When Transformers Fail

When a transformer does fail, the results are often catastrophic. If the failure was not caused by an existing fire, the potential for a new fire resulting from the failure is extremely high. A power substation by its nature contains all of the right ingredients to generate the perfect fire storm. A typical substation transformer bank is comprised of three or more transformer tanks, each containing up to 45,000 gallons of extremely flammable mineral oil. The ignition of the transformer oil can come from any number of sources including solid particles of insulation and conductor that are produced by incipient arcing fault, internal component failure, or short circuit electrical arcing inside the tank, any of which can generate resulting heat and pressure sufficient to cause the tank to rupture.

The Consequences of Fire

Once a rupture has occurred, air rushes into the tank and the oil explodes resulting in a blast of intense radiation scattering flaming oil, steel shrapnel, gaseous decomposition products, solid insulation, and molten conductor material onto the surrounding area. The effect of the explosion and radiation is instantaneous and has been documented to ignite neighboring transformers more than 60 feet from the initial fire. The temperature of an oil fire is in the range of 1760° F and 2190° F. The duration of a transformer oil fire can range from 4 to 28 hours, which in most cases is the time it takes the fire to burn itself out. As larger substations are often located in outlying areas, response times from the local fire department can be lengthy. In addition, fire trucks are rarely equipped to suppress these supersized oil fires.

Assets Worth Protecting

The cost to replace a large failed transformer can range from 2 to 4 million dollars, depending on transformer type. However, the higher cost by far is the replacement energy, which must be purchased from the spot market at premium prices. During peak hours, rates could spike up to $200,000 per hour.⁴ Uncontained fires caused by transformer failure can quickly result in the partial or total loss of the entire electrical substation. Specific transformer failures are difficult to anticipate and prevent, however, additional damage is preventable with the proper fire containment plan in place.

Fire Containment Planning

Often, the best defense is a good offense. Anticipating and planning for transformer failure is the first step to minimize damage to other nearby transformers, equipment, structures and property.