Method and system for automatically adjusting braking coefficient of line multi-terminal current differential protection

Abstract

The application discloses a method and system for automatically adjusting a braking coefficient of line multi-terminal current differential protection, and comprises the following steps: determining the identities of a master and each slave; identifying the slave with the current differential protection function; judging whether the protection is started for the master and the slave with the current differential protection function, if the protection on each side is not started, judging the closing state, opening state and maintenance state of each terminal protection device, determining the number of terminals in the closing state of the protection device, and executing the corresponding protection strategy for the protection device in the maintenance state; when the number of terminals in the closing state is greater than or equal to 1, automatically adjusting the braking coefficient k according to the number of terminals in the closing state of the protection device for the current differential protection action judgment, otherwise setting the initial threshold of the braking coefficient k for the current differential protection action judgment. The application can improve the action sensitivity of the multi-terminal current differential protection.

Description

Technical Field

[0001] This invention belongs to the field of power system protection technology, and relates to a method and system for automatically adjusting the braking coefficient of multi-terminal current differential protection of lines. Background Technology

[0002] Currently, efforts are being accelerated to build a new power system based on new energy sources. However, most areas rich in wind and solar power resources are far from load centers and require long-distance transmission to connect to the regional power grid. Considering factors such as saving equipment investment and reducing land acquisition, multi-terminal current differential protection is increasingly being used in high-voltage transmission lines.

[0003] The multi-terminal current differential protection of the line can adapt to different operating states such as branch maintenance and hot standby, and can currently meet the application scenarios of different line terminal numbers from two to nine terminals.

[0004] Unlike two-terminal lines, when a fault occurs in a multi-terminal line area, current is drained between non-faulty branches, which will increase the restraining current of the current differential protection. If the current differential protection uses a fixed restraining coefficient, it will lead to insufficient sensitivity of the current differential protection when used on lines with different numbers of terminals and different operating conditions.

[0005] Therefore, the multi-terminal current differential protection of the line needs to be able to automatically adjust the braking coefficient of the current differential protection according to the change in the number of line terminals and different operating conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method and system for automatically adjusting the braking coefficient of multi-terminal current differential protection for lines.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for automatically adjusting the braking coefficient of a multi-terminal current differential protection system for lines, the method being designed for a multi-terminal current differential protection system for lines, the method comprising the following steps:

[0009] Step 1: Determine the identity of the master and slave devices based on the fiber optic channel's ranking and the setting sheets of the current differential protection devices at each end.

[0010] Step 2: Based on the activation / deactivation status of the corresponding fiber channel pressure plates of the protection devices on both sides of the fiber channel, determine the activation status of the fiber channel, and the host identifies the slave device with the current differential protection function activated.

[0011] Step 3: Determine whether the protection is activated on the master and slave units with the current differential protection function. If the protection on each side is not activated, proceed to step 4; otherwise, proceed to the fault handling procedure.

[0012] Step 4: The host determines the closing status, opening status, and maintenance status of each protection device, determines the number of protection devices in the closing status, and executes the corresponding protection strategy for the protection devices in the maintenance status.

[0013] Step 5: If the number of terminals in the closed state is greater than or equal to 1, proceed to step 6; otherwise, set the initial threshold of the braking coefficient k to judge the current differential protection action and return to step 1.

[0014] Step 6: Automatically adjust the braking coefficient k according to the number of terminals of the protection device in the closed state, so as to be used for the judgment of the current differential protection action.

[0015] The present invention further includes the following preferred embodiments:

[0016] Preferably, in the multi-terminal current differential protection system for the line, a current differential protection device, a current transformer, and a circuit breaker are installed at each end of the line.

[0017] One of the current differential protection devices at each end is set as the master, and the rest are set as slaves. The master communicates with each slave respectively.

[0018] The host is installed on the power grid side, and the slaves are arranged in order of proximity to the host. For slave 1, its branch is directly connected to the host branch through a connection point, without a tie line. The host communicates with each slave through a corresponding fiber optic channel, but the slaves do not communicate with each other.

[0019] Preferably, each protection device is equipped with 1 to 8 fiber optic interfaces, and each fiber optic interface is equipped with a fiber channel pressure plate. The host and each slave device are connected to the fiber optic channel through the fiber optic interface configured in their respective devices. The corresponding fiber optic channel is put into and taken out by putting on and taking off the fiber optic channel pressure plate.

[0020] The serial number of the Fibre Channel pressure plate is the same as the serial number of the corresponding Fibre Channel interface, and the serial number of the Fibre Channel is the same as the serial number of the host Fibre Channel interface. The host connects to each slave device in sequence starting from Fibre Channel 1, and each slave device uses Fibre Channel 1 to connect to the host.

[0021] The protection device is configured with a setting sheet, in which the host sets the local address code and the opposite identification code of each fiber optic channel, and each slave sets the local address code and the opposite identification code of the first fiber optic channel used for communication with the host.

[0022] The local address code of the master is greater than the local address code of each slave device;

[0023] The identification code setting of the opposite side of the fiber optic channel used by each slave device for communication with the host is the same as the setting value of the local address code of the host. When the local address code of the slave device on either side of any fiber optic channel is consistent with the corresponding identification code setting value of the opposite side of the host, the host and the slave device can achieve normal communication.

