TABLE OF CONTENTS The equivalent circuit parameters of a transformer can be determined by performing two tests: the open-circuit test and the short-circuit test.
As the name implies, one winding of the transformer is left open while the other is excited by applying the rated voltage. The frequency of the applied voltage must be the rated frequency of the transformer. Although it does not matter which side of the transformer is excited, it is safer to conduct the test on the low-voltage side. Another justification for performing the test on the low-voltage side is the availability of the low-voltage source in any test facility.
Figure 4.21 shows the connection diagram for the open-circuit test with ammeter, voltmeter, and wattmeter inserted on the low-voltage side. If we assume that the power loss under no load in the low-voltage winding is negligible, then the corresponding approximate equivalent circuit as viewed from the low-voltage side is given in Figure 4.22. From the approximate equivalent of the transformer as referred to the low-voltage side (Figure 4.22), it is evident that the source supplies the excitation current under no load. One component of the excitation current is responsible for the core loss, whereas the other is responsible to establish the required flux in the magnetic core. In order to measure these values exactly, the source voltage must be adjusted carefully to its rated value. Since the only power loss in Figure 4.22 is the core loss, the wattmeter measures...
