# What is Open Circuit Test of Transformer ? Phasor Diagram & Calculation

## Why Open Circuit Test is Performed on L.V. Side only ?

#### The main thing is that an open circuit of a transformer is performed on any side of the transformer i.e., either on H.V. ( high voltage ) or L.V. ( low voltage ). But there are some benefits while performing the O.C. test on L.V. side of the transformer. (adsbygoogle = window.adsbygoogle || []).push({});      The aim of this test is to determine the no-load losses i.e., core loss at rated voltage. The term rated voltage means we have to apply the rated value of the voltage on the L.V. side. This rated value of voltage is smaller ( 440V, 11kV ) when compared to the H.V. side ( 33kV, 132kV, and above ).     So when we prefer H.V. side to test it becomes harder, costlier, and care must be taken while performing the test. Because the equipment ( measuring instruments ) used for tests i.e., to apply high voltages about 33kV, 132kV, and above becomes costlier. And precautions must be taken with proper insulation to the body to avoid shocks that may lead to death.     The turns on the L.V. side of the transformer are less than the turns present on the H.V. side. Hence the power loss ( i.e., due to copper loss ) is less almost negligible on the L.V. side of the transformer when it is on no-load.     As we know that the open circuit test is to determine the core loss. Thus when a rated voltage is applied on the L.V. side power loss occurred is very small. Therefore, the wattmeter reads only the core loss component of the transformer.

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