题目内容
( ) are powered directly by the main switchboard.
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A three-phase asynchronous induction motor running in a three-phase insulated ship power system, only the stator single-phase winding and the grounded shell are short-circuited accidentally, then ( ).
Protection that cannot be done by air circuit breaker alone is ( ).
In the contacts system of generator main switch on the distribution board, the contacts used to connect and disconnect the power grid is ( ).
For the frame-type automatic air circuit breaker, if we can move the handle but cannot be closed, we should check ( ) first.
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