[0024] Preferably, in step 1, the location of the host and each slave is determined according to the arrangement of the fiber optic channels, and the corresponding values ​​are entered into the setting sheet;

[0025] By comparing the values ​​of the local address codes in the setting sheets of each protection device, the protection device with the largest local address code is determined to be the master device, and the others are slave devices.

[0026] The identity of each slave device is determined based on the correspondence between the assigned values ​​of the identification codes on the opposite side of each fiber optic channel in the host configuration sheet and the assigned values ​​of the identification codes on the local side in the slave configuration sheet.

[0027] Preferably, in step 2, if the fiber channel pressure plate of the slave device and the corresponding fiber channel pressure plate of the master device are engaged, it indicates that the corresponding fiber channel is engaged, and the corresponding branch and slave device are engaged with the current differential protection function.

[0028] If the fiber channel pressure plate of the slave device and the corresponding fiber channel pressure plate of the master device are disconnected, it means that the corresponding fiber channel is disconnected, and the branch corresponding to the fiber channel and the slave device will lose the current differential protection function.

[0029] If the fiber channel pressure plate on / off status of the master and slave devices are inconsistent, both the master and slave devices will report an alarm indicating inconsistency of the corresponding channel pressure plate and will exit the multi-terminal current differential protection function.

[0030] Preferably, in step 4, the determination of the closed and open states is as follows:

[0031] If the protection device meets the following conditions at the same time, the operating status is determined to be the closed state: the protection is not started, the fiber optic channel pressure plate is engaged, the fiber optic channel is engaged, and there is no trip position input.

[0032] If the protection device simultaneously meets the following conditions, the operating state is determined to be the tripped state: the protection has not been activated, the fiber optic channel pressure plate is engaged, the fiber optic channel is engaged, a trip position input is available, and the currents of phases A, B, C, and zero sequence are all less than 0.05I. N ;

[0033] Among them, I N This is the rated value for the secondary current.

[0034] Preferably, in step 4, if the fiber optic channel is abnormal or the protection device malfunctions, the corresponding protection device enters the maintenance state.

[0035] When a slave device with a single set of protection on each side is under maintenance, the corresponding circuit breaker will be tripped, and the corresponding fiber optic channel pressure plate will be deactivated, thus deactivating the current differential protection function of the branch where the slave device is located.

[0036] When the host with a single set of protection on each side is under maintenance, the host circuit breaker is tripped, the fiber optic channel pressure plate at each end is removed, and the current differential protection function of all branches is turned off, without affecting the normal operation of the slave backup protection.

[0037] If either end of one of the dual protection systems on each side is under maintenance, the fiber optic channel pressure plate at the maintenance end will be deactivated, and the fiber optic channel pressure plates at the other ends will also be deactivated, thus deactivating the current differential protection function of all branches. However, the circuit breaker will remain in the closed position, retaining backup protection at the other ends, without affecting the normal operation of the other protection system.

[0038] Preferably, in step 5, the initial threshold value of the braking coefficient k is 0.6.

[0039] Preferably, in step 6, the braking coefficient k is adjusted as follows:

[0040]

[0041] In the formula, m is the number of terminals in the closed state.

[0042] This invention also provides a system for automatically adjusting the braking coefficient of multi-terminal current differential protection for lines. The system for automatically adjusting the braking coefficient is designed for multi-terminal current differential protection systems for lines, and includes:

[0043] The master-slave identification module is used to determine the identity of the master and each slave device based on the fiber optic channel's ranking and the setting sheets of the current differential protection devices at each end.

[0044] The protection function activation identification module is used to determine the activation status of the fiber optic channel based on the activation / deactivation status of the corresponding fiber optic channel pressure plates of the protection devices on both sides of the fiber optic channel. The host identifies the slave device that has activated the differential current protection function.

[0045] The protection start-up discrimination module is used to determine whether the protection has been started for the master and slave devices with the current differential protection function. If the protection on each side is not started, the system enters the protection device status discrimination module; otherwise, it enters the fault handling program.

[0046] The protection device status determination module is used by the host to determine the closing status, opening status, and maintenance status of each protection device, determine the number of protection devices in the closing status, and execute corresponding protection strategies for protection devices in the maintenance status.

[0047] The closing status terminal number judgment module is used to determine whether the number of terminals in the closing status is greater than or equal to 1. If so, it enters the braking coefficient adjustment module; otherwise, it sets the initial threshold value of the braking coefficient k to judge the current differential protection action and returns to the master-slave identity determination module.

[0048] The braking coefficient adjustment module is used to automatically adjust the braking coefficient k according to the number of terminals of the protection device in the closed state, so as to make judgment on the operation of the current differential protection.

