Hydro Generator High Voltage Stator Windings: Part 1 – Essential Characteristics and Degradation Mechanisms

Abstract

About 17% of global electricity is generated from hydro power, which is still the only commercially viable renewable energy produced on a large scale (IEA, 2001). Only about 33% of Earth’s hydro potential has been developed so far, and given the increased environmental awareness and scrutiny, it is most unlikely that much of the available hydro potential will ever be utilised. The ageing Australian installed hydro generating capacity of approximately 7600 MW is mostly 30–60 years old and approaching its half-life refurbishment. Most of the generators of that vintage were generously sized by today’s standards, and offer an opportunity for uprating of their output as part of the refurbishment process. The understanding and correct specification of hydro generator high voltage (HV) stator windings is vital to the success of generator renewal process. The high voltage hydro generator stator windings are exposed to a variety of continuous and transient stresses, all having deleterious effect on the windings’ long-term durability. In general, HV winding life expectancy will depend on thermal degradation of insulation, electrical degradation of insulation, mechanical stresses and environmental winding contamination. Most often, the winding degradation occurs as a result of combined stresses, and is often referred to as multi-stress or multi-factor insulation ageing. The author has spent his working life designing and manufacturing high voltage stator windings, and is presenting a series of four informative papers on hydro generator HV stator windings as an Australian contribution aimed at the engineers involved with hydro generator refurbishment and uprates. This paper is the first in this series describing the essential characteristics of hydro generator stator windings and their degradation mechanisms.