A multi-terminal transmission line differential protection system and method

Abstract

The application discloses a multi-terminal power transmission line differential protection system and method, the system is under a master-slave channel topology, two hosts exist in the system, and channels are connected between the hosts and slaves; when the channels between the hosts and slaves are normal, the two hosts both perform differential logic operation; the differential protection device executes a tripping outlet only when there are tripping signals of the two hosts, so that the reliability of multi-terminal differential calculation is improved; when any channel of the host and the slave is faulty, the multi-terminal differential protection function is ensured not to be exited through a redundant channel design. The application effectively improves the reliability of multi-terminal differential protection operation without sacrificing the speediness and flexibility of the multi-terminal line differential protection, and is easy to implement.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, specifically to a system and method for differential protection of multi-terminal transmission lines. Background Technology

[0002] With the large-scale integration of photovoltaic and wind power into the grid, multi-terminal transmission lines are increasingly appearing in high-voltage transmission lines. For multi-terminal transmission lines, longitudinal current differential protection has become the preferred choice. Currently, there are multi-terminal differential protection systems using a master-slave topology, where the master unit and multiple slave units are connected via fiber optic channels, but there are no channel connections between the slave units themselves. This approach simplifies node expansion, and the differential action time is only related to the maximum channel delay. However, the disadvantages are that the differential protection must be deactivated if any channel fails. Furthermore, the entire system relies on a single master unit for differential logic operations, which can lead to lower reliability for critical systems. Summary of the Invention

[0003] The purpose of this invention is to address the above problems by proposing a system and method for differential protection of multi-terminal transmission lines, which improves the reliability of multi-terminal line differential protection without sacrificing its speed and flexibility of expansion.

[0004] To achieve the above objectives, this application adopts the following technical solution:

[0005] In its first aspect, this application proposes a differential protection system for multi-terminal transmission lines. Each side of the multi-terminal transmission line is equipped with a differential protection device. Any two differential protection devices are selected as master devices, and the remaining differential protection devices are slave devices. The master devices are connected to the slave devices on each side via a single channel, and the master devices themselves are connected via a dual-channel connection. When both channels of the master and slave devices are normal, both master devices perform differential calculations. If the master device meets the differential action conditions, it outputs a protection trip signal. The slave device only outputs a trip signal upon receiving trip signals from both master devices. When any channel of the master or slave device fails, that master device exits the differential calculation. The master device that has exited differential calculation outputs a trip signal upon receiving a trip signal from the other master device. The slave device outputs a trip signal upon receiving a trip signal from one master device and a differential calculation exit signal from the other master device.

[0006] Preferably, the differential protection device is equipped with a master pressure plate, which operates as the master when the master pressure plate is engaged and as the slave when the pressure plate is disengaged.

[0007] Preferably, the differential protection device is provided with a master control word. When the master control word is set, it operates as a master device; when the master control word is reset, it operates as a slave device.

[0008] Preferably, the host and slave are connected via a dedicated fiber optic channel or a multiplexed channel; the hosts are connected via a dedicated fiber optic channel or a multiplexed channel.

[0009] Preferably, each differential protection device includes: a data acquisition module, a channel information processing module, a fault initiation module, a differential calculation module, and a tripping module, with each module interconnected via a bus;

[0010] The acquisition module: completes the acquisition of analog and digital signals on this side;

[0011] The channel information processing module: completes sampling synchronization, monitors the status of the channel, and completes data interaction between the local side and the opposite side of the channel;

[0012] The fault start-up module: Based on the local current data of the acquisition module, it determines whether the local start-up criterion is met. If so, it sends the local start-up signal to the opposite side of the channel through the channel information processing module. The host also determines whether the multi-terminal differential start-up condition is met based on the start-up signals of each side summarized by the channel information processing module. If so, it sends the multi-terminal differential start-up signal to the differential calculation module.

[0013] The differential operation module: For slave devices, the differential operation module is always off; for master devices, after receiving the multi-terminal differential start signal from the fault start module, it completes differential logic operation based on the synchronously sampled current data from the acquisition module and the channel information processing module. When the differential action criterion is met, it sends a trip signal to other differential protection devices; when the master device and any slave device channel fail, the differential operation module exits the calculation and sends a differential calculation exit signal to other differential protection devices.

