Power System

Potential Transformer (PT)

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Potential Transformer (PT) is used to measure large value of voltages. It is basically a step up transformer which lowers down the current so that it can be measured by simple voltmeter. The primary winding is connected to the high-voltage circuit or the source of the voltage that needs to be measured monitored.

Basic Components 

  1. Primary Coil: The primary winding is connected to the high-voltage circuit (the source of the voltage that needs to be measured or monitored). In many cases, the primary winding may consist of just one turn, which could be directly connected to the high-voltage line or to a network.
  2. Core: The core of the transformer is typically made of magnetic material (like silicon steel), which facilitates the transfer of energy from the primary to the secondary winding via magnetic flux.
  3. Secondary Coil: The secondary winding produces a lower voltage that is proportional to the high voltage in the primary winding, based on the transformer’s turns ratio.

Current Transformer (CT)

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Current Transformer is used to measure large value of currents. It is basically a step up transformer which lowers down the current so that it can be measured by simple ammeter. The main line conductor works as single turn primary winding and secondary winding is connected to the ammeter and monitored by relays or protection system. Thus a CT is connected in series with the line.

Basic Components 

  1. Primary Coil: The primary winding of a CT usually has only one or a few turns and has a current carrying conductor  across the base. 
  2. Core: The magnetic core is usually made of ferromagnetic material such as iron, which improves the magnetic coupling between the primary and secondary windings.
  3. Secondary Coil: The secondary coil wound around the magnetic core produces a small and equal amount of current. The ratio of the primary and secondary current is determined by the displacement of the primary and secondary windings.

Types

  1. Measuring CTs: Used for accurate measurement of current, typically in metering applications.
  2. Protection CTs: Used in protection circuits, where accuracy under fault conditions is essential.