Differential protection method and system for multi-terminal line

Abstract

The invention relates to a differential protection method and system for a multi-terminal line, and belongs to the technical field of power transmission line protection. According to the invention, the protection device at any end is selected as a host, the protection devices at other ends are all sub-machines, and the host obtains analog quantity data of other ends and logic states related to differential protection through a communication channel, and performs differential current starting and differential action judgment in combination with the analog quantity data of the local end and the logic states related to differential protection. The judgment result and the voltage change state are sent to the sub-machine; and the sub-machine carries out differential action judgment according to the differential action judgment result sent by the host and the logic state, related to differential protection, of the end where the sub-machine is located. The protection devices arranged at all ends have the same function, so that when the host fails and cannot perform differential protection, any protection device can be selected from the sub-machines as the host to continue differential protection, and the reliability of differential protection is effectively improved.

Description

Technical Field

[0001] The invention relates to a differential protection method and system for a multi-terminal line, belonging to the technical field of power transmission line protection. Background Art

[0002] With the access of large-scale distributed power sources and the increasing complexity of the power system structure, T-shaped or multi-terminal distributed power plant interconnection lines are increasingly appearing in the grid framework structure, making the operation of the grid system more complicated, resulting in huge challenges for the relay protection configured according to the conventional system. Once a line fails, the protection is required to be able to reliably cut off the faulty part in a short time and reduce the economic loss to the minimum. The main line protection generally chooses longitudinal differential protection. Compared with the longitudinal differential protection configured for multi-terminal lines and the two-terminal line protection, the multi-terminal line operation is more flexible and convenient. Therefore, it is of great significance to study the reliability, selectivity and sensitivity of the protection after a multi-terminal transmission line fails.

[0003] The Chinese patent application document with publication number CN116154733A discloses a method and system for automatically adjusting the braking coefficient of multi-terminal current differential protection of a line. The method is based on a master-slave protection mechanism. The slave transmits its own current, voltage and other information to the host through an optical fiber channel, and the host makes a differential protection judgment through comparison and analysis. However, this method sets the protection device on the power grid side to the host by default, and the host is fixed in position. When the host fails, for example, it cannot transmit data with the slave or the host cannot make a differential protection judgment, resulting in the inability of each end to perform differential protection in a timely and effective manner, thereby affecting the reliability of the entire circuit system. Summary of the invention

[0004] The object of the present invention is to provide a differential protection method and system for multi-terminal lines, so as to solve the problem that the main engine position is fixed and the reliability of differential protection cannot be guaranteed.

[0005] To achieve the above object, the solution of the present invention includes:

[0006] A differential protection method for a multi-terminal line of the present invention comprises the following steps:

[0007] Select any one of the protection devices corresponding to each end of the multi-terminal line as the master, and the other protection devices as slaves;

[0008] The control host establishes communication with each slave to obtain analog data from other terminals and logic states related to differential protection, and makes differential current start judgment and differential action judgment based on the analog data and logic states of differential protection from other terminals and the analog data and logic states related to differential protection from the host terminal, and sends the judgment result and voltage change state to the slave;

[0009] The slave performs differential current starting judgment according to the differential current starting judgment result and voltage change status sent by the host, and the slave performs differential action judgment according to the differential action judgment result sent by the host and the logic status related to the differential protection at the slave end.

[0010] Furthermore, each protection device is equipped with a fiber optic communication channel for communicating with other protection devices. The protection device selected as the host is invested with N fiber optic communication channels, N is the number of slaves, and the protection device selected as the slave is only invested with the fiber optic communication channel connected to the host.

[0011] Furthermore, the differential current starting judgment logic adopted by the host is to meet the first differential current starting judgment condition or the second differential current starting judgment condition; the first differential current starting judgment condition is met when the zero-sequence current at any two ends is greater than the zero-sequence starting setting and the zero-sequence differential current is greater than the zero difference setting; the second differential current starting judgment condition is met when the voltage at any end meets the voltage change condition or only the circuit breaker at one end is in the closed position, and the differential current of one phase in the three-phase electricity is greater than the differential setting.

