Why Are the Opening and Closing Time and Synchronicity of Circuit Breakers Both Crucial?

Many engineers have completed circuit breaker characteristic tests and know that the opening and closing time should meet the standards, but their understanding of the significance of synchronicity is not deep enough - they think that a few milliseconds of three-phase difference is not a big deal. In fact, the harm of synchronous disqualification is sometimes more serious than exceeding the closing time of the score.

Definition of opening and closing time

The term definition given in the HZC-4080 manual is very clear: the opening (closing) time refers to the time from when the opening (closing) wire coil is powered on as the starting point for timing to when the dynamic and static contacts just open (close).

This definition includes two stages: first, the electromagnetic delay from the coil being powered on to the start of the operating mechanism; The second is the mechanical transmission time from the action of the operating mechanism to the just opening/closing of the contact. The sum of the two is the inherent opening and closing time.

If the inherent time exceeds the upper limit specified by the manufacturer, it indicates that there is a problem with the operating mechanism and it needs to be repaired. If the time is too short, it may indicate that the mechanism has been adjusted excessively or the spring is too strong, the action is too intense, and it can also lead to an increase in bounce.

The difference between same phase and same period and same period between phases

Same phase and same period: the difference between the maximum and minimum opening and closing times of each circuit breaker (multi circuit breaker) in the same phase.

Phase to phase synchronization: the difference between the maximum and minimum values of the opening and closing time between three phases.

HZC-4080 measures and displays both values simultaneously, without the need for manual calculation.

Why is synchronous exceedance dangerous

Three phases in different stages mean that the three-phase contacts do not simultaneously disconnect or connect the circuit. When closing, the phase that closes first will bear all the impact of the closing surge, and compared with normal three-phase simultaneous closing, single-phase will bear greater stress; When disconnecting, if the three phases are not synchronized, the last disconnected phase is responsible for extinguishing the arc. At this time, the neutral point displacement caused by the disconnection of the other two phases may have already occurred in the power grid, resulting in the actual voltage borne by that phase being higher than the rated voltage, greatly increasing the difficulty of extinguishing the arc. In severe cases, the contacts may not be able to effectively extinguish the arc.

The industry usually requires that the period between phases should not exceed 5ms, and the specific requirements shall be subject to the manufacturer's requirements. HZC-4080 has a resolution of 0.01ms, which fully meets the needs of accurate judgment.