WO2021103662A1

WO2021103662A1 - Method for positioning fault in flexible dc distribution network

Info

Publication number: WO2021103662A1
Application number: PCT/CN2020/109238
Authority: WO
Inventors: 吴通华; 姚刚; 王小红; 郑玉平; 洪丰; 戴魏; 李新东; 陈国洲; 江源; 郑小江; 侯小凡; 胡子龙; 郑坤承
Original assignee: 国电南瑞科技股份有限公司; 国电南瑞南京控制系统有限公司; 南瑞集团有限公司
Priority date: 2019-11-29
Filing date: 2020-08-14
Publication date: 2021-06-03
Also published as: CN110927523A

Abstract

Provided is a method for positioning a fault in a flexible DC distribution network, comprising the steps of arranging a DC bus protection area and a DC line protection area in the DC distribution network, wherein switches in the DC bus protection area and the DC line protection area are all provided with protection devices, and all of the protection devices are connected through a high-speed communication network; when the differential protection is normal, the differential protection is used for fault positioning, when the differential protection is withdrawn, a multi-point direction-based comprehensive fault positioning method is used for fault positioning; solving the problem of long delay in action of networked protection applied to the DC distribution network; solving the problem that the DC distribution network loses backup protection when the differential protection fails to work due to abnormallity thereof; and solving the problem that the overcurrent start-up sensitivity of the DC distribution network and the ease of setting and coordination cannot be possessed at the same time.

Description

A fault location method for flexible DC distribution network

Technical field

The invention relates to a method for locating faults in a flexible direct current distribution network, and belongs to the technical field of power system protection and control.

Background technique

With the emergence of voltage source converters, flexible DC transmission technology based on modular multilevel converters (MMC) has developed rapidly. At the same time, with the massive access of DC loads and distributed new energy sources, the current distribution network source-load-storage DC characteristics are becoming more and more prominent. Flexible DC power distribution provides a flexible, efficient and environmentally friendly way of power distribution and does not require auxiliary equipment such as filters and reactive power compensation.

The development of the DC distribution network is still facing several key technical problems to be solved urgently, including the rapid and reliable location and isolation of the DC fault section. In the DC distribution system, the damping value of the DC line is very small. Once a fault occurs in the DC field, all DC lines will quickly overcurrent. It is difficult to achieve fault selectivity through the traditional level difference coordination of fault currents at different locations; and due to the fragility of the power electronic devices that constitute the DC power supply, the protection of the DC distribution network requires fault location and isolation within a few milliseconds, and the location and The technical level of isolation puts forward extremely high requirements.

The protection of the DC distribution network is an inevitable action when the DC distribution network fails. How to coordinate protection and fault location is also an urgent problem to be solved. When the DC distribution network fails, there will be one failure and multiple protection installation points. Overcurrent may cause protections at multiple installation points to operate, which is unfavorable for fault location and narrowing the scope of power outages.

The existing methods for locating faults in DC distribution networks still have the following limitations:

The fault current of the DC distribution network exhibits rapid amplitude changes, and the protection circuit of the power electronic components itself operates faster, making the fault duration shorter, and the characteristics are completely different from that of the AC power grid. The technical method of achieving fault branch location through multi-layer delay coordination may cause the delay action to fail to meet the conditions when the fault current disappears, making the action fail and the fault location cannot be located.

It is applied to the busbar differential protection and line optical fiber differential protection of DC distribution network. It has absolute selectivity for the faults in their respective areas. When the differential protection works normally, it has the characteristics of simple principle, reliable action and fast speed for fault location. . However, there is no corresponding backup protection measure for the situation that the differential protection exits due to sampling abnormality, fiber channel abnormality or other abnormalities.

The existing networked protection technology scheme of distribution network starts the fault current direction judgment only when the collected current is greater than the set over-current threshold. This set value must take into account that any fault can be effectively identified to ensure sensitivity , It is necessary to avoid the load fluctuation that may occur during normal operation or the overcurrent generated by the load current under heavy load conditions, which makes it difficult to set the value.

Summary of the invention

Purpose: In order to solve the problem of locating faults in flexible DC distribution networks, the present invention provides a method for locating faults in flexible DC distribution networks.

Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention is:

A method for locating faults in a flexible DC distribution network, which is characterized in that it includes the following steps:

Set up DC bus protection area and DC line protection area in the DC distribution network, and set protection devices in the switches in the DC bus protection area and DC line protection area, and all protection devices are connected through the high-speed communication network;

The protection device in the DC busbar protection zone adopts busbar differential protection for fault location;

The protection devices on both sides of each line in the DC line protection zone are connected by optical fibers, and optical fiber differential protection is used to locate faults;

When the bus differential protection in the DC bus protection zone exits, and the protection device detects that the current change is greater than the set threshold or the current value is greater than the set threshold, the DC bus protection zone is seamlessly switched to the DC bus based multiple Comprehensive fault location method in point direction;

When the optical fiber differential protection in the DC line protection zone exits, and the protection device detects that the current change is greater than the set threshold or the current value is greater than the set threshold, the DC line protection zone is seamlessly switched to the DC line based multi-channel protection. Comprehensive fault location method in point direction.

As a preferred solution, the DC bus protection zone includes an outgoing bus of a converter station, a switch directly connected to the outgoing bus of the converter station and/or a switch directly connected to the outgoing bus to open and close the outgoing bus.

As a preferred solution, the DC line protection zone includes the outlet of the converter station, the switch on the outlet of the converter station and/or the switch on the outlet of the converter station, and the switch on the outlet of the converter.

As a preferred solution, the protection device is used to detect the current flowing through the switch, and mark the direction of the current flowing from the bus to the line as the positive direction, and the direction of the current flowing from the line to the bus as the reverse direction.

As a preferred solution, the operating criterion conditions of the optical fiber differential protection are as follows:

Where:

Are the instantaneous current values of the protection devices on both sides of the DC line; I _set is the differential current threshold value,

Is the braking current value, and k _set is the braking coefficient.

As a preferred solution, the operating criterion conditions of the busbar differential protection are as follows:

Among them, I _dpj and I _dnj are the positive and negative currents of the j-th connecting branch of the bus, respectively; I _resn = max(|I _dnj |), j = 1...m, I _resp = max(|I _dpj |), j = 1...m, m represents the total number of connected branches; I _set is the threshold value of the differential current, and k _set is the braking coefficient.

As a preferred solution, when the optical fiber channel of the protection device in the DC line protection zone experiences bit error, frame loss, interruption, or sampling abnormality occurs, and the current sampling loop is disconnected, the optical fiber differential protection exits.

As a preferred solution, a comprehensive fault location method based on multi-point directions for DC lines includes the following steps:

After a delay, if any line protection device of all outgoing lines connected to the same bus determines that the fault current is in the positive direction, and the current collected by the protection device is greater than the set positive direction current threshold and the protection device on the opposite side of the line It is also determined that the fault current is in the positive direction, and the protection devices on the other outgoing lines determine that the fault current is in the reverse direction, and the outgoing line is determined to be a fault line;

The directional overcurrent protection of this faulty line will act after a delay.

As a preferred solution, when any protection device on the bus in the DC bus protection zone has a sampling abnormality and the current sampling loop is disconnected, the bus differential protection on the bus is withdrawn.

As a preferred solution, it includes the following steps:

After a delay, if all incoming and outgoing protection devices connected to the same busbar determine the direction of the fault current as the reverse direction, and the collected current value is greater than the set reverse direction current threshold, it is determined that the busbar is Fault bus

The action signal is sent by the line protection device of all incoming and outgoing wires connected to the bus.

Beneficial effects: The flexible DC distribution network fault location method provided by the present invention solves the long delay of the networked protection action of the DC distribution network application through the cooperation of the differential and the comprehensive fault location method based on multi-point directions. Problem: Solve the problem that the DC distribution network loses backup protection when the differential protection fails to work abnormally; It solves the problem that the DC distribution network cannot have both the overcurrent start-up sensitivity and the ease of setting and coordination at the same time. Its advantages are as follows:

1. Through the DC bus differential protection and the DC line optical fiber differential protection, the accurate fault location of each branch fault in the protection area is realized. When the differential protection exits due to an abnormality, it will instantly and seamlessly switch to the multi-point directional information protection based on the high-speed communication network to realize fault location. Through the cooperation of the two, the reliability of the protection of the distribution network is improved.

2. On the basis of the current commonly used current amplitude greater than the set value to start and trigger the fault current direction judgment, the start method of the current change greater than the set value is added, which improves the sensitivity of fault judgment and reduces Because the current amplitude is greater than the set value, there is a risk of difficulty in setting.

3. The criterion that the voltage is less than the fault voltage threshold is integrated, the reliability of the current variation algorithm is improved, and the false start caused by load fluctuations and other conditions are avoided.

