A differential grounding fault detection method and device based on external signal method

Abstract

The present invention discloses a differential grounding fault detection method and device based on an externally applied signal method, applies the differential protection method to the externally applied signal grounding line selection technology, forms a switch action strategy by detecting an externally applied characteristic current waveform sequence, and completes the local isolation of the grounding fault. Compared with the traditional externally applied signal method, it effectively eliminates the risk of all switches upstream of the fault point tripping at the same time when a fault occurs, can quickly cut off the grounding fault and significantly reduce the scope of the fault power outage, and synchronously pushes the fault information to the handheld mobile terminal of the on-site operator through the distribution monitoring system, accurately guiding the on-site operator to complete the grounding fault repair, significantly improving the fault repair efficiency, shortening the fault power outage time, and improving the power supply reliability of the distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of ground fault detection, and in particular relates to a differential ground fault detection method and device based on an externally applied signal method. Background Art

[0002] At present, most of the distribution networks in China adopt the neutral point indirect grounding system, and some areas adopt the neutral point indirect grounding method. When a single-phase grounding fault occurs in this type of system, the fault current is small and the fault characteristics are complex. It is difficult to effectively complete the detection, positioning and search of the grounding fault point using traditional methods, which seriously restricts the efficiency of grounding fault handling. Therefore, it is necessary to use various new technologies and methods to complete the detection and positioning of grounding faults in the neutral point indirect grounding system, so as to improve the efficiency of grounding fault handling and power supply reliability.

[0003] At present, the external signal method is used for ground fault monitoring. The external signal method can make the fault line flow with obvious characteristic current signals for fault detection device to detect, and the detection method is not affected by the system operation mode, topology structure, neutral point grounding mode, and has high fault judgment accuracy. It has great application advantages in the system where the neutral point is not directly grounded. However, the current external signal method. When a single-phase grounding fault occurs in the line, the grounded relative ground voltage decreases, the non-grounded relative ground voltage increases, and the zero-sequence voltage increases; after the asymmetric current source detects that the line has grounding characteristics, it controls the high-voltage contactor to generate a characteristic signal on the fault line. After the fault indicator installed on the line detects the characteristic signal, it flips the card and flashes the light on the spot to give an alarm, thereby realizing fault line selection and fault point location. The current external signal method cannot locate more accurately and cannot cut off the fault point in time. When a grounding fault occurs, all switches upstream of the fault point have the risk of tripping at the same time, which will cause a large-scale power outage. Summary of the invention

[0004] (1) Technical issues to be resolved

[0005] In view of the problem that the existing external signal method cannot locate more accurately and cannot cut off the fault point in time, and when a ground fault occurs, all switches upstream of the fault point trip simultaneously, causing a large-scale power outage, the present invention provides a differential ground fault detection method and device based on the external signal method to solve the above problems.

[0006] (2) The technical solution adopted by the present invention is as follows:

[0007] A differential grounding fault detection method based on an externally applied signal method includes: when a grounding fault occurs in a line, a characteristic current waveform sequence is formed after an external signal is applied on the line, the characteristic current waveforms of switches at various positions of the line are detected, and the tripping conditions of the switches at various positions on the line are set, wherein the switch tripping conditions are: the switches at various positions correspond to different numbers of characteristic current waveforms, the number of waveforms of the characteristic current waveform sequence of the externally applied signal includes the number of characteristic current waveforms corresponding to the switches at various positions, and if it is detected that the number of waveforms of one of the switches is the same as the number of waveforms of the characteristic current waveform sequence of the externally applied signal, then the line controlled by the switch at that position has a grounding fault, and the switch at that position is controlled to be tripped.

[0008] A further technical solution is that each position switch includes a main line section switch FS1 to FSN, the first branch switches downstream of each main line section switch FS2-1 to FSN-1 and the first boundary switch downstream of each branch switch YS3-YSN, wherein there is no first downstream branch switch after the main line section switch at the end, and there is no first downstream boundary switch after the first downstream branch switch at the end, and the opening condition of the main line section switch is set as follows: the number of characteristic current waveforms is N, the opening condition of the first branch switch downstream of each main line section switch is set as follows: the number of characteristic current waveforms is N-1, and the opening condition of the first boundary switch downstream of each branch switch is set as follows: the number of characteristic current waveforms is N-2.

[0009] A further technical solution is that the number of waveforms in the characteristic current waveform sequence of the line external signal is formed in sequence according to the waveforms corresponding to the line main line segmentation switches from far to near the line external signal source, and the direction of the line main line segmentation switches from far to near is from FS1 to FSN.

