Why may a rectifier transformer have a different KVA rating on the primary and secondary?
The difference in KVA rating on the secondary of rectifier transformers varies depending on the rectifier circuit used. Some examples are as follows: single phase full wave- the transformer secondary KVA is approximately 40% greater than the primary; single phase bridge circuit- the primary and secondary KVA are equal; 3 phase half wave- the secondary is approximately 22% greater than the primary KVA; 3 phase full wave rectifier circuit- the transformer primary and secondary KVA are equal. The reason for the difference in KVA rating on the secondary compared to the primary of the transformer is due to the irregular wave shape occurring on the secondary. Different types of wave shapes will cause different amounts of heating. Therefore, the windings of the transformer must be increased to make allowance for this heating effect depending on the type of rectifier circuit used.
