Interphase transformers are used in a circuit with a rectifier transformer having both delta and wye secondaries which create a current imbalance. The interphase transformer corrects this imbalance.
The Interphase Transformer is used “to absorb the difference between the direct voltages of the individual systems and must be designed for the times integral of this voltage” (Schaefer, 1965).
Interphase transformers are used in systems that have two rectifier systems being used in parallel. The need for the Interphase Transformer is present because when connecting rectifiers in parallel, their direct voltages fluctuate. Furthermore, rectifier systems can only be connected in parallel if their fluctuating voltages are equal at any instant. Essentially, their average values must equal and the ripple voltages must coincide. “Under this condition rectifier installations for very high current ratings are sometimes built of several simultaneously commutating and directly paralleled groups” (Schaefer, 1965). In practice, this setup is rarely found.
It is most commonly desired, instead, to displace the ripple voltages so that the combination results in a system with a higher pulse number. “The parallel connection must then be made in such a manner that it does not affect the operation of the individual groups. This is accomplished with an Interphase Transformer” (Schaefer, 1965).