[0049] The beneficial effects of this invention are compared with those of the prior art:

[0050] This invention includes determining the identities of the master and slave devices; identifying slave devices that have activated the current differential protection function; determining whether the protection has been activated for the master and slave devices; if the protection on all sides is not activated, determining the closing, opening, and maintenance status of each protection device, determining the number of devices in the closing state, and executing corresponding protection strategies for devices in the maintenance state; if the number of devices in the closing state is greater than or equal to 1, automatically adjusting the braking coefficient k based on the number of devices in the closing state for current differential protection action judgment; otherwise, setting an initial threshold for the braking coefficient k for current differential protection action judgment. This invention can automatically adjust the braking coefficient of the current differential protection according to changes in the number of line terminals and different operating states, improving the sensitivity of multi-terminal current differential protection and solving the problem of insufficient sensitivity that may occur with multi-terminal current differential protection using a fixed braking coefficient, thus meeting various operating modes with different line terminal numbers. Attached Figure Description

[0051] Figure 1 This is a schematic diagram illustrating the typical operating characteristics of a multi-terminal differential current protection system in an embodiment of the present invention.

[0052] Figure 2 This is a schematic diagram of the line multi-terminal current differential protection system in an embodiment of the present invention;

[0053] Figure 3 This is a schematic diagram of the steps involved in the method for automatically adjusting the braking coefficient of the multi-terminal current differential protection for lines proposed in this invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0055] The basic industry terms used in this invention are explained as follows:

[0056] Line current differential protection calculates the differential current and braking current of each phase current and zero-sequence current, and determines the operating characteristics through the braking coefficient k. After the protection is started, the current differential protection will operate when the operating conditions are met.

[0057] Protection activation is used to monitor whether a fault has occurred in the power system. If a fault is confirmed, the power supply to the protection trip output relay is turned on, and the fault handling procedure is entered. The protection will then activate when the conditions are met.

[0058] The starting elements of a current differential protection device include current surge start, zero-sequence auxiliary start, static stability failure start, weak feeder start, trip start, and reclosing start. Once any one of the starting elements activates, the protection function is activated and self-held until the entire device resets.

[0059] Figure 1 This is a schematic diagram illustrating the typical operating characteristics of a multi-terminal differential current protection system in an embodiment of the present invention. The differential current protection system operates when the following relationship is satisfied.

[0060]

[0061] In the formula, For differential current,

[0062] For braking current,

[0063] Let j be the phase A, phase B, phase C, or zero-sequence current, and j can be 1 to n.

[0064] I DZ Set the differential operating current value;

[0065] n represents the number of line terminals. When running a single-ended line, n is 1; when running a two-ended line, n is 2; when running a three-ended line, n is 3; when running a four-ended line, n is 4... and so on. Currently, the maximum value of n is 9.

[0066] The method and system for automatically adjusting the braking coefficient of multi-terminal current differential protection of lines of the present invention are designed for multi-terminal current differential protection systems of lines. In the preferred but non-limiting embodiment of the present invention, in the multi-terminal current differential protection system of lines, a current differential protection device, a current transformer and a circuit breaker are respectively installed at each end of the line.

[0067] One of the current differential protection devices at each end is set as the master, and the rest are set as slaves. The master communicates with each slave respectively.

[0068] The host computer is installed on the power grid side, and the slave computers are arranged sequentially from nearest to farthest from the host. For a nine-terminal line, they are designated as Slave 1, Slave 2, Slave 3, Slave 4… Slave 8. Slave 1's branch is directly connected to the host branch via a connection point, without a tie line. The host communicates with each slave computer via a corresponding fiber optic channel; the slave computers do not communicate with each other. The host computer, installed on the power grid side (i.e., at the point of power supply), is designed for rapid startup and fast operation.

[0069] Each protection device is equipped with 8 fiber optic interfaces, numbered 1 to 8. Each fiber optic interface is equipped with a fiber channel pressure plate. The host and each slave device are connected to the fiber channel through the fiber optic interface configured on their respective devices. The corresponding fiber channel is put into and taken out by turning on and off the fiber channel pressure plate.

[0070] The serial number of the Fibre Channel pressure plate is the same as the serial number of the corresponding Fibre Channel interface, and the serial number of the Fibre Channel is the same as the serial number of the host Fibre Channel interface. The host connects to each slave device in sequence starting from Fibre Channel interface 1, and each slave device uses Fibre Channel interface 1 to connect to the host.

[0071] The protection device is equipped with fiber optic interfaces 1 to 8, and corresponding fiber optic channel 1 to fiber optic channel 8 pressure plates are set up. According to the number of fiber optic channels, they are defined as fiber optic channel 1, fiber optic channel 2, etc. The host's fiber optic interface 1 is connected to fiber optic channel 1, fiber optic interface 2 is connected to fiber optic channel 2, etc., and each slave device is connected to only one fiber optic channel through fiber optic interface 1.

[0072] The protection device is equipped with a setting sheet, which can be used to set the setting items for the local address code and the identification code of each fiber optic channel.

[0073] Furthermore, the host sets its own address code and the opposite side identification code of each fiber optic channel, and each slave sets its own address code and the opposite side identification code of the fiber optic channel one used for communication with the host (the fiber optic channel one is relative to the slave, indicating that it corresponds to the fiber optic interface 1 of the slave).

[0074] The local address code of the master is greater than the local address code of each slave device;

[0075] The identification code setting of the opposite side of the fiber optic channel used for communication with the host is the same as the identification code setting of the host. When the identification code of the slave on both sides of any fiber optic channel is consistent with the corresponding identification code setting of the host, the host and the slave can communicate normally.

