The frequency of the alternating current generated by a synchronous generator is governed by the speed and the（）

单项选择题When two DC generators operate in parallel, they are protected against motorizing by（）

A.blow out coils
B.governor relay
C.under voltage trips
D.reverse current trips

单项选择题The correct phase rotation of a three-phase alternator can be checked with a（）

A.dynamometer
B.power factor meter
C.three-phase motor
D.polyphase voltmeter

单项选择题A probable cause for a turbo generator tripping out on overspeed is a sudden（）

A.loss of field excitation
B.total loss of load
C.large increase in load
D.loss of steam pressure

单项选择题All of the following operating characteristics are listed on the name-plates of motors used aboard ship except the（）

A.temperature rise
B.input kilowatts
C.horsepower
D.operating voltage

单项选择题When would you ground an electric hand tool?（）

A.When it is a DC machine
B.When it is an AC machine
C.Any machine that operates on over 100 volts
D.Only when working on wet steel plates