Open Circuit Testing

In transformers, the open circuit test is performed by applying rated voltage to the primary winding while the secondary terminals are open.

In order to obtain the correct model it is important to note that in this test it is done in a winding different from that used in the short test, the correct changes must be made so that all impedances are referred to the same side of the transformer.

We see that the entire current drained from the source is used as the excitation current Iexc for the establishment of the flux in the transformer core and for the aid of the losses in a vacuum.

Since the current IOC Bearing 23232 CC/W33 is relatively small and still Zm >> Z1, the voltage drop in Z1 can be neglected, and the circuit representing the open circuit test of the transformer can be simplified.

In the same way as the short-circuit test, a voltmeter (V), an ammeter (A) and a wattmeter (W) are required in the open-circuit test to be mounted in the circuit. To do this, adjust the voltage source to the nominal winding voltage to be tested.

If the transformer is to operate at a voltage other than nominal, then this will be the VOC voltage to be used during the test. During the test the instruments allow us to measure the applied VOC voltage, the drained IOC current and the POC power supplied to the transformer.

Open Circuit Testing