A fast method for identification of symmetrical components for power system protection

This paper presents a novel dynamic technique for identifying and measuring the symmetrical components of three-phase voltage or current waveforms in electrical power systems. The proposed technique is based on stochastic estimation theory. The problem is formulated as an estimation problem and presented in state space form. The algorithm is then used to estimate the active and reactive components of the positive, negative and zero components of unsymmetrical waveforms. The method is tested using practical study cases. Different factors affecting the identification process such as data window size, sampling frequency and number of samples are studied. Effects of bad data on the solution accuracy are also studied. The speed of convergence is examined by changing the estimator initial Conditions. The results obtained show that the proposed technique can estimate and track the symmetrical components of non-stationary three-phase unbalance voltage or current waveforms in noisy environments. Fast accurate solutions are guaranteed regardless of the initial conditions. It is also shown that bad measurements have no effect on the final accuracy of the estimation. (C) 2001 Elsevier Science Ltd. All rights reserved.