Summary
Short circuit events contribute to transformer failures (12% of all transformer failures according to CIGRE Technical Brochure 939 on Transformer Reliability). Transformer short circuit failures typically cause catastrophic damage to the transformer windings requiring the transformer to need new windings or for the transformer to be replaced. For this reason, a large portion of the transformer electrical design effort is focused on calculating the possible internal short circuit forces and designing the transformer windings to be strong enough to sustain the huge resulting mechanical forces. The investigation and repair of actual transformer short circuit failures can provide insight into the transformer short circuit phenomena and improvement / validation of transformer design rules. This paper describes the detailed investigation of three transformer short circuit failures and the winding redesign during the repair of the transformers. Each transformer was from a different era and designed for a different application.
Read more Read lessThe first transformer was a 1970’s vintage arc furnace application transformer that failed during re-energization after an initial fault. The low voltage windings failed catastrophically, and the failure was so severe that some low voltage winding leads were pulled apart from brazed connections on copper bus. The high voltage windings were mechanically undamaged. The original transformer design was available, and the transformer windings were able to be redesigned with modern tools for improved short circuit strength. The transformer was remanufactured with new windings and returned to service.
The second transformer was a 1980’s vintage auto transformer that was removed from service due to high electrical arcing gas generation. The approximate location of the gas generation was pinpointed with partial discharge measurement while the transformer underwent high voltage induce voltage testing at site. Later dismantling of the transformer windings showed that the innermost winding (the tertiary voltage winding) had suffered short circuit damage causing winding buckling. The buckled tertiary voltage winding had arced to the core (causing the electrical arcing gas generation) due to decreased electrical clearance. Further investigation found the short circuit event on the tertiary voltage winding occurred more than 10 years previously. Surprisingly, the transformer operated without issue for a long time after the short circuit event. The transformer windings were all redesigned with modern tools with higher short strength for the tertiary voltage winding.
The third transformer was a 2010’s vintage generator transformer that suffered a fault to ground on the low voltage circuit. The low voltage winding of one phase had significant mechanical telescoping damage while the low voltage windings on the other 2 phases had only minor mechanical damage. The high voltage windings had no mechanical damage. The transformer was rewound according to the original modern design.
The transformer short circuit failure cases presented in the paper provided different examples of short circuit fault failure events, application and vintage. Transformer short circuit design technology, including design tools and manufacturing methods, is validated by complex simulation and actual short circuit tests. Increased understanding of in-service transformer short circuit failures enhances transformer short circuit design technology for new transformers and repair of failed transformers.
Additional informations
| Publication type | Session Materials |
|---|---|
| Reference | A2_11719_2026 |
| Publication year | |
| Publisher | CIGRE |
| Country | Canada |
| Study committees | |
| File size | 1 MB |
| Price for non member | 30 € |
| Price for member | 30 € |
Authors
TENYENHUIS Ed - Hitachi Energy Canada
Keywords
