Current Transformer And Potential Transformer Theory Pdf

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Free download application of potential transformer pdf. Potential Transformer PT Definition — The potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. This transformer step down the voltage to a safe limit value which can be easily measured by the ordinary low voltage instrument like a voltmeter, wattmeter and watt-hour meters, etc.

A current transformer CT is a type of transformer that is used to reduce or multiply an alternating current AC. It produces a current in its secondary which is proportional to the current in its primary. Current transformers, along with voltage or potential transformers, are instrument transformers. Instrument transformers scale the large values of voltage or current to small, standardized values that are easy to handle for measuring instruments and protective relays. The instrument transformers isolate measurement or protection circuits from the high voltage of the primary system.

Electrical Sensors: Potential Transformers (PTs) and Current Transformers (CTs)

The electrical instruments are not directly connected to the meters or control apparatus of high voltage for safety purpose. The instrument transformers like voltage transformer and current transformer are used for connecting the electrical instruments to the measuring instruments. These transformers reduce the voltage and current from high value to the low value which can be measured by conventional instruments. The construction of the current and potential transformer is similar as both have the magnetic circuit in their primary and secondary winding. But they are different in the method of working. There are several types of differences between the voltage and the current transformer.

Potential and Current Transformers

Transformers Engr. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force EMF or "voltage" in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In the vast majority of transformers, the coils are wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids.

Basics of CT and PT

Current Transformers CT and Potential Transformers PT are used to measure the current and voltage in a circuit of the order of hundreds of amperes and volts respectively. A CT has large number of turns on its secondary winding, but very few turns on its primary winding. The primary winding is connected in series with the load so that it carries full load current. A low voltage range ammeter A is connected across the secondary winding terminals.

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Hence the secondary of current transformer is never left open. Accuracy class: Metering needs high accuracy at load current while Protection need not have that high accuracy.

5 Response
  1. Verney B.

    Current Transformers CT and Potential Transformers PT are used to measure the current and voltage in a circuit of the order of hundreds of amperes and volts respectively.

  2. Laurent L.

    From these primary variables, we may determine impedance, reactance, resistance, as well as the reciprocals of those quantities admittance, susceptance, and conductance.

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