LV Current Transformers: Technical Definition & Features

What is a Current Transformer (CT)? A current transformer is an instrument transformer used to measure high currents passing through a circuit. Since direct measurement of high currents is costly and hazardous, CTs reduce these values to lower, safer levels (typically 5A or 1A) for easy reading by instruments.

Structure and Operating Principle: It consists of a magnetic iron core with primary and secondary windings. The current flowing through the primary winding creates a magnetic flux in the core, inducing a proportional current in the secondary winding. This induced current is measured by monitoring devices.

Key Features:

• Connection: Connected in series with the circuit.

• Phase Compatibility: In 3-phase systems, separate CTs must be used for L1, L2, and L3 phases.

• Safety: Provides isolation between high voltage/current and the measuring devices, ensuring equipment and operator safety.

• Selection Criteria: Type (measurement/protection), primary current, transformation ratio, accuracy class, busbar size, and nominal power (VA) should be considered.