding fault at a first time interval; after the zero sequence current is injected for a second time, sending a data calling command to each collector, receiving outlet current values and variable quantities thereof collected by each collector in the grounding system, finally determining the abnormal position of the grounding system before and after the zero sequence current is injected, wherein the abnormal position is positioned as a grounding point;

the aggregator is in communication connection with the control background and each collector in the circuit, and is used for receiving an acquisition command or a data call command issued by the control background and correspondingly controlling the collectors to acquire data or upload data according to the command;

The collector comprises a plurality of collectors arranged on a line, and the collectors are respectively connected with a concentrator and used for correspondingly collecting the line current value of the position where the collector is located according to the control of the concentrator and reporting the line current value of the position where the collector is located;

and the zero sequence current injection unit is used for correspondingly injecting zero sequence current or quitting according to the command of the control background.

7. The ground fault positioning system of small-current grounding system as claimed in claim 6, wherein the control background further comprises at least one of a longitudinal comparison unit, a transverse comparison unit, and an increment comparison unit for determining the abnormal position according to the collected outgoing line current value and positioning the grounding point;

The longitudinal comparison unit is used for: calculating difference delta I of current values of outgoing lines of the line collector mounting point before and after zero sequence current is injected into the system for each outgoing line respectively'_j＝I′_j2-I′_j1(ii) a If collector S₁To collector S_mis greater than or equal to a first threshold value, and the collector S_m+1To collector S_nIf the current difference is smaller than the second threshold value, the grounding point is determined to be positioned in the collectorS_mTo collector S_m+1To (c) to (d); if the current difference value delta I of the line collector_jIf no obvious change exists, determining that the grounding point is not on the line; if all lines are judged to have no grounding points, determining that the grounding points are located on the bus;

The transverse comparison unit is used for: calculating two collectors S adjacent to the local line for each outgoing line_j,S_j+1Difference value I 'of line current value after injecting zero sequence current'_j2-I′_(j+1)2if S is₁To S_mthe difference between the current of two adjacent collectors is smaller than the first difference, and the collector S_mto collector S_m+1The obtained current difference value I 'is collected'_m2-I′_(m+1)2is greater than a second difference value, and the current difference value I'_m2-I′_(m+1)2If the maximum difference value of the line is the maximum difference value of the line, determining that the grounding point is positioned between the collector and the collector; if the current difference values of adjacent collectors of the line have no obvious change, determining that the grounding point is not on the line; if all lines are judged to have no grounding points, determining that the grounding points are located on the bus;

The increment comparison unit is used for: for each outgoing line, firstly, calculating the difference delta I of the current values acquired by the collectors in two times before and after the zero-sequence current is injected into each outgoing line'_j＝I′_j2-I′_j1Then calculating two adjacent collectors S_m,S_m+1Delta l 'between the current difference values'_m-⊿I′_m+1If the variation reaches a fifth threshold, determining that the grounding point is positioned at the collector S_mAnd collector S_m+1to (c) to (d); if the current difference variation of the adjacent collectors of the line is smaller than a fifth threshold, determining that the grounding point is not on the line; if all lines are judged to have no grounding points, determining that the grounding points are located on the bus;

The current values adopted by the longitudinal comparison unit, the transverse comparison unit and the increment comparison unit comprise scalars or vectors.

8. The system of claim 7, wherein the control background further comprises a measured current normalization processing unit, configured to normalize the values of outgoing currents collected by the collectors uploaded by the collectors according to the following steps:

The outgoing line current value acquired by each collector of the circuit before injecting the zero sequence current is as follows:

I₁₁,I₂₁,…，I_m1，I_(m+1)1，…，I_n1；

the value of the outgoing line current acquired after the zero-sequence current is injected is as follows:

I₁₂,I₂₂,…，I_m2，I_(m+1)2，…，I_n2；

wherein j is 1,2, …, m, m +1, …, N (N belongs to N) is the number of the collector arranged on the line; selecting a reference current I_baselet the following hold:

I_base＝k_jI_j1，j∈n；

According to the reference current and the acquired current value, a group of normalization systems k of each line can be obtained through calculation₁,k₂,…,k_j，…,k_n(ii) a The normalization coefficient is real number or complex number; normalizing two groups of collected data before and after the injected zero-sequence current obtained by each collector of each line by using the normalization coefficient, and respectively recording as I'_j1＝k_jI_j1，I'_j2＝k_jI_j2J is 1,2,. n; normalizing each line of the grounding system one by one; wherein the reference current comprises a phase current of a grounding wire of the line or a measured value designated as one of collectors of the line.

