Problems in Using State Estimation in Power Systems which have Poor Quality High Voltage Measurements, Phase Imbalance and High Levels of Harmonics

Abstract

An accurate indirect method of high voltage measurement calibration is presented which uses only portable low voltage test equipment and measures the voltage, active and reactive power on the low voltage side of the generator (or supply) transformer and calculates high voltage on the other side. A one-to-one correspondence almost exists between the accuracy of the low voltage measurement and the accuracy of the high voltage calibration. Inaccuracies in the low voltage active and reactive power measurements have only a negligible effect on the accuracy of the high voltage calibration. The same technique can be used to recalibrate switchyards which are connected to calibrated switchyards by transmission lines. Redundant checks are also possible. When state estimation is used in power systems which have poor quality high voltage measurements then measurements should be made on the low voltage site of the generator (or supply) transformer because these readings are more accurate and more immune to harmonics and voltage imbalance than those on the high voltage side. The manner in which harmonics affect measurements is also discussed.