Network Transformer Explosion

Project Info

In March of 2007 representatives from the Connecticut Light and Power Company (CL&P) contacted RTI to conduct a forensic investigation and determine the most probable cause of an oil filled network transformer primary switch explosion.  An explosion, that resulted in the death of a contract employee.

Assigned Task
RTI was tasked to investigate and analyze why the switch nut failed.

RTI conducted several lab tests to understand the fluid dynamics characteristics of the primary switch compartment insolating oil and the reaction of air being introduced.  We fabricated a replica of the switch compartment and conducted experiments under a varied matrix of conditions to determine the exact trigger of the explosion.  The triggering event occurred when the contract employee took an attempt to take sample of oil from the tank.  The explosion was caused by air from the sampling apparatus being released into the tank, as the fill valve at the top of the tank had not been opened prior to sampling.   At the time of sampling a vacuum existed in the air space at the top of the compartment.  The pull from the vacuum in the space at the top of the tank allowed air bubbles to carry conductive sediment across the energized center phase conductive parts.  A phase to ground fault resulted that over pressurized the compartment causing the explosion.

RTI determined the exact cause of the explosion enabled it to provide loss prevention recommendations.


  • Electrical Engineering
  • Expert Witness
  • Utilities