Reclassification of Relay-Class Current Transformers for Revenue Metering Applications

A system has been developed to enable the reuse of existing relay-class current transformers (CT) for revenue metering applications. In this paper, a new methodology demonstrates the ability to perform live, dynamic characterization and reclassification of existing relay-class CTs. The system relies on a highly accurate split-core reference current sensor that is live-line deployed at high voltage (HV) substations, and rated up to 765 kV. Through the comparison of the measurements from the reference current sensor and the existing relay-class CT, the system can produce error correction parameters for the reclassification of the existing CT. These error correction parameters are programmed into an advanced revenue meter, which in turn dynamically corrects and effectively reclassifies the accuracy rating of the existing relay-class CT. Experimental results from laboratory and field testing illustrate the effectiveness of the new system and its ability to increase the accuracy of the overall revenue metering system