6.3 Open Circuit Voltage (VOC)
Open circuit voltage is the voltage appearing across a secondary winding when the primary is energized at a specified voltage and frequency, with the secondary at no-load. The voltage is dependent not only on the turns ratio of the transformer, but also on the voltage drop in the primary winding due to the magnetizing current.
Open circuit voltage measurements are the preferred tests for line frequency transformers,designed to operate over the full extent of the B-H curve, including the non-linear regions. An open circuit voltage test is be used to confirm the turns ratio between winding and also the phasing of windings on these types of transformers.