[0014] The tripping module controls the tripping output based on the tripping signal and the host differential calculation exit signal.

[0015] As a second aspect of this application, a protection method for a multi-terminal transmission line differential protection system is proposed, comprising:

[0016] Step 1, Operation mode determination: Randomly select two differential protection devices as master units and other differential protection devices as slave units;

[0017] Step 2, Data Acquisition on Each Side: The host and slave devices respectively acquire analog and digital signals on their respective sides;

[0018] Step 3, sampling synchronization and data exchange: Select any one host as the sampling reference end, and adjust the sampling of the other host and all slaves to synchronize with the sampling reference end; the sampling data after the two hosts are exchanged and synchronized is set up so that the differential protection device of the slave can send the synchronized sampling data of this side to the two hosts respectively.

[0019] Step 4, Channel Status Monitoring: Real-time monitoring of the channel status of the master and slave devices. If the channel status of both the master and slave devices is normal, proceed directly to Step 5. If a channel failure occurs between any master and any slave device, the master will exit the differential calculation and send the channel failure signal with the slave device to the differential protection device on the other side, and then proceed to Step 5.

[0020] Step 5, Start-up Judgment: The master and slave units perform start-up judgment based on their local current data. If the local start-up criteria are met, a local fault start-up signal is sent to the differential protection device on the opposite side of the channel. When both the master and slave channels are normal, the two master units summarize the start-up signals from each side to determine whether the multi-terminal differential start-up conditions are met. When a fault occurs in the channel between any master unit and any slave unit, a master differential calculation exit signal is sent to other differential protection devices, and the other master unit summarizes the start-up signals from each side to determine whether the multi-terminal differential start-up conditions are met.

[0021] When the multi-terminal differential start-up conditions are met, the host enters step 6 to determine the differential fault; otherwise, both the host and the slave return to step 1.

[0022] Step 6, Differential Fault Judgment: When both the master and slave channels are normal, the two masters perform differential calculations based on the aggregated sampled data from each side. If both meet the differential action criteria, the action condition is met. When one master receives a differential calculation exit signal from the other master, and the differential action criteria are met on this side, the action condition is met. If the action condition is met, proceed to step 7; otherwise, return to step 1 after a delay.

[0023] Step 7, Trip Judgment: Control the trip output based on the trip signal and the host differential calculation exit signal.

[0024] Preferably, in step 4, if the host with the faulty channel between the slave and the slave is the sampling reference end, another host is needed as the sampling reference end before proceeding to step 5, and other differential protection devices adjust the sampling synchronization according to the new sampling reference end.

[0025] Preferably, in step 5, at least the N-1 side differential protection device start signal is set, indicating that the multi-terminal differential start condition is met.

[0026] Preferably, in step 7, controlling the trip output based on the trip signal and the host differential calculation exit signal specifically includes: the host sending a trip signal to other differential protection devices and tripping; if the host exits differential calculation, the host that has exited differential calculation will trip when it receives a trip signal from the host on the other side; the slave device will trip when it receives trip signals from both hosts, or when it receives a trip signal from one host and a differential calculation exit signal from the host on the other side.

[0027] Preferably, step 7 further includes: when the slave receives a trip signal from both masters, it directly trips without delay; when the slave receives a trip signal from a single master and a differential calculation exit signal from the other master, it trips after a fixed delay.

[0028] The beneficial effects of this invention are: it proposes a system and method for differential protection of multi-terminal transmission lines, which ensures that the multi-terminal differential protection function does not exit when any protection channel fails, through redundant host and channel design; by having two hosts perform differential logic operations simultaneously, the differential protection device executes the trip output when there are trip signals from two hosts, thus ensuring the reliability of the system. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a multi-terminal transmission line differential protection system.

[0030] Figure 2 This is a schematic diagram of the differential protection device.

