Transformer Corona Testing

The progress made to date in corona testing transformers at the factory is reviewed and the importance of sonic detection and location of corona sources is shown. Major improvements in sonic techniques are reported. Test curves of RIV vs. transformer test voltage are given for units having defects. The various corona test proposals being considered by the industry are described and discussed. The best assurance of product quality is stated to be a corona test, using RIV and advanced sonic techniques, made at full transformer induced test voltage with a limit of 1000 microvolts.