Attenuation of harmonic pollution due to the adjustable speed drives in the electric circuits of the power plant auxiliary services

The adjustable speed drives are now designed for so high power usage to be employed without restrictions for the power plant auxiliary services. Unfortunately, they employ power electronic devices to generate the variable frequency power supply for AC motor speed control with the consequent generation of harmonics and interharmonics which add to distortions already present. In this paper the harmonic and interharmonic analysis of the electric circuits of the power plant auxiliary services is performed with reference to the standardized 320 MW thermal power plant of the Italian Utility Company (ENEL); adjustable speed drives for boiler inlet air fans and for feed water pumps are considered. After the evaluation of the voltage distortion levels, suitable compensation devices, active and passive, are chosen in order to constraint the harmonics and interharmonics under limits suggested by Standards.