32 Coil Design
Reducing partial discharge in diamond coils Preformed Windings, a specialist manufacturer of coils for motors and transformers, explains some of the key factors which go into manufacturing diamond coils which minimise the occurrence of partial discharge and offer longer asset life.
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here is a growing awareness in the motor and generator repair industry that partial discharge (PD) levels play a significant role in the life expectancy of MV/HV assets. PD is defined as an electrical discharge occurring between two conducting electrodes without completely bridging the gap. It can significantly reduce asset life due to the energy caused by such discharges deteriorating insulation. The risk of PD occurring is increased considerably above 6kV, and therefore careful consideration should be given when designing and manufacturing components for these machines. Diamond coils should be designed with low PD in mind as this is an effective indicator of the quality and integrity of a coil’s insulation and, therefore, its life expectancy. Preformed Windings, based in Sheffield, UK, has been a thought leader in the manufacture of high-quality diamond coils for over 50 years and is very fortunate to work with leading OEM’s and independent repair facilities across the globe in industries such as hydro, nuclear and oil and gas. In these industries and many others, it is critical to have machines operating reliably even as is often the case, they are expected to last significantly longer than the original design life of the machine. Due to its global presence along with close relationships with the Association of Electrical and Mechanical Trades (AEMT), The Electrical Apparatus
Quarter 3 2021
Service Association (EASA), leading insulation manufacturers, repair facilities and PD monitoring companies, Preformed Windings has been approached by several leading OEM’s to carry out significant R&D projects over the past few years, with a focus on reducing PD levels in windings. This research and development has allowed Preformed Windings to assist end-users and repair companies alike to clearly define specifications that reduce PD levels in assets providing the benefit of reduced maintenance costs and long-term reliability.
“Reducing voids or cavities in diamond coils significantly improves PD results.”
PARTIAL DISCHARGE IN COILS There are many quality control considerations when designing and manufacturing diamond coils, but for this introduction, the focus is on the reduction or elimination of voids within coils. Reducing voids or cavities in diamond coils significantly improves PD results. Strictly controlled manufacturing processes allow for significant reduction, or even elimination, of the voids typically found in locations such as between conductors and the mainwall or turn insulation, within the mainwall insulation itself, or between the coils and the stator.
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