题目内容

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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三相异步电动机以转速n 正常运转，现突然调换定子的两根进线，电动机最终会反转。在这期间，电动机处于（）状态。

A. 再生制动
B. 能耗制动
C. 反接制动
D. 正常

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

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 ( ).

三相异步电动机以转速n 正常运转，现突然调换定子的两根进线，电动机最终会反转。在这期间，电动机处于（ ）状态。

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

三相异步电动机以转速n 正常运转，现突然调换定子的两根进线，电动机最终会反转。在这期间，电动机处于（）状态。