Figure 1.32 shows the equivalent circuit of a single-phase transformer having load impedance ZL. Figure 1.33 is the equivalent circuit of Figure 1.32. The secondary winding resistance (R2), leakage reactance (X2) and load impedance (ZL) connected to secondary terminal is transferred to primary side.
Figure 1.32 Equivalent Circuit
Figure 1.33 Exact Equivalent Circuit
Figure 1.34 Approximate Equivalent Circuit
Since I0 is small compared to full-load current, we can shift the excitation circuit towards the terminal voltage side shown in Figure 1.34. Figure 1.34 is the approximate equivalent circuit, whereas Figure 1.33 is the exact equivalent circuit of Figure 1.32.
From Figure 1.33, the total input impedance between input terminals becomes
and is the impedance of the exciting circuit.
R0, X0, R01 and X01 are the four important parameters of the transformer. From open circuit and short circuit test of a transformer, R0, X0and R01, X01 can be determined respectively.