Gas turbines with free-running power turbines are used primarily as drive systems for widely varying power requirements in power plants and on board ships, locomotives, and motor vehicles.

The ET 794 trainer investigates the behaviour during operation of a system with two independent turbines in a two-shaft arrangement. One turbine (the high-pressure turbine) drives the compressor and the other turbine (the power turbine) supplies the effective power. Changes in power output in the power turbine have no influence on the compressor, which is able to keep running at optimum speed at the best efficiency point.

The trainer includes the following components: compressor, tubular combustion chamber and high-pressure turbine; fuel system; starter and ignition system; lubrication system; power turbine; generator; and measuring and control equipment.

The complete unit is called gas turbine. The gas turbine works as an open cyclic process, with the ambient air being drawn out and fed back in. The high-pressure turbine together with the compressor and the combustion chamber are called gas generator as they produce the required gas for the power turbine. To do so, the ambient air drawn in is brought to a higher pressure in the single-stage radial compressor. When the air enters the combustion chamber, only part of it is used for combustion. This air is decelerated with the aid of a turbulence generator such that the added fuel is able to burn with a stable flame. The greater portion of the air is used to cool the combustion chamber components, and is mixed into the combustion gases at the end of the combustion chamber. This reduces the gas temperature to the permissible inlet temperature of the high-pressure turbine.

The gas flows out of the combustion chamber into the single-stage radial high-pressure turbine and discharges a portion of its energy to the turbine. This energy drives the compressor.

In the power turbine, the gas discharges the remaining portion of its energy, which is converted into mechanical energy and drives a generator. The electrical energy generated is dissipated using braking resistors. The gas turbine is started with the aid of a start-up fan.

The speed, temperatures, and pressures and the mass flow rates of the air and fuel are recorded and displayed using sensors. Typical characteristic variables are determined.