This is the tip that was originally published in Maintenance Tips:

Infrared Thermal Imaging Tip

Preventing a Transformer Fireworks Display Infrared inspections of oil filled transformers can help to increase reliability and extend transformer life. Detecting hotspots on the bushings of these transformers may also help to prevent a catastrophic explosion.

Hot spots on transformer bushings are usually due to a loose or deteriorated electrical connection. Frequently, the source of a hot bushing connection is external to the transformer and can be corrected by repairing the defective connection. However, loose connections which originate within the transformer case can represent an extremely dangerous condition.

Loose electrical connections within an oil-filled transformer can lead to a condition known as arcing. When arcing occurs in oil, the molecular structure of the transformer oil breaks down forming several combustible gases. The most significant gases produced are acetylene, hydrogen, methane, ethane, and ethylene.

The amount of gas produced will depend upon the temperature of the arc and length of time; however, even small amounts of gas can lead to a potentially explosive condition. In a sealed, oil-filled transformer these gasses can build to a potentially explosive level within a very short time. In short, combustible gases combined with an arcing condition within a transformer are a recipe for potential disaster.
When inspecting oil filled transformers, any inexplicable temperature rise on bushings should be investigated and corrected immediately. Performing a dissolved gas analysis of the transformer oil is recommended if the cause of the problem is suspected to originate within the transformer.

We got several emails summarized below and we request further opinions from people in the know.

From a devoted Maintenance-Tips reader:

I know that you rely on your contributors for content and accuracy of their articles. I also don't want to be in the middle of a thermographer battle. However, the recent IR tip you sent out titled "Preventing a Transformer Fireworks Display" had some statements which can confuse your readers. While it is true that gases are produced when arcing takes place in an oil-filled transformer, it is not true that the risk to the transformer is the explosion of these gases. The detection of these gases is accomplished by taking an oil sample, and performing gas chromatography on the dissolved gases in the oil. These gases are hydrogen, acetylene, methane, ethane, ethylene, carbon monoxide, carbon dioxide, nitrogen, and oxygen.
They are produced by 3 different fault mechanisms (not just arcing): Partial discharge or corona, Localized hot spots and Arcing. The ratios of their concentrations gives indication of one of the fault mechanisms, and may be indicative of burning cellulose, burning oil, arcing, etc. The explosion of a transformer is almost always due to the electrical fault going to ground or across phases, and the rapid expansion of the gases from that fault causing the transformer to explode. (another possible cause is water leaking into the transformer).

Its not the first time that I've heard the misconception that the dissolved gases ignite to cause the explosion, but it is not helpful to see it reinforced in a publication like yours that so many rely on for information. Just wanted to give you that feedback. To avoid a he-said/she-said problem, you may want to hit an independent transformer or DGA oil analysis expert to provide this kind of insight to your readers.

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