Technical Field

the invention relates to the technical field of ground fault processing of medium and low voltage distribution networks, in particular to a single-phase ground fault positioning method and system of a low-current grounding system.

Background

At present, a medium-low voltage (3-66 kV) power distribution network generally adopts 3 grounding modes of grounding with a neutral point not grounded, grounding with a neutral point grounded through an arc suppression coil and grounding with a neutral point grounded through a small resistor, wherein the two grounding modes are called as a small current grounding mode to form a small current grounding system. When a single-phase earth fault occurs in the low-current earth system, the voltage of a non-fault phase rises to be line voltage, three phases are still symmetrical, the operation can be continued for 2 hours, and the power supply reliability is ensured. However, long-term operation can cause insulation aging, cause interphase short circuit and result in expansion of grid accidents. Therefore, when a single-phase earth fault occurs in a low-current earth system, it is required to quickly locate a fault line and a fault point so as to eliminate the fault in time.

Line selection and fault location of low-current ground faults are difficult problems which confuse the power grid for many years. The existing line selection and fault location methods are various, and can be generally classified into two categories, namely a passive type and an active type according to different detected signal modes.

The passive line selection method can be further divided into a line selection method based on a steady-state signal and a line selection method based on a transient-state signal. The principle of the steady-state line selection method is as follows: when a ground fault occurs, the system enters a steady state, and a line is selected according to the electric gas quantity characteristics of a fault phase and a non-fault phase, wherein the main method comprises the following steps: firstly, determining a fault line according to the amplitude and the direction of the zero sequence current of the line. Secondly, determining a fault line according to the 5 th harmonic content in the zero sequence current of the line. Thirdly, determining a fault line according to the zero sequence active component of the line; the principle of the line selection method of the transient signal is as follows: after a ground fault occurs, a fault line is identified by utilizing an electric quantity change transient signal, and the method mainly comprises the following steps: first half-wave method. ② wavelet method. And thirdly, a transient energy method. And fourthly, a traveling wave method.

The active line selection method is characterized in that after a line has a ground fault, a specific power frequency signal or a high-frequency signal is injected into a grounding system, and the fault line is identified by detecting the characteristics of the injected signal in the line. Mainly, there are a medium resistance method, an S-implant method, a residual increment method, and the like.

fault location (fault indication) is to further identify a fault occurrence area after a ground fault occurs, and to narrow a search range, so that an operator can quickly process the fault. Fault indicators are classified into two major categories, in-situ type and remote transmission type. The in-situ type comprises two types of transient characteristics and applied signals; the remote transmission type comprises three types of transient characteristics, transient recording and external signals. The fault indication judges a fault point by collecting an electric quantity signal of a fault line, or indicates the fault point by turning over a board and flashing with an indicator.

however, the principle of the existing fault indication technology is to detect a transient state or (and) a steady state zero sequence current condition along the ground line to indicate a fault point when a ground fault occurs. For the overhead line, the zero sequence current of the line cannot be directly measured, and only the zero sequence current of the line is obtained by measuring three phase currents and summing instantaneous values, namely, a collector is required to synchronously sample three phases, and the zero sequence current is obtained by background synthesis after sampling data is obtained. Therefore, the collector needs high precision, high speed data collection capability, large capacity data storage capability, high precision three-phase synchronous sampling capability, high precision GPS timing capability and large capacity data exchange capability. Because data collection station installs in distribution lines, the operational environment is abominable for the performance parameter of device changes along with the environment variation. In order to achieve the necessary functions and technical performance, the whole set of system has complex structure, high cost, difficult maintenance and poor reliability. In addition, the existing fault line selection and fault indication technology can not judge the special grounding types of high-resistance grounding, resonance grounding, intermittent grounding and the like in principle. Therefore, the failure point is often not accurately indicated in actual operation. None of the fault indicators so far perform satisfactorily in operation.

