Did You Know That There Is So Much Knowledge About Circuit Breaker Protection? (four)

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Today we will focus on three-phase inconsistency protection:
1. The origin of three-phase inconsistency:
For circuit breakers operating in separate phases, due to equipment quality and operation reasons, the three-phase circuit breaker may have inconsistent actions during operation, eventually resulting in only one or two phases tripping and being in an abnormal state of non-all phases.
2. The harm of three-phase inconsistency:
When the system is in non-full-phase operation, the negative sequence, zero sequence and other components that appear in the system will cause certain harm to the electrical equipment and also affect the correct action of the system protection device. Therefore, the power system is not allowed to operate in non-full-phase for a long time. .
If the line reclosure is unsuccessful, there will be no other protection to eliminate this fault when the system enters non-full-phase operation. Therefore, non-full-phase protection (three-phase inconsistent protection) is installed on the circuit breaker for split-phase operation. When the system enters non-full-phase operation, When a phase reaches a certain time, other phases will be jumped away.
3. Realization of three-phase inconsistency:
The protection function of eliminating inconsistent abnormal states of three phases is generally implemented in the circuit breaker body in high-voltage or ultra-high-voltage systems, but it is also implemented in circuit breaker protection (or line protection).
Inconsistency protection is in the circuit breaker body. The State Grid's eighteen countermeasures require: circuit breakers with voltage levels of 220kV and above should be equipped with three-phase position inconsistency protection on the circuit breaker body.
After the circuit breaker single-phase tripped, if the reclosing action occurs, the circuit breaker does not successfully reclose due to pressure, mechanical, secondary circuit, etc., and the three phases must be tripped within 2-2.5s and no longer reclosed. Ensure system security.
When there is no three-phase inconsistency protection in the circuit breaker, an independent three-phase inconsistency protection device can be installed. In addition to using the circuit breaker auxiliary contacts or position contacts to form a starting circuit for judging three-phase inconsistency, the independent three-phase inconsistency protection can also use zero-sequence current and negative sequence current to block the circuit to improve the reliability of the circuit.

4. Investment in three-phase inconsistency protection:
The three-phase inconsistency protection function only works when both the three-phase inconsistency protection soft pressure plate and the hard pressure plate are turned on (control word).
5. Inconsistent starting of three phases: Inconsistency of three-phase jump opening + no flow of jump phase.
6. Action of three-phase inconsistency protection: Inconsistency is activated by the zero-sequence open control word, inconsistency starts and is activated by the inconsistent zero-sequence current criterion, and then the three phases of the circuit breaker are tripped through the inconsistency delay outlet. The inconsistent negative sequence opening control word is put into operation, the inconsistent start is activated by the inconsistent negative sequence current criterion, and then the three phases of the circuit breaker are tripped through the inconsistent delay outlet. When the above two control words are exited, the three phases of the circuit breaker will be tripped through the inconsistent delay outlet after the three-phase inconsistency starts.
The three-phase inconsistency protection action does not start and fails, and the reclosing is blocked at the same time.
7. Lockout of three-phase inconsistency protection: If the circuit breaker is in the three-phase inconsistency state for 12 seconds, a position inconsistency alarm will be issued and the three-phase inconsistency protection will be blocked.
8. Setting principle of time relay for three-phase inconsistency protection: The three-phase inconsistency protection delay setting of the relay protection device must be able to avoid the reclosing action time.