Here I will explain the steam turbine components.
1. Stop Valve
The stop valve of the steam turbine serves to isolate the turbine from the steam stream and also to quickly stop the supply of steam to the turbine under certain conditions. For example in case of loss of electrical load at a steam power plant from the the grid – we know it as a load rejection – the stop valve will quickly close in a split second. This is useful for avoiding overspeed on the turbine due to the presence of pressurized steam entering the turbine but no electrical load on the generator. The stop valve opens by the working of the hydraulic actuator and closes by the spring.
2. Control Valve
Control Valve is to control the flow of steam into the turbine in accordance with the existing load. In the steam power plant, the control valve opening depends on the amount of electrical load in the generator.
3. Electrohydraulic actuators on Stop and Control Valve
The actuators for stop and control valve on steam turbine power plant use the “fail-safe” principle. That is, the valves are opened by the hydraulic actuator and closed by force from the spring. The differences between the stop valve and control valve actuators is on the stop valve does not need to use the valve position sensor as in the control valve. The stop valve uses only a limit switch sensor.
4. Extraction Steam Line and its Check Valve
Extraction steam is a steam taken from certain stages in a steam turbine that is used for many things, such as preheating water (feedwater before boiler entry), turbine sealing system, sootblower system, etc.
In the pipeline extraction steam shall be installed check valve to prevent backflow from the steam. For example in the case of load rejection above, the flow of water back into the turbine, especially on the side of the superheater turbine will cause a termal stress on the steam turbine components.
The check valve is commonly using Swing Check Valve or Power Assisted Swing Check Valve type. Swing Check Valve opens up by the large differences in steam pressure. And in the event of steam flow interuption (as in the case of load rejection) this check valve will close as the result of the weight of the valve itself. While the Power Assisted Swing Check Valve uses additional actuators to close the valve. Otherwise, to open the valve does not need to use the actuator. It will open by the pressure difference of the steam flow in the pipe.
The steam turbine use bearing as a part to reduce friction between the shaft (the rotating part) with the casing (stator). Bearings are equipped with circulating and pressurized lubricating oil. To compensate the gravity of the turbine the journal bearing is used, whereas to compensate for the axial forces arising from the steam flow inside the turbine, thrust bearing is used.
6. Hydraulic Turning Gear
It is a mechanism to rotate the turbine rotor at initial start or at the time after shut down to prevent distortion/bending resulting from uncoordinated heating or cooling process on the rotor. This system uses a hydromatic motor whose rotating power comes from a high pressure hydraulic system.
7. Balance Piston
Balance Piston on steam turbine is to compensate the emergence of axial forces due to the flow of the steam insidenthe turbine. This component mitigates the work of thrust bearing.