Current Transformers (CT)

Current Transformers (CTs) are devices used in electrical power systems to convert high alternating current (AC) to a lower, safer level for measurement and protection purposes. They are essential components in power distribution and control systems.

Definition:
A current transformer is an instrument transformer designed to provide a current that is proportional to the current in a primary circuit. It typically consists of a toroidal core with a primary winding and a secondary winding. The primary winding is connected in series with the load, while the secondary winding is connected to the measuring or protective devices.

Function:
1. Measurement: CTs allow for the accurate measurement of current in high-voltage circuits without the need for high-voltage-rated meters or protection relays.
2. Protection: They are used in conjunction with relays to provide overcurrent, short-circuit, and earth-fault protection in power systems.
3. Control: CTs enable the control of power flow in circuits by providing feedback to control systems.

Applications:
1. Power Distribution: In substations and distribution boards to monitor and control the flow of electricity.
2. Metering: For billing purposes in utility companies to measure the amount of electricity consumed by customers.
3. Protection Systems: To detect faults and initiate circuit breakers to prevent damage to the electrical infrastructure.

Selection Criteria:
1. Rated Current: The CT should be rated for the maximum current expected in the primary circuit.
2. Accuracy Class: Depending on the application, CTs are classified by their accuracy (e.g., 0.5, 0.2, 0.1 class).
3. Turns Ratio: The ratio of primary to secondary turns determines the current transformation ratio.
4. Insulation Level: Must be suitable for the voltage level of the primary circuit.
5. Environmental Conditions: CTs must be rated for the environmental conditions they will be exposed to, such as temperature, humidity, and pollution levels.
6. Size and Physical Characteristics: The physical size and shape of the CT must be compatible with the installation location and the equipment it is connected to.

In summary, current transformers are vital for the safe and efficient operation of electrical systems, providing a means to measure, control, and protect against electrical faults in high-current applications. Their selection should be based on the specific requirements of the system they will be used in.
Please refer to the product rule book for details.