What is the difference between rated voltage and full load voltage of a transformer? Are the ratings given on the nameplate at full load?
The rated voltage will apply to the primary. The primary voltage will be equal to the voltage of the supply.
The full load voltage will apply to the secondary at full load when the transformer is supplied with the rated primary voltage. You can expect the voltage to rise when the transformer is partially loaded or open-circuit.
Suppose if transformer is at full load, then are the voltages on primary & secondary side equal to their rated values?
The primary voltage will be the mains voltage no matter what it says on the rating plate.
The secondary voltage will be the primary voltage divided by the transformer turns ratio.
Example:
- Rating primary voltage: 240 V.
- Rating secondary voltage: 120 V.
- Turns ratio is N:n = 240:120 = 2:1, where N = primary and n = secondary turns.
- Actual primary voltage: 220 V
Output at full load should be \$ V_{OUT} = \frac {n}{N}V_{IN} = \frac{120}{240} 220 = 110~V \$.