Connection method of residual current vacuum circuit breaker: Under normal operation, regardless of whether the three-phase load is balanced, the sum of the three-phase current phasors through the zero-sequence current transformer main circuit is equal to zero. Therefore, no induced electromotive force is generated in its secondary winding, and the residual current device operates in the closed state. If a leakage or electric shock accident occurs, the sum of the three-phase currents is no longer equal to zero, but equal to a certain current value Is. Is will form a loop through the human body, the ground, and the transformer neutral point. In this way, an induced electromotive force corresponding to Is is generated on the secondary side of the zero-sequence current transformer and applied to the trip unit. When Is reaches a certain value, the trip unit operates, pushing the latch of the main switch and disconnecting the main circuit.
Precautions for residual current vacuum circuit breaker circuits:
1. Residual current vacuum circuit breakers are generally classified as two-pole, three-pole, and four-pole, each used in different circuits. Only proper selection and use will ensure they function as intended.
2. The rated voltage and current of the vacuum circuit breaker should be greater than or equal to the normal operating voltage and current of the line equipment;
3. The leakage current that the circuit should protect against should be less than or equal to the specified leakage protection current of the vacuum circuit breaker;
4. The ultimate breaking capacity of a vacuum circuit breaker should be greater than or equal to the maximum short-circuit current of the circuit;
5. The rated current of the overload trip unit is greater than or equal to the maximum load current of the line;
6. It has a short interruption response time, which can protect the lines and equipment;
7. After the vacuum circuit breaker circuit is connected, check whether the wiring is correct. This can be checked using the test button. If the circuit breaker disconnects correctly, the residual current device (RCD) is installed correctly; otherwise, check the wiring and troubleshoot the problem. After the RCD is put into operation, the user should check whether the circuit breaker is operating normally using the test button every certain period of time.
