What is the difference between current transformer and voltage transformer?

The difference between voltage transformer and current transformer

In the power system, the transformer is an indispensable device, mainly used to measure and isolate high voltage. The following are the main differences between voltage transformer (PT) and current transformer (CT):

Function and application scenario

Current transformer (CT): Mainly used to convert large current into standard current for measurement and relay protection. It is connected in series in the circuit to ensure accurate current measurement, while isolating high voltage and protecting the safety of operators.

Voltage transformer (PT): Used to convert high voltage into low voltage for easy measurement with a standard voltmeter. It is connected in parallel in the circuit to provide a safe voltage measurement environment, while isolating high voltage to prevent direct contact.

Structure and working principle

Current transformer: The primary winding has fewer turns, usually only one or a few turns, and is connected in series with the measured current. The secondary winding has more turns, and the impedance of the connected instrument current coil is small, which is close to a short-circuit state during normal operation.

Voltage transformer: The primary winding has more turns and is connected in parallel with the high voltage to be measured; the secondary winding has fewer turns, and the voltage coil of the connected voltmeter or power meter. During normal operation, the primary internal impedance is small and can be regarded as a voltage source.

Safety and operating precautions

Current transformer: The secondary terminals cannot be open circuited to prevent excessive iron loss or increased voltage of the secondary winding from causing insulation breakdown.

Voltage transformer: The secondary terminals can be open circuited, but short circuit is not allowed to prevent excessive short-circuit current. A fuse needs to be installed for short-circuit protection.

Comprehensive recommendation and risk warning

When selecting and using these two types of transformers, they should be selected according to specific measurement requirements and safety standards. Current transformers are suitable for occasions where large currents need to be measured, while voltage transformers are more suitable for occasions where high voltages need to be measured. At the same time, operators should strictly abide by safety operating procedures, regularly inspect and maintain equipment, and ensure that the equipment operates in the best condition.