Evaluation of Transformer Insulation by Frequency Domain Technique

Measurements of Dielectric Response in Frequency domain is being employed for assessing the condition of the paper-oil insulation system in Transformers. The laboratory measurements were carried out on Models based on simple Transformer insulation system. The dependence of frequency, temperature, voltage and ageing of the insulation system on the spectral behaviour of dielectric responses are discussed. The paper also presents correlation and comparison of the laboratory results, to the measurements performed on in-service Power Transformers. The healthiness of the insulation system of the in-service Transformers were evaluated and recommendations were made to improve the condition of the insulation system to extend the service life of the Transformers.