[0012] Furthermore, the differential action judgment adopted by the host is to simultaneously meet the first, second and third differential action judgment conditions; the first differential action judgment condition is met when the sudden change at either end is started or the differential current at either end is started, the second differential action judgment condition is met when the differential protection at either end is started or only the circuit breaker at one end is in the closed position, and the third differential action judgment condition is met when the point difference of one phase in the three-phase electricity exceeds the preset threshold, the incremental difference exceeds the preset threshold, or the phase difference with other phases changes.

[0013] Furthermore, when the slave receives the voltage change status of any end sent by the host or the differential current start status sent by the host, it means that the slave meets the differential current start judgment condition and sends the differential current start status of the end where the slave is located to the host.

[0014] Furthermore, when the slave receives the differential action status sent by the host and detects that the differential protection is started at the end where the slave is located, the differential action is performed.

[0015] Furthermore, the method is also used to determine whether the optical fiber communication channel connection is normal, and the judgment process includes: setting a local identification code and an opposite side identification code of the optical fiber communication channel for each protection device, and the opposite side identification code of the optical fiber communication channel is the local identification code of the opposite side protection device; when the identification code sent by the opposite side protection device received by the protection device through the optical fiber communication channel is consistent with the opposite side identification code set for the optical fiber communication channel, it is determined that the optical fiber channel connection is correct.

[0016] A differential protection system for a multi-terminal line of the present invention comprises a protection device corresponding to each end of the multi-terminal line, each protection device is equipped with a differential current start judgment module, a differential action judgment module and a communication channel for data transmission, any protection device is set as a host, and the other protection devices are all slaves; the host is controlled to establish communication with each slave through the communication channel to obtain analog data of other ends and logical states related to differential protection, the differential current start judgment module and the differential action judgment module respectively perform differential current start judgment and differential action judgment according to the analog data of other ends and the logical states related to differential protection obtained and the analog data of the end where the host is located, and send the judgment result and voltage change state to the slave; the slave performs differential current start judgment according to the differential current start judgment result and voltage change state sent by the host, and the slave performs differential action judgment according to the differential action judgment result sent by the host and the logical state related to differential protection at the end where the slave is located.

[0017] Furthermore, the communication channel is a fiber optic communication channel, and the protection device selected as the host machine invests in N fiber optic communication channels, where N is the number of slave machines, and the protection device selected as the slave machine only invests in the fiber optic communication channel connected to the host machine.

[0018] Furthermore, each protection device is set with a local identification code and an opposite side identification code of the optical fiber communication channel, and the opposite side identification code of the optical fiber communication channel is the local identification code of the opposite side protection device; the protection device determines whether the optical fiber channel connection is correct by comparing whether the identification code sent by the opposite side protection device received by the optical fiber communication channel is consistent with the opposite side identification code set for the optical fiber communication channel.

[0019] The beneficial effects of the present invention are as follows: the present invention is an improved invention creation, the present invention selects any one end of the protection device as the host, and the other end of the protection device is a slave, the host obtains the analog data and the logic state related to the differential protection of the other end through the communication channel, and combines the analog data of the local end to judge the differential current start and differential action, and sends the judgment result and the voltage change state to the slave; the slave obtains the judgment result and the voltage change state sent by the host through the communication channel, and combines the logic state related to the differential protection of the local end to judge the differential current start and differential action, and sends the judgment result to the host and the circuit breaker. The functions of the protection devices set at each end of the present invention are the same, so when the host fails and cannot perform differential protection, any protection device can be selected from the slave as the host to continue to perform differential protection, which effectively solves the reliability of differential protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of optical fiber channel connection between a master and slave machine of the present invention;

[0021] Figure 2It is a schematic diagram of a master-slave communication mode of the present invention;

[0022] Figure 3 It is a logic diagram of the master-slave differential current startup of the present invention;

[0023] Figure 4 It is a logic diagram of the differential current action of the master and slave machines of the present invention;

[0024] Figure 5 It is a schematic diagram of the overall flow of the differential protection method of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0026] The idea of ​​the present invention is to use the form of a master and a slave to perform differential protection on multi-terminal lines. Taking into account the reliability of differential protection, one protection device is selected from the protection devices at each end as the master, and the remaining protection devices are slaves. The master receives data sent by the slave through a communication channel to perform differential current start-up judgment and differential action judgment; the slave receives data sent by the host through a communication channel to perform differential current start-up judgment and differential action judgment.

