Simulation and experimental illustration of vibration at load rejection in a continuously overloaded large hydrogenerator

Abstract

Large hydro generators are usually overloaded at various situations such as the period when excess water isavailable and when excess inflow is to be discharged. The period may have extended to many weeks under exigent conditionse.g. six weeks in case of a 1000 MW hydropower plant (HPP) located at northern region, India at 20% overload. All theperformance related parameters including vibrations were observed during commissioning except runaway speed test at loadrejection. At overloads, if there is a sudden load rejection the vibration transients will be even more severe due to drop in currentand internal impedance. Hence this paper aims to analyze the vibration signature of large synchronous generator (SG) whenoperated at overloads and subjected to sudden load rejection. The substantiation of the factual model of 250 MW hydrogenerating units (HGU) replicating the case plant has been simulated using SIMSEN software. Apart from case report andsimulative validation an experimental verification is also conducted with a prototype model of 2.2 kW SG. This paper providesthe feasibility to operate the SG's 20% beyond its rated load as designed with proper maintenance and safety carried out byplant operators.