Investigation on the performance of a 277.8 MVA synchronous air-cooled hydrogenerator through loss models

Synchronous generators (SGs) are widely used in power generating plants including hydropower as it is easy to control, supports large amount of reactive power, and offers higher energy efficiency in comparison with asynchronous generators. SGs are often overloaded through hydro-turbines by utilizing excess water flow in the river (e.g. 1000 MW Kancham Wangtoo hydropower station (India) at 20% continuous overloading condition for more than six weeks). This paper investigates the efficiency of a 277.8 MVA SG, through its loss models, under two operating conditions: (i) at rated load, (ii) at 20% overload. Temperature of cooling air inlet to the stator of SG (primary cooling) and the temperature of water inlet to the cooler (secondary cooling) are considered for the analysis. Simulated results are compared with a commissioned generator through the on-site measurements. From the test results, it is observed that the cooler performance (temperature of air leaving from the cooler) was poor at overloads which causes reduction in efficiency and temperature-rise in stator windings of tested SG.