[0010] A differential ground fault detection device based on an externally applied signal method used in the above method comprises an externally applied characteristic signal generating device and a line state monitoring and control device. The externally applied characteristic signal generating device is connected to the line for ground fault detection, and after the externally applied characteristic signal generating device detects a ground fault, it can form an externally applied characteristic current signal waveform between the grounding point of the externally applied characteristic signal generating device, the line fault phase, the non-fault phase, and the fault grounding point; each position switch is connected to a line state monitoring and control device, and the line state monitoring and control device comprises a voltage and current sampling board, a main control board, and a power supply module. The voltage and current sampling board is connected to the switch and the main control board, the main control board is connected to the switch, and the power supply module is connected to the voltage and current sampling board and the main control board.

[0011] A further technical solution is that the external characteristic signal generating device includes a voltage sensor, a high-voltage AC contactor, a grounding resistor, a current transformer and a signal control device. The voltage sensor connection line is connected to the signal control device. The voltage sensor is connected to the load end of the high-voltage AC contactor, the grounding resistor and the current transformer in sequence and then to ground. The signal control device is connected to the control end of the high-voltage AC contactor.

[0012] A further technical solution is that the main control board is connected to the first communication module, the signal control device is connected to the second communication module, the first communication module and the second communication module are both connected to the power distribution monitoring system, the power distribution monitoring system is connected to the mobile terminal via the 4G / 5G module, and the power distribution monitoring system pushes the fault information to the mobile terminal, and completes fault detection, positioning and repair according to the fault information on the mobile terminal.

[0013] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0014] 1. The differential protection method is applied to the external signal grounding line selection technology. By detecting the external characteristic current waveform sequence, a switch action strategy is formed to complete the local isolation of the grounding fault. Compared with the traditional external signal method, it effectively eliminates the risk of all switches upstream of the fault point tripping at the same time when a fault occurs, and can quickly cut off the grounding fault and significantly reduce the scope of the fault power outage.

[0015] 2. The power distribution monitoring system will synchronously push the fault information to the handheld mobile terminal of the on-site workers, accurately guide the on-site workers to complete the emergency repair of the grounding fault, significantly improve the fault repair efficiency, shorten the fault power outage time, and improve the power supply reliability of the distribution network.

[0016] 3. By setting the opening conditions of the switches at each position on the line, the switch opening conditions are: the switches at each position correspond to different numbers of characteristic current waveforms, and the number of waveforms of the characteristic current waveform sequence of the external signal includes the number of characteristic current waveforms corresponding to the switches at each position. If it is detected that the number of waveforms of one of the switches is the same as the number of waveforms of the characteristic current waveform sequence of the external signal, then the switch at that position is opened. In this way, the location of the grounding fault can be determined more accurately and the switch of the grounding fault line can be cut off in time to avoid affecting the power supply of the upstream line. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The externally applied characteristic current sequence waveform of the present invention;

[0018] Figure 2 The technical solution for matching the number of characteristic current waveforms of all switches in the circuit of the present invention;

[0019] Figure 3It is a connection relationship diagram of various components of a differential type ground fault detection device based on an external signal method of the present invention;

[0020] Figure 4 A schematic diagram of the connection relationship of the signal control device of the present invention;

[0021] Figure 5 The figure is a schematic diagram of the connection relationship of the main control board of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0023] like Figure 1-Figure 5 A differential ground fault detection method based on an externally applied signal method includes: when a ground fault occurs in a line, a characteristic current waveform sequence is formed after an external signal is applied on the line, the characteristic current waveform of each position switch of the line is detected, and the opening condition of each position switch on the line is set, and the switch opening condition is: each position switch corresponds to a different number of characteristic current waveforms, and the number of waveforms of the characteristic current waveform sequence of the externally applied signal includes the number of characteristic current waveforms corresponding to each position switch. If it is detected that the number of waveforms of one of the switches is the same as the number of waveforms of the characteristic current waveform sequence of the externally applied signal, then the line controlled by the switch at that position has a ground fault, and the switch at that position is controlled to open.

[0024] Each position switch includes the main line section switches FS1 to FSN, the first branch switches downstream of each main line section switch FS2-1 to FSN-1 and the first boundary switch downstream of each branch switch YS3-YSN, among which there is no first downstream branch switch after the main line section switch at the end, and there is no first downstream boundary switch after the first downstream branch switch at the end. The opening condition of the main line section switch is set as follows: the number of characteristic current waveforms is N, the opening condition of the first branch switch downstream of each main line section switch is set as follows: the number of characteristic current waveforms is N-1, and the opening condition of the first boundary switch downstream of each branch switch is set as follows: the number of characteristic current waveforms is N-2.

