Potential Transformer

Potential Transformer

A voltage transformer, also known as a potential transformer, is a type of instrument transformer used to measure and transform high voltage levels into manageable, low-voltage values suitable for monitoring and controlling devices. Its primary function is to repeat the fundamental voltage waveform while maintaining the phase connection.

Potential transformers are constructed with a main winding connected to the high voltage side of the circuit and a secondary winding connected to the low voltage side of the circuit. The ratio of turns between the main and secondary winding determines the transformation ratio of the potential transformer. This ratio permits precise voltage monitoring and the application of electrical system protection measures.

Construction

The potential transformer is built with a high-quality core that runs at a low flux value, resulting in a low magnetizing current. The transformer's terminals must be designed such that the voltage rating variations with load, as well as the phase shift between the output and input voltage, are as little as feasible.

The primary section has a considerable number of turns, whereas the secondary section has far less. A co-axial arrangement is employed in the potential transformer to minimise leakage reactance. Insulation costs are also decreased by dividing the major piece into particular sections, which minimizes the insulation between the layers.

 

Working of Potential Transformer

the voltage to be measured is linked between the potential transformer phase and ground in the power circuit. That is, the main winding of the potential transformer is linked to a high voltage circuit, while the secondary winding is connected to a voltmeter. The two winding are magnetically connected and operate by electromagnetic induction due to mutual induction.

The voltage across the secondary winding is measured in proportion to the voltage across the primary winding using the  multi meter or voltmeter. Because of the potential transformer's high impedance, only a small current flows through the secondary winding, and it functions similarly to an ordinary transformer with no or low load.

The voltage induced in the secondary is quite low because the primary has more turns than the secondary, which has less turns. A typical low voltage voltmeter is used to measure the secondary voltage. We can determine the primary voltage using the transformer's turn ratio equation.

VP/VS = NP/NS

 

Where

Primary Voltage = VP.

Secondary Voltage = VS.

Number of Primary Turns = NP

No. of Secondary Turns = NS

There is virtually little current flowing through the secondary windings of the PT because of the voltmeter's extremely high impedance. The PT has very low VA ratings of only 200 VA for the same reason.

Types of Potential Transformers

• Protection voltage transformers
• Metering voltage transformers

Pros

• When employing the capacitive potential transformer, it is very useful for measuring extremely high voltages.
• A regular voltmeter is capable of measuring extremely high voltages thanks to a potential transformer.
• Electrical separation between the voltmeter and the high voltage line provides protection.

Cons

• Only AC can be measured using it; high voltage DC is not allowed.
• They are more expensive than a regular transformer.

Applications Potential Transformer 

• Typically found in relay and metering circuits.
• Applications include power line carrier communication circuits.
• Electrically used in protective systems
• Used to keep feeders safe.
• Used in generators to shield the impedance.
• It is used to synchronize generators and feeds.
• Used as voltage protection transformers