The experience of retrofitting the highlow speed switching facilities for induced draft fans of 350 MW units in Huaneng Nantong Power Plant has been presented. Through startstop speedswitching control method by using electric switch carbinet

the original isolating switch control is replaced by startstop switching through two 6 kV highlow speed switching carbinets

realizing the retrofit of switching control system of motors used for driving induced draft fans of two boilers. At the same time

in order to reduce the perturbation influence of speedswitching for incluced draft fans upon the pressure in furnace

the regulating system of pressure in the furnace has also been modified correspondingly.