Partial discharge study is a minor, but important, field of research. The continuing
desire to find new, cheaper materials or subject existing materials to ever higher stress
levels in a quest to cut costs will keep it so. The 1950s and 1960s saw the emergence
and development of PD measurement techniques culminating in correlations being
identified among PD activity and specific forms of degradation. These decades also
witnessed a developing understanding, based on strong physical principles, of the
mechanisms of partial discharge degradation and breakdown. In many senses this
was the golden age of partial discharge study. The 1970s saw steady progress in
electrical and acoustic measuring techniques and progress in chemical techniques for
oil analysis. However, in degradation studies, the optimism of the 1950s and 1960s
was waning. With a few conspicuous exceptions, many researchers were moving
to empirical rate studies to breakdown. Accelerated frequency ageing of materials
to breakdown under partial discharge stressing was replacing the more fundamental
studies designed to elucidate the physical and chemical mechanisms of degradation.
There appeared to be a recognition that an understanding of partial discharge degradation
mechanisms was more complex – and more unattainable – than had been
thought in earlier years. A more pragmatic, if limited, approach had emerged. The
1980s and 1990s saw another major shift in activity. Fuelled by the advent of digital
microprocessor technologies, the ability to capture, store and process data on partial
discharges – to measure partial discharge activity – made an enormous leap forward.
The excitement of these new technologies and how they could be applied to partial
discharge measurement far outpaced the research on degradation studies – again with