Influence of Ageing on Properties of Insulating Oil and Life Estimation of In-Service Transformer and Reactors: A Latent Variable Approach

This paper aims at analysing the degradation properties of oil parameters such as breakdown voltage (BDV), interfacial tension (IFT), resistivity, acidity, moisture, dielectric loss tangent and total gas content due to ageing of transformer and reactors. For ensuring long term reliability of transformer and reactor it is necessary to ascertain the degradation characteristics of the insulating oil along with its impact on healthiness of the equipment. The paper investigates the correlation among different aged oil parameters and finds the significance of individual oil characteristic and dissolved gases for evaluating the condition of oil filled equipment. Thereafter, factor analysis is performed for identifying any interdependency between various oil parameters. Subsequently, structural equation modelling is carried out for evaluating the contribution of common factors on total ageing of the transformer and reactors. Finally, the ageing health index has been calculated and based on that the residual life estimation of equipment is done. The data considered comprises of actual oil test data of 442 samples collected from 60 numbers of in-service transformers and reactors of various age groups. The outcome of this study can be used for monitoring the deteriorating characteristics of the oil filled equipment as well as for determining the residual life of in-service transformers and reactors along with planning of maintenance strategies.