TRANSFORMER RATINGS
Most transformers contain a nameplate that lists information concerning the transformer. The information listed is generally determined by the size, type, and manufacturer. Almost all nameplates will list the primary voltage, secondary voltage, and kVA rating. Transformers are rated in kilovolt amps and not kilowatts because the true power is determined by the power factor of the load. Other information oil, gallon of insulating oil, serial number, type number, model number, and whether the transformer is single phase or three phase.
DETERMINING MAXIMUM CURRENT
Notice that the nameplate does not list the current rating of the windings. Because power input must equal power output, the current rating for a winding can be determined by dividing the kVA rating by the winding voltage. For example, assume a transformer has a kVA rating of 0.5 kVA, a primary voltage of 480 volts, and a secondary voltage of 120 volts. To determine the maximum current that can be supplied by the secondary, divide the kVA rating by the secondary voltage.
