Electronic system for increasing the accuracy of in-service instrument-current transformers

Abstract

An electronic error compensator is proposed for instrument current transformers. It is specially intended for transformers used in high voltage networks at power frequency. In these transformers, the magnetizing current is the main cause of errors. The proposed system compensates this current, reducing the ratio and phase errors. Neither auxiliary windings nor auxiliary cores are needed, so the method can be applied to in-service transformers. Large variations of the burden connected to the secondary winding are permitted, as it is required by the standard. The power needed by the device is a small fraction of the power delivered to the burden, so that the proposed compensation requires only small and cheap electronic devices.