[0025] like Figure 1 , 2As shown: if a single-phase grounding fault occurs at the branch head switch FS2-1, the external signal generating device 1 detects the grounding fault, and the high-voltage contactor inside the device is switched to generate a characteristic current waveform sequence. At this time, FS2, FS3, ..., FSN-1, and FSN upstream of the fault point can all detect the characteristic current waveform synchronously. When the number of characteristic current waveforms detected by FS2-1, FS2, FS3, ..., FSN-1, and FSN is 1, FS2-1 trips, and FS2, FS3, ..., FSN-1, and FSN upstream of FS2-1 do not trip because the number of waveforms detected has not reached their respective tripping conditions, thereby achieving local isolation of the fault area. If this method is not used, FS2-1, FS2, FS3, ..., FSN-1, and FSN will trip at the same time, the entire line will be out of power, and the fault outage area will be significantly expanded.

[0026] If a single-phase grounding fault occurs at the first boundary switch YSN downstream of each branch switch, the external signal generating device 1 detects the grounding fault, and the high-voltage contactor inside the device is switched to generate a characteristic current waveform sequence. At this time, the YSN, FSN-1, and FSN upstream of the fault point can all detect the characteristic current waveform synchronously. When the number of characteristic current waveforms detected by YSN, FSN-1, and FSN is N-2, YSN trips, and FSN-1 and FSN upstream of YSN do not trip because the number of waveforms detected has not reached the tripping condition, thereby achieving the nearest isolation of the fault area. If this method is not used, YSN, FSN-1, and FSN will trip at the same time, and the fault power outage area will be significantly expanded. The farther the fault point is from the power supply point, the larger the power outage area.

[0027] The number of waveforms of the characteristic current waveform sequence of the line external signal is formed in sequence according to the waveforms corresponding to the line main line segmentation switches from far to near from the line external signal source, and the direction of the line main line segmentation switches from far to near is from FS1 to FSN. This is conducive to quickly finding and cutting the grounding fault line.

[0028] A differential ground fault detection device based on an externally applied signal method used in the above method comprises an externally applied characteristic signal generating device and a line state monitoring and control device 2, wherein the externally applied characteristic signal generating device is connected to the line for ground fault detection, and after the externally applied characteristic signal generating device detects a ground fault, it can form an externally applied characteristic current signal waveform between the grounding point of the externally applied characteristic signal generating device, the line fault phase, the non-fault phase, and the fault grounding point; each position switch is connected to a line state monitoring and control device 2, and the line state monitoring and control device 2 comprises a voltage and current sampling board 21, a main control board 22, and a power supply module 23, wherein the voltage and current sampling board 21 is connected to the switch and the main control board 22, the main control board 22 is connected to the switch, and the power supply module 23 is connected to the voltage and current sampling board 21 and the main control board 22.

[0029] When in use, the voltage and current sampling board 21 is connected to the switch on the 10kV line pole through the aviation plug; the voltage and current sampling board 21 is connected to the main control board 22, and can collect the line voltage and current values ​​and transmit them to the main control board 22; the main control board 22 can analyze and monitor the line voltage, current and switch operation status, and the main control board 22 is connected to the line switch to control the switch opening and closing to achieve automatic fault removal; the power module 23 provides a 24V stable DC voltage for the entire device. When the line switch flows through the characteristic current, the characteristic current is converted into a secondary side small current signal through the current transformer inside the switch, and the small current signal enters the voltage and current sampling board 21 through the switch body current aviation plug line. The voltage and current sampling board 21 can process the small current signal into a digital signal, and transmit the digital signal to the main control board 22 through the FC serial data line. After the main control board 22 converts and analyzes the digital signal, it can send a control opening signal, and through the control aviation plug line, control the internal opening circuit of the switch to achieve the opening of the switch. The voltage and current sampling board 21 and the main control board 22 are both existing technologies. The main control board 22 includes an analysis and monitoring module, which is connected to a communication module interface, a power interface, a remote signal / remote control interface, a current sampling circuit and interface, and a voltage sampling circuit and interface.

