Benefits of dry

The steady uptake of dry-type transformers in the African market is being driven by the range of advantages offered by this technology, and there has been wider application as use is becoming more universal.

"We have seen wider application of dry-type transformers in Africa, as they move from niche products to more universal use," says David Claassen, managing director of dry-type transformer specialist Trafo Power Solutions. "The reasons are not hard to find, and include safety, reliability and low installation costs."

A key differentiator is that the electrical core and coils in a dry-type unit are cooled by normal air ventilation. By contrast, liquid-filled transformers are cooled by oil, silicone or other liquid. The risk of this liquid spilling is one of the main factors behind the increased use of dry-type transformers. The latter has higher levels of safety and does not present an environmental hazard.

"This makes dry-type units more suitable for indoor use, and also for underground and marine applications," he says. "At the same time, they are also resilient enough for hostile outdoor environments."

To insulate the windings and protect them from dirt, moisture, corrosive fumes and conductive dust, special treatment techniques are applied. Depending on the application, one of three main types of insulation is used: open-wound, vacuum pressure impregnated (VPI) or cast coil.

Among their safety benefits is their low fire hazard, with their transformer insulation made up of epoxy resin and eco-friendly quartz powder, the winding is flame-retardant. This also means it will not generate toxic gases when arcing occurs. The cost implication is that costly fire extinguishing equipment is rendered unnecessary.

"When locations are remote, as they often are in African applications, the installation of dry-type transformers makes good sense," Claassen says. "This is because they are reliable and need little maintenance, while being easier and more economical to install."

Without the risk of oil spillage, no concrete bund wall or significant civils works is required – saving time and money. Using only air for cooling, liquid testing is not required. At the same time, the smooth coil surface eliminates the build-up of heavy dirt. Designed to meet Class E2 environmental requirements, the units resist condensation and heavy pollution.

"In terms of high reliability, cast resin transformers typically have a service life of over 25 years and the failure rate has been shown to be very low," concludes Claassen.

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