Voltage grading model for high voltage electric generator stator coil end turn regions

Semiconductive tapes are applied to the end turn region of high voltage stator coils to reduce corona discharge at the slot exit region. The nonlinear, stress grading tapes are used to even out the voltage stress resulting in a more even distribution which also reduces the maximum stress level. To be able to optimize the stress grading capabilities of the insulation design and the stress grading electrode, it is necessary to be able to accurately calculate the end turn voltage distribution. In order to be able to calculate the voltage distribution, a model of the end turn region was developed. The equivalent circuit models the capacitance between the insulation and the conductor, as well as the nonlinear stress grading characteristics of the voltage grading electrode. The model is used to calculate and demonstrate a typical voltage distribution. The voltage distribution predicted by the model is shown to be in agreement with experimental measurements.