The influence of temperature and electric field frequency on the dielectric properties of electrical machines insulation systems

Electrical machines´ composite insulations conditions can be characterized by the values of the dielectric properties. In this paper, an experimental study of the variation of these properties with temperature and applied electric field frequency are presented. The tests were done on plane samples and bars containing CALMICAGLAS, made of glass texture (13 %), mica paper (47 %) and epoxy resins (40 %). After their conditioning (48 h at 190 °C), real and imaginary parts of the complex permittivity and conductivity - for electric field frequencies varying from 10^-3 to 10⁶ Hz and temperatures between 30 and 90 °C - were measured using a NOVOCONTROL dielectric spectrometer. The results show important increases of the measured values with small frequency and increased temperature values. Finally, the possibility of characterizing the electrical machines insulations degradation conditions based on dielectric properties measured at low frequencies (10^-3-10⁶ Hz) is analyzed.