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三相2极异步电动机接在50Hz的电源上,若额定转差率sN=0.04,则该异步电动机的额定转子转速为( )。

A. 3000 r/min
B. 1000 r/min
C. 2880 r/min
D. 1440 r/min

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( ) is the working grounding.

A. Grounding of potential transformers’ iron core
B. Grounding of current transformers’ iron core
C. Grounding of electrical welding machine
D. Grounding of transformers’iron core

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For three-phase insulated power systems, in order to prevent the risk of personal electric shock, measures ( ) are generally adopted for necessary electrical equipment.

A. working grounding
B. protective grounding
C. protective neutral line connection
D. shield grounding

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For a fluorescent lamp with a rated voltage of 220V, the starting voltage (the minimum voltage required to light the fluorescent lamp) and the extinguishing voltage (the highest voltage required to extinguish the fluorescent lamp) are generally around ( ).

A. 200V and 200V
B. 200V and 100V
C. 100V and 200V
D. 100V and 100V

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Many ships have two types of emergency lighting systems: emergency power system and temporary emergency power system. In terms of power distribution, emergency power system ( ).

A. is a part of normal lighting system
B. can only be powered by an emergency generator
C. no power distribution switch for branch line
D. no control switch for lighting equipment

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三相2极异步电动机接在50Hz的电源上,若额定转差率sN=0.04,则该异步电动机的额定转子转速为( )。

A. 3000 r/min B. 1000 r/min C. 2880 r/min D. 1440 r/min

( ) is the working grounding.

For three-phase insulated power systems, in order to prevent the risk of personal electric shock, measures ( ) are generally adopted for necessary electrical equipment.

For a fluorescent lamp with a rated voltage of 220V, the starting voltage (the minimum voltage required to light the fluorescent lamp) and the extinguishing voltage (the highest voltage required to extinguish the fluorescent lamp) are generally around ( ).

Many ships have two types of emergency lighting systems: emergency power system and temporary emergency power system. In terms of power distribution, emergency power system ( ).

A. 3000 r/min
B. 1000 r/min
C. 2880 r/min
D. 1440 r/min