Tandem Steam Turbine | Operation

The steam turbine subsystem is responsible for producing the required mechanical torque. In this typical configuration of turbines, 3 pressure stages are implemented. The name “Tandemturbine” comes form this installation, where the steam flow has to pass through different turbine stages, all mounted on the same shaft. Between each turbine stage, various equipment, like reheater or crossover, can be modelized via their response time constants.
As inputs, this subsystem receive the steam pressure psih and the gate opening x. As a result, three mechanical torque th, ti, tl, are produced. The physical modeling of the tandem steam turbine is presented in Figure 5 - 27. It describes most common configuration of tandem steam turbine, with single reheat, double reheat, and steam crossover.

Typical Configuration of Tandem Steam Turbine

On the modelling aspect, the block diagram of the steam turbine is shown in Figure 5 - 27, describing the steam chest, the three turbine stages and the available reheaters. About parameter settings, it is important that the sum of power fraction factor, fh, fi, fl, must always be equal to 1.0. Also, the parameter Tr1 and Tr2 can represents reheaters or crossover, depending on turbine configuration.
Third, the parameter sw1 allow users to by-pass the second reheater.

Steam Turbine Block Diagrams