Motor drives, such as variable frequency and adjustable speed, are becoming more and more popular because they are easy to control and help save energy. The basic motor drive uses a rectifier to convert AC to DC. Rectifiers are made up of diode bridges or silicon controlled rectifiers (SCR).
In three-phase circuits, there is a brief moment when more than one SCR is on at the same time creating a momentary short. This short puts stress on the upstream transformer and causes a distorted voltage waveform which can have a damaging effect on the transformer itself and electrical equipment connected to the circuit.
A Drive Isolation Transformer (DIT) is designed to specifically handle the mechanical stresses, voltage distortions and harmonics associated with SCR applications. Midwest Drive Isolation Transformers have symmetrically placed taps and added coil bracing to withstand the mechanical forces caused by severe SCR duty cycles. These features also help to protect the transformer from the regenerative duty and more frequent short-circuits associated with SCR’s. Drive Isolation Transformers also help to filter the electrical noise caused by SCR’s. The Midwest delta-wye designs meet the NEC requirements for grounded secondary neutrals that isolate primary distribution systems. Midwest Drive Isolation Transformers are UL 1561 listed for non-sinusoidal current loads.