A novel approach to detect CT saturation using standalone CT measurements

Abstract: The requirement for reliability and security in power system is increasing every passingday with the increase in complexity of the power system. To ensure highest level ofreliability, protection relays have to receive correct measurements. One of the most importantmeasurement that is needed by a relay as an input is current. However, currentmeasurements received from current transformer (CT) can become inaccurate due to aphenomenon called CT saturation. This Master's thesis objective is to build a novel algorithmfor the protection relays to detect CT saturation. The algorithm should be basedon a stand-alone method that is able to detect CT saturation within 1-2 ms for a samplingfrequency of 4 kHz.This project comprises a study of the background about CTs and CT saturation. Therelated work done to detect CT saturation is also studied. Later, major existing methodsused in the industry to deal with CT saturation are investigated in detail and modelledin Simulink. A novel method is proposed to exclusively detect CT saturation, keeping inmind the strict requirements, set in the beginning of the project. The proposed methodis implemented in Simulink and HiDraw(in-house software in ABB to create C code forprotection functions). Lastly, the proposed method and the existing methods are testedin Simulink for more than 1300 test cases based on dierent power system conditions,IEC-60255-187-1 and real current recordings from relays.The results of the tests showed that the proposed method successfully detect CT saturationand was better than the existing methods in terms of speed and accuracy. It was concludedthat the proposed method successfully detects CT saturation and hence, can be used withany protection function in a relay where there is a need to detect CT saturation.