Description of the drawings

Figure 1 is the structure diagram of the DC distribution grid;

Figure 2 is a schematic diagram of the DC bus protection zone;

Figure 3 is a schematic diagram of the DC line protection zone;

Figure 4 is a schematic diagram of the location of a DC bus fault;

Figure 5 is a schematic diagram of the location of a DC line fault;

Figure 6 is a flow chart of DC line fault location based on multi-point directions;

Figure 7 is a flow chart of DC bus fault location based on multi-point directions;

Figure 8 is a schematic diagram of the location of the bus tie branch fault in the DC bus fault;

Figure 9 is a flow chart of fault location of the bus tie branch based on multi-point directions.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings.

The protection method of a DC distribution network system provided by the present invention includes the following steps:

Step 1: The DC bus of the flexible DC distribution network system and all the protection devices in the DC line protection area are configured according to the DC switch, and all the protection devices are connected to the high-speed communication network; the protection devices in the DC line protection area are not only connected to the high-speed communication network , And the protection devices installed on the switches on both sides of each DC line are also connected through the optical fiber channel to realize the optical fiber differential protection of the line.

Step 2: The protection device in the protection zone detects the current flowing through the switch and judges the direction of the fault current.

Step 3: The optical fiber differential protection on both sides of each DC line in the DC line protection zone performs fault location through the respective optical fiber differential protection under normal working conditions;

Step 4: The protection device configured in the DC bus protection zone adopts bus differential protection. When the bus differential protection works normally, the bus differential current is used to locate the fault;

Step 5: When the optical fiber differential protection of the DC line protection zone exits due to an abnormality, the DC line protection zone is seamlessly switched to the integrated fault location method based on multi-point directions of the DC line;

Step 6: When the busbar differential protection of the DC busbar protection zone exits due to an abnormality, the DC busbar protection zone seamlessly switches to the integrated fault location method based on the multipoint direction of the DC busbar.

Step 7: When the current change is greater than the set threshold or the current value is greater than the set threshold, any one of the two conditions is met, and then the comprehensive fault location method based on the multi-point direction can be triggered.

In the above step 1, the DC bus protection zone includes the outgoing bus of the converter station, the switch directly connected to the outgoing bus of the converter station, and the switch that opens and closes the outgoing bus, and opens and closes the switch that is directly connected to the outgoing bus. The DC line protection zone includes the outlet of the converter station, the switch on the outlet of the converter station, and the switch on the outlet of the switch. The high-speed communication network is a network used for information transmission between the protection devices on the switches in the protection zone. All the protection devices in the DC bus protection zone and the DC line protection zone are connected to the same high-speed communication network to realize the mutual information of the protection devices in the DC distribution network.

In step 2 above, the protection device in the DC line protection zone detects the current and voltage flowing through the switch. The fault current flowing from the bus to the line is marked as the positive direction, and the fault current flowing from the line to the bus is marked as the reverse direction.

In the above step 3, the DC line protection zone adopts optical fiber differential protection on the switches on both sides of each line. Specifically, the protection devices on both sides of each DC line exchange data signals through optical fibers, and perform differential current calculations and differential protection actions. Identify and locate this line.

In the above step 3, the DC line protection zone is equipped with optical fiber differential protection on both sides of each line. Specifically, the differential protection uses a dedicated optical fiber communication channel and runs in parallel with the high-speed communication network used for multi-point directional protection. The dedicated optical communication channel on each DC line only interacts with the data signals collected by the protection devices on the switches on both sides of the line. The operating criteria of the optical fiber differential protection are as follows:

Where:

They are the instantaneous current values of the protection devices on both sides of the line; I _set is the threshold value of the differential current. The setting of this current is mainly due to the current difference caused by some factors unrelated to the braking current, such as transformer stray noise and faults. Line distribution capacitance current at time;

Is the corresponding braking current of each pole; k _set is the braking coefficient.

In the above step 4, the protection device in the DC bus protection zone adopts bus differential protection, which specifically refers to the differential current calculation by collecting the current flowing through all the in and out switches of the bus. When the protection device in the DC bus protection zone is working normally, pass Differential flow to judge whether this bus is faulty. The fault location of the busbar is realized by the action signal of the busbar protection device.

The protection device of the DC busbar protection zone in the above step 4 adopts busbar differential protection, and the operation criterion conditions of the busbar differential protection are as follows:

Among them, I _dpj and I _dnj are the positive and negative currents of the j-th connecting branch of the bus, and the direction of the bus is taken as the positive direction; I _resn = max(|I _dnj |), j = 1...m, I _resp =max(|I _dpj |), j=1...m, m represents the total number of connected branches; I _set is the threshold value of the differential current, and k _set is the braking coefficient.