[0030] The external characteristic signal generating device includes a voltage sensor 11, a high-voltage AC contactor 12, a grounding resistor 14, a current transformer 15 and a signal control device 13. The voltage sensor 11 connects the circuit and the signal control device 13. The voltage sensor 11 is connected to the load end of the high-voltage AC contactor 12, the grounding resistor 14 and the current transformer 15 in sequence and then grounded. The signal control device 13 is connected to the control end of the high-voltage AC contactor 12. The voltage sensor 11 can convert the primary side voltage of the 10kV distribution network line into a low voltage for detection by the signal control device 13; the signal control device 13 includes a core control board, a relay driver board, a power module, and a time relay. The core control board is connected to the relay driver board, the relay driver board is connected to the time relay and the bottom plate, the time relay is connected to the high-voltage AC contactor 12, the bottom plate is connected to the voltage sensor 11, and the power module supplies power to the signal control device 13 as a whole. The signal control device 13 is connected to the primary side of the 10kV distribution network line via the voltage sensor 11. The signal control device 13 has a ground fault detection function; the high-voltage AC contactor 12 is controlled by the signal control device 13. When a ground fault occurs in the line, the signal control device 13 detects the ground signal and controls the high-voltage AC contactor 12 to switch regularly, and forms an external characteristic current signal waveform between the grounding point of the external signal device, the line fault phase, the non-fault phase, and the fault grounding point; the grounding resistor 14 is located between the contactor and the grounding point, which can further limit the grounding current and ensure the stable operation of the external signal generating device 1; the current transformer 15 can detect the pulse current flowing through the external signal generating device 1,

[0031] The main control board 22 is connected to the first communication module 24, and the first communication module 24 is connected to the communication module interface of the main control board 22. The first wireless communication module has two RS232 serial ports and multiple Ethernet ports, and has two SIM cards installed inside, which can realize wireless 4G / 5G communication and has dual-card dual-transmission and dual-reception functions. It can receive various event information from the main control board 22 and send all the information to the power distribution monitoring system 3. The signal control device 13 is connected to the second communication module 16. The second communication module 16 has wireless 4G / 5G / WIFI communication function and can be connected to the power distribution monitoring system 3 to realize real-time online monitoring of the external signal generating device 1. The first communication module 24 and the second communication module 16 are both connected to the power distribution monitoring system 3. The power distribution monitoring system 3 is connected to the mobile terminal 4 through the 4G / 5G module. The power distribution monitoring system 3 pushes the fault information to the mobile terminal 4, and completes the fault finding, positioning and repair according to the fault information on the mobile terminal 4. The first communication module 24 and the second communication module are equipped with SIM cards, and the power distribution monitoring system 3 is equipped with a SIM card. The power distribution monitoring system 3 communicates with the first communication module and the second communication module 16 via the SIM cards in a 4G / 5G manner.

[0032] The power distribution monitoring system 3 includes 2 front-end servers, 2 database servers, 7 application servers, 1 astronomical clock, 1 maintenance workstation and a power distribution encryption device, which has a built-in SIM card and a human-computer interaction interface. It is connected to the external signal generating device 1 and the status monitoring and control device 2 through wireless 4G / 5G communication. It can monitor the operating status of the external signal generating device 1 and the status monitoring and control device 2 in real time, and receive various fault information sent by the status monitoring and control device 2. The mobile terminal 4 includes various micro-application modules and supports receiving various fault information pushed by the power distribution monitoring system 3 through 4G / 5G and other methods. The power distribution monitoring system 3 can realize on-site 10kV line model maintenance and display the on-site model on the human-computer interaction interface. The line model includes the line name, switch position and name, and the installation position of the external signal generating device; the external signal generating device 1 transmits the device online status and voltage and current data information to the power distribution monitoring system 3 in real time through the second communication module 16, and displays it in real time on the line model, thereby realizing real-time online monitoring of the operating status of the external signal generating device 1; the status monitoring and control device 2 transmits the device online status, the voltage, current, power and other electrical quantities of the switch, and the opening and closing information of the switch to the power distribution monitoring system 3 through the first communication module 24, and displays it in real time on the line model, thereby realizing real-time online monitoring of the operating status of the status monitoring and control device 2 and the line switch.

[0033] The present invention performs the following steps when used:

[0034] (1) The external signal generating device 1 is installed at the feeder position of the 10kV distribution network overhead line;

[0035] (2) The status monitoring and control device 2 is installed to each section, branch, and boundary connection switch of the overhead line through an aerial plug;

[0036] (3) When a ground fault occurs in the line, the contactor inside the external signal generating device 1 is switched on and off to form a characteristic current waveform sequence;

[0037] (4) The line status monitoring and control device 2 detects the characteristic sequence, forms an action strategy and controls the corresponding switches to open according to the coordination scheme of the upper and lower levels of each section, branch, and boundary switch, and removes the fault nearby;

[0038] (5) The line status monitoring and control device 2 sends the line fault information and switch action information to the power distribution monitoring system 3 (3);

[0039] (6) The power distribution monitoring system 3 pushes the fault information to the operator's handheld mobile terminal 4 (4) via wireless 4G / 5G;

[0040] (7) On-site operators complete fault finding, positioning and repair based on the fault information from mobile terminal 4.

