The CT Reclassification System

A number of independent system operators (ISO) and utilities have begun to explore the possibility of reusing existing relay-class current transformers (CT) for high accuracy metering applications. However, this would require the development of a new CT reclassification system. A key component of the system is an innovative, highly accurate reference current sensor that can be easily deployed using live-line methods in a high-voltage environment. The system first analyzes the accuracy of an existing CT, calculating its characteristic performance. Corresponding error-correction parameters are then derived and programmed into an advanced revenue meter, enabling dynamic accuracy reclassification of the existing CT while operational in the field. The new system has been proven in a live, operational high-voltage environment at a 138-kV utility substation.