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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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For a step-up transformer, the relationship between primary winding N1 and secondary winding N2 is ( ).

A. N2>N1
B. N2=N1
C. N2
D. denpends on its model

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When the AC magnetic contactor is energized, for the flux before and after the moving part is attracted, ( ).

A. F(before)>F(after)
B. F(before)=F(after)
C. F(befoer)

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For the of the phase compound excitation type AVR of a self-excited synchronous generator, the AC side of the rectifier is connected with capacitors delta connected. The function of these capacitor are ( ).

A. resistance-capacitance protection of rectifier
B. compensate the generator terminal voltage change caused by the change of load current
C. compensate the generator terminal voltage change due to load current phase change
D. accelerated voltage built-up process

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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

For a step-up transformer, the relationship between primary winding N1 and secondary winding N2 is ( ).

When the AC magnetic contactor is energized, for the flux before and after the moving part is attracted, ( ).

For the of the phase compound excitation type AVR of a self-excited synchronous generator, the AC side of the rectifier is connected with capacitors delta connected. The function of these capacitor are ( ).

A. ①②③④
B. ⑤⑥⑦
C. ③④⑤⑥
D. ②③④⑤