What is NCT or Neutral Current Transformer ?

A neutral current transformer (NCT) is a type of current transformer that is used to measure the neutral current in a three-phase electrical system. It is typically used in applications where the neutral point of the system is not grounded, such as in unbalanced or delta-connected systems.

The NCT consists of a primary winding, a secondary winding, and a magnetic core. The primary winding is connected in series with the neutral conductor of the electrical system, and the secondary winding is connected to the measuring instrument. The magnetic core helps to accurately transform the primary current to a proportionate secondary current.

One important property of the NCT is its turn ratio, which is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. The turn ratio of the NCT is typically chosen so that the secondary current is within the operating range of the measuring instrument.

In operation, the NCT measures the neutral current flowing through the primary winding and produces a proportional current in the secondary winding. This secondary current is then measured by the instrument, which displays the neutral current of the system.

In addition to measuring neutral current, the NCT can also provide protection against overcurrents and fault conditions in the electrical system. The secondary winding of the NCT can be connected to a protective device, such as an earth fault relay which is connected to the master tripping circuit or trip relay circuit, which operates the circuit breaker and interrupt the flow of current in the event of an overcurrent or fault condition.

A neutral current transformer is an essential device for measuring and protecting against fault or excessive currents in three-phase electrical systems.