What are the differences between PT and CVT?

Answer 1

a PT, potential transformer, can be thought of as a pure transformer with primary and secondary windings; PT's are sometimes referred to as magnetic Transformers due to the fact that their mode of operation is purely magnetic. It is used to step-down the input voltage from a power line to a voltage level that can be processed by metering devices and protection relays in a substation. CVT or CCVT, capacitor-coupled voltage transformer, is made with two capacitor sets acting as a voltage divider that brings the line (actually the phase) voltage down to around 12Kv then this voltage is fed to a relatively small transformer for the voltage signal to be processed. CVT is rated for extremely high voltage levels above 230KV, while PT's aren't designed for such large values. CVT's offer the advantage that the voltage divider capacitor, being itself relatively smaller and lighter, configuration makes the transformer's iron core much smaller in size, and hence more economical, versus what it would be if a pure magnetic transformer would be used. Also the CVT's can be tuned to the fundamental frequency of the line, and the capacitance prevents the inductive "fire-back" of the coils in the transformer when a breaker trips. PT's can't provide such advantage. some CVT's are also used to tune to PLCC, Programmable Logic Controller Carrier frequency, which is a signal transmitted over power lines providing inter-PLC communication.