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The configuration of busbar configuration and line protection is an important part of ensuring safe operation in the power system. As a key node in the power system, the busbar connects multiple lines and equipment, so a special protection scheme is required. Line protection ensures the reliability and safety of power transmission. The following is a detailed introduction to the busbar configuration and line protection configuration:
A. Busbar protection configuration
The busbar is a common point connecting generators, transformers, lines and loads. Any busbar fault will cause serious system impact. Therefore, the requirements for busbar protection are very high, and it needs to be fast, reliable and highly selective.
1. Differential protection
Differential protection is one of the main forms of busbar protection and is suitable for important high-voltage buses. It determines whether a fault occurs by comparing the difference between the current entering the busbar and the current leaving the busbar.
- Principle: All currents on each side of the busbar are summed through the current transformer (CT). If the algebraic sum of the current is not zero, it means that a fault has occurred inside the busbar, and the differential relay trips.
- Features: quick action, high sensitivity, strong selectivity, only responds to internal bus faults, no response to external bus faults.
2. Current quick-break protection
Current quick-break protection is used to quickly cut off the fault when a serious bus fault occurs, usually as a backup protection for differential protection.
- Principle: When the current on the bus exceeds the set value, the current quick-break protection immediately trips to protect the bus from greater damage.
- Features: fast response speed, but lack of selectivity, may misoperate for external faults, so it is usually used in conjunction with differential protection.
3. Bus tie protection
Bus tie protection is used to protect the interconnection line (bus tie) between two buses. When the system needs to switch loads, the protection of the bus tie plays a key role.
- Principle: By monitoring the current and voltage of the bus tie, detect whether there is a fault between the buses, and quickly cut off the faulty bus.
- Features: It can protect the fault in the bus connection and prevent the fault from spreading to other bus parts.
4. Compound voltage protection
Compound voltage protection is used to protect the busbar from overvoltage or undervoltage, and is usually an auxiliary protection device.
- Principle: When the busbar voltage exceeds the set range, the protection device sends an alarm signal or trip command to prevent equipment damage.
- Application: Applicable to abnormal voltage conditions at the busbar, and can effectively prevent overvoltage and undervoltage problems.
5. Automatic standby switching (BZT)
In the event of a busbar fault, in order to maintain the stable operation of the system, the automatic standby switching device will automatically switch the load to the standby busbar.
- Principle: When a busbar fails and is cut off, the BZT device will automatically transfer the load to the standby busbar and restore power supply.
- Features: Avoid power outages in the entire system due to busbar failures and improve system reliability.
6. Fast switching protection
When a transformer or other equipment connected to the busbar fails, the fast switching protection can quickly switch the load to the standby line or busbar to ensure the continuity of power supply.
- Principle: By detecting busbar fault signals, the load is switched immediately to ensure the stability of the system.
- Features: Suitable for large-capacity busbars, reducing the power supply interruption time caused by faults.
B. Line protection configuration
Line protection is an important measure to ensure the safety of power transmission in the power system. Line protection is configured according to factors such as line length, voltage level, and system importance. The main goal is to protect the line from short circuit, overcurrent, grounding and other faults.
1. Distance protection
Distance protection is the most commonly used main protection method for transmission lines, especially for long-distance transmission lines. It determines whether a fault has occurred based on the electrical distance from the fault point to the protection device.
- Principle: The fault distance is determined by measuring the impedance from the fault point to the protection device. When the impedance is lower than the set value, it is considered that the fault occurs in the protection zone, and the protection device trips.
- Advantages: It acts quickly and can accurately determine the fault location, which is suitable for long-distance transmission lines.
2. Longitudinal differential protection
Longitudinal differential protection is usually used for high-voltage or ultra-high-voltage lines. It detects faults by comparing the difference in current at both ends of the line. It is suitable for the protection of long-distance lines or important lines.
- Principle: Current transformers are installed at both ends of the line, and the current information at both ends is compared through the communication line. When the difference exceeds a certain range, the protection device trips.
- Features: Good selectivity for faults, can accurately identify faults on the line, especially suitable for high-voltage and ultra-high-voltage transmission lines.
3. Current quick-break protection
Current quick-break protection is a simple and fast line protection method, mainly used to deal with severe short-circuit faults.
- Principle: When the current passing through the line exceeds the set value, the protection device immediately acts to cut off the line power supply.
- Advantages: Rapid action, suitable for dealing with more serious short-circuit faults. However, since quick-break protection has no selectivity, it is usually used in combination with other protection methods (such as distance protection).
4. Reclosing protection
Reclosing protection is used to deal with temporary faults of the line, such as lightning strikes, wind-blown branches contact and other short-term faults. Through automatic reclosing, the line can quickly restore power supply and reduce power outage time.
- Principle: After the line fault is removed, the automatic reclosing device will automatically reclose the switch in a short time to restore power supply. If the fault is temporary, the line can resume normal operation.
- Application: Reclosing protection is often used in overhead lines because such lines have more temporary faults.
5. Zero-sequence protection
Zero-sequence protection is used to detect ground faults, especially in systems that are not directly grounded or grounded through arc suppression coils. Once a single-phase ground fault occurs in the line, the zero-sequence protection can quickly detect and remove the fault.
- Principle: Determine whether a ground fault occurs by detecting the zero-sequence current (i.e. the vector sum of the three-phase currents). If the zero-sequence current exceeds the set value, the protection trips.
- Features: The protection effect against ground faults is good and is suitable for grounded and ungrounded systems.
6. Overcurrent protection
Overcurrent protection is a simple and widely used line protection method, mainly used for the protection of short lines or small-capacity lines.
- Principle: When the current of the line exceeds the set value, the overcurrent protection device trips to prevent damage to equipment and lines.
- Features: It is suitable for the protection of short lines and small-capacity lines, but for long-distance transmission lines, overcurrent protection may not be accurate enough, so it is usually used as backup protection.
7. Directional overcurrent protection
Directional overcurrent protection adds a directional discrimination function to overcurrent protection, which is used to determine the direction of the fault current and ensure that the protection device only responds to faults in a specific direction.
- Principle: By monitoring the direction of the fault current, determine whether the area where the fault occurs is within the protection range, and then decide whether to trip.
- Application: Suitable for complex power grid structures and lines powered by multiple power sources.
C. Comprehensive configuration of line protection
Depending on the different characteristics of the line (such as length, capacity, importance, etc.), line protection is usually a combination of multiple protection schemes to ensure that the system can quickly and effectively remove the fault when a fault occurs. The following are common line protection configuration schemes:
- Long-distance transmission lines:
- Main protection: distance protection, longitudinal differential protection
- Backup protection: current quick-break protection, overcurrent protection
- Auxiliary protection: reclosing protection, zero-sequence protection
- Short-distance transmission lines:
- Main protection: current quick-break protection, overcurrent protection
- Auxiliary protection: reclosing protection
- Important lines or high-voltage lines:
- Main protection: longitudinal differential protection, distance protection
- Backup protection: directional overcurrent protection, overcurrent protection
- Auxiliary protection: zero-sequence protection, reclosing protection
In summary
- Busbar protection: Busbar protection usually uses differential protection as the main protection, combined with current quick-break protection, busbar protection, composite voltage protection, etc., to ensure fast and reliable protection of the busbar.
- Line protection: Line protection mainly includes distance protection, longitudinal differential protection, current quick-break protection, overcurrent protection, etc.
