题目内容

The nominal power factor of a 3-phase induction motor is 0.85, then the power factor under light load condition can be ( ).

A. 0.9
B. 0.87
C. 0.85
D. 0.5

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The nominal voltage UN and nominal current IN on the nameplate of a 3-phase asynchronous motor refers to ( ) respectively.

A. line voltage/phase current
B. phase voltage/line current
C. line voltage/ line current
D. phase voltage/ phase current

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For a Δ connection 3-phase induction motor, we connect it in Y connection when it is running under no-load condition, but with same power source, then ( ).

A. the motor will stop because under voltage
B. same speed as Δ connection
C. the motor will running at a higher rotating speed
D. the motor will running at a lower rotating speed

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( ) are rotor parts of DC machines. ①main magnet poles②commutating poles③brushes④bedplate⑤armature iron core⑥commutator⑦armature windings

A. ①②③④
B. ⑤⑥⑦
C. ③④⑤⑥
D. ②③④⑤

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For a real transformer, the norminal voltage of primary windings is 440V. When the primary windings is connected to 440V power source, the open-circuit voltage of secondary windings is 110V, and the voltage decrease to 105V as the load current increase to nominal value. So the turns ratio of the transformer is ( ).

A. 4
B. 4.19
C. 0.25
D. 0.24

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The nominal power factor of a 3-phase induction motor is 0.85, then the power factor under light load condition can be ( ).

A. 0.9 B. 0.87 C. 0.85 D. 0.5

The nominal voltage UN and nominal current IN on the nameplate of a 3-phase asynchronous motor refers to ( ) respectively.

For a Δ connection 3-phase induction motor, we connect it in Y connection when it is running under no-load condition, but with same power source, then ( ).

( ) are rotor parts of DC machines. ①main magnet poles②commutating poles③brushes④bedplate⑤armature iron core⑥commutator⑦armature windings

A. 0.9
B. 0.87
C. 0.85
D. 0.5