A method and system for locating a small current grounding fault independent of voltage polarity

Abstract

The invention discloses a small current grounding fault locating method and system which are not dependent on voltage polarity, and belongs to the field of electric power technology. The method and system include: all devices adopt high-speed sampling and perform fault detection in real time according to high-speed sampling data; after all devices perform data synchronization through the ping-pong principle, the moment when the fault detection and discrimination condition is first detected is taken as the fault moment, which is recorded as the moment of t=0ms; and the zero-sequence current sampling value of t=0ms is marked with a time stamp and transmitted to the opposite side to perform transient zero-mode current correlation coefficient discrimination and determine the fault position, thereby solving the technical problem that the specific fault section cannot be located after the line is selected through the small current grounding fault. The invention does not rely on the voltage information on both sides, and can judge the fault area inside and outside the area only through the correlation of the current after synchronization, thereby preventing the event of misjudgment of the direction.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and in particular relates to a method and system for locating a small current grounding fault that is independent of voltage polarity. Background Art

[0002] Nowadays, most of the distribution networks in my country adopt the operation mode of small current grounding. The probability of single-phase grounding short circuit can reach about 80%. When a fault occurs, only the capacitance of the line to the ground creates a path between the earth and the fault line, so the short-circuit current value is not large. After the fault, since the system voltage is still symmetrical, the line voltage value has not changed, and the normal load power supply has not been damaged, the system can be allowed to run for another 1 to 2 hours after the fault. However, after single-phase grounding, the phase voltage will increase to √3 times of itself, so if the fault is not removed and it continues to operate for a long time, it may damage the insulation of the device, cause arc overvoltage, and cause phase-to-phase faults, which will endanger the system.

[0003] There are many detection methods for small current grounding line selection, including the judgment method based on the steady-state signal generated by the fault, and the judgment method based on the transient signal generated by the fault, such as the first half-wave method, the transient direction method, the transient zero-mode current polarity method, etc. Through these methods, the lines with small current grounding faults can be selected, but the section where the fault point is located still needs to be detected to further shorten the time for fault isolation or search and repair.

[0004] When performing fault detection and identification, due to the fact that many sites are undergoing renovation, the PT has been put into operation and the PT cabinet cannot be pulled out for viewing. It is also impossible to distinguish the polarity of the zero-sequence PT through other effective means. The zero-sequence CT has a separate tap. Although the polarity can be measured through traditional polarity detection methods, if the PT polarity is reversed at this time, the traditional transient zero-mode polarity method will misjudge the direction because it relies on voltage. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for locating a small current grounding fault that is independent of voltage polarity, thereby solving the technical problem that after selecting a line for a small current grounding fault, the specific fault section cannot be located.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for locating a small current ground fault that is independent of voltage polarity, including all devices using high-speed sampling and performing fault detection in real time based on high-speed sampling data;

[0008] After all devices have synchronized data through the ping-pong principle, the moment when the fault detection and judgment conditions are first detected is taken as the fault moment, recorded as t=0ms; and the zero-sequence current sampling value of t=0ms is time-stamped and transmitted to the opposite side for transient zero-mode current correlation coefficient judgment to determine the fault location.

[0009] Preferably, all of the devices use optical fiber communication.

[0010] Preferably, the transient zero-mode current correlation coefficient determination is to perform correlation determination on the current values ​​at the moment when a sudden voltage change occurs on both sides of the line.

[0011] Preferably, when determining the transient zero-mode current correlation coefficient, the method specifically includes: when the transient zero-mode current correlation coefficient is determined to be positively correlated, selecting that the fault is on the trunk line between the two switch stations, and removing the fault;

[0012] When the transient zero-mode current correlation coefficient is judged to be negatively correlated, it indicates that the fault is outside the zone.

[0013] A small current grounding fault location system that does not rely on voltage polarity includes establishing a distribution line in a small current grounding distribution network. The distribution line is provided with multiple devices, and the devices divide the distribution line into several line sections.

[0014] Preferably, the device is a distribution transformer terminal.