Disclosure of Invention

The invention provides a method and a system for positioning a ground fault of a low-current grounding system aiming at the defects of the prior art, and aims to solve the problems that the conventional fault indicator has low fault indication accuracy, a complex system, poor reliability, high device cost, large influence of environmental factors on performance and incapability of identifying a special type of ground fault. The invention specifically adopts the following technical scheme.

Firstly, in order to achieve the above object, a method for positioning a ground fault of a low-current grounding system is provided, which comprises the following steps after a transient process of the ground fault is finished: the method comprises the following steps that firstly, a background is controlled to send acquisition commands to collectors in a low-current grounding system, so that each collector controls a collector arranged on each line connected with the collector to acquire the current value of the line arranged on the collector; secondly, after issuing an acquisition command by the control background, injecting zero-sequence current into the low-current grounding system with the grounding fault at a first time interval; thirdly, the control background sends out a command of quitting the injection of the zero-sequence current at a second time interval after sending out the command of injecting the zero-sequence current; fourthly, the control background sends a data calling command to a collector of each line grounding phase of the grounding system, so that the collector controls a collector connected with the collector to upload the collected current value; and fifthly, calculating the current value and the variable quantity of each line before and after the zero-sequence current is injected according to the acquired current value, and positioning the current change abnormal position point according to the current value and the variable quantity of each line, wherein the abnormal position is a grounding point.

Optionally, in the method for positioning a ground fault of a low-current grounding system, the zero-sequence current is injected into the low-current grounding system through the following steps: and putting arc suppression coil parallel resistors into the small current grounding system or sending a putting command to a zero sequence current injection device in the small current grounding system.

Optionally, in the method for locating a ground fault of a low-current grounding system, the current value and the variation thereof according to each line are determined in any one of the following manners:

longitudinal comparison mode: calculating difference value delta I of outgoing line current values obtained by acquiring each collector of the line twice before and after zero-sequence current injection respectively for each outgoing line_jWherein j is 1,2, ┄, m, m +1, ┄, n is a collector S arranged on a certain line₁To collector S_nThe number of (2); if collector S₁To S_mCurrent difference delta I of collector_jgreater than or equal to a first threshold value, and collector S_m+1To collector S_nIs less than a second threshold value, it is determined that the abnormal position is located at the collector S_mTo collector S_m+1The grounding point is positioned at the collector S_mTo collector S_m+1To (c) to (d); if the current difference value delta I of the line collector_jif the grounding point is smaller than the third threshold value, the grounding point is not on the line; if all lines are judged to have no grounding points, the grounding points are located on the bus, wherein the first threshold value is larger than the second threshold value and larger than the third threshold value;

Transverse comparison mode: for each outgoing line, respectively calculating two collectors (S) adjacent to the line_k,S_k+1) Difference value (I) of current values acquired after injecting zero sequence current_k-I_k+1) If S is₁To S_mThe difference between the current of two adjacent collectors is smaller than the first difference, and the collector S_mTo collector S_m+1The obtained current difference (I) is collected_m-I_m+1) Greater than the second difference, and the difference (I)_m-I_m+1) If the maximum difference value of the line is the maximum difference value of the line, the abnormal position is judged to be positioned in the collector S_mto collector S_m+1The grounding point is positioned at the collector S_mAnd collector S_m+1In the meantime. And if the current difference values of the adjacent collectors of the line are smaller than the fourth threshold value, the grounding point is not on the line. If all lines are judged to have no grounding points, the grounding points are located on the bus;

An increment comparison mode: for each outgoing line, firstly calculating the difference value delta I of the current values acquired by the collectors in two times before and after zero-sequence current injection_mThen calculating two adjacent collectors S_m,S_m+1The amount of change Δ I of the current difference therebetween_m-ΔI_m+1if the variation reaches a fifth threshold, the abnormal position is judged to be positioned in the two collectors S with the maximum difference variation_m,S_m+1the grounding point is positioned at the collector S_mAnd collector S_m+1In the meantime. And if the current difference variation of the adjacent collectors of the line is smaller than the fifth threshold, the grounding point is not on the line. If all lines are judged to have no grounding points, the grounding points are located on the bus;

The parameters and results of the longitudinal comparison unit, the transverse comparison unit and the incremental comparison unit can be selected to be scalars or vectors according to requirements.

optionally, in the method for positioning a ground fault of a low-current grounding system, the control background further normalizes the received current value collected by each collector of each outgoing line in the low-current grounding system, and determines the grounding point according to an abnormality of a change of the current value of the outgoing line before and after zero-sequence current is injected into the grounding system in any one of a longitudinal comparison mode, a transverse comparison mode and an incremental comparison mode after the normalization.

