A digital compensation method for improving current transformer accuracy

This paper deals with error compensation in current transformers. Usually the manufacturer tries to limit these errors by stating a transformer nominal ratio slightly different from the turns ratio. On the other hand techniques have been developed that allow software current compensation. The proposed method requires acquisition of the instantaneous secondary current and its adjustment with magnetizing current, taking into account hysteresis effects. To do this, a preliminary procedure is performed for core and transformer parameter identification. The compensation method has been tested on a variety of instrument transformers, with sinusoidal primary current. Test results show, in all examined cases, an improvement in primary current reproduction accuracy, compared with that achieved using CTs nominal ratio, even for core partial saturation. A further development of the compensation technique is in progress, with a view to eliminating some restrictive hypothesis introduced in the present study.