ABB ACS800 Series Hardware Manual page 37

Grid air-circuit breaker (MCB1)
opening (emergency shutdown –
stator air-circuit breaker/contactor
(MCB3) fault)
Grid air-circuit breaker (MCB1)
opening (emergency shutdown –
eg, first stator air-circuit breaker/
contactor (MCB3) fault, then grid
air-circuit breaker (MCB1) fault)
2. Stator air-circuit breaker/contactor (MCB3) FAULT
In case the stator air-circuit breaker/contactor does not obey OPEN
command from the converter, the monitoring circuit will find that stator
air-circuit breaker/contactor (MCB3) is still closed (K31 relay is ON)
after the time delay of 2 sec. MCB1 will then be forced to open by de-
energizing K24 relay to disconnect the converter from the grid.
3. Grid air-circuit breaker (MCB1) FAULT
The worst case is that the grid air-circuit breaker fails to open itself. In
this case the monitoring circuit will find that grid air-circuit breaker
(MCB1) is closed (K21 relay is ON) despite of OPEN command (K20
relay is OFF). After 1 sec delay K36 time relay will be de-energized.
The contacts of K36 can be used to control medium-voltage grid
disconnecting device (X60 control cable connector).
This example diagram describes a situation when stator air-circuit
breaker/contactor (MCB3) and grid air-circuit breaker (MCB1) fail one
after the other.
37
Hardware description