[0027] Method Example:

[0028] This embodiment provides a differential protection method for multi-terminal lines. This method supports differential protection from 3-terminal lines to 9-terminal lines. The protection device used in this method for differential protection of multi-terminal lines supports differential protection of three-phase electricity with a maximum of 9-terminal differentials. When the actual number of terminals on site is less than 9, the number of line terminals in the configuration file can be kept consistent with the actual number of terminals on site, that is, redundant parameters and related data are shielded. There is no need to consider the activation, deactivation and setting of redundant differential-related parameters, which is convenient for operation and maintenance personnel to set.

[0029] The protection device of the present invention adopts a master-slave communication mode when performing differential protection. The master and slave have the same hardware. Each protection device integrates N (maximum 8) optical fiber channels for optical fiber communication connection with other end line protection devices, forming a maximum of 9-end differential. The optical fiber channels of the master and slave can be flexibly selected. The slave can select any optical fiber channel to be connected to the optical fiber channel of the master. The optical fiber channels of the master and slave are connected as follows: Figure 1 shown.

[0030] The host and slave in multi-terminal line protection have the same software. Only the host can obtain the analog data sent from each end and the logical state related to the differential protection through the optical fiber channel. These states related to the logical differential protection are specifically expressed as "0" or "1", and perform differential flow calculation. The slave cannot obtain the analog data of other ends, so it cannot perform differential flow calculation. The present invention selects any one protection device from the protection devices corresponding to each end as the host, and the other protection devices are all slaves. As a typical implementation method, the optical fiber channel of the host is put into multiple optical fiber channel pressure plates, while the optical fiber channel of the slave can only be put into one optical fiber channel pressure plate. When the optical fiber channel of a certain protection device is only put into a single optical fiber channel pressure plate and the optical fiber channel is self-looped (the output pin of one optical fiber channel is connected to its own input pin), the protection device is also considered to be the host at this time, and the differential flow calculation is performed on the line at its own end; when the optical fiber channel of a certain protection device is put into multiple optical fiber channel pressure plates, and the put-in optical fiber channels are all self-looped, that is, multiple optical fiber channels of a device are connected to another optical fiber channel of the same device, the protection device is not considered to be the host at this time, and the differential flow calculation is not performed. When multiple protection devices simultaneously activate multiple fiber channel pressure plates, it is determined that the fiber channel is activated incorrectly. Since there are multiple hosts at this time, multi-terminal differential cannot be formed, so the differential protection is locked.

[0031] The optical fiber channels of each protection device are set to 0-7 as channel numbers, such as Figure 2 The master-slave star communication mode shown in the figure illustrates the differential protection line of the present invention by taking a 9-terminal line as an example, wherein optical fiber channels 0, 1, 2, 3, 4, 5, 6, and 7 of the master are connected to optical fiber channels 1, 2, 3, 4, 5, 6, 7, and 0 of slaves 8, 1, 2, 3, 4, 5, 6, 7, and 8 respectively; for data transmitted by the optical fiber channels, logical states and analog data related to differential protection are transmitted to the opposite side through the optical fiber channels, and the data transmitted by the 8 optical fiber channels are consistent except for the optical fiber channel numbers. The host can receive analog data (zero-sequence current, zero-sequence voltage, etc.) and differential protection logic status (circuit breaker opening and closing status, differential current start status, etc.) transmitted by slaves 1-7 through the optical fiber channel, and perform differential current start discrimination and differential action discrimination in combination with the analog data and differential protection logic status at its own end; slaves 1-7 can only receive the logic status (voltage change status, differential current start status, differential action status, etc.) transmitted by the host through their respective optical fiber channels to perform differential current start logic discrimination, and perform differential action discrimination in combination with the differential protection logic status detected on their own side. As another implementation method, the star communication mode may not be selected, as long as each slave can be connected to the optical fiber channel of the host using only one optical fiber channel.

