Current transformers

A Current Transformer (CT) is a type of instrument transformer that is used to measure high alternating currents in a power system. It is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary.

Current transformers are the current-sensing units of the power system and are used at generating stations, electrical substations, and in industrial and commercial electric power distribution. 

They are primarily used for protection and measurement purposes in a power system.

The CT’s primary winding consists of a single ‘turn’, which can be a heavy copper bar to carry current through the core. Window-type current transformers are also common, which can have circuit cables run through the middle of an opening in the core to provide a single-turn primary winding.

The secondary winding may have a large number of coil turns wound on a laminated core of low-loss magnetic material. This arrangement allows the CT to maintain an accurate ratio between the currents in its primary and secondary circuits over a defined range.



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Advantages of testing Current Transformers

In essence, current transformers play a crucial role in maintaining the health and efficiency of power systems by providing a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line.

Testing current transformers is paramount for several reasons:

  1. Accuracy: Regular testing ensures that the current transformers are performing accurately. This is crucial as they are used for metering purposes and must have a high degree of accuracy to ensure precise billing.

  2. Protection: Current transformers used for protection must react quickly and correctly in the event of a fault. Testing helps verify this.

  3. Early Fault Detection: Electrical changes in a current transformer, caused for example by aging insulation, can be identified at an early stage through testing.

  4. Preventive Maintenance: Regular testing can identify minor issues before they become major ones, saving time and money in the long run. It also extends the lifespan of transformer units.

  5. Safety: Testing reduces risks such as confusing instrument transformers for metering and protection, or mixing up connections.

  6. Cost-Effective: Instrument transformer-based transformers are less costly, and damaged parts can be easily replaced.

In summary, regular testing of current transformers is crucial for maintaining the health and efficiency of power systems.


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