[0031] Figure 3 This is a schematic diagram of the differential protection method for multi-terminal transmission lines. Detailed Implementation

[0032] To improve the reliability of differential protection for multi-terminal transmission lines, this application provides a differential protection system for multi-terminal transmission lines. Each side of the multi-terminal transmission line is equipped with a differential protection device. Any two differential protection devices are selected as master devices, and the remaining differential protection devices are slave devices. The master devices are connected to the slave devices on each side via a single channel, and the master devices themselves are connected via a dual-channel connection. Figure 1 The diagram shows a five-terminal transmission line system. Each terminal is equipped with a differential protection device. Two differential protection devices can be selected as master devices, and the others as slave devices. In this embodiment, the differential protection devices on the E1 and E5 power supply sides are selected as master device 1 and master device 2, respectively; the differential protection devices on the E2, E3, and E4 power supply sides are selected as slave device 1, slave device 2, and slave device 3, respectively. The master devices are connected to the slave devices on each side via a single channel, and the two master devices are connected via a dual-channel connection. When both master and slave channels are normal, both master devices perform differential calculations. If the master device meets the differential action conditions, it trips the circuit breaker. The slave device only trips when it receives trip signals from both master devices, thus improving the reliability of multi-terminal differential calculations. If any channel of the master or slave device fails, that master device exits the differential calculation. The master device that has exited differential calculations trips when it receives a trip signal from the other master device. The slave device trips when it receives a trip signal from one master device and a differential calculation exit signal from the other master device. By employing redundant channel design, the multi-terminal differential protection function is ensured to remain operational. This solution effectively improves the reliability of multi-terminal differential protection operation without sacrificing its speed of operation or flexibility of expansion, and is easy to implement in engineering.

[0033] In a preferred embodiment, the distinction between master and slave devices can be made in one of the following two ways.

[0034] Option 1 involves using a master switch plate in the differential protection device to identify the master and slave units. When the master switch plate is engaged, the device operates as the master unit; when the plate is disengaged, it operates as the slave unit.

[0035] Option 2 involves setting a master control word in the differential protection device to identify the master and slave devices. When the master control word is set, the device operates as the master; when the master control word is reset, the device operates as the slave.

[0036] In some embodiments, the host and slave are connected via a dedicated fiber optic channel or a multiplexed channel; the hosts are connected via a dedicated fiber optic channel or a multiplexed channel.

[0037] like Figure 2 As shown, each differential protection device includes: a data acquisition module, a channel information processing module, a fault initiation module, a differential calculation module, and a tripping module. These modules are interconnected via a bus. Among them:

[0038] Acquisition Module: Used to acquire analog and digital data on this side. Analog data includes three-phase voltage and current. Digital data includes circuit breaker position signals.

[0039] Channel information processing module: used to complete sampling synchronization, monitor the status of the input channel, and complete data interaction between this side and the other side of the channel.

[0040] Fault Initiation Module: Based on the local current data from the acquisition module, this module determines whether the local initiation criteria are met. If so, it sends the local initiation signal to the opposite side of the channel via the channel information processing module. Common initiation criteria include current change and zero-sequence current. Current change initiation specifically checks whether the half-wave integral value of the current change is greater than a set threshold; if so, the initiation criterion is met. Zero-sequence current initiation specifically checks whether the zero-sequence current is greater than a set threshold; if so, the initiation criterion is met. The host also determines whether the multi-terminal differential initiation conditions are met based on the initiation signals from each side aggregated by the channel information processing module. If so, it sends the multi-terminal differential initiation signal to the differential calculation module.

[0041] The differential operation module operates as follows: For slave devices, the differential operation module is always off; for master devices, upon receiving the multi-terminal differential start signal from the fault start module, it performs differential logic operations based on the synchronously sampled current data from the acquisition module and the channel information processing module. When the differential action criteria are met, it sends a trip signal to other differential protection devices. When the master device or any slave device experiences a channel fault, the differential operation module exits the calculation and sends a differential calculation exit signal to other differential protection devices. Specifically, for slave devices, it determines whether the local start criteria are met based solely on the local current data from the acquisition module. If met, it sets the local start signal and sends it to the device on the other side of the channel. For master devices, it determines whether the local start criteria are met based on the local current data from the acquisition module. If met, it sets the local start signal and sends it to the device on the other side of the channel. Simultaneously, it combines the start signal from the other side of the channel information processing module to determine whether the multi-terminal differential start conditions are met. If met, it sets the multi-terminal differential start signal and sends it to the differential operation module.