[0041] When a ground fault occurs in the line, the signal generating device detects the grounding signal and controls the high-voltage AC contactor 12 inside the device to switch on and off, forming a characteristic current sequence waveform. The line status monitoring and control device 2 connected to the line main line section switch, branch switch, and first branch boundary switch (user switch) can detect the characteristic current waveform and, depending on the number of characteristic waves, act on the corresponding switch to alarm or trip, thereby achieving upper and lower level coordination of the ground fault and completing on-site isolation of the fault area.

[0042] The above are only preferred embodiments of the present invention.

Claims

1. A differential ground fault detection method based on an external signal method, characterized in that: It includes forming a characteristic current waveform sequence after applying a signal on the line when a ground fault occurs in the line, detecting the characteristic current waveforms of switches at various positions of the line, and setting the tripping conditions of switches at various positions on the line. The switch tripping conditions are: switches at various positions correspond to different numbers of characteristic current waveforms, and the number of waveforms of the characteristic current waveform sequence of the externally applied signal includes the number of characteristic current waveforms corresponding to switches at various positions. If it is detected that the number of waveforms of one of the switches is the same as the number of waveforms of the characteristic current waveform sequence of the externally applied signal, then the line controlled by the switch at that position has a ground fault, and the switch at that position is controlled to trip. The switches at each position include the line main line section switches FS1 to FSN, the first branch switches FS2-1 to FSN-1 downstream of each section switch of the main line, and The first downstream boundary switch of each branch switch is YS3-YSN, among which there is no first downstream branch switch after the main line section switch at the end, and there is no first downstream boundary switch after the first downstream branch switch at the end. The opening condition of the main line section switch is set as follows: the number of characteristic current waveforms is N, the opening condition of the first branch switch downstream of each section switch of the main line is set as follows: the number of characteristic current waveforms is N-1, and the opening condition of the first downstream boundary switch of each branch switch is set as follows: the number of characteristic current waveforms is N-2. The number of waveforms of the characteristic current waveform sequence of the line external signal is formed in sequence according to the waveforms corresponding to the line main line section switches from far to near from the source of the line external signal, and the direction of the line main line section switches from far to near is from FS1 to FSN.

2. A differential ground fault detection device based on an external signal method used in the method of claim 1, characterized in that: The invention comprises an external characteristic signal generating device and a line state monitoring and control device (2), wherein the external characteristic signal generating device is connected to the line and is used for ground fault detection, and after the external characteristic signal generating device detects a ground fault, it can form an external characteristic current signal waveform between the ground point of the external characteristic signal generating device, the line fault phase, the non-fault phase, and the fault ground point; each position switch is connected to a line state monitoring and control device (2), and the line state monitoring and control device (2) comprises a voltage and current sampling board (21), a main control board (22), and a power module (23); the voltage and current sampling board (21) is connected to the switch and the main control board (22), the main control board (22) is connected to the switch, and the power module (23) is connected to the voltage and current sampling board (21) and the main control board (22).

3. The differential ground fault detection device based on the external signal method according to claim 2 is characterized in that: The externally applied characteristic signal generating device comprises a voltage sensor (11), a high-voltage AC contactor (12), a grounding resistor (14), a current transformer (15) and a signal control device (13); the voltage sensor (11) is connected to a line and the signal control device (13); the voltage sensor (11) is connected to a load end of the high-voltage AC contactor (12), a grounding resistor (14) and a current transformer (15) in sequence and then grounded; and the signal control device (13) is connected to a control end of the high-voltage AC contactor (12).

4. The differential ground fault detection device based on the external signal method according to claim 3 is characterized in that: The main control board (22) is connected to a first communication module, the signal control device (13) is connected to a second communication module, the first communication module and the second communication module are both connected to a power distribution monitoring system (3), the power distribution monitoring system (3) is connected to a mobile terminal (4) via a 4G / 5G module, the power distribution monitoring system (3) pushes fault information to the mobile terminal (4), and completes fault finding, positioning and repair based on the fault information on the mobile terminal (4).

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