Steam turbine

A steam turbine, comprising:

• a boiler unit including an auxiliary boiler and a main boiler that supply steam to a high-pressure turbine and an intermediate-pressure turbine;
• first supply pipes diverging from the auxiliary boiler and respectively extending to the high-pressure turbine and the intermediate-pressure turbine;
• a second supply pipe coupled with the high-pressure turbine, the intermediate-pressure turbine, and a condenser so that steam supplied through the first supply pipes is transferred to the condenser via the high-pressure turbine and the intermediate-pressure turbine;
• a plurality of valve units respectively disposed on each of the first supply pipes and configured to be operated when the auxiliary boiler is operated;
• a drain valve unit disposed on the second supply pipe and configured to discharge condensate water that has passed through the high-pressure turbine and the intermediate-pressure turbine;
• and
• a controller configured to control an opening amount of each of the valve units and the drain valve unit and to control an operation state of the boiler unit based on a first setting temperature to which temperatures of the high-pressure turbine and the intermediate-pressure turbine are preset, wherein
• the controller is configured to control, before rotation of the intermediate-pressure turbine starts, an operation time and temperature of the auxiliary boiler so that the temperatures of the high-pressure turbine and the intermediate-pressure turbine are increased to the first setting temperature, and
• the controller is configured to control, after determining that the temperatures of the high-pressure turbine and the intermediate-pressure turbine are maintained at the first setting temperature, operation of the main boiler such that the temperature of the intermediate-pressure turbine reaches a second setting temperature while operation of the auxiliary boiler is interrupted, and
• the controller is configured to control, after determining that the temperature of the intermediate-pressure turbine is maintained at the second setting temperature, the operation of the main boiler such that steam is supplied to the high-pressure turbine.