[0076] like Figure 2As shown, taking a 5-terminal line as an example, the multi-terminal current differential protection system is described. The multi-terminal current differential protection is installed on the M side, O side, P side, Q side, and N side, respectively. The current transformers at each terminal are CT1, CT2, CT3, CT4, and CT5, respectively. The protection collects the currents of the current transformers at the protection installation locations as I1, I2, I3, I4, and I5, respectively. The circuit breakers at each terminal are B1, B2, B3, B4, and B5, respectively. The connection points of the multi-terminal line are T1, T2, and T3, respectively. M to T1 is the L1 branch, O to T1 is the L2 branch, P to T2 is the L3 branch, Q to T3 is the L4 branch, N to T3 is the L5 branch, T1 to T2 is the LT1T2 tie line, and T2 to T3 is the LT2T3 tie line.

[0077] Figure 2 When all branches of the multi-terminal line are in normal operation, and a fault occurs at K1 within the zone, the protection range of the multi-terminal line current differential protection is the area between the CTs at each terminal. If the circuit breaker of a branch needs to be disconnected due to maintenance, hot standby, equipment failure, fiber optic channel failure, etc., such as when circuit breaker B4 is disconnected, I4 will not be able to collect the fault current, and the protection range of the multi-terminal current differential protection will be between CT1, CT2, CT3, B4, and CT5.

[0078] Figure 2 The system employs a master-slave architecture, meaning there is only one master unit, which communicates with each slave unit individually. The master unit should be installed on the power grid side. The slave units are arranged sequentially from nearest to farthest from the master unit, designated as Slave 1, Slave 2, Slave 3, and Slave 4. The master unit branch and Slave 1 branch are directly connected via a T1 connection point without any tie lines. However, the master unit branch and the other slave unit branches are connected via tie lines. The corresponding fiber optic longitudinal interconnects are designated as Fiber Channel 1, Fiber Channel 2, Fiber Channel 3, and Fiber Channel 4. The master unit connects to each slave unit via its respective fiber optic channel; the slave units are not connected to each other.

[0079] The host and each slave unit are connected to the Fiber Optic Channel via fiber optic interfaces configured on the device. Each device can be configured with 8 fiber optic interfaces, numbered 1 to 8. The fiber optic interfaces of the host and each slave unit can be connected using a dedicated Fiber Optic Channel or a multiplexed Fiber Optic Channel. Fiber optic interfaces 1 to 4 of the host are connected to fiber optic interfaces 1 of slave units 1, 2, 3, and 4, respectively. Each slave unit uses fiber optic interface 1.

[0080] The serial numbers of the Fibre Channel pressure plates and the Fibre Channel interfaces are the same. During normal operation, each slave device only needs to engage one Fibre Channel pressure plate, while the master device needs to engage each Fibre Channel pressure plate for the Fibre Channel it is using.

[0081] according to Figure 2 After wiring, the multi-terminal differential current protection can be put into operation.

[0082] Figure 3 This is a schematic flowchart illustrating the steps of the method for automatically adjusting the braking coefficient of multi-terminal current differential protection for lines proposed in this invention. In a preferred but non-limiting embodiment of this invention, the method specifically includes the following steps 1 to 6:

[0083] Step 1: Determine the identity of the master and slave devices based on the fiber optic channel's ranking and the setting sheets of the current differential protection devices at each end.

[0084] The master unit should be located on the power grid side, and the slave units should be arranged in order of proximity to the master unit. They should be designated as slave unit 1, slave unit 2, etc. according to the number and order of the fiber optic channels. Otherwise, the ranging function of the multi-terminal current differential protection will be affected.

[0085] Based on the fiber optic channel arrangement, determine the location of the master and slave devices, and input the corresponding set values.

[0086] The setting sheet of the multi-terminal current differential protection device can be set with setting items for local address code, fiber optic channel one-side identification code, fiber optic channel two-side identification code, ..., fiber optic channel eight-side identification code.

[0087] Therefore, by comparing the local address code settings of the current differential protection devices at each end, the protection device with the largest local address code can be determined as the master device, and the other ends are slave devices.

[0088] As can be seen from the above introduction to the multi-terminal current differential protection system, each slave unit communicates with the master unit through its own fiber optic channel, and the slave units do not communicate directly with each other.

[0089] The main unit collects the current at the protection installation location and receives the current sent by each slave unit. After the current differential protection trips when the conditions for operation are met, it also trips each slave unit.

[0090] The main unit is installed on the grid side, allowing for rapid startup in the event of a fault within the line area, ensuring fast operation of the current differential protection. If the main unit is placed on the renewable energy side, which typically exhibits weak feed characteristics, it may start via weak feed, resulting in slow startup and affecting the operating speed of the current differential protection.

[0091] The master communicates with each slave device separately, so the master needs to input its own address code and the identification code of each fiber channel. The address codes are of different values. Each slave device only communicates with the master device, so each slave device only needs to input its own address code and the identification code of each fiber channel. Other identification codes are invalid.

[0092] The assigned values ​​of the fiber optic channel identification codes on both sides of the slave device should be the same as the assigned values ​​of the local identification codes on the master device; the assigned values ​​of the fiber optic channel identification codes on both sides of the master device should be the same as the assigned values ​​of the local identification codes on slave device 1; and the assigned values ​​of the fiber optic channel identification codes on both sides of the master device should be the same as the assigned values ​​of the local identification codes on slave device 2. The identity of each slave device should be determined in this way.

