Sentinel Engineering Analysis

Your equipment failures, investigated

Independent investigation of electrical equipment failures

Sentinel Engineering Analysis Ltd offers technical expertise to investigate, understand and resolve issues relating to electrical equipment failures or other operational problems.


Case study: oil-filled transformer arcing

Oil-filled transformers can fail spectacularly if an arcing fault develops within the tank. Some well-known examples can be seen in the following videos:

Dr Lockwood was asked to investigate the failure of a 20 kV to 400 kV generator step-up unit (GSU) at a combined-cycle generating station in Central America. The station had been operating for about 4 years when the transformer developed an in-tank failure. The resultant high temperature and pressure split the tank (about twice the size of a London bus) and sent a sheet of burning oil approximately 100 metres across the site.

Although the site operators had been told by their insurance company not to do anything to the transformer until it had been inspected, they decided to empty the oil from the tank and seal the gap in the tank by welding a metal strip along the split seam. The inevitable happened and the splatter from the weld ignited the debris in the tank. In order to extinguish the fire, they filled the tank with water.

When Dr Lockwood arrived on site, they were bailing the last of the water out of the tank.

The split transformer tank with its inspection hatch open, standing water visible inside. A bucket tipped through the hatch, throwing oily water across the walkway grating.
Transformer tank … being bailed out.