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【正文】 ero and ? φm, where φm is the maximum value of the core flux。 and (2) it provides a ponent to account for the hysteresis and eddy current losses in the core. There bined losses are normally referred to as the core losses. The noload current Iθ is usually few percent of the rated fullload current of the transformer (about 2 to 5%). Since at noload the primary winding acts as a large reactance due to the iron core, the noload current will lag the primary voltage by nearly 90186。. It is readily seen that the current ponent Im= I0sinθ0, called the magizing current, is 90186。 in phase behind the primary voltage VP. It is this ponent that sets up the flux in the core。 φ is therefore in phase with Im. The second ponent, Ie=I0sinθ0, is in phase with the primary voltage. It is the current ponent that supplies the core losses. The phasor sum of these two ponents represents the noload current, or emo III ?? It should be noted that the noload current is distortes and nonsinusoidal. This is the result of the nonlinear behavior of the core it is assumed that there are no other losses in the transformer, the induced voltage In the primary, Ep and that in the secondary, Es can be shown. Since the magic flux set up by the primary winding， there will be an induced EMF E in the secondary winding in accordance with Faraday’s law, namely, tNE ???? /? . This same flux also links the primary itself, inducing in it an EMF, Ep. As discussed earlier, the induced voltage must lag the flux by 90186。, therefore, they are 180186。 out of phase with the applied voltage. Since no current flows in the secondary winding, Es=Vs. The noload primary current I0 is small, a few percent of fullload current. Thus the voltage in the primary is small and Vp is nearly equal to Ep. The primary voltage and the resulting flux are sinusoidal。 thus the induced quantities Ep and Es vary as a sine function. The average value of the induced voltage given by Eavg = turns c h a n g e in flu x in a g iv e n tim eg i
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