Experiences of dielectric response measurement in frequency domain for diagnostics of transformer insulation system

Moisture and aging strongly influence the dielectric properties of composite oil/cellulose insulation system used in power transformer. So the knowledge about moisture content in oil impregnated paper is essential when estimating remaining life time of such system. A scaled down transformer insulation model was developed to gain wide experiences of on-site measurements of moisture content using dielectric response method. In order to provide reliable diagnostics of HV transformer insulation, various aspects like sensitivity of dielectric response to oil quality (oil conductivity and tanδ) etc. are discussed that may benefits the utilities and the service providers while using this technique. An investigation of moisture content on different parts of the insulation on a scaled down transformer model is performed using chemical analysis. Variation in the moisture content measured by FDS technique and Chemical method are also presented. The causes of variation in the results are analyzed.