Steam Turbine Generator (STG) in combined cycle power plant

In general, the design of a steam turbine is classified by the condition of the turbine exhaust i.e. backpressure, condensing, extraction and reheat. Steam turbines in combined cycle applications are specifically developed as multi-pressure condensing types, using water cooling provided from a cooling tower or air cooler, and direct coupled to a generator and optimized for reheat. A steam turbine generator is defined by the various system components, such as: HP-IP-LP turbine, generator, lubrication and hydraulic oil system, gland steam supply, vacuum breaking and drain systems, and turbine measurement, protection and control system.

In a triple pressure with reheat HRSG, the high-pressure steam bypass is located downstream of the HP superheater. During plant start-up the high-pressure steam bypass will release the HP steam to the cold reheat system according to the requirements of the steam turbine. If, in this system, the pressure of the HP steam exceeds the setpoint of the steam bypass controller, the HP steam bypass opens and releases the HP steam to the cold reheat system. Then, via the reheater section through the intermediate-pressure bypass station to the steam is released to the steam turbine condenser. Many of these industrial boiler co-generation applications are also able to run in Island Operation in case of a national power grid failure, to provide the required process steam to the adjacent production plant, and facilitate a safe shut down.

Pressure and temperature measurements are pivotal for a safe and efficient turbine operation. KROHNE offers a full range of state of the art OPTIBAR absolute-, gauge- and differential-pressure transmitters. The OPTITEMP temperature measurement series offers a complete capability, including thermowells, sensors and transmitters suited for power generation applications, all supplied with static and dynamic stress calculations and the required documentation.