Adding power quality monitoring to a smart kWh meter

This article describes a method that gives some power quality quantities, like total voltage distortion and voltage unbalance, from relatively sparsely sampled measurements. It is based on an adaptive state observer for the voltage phasors. Requirements for power quality monitoring in power distribution are listed and the results of the laboratory and field tests of new power quality monitoring kWh meters summarised together with field use experience. Finally, the needs and possibilities for future development are discussed.