In the above step 5, the optical fiber differential protection is out of operation due to an abnormality. Specifically, it means that the optical fiber channel of the protection device on the DC line has an error, frame loss, or interruption, or the protection device on either side has a sampling abnormality or the current sampling loop is broken. The optical fiber differential protection is out of operation caused by other abnormal conditions. For a DC line, when the protection device on either side detects the exit of the optical fiber differential protection, the protection devices on both sides of the DC line block the optical fiber differential protection at the same time to avoid the misoperation or refusal of the optical fiber differential protection. The optical fiber differential protection exit signal of the DC line is sent to the protection devices of other DC lines through the high-speed communication network.

In the above step 5, seamless switching to the integrated fault location method based on multi-point direction, specifically refers to the high-speed communication network receiving the optical fiber differential protection exit signal from a line in the DC line protection zone, and confirming it by short-delay reception After the DC line protection zone is switched to a comprehensive fault location method based on multi-point directions.

Specifically, the comprehensive fault location method based on multi-point direction means that when the protection device on the DC line is activated and triggers the judgment of the fault current direction, for all the protection devices in the DC line protection zone, if all the outgoing lines of the same bus are connected The protection device of any line determines that the fault current is in the positive direction, and the current collected by the protection device is greater than the set current threshold value in the positive direction, and the protection device on the opposite side of the line also determines that the fault current is in the positive direction, while the other outgoing lines are protected If the device determines that the fault current is in the opposite direction, it is determined that the outgoing line is a fault line. The directional overcurrent protection of the fault line realizes fault location and protection through short delay action.

Furthermore, after the DC line protection starts to trigger the judgment of the fault current direction, if it is determined that the direction of the fault current flowing through the protection device is the above-mentioned positive direction, the positive direction signal of the fault current of the line is sent to the high-speed communication network. If the line determines that the fault current is in the opposite direction, it will send a signal of the fault current in the opposite direction to the high-speed communication network.

Furthermore, the judgment of the fault current direction of the DC line protection described above needs to be confirmed after a short delay after its activation is triggered. The fixed fault current direction is satisfied within this delay time before the fault current direction is finally confirmed. After confirming the fault current direction, send the direction judged by this protection to the high-speed communication network.

The bus differential protection in the DC bus protection zone in the above step 6 exits due to an abnormality. Specifically, it means that any protection device on the bus in the DC bus protection zone has sampling abnormality, current sampling loop disconnection or other abnormal conditions. The busbar differential protection exits on the busbar, and the protection device on the busbar blocks the busbar differential protection to avoid misoperation or refusal of the differential protection. At the same time, the busbar differential protection exit signal is sent to the DC connection through the high-speed communication network. All protection devices in the busbar protection zone.

In step 6 above, seamlessly switch to the integrated fault location method based on multi-point direction. Specifically, after the high-speed communication network receives the exit signal of a busbar differential protection, it switches to the multi-point-based method after receiving confirmation with a short delay. Comprehensive fault location method in point direction. A comprehensive fault location method based on multi-point directions is used to locate bus faults.

The multi-point integrated fault location method is the steps of bus fault location work. Specifically, if all the protection devices of the incoming and outgoing lines connected to the same bus will determine the direction of the fault current as the opposite direction, and the collected current value If it is greater than the set reverse direction current threshold, it is determined that the bus is a faulty bus. After the faulty bus is marked, the line protection of all incoming and outgoing wires connected to the bus will send out an action signal.

The following describes the high-speed communication network described in the present invention in detail: in the form of a process-level GOOSE network, as a channel for information interaction between protection devices in the DC distribution network system, it can transmit the differential protection exit judged by the protection device in real time. The signal, the forward direction and the reverse direction signal of the fault current provide a reliable and effective way for fault identification, fault location and fault isolation.

First, the DC line protection device is required to compare the current flowing through the respective switch with a preset threshold. Only when the detected current is greater than the set fault current threshold, can it be determined that there is a fault current. Specifically, because the protection of the DC distribution network system is different from the AC power supply system, it is divided into a positive system and a negative system. The independence of the positive system and the negative system is not only in the normal steady-state operation, but also in the case of a failure. The systems are also independent of each other. That is to say, when the equipment in the positive electrode system fails, because the fault current only exists in the positive electrode system, it is only necessary to transmit the fault information with the positive electrode protection device to complete the identification of the fault area. This is also true when the negative system fails.