Optionally, in the method for positioning a ground fault of a low-current grounding system, the step of normalizing the outgoing line current values collected by the collectors uploaded by the collectors includes:

Recording the outgoing line current values acquired by each acquisition device of the line before injecting the zero sequence current as follows:

I₁₁,I₂₁,…，I_m1，I_(m+1)1，…，I_n1

The value of the outgoing line current acquired after the zero-sequence current is injected is as follows:

I₁₂,I₂₂,…，I_m2，I_(m+1)2，…，I_n2

Wherein j is 1,2, …, m, m +1, …, N (N belongs to N) is the number of the collector arranged on the line. Selecting a reference current I_baseLet the following hold:

I_base＝k_jI_j1，j∈n

according to the reference current and the acquired current value, a group of normalization systems k of each line can be obtained through calculation₁,k₂,…,k_j，…,k_n. The normalization coefficients are real or complex. Normalizing two groups of collected data before and after the injected zero-sequence current obtained by each collector of each line by using the normalization coefficient, and respectively recording as I'_j1＝k_jI_j1，I'_j2＝k_jI_j2J is 1,2,. n; and normalizing each line of the grounding system one by one. Wherein the reference current can be selectedthe phase current of the grounding wire of the line is selected or is specified as the measured value of one collector of the line. The normalization processing unit parameters and the results may be chosen to be scalar or vector.

Meanwhile, the invention also provides a system for positioning the ground fault of the low-current grounding system, which comprises: the control background is connected with the zero sequence current injection unit and each concentrator and/or collector in the low current grounding system and is used for issuing acquisition commands to each concentrator so that each concentrator controls the collector arranged on each line connected with the concentrator to acquire the current value of the line arranged on the collector; after the acquisition command is issued, the zero sequence current injection unit is controlled to inject zero sequence current into the small current grounding system with the grounding fault at a first time interval; and after the zero sequence current is injected for a second time, sending a data calling command to each collector, receiving outlet current values and variable quantities thereof collected by each collector in the grounding system, finally determining the abnormal position of the grounding system before and after the zero sequence current is injected, wherein the abnormal position is positioned as a grounding point by calculating the current values and the variable quantities of each line. And the aggregator is in communication connection with the control background and each collector in the circuit and is used for receiving a collection command or a data call command issued by the control background and correspondingly controlling the collectors to collect data or upload data according to the command. The collector comprises a plurality of collectors arranged on a line, and the collectors are respectively connected with a concentrator and used for correspondingly collecting the line current value of the position of the collector according to the control of the concentrator and reporting the line current value of the position of the collector. And the zero sequence current injection unit is used for correspondingly injecting zero sequence current or quitting according to the command of the control background.

Optionally, in the system for positioning a ground fault of a low-current grounding system, the control background further includes a measured current normalization processing unit, which is configured to perform normalization processing on outgoing line current values collected by the collectors uploaded by the collectors according to the following steps: before each collector of the recording circuit injects zero sequence currentThe current value of the outgoing line obtained by collection is as follows: i is₁₁,I₂₁,…，I_m1，I_(m+1)1，…，I_n1(ii) a And recording the value of the outlet current acquired after the zero-sequence current is injected as follows: i is₁₂,I₂₂,…，I_m2，I_(m+1)2，…，I_n2(ii) a Wherein j is 1,2, …, m, m +1, …, N (N belongs to N) is the number of the collector arranged on the line. Selected reference Current I_baseLet the following hold:

I_base＝k_jI_j1，j∈n；

Then, according to the reference current and the collected current value, a group of normalization systems k of each line can be obtained through calculation₁,k₂,…,k_j，…,k_n. The normalization coefficients are real or complex. Normalizing two groups of collected data before and after the injected zero-sequence current obtained by each collector of each line by using the normalization coefficient, and respectively recording as I'_j1＝k_jI_j1，I'_j2＝k_jI_j2J is 1,2,. n; and normalizing each line of the grounding system one by one. The reference current can be selected from the phase current of the grounding wire of the line or can be specified as the measured value of one collector of the line. The normalization processing unit parameters and the results may be chosen to be scalar or vector.

