Abstract
The effects of high frequency sinusoidal voltages on the electric field and temperature in a nonlinear field grading (NFG) material for high voltage rotating machines are investigated. The test setup consists of an electro-optic probe measuring the electric field non-invasively, as well as optical temperature sensors for temperature mapping along the field grading. Frequencies ranging from 50 Hz to 9 kHz and peak-to-peak voltages from 1 to 10 kV are applied to the test object, which consists of an insulated brass rod with NFG at the ends, emulating the end-winding of a stator coil. The results show that increasing the voltage frequency results in both increased temperature and electric field towards the grounded side of the NFG. This should thus be considered when high-frequency voltages, such as those from power electronic converters, are applied to electric machines.