Considerations for Maximum Operational Stresses in Electrical Insulation for High Voltage Machines Stator Windings for Different Rated Voltages

Historically, groundwall insulation for high voltage rotating machine (HVRM) stator windings operate at higher electrical stresses for machines with a higher rated voltage. Thus, the insulation thickness is not proportional to the machine rated voltage. Both mechanical and electrical capabilities of insulation are taken in account to define groundwall insulation thickness based on long term practical experience. With the replacement of an older insulation system with a newer insulation system the aforementioned design concept for insulation wall thickness is preserved. While a newer system usually has increased electrical stresses, the consideration of lower electrical stresses for lower rated voltages usually stays unchanged. In some cases however the newer insulation system may allow for a different approach, but which should be carefully evaluated. The authors have observed that voltage endurance life expectancy for a thinner insulation for high voltage rotating machine stator windings made of a modern insulation based on mica paper and a thermosetting matrix provides the same or better voltage endurance life expectancy as a thicker insulation wall when voltage endurance tests are performed at the same electrical stress. Also mechanical stresses are lower in a thinner insulation if the insulation itself is not a part of the winding structural support. Conversely, for a thinner insulation wall, the impact of a single layer of taped insulation more or less is more significant than for a thicker insulation. This paper considers factors to be taken in to account to design reliable and efficient stator winding ground wall insulation for high voltage rotating machines with different rated voltages.