[0015] The method and system for locating a small current grounding fault that is independent of voltage polarity described in the present invention solves the technical problem that after selecting a line for a small current grounding fault, the specific fault section cannot be located. The present invention does not rely on voltage information on both sides, and can identify the fault area inside and outside the area only through the correlation of the current after synchronization, thereby eliminating the incident of misjudgment of direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of the system architecture of the present invention;

[0017] Figure 2 It is an equivalent network diagram of the transient zero-mode current distribution characteristics of the present invention;

[0018] Figure 3 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Embodiment 1:

[0021] Depend on Figure 1-Figure 3 A method for locating a small current ground fault that is independent of voltage polarity is shown, including all devices using high-speed sampling and performing fault detection in real time based on high-speed sampling data;

[0022] After all devices have synchronized data through the ping-pong principle, the moment when the fault detection and judgment conditions are first detected is taken as the fault moment, recorded as t=0ms; and the zero-sequence current sampling value of t=0ms is time-stamped and transmitted to the opposite side for transient zero-mode current correlation coefficient judgment to determine the fault location.

[0023] Preferably, all of the devices use optical fiber communication.

[0024] Preferably, the transient zero-mode current correlation coefficient determination is to perform correlation determination on the current values ​​at the moment when a sudden voltage change occurs on both sides of the line.

[0025] Preferably, when determining the transient zero-mode current correlation coefficient, the method specifically includes: when the transient zero-mode current correlation coefficient is determined to be positively correlated, selecting that the fault is on the trunk line between the two switch stations, and removing the fault;

[0026] When the transient zero-mode current correlation coefficient is judged to be negatively correlated, it indicates that the fault is outside the zone.

[0027] like Figure 3 The flowchart of this embodiment is shown, which specifically includes:

[0028] Step 1: The optical fibers on both sides use the ping-pong principle to calculate the data difference between the two transmitted data, and synchronize the data based on this time difference (that is, when performing calculations, the data on both sides are at the same time);

[0029] Step 2: Set the device to use a higher sampling rate, mainly for detecting the time when the fault occurs; for example, a high sampling rate of 12000Hz, that is, 240 sampling points per cycle. The device compares the zero-sequence voltage data sampled at high speed, and compares the difference between the sampling point at a certain moment and the value at the same moment of the previous cycle (240 points ago). When the voltage change is greater than the preset change threshold, it is determined that the system is abnormal, the protection device starts the device, and records the start time of the fault as t=0ms;

[0030] Step 3: After high-speed sampling, the zero-sequence current value is quickly transmitted to the opposite side. Within 2ms from the moment of zero-sequence voltage mutation, the transient zero-mode current correlation is judged, and the transient zero-mode current correlation coefficient of line m is defined as:

[0031]

[0032] Where i is the current value, t is the time, M and N represent the M side and N side respectively. If D m <0, it means the current is negatively correlated. If D m >0, it means the current is positively correlated;

[0033] Step 4: After 2ms, obtain the judgment results of the devices on both sides. If the transient zero-mode current correlation coefficient is less than 0, it means that the two currents are negatively correlated, and the fault point is not between the two switch stations; if the transient zero-mode current correlation coefficient is greater than 0, it means that the fault point is between the two terminals.

[0034] Embodiment 2:

[0035] like Figure 1 and Figure 2 As shown, a small current grounding fault location system that is independent of voltage polarity described in Example 2 is matched with a small current grounding fault location method that is independent of voltage polarity described in Example 1, including establishing a distribution line in a small current grounding distribution network, wherein a plurality of devices are arranged in the distribution line, and the devices divide the distribution line into a plurality of line sections.

[0036] Preferably, the device is a distribution transformer terminal. In this embodiment, the distribution transformer terminal is a switch station.

[0037] like Figure 1 In the present embodiment, a distribution line in a small current grounding distribution network is taken as an example. The line section is composed of multiple distribution transformer terminals (switch stations), which are divided into 5 sections, namely L1, L2, L3, L4, and L5. On the line section L3, a single-phase grounding fault occurs at the K1 point between the switch station 2 and the switch station 3, and the following is obtained: Figure 2 The equivalent network diagram of the transient zero-mode current distribution characteristics on the line shown.

[0038] exist Figure 2 In the equivalent diagram shown, each line section is equivalent to a circuit composed of a series inductor and a parallel capacitor. The direction of the transient zero-mode current of the fault point auxiliary switches Z04 and Z05 is to flow into the bus (switch station), and the direction of the transient zero-mode current of the fault point auxiliary switches Z03 and Z05 is to flow out of the bus (switch station). Therefore, by determining the correlation between the transient zero-mode currents of the two adjacent switches, the section where the fault point is located can be located.