Optionally, the above-mentioned ground fault location method and system can be used for a low-current grounding system or a low-current ungrounded system.

Optionally, in the system for positioning a ground fault of a low-current grounding system, the control background further includes any one of a longitudinal comparison unit, a transverse comparison unit, and an increment comparison unit, which is connected to the output end of the normalization processing unit, and determines the abnormal position according to the value of the outgoing line current collected after normalization processing, so as to position the grounding point. Wherein the longitudinal comparison unit is configured to: calculating difference delta I of current values of outgoing lines of the line collector mounting point before and after zero sequence current is injected into the system for each outgoing line respectively'_j＝I′_j2-I′_j1. If it isCollector S₁To S_mThe difference of the collector currents is greater than or equal to a first threshold value, and the collector S_m+1to collector S_nIs less than a second threshold value, it is determined that the abnormal position is located at the collector S_mTo collector S_m+1The grounding point is positioned at the collector S_mto collector S_m+1In the meantime. If the current difference value delta I of the line collector_jand if the grounding point is smaller than the third threshold value, the grounding point is not on the line. If all lines are judged to have no grounding point, the grounding point is located on the bus. The transverse comparison unit is used for: for each outgoing line, respectively calculating two collectors (S) adjacent to the line_j,S_j+1) Difference (I ') in line current values after injection of zero sequence current'_j2-I′_(j+1)2) If S is₁To S_mThe difference between the current of two adjacent collectors is smaller than the first difference, and the collector S_mTo collector S_m+1The obtained current difference (I ') was taken in between'_m2-I′_(m+1)2) Greater than a second difference value, and the difference value is (I'_m2-I′_(m+1)2) If the maximum difference value of the line is the maximum difference value of the line, the abnormal position is judged to be positioned in the collector S_mTo collector S_m+1And the grounding point is positioned between the collectors. And if the current difference values of the adjacent collectors of the line are smaller than the fourth threshold value, the grounding point is not on the line. If all lines are judged to have no grounding point, the grounding point is located on the bus. The increment comparison unit is used for: for each outgoing line, firstly, calculating the difference delta I of the current values acquired by the collectors in two times before and after the zero-sequence current is injected into each outgoing line'_j＝I′_j2-I′_j1then calculating two adjacent collectors S_m,S_m+1Delta l 'between the current difference values'_m-⊿I′_m+1If the variation reaches a fifth threshold, the abnormal position is judged to be positioned in the two collectors S with the maximum difference variation_m,S_m+1The grounding point is positioned at the collector S_mAnd collector S_m+1In the meantime. And if the current difference variation of the adjacent collectors of the line is smaller than the fifth threshold, the grounding point is not on the line. If all lines are judged to be absentAnd the grounding point is positioned on the bus.

The parameters and results of the longitudinal comparison unit, the transverse comparison unit and the incremental comparison unit can be selected to be scalars or vectors according to requirements.

Advantageous effects

According to the method, after a single-phase ground fault occurs in a small-current grounding system (or an ungrounded system), zero-sequence current is injected into a neutral point of a grounding system of a transformer substation, and a ground fault point is determined by judging distribution and change conditions of outgoing line currents of the grounding system after the zero-sequence current is injected into the neutral point. The method comprises the steps of firstly collecting grounding phase currents by a plurality of collectors installed on a grounding system line, then injecting zero sequence currents into a neutral point of a transformer substation grounding system, or injecting zero sequence currents into other equipment, measuring the grounding phase currents of the grounding system line again, and judging the grounding point by comparing the two-time collection of the grounding line before and after the zero sequence currents are injected into the grounding system to obtain line currents and change conditions thereof. Therefore, the zero sequence current of the line does not need to be synthesized in the control main station. In order to further improve the positioning precision, the invention carries out normalization processing on the acquired data, thereby completely overcoming the defects of the existing fault indication system, having simple device structure, not needing GPS timing and high-speed data acquisition, not needing large-capacity data communication, not being influenced by CT (computed tomography) transformation ratio error of the acquisition device and environmental factors, and being capable of accurately identifying and positioning the special type ground fault.

