Current Transformer

The range of a current transformer (CT) refers to its nominal current rating and the range of currents it can accurately measure and transform into a proportional secondary current. CTs are widely used in electrical power systems for measuring and monitoring current flow in conductors.

1. Nominal Current: The nominal current of a CT is the primary current that corresponds to its standard rating. It is typically expressed in amperes (A) and represents the maximum current that the CT is designed to handle under normal operating conditions without saturating its core. Common nominal currents for CTs range from a few amperes to several thousand amperes, depending on the application.

2. Primary Current Range: The primary current range of a CT refers to the range of currents that the CT can accurately measure and transform into a proportional secondary current. It extends from the minimum measurable current to the maximum measurable current, typically expressed as a percentage of the nominal current. For example, a CT with a nominal current of 1000 A might have a primary current range of 0-2000 A, allowing it to accurately measure currents from 0 A to 2000 A.

3. Accuracy Class: The accuracy class of a CT specifies the maximum permissible error in the secondary current output under specified operating conditions. CTs are classified into accuracy classes such as Class 0.1, Class 0.2, Class 0.5, Class 1, Class 3, etc., based on their accuracy requirements. The primary current range and accuracy class of a CT are closely related, as higher accuracy classes typically require narrower primary current ranges to achieve the specified accuracy.

4. Burden: The burden of a CT refers to the impedance presented to its secondary winding by the connected measuring or protective devices. The burden affects the accuracy and performance of the CT and should be considered when selecting a CT for a particular application.

In summary, the range of a current transformer encompasses its nominal current rating, primary current range, accuracy class, and other factors that determine its suitability for measuring and monitoring current in electrical power systems. Choosing the appropriate CT range is essential to ensure accurate measurement and protection of electrical equipment.