[0093] The master and slave devices can only communicate normally when their identification codes correspond to each other on both sides of any fiber optic channel.

[0094] After the identities of the master and slave devices are determined in step 1, the process proceeds to step 2, where the master identifies the slave devices that have activated the differential current protection function.

[0095] Step 2: Based on the activation / deactivation status of the corresponding fiber channel pressure plates of the protection devices on both sides of the fiber channel, determine the activation status of the fiber channel, and the host identifies the slave device with the current differential protection function activated.

[0096] The multi-terminal differential current protection device is equipped with fiber optic channel pressure plates. The host unit can select and activate the corresponding fiber optic channel one pressure plate, fiber optic channel two pressure plate, ... fiber optic channel eight pressure plate, according to the required number of fiber optic channels to be activated, thereby controlling the activation and deactivation of fiber optic channels one, two, ... eight respectively. Therefore, the activation or deactivation of each fiber optic channel is achieved by activating or deactivating the corresponding fiber optic channel pressure plates on both sides of the fiber optic channel. The host unit activates or deactivates each fiber optic channel by activating or deactivating the corresponding fiber optic channel pressure plate, while the slave unit activates or deactivates its respective fiber optic channel by activating or deactivating the fiber optic channel one pressure plate.

[0097] If the fiber channel pressure plate of the slave device and the corresponding fiber channel pressure plate of the master device are engaged, then the fiber channel is engaged, and the current differential protection function of the branch corresponding to the fiber channel and the slave device is activated; if the fiber channel pressure plate of the slave device and the corresponding fiber channel pressure plate of the master device are disengaged, then the corresponding fiber channel is disengaged, and the current differential protection function of the branch corresponding to the fiber channel and the slave device is deactivated.

[0098] Furthermore, the engagement or disengagement of the fiber channel pressure plates on both sides must be consistent. If a fiber channel is in normal use, the corresponding fiber channel pressure plates of the host and slave on both sides of the channel should be engaged; if the channel is not configured or the channel is faulty, the corresponding fiber channel pressure plates of the host and slave on both sides of the channel should be disengaged.

[0099] When the fiber channel pressure plate on / off states of the master and slave devices are inconsistent, both the master and slave devices will report an alarm indicating inconsistency of the corresponding channel pressure plate and will exit the multi-terminal current differential protection function.

[0100] When a fiber optic channel is put into operation, the host can identify the slave device of the channel, receive data such as current and voltage from the slave device, and control the slave device to trip. The protection devices on both sides monitor the channel's delay, frame loss, bit error, etc., and issue a channel alarm when abnormalities occur.

[0101] Step 3: Determine whether the protection is activated on the master and slave units with the current differential protection function. If the protection on each side is not activated, proceed to step 4; otherwise, proceed to the fault handling procedure.

[0102] When a system fault occurs, the protection is activated, and the fault handling procedure is entered until all protections on each side fail to activate, at which point the system returns to step 1.

[0103] System faults or other reasons may cause circuit breakers to trip and close, potentially resulting in some circuit breakers being in the open state. In this case, the current differential protection on the corresponding branch side will no longer participate in the differential calculation, and the host system needs to re-determine the actual number of terminals participating in the current differential calculation. Therefore, step 4 can only proceed when no protection is activated.

[0104] In practice, the current differential protection device determines protection activation when any of the following conditions are met:

[0105] The phase-to-phase current change or the zero-sequence current change reaches the change in the starting current setting; the zero-sequence current reaches the zero-sequence starting current setting; all three phase currents reach the oscillation blocking overcurrent setting or all three phase impedances fall within the impedance III range; the differential current reaches the setting and a starting signal is received from the other side, while the voltage changes; the tripping operation initiates reclosing.

[0106] Step 4: The host determines the closing, opening, and maintenance status of each protection device, determines the number of protection devices in the closing state (if the host is in the closing state, the host end is also included), and executes the corresponding protection strategy for the protection devices in the maintenance state.

[0107] Once the fiber optic channel is activated, during normal communication, the master and slave units can transmit information such as start-up, current, voltage, position, fiber optic channel switch engagement, and device status. Multi-terminal differential current protection operates in different states, including closed, open, and maintenance states. The master unit itself can determine whether it is in the closed or open state. The slave unit transmits information such as start-up, current, voltage, circuit breaker position, fiber optic channel switch engagement, and device status to the master unit via the fiber optic channel, allowing the master unit to determine whether the slave unit is in the closed or open state.

[0108] Specifically, the methods for determining the closed and open states are as follows:

[0109] The protection is determined to be in the closed state if the following conditions are met simultaneously:

[0110] Protection was not activated. Fiber optic channel was engaged, and no trip position was entered.

[0111] The protection is determined to be in the tripped state if the following conditions are met simultaneously:

[0112] The protection was not activated. The fiber optic channel was engaged, and a trip position was established. The currents for phases A, B, and C, as well as the zero-sequence current, were all less than 0.05I. N , among which, I N This is the rated value for the secondary current. 0.05I N It is currently the minimum precise operating current for multi-terminal differential current protection devices.

