Few transformers fail due to old age per se, but rather as a consequence of external faults, short circuit faults, insulation failure (dielectric failure), local overheating (causing gassing) or accessory failure (e.g. bushings, tap changers, coolers, surge-arresters).
Repairing a transformer instead of replacing can substantially reduce investment costs and provide a faster turnaround than buying a new transformer. In repairing old transformers where the manufacturer may no longer be in existence and/or the design is obsolete and a like for like new replacement cannot be obtained, there may be significant savings in infrastructure costs and civil works in using the existing tank and design.
Scope of work
Upon receipt of the transformer in the factory, a visual inspection and electrical control will be performed as to provide a root cause of failure or what rehabilitation actions will be taken, as well as to provide a delivery date. Pending the root cause and agreed actions taken, the core and coil or active part will be untanked, inspected and partial or full manufacturing of coils will be initiated.
Following upgrade/service of noble parts, accessories and other auxiliary equipment, the active part is dried and replaced in the tank, which is refilled with fresh oil and high-voltage test performed. After the factory acceptance test the newly revitalized transformer is ready to be delivered back to its owner. If requested, ABB can of course cater for the transport of the unit back and forth from the site.