[0032] Each protection device has a local identification code and an opposite side identification code for fiber channels 0-7. The correct connection of the fiber channels can be determined by comparing the identification code received by each fiber channel with the opposite side identification code of the channel set by the device. For example, the local identification code of the host is 1, and the local identification codes of the slaves 1-8 are 2-9 respectively. Then the opposite side identification codes corresponding to the fiber channels 0-7 of the host are 9, 2, 3, 4, 5, 6, 7, 8, and the opposite side identification code of the fiber channel selected by the slaves 1-7 to communicate with the host is 1. When the fiber channel of each protection device is connected for the first time, the corresponding identification code relationship is stored in a table. Then, when collecting data, the fiber channels on both sides are judged to be correctly connected by comparing the table. The identification codes do not need to be assigned in ascending order. As long as the uniqueness of the local identification code of each protection device is guaranteed, it can be set.

[0033] When each protection device is connected correctly and the host and slave are identified normally through the input of the fiber channel pressure plate, the differential current start logic will be identified. Figure 3 As shown, when the protection device is the host, and the zero-sequence current collected by the optical fiber channel on either side is greater than the zero-sequence start-up setting, and the zero-sequence differential current is greater than 0.8 times the zero-difference setting, the first differential current start-up judgment condition is met, and it is judged as differential current start-up; when the protection device is the host, and the voltage collected by the optical fiber channel on either side meets the preset voltage change condition (such as zero-sequence voltage greater than 5V, 2-cycle phase voltage change greater than 8V) or the logic state received from the slave is that only one side of the circuit breaker is in the closed position, and the optical fiber channel collected by the optical fiber channel on a certain phase is greater than 0.8 times the differential setting, the second differential current start-up judgment condition is met, and it is judged as differential current start-up. Among them, 0.8 is commonly used in engineering, and it can also be selected near 0.8. The host sends the differential current start-up state and the voltage change state on either side to all slaves. When the protection device is a slave, after the slave receives the differential current start-up state or the voltage change state on either side from the host, it is judged as differential current start-up.

[0034] Differential action logic judgment Figure 4As shown, when the protection device is the host, and the fiber optic channel it puts into collects the sudden change amount or differential current start on either side, the first differential action judgment is satisfied, and the protection on either side is started or only one side of the circuit breaker is in the closed position in the differential protection logic state received from the slave, which satisfies the second differential action judgment, and the point difference of one phase in the three-phase electricity exceeds the preset threshold, the phase difference with other phases changes or the incremental difference exceeds the preset threshold, which satisfies the third differential action judgment. At this time, the differential judgment is satisfied, and the corresponding phase is differentially protected, and the differential action state is sent to all slaves. When the protection device is a slave, the slave receives the differential action state sent by the host and detects that the differential protection is started on this side, and sends a trip signal to the circuit breaker on this side, so that all the circuit breakers in the three-phase electricity trip at the same time. Among them, the differential protection start includes the differential current start.

[0035] The overall process of the present invention when performing differential protection on multi-terminal lines is as follows: Figure 5 As shown, the host continuously performs differential current start-up judgment and differential action judgment according to various types of data sent by itself, and sends corresponding differential actions to the slave machine when the differential current start-up judgment and differential action judgment are met; the slave machine continuously performs differential current start-up judgment and differential action judgment according to various types of data sent by the host, and sends differential direct jump actions when the slave machine meets the differential current start-up judgment and differential action judgment.

[0036] System Example:

[0037] This embodiment provides a differential protection system for multi-terminal lines. The protection devices in the system are all equipped with a differential current start-up judgment module, a differential action judgment module and a communication channel for data transmission. The protection devices at each end adopt the method described in the method embodiment when performing differential protection. Since the introduction of the method is clear enough, it will not be repeated here.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A differential protection method for a multi-terminal line, characterized in that: The method comprises the following steps: Select any one of the protection devices corresponding to each end of the multi-terminal line as the master, and the other protection devices as slaves; The control host establishes communication with each slave to obtain analog data and differential protection logic status from other terminals, and performs differential current start judgment and differential action judgment based on the analog data and logic status related to differential protection from other terminals and the analog data and logic status related to differential protection from the host terminal, and sends the judgment result and voltage change status to the slave; The slave performs differential current starting judgment according to the differential current starting judgment result and voltage change status sent by the host, and the slave performs differential action judgment according to the differential action judgment result sent by the host and the logic status related to the differential protection at the slave end.

