Modeling Electromechanical Overcurrent Relays Using Singular Value Decomposition

This paper presents a practical and effective novel approach to curve fit electromechanical EM overcurrent OC relay characteristics. Based on singular value decomposition SVD , the curves are fitted with equation in state space under modal coordinates. The relationships between transfer function and Markov parameters are adopted in this research to represent the characteristic curves of EM OC relays. This study applies the proposed method to two EM OC relays: the GE IAC51 relay with moderately inverse-time characteristic and the ABB CO-8 relay with inversetime characteristic. The maximum absolute values of errors of hundreds of sample points taken from four time dial settings TDS for each relay between the actual characteristic curves and the corresponding values from the curve-fitting equations are within the range of 10 milliseconds. Finally, this study compares the SVD with the adaptive network and fuzzy inference system ANFIS to demonstrate its accuracy and identification robustness.