Furthermore, in order to ensure that the grounding point can be accurately judged by analyzing the data provided by the collector, and eliminate the influence of the CT ratio error of the collector, the parameters of the collector device and environmental factors on the measurement precision of the collector, the invention further performs normalization processing on the data of the outgoing line current values collected by the collectors uploaded by the collectors in the control background. And judging the abnormal position according to the normalized current values of the outgoing lines, and positioning the grounding point. Therefore, the invention can accurately position the grounding fault.

In addition, because the invention only needs to carry out direct linear comparison on the data and does not need complex calculation, the positioning of the grounding fault can be more timely, the occupation of the computing resource of the system is less, and the method is easier to realize in various low-performance platforms.

The invention has another outstanding advantage that the line selection and the positioning are realized by comparing the current, and the line selection and the positioning process can be repeated, thereby obtaining more accurate positioning information.

additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

Fig. 1 is a schematic diagram of a low current grounding system ground fault location system of the present invention.

Fig. 2 is a flow chart of a method for locating a ground fault of a low-current grounding system according to the invention.

Detailed Description

In order to make the purpose and technical solution of the embodiments of the present invention clearer, the technical solution of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

fig. 1 is a fault location (fault indication) system for a distribution line (including a cable) in which a neutral point of an electric power system is not grounded or is grounded via an arc suppression coil, when a ground fault occurs, according to the present invention, which includes:

controlling a background: the collector is connected with a zero sequence current injection unit and each concentrator and/or collector in the low current grounding system and is used for issuing a collection command to each concentrator, so that each concentrator controls the collector arranged on each line connected with the concentrator to collect the current value of the line arranged on the collector; after the acquisition command is issued, the zero sequence current injection unit is controlled to inject zero sequence current into the small current grounding system with the grounding fault at a first time interval; after the zero sequence current is injected for a second time, sending a data calling command to each collector, receiving outlet current values and variable quantities thereof collected by each collector in the grounding system, finally determining the abnormal position of the grounding system before and after the zero sequence current is injected, wherein the abnormal position is positioned as a grounding point; the first time or the second time is set according to needs, the first time and the second time are both short, and the first time and the second time can be the same or different and are not limited herein;

A collector: the concentrator comprises a plurality of collectors arranged on each line, wherein each collector is connected with a concentrator respectively and used for correspondingly collecting outgoing line current values of the positions of the collectors according to the control of the concentrator and reporting the outgoing line current values of the positions of the collectors to the concentrators according to the command of the concentrators;

An aggregator: the control background is arranged beside the collector, is in communication connection with the control background and each collector in the circuit, and can be in communication with the control background and a plurality of collectors; the aggregator is used for receiving a control background command, receiving an acquisition command and a data calling command issued by the control background, issuing the acquisition command to the acquisition device according to the command correspondingly to control the acquisition device to acquire data, or uploading a line current value acquired by the acquisition device to the control background;

and the zero sequence current injection unit is used for correspondingly injecting zero sequence current or quitting according to the command of the control background.

the fault positioning system can be used for a low-current grounding system and can also be applied to an ungrounded system.

In a more specific implementation manner, the zero sequence current injection unit may inject the zero sequence current by putting an arc suppression coil parallel resistor in the small current grounding system or sending a putting command to a zero sequence injection device in the small current grounding system. Under the mode of putting an arc suppression coil parallel resistor into use, the zero sequence current injection unit comprises an arc suppression coil parallel resistor and a control switch, the arc suppression coil parallel resistor is connected with the control switch in series and then connected with two ends of the arc suppression coil in parallel, and two ends of the arc suppression coil are respectively connected with a power supply and the ground of the small current grounding system; and the control background controls the conduction of the control switch at a short time interval after the acquisition command is reached, so that the zero-sequence current injection unit injects the zero-sequence current.

