OPEN CIRCUIT TEST (No load test)

When a test is performed by leaving one winding open and giving supply to the another side,the test on the transformer is performed to ensure the working condition to the transformer.The main of the open circuit test are as follows:

(a)To find no-load current (Io)

(b)To obtain no-load parameters i.e,IuIwRo1Xo

(c)To find core loss (V1Iocos)

Supply is given to low voltage side of the transformer because it is either to use lower rating equipment for the measurement.Supply is given through auto transformer to get variable voltage and also for matching winding voltage capacity.Supply voltage V1 is indicated by voltmeter,no load current.Io is measured by ammeter and core loss is given by watt meter.Secondary side was no current hence there is no copper (Cu) loss and primary side has small amount of no load current hence small copper loss is there which can be ignored.In this way,open circuit test is carried out in the transformer.