[0113] When the protection device is in the closed state, it participates in the differential calculation of the multi-terminal current differential protection. (If the master unit is in the tripped position and the fiber optic channel pressure plate is engaged, each slave unit participating in the differential calculation transmits information such as the protection start signal, position signal, current, voltage, fiber optic channel pressure plate engagement, and device status to the master unit. The master unit then calculates the current differential and trips each slave unit after the operating conditions are met.) However, the protection device on the open side has no current and does not participate in the differential calculation of the multi-terminal current differential protection. No drain current is generated during faults within the multi-terminal line area. Therefore, the master unit needs to determine the number of terminals in the closed state.

[0114] If the fiber optic channel is abnormal or the device malfunctions, and the protection system needs to be taken out of service, then it will enter maintenance mode.

[0115] For fiber optic channel anomalies, including fiber optic channel problems, fiber optic interface problems, and device malfunctions, if only a specific fiber optic channel is malfunctioning, and the host cannot receive information from that slave, or the slave cannot receive information from the host, while other fiber optic channels are functioning normally, simply shut down the operation of that channel and inspect it. If the host cannot communicate normally with all slaves, all fiber optic channels should be shut down and inspected.

[0116] When the device malfunctions, it cannot work normally, locks out the protection function, issues an alarm message, and transmits the device status information to the opposite protection device through the fiber optic channel. The opposite protection device then issues a "opposite protection off" alarm, indicating that the device needs to be repaired.

[0117] For lines of 110kV and below, one line current differential protection device is typically configured on each side, forming a single main protection system. The main protection is current differential protection, and backup protection includes distance protection, zero-sequence protection, or overcurrent protection. For lines of 220kV and above, two line current differential protection devices are typically configured on each side, forming a dual main protection system. Each system's main protection is current differential protection, and backup protection includes distance protection, zero-sequence protection, etc. The two protection systems operate independently but protect the same line and related equipment. Based on this, the following protection strategy is proposed:

[0118] When a slave device with a single set of protection on each side is under maintenance, the circuit breaker needs to be tripped and the corresponding fiber optic channel pressure plate needs to be deactivated. Once the fiber optic channel is deactivated, the current differential protection function of the branch where the slave device is located will be deactivated.

[0119] When the host with a single protection set on each side is under maintenance, the host circuit breaker needs to be tripped, the fiber optic channel pressure plates at each end need to be removed, the current differential protection function of all branches needs to be deactivated, and no further calculations are needed. The main protection is out of operation, but the backup protection can work normally. If the line needs to continue to operate, the slave backup protection can be activated.

[0120] If any end of one of the dual protection systems on each side is under maintenance, the fiber optic channel pressure plate at that end needs to be deactivated, and the fiber optic channel pressure plates at the other ends also need to be deactivated. The current differential protection function of all branches needs to be deactivated, and no further calculations are required. However, the circuit breaker remains in the closed position, and the backup protection at the other ends is retained. At the same time, the normal operation of the other protection system is not affected. The other main protection system can be put into normal operation, and the backup protection system can also be put into operation.

[0121] Step 4 determines the number of terminals in the closed state and provides this information to step 5.

[0122] Step 5: If the number of terminals in the closed state is greater than or equal to 1, proceed to step 6; otherwise, set the initial threshold of the braking coefficient k to judge the current differential protection action and return to step 1.

[0123] The initial threshold value of the braking coefficient k is preferably 0.6.

[0124] Before all circuit breakers are closed, the number of terminals in the closed state is 0. If a circuit breaker is closed due to a fault, the protection is activated. There is not enough time to adjust the braking coefficient, but the current differential protection still needs to operate. At this time, the differential current is equal to the braking current, and the slope is 1. When the initial threshold of the braking coefficient k is preferably 0.6, the operation requirements can be fully met. A braking coefficient of 0.6 can also meet the situation where two circuit breakers are closed at the same time.

[0125] Step 6: Automatically adjust the braking coefficient k according to the number of terminals of the protection device in the closed state, so as to be used for the judgment of the current differential protection action.

[0126] The restraining coefficient k of multi-terminal current differential protection satisfies the following relationship:

[0127]

[0128] In the formula, m is the number of terminals in the closed state, which is 1, 2, 3, ... 9.

[0129] When m is 1, 2, 3, 4, 5, 6, 7, 8, 9, the braking coefficients are 0.80, 0.61, 0.54, 0.50, 0.47, 0.45, 0.43, 0.42, 0.41, respectively. As the number of terminals in the closed state increases, the braking coefficient of the multi-terminal current differential protection gradually decreases, which can meet the operating modes of different numbers of terminals and different states.

[0130] The maximum value of m is 9, meaning that the current multi-terminal current differential protection can meet the requirements of up to 9 terminals and 8 fiber optic channels being put into operation, with each terminal in the closed position.

[0131] The minimum value of m is 1, which means that the multi-terminal current differential protection has only one closed state and the other ends are open. At least one fiber optic channel is put into operation, the multi-terminal line is in hot standby state, and when there is power at the closed end, the multi-terminal current differential protection can still protect the fault within the protection area.

[0132] When m is 2, the multi-terminal current differential protection can meet the requirement of one fiber optic channel being put into operation with two ends in the closed state.

