Open-circuit Test

This test consists of applying to the primary of the transformer the Nominal voltage, being the secondary in open circuit. At the same time, the absorbed power Po, the no-load current Io and the secondary voltage must be measured, according to the connection scheme of Fig. 1. Since the losses R, Io in vacuum are negligible (due to the small value of Lo), \ the power absorbed in vacuum practically coincides with the losses in the iron, which is in accordance with the approximate equivalent circuit of Fig. 2, which is deduced from the general diagram of Fig. 3 since it is I2= 0.

From the measurements made, the power factor can be obtained in vacuum, according to the equation:

Citation

Universidad Nacional de Educacion a Distancia: Teoria de Circuito