What is the voltage transformer?
Voltage transformers (VT), also called potential transformers (PT), are a parallel connected type of instrument transformer. They are designed to present negligible load to the supply being measured and have an accurate voltage ratio and phase relationship to enable accurate secondary connected metering.
A current transformer (CT) is a type of transformer that is used to measure alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.
- The ratio of a CT's primary rating to its secondary rating is equal to the number of secondary turns. For example, a CT with a 5-A secondary and 20 turns will have a nameplate ratio of 100:5. This ratio is based on the primary conductor passing once through the transformer window.
- A distribution transformer or service transformer is a transformer that provides the final voltage transformation in the electric power distribution system, stepping down the voltage used in the distribution lines to the level used by the customer. If mounted on a utility pole, they are called pole-mount transformers.
- When the circuit burden gets too large, the CT secondary voltage becomes distorted. This is because the CT is beginning to have a flux density that is much greater than normal operation. As the secondary burden increases the transformer excitation voltage also increases above the normal level.
Updated: 28th September 2018