Temperature Distribution of 250 MW Hydro Turbine Synchronous Generator at Continuous Overloading Conditions

Hydrogenerators are usually operated at over-load condition during the period when excess water, within permissible silt content, would be available in the river. The period may be extended to many weeks under extensive conditions e.g. six weeks in case of Karcham Wangtoo Hydropower Station (India) at 20% overloads. High-power, low-speed, direct-driven Hydro Turbine Synchronous Generators (HTSGs) apply their own cooling techniques to withstand temperature rise at various load points. This paper presents the temperature distribution of a 250 MW CB 870/300-28 HTSG running under distinct stages of long time interval overloads. The machine modelling and simulations are carried out by means of three-dimensional commercial finite-element analysis (FEA) software package MagNet 7.5. The analysis is initiated with a basic electromagnetic design of CB 870/300-28 using FEA solver. Then, extended to the investigation of thermal distribution via a coupled thermal and fluid-dynamical model based on ThermNet 7.5. The simulated thermal metaphors at continuous overloads are presented and validated with a case study of 250 MW HTSG. The utility of these generalized results of thermal distribution guarantees the desirable operation of this kind of machine. Moreover, this paper shows the feasibility to design HTSG which intends to operate at continuous overloads.