Local detection of voltage imbalance in three-phase power systems based on PMU output

The problem of voltage imbalance detection in a three-phase power system using phasor measurement unit (PMU) data is considered within a hypothesis testing framework. A general model for the symmetrical sequences from a PMU measurement at off-nominal frequencies is presented. The new formulation takes into account the fact that minor degree of imbalance in the system is acceptable and does not indicate interruptions, failures, or degradation of physical components. Therefore, a generalization of the locally most powerful test (LMP), named the generalized LMP (GLMP) test, is developed for local detection in the presence of additional nuisance parameters. The GLMP concept is similar to that of the generalized likelihood ratio test (GLRT) and is obtained by substituting the maximum likelihood (ML) estimators of the nuisance parameters into the LMP test. The numerical performance analysis shows improved performance over benchmark techniques and detection performance robustness to ML estimation errors.