[0042] The tripping module controls the trip output based on the tripping signal and the host differential calculation exit signal. Specifically, the host controls the trip output based on its own tripping signal. If the host exits differential calculation, it will trip when it receives a tripping signal from the other host. The slave device will trip when it receives tripping signals from both hosts, or when it receives a tripping signal from one host and a differential calculation exit signal from the other host.

[0043] This application also proposes embodiments of a multi-terminal transmission line protection method for application in the aforementioned multi-terminal transmission line differential protection system, such as... Figure 3 The steps shown are as follows:

[0044] Step 1, Operation Mode Determination: Select any two differential protection devices as master units, and the remaining differential protection devices as slave units. Specifically, this can be achieved by setting a master unit control plate on the differential protection devices; the master unit operates when the master unit is engaged, and the slave unit operates when the master unit is disengaged. Alternatively, a master control word can be set in the differential protection devices to identify the master and slave units; when the master control word is set, the device operates as the master unit, and when the master control word is reset, the device operates as the slave unit.

[0045] Step 2, Data Acquisition on Each Side: The master and slave units respectively acquire analog and digital data on their respective sides. Specifically, this includes three-phase voltage, current, and circuit breaker position signals.

[0046] Step 3, Sampling Synchronization and Data Exchange: Select any one host as the sampling reference end, and adjust the sampling of the other host and all slaves to synchronize with the sampling reference end; the sampling data after synchronization processing between the two hosts is set up so that the differential protection device of the slaves can send the synchronized sampling data of their respective sides to the two hosts. For example, when host 1 is the sampling reference end, host 2 and all slaves adjust their sampling to synchronize with host 1, and all slaves send the synchronized sampling data of their respective sides to host 1 and host 2, while host 1 and host 2 exchange their respective sampling data.

[0047] Step 4, Channel Status Monitoring: Real-time monitoring of the channel status of the master and slave devices. If the channel status of both the master and slave devices is normal, proceed directly to Step 5. If a channel fault occurs between any master and any slave device, the master device exits the differential calculation and sends the channel fault signal with that slave device to the differential protection devices on other sides, then proceeds to Step 5. For example, if the channel status of both the master and slave devices is normal, proceed directly to Step 5. Suppose a channel fault occurs between master 2 and slave devices, master 2 exits the differential calculation and sends the signal to master 1 and all slave devices.

[0048] In a preferred embodiment, in step 4, if the host with the channel failure between the host and slave is the sampling reference, another host is needed as the sampling reference before proceeding to step 5. Other differential protection devices adjust sampling synchronization according to the new sampling reference. For example, when host 1 is the sampling reference, when a channel failure occurs between host 1 and slave 1, host 1 exits the differential calculation and sends the signal to host 2 and all slaves. Host 2 then switches to the sampling reference, and both host 1 and slaves adjust their sampling to synchronize with host 2. When a channel failure occurs between host 2 and slaves, host 2 exits the differential calculation and sends the signal to host 1 and all slaves. Host 1 continues to be the sampling reference without needing to switch sampling references.

[0049] Step 5, Start-up Judgment: The master and slave units perform a start-up judgment based on the local current data. If the local start-up criteria are met, a local fault start signal is sent to the differential protection device on the opposite side of the channel. Commonly used start-up criteria include current change and zero-sequence current criteria. For current change start-up, it is determined whether the half-wave integral value of the current change is greater than a set threshold value; if so, the start-up criterion is met. For zero-sequence current start-up, it is determined whether the zero-sequence current is greater than a set threshold value; if so, the start-up criterion is met.

[0050] When both the master and slave channels are functioning normally, the two master units aggregate the start signals from each side to determine whether the multi-terminal differential start condition is met. Preferably, at least the start signal of the differential protection device on the N-1 side is set, indicating that the multi-terminal differential start condition is met.

