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There’s no way around it: transformer fires are highly dangerous, and they can be very expensive. And although they don’t occur frequently, it only takes one catastrophic event to put lives, property, and businesses at great risk. That’s why effective fire suppression systems are so important. With that in mind, how do you protect a transformer from fire? We will briefly explore the essentials of transformer fire protection—including key causes and best practices for preventing transformer fires.

What Would Cause a Transformer to Catch on Fire?

The three most common transformer fire causes are severe weather conditions, mechanical failure, and electrical issues.

  •  Lightning, high winds, and other severe weather conditions can damage buildings and/or equipment, which may have an adverse effect on indoor transformers.
  • Depending on the type of transformer, mechanical failures can include cable termination failure, tank ruptures, internal arcing, or conductor tipping.
  • Transformer fire risk is also elevated when electrical issues such as power surges, poor insulation, and over-voltage are present.

 How Often Do Transformers Catch Fire?

Fortunately, transformer fires are rare, with T&D determining “the average probability of a serious transformer fire” to be ”on the order of 0.06% to 0.1% per service year” (which equates to roughly “one fire per 1,000 to 1,500 transformer service years”). Additionally, throughout an average transformer’s lifespan of around 40 service years, “2.4% to 4% of all transformers can be expected to cause a fire”.

When Are Transformers a Fire Hazard?

Transformers can become a fire hazard any time they’re introduced to the primary causes of transformer fires—inclement weather, mechanical failures, and electrical issues. Without appropriate transformer fire safety practices in place, an organization’s equipment and people are subjected to unnecessary risk. The National Fire Protection Association (NFPA) notes that the most dangerous element of a transformer is the oil used “for insulation, to prevent electrical arcing, and to serve as a coolant” since it “is similar to mineral oil and very flammable.”

Does a Dry-Type Transformer Pose the Same Risk?

Generally speaking, dry-type transformers pose less risk of fire or explosion. This transformer type, ideal for medium- and low-voltage indoor applications, does not contain any flammable liquid (i.e., oil), eliminating that particular risk.

What Happens When a Transformer Catches Fire?

When a transformer catches fire, a dangerous chain reaction begins. Let’s use the example of a transformer fire caused by electrical issues, like poorly-insulated wire or a lightning strike. Initially, heat (and a spark) is created, sufficient to ignite the mineral oil meant to serve as a coolant. All three elements of the fire triangle are present: oxygen, heat, and fuel. As the oil burns, it generates enough pressure to cause an explosion.

How Can You Prevent a Transformer from Exploding?

As we’ve mentioned, the best fire protection is prevention. Transformer fires can be catastrophic, so it’s not wise to simply “hope it doesn’t happen to me.” Instead, a comprehensive transformer fire protection system is the best course of action.

If you’re looking for more information about preventive measures to protect transformers from fire, the NFPA is a great place to start. This organization publishes transformer fire protection standards, including:

  • NFPA 70: The National Electrical Code (NEC) is a set of benchmarks adopted by all 50 states and includes regulations and requirements related to “safe electrical design, installation, and inspection to protect people and property from electrical hazards.” Review NFPA 70 here.
  • NFPA 850: NFPA 850 (“Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations”) outlines fire safety recommendations directly related to electricity generating plants, converter stations, and combustion turbine units. Review NFPA 850 here.

How Do You Stop a Transformer Fire?

If a transformer fire does occur, there are a few main methods for suppressing or extinguishing it. These include:

  •  Water-Based Systems: One approach is a sprinkler system for transformers. Depending on the use case, there are several types of water-based systems for transformer fire protection, including deluge, fixed water spray, water mist, and pre-action water mist systems. Water is a common suppression method, but it’s an imperfect one, especially in environments where water could potentially damage other electrical systems and equipment.
  • Direct Release Systems: A direct release suppression system provides an alternative to water-based systems that instead uses a specific suppressant that is kept pressurized in a canister attached to a detection tube. If a fire ignites, the detection tube degrades, which causes the suppression agent to be released, quickly working to mitigate the fire.
  • Indirect Release Systems: An indirect release system works similarly, except when the suppressant is released, it is diffused over a much larger area, making indirect release systems preferable in cases where a larger area might be impacted.

Learn More: How do you handle a transformer fire

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