When the distribution line has a ground fault, the control background detects the occurrence of the ground fault according to the change condition of the three-phase voltage of the bus, and after the fault transient process is finished, the control background sends a data acquisition command to the concentrator, the concentrator receives the command and then forwards the command to the collectors, and the collectors acquire and calculate the line current. After the control background sends the acquisition command for a short time delay, the arc suppression coil parallel resistor is switched in, or a switching control command (when no arc suppression coil exists) is sent to the zero sequence injection device, and zero sequence current is injected into the fault system. And after the short time delay of the second time, the control background sends a data calling command to the collector, the collector forwards the command to the collector, and the collector uploads the collected line current. After the fault analysis and judgment are completed, the background is controlled to send a command to quit the parallel resistance of the arc suppression coil or the zero sequence current injected by the injection device, the whole process is as shown in fig. 2, and the fault line selection and fault positioning are realized in the system according to the following modes:

The method comprises the following steps that firstly, a control background issues acquisition commands to collectors in a low-current grounding system, and each collector controls a collector connected with the collector to acquire the current value of an installed line;

secondly, controlling a background to issue an acquisition command and inject zero sequence current into a small current grounding system with a grounding fault after a short interval of first time;

Thirdly, issuing a control command after a short interval of a second time elapses after the control background issues the command for injecting the zero-sequence current, and quitting injecting the zero-sequence current; the first time and the second time are selected according to needs, and can be set to be the same or different;

Fourthly, the background is controlled to send a data calling command to the collector of each line grounding phase of the grounding system, so that the collector controls the collector connected with the collector to upload the collected current value;

And fifthly, the control background normalizes the received current values acquired by the line collectors, positions current change abnormal position points according to the normalized line grounding phase current values and the change conditions thereof, and takes the abnormal positions as grounding points.

The above steps are repeated as necessary to obtain a more accurate fault location.

Optionally, the method is performed after the end of the ground fault transient process or at a predetermined time after the ground fault occurs to achieve ground fault localization. After the ground fault occurs, waveforms of various parameters such as current or voltage in the grounded system or ungrounded system can be monitored through a ground fault monitoring device or a sensor or other real-time monitoring modes, and the method belongs to the conventional technology in the field and is not described herein again. It should be understood that the ground fault location and system of the embodiment of the present invention are not limited by the ground fault monitoring method, and both the existing ground fault monitoring method and the ground fault monitoring method developed in the future are applicable to the ground fault location and system of the embodiment of the present invention.

The operation of the above system will be described below by taking a primary circuit ground fault as an example.

First, inAfter the circuit grounding fault occurs, the control background issues an acquisition command to collectors in the low-current grounding system, so that each collector controls the collectors arranged on each line connected with the collector to acquire the fault line phase current I of the arranged line before the zero-sequence current is injected into the arranged line_1m；

And secondly, controlling the background to issue an acquisition command and inject zero sequence current into the small current grounding system with the grounding fault at short time intervals.

Thirdly, after the command of injecting the zero sequence current is sent for a short interval after the control, a command of quitting the injection of the zero sequence current is sent;

Fourthly, the control background sends a data calling command to a collector of each line grounding phase of the grounding system, so that the collector controls a collector connected with the collector to upload the collected current value;

And fifthly, normalizing the data collected by each line after the control, then calculating the current value and the variable quantity of each line before and after the zero sequence current is injected by adopting the normalized data, and positioning the current change abnormal position point according to the line grounding phase current value and the change condition thereof, wherein the abnormal position is a grounding point.

the line current normalization method comprises the following steps:

assuming that the value of the outgoing line current acquired by each acquisition device of one line fault phase before injecting the zero sequence current is as follows:

I₁₁,I₂₁,…，I_m1，I_(m+1)1，…，I_n1

The value of the outgoing line current acquired after the zero-sequence current is injected is as follows:

I₁₂,I₂₂,…，I_m2，I_(m+1)2，…，I_n2

Wherein j is 1,2, …, m, m +1, …, N (N is N) is the reference current I selected by the number of the collector installed on each line_baseLet the following hold:

I_base＝k_jI_j1，j∈n

According to the reference current and the collected current valueThe over-calculation can obtain a set of normalization coefficients k of the line₁,k₂,…,k_j，…,k_n. The normalization coefficients are real or complex. Normalizing the two groups of current data obtained by each acquisition unit of the line by using a normalization coefficient, and respectively recording as I'_j1＝k_jI_j1，I'_j2＝k_jI_j2，

j ═ 1,2,. n; reference current I_baseThe phase current I of the grounding wire of the line is selected_fh. And (4) judging the ground fault point by using the normalized data and adopting a longitudinal comparison method, a transverse comparison method and an increment comparison method. The reference current can be selected from the phase current of the grounding wire of the line or can be specified as the measured value of one collector of the line. The normalization processing unit parameters and the results may be chosen to be scalar or vector.