[0051] When the channel between any master unit and any slave unit fails, the master unit sends a differential calculation exit signal to other differential protection devices. The other master unit then aggregates the start signals from each side to determine whether the multi-terminal differential start conditions are met.

[0052] When the multi-terminal differential start-up conditions are met, the host enters step 6 to determine the differential fault; otherwise, both the host and slave return to step 1.

[0053] Step 6, Differential Fault Judgment: When both the master and slave channels are normal, the two masters perform differential calculations based on the aggregated sampled data from each side. If both meet the differential action criteria, the action condition is met. When one master receives a differential calculation exit signal from the other master, and the differential action criteria are met on this side, the action condition is met. When the action condition is met, proceed to step 7; otherwise, return to step 1 after a delay.

[0054] There are several commonly used differential action criteria, including full current phasor differential based on power frequency sinusoidal quantities, zero-sequence current differential, full current differential, and other types.

[0055] Taking the total current phasor differential criterion based on the power frequency sinusoidal quantity as an example, the expression is as follows:

[0056]

[0057] Among them, I cd For differential current, I set I is the threshold value for the differential action that is set. res The braking current is K, which is the set braking coefficient between 0 and 1. Differential current. The vector sum of currents at each terminal; braking current. This is the scalar sum of the currents at each terminal.

[0058] When the host calculates that the differential current satisfies equation (1), it is determined that the differential action criterion is met.

[0059] Step 7, Trip Judgment: Control the trip output based on the trip signal and the host differential calculation exit signal.

[0060] Specifically, this includes: the master device sending a trip signal to other differential protection devices and outputting a trip signal; if the master device exits differential calculation, it will output a trip signal when it receives a trip signal from the other master device; the slave device will output a trip signal when it receives trip signals from both masters, or when it receives a trip signal from one master device and a differential calculation exit signal from the other master device.

[0061] Optionally, when the slave receives a trip signal from both master units, it directly trips without delay; when the slave receives a trip signal from a single master unit and a differential calculation exit signal from the other master unit, it trips after a fixed delay.

[0062] This invention is not limited to the above embodiments. The descriptions in the above embodiments are only used to help understand the core ideas of this invention. Any modifications or equivalent substitutions made to this invention based on the ideas of this invention, as well as any changes made to the specific implementation methods and application scope, should fall within the protection scope of this invention.

Claims

1. A protection method for a multi-terminal transmission line differential protection system, characterized in that, The architecture of the multi-terminal transmission line differential protection system includes: a differential protection device is configured on each side of the multi-terminal transmission line, any two differential protection devices are selected as master devices, and the other differential protection devices are slave devices; the master devices and the slave devices on each side are connected by a single channel, and the master devices are connected by a dual channel; when both channels of the master device and the slave device are normal, both master devices perform differential calculations. If the master device meets the differential action conditions, it will trip the protection output. The slave device will only trip the protection output when it receives the trip signals from both master devices; when any channel of the master device or the slave device fails, the master device will exit the differential calculation. The master device that has exited the differential calculation will trip the protection output when it receives the trip signal from the master device on the other side. The slave device will trip the protection output when it receives the trip signal from one master device and the differential calculation exit signal from the other master device. Protection methods include: Step 1, Operation mode determination: Randomly select two differential protection devices as master units and other differential protection devices as slave units; Step 2, Data Acquisition on Each Side: The host and slave devices respectively acquire analog and digital signals on their respective sides; Step 3, sampling synchronization and data exchange: Select any one host as the sampling reference end, and adjust the sampling of the other host and all slaves to synchronize with the sampling reference end; the sampling data after the two hosts are exchanged and synchronized is set up so that the differential protection device of the slave can send the synchronized sampling data of this side to the two hosts respectively. Step 4, Channel Status Monitoring: Real-time monitoring of the channel status of the master and slave devices. If the channel status of both the master and slave devices is normal, proceed directly to Step 5. If a channel failure occurs between any master and any slave device, the master will exit the differential calculation and send the channel failure signal with the slave device to the differential protection device on the other side, and then proceed to Step 5. Step 5, Start-up Judgment: The master and slave units perform start-up judgment based on their local current data. If the local start-up criteria are met, a local fault start-up signal is sent to the differential protection device on the opposite side of the channel. When both the master and slave channels are normal, the two master units summarize the start-up signals from each side to determine whether the multi-terminal differential start-up conditions are met. When a fault occurs in the channel between any master unit and any slave unit, a master differential calculation exit signal is sent to other differential protection devices, and the other master unit summarizes the start-up signals from each side to determine whether the multi-terminal differential start-up conditions are met. When the multi-terminal differential start-up conditions are met, the host enters step 6 to determine the differential fault; otherwise, both the host and the slave return to step 1. Step 6, Differential Fault Judgment: When both the master and slave channels are normal, the two masters perform differential calculations based on the aggregated sampled data from each side. If both meet the differential action criteria, the action condition is met. When one master receives a differential calculation exit signal from the other master, and the differential action criteria are met on this side, the action condition is met. If the action condition is met, proceed to step 7; otherwise, return to step 1 after a delay. Step 7, Trip Judgment: Control the trip output based on the trip signal and the host differential calculation exit signal.