2. The differential protection method for multi-terminal lines according to claim 1, characterized in that: Each protection device is equipped with a fiber optic communication channel for communicating with other protection devices. The protection device selected as the host is equipped with N fiber optic communication channels, where N is the number of slaves. The protection device selected as the slave is equipped with only the fiber optic communication channel connected to the host.

3. The differential protection method for multi-terminal lines according to claim 1, characterized in that: The differential current starting judgment logic adopted by the host is to meet the first differential current starting judgment condition or the second differential current starting judgment condition; the first differential current starting judgment condition is met when the zero-sequence current at any two ends is greater than the zero-sequence starting setting and the zero-sequence differential current is greater than the zero difference setting; the second differential current starting judgment condition is met when the voltage at any one end meets the voltage change condition or only the circuit breaker at one end is in the closed position, and the differential current of one phase in the three-phase electricity is greater than the differential setting.

4. The differential protection method for multi-terminal lines according to claim 1, characterized in that: The differential action judgment adopted by the host is to simultaneously meet the first, second and third differential action judgment conditions; the first differential action judgment condition is met when a sudden change in quantity at any two ends is started or a differential current at any one end is started, the second differential action judgment condition is met when the differential protection at any two ends is started or only the circuit breaker at one end is in the closed position, and the third differential action judgment condition is met when the point difference of one phase in the three-phase electricity exceeds a preset threshold, the incremental difference exceeds a preset threshold, or the phase difference with other phases changes.

5. The differential protection method for multi-terminal lines according to claim 3, characterized in that: When the slave receives the voltage change status of any end sent by the host or the differential current start status sent by the host, it means that the slave meets the differential current start judgment condition and sends the differential current start status of the end where the slave is located to the host.

6. The differential protection method for multi-terminal lines according to claim 4, characterized in that: When the slave receives the differential action status sent by the host and detects that the differential protection is started at the end of the slave, the differential action is performed.

7. The differential protection method for multi-terminal lines according to claim 2, characterized in that: The method is also used to determine whether the optical fiber communication channel connection is normal, and the determination process includes: setting a local identification code and an opposite side identification code of the optical fiber communication channel for each protection device, wherein the opposite side identification code of the optical fiber communication channel is the local identification code of the opposite side protection device; when the identification code sent by the opposite side protection device received by the protection device through the optical fiber communication channel is consistent with the opposite side identification code set by the optical fiber communication channel, it is determined that the optical fiber channel connection is correct.

8. A differential protection system for a multi-terminal line, comprising a protection device corresponding to each end of the multi-terminal line, characterized in that: Each protection device is equipped with a differential current start-up judgment module, a differential action judgment module and a communication channel for data transmission. Any protection device is set as a host, and the other protection devices are all slaves; the control host and each slave establish communication through the communication channel to obtain analog data from other ends and logical states related to differential protection. The differential current start-up judgment module and the differential action judgment module respectively perform differential current start-up judgment and differential action judgment based on the analog data from other ends and logical states related to differential protection obtained and the analog data at the end where the host is located, and send the judgment result and voltage change state to the slave; the slave performs differential current start-up judgment based on the differential current start-up judgment result and voltage change state sent by the host, and the slave performs differential action judgment based on the differential action judgment result sent by the host and the logical state related to differential protection at the end where the slave is located.

9. The differential protection system for multi-terminal lines according to claim 8, characterized in that: The communication channel is an optical fiber communication channel. The protection device selected as the host machine invests in N optical fiber communication channels, where N is the number of slave machines. The protection device selected as the slave machine only invests in the optical fiber communication channel connected to the host machine.

10. The differential protection system for multi-terminal lines according to claim 9, characterized in that: Each protection device is set with a local identification code and an opposite side identification code of the optical fiber communication channel. The opposite side identification code of the optical fiber communication channel is the local identification code of the opposite side protection device. The protection device determines whether the optical fiber channel connection is correct by comparing whether the identification code sent by the opposite side protection device received by the optical fiber communication channel is consistent with the opposite side identification code set for the optical fiber communication channel.

Images