Calculated Substantiation of the Time Taken to Forcedly Cool Down with Air the CLN660-24.2/566/566 Steam Turbine of the Troitsk District Power Plant 660 MW Power Unit

At the Troitsk District Power Plant (a Branch of PJSC Wholesale Generating Company No. 2), a 660 MW coal fired power unit is in operation. The power unit is equipped with a CLN660-24.2/566/566 condensing steam turbine manufactured in the People’s Republic of China. Among the power unit’s variable operation modes, the steam turbine cooling down modes play an essential role; these modes are of importance when the turbine is shut down for carrying out equipment repairs, because its casing parts cool under natural conditions to acceptable temperatures (150°С), at which thermal insulation can be dismantled from the turbine high-temperature casings, for as long as 170‒200 h. This generates the need to perform forced cooldown, which can be carried out by using steam under load, air, and combination of these two methods, with the last option regarded to be the most effective one. The article presents the result of applying the currently existing technologies for cooling down the combined high and intermediate pressure cylinder. The time taken to accomplish the turbine forced cooldown was estimated by calculation with the use of various techniques, in particular, the finite element method implemented by means of the ANSYS software system. The calculated assessment of the cooldown time was carried out with taking into account the thermally stressed state of the key “critical” components and the steam turbine low cycle fatigue strength.