Question

What is difference between PT and CVT?

Answer 1

Answer:

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.

where as, A 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 12-20 kV then this voltage is fed to a relatively small transformer for the voltage signal to be processed.CVT is rated for high voltage levels above 100 kV, 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, Power Line Carrier Communication, which is a signal transmitted over power lines providing carrier signal for Distance protection and communication between the connecting Substations.

Thus CVT shall be used when voltage level is high and we need Power Line Carrier Communication. It may be that CVT is just used for Metering and Protection Purpose but when a CVT is used in the Transmission Line then it also serves the purpose of PLCC.

Answer 2

Answer:

Concept:

Voltage transformers, sometimes termed potential commutator, are a parallel-connected type of power transformer. They're made to put a little load on the supply being measured, and they have a precise voltage ratio and phase relationship to allow for accurate secondary connected metering. For measurement purposes, a CT lowers current signals, whereas a PT lowers high higher voltages into lower ones. The transformers are used to determine whether or not electricity systems are accurate and safe. In addition, the CT and PT transformer diminishes the voltage and current from high to low value.

Given:

What is difference between PT and CVT?

Find:

What is the distinction between PT and CVT?

Answer:

Potential Transformer

• A potential transformer is an instrument transformer that transforms voltage from a higher to a lower value.
• This transformer reduces the voltage to a safe level that can be measured with common low-voltage instruments such as voltmeters, watt meters, and watt-hour meters, among others.
• The magnetizing current is minimal because the potential transformer is made with a high-quality core that operates at a low flux density.
• The transformer's terminal should be built so that the voltage ratio varies minimally with load and the phase shift between both the voltage rating is minimal.
• The primary winding has a lot of turns, while the secondary winding has a lot less. The co-axial winding is utilised in the potential transformer to reduce leakage reactance.
• By separating the primary winding into parts and reducing the insulation between the layers, the insulation cost is also lowered.

Capacitive Voltage Transformer

• The capacitive voltage transformer reduces the high voltage input signals to low voltage signals that can be measured easily with the measuring instrument.
• Capacitive power inverter (CVT) or capacitive potential transformer (CPT) is a type of capacitive voltage transformer.
• The capacitive transformer is made up of three primary parts: a capacitive potential divider, an inductive element, and an auxiliary transformer.
• The auxiliary transformers and the inductive element are used in conjunction with the capacitive potential divider.
• The capacitive prospective divider converts high voltage signals to low voltage signals. With the help of the auxiliary transformer, the capacitive potential transformer's output voltage is further reduced.

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