Explosion and Fire Protection Systems of Transformers and Reactors - Relevance of Product Design and Service Maintenance Practices

The analysis of global statistics shows a failure rate of transformers in the range of 0.5% to 1.0% of the ‘transformer years’ in service. Fortunately, every transformer failure does not cause explosion and/or fire. Reportedly only around 10% of the failures cause major destructions. But this number in absolute terms is significant enough considering the large number of transformer population. A transformer explosion and the consequential fire is often dangerous to the equipments and the nearby habitat and every effort need to be applied to minimise this hazard.

This paper presents the first hand experience of the transformer failure instances and the effectiveness of the Nitrogen Injection based Explosion Prevention and Fire Extinguishing System (NIEPFES) in preventing the explosion and resultant fire and aspects to be maintained post installation in view of desired performance on field. The exhaustive data base, perhaps the only such data base available in the domain, nearly 140 transformer fault instances EPFES operated satisfactorily and avoided tank rupture in almost all cases, covers over 15000 EPFES protecting the transformers installed at the utilities around the world over the last 3 decades. The range covers rating 11kV to 765kV and 750KVA to 1500 MVA. The EPFES sensed the faults, depressurised the transformer tank by draining the oil, admitted Nitrogen into the transformer tank and limited the damage. It is interesting to note from the data recorded by the utilities that most of the EPFES protected failed-transformers could be repaired quickly and put back in service within a few days and the refurbishment cost of the transformer was recorded to be only a small fraction of the cost of a new replacement transformer. Also avoidance of carrying the huge inventory of spare transformers, containment of consequential damage to the nearby substation apparatus and the operating personnel have been reported by the utilities as reasons for preferring the EPFES.

The paper highlights the technical design and service aspects based on the actual field data.