Electrostatic field analysis and verification of air cooled generator end turn insulation models

Abstract

Electrostatic field analysis was performed on generic electrodes for assessment of generator end turn electrical insulation design. A number of coil end turn configurations were analyzed near highly stressed electrode corners and along support block creep surfaces for various insulation thickness, and a range of air gap spacings. A finite element electrostatics code was employed to generate two dimensional equipotential plots for insulated electrodes with and without dielectric support blocks. Empirical theories based upon local stress enhancement were used to estimate corona onset, creep discharge, and spark breakdown as a function of insulation thickness and air gap spacing. The corona onset calculations were verified using actual test setups and monitoring the corona with the Corona Scope/sup TM/. Sparkover tests were also done to verify the calculations.