2. The protection method based on claim 1, characterized in that: In step 4, if the host with the faulty channel between the slave and the slave is the sampling reference end, another host is needed as the sampling reference end before proceeding to step 5. Other differential protection devices adjust the sampling synchronization according to the new sampling reference end.

3. The protection method based on claim 1, characterized in that: In step 5, at least the differential protection device start signal on the N-1 side is set, indicating that the multi-terminal differential start condition is met.

4. The protection method based on claim 1, characterized in that: In step 7, controlling the trip output based on the trip signal and the host differential calculation exit signal specifically includes: the host sending a trip signal to other differential protection devices and trip outputting a trip signal; if the host exits differential calculation, the host will trip outputting a trip signal when it receives a trip signal from the host on the other side; the slave device will trip outputting a trip signal when it receives trip signals from both hosts, or when it receives a trip signal from one host and a differential calculation exit signal from the host on the other side.

5. The protection method as described in claim 1, characterized in that: Step 7 further includes: when the slave receives the trip signal from both hosts, it directly trips without delay; when the slave receives the trip signal from one host and the differential calculation exit signal from the other host, it trips after a fixed delay.

6. The protection method as described in claim 1, characterized in that: The differential protection device is equipped with a master pressure plate. When the master pressure plate is engaged, it operates as the master unit; when the pressure plate is disengaged, it operates as the slave unit.

7. The protection method as described in claim 1, characterized in that: The differential protection device is equipped with a master control word. When the master control word is set, it operates as the master device; when the master control word is reset, it operates as the slave device.

8. The protection method as described in claim 1, characterized in that: The host and slave are connected via a dedicated fiber optic channel or a multiplexed channel; the hosts are connected via a dedicated fiber optic channel or a multiplexed channel.

9. The protection method as described in claim 1, characterized in that: Each differential protection device includes: a data acquisition module, a channel information processing module, a fault activation module, a differential calculation module, and a tripping module, and the modules are interconnected via a bus. The acquisition module: completes the acquisition of analog and digital signals on this side; The channel information processing module: completes sampling synchronization, monitors the status of the channel, and completes data interaction between the local side and the opposite side of the channel; The fault start-up module: Based on the local current data of the acquisition module, it determines whether the local start-up criterion is met. If so, it sends the local start-up signal to the opposite side of the channel through the channel information processing module. The host also determines whether the multi-terminal differential start-up condition is met based on the start-up signals of each side summarized by the channel information processing module. If so, it sends the multi-terminal differential start-up signal to the differential calculation module. The differential operation module: For slave devices, the differential operation module is always off; for master devices, after receiving the multi-terminal differential start signal from the fault start module, it completes differential logic operation based on the synchronously sampled current data from the acquisition module and the channel information processing module. When the differential action criterion is met, it sends a trip signal to other differential protection devices; when the master device and any slave device channel fail, the differential operation module exits the calculation and sends a differential calculation exit signal to other differential protection devices. The tripping module controls the tripping output based on the tripping signal and the host differential calculation exit signal.

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