Substation distribution transformers failures and spares

Electric utilities should have a sufficient number of spare transformers to backup substation distribution transformers to replace transformers that fail and require factory rebuild or replacement. To identify such a number, the statistical methodology was developed to analyze available failure data for different groups of transformer. That methodology enables the estimation of future numbers of failures with associated probabilities, recommends the proper number of spares, identifies the necessity and shows the means to shorten the transformer's replacement time.