Current Transformer Explained

By R.W. Hurst, The Electricity Forum

Current Transformer Explained
Current Transformer

A current transformer (commonly referred to as a "CT") has a primary winding, a transformer core and a secondary winding. On the other hand, some transformers, including CTs, use an air core. In principle, the big difference between a current transformer and a voltage transformer is that a current transformer is supplied with constant current, while a voltage transformer is supplied with constant voltage.

A current transformer is designed to both reduce high voltage currents to a much lower level and also provide a convenient way to safely monitor the actual electrical current flowing. This is done using a standard ammeter. The basic design and operating principal of a current transformer is the same as an ordinary electrical transformer.

Current transformers are normally used to measure currents of high magnitude. Current transformers step down the current to be measured, so that it can be measured with a normal range ammeter. A Current transformer has only one or very few number of primary turns. The primary winding may be just a conductor or a bus bar placed in a hollow core. The secondary winding has large number turns accurately wound for a specific turns ratio. Thus the current transformer steps up, the voltage while stepping down the current.

Current Transformers Convert Primary Power Signals to Manageable Values for:

• Indicating Meters

• Revenue Metering

• Protective Relay Systems

• Power Generation

• Plant Monitoring Systems

• Fault Recorders


• Overall Electric Grid Monitoring

• Building Energy Management Systems

• Load Control

Read Our Other Transformer Pages: Potential Transformer Explained, Control Transformer Explained, Current Transformer Basics, Dry Type Transformers Explained, Isolation Transformer Explained, When To Use a Step Down Transformer