[0133] After adjusting the braking coefficient k, if the host trips and the fiber channel pressure plate is engaged, each slave participating in the differential calculation will transmit the protection start signal, position signal, current, fiber channel pressure plate engagement, device status and other information to the host. The host will then calculate the current differential and make a current differential protection action judgment based on the braking coefficient k. When the judgment condition (i.e., formula (1)) is met, each slave in the closed state will be tripped.

[0134] The present invention relates to a system for automatically adjusting the braking coefficient of a multi-terminal current differential protection system for lines. This system is designed for multi-terminal current differential protection systems for lines and includes:

[0135] The master-slave identification module is used to determine the identity of the master and each slave device based on the fiber optic channel's ranking and the setting sheets of the current differential protection devices at each end.

[0136] The protection function activation identification module is used to determine the activation status of the fiber optic channel based on the activation / deactivation status of the corresponding fiber optic channel pressure plates of the protection devices on both sides of the fiber optic channel. The host identifies the slave device that has activated the differential current protection function.

[0137] The protection start-up discrimination module is used to determine whether the protection has been started for the master and slave devices with the current differential protection function. If the protection on each side is not started, the system enters the protection device status discrimination module; otherwise, it enters the fault handling program.

[0138] The protection device status determination module is used by the host to determine the closing status, opening status, and maintenance status of each protection device, determine the number of protection devices in the closing status, and execute corresponding protection strategies for protection devices in the maintenance status.

[0139] The closing status terminal number judgment module is used to determine whether the number of terminals in the closing status is greater than or equal to 1. If so, it enters the braking coefficient adjustment module; otherwise, it sets the initial threshold value of the braking coefficient k to judge the current differential protection action and returns to the master-slave identity determination module.

[0140] The braking coefficient adjustment module is used to automatically adjust the braking coefficient k according to the number of terminals of the protection device in the closed state, so as to make judgment on the operation of the current differential protection.

[0141] The beneficial effects of this invention are compared with those of the prior art:

[0142] This invention automatically adjusts the braking coefficient of the current differential protection according to the change in the number of line terminals and different operating states, which can improve the operating sensitivity of multi-terminal current differential protection and solve the problem of insufficient sensitivity that may occur when using multi-terminal current differential protection with a fixed braking coefficient. It can meet the various operating modes with different numbers of line terminals.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for automatically adjusting the braking coefficient of a multi-terminal current differential protection system for lines, the method being designed for a multi-terminal current differential protection system for lines, characterized in that: The method includes the following steps: Step 1: Determine the identity of the master and slave devices based on the fiber optic channel's ranking and the setting sheets of the current differential protection devices at each end. Step 2: Based on the activation / deactivation status of the corresponding fiber channel pressure plates of the protection devices on both sides of the fiber channel, determine the activation status of the fiber channel, and the host identifies the slave device with the current differential protection function activated. Step 3: Determine whether the protection is activated on the master and slave units with the current differential protection function. If the protection on each side is not activated, proceed to step 4; otherwise, proceed to the fault handling procedure. Step 4: The host determines the closing status, opening status, and maintenance status of each protection device, determines the number of protection devices in the closing status, and executes the corresponding protection strategy for the protection devices in the maintenance status. Step 5: If the number of terminals in the closed state is greater than or equal to 1, proceed to step 6; otherwise, set the braking coefficient. k The initial threshold is used to determine the current differential protection action, and then the process returns to step 1; Step 6: Automatically adjust the braking coefficient based on the number of terminals of the protection device in the closed state. k For use in determining the action of current differential protection, braking coefficient k The adjustment method is as follows: In the formula, m is the number of terminals in the closed state.

2. The method for automatically adjusting the braking coefficient of multi-terminal current differential protection for lines according to claim 1, characterized in that: In the multi-terminal current differential protection system of the line, a current differential protection device, a current transformer and a circuit breaker are installed at each end of the line. One of the current differential protection devices at each end is set as the master, and the rest are set as slaves. The master communicates with each slave respectively. The host is installed on the power grid side, and the slaves are arranged in order of proximity to the host. For slave 1, its branch is directly connected to the host branch through a connection point, without a tie line. The host communicates with each slave through a corresponding fiber optic channel, but the slaves do not communicate with each other.

3. The method for automatically adjusting the braking coefficient of multi-terminal differential current protection for lines according to claim 1, characterized in that: Each protection device is equipped with 8 fiber optic interfaces (1 to 8). Each fiber optic interface is equipped with a fiber channel pressure plate. The host and each slave device are connected to the fiber channel through the fiber optic interface configured on their respective devices. The corresponding fiber channel is put into and taken out by opening and closing the fiber channel pressure plate. The serial number of the Fibre Channel pressure plate is the same as the serial number of the corresponding Fibre Channel interface, and the serial number of the Fibre Channel is the same as the serial number of the host Fibre Channel interface. The host connects to each slave device in sequence starting from Fibre Channel 1, and each slave device uses Fibre Channel 1 to connect to the host. The protection device is configured with a setting sheet, in which the host sets the local address code and the opposite identification code of each fiber optic channel, and each slave sets the local address code and the opposite identification code of the first fiber optic channel used for communication with the host. The local address code of the master is greater than the local address code of each slave device; The identification code setting of the opposite side of the fiber optic channel used by each slave device for communication with the host is the same as the setting value of the local address code of the host. When the local address code of the slave device on either side of any fiber optic channel is consistent with the corresponding identification code setting value of the opposite side of the host, the host and the slave device can achieve normal communication.

