These tests are made to measure the resistance of each winding to calculate power loss, the resistance component of the voltage drop under load, to determine the temperature rise under load, and to ascertain that the internal connections are correct. A dc source should be used, together with ammeters and voltmeters of proper ranges. Temperature measurements of the windings should be taken while the resistance measurements arc made�these may be thermometers or thermocouples. As a precaution, to avoid possible damage from voltages induced by the dc current causing the magnetic field to build up and collapse on being switched on and off, the winding whose resistance is not being measured should be temporarily short-circuited The re-
sistance of each winding is obtained from the Ohms Law derived equation. R = E/i or voltage value (volts) divided by the current flowing (amperes).
Ref:
Electrical Transformers and Power Equipment by Anthony J. Pansini