Common Problems and Challenges of Circuit Breaker Failure Protection

Circuit breaker failure protection faces some common problems and challenges in practical applications, which may affect the stability and safety of the power system. The following are some of the main problems and challenges:

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1. Protection action information and current discrimination element sensitivity issues:

Circuit breaker failure protection needs to use protection action information and current information to determine whether the circuit breaker has failed. The current discrimination element should not act when the system is operating normally and the fault line switch is disconnected, and at the same time have sufficient sensitivity when various faults occur at the end of the line. If the sensitivity of the current discrimination element is not enough, it may cause false action or refusal to act, affecting the reliability of protection.

2. Insufficient sensitivity of voltage blocking element:

The voltage blocking element is an important part of circuit breaker failure protection, but its insufficient sensitivity may cause false action or refusal to act. In particular, when an internal fault occurs on the low-voltage side of the transformer, the composite voltage blocking element installed in the bus differential protection may not be opened in time, resulting in the failure protection failing to start correctly.

3. Reliability of the starting circuit:

The starting circuit is the key to ensuring the correct operation of the entire set of protection and must be safe and reliable. The starting circuit includes a starting element and a discrimination element, which form an “AND” logic. The starting element usually uses the circuit breaker’s automatic tripping outlet circuit itself, and the failure of the contact action to return indicates that the circuit breaker has failed. If the starting circuit design is unreasonable, it may cause false start or false operation.

4. The setting problem of protection setting value:

The setting of protection setting value needs to comprehensively consider the system operation mode and the current situation when the line end fault occurs after the bus tie switch is tripped. If the setting value is unreasonable, it may cause the current discrimination element to be in action during normal operation, thus failing to prevent false operation.

5. The problem of non-electrical quantity protection as the starting quantity:

Non-electrical quantity protection such as main transformer heavy gas, pressure release, and generator water cut protection outlet should not start failure protection, because these protection contacts have slow action and return time, and the reliability of starting failure protection is poor.

6. Backup protection cannot directly start failure protection:

It is inappropriate to design the generator inverse time symmetrical overload protection, inverse time asymmetrical overload protection, and overexcitation protection as outlet start failure, because these protection actions and return times are long, which may cause failure protection to malfunction.

7. Auxiliary protection should not start failure protection:

Auxiliary protection such as the main transformer cooler full stop protection should not start failure protection, because the contacts will not return immediately after these protections are activated, which may cause protection malfunction.

8. The difference between the failure protection of the generator-transformer group and the line failure protection:

The generator-transformer group generally adopts a three-phase linkage switch, which has a longer action time than the line phase operation switch. Therefore, in actual application, the component start failure protection and the line start failure protection should be distinguished to improve the reliability of protection.

9. Implementation of circuit breaker failure protection:

In actual application, the implementation of circuit breaker failure protection is different in different situations. For example, the implementation of fault phase failure and non-fault phase failure requires different logic and delay settings.

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Through the above analysis, it can be seen that circuit breaker failure protection needs to consider multiple factors in actual application to ensure its reliability and accuracy, so as to ensure the stable operation of the power system.