Examples:

In order to illustrate the positioning method of the present invention, as shown in Fig. 1, the following examples are given. The DC distribution network includes a connection transformer, a converter station H1, a switching station K1, and a power distribution room, in which the bus at the outlet end of the converter station, The bus bar of the opening and closing station, and the branch line connected to the bus bar. As shown in Figure 2, the DC bus protection zone includes 1 bus at the outlet end of the converter station, 2 switches connected to it, 2 switching station bus bars, and 6 switches connected to it. As shown in Figure 3, the DC line protection zone includes 1 bus outlet at the outlet end of the converter station, and 2 switches on the outlet line, each bus outlet of the two switching stations, and 4 switches on the outlet line. However, the DC distribution network structure is only used as an implementation form of the idea of the present invention, and the present invention is also applicable to similar power supply system structures. This method deals with the fault analysis of the DC distribution network as follows.

1. The DC bus protection zone in Figure 4 has a bus failure at point K1, and the protection devices on the bus incoming switches QL3, QL4 and outgoing switches QL7, QL8, QL10, and QL11 can all detect the fault current. When the busbar differential protection works normally, its differential protection action sends an action signal to mark the faulty busbar.

As shown in Figure 6, if this fault occurs in the busbar differential protection, the busbar differential protection has been abnormally exited, and the busbar differential protection will send its differential protection exit signal to the high-speed communication network when exiting. After receiving the differential protection exit signal from the DC bus protection zone, it seamlessly switches to the fault location method based on multi-point information: the protection devices on the incoming switches QL3, QL4 and the outgoing switches QL7, QL8, QL10, QL11 are due to the failure of the bus K1 The current change amount is greater than the set threshold, and the fault location method based on multi-point information is triggered instantaneously. Because the fault on the busbar is real, all these line protection devices can reliably determine that the direction of the fault current flows from the line to the busbar, which is the opposite direction of the definition. After interaction through the high-speed communication network, it is determined that the busbar is faulty, and each The action signal is issued to realize the isolation of the busbar fault in the form of joint jump.

2. The DC line protection zone in Figure 5 has a fault at point K2, that is, the line fault bus incoming switch QL3, QL4 and the outgoing switch QL7, QL8, QL9, QL10, QL11 protection devices can detect the fault current. When the line differential protection on the DC line protection zone works normally, the line is marked as a fault line by its differential protection action to send an action signal.

As shown in Figure 7, if the K2 point fault occurs, the differential protection of the DC line has been withdrawn due to an abnormality, and the protection device sends its differential protection exit signal to the high-speed communication network. The DC line protection installed at QL3, QL7, QL8, QL4, and QL10 in the DC line protection zone seamlessly switches to the fault location method based on multi-point information after receiving the exit signal of the differential protection. The K2 point failure makes the QL11 The fault currents at QL15 and QL15 are all flowing into the line from the bus, that is, both are in the set positive direction. Because the fault current and the load current are superimposed in the same direction, the fault current flowing through QL11 and QL5 is relatively large, which meets the condition that the current value is greater than the set positive direction current threshold. At the same time, for other switches QL3, QL7, QL8, QL4, QL10 on the DC line protection zone, the fault current is in the opposite direction of the setting. These protection devices send the identified reverse fault signals to the high-speed communication network. After the protection device at QL11 receives the reverse direction signal from other protection devices, it is determined that the line where QL11 and QL5 are located is a fault line. The direction overcurrent protection of this fault line realizes fault location through a short delay T action.

3. The bus tie branch K3 in the DC bus protection zone in Figure 8 fails. When the bus tie branch differential protection of the bus tie branch works normally, its differential protection action will send an action signal to mark the faulty bus.

As shown in Figure 9, if this fault occurs, the busbar differential protection has been abnormally exited, and the protection device will send its differential protection exit signal to the high-speed communication network when exiting. The protection devices on the bus incoming switches QL3, QL4 and the outgoing switches QL7, QL8, QL10, QL11 can detect the fault current, and because the current change is greater than the set threshold, the fault location method based on multi-point information is triggered instantaneously. Due to the failure of the bus tie branch, the fault current flows from the line to the bus for the connected protection device. That is, all the switches on the bus I: the protection devices on QL3, QL7, and QL8 are all judged as the fault current in the opposite direction, and all the switches on the bus II: QL4, QL10, and the protection devices on the QL11 are also judged as the fault current. For the opposite direction. At the same time, when the current value collected by the protection installed at the bus tie branch is greater than the set bus tie fault current threshold, the reverse direction signals from all outgoing line protection devices on all two bus sections connected to the bus tie are received, then It is determined that the bus tie branch is faulty. After a short time delay T, the protection device installed at the bus tie branch sends an action signal and marks the bus tie branch as a faulty branch.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also It should be regarded as the protection scope of the present invention.

