A need to review total harmonic distortion measurement in power systems

Introduction of thyristor drives and different types of loading pattern have brought in a lot of distortion in the waveforms, beyond the conventionally accepted 3rd, 5th, 7th, 11th & 13th harmonic disturbances. For analysis, the waveforms are decoded by harmonic analysers into various harmonic elements, so that the added sum gives the final waveform. This basic principle is based on Fourier series of estimation. The total harmonic distortion (THD) is conventionally mentioned as THD.%=(/spl radic/(V2/sup 2/+V3/sup 2/....VN/sup 2//V1/sup 2/))/spl times/100% As this value does not tally with the working parameters for comparison, the standards like IEEE 519, G 5/3 etc. have adopted limitations by direct summation. This paper presents a need for reviewing both so that the measurements can be compared easily with the working conditions. This is based on studies conducted at various sites during the last 8 years. Some of the waveforms recorded are presented here. This would easily pave a way for providing simpler protection in the power distribution systems.