ASSESSING THE RELIABILITY OF TRANSFORMER TOP OIL TEMPERATURE MODEL

Abstract

The hot spot temperature (HST) plays a most important role in the insulation life of the transformer. Ambient temperature and environmental variable factors involved in the top oil temperature (TOT) computations in all transformer thermal models affects insulation lifetime either directly or indirectly. The importance of the ambient temperature in transformer's insulation life, a new semi-physically-based model for the estimation of TOT in transformers has been proposed in this paper. The winding hot-spot temperature can be calculated as function of the TOT that can be estimated by using the ambient temperature, wind velocity and solar heat radiation effect and transformer loading measured data. The estimated TOT is compared with measured data of a distribution transformer in operation. The proposed model has been validated using real data gathered from a 100 MVA power transformer. For a semi-physically-based model to be acceptable, it must have the qualities of: adequacy, accuracy and consistency. We assess model adequacy using the scale: prediction R2, and plot of residuals against fitted values. To assess model consistency, we use: variance inflation factor (VIF) (which measure multicollinearity), condition number. To assess model accuracy we use mean square error, maximum and minimum error values of semi-physically-based model parameters to the existing model parameters.