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.
