Dielectric response of transformer insulation - comparison of time domain and frequency domain measurements

Nowadays, time domain and frequency domain polarisation tests are popular in power utilities for transformer insulation diagnostics. Therefore, it is quite essential to understand the impact of temperature and moisture on dielectric response under a controlled condition. This paper presents the dielectric response of pressboard samples with different moisture and temperature conditions. Both, time domain and frequency domain measurements were carried out in sequence and impact of temperature and moisture on dielectric response were studied in detail. In addition, dc conductivity (σ₀) of pressboard insulation is calculated from both methods and comparison between FDS and PDC methods is made. It has been observed by comparing dc conductivities that both methods are in agreements with each other and almost same level of accuracy in the result can be obtained with both methods.