Claims

A method for locating faults in a flexible DC distribution network, which is characterized in that it includes the following steps:

Set up DC bus protection area and DC line protection area in the DC distribution network, and set protection devices in the switches in the DC bus protection area and DC line protection area, and all protection devices are connected through the high-speed communication network;

The protection device in the DC busbar protection zone adopts busbar differential protection for fault location;

The protection devices on both sides of each line in the DC line protection zone are connected by optical fibers, and optical fiber differential protection is used to locate faults;

When the bus differential protection in the DC bus protection zone exits, and the protection device detects that the current change is greater than the set threshold or the current value is greater than the set threshold, the DC bus protection zone is seamlessly switched to the DC bus based multiple Comprehensive fault location method in point direction;

When the optical fiber differential protection in the DC line protection zone exits, and the protection device detects that the current change is greater than the set threshold or the current value is greater than the set threshold, the DC line protection zone is seamlessly switched to the DC line based multi-channel protection. Comprehensive fault location method in point direction.
The method for locating faults in a flexible DC distribution network according to claim 1, wherein the DC bus protection zone includes an outlet bus of a converter station, and switches and/or switching stations directly connected to the outlet bus of the converter station Outgoing bus, open and close the switch directly connected to the outgoing bus.
The method for locating a fault in a flexible DC distribution network according to claim 1, wherein the DC line protection zone includes a converter station outlet, a switch on the converter station outlet and/or a switch outlet, and Turn off the switch on the outlet line.
The method for locating a fault in a flexible DC distribution network according to claim 1, wherein the protection device is used to detect the current flowing through the switch, and mark the direction of the current flowing from the bus to the line as the positive direction. The direction from the line to the bus is marked as the opposite direction.
The method for locating a fault in a flexible DC distribution network according to claim 1, characterized in that: the operation criterion condition of the optical fiber differential protection is as follows:

Where:
Are the instantaneous current values of the protection devices on both sides of the DC line; I set is the differential current threshold value,
Is the braking current value, and k set is the braking coefficient.
The method for locating a fault in a flexible DC distribution network according to claim 1, characterized in that: the operation criterion condition of the busbar differential protection is as follows:

Among them, I dpj and I dnj are the positive and negative currents of the j-th connecting branch of the bus, respectively; I resn = max(|I dnj |), j = 1...m, I resp = max(|I dpj |) ,j=1...m, m represents the total number of connected branches; I set is the differential current threshold value, and k set is the braking coefficient.
The method for locating faults in a flexible DC distribution network according to claim 1, characterized in that: when the optical fiber channel of the protection device in the DC line protection area experiences bit error, frame loss, interruption, or abnormal sampling, current sampling When the circuit is disconnected, the optical fiber differential protection will exit.
The method for locating a fault in a flexible DC distribution network according to claim 1, wherein the method for locating a comprehensive fault based on a multipoint direction for a DC line comprises the following steps:

After a delay, if any line protection device of all outgoing lines connected to the same bus determines that the fault current is in the positive direction, and the current collected by the protection device is greater than the set positive direction current threshold and the protection device on the opposite side of the line It is also determined that the fault current is in the positive direction, and the protection devices on the other outgoing lines determine that the fault current is in the reverse direction, and the outgoing line is determined to be a fault line;

The directional overcurrent protection of this faulty line will act after a delay.
The method for locating faults in a flexible DC distribution network according to claim 1, characterized in that: when any of the protection devices on the bus in the DC bus protection zone has a sampling abnormality or the current sampling loop is disconnected, the bus on the bus The busbar differential protection exits.
The method for locating faults in a flexible DC distribution network according to claim 1, characterized in that: a comprehensive fault locating method based on multi-point directions for a DC bus: comprising the following steps:

After a delay, if all incoming and outgoing protection devices connected to the same busbar determine the direction of the fault current as the reverse direction, and the collected current value is greater than the set reverse direction current threshold, it is determined that the busbar is Fault bus

The action signal is sent by the line protection device of all incoming and outgoing wires connected to the bus.