Multi-factor ageing of stator coil insulation of HV machines and degree of correlation among non-destructive test parameters

Multifactor accelerated ageing studied have been carried out on scaled-down model coils of an 11-kV insulation system. The test parameters tan delta tip-up (δT), capacitance tip-up (ΔC/C), integrated discharge energy (IDE), and discharge inception voltage (Vi) were monitored at regular intervals during the ageing period to characterize the ageing processes. Attempts have been made to find the correlation between different test parameters as a function of ageing time. A good correlation is found to exist between δT and δC/C. The degree of correlation between different test parameters tends to increase as the ageing proceeds