ABSTRACT
For the relaying applications, the high system voltages and currents are reduced through the potential and current transformers. These also protect and insulate the personnel and relays from high voltages and currents. The instrument transformers have two distinct accuracy classifications: metering and relaying. The bushing current transformers are most widely used for relaying because their installation cost is low. It consists of a tapped secondary winding on an annular magnetic core and is referred as multi-ratio bushing current transformer. A class C or T transformer will deliver to the standard burden a secondary terminal voltage at 20 times the secondary current, without exceeding 10" ratio correction. Saturation voltage is defined as the voltage across the secondary winding at which peak induction just exceeds the saturation flux density. Saturation factor is the ratio of the saturation voltage to the excitation voltage.
