Frequency response analysis and modeling of measurement transformers under distorted current and voltage supply

The time and frequency response of current and potential transformers (CTs and PTs) operating under fundamental frequency conditions are well known. However, in the presence of harmonic frequencies, these transformers can exhibit significant errors. The authors present CT and PT comprehensive frequency domain equivalent circuits which, in addition to previous study features, include the hysteresis and eddy current effects. Furthermore, a practical approach which calculates the stray capacitances is proposed. By comparing theoretical and practical results the importance of considering parameters which are usually ignored in such studies is highlighted