Effectiveness of Stress Grading System Builds on the Heat Production in a Form-Wound Coil of an Inverter-fed Rotating Machine

Limiting the temperature rise in the stress grading system in a medium voltage form-wound coil of a rotating machine driven by an adjustable speed drive is essential to prolong the life of a motor. The common way of increasing the electrical conductivity of the system, thereby to lower joule heat production and temperature rise, is to increase the build of the tape system. Simulation studies on various stress grading system builds on the heat production has been evaluated in this study. A good correlation between measured and simulated temperature profiles under pulse voltage condition confirms the validity of the simulation. The stress grading system has been simulated using the 2D axisymmetric module in COMSOL® 5.2a. The results show that increasing the number of layers of conductive armor tape can reduce the heat production in CAT region but by increasing the number of layers of stress grading tape leads to increase in heat production in SGT region. The study suggests that use of other non-linear tape materials for SGT may be needed to effectively lower the temperature rise in the stress grading system.