4. The method for automatically adjusting the braking coefficient of multi-terminal current differential protection for lines according to claim 1, characterized in that: In step 1, the location of the host and each slave device is determined according to the fiber optic channel arrangement, and the corresponding settings are entered into the setting sheet. By comparing the values ​​of the local address codes in the setting sheets of each protection device, the protection device with the largest local address code is determined to be the master device, and the others are slave devices. The identity of each slave device is determined based on the correspondence between the assigned values ​​of the identification codes on the opposite side of each fiber optic channel in the host configuration sheet and the assigned values ​​of the identification codes on the local side in the slave configuration sheet.

5. The method for automatically adjusting the braking coefficient of multi-terminal current differential protection for lines according to claim 1, characterized in that: In step 2, if the fiber channel pressure plate of the slave device and the corresponding fiber channel pressure plate of the master device are engaged, it means that the corresponding fiber channel is engaged, and the current differential protection function of the corresponding branch and slave device is engaged. If the fiber channel pressure plate of the slave device and the corresponding fiber channel pressure plate of the master device are disconnected, it means that the corresponding fiber channel is disconnected, and the branch corresponding to the fiber channel and the slave device will lose the current differential protection function. If the fiber channel pressure plate on / off status of the master and slave devices are inconsistent, both the master and slave devices will report an alarm indicating inconsistency of the corresponding channel pressure plate and will exit the multi-terminal current differential protection function.

6. The method for automatically adjusting the braking coefficient of multi-terminal current differential protection for lines according to claim 1, characterized in that: In step 4, the determination methods for the closed and open states are as follows: If the protection device meets the following conditions at the same time, the operating status is determined to be the closed state: the protection is not started, the fiber optic channel pressure plate is engaged, the fiber optic channel is engaged, and there is no trip position input. If the protection device simultaneously meets the following conditions, the operating state is determined to be the tripped state: the protection has not been activated, the fiber optic channel pressure plate is engaged, the fiber optic channel is engaged, a trip position input is available, and the currents of phases A, B, C, and zero sequence are all less than 0.

05. I N ; in, I N This is the rated value for the secondary current.

7. The method for automatically adjusting the braking coefficient of multi-terminal differential current protection for lines according to claim 1, characterized in that: In step 4, if the fiber optic channel is abnormal or the protection device malfunctions, the corresponding protection device will enter maintenance mode. When a slave device with a single set of protection on each side is under maintenance, the corresponding circuit breaker will be tripped, and the corresponding fiber optic channel pressure plate will be deactivated, thus deactivating the current differential protection function of the branch where the slave device is located. When the host with a single set of protection on each side is under maintenance, the host circuit breaker is tripped, the fiber optic channel pressure plate at each end is removed, and the current differential protection function of all branches is turned off, without affecting the normal operation of the slave backup protection. If either end of one of the dual protection systems on each side is under maintenance, the fiber optic channel pressure plate at the maintenance end will be deactivated, and the fiber optic channel pressure plates at the other ends will also be deactivated, thus deactivating the current differential protection function of all branches. However, the circuit breaker will remain in the closed position, retaining backup protection at the other ends, without affecting the normal operation of the other protection system.

8. The method for automatically adjusting the braking coefficient of multi-terminal differential current protection for lines according to claim 1, characterized in that: In step 5, the braking coefficient k The initial threshold is 0.

6.

9. A system for automatically adjusting the braking coefficient of a multi-terminal differential current protection system for lines, wherein the system for automatically adjusting the braking coefficient is designed for a multi-terminal differential current protection system for lines, characterized in that, The system for automatically adjusting the braking coefficient of the multi-terminal current differential protection of the line includes: The master-slave identification module is used to determine the identity of the master and each slave device based on the fiber optic channel's ranking and the setting sheets of the current differential protection devices at each end. The protection function activation identification module is used to determine the activation status of the fiber optic channel based on the activation / deactivation status of the corresponding fiber optic channel pressure plates of the protection devices on both sides of the fiber optic channel. The host identifies the slave device that has activated the differential current protection function. The protection start-up discrimination module is used to determine whether the protection has been started for the master and slave devices with the current differential protection function. If the protection on each side is not started, the system enters the protection device status discrimination module; otherwise, it enters the fault handling program. The protection device status determination module is used by the host to determine the closing status, opening status, and maintenance status of each protection device, determine the number of protection devices in the closing status, and execute corresponding protection strategies for protection devices in the maintenance status. The terminal count determination module for the closing status is used to determine whether the number of terminals in the closing status is greater than or equal to 1. If so, it proceeds to the braking coefficient adjustment module; otherwise, it sets the braking coefficient. k The initial threshold is used to determine the current differential protection action and then returned to the master / slave identification module. The braking coefficient adjustment module is used to automatically adjust the braking coefficient based on the number of terminals of the protection device in the closed state. k For use in determining the action of current differential protection, braking coefficient k The adjustment method is as follows: In the formula, m is the number of terminals in the closed state.

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