[0039] The method and system for locating a small current grounding fault that is independent of voltage polarity described in the present invention solves the technical problem that after selecting a line for a small current grounding fault, the specific fault section cannot be located. The present invention does not rely on voltage information on both sides, and can identify the fault area inside and outside the area only through the correlation of the current after synchronization, thereby eliminating the incident of misjudgment of direction.

[0040] In the present invention, any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code including one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention belong.

[0041] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute the instructions, or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus or in combination with these instruction execution systems, devices or apparatuses. A more specific example non-exhaustive list of computer-readable media includes the following: an electronic device with one or more wiring electrical connections, a portable computer disk cartridge magnetic device, a random access memory RAM, a read-only memory ROM, an erasable and programmable read-only memory EPROM or flash memory, an optical fiber device, and a portable compact disk read-only memory CDROM. In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0042] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array PGA, a field programmable gate array FPGA, etc.

[0043] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0044] In addition, each functional unit in each embodiment of the present invention may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0045] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for locating a small current ground fault that is independent of voltage polarity, characterized in that: Including all equipment adopting high-speed sampling and real-time fault detection based on high-speed sampling data; After all devices have synchronized data through the ping-pong principle, the time when the fault detection and judgment conditions are first detected is taken as the fault time, which is recorded as t = 0ms; The zero-sequence current sampling value at t=0ms is time-stamped and transmitted to the opposite side to identify the transient zero-mode current correlation coefficient and determine the fault location, including: Step 1: The optical fibers on both sides use the ping-pong principle to calculate the data difference between the two transmitted data, and synchronize the data based on this time difference, that is, when performing calculations, the data on both sides are at the same time; Step 2: Set the device to use a high sampling rate, mainly used to detect the time when the fault occurs; the high sampling rate is 12000Hz, that is, 240 sampling points per cycle; the device compares the zero-sequence voltage data sampled at high speed, and compares the difference between the sampling point at a certain moment and the value at the same moment of the previous cycle. When the voltage change is greater than the preset change threshold, it is determined that the system is abnormal, the protection device starts the device, and records the start time of the fault as t=0ms; Step 3: After high-speed sampling, the zero-sequence current value is quickly transmitted to the opposite side. Within 2ms from the moment of zero-sequence voltage mutation, the transient zero-mode current correlation is judged, and the transient zero-mode current correlation coefficient of line m is defined as: Where i is the current value, t is the time, M and n represent the M side and the n side respectively. If D m <0, it means the current is negatively correlated. If D m >0, it means the current is positively correlated; Step 4: when determining the transient zero-mode current correlation coefficient, specifically including: when the transient zero-mode current correlation coefficient is determined to be positively correlated, selecting that the fault is on the trunk line between the two switch stations, and removing the fault; When the transient zero-mode current correlation coefficient is judged to be negatively correlated, it indicates that the fault is outside the zone, as follows: After 2ms, the judgment results of the devices on both sides are obtained. If the transient zero-mode current correlation coefficient is less than 0, it means that the two currents are negatively correlated, and the fault point is not between the two switch stations; if the transient zero-mode current correlation coefficient is greater than 0, it means that the fault point is between the two terminals.

2. A method for locating a small current ground fault that is independent of voltage polarity as claimed in claim 1, characterized in that: All the devices described use optical fiber communications.

3. A method for locating a small current ground fault that is independent of voltage polarity as claimed in claim 1, characterized in that: The transient zero-mode current correlation coefficient determination is to perform correlation determination on the current values ​​at the moment when voltage mutation occurs on both sides of the line.

4. A small current grounding fault location system that is independent of voltage polarity, applied to a small current grounding fault location method that is independent of voltage polarity as claimed in any one of claims 1 to 3, characterized in that: The method includes establishing a distribution line in a small current grounding distribution network, wherein a plurality of devices are arranged in the distribution line, and the devices divide the distribution line into a plurality of line sections.

5. A low current ground fault location system independent of voltage polarity as claimed in claim 4, characterized in that: The device is a distribution transformer terminal.

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