CT Instrumentation Channel Error Correction Using Dynamic State Estimation

Abstract

Protective relays depend on the fidelity of Protection-Class current transformer (CT) instrumentation channel outputs to perform reliably. Such channel errors as caused by CT saturation thus pose serious protection reliability challenges. This paper presents a new method for estimating the CT primary current in real-time through a Dynamic State Estimation (DSE) process. Specifically, the method involves obtaining discrete measurements of the CT secondary burden voltage through a continuous monitoring process. The CT primary current is then continuously estimated by the DSE process, based on fitting the continuously obtained measurement samples to the detailed and non-ideal CT channel model. The continuously estimated primary current can then be made readily available for protection functions. The CT primary current is one of multiple state variables dynamically estimated using this method. The paper also presents a simple algorithm that can detect CT saturation nearly instantaneously, based on using the dynamically estimated flux linkage.