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The Exact Equivalent Circuit
Figure 66(a) shows the equivalent circuit of an ideal transformer modified to take into account the exciting current of an ironcore transformer. Equations 644 and 645 suggest further modifications of the ideal transformer
by taking into account the effect of the resistance and leakage reactance of the windings. Equation 644 and 645 are satisfied by the relationships shown in the equivalent circuits of Figs. 610(a) and 610(b) respectively. The equivalent circuit that completely represents an ironcore transformer in which capacitance effects are negligible and in which the leakage inductances are linear combines the circuits of Figs. 610(a) and 610(b) with that of Fig. 66(a) as shown in Fig. 611. A phasor diagram based on the exact equivalent circuit of Fig. 611(b) is shown in Fig. 612. In this phasor diagram θ_{L} is the power factor angle of the load connected to the secondary terminals of the transformer. Also, the flux is shown lagging the induced emf by an angle of 90° in accordance with the phasor diagram of Fig. 59.
All three of the equivalent circuits shown in Fig. 611 lead to exactly the same values of primary current, I_{1}, and primary applied voltage, V_{1} as were obtained in the solution of Example 62.


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