General characteristics of single shaft microturbine set at variable speed operation and its optimization

Microturbine is widely applied now in distributed generation. Here the capacity of microturbine is defined as about 200 kW power. Commonly when the load changes, the generating gas turbine has still to run at design rotating speed. This results in lower part-load efficiency. However, the part-load performance of microturbine can be improved by variable speed operation since constant frequency of electricity can be guaranteed through the control of the electronic equipment. This optimum operation mode has not yet been theoretically studied thoroughly. The paper firstly analytically investigates the general optimum speed variation for off-design efficiency with an analytical approach proposed by the last two authors. Furthermore, the study shows that the optimum part-load performance is basically not influenced by the design temperature ratio and pressure ratio. Because of using a typical component performances and analytical approach of off-design performance analysis, the conclusions are general and typical for common microturbines but not fully accurate for any special microturbine.