Current Transformer (CT) – Construction and Working Principle

What is a Potential Transformer?

Transformers are the passive electromagnetic instruments that operate based on the principle of electromagnetic induction rules, which transmit electrical power from one circuit to another one magnetically. It includes two coils; one is the primary section, and the other is the secondary coil. Both the coils (windings) are magnetically combined without any magnetic part and electrically divided.
The transformer transmits the electricity (current/voltage) from one winding to another coil (coil) using a mutual induction. There is no variation in frequency during the energy transformation. Transformers are divided into two classes according to the core construction, like core types and shell types.
They are also categorized into step-up and step-down transformers based on the voltage rating conversion and winnings. There are different forms of transformers applied in the AC networks, such as potential transformers, power transformers, autotransformers, and three-phase transformers. In this post, we will discuss potential transformers completely.

Definition

The potential transformer can be defined as an instrument employed to transmit the voltage from a higher value to a lower output. 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.

what is a Potential Transformer (Reference: elprocus.com)

Circuit Diagram

The potential transformer contains primary winding with more twists and a secondary section with fewer turns. The great input AC voltage is presented to the primary section (or connected to the high voltage network to sense). The lower output voltage can be obtained through the secondary side using a voltmeter. The two windings are combined magnetically to each other without any attachment between them.

Potential Transformer Circuit Diagram
Potential transformers are produced with high quality to perform at low magnetic current, low flux density, and minimized load. While compared to a conventional type, it employs great conductors and an iron center. It can be constructed in the form of a shell type and core type to achieve the highest precision. Typically, core-type potential transformers are suitable to transmit the high voltage to the lower output.
It employs co-axial sections to decrease the leakage reactance. As the potential types are performed at high voltages, the great voltage primary section is divided into small parts coils/turns to decrease the insulation cost and problems. The phase shift between the output voltage and the input voltage should be controlled accurately to keep the lower voltage by changing the load. Windings layered with vanish cambric and cotton tape to decrease the insulation price.
Hard fiber separators are applied to cover the coils. Oil-filled bushings are also employed to send the high voltage outputs (above 7kV) to the basic lines. The primary section of a potential transformer has a great number of turns, while the secondary side has fewer turns. The voltmeter or multimeter is used to detect the lower output voltage.