电机学电机学电机学 (23).ppt

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1、Electrical MachineryMMF of AC winding 4.4 MMF of AC winding I.MMF of one phase of winding Assume So the max.amplitude of rectangular wave is:So the max.amplitude of fundamental wave is:4.4 MMF of AC winding I.MMF of one phase of winding Expression of the fundamental wave of magnetomotive force produ

2、ced by the full-pitch coil is:For an electric machine which has p pairs of poles,it can be inferred that MMF of one phase of winding is expressed with:4.4 MMF of AC winding I.MMF of one phase of winding Conclusion:(1)MMF of single phase of winding is pulsating MMF,and pulsating frequency is frequenc

3、y of current;(2)Amplitude of fundamental wave magnetomotive force is in direct proportion to instantaneous value of current;(3)The amplitude is corresponding to the axis position of one phase of winding.4.4 MMF of AC winding What nature of MMF will be generated when three-phase symmetrical AC curren

4、t goes through three-phase symmetrical AC windings？4.4 MMF of AC winding II.MMF of three phases of windings(1)4.4 MMF of AC winding II.MMF of three phases of windings(2)4.4 MMF of AC winding II.MMF of three phases of windings(3)4.4 MMF of AC winding II.MMF of three phases of windings(3)4.4 MMF of AC

5、 winding II.MMF of three phases of windings 4.4 MMF of AC winding II.MMF of three phases of windings Conclusion:(1)When three-phase symmetrical current passes through three-phase symmetrical windings,the fundamental wave of the resultant MMF is a rotating MMF of constant amplitude,and the amplitude

6、is 3/2 times max.amplitude of each phase of pulsating MMF.(2)When some phase current reaches maximum,the amplitude of resultant MMF wave is corresponding to the axis of the phase of winding.(3)The rotating speed of the resultant MMF wave is(4)The rotating direction of resultant MMF wave is related to the phase sequence of current,that is,from the axis of phase winding of leading current to the axis of phase winding of lagging current.4.4 MMF of AC winding II.MMF of three phases of windings THANKS FOR WATCHING!