D.-G. Lee, S.-H. Kang, Y.I. Son, and Y.-C. Kang (Korea)
CT Saturation, Real Time Compensation, Auto Regressive Model
Current transformer (CT) saturation may cause the mal operation or operating time delay of protection relays. The secondary current can be expressed as the linear combination of sinusoidal and exponential signals, if no saturation occurs. In this paper, an advanced algorithm for the compensation of the distorted secondary current due to CT saturation is proposed. At first, the 3rd difference function detects the start and end of saturation in real-time. Secondly, the autoregressive model-based FIR filter and the least mean square curve fitting method are used to estimate the exponential component and the sinusoidal component. During saturated periods, the proposed algorithm estimates the unsaturated secondary current which is equal to the scaled primary current. Test results indicate that the proposed algorithm compensates the distorted currents accurately under a variety of fault conditions.
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