Many times of servo valve's abnormal action have occurred in DEH control system of a 300 MW steam turbine in one power plant of Henan Province

made the regulating valve to be abnormally closed and to be automatically opened

resulting in large load fluctuation of the unit

seriously affecting safe and economic operation of the steam turbine.For this

through analysis in many aspects

it is believed that the oil-sludge resulted from contamination and deterioration of fire-resistant oil is the main cause leading to abnormal action of the servo valve.Using the opportunity of repair after shutdown

a fully cleaning and flushing of the oil system has been carried out

and the fire-resistant oil being filtered

making the indices of fire-resistant oil

such as the particle size

the acidic value

and the resistivity etc.

to be up the set standard

finally

making the frequency of load fluctuation for said unit being greatly reduced

up till being fully eliminated.