Suppression system averts oil transformer fires

Mitigating risks on oil-filled transformers is a primary concern for various firms that make use of this high-value equipment.

Although safety in the engineering of transformers is increasingly being improved, efficient fire-suppression technology that will mitigate the risk posed on the business operations and safety of humans is required, says environmental management company I-CAT.

“When a transformer catches fire, all the power feeding downstream equipment is lost. Therefore, any moving machinery, fixed drives and/or pumps, heaters and electrical equipment cannot be used and, consequently, adjacent processes cannot continue,” says I-CAT system design engineer Percy van Zyl.

Further, he highlights that as secondary or standby systems rarely exist, the only supply of electricity is from the dedicated transformer in question.

“Protecting such equipment is of utmost importance and should be implemented in all industries.”

Van Zyl explains that most transformer fires are caused by oil overheating and, to a lesser extent, improper connections.

Although he acknowledges the existence of measures such as Buchholz relays, which are connected to the oil piping between the conservator and oil tank of a transformer, Van Zyl tells Engineering News that these are not fool-proof and fires are bound to start on ONAN- (oil natural air natural-) and OFAF- (oil forced air forced-) type oil transformers.

Dry-type transformers use aluminium or a similar metal with a low melting point as fire- suppression measures. The metal blocks melt when exposed to fire, thereby extracting heat energy from the reaction.

I-CAT sales and marketing manager Jacques Bodenstein says the company’s localised fire-suppression solution is suited to electrical transmission applications where oil-filled transformers are in use, as it employs technology relevant to the risks involved.

“Atomised water mist suppresses heat generation and cools equipment to below reignition point. Transformer fire suppression requires a system that reacts at the onset of a fire, cools equipment, removes oxygen from the tetrahedron (the chain reaction required to sustain a fire) and maintain these circumstances until a safe environment is ensured.”

Van Zyl explains that, as soon as a fire is detected, either pneumatically or electrically by the localised fire-suppression system, the valve on the self- contained agent cylinders opens and initiates a chain reaction.

Water and foam are forced to the nozzles by nitrogen gas using a stainless-steel piping network. The system identifies as a low-pressure system under NFPA750 as it discharges with less than 12.1 bar pressure through the piping network.

The nozzles atomise the media, creating a super-enlarged surface area over which the water droplets interact with the fire.

“The fine water-[Unknown A2]mist removes heat, creates an inert atmosphere and reduces surface temperatures to below reignition point, without causing any thermal shock to the equipment,” states Van Zyl.

The foam additive, lastly, creates a barrier between the fuel and surrounding atmosphere, preventing it from producing additional flammable vapours, he adds.

Advantages of the system are its small footprint, easy installation and effective operation without any external inputs, including water supply through tanks and pumps or electricity for fire detection purposes.

The system, which went to market in 2017, is standalone and operates independently, regardless of operational circumstance. It has also been tested and verified by fire protection testing laboratory, inspection and certification body in Austria Institut für Brandschutztechnik und Sicherheitsforschung.

Bodenstein says the system has been “very well received” as it does not use continuous flow of water when the system is activated and, subsequently, uses a lot less water.

“Most fire-suppression systems incorporate third-party detection, whereby smoke-, heat- or flame- detection is employed. These systems are not standalone as they require electricity to operate and depend greatly on human aptitude, whereas the I-CAT localised fire-suppression system is fitted with a linear heat-detection tube that can activate the system mechanically for a quick response, which is crucial to initiate the suppression system while a flame is still in its infancy/growth phase.”

Numerous mining groups, State-owned entities and large industrial firms across Africa have installed the system, with the most recent installation undertaken for a railway agency.

“We have several installations for transformers scheduled for clients in Mozambique and Ghana that include the localised suppression system.”