FIVE PREVENTIONS/INTERLOCKS for High Voltage switchgears
1. The circuit breaker only can be closed and opened when the circuit breaker trolley is at testing or working position and the trolley can not be moved after circuit breaker closed, this function prevents pulling and pushing circuit breaker with load.
2. The circuit breaker trolley only can be moved from testing/opening position to working position when the earthing switch is at opening position. The earthing switch only can be closed (may be fitted with charged display device) when circuit breaker trolley is rotated to testing/disconnecting position. This function prevents earthing switch from mistake-closing with load, and prevents maintainer from closing circuit breaker while the earthing switch was on closing position.
3. The back door and lower door can not be opened when the earthing switch is at opening position, and this function prevents maintenance people from entering working compartment (electrified) in error.
4. When the circuit breaker trolley is rotated to testing or working position without control voltage, and it can only be opened manually, but not closed.
5. When the circuit breaker trolley is at working position, the secondary plugs has been locked and can not be moved.