The longitudinal comparison method adopted in the process of judging the ground fault point comprises the following steps: calculating difference delta I of outgoing line current values obtained by two times of acquisition of each acquisition device of the line before and after zero sequence current injection for each outgoing line'_j＝I′_j2-I′_j1. If collector S₁To S_mCurrent difference (delta I) of collector'_jLarger, e.g. reaching a first threshold, and collector S_m+1to collector S_nIs smaller, for example smaller than a second threshold value, it is determined that the abnormal position is located at the collector S_mto collector S_m+1The grounding point is positioned at the collector S_mTo collector S_m+1in the meantime. If the current difference value delta I of the line collector_jAnd if the grounding point is smaller than the third threshold value or no obvious change exists, the grounding point is not on the line. If all lines are judged to have no grounding points, the grounding points are located on the bus; the first threshold value is larger than the second threshold value and larger than the third threshold value, and 3 threshold values can be set according to needs;

Or adopting a transverse comparison method: calculating two collectors S adjacent to the local line for each outgoing line_k,S_k+1Difference (I ') of current values acquired after injection of zero sequence current'_j2-I′_(j+1)2) If S is₁to S_mThe difference between the current of two adjacent collectors is smaller, for example, smaller than the first difference, and the collector S_mTo collector S_m+1The obtained current difference (I ') was taken in between'_m2-I′_(m+1)2) If the difference is larger than the second difference, and the difference is the maximum difference of the present line, it is determined that the abnormal position is located in the collector S_mTo collector S_m+1And the grounding point is positioned between the collectors. And if the current difference values of the adjacent collectors of the line are not obviously changed, for example, the current difference values are smaller than a fourth threshold value, the grounding point is judged not to be on the line. If the grounding points are judged to be completely free of the grounding points, the grounding points are located on the bus;

Or adopting an increment comparison method: for each outgoing line, firstly calculating the difference value delta I of the current values acquired by the collectors in two times before and after zero-sequence current injection_mthen calculating two adjacent collectors S_m,S_m+1the amount of change Δ I of the current difference therebetween_m-ΔI_m+1If the variation is large, for example, the variation reaches a fifth threshold, it is determined that the abnormal position is located in the two collectors S with the largest difference variation_m,S_m+1The grounding point is positioned at the collector S_mAnd collector S_m+1In the meantime. And if the current difference value variation of the adjacent collectors of the line is not obvious or is smaller than a fifth threshold value, the grounding point is not on the line. If all lines are judged to have no grounding points, the grounding points are located on the bus;

The parameters and results of the longitudinal comparison unit, the transverse comparison unit and the incremental comparison unit can be selected to be scalars or vectors according to requirements. The first difference, the second difference, the fourth threshold or the fifth threshold can be set according to the requirement, and can be equal or different. The parameters and the results can be selected as scalar or vector according to the requirement.

the invention fully utilizes the characteristic that the current of the grounding wire is not changed when the grounding fault occurs, injects zero sequence current into a grounding system, and identifies fault points by detecting the distribution of the current on a grounding phase. Therefore, the acquisition terminal acquires and calculates the line current only after receiving the command without synthesizing the zero sequence current, so the structure is simple and the data exchange with the control background is very little. After data normalization processing is adopted, the measurement precision of the collector is not influenced by environmental change and device parameter change, the device interchangeability is good, the operation and maintenance are simple, and meanwhile, the equipment cost is greatly reduced. The new discrimination principle is adopted, the principle avoids complex technical functions and performance requirements, the identification process is simple and clear, and different identification methods are changed to adapt to different system characteristics and grounding types, so that the identification accuracy is greatly improved. In addition, the fault identification process can be repeated, namely, the positioning accuracy can be further improved through multiple times of identification.

The above are merely embodiments of the present invention, which are described in detail and with particularity, and therefore should not be construed as limiting the scope of the invention. It should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the spirit of the present invention, and these changes and modifications are within the scope of the present invention.