To elucidate the evolution laws of dielectric response and degradation mechanisms of epoxy-mica insulation in high-voltage motors under combined electro-thermal stress

a combined electro-thermal accelerated aging platform was established. Insulation specimens were subjected to combined electro-thermal aging experiments across various temperatures(25锝?80 鈩?and durations. Broadband dielectric spectra(10

-2

锝?0

7

Hz)was measured at different ag

ing stages

and the microscopic morphology changes were observed using scanning electron microscopy(SEM). Furthermore

the internal degradation process was analyzed by combining Havriliak-Negami model parameter identification with the distribution of relaxation times(DRT)method. The results indicate that under accelerated aging conditions at 180 鈩? at 0.01 Hz

the real part of relative permittivity

蔚

'

increases from 3.6 to 9.36 over the aging period

marking an increase of approximately 160%

while the dielectric loss tan

未

surges from 0.035 to 2.21

representing an approximately 62-fold increase. The low-frequency loss of severely aged specimens conforms to the quasi-DC(QDC)conduction characteristic

governed by Jonscher's power law with an exponent

n

=0.500 7. High temperatures drive the main peak of interfacial polarization to shift towards shorter relaxation times; specifically

at 216 h of aging

the central relaxation time drastically shortens from approximately 513 s at 25 鈩?to 145 s at 180 鈩? a reduction of 71.73%. Additionally

long-term aging leads to the broadening of DRT peaks

accompanied by the emergence of asymmetric tailing and shoulder peaks. The time-domain evolution of the DRT spectra corroborates the enhancement of microscopic environmental heterogeneity and the formation of multi-scale defect networks within the insulation.