{"id":1835,"date":"2026-08-22T02:34:02","date_gmt":"2026-08-21T18:34:02","guid":{"rendered":"https:\/\/q8bbzjnpm5.wpdns.site\/?p=1835"},"modified":"2026-08-29T23:43:46","modified_gmt":"2026-08-29T15:43:46","slug":"dry-type-vs-oil-immersed-transformers-how-to-choose-the-right-one-for-your-project","status":"publish","type":"post","link":"https:\/\/subian-electric.com\/ru\/news\/dry-type-vs-oil-immersed-transformers-how-to-choose-the-right-one-for-your-project\/","title":{"rendered":"\u0422\u0440\u0430\u043d\u0441\u0444\u043e\u0440\u043c\u0430\u0442\u043e\u0440\u044b \u0441 \u0441\u0443\u0445\u0438\u043c \u0438\u0437\u043e\u043b\u044f\u0446\u0438\u0435\u0439 \u043f\u0440\u043e\u0442\u0438\u0432 \u0442\u0440\u0430\u043d\u0441\u0444\u043e\u0440\u043c\u0430\u0442\u043e\u0440\u043e\u0432 \u0441 \u043c\u0430\u0441\u043b\u044f\u043d\u043e\u0439 \u0438\u0437\u043e\u043b\u044f\u0446\u0438\u0435\u0439: \u041a\u0430\u043a \u0432\u044b\u0431\u0440\u0430\u0442\u044c \u043f\u0440\u0430\u0432\u0438\u043b\u044c\u043d\u044b\u0439 \u0434\u043b\u044f \u0432\u0430\u0448\u0435\u0433\u043e \u043f\u0440\u043e\u0435\u043a\u0442\u0430"},"content":{"rendered":"

A project manager in a Malaysian hospital was evaluating two quotes for a transformer rated at 1,000 kVA: the cheaper, oil-immersed transformer being priced at $16,000 and the costlier, cast-resin transformer being charged at $26,000. The less expensive alternative would save $10,000. However, since the hospital is located two floors above where the electrical equipment is installed, the fire regulations mandated that there should be a pit to retain any oil in the event of a leak. Moreover, the insurance company has already asked if the hospital intended to use mineral oil since it cannot be used indoors. Thus, in this case, the dry type of transform is not necessarily superior, but rather due to the hospital construction predicaments. The questions raised above help to understand more about the essence of the issue related to the comparison between dry-type and oil-immersed transformers: in this regard it should be stated that the issue has nothing to do with superiority as such; it is merely related to the project specific circumstances regarding its site, fire risks, loading requirements, and budget constraints.<\/p>\n

The quick answer to this question is that dry-type transformers should be selected when the equipment is used in indoor locations, fire safety is of utmost importance, or when the available space is limited; like in the case of buildings, hospitals, tunnels, data centers etc. If the equipment has to be placed outside, the an oil-immersed transformer will be a more suitable option when overload capacity is a key requirement or budget constraints come into play; for instance, it is usually seen at utility substations, industrial facilities and solar farms.<\/p><\/blockquote>\n

\"Dry<\/p>\n

\n

The Core Difference Between the Two Technologies<\/h2>\n

The names indicate the cooling and insulating materials. Oil-immersed transformers use mineral oil (or an ester fluid) to insulate as well as remove heat through the tank walls. A dry-type transformer uses air to run in ventilated coils or coils encapsulated in cast epoxy resin. This one thing makes everything else possible: how they fail, how they cool down, etc.<\/p>\n

Oil is the best insulator and coolant, which is why oil-immersed technologies have taken charge of the utility and external industry where the cost per kVA and the overload feature is important. But oil is highly flammable and has leaking problems, which is why dry-type technologies are used in buildings and fire-sensitive areas even though their prices are high.<\/p>\n

Safety and Fire Behavior<\/h2>\n

The first decision made in regard to fire risk is that both mineral and insulating oil has flashpoint of around 140-150 \u00b0C and fire point of approximately 160 \u00b0C. An oil-based device can leak and ignite in case of malfunctions; this is why almost all building and electrical codes prohibit oil-immersed devices indoors unless they have either a fire-rated enclosure with additional draining or fire-resistance wall enclosures allowing for oil containment.<\/p>\n

Dry-type transformers do not pose any fire risk as they do not burn under IEC 60076-11 fire tests, nor do they release any flammable oils; therefore, dry-type transformers are the preferred choice for indoor application.<\/p>\n\n\n\n\n\n\n\n\n\n
Safety Aspect<\/th>\n\u041c\u0430\u0441\u043b\u043e-\u0438\u043c\u043c\u0435\u0440\u0441\u0438\u043e\u043d\u043d\u044b\u0435<\/th>\n\u0421\u0443\u0445\u043e\u0439 \u0442\u0438\u043f (\u043b\u0438\u0442\u0430\u044f \u0441\u043c\u043e\u043b\u0430)<\/th>\n<\/tr>\n<\/thead>\n
\u041e\u0445\u043b\u0430\u0436\u0434\u0430\u044e\u0449\u0430\u044f \u0441\u0440\u0435\u0434\u0430<\/td>\nMineral oil \/ ester (flammable)<\/td>\nAir \/ epoxy resin (self-extinguishing)<\/td>\n<\/tr>\n
Oil flash point<\/td>\n140\u2013150\u00b0C (mineral)<\/td>\nN\/A<\/td>\n<\/tr>\n
\u0420\u0438\u0441\u043a \u0432\u043e\u0437\u0433\u043e\u0440\u0430\u043d\u0438\u044f<\/td>\nRequires vault or containment indoors<\/td>\nVery low, passes IEC 60076-11 fire test<\/td>\n<\/tr>\n
Indoor installation<\/td>\nRestricted by code<\/td>\n\u0421\u0442\u0430\u043d\u0434\u0430\u0440\u0442<\/td>\n<\/tr>\n
Environmental risk<\/td>\nOil spill needs containment<\/td>\nNo liquid \u2014 clean<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\"Safety<\/p>\n

Cost Comparison at Every Rating<\/h2>\n

Dry-type transformers are more expensive than oil-immersed transformers by 40-80% for the same kVA capacity. Among the factors contributing to the higher price of dry-type transformers are the use of copper windings (dry-types invariably use copper due to the less efficient air cooling as compared to oil cooling), heralding and casting resin encapsulation as well as the better thermal design that is necessary when operating at 100 K temperature rise.<\/p>\n\n\n\n\n\n\n\n\n\n
\u0420\u0435\u0439\u0442\u0438\u043d\u0433<\/th>\nOil-Immersed (FOB China)<\/th>\nDry-Type \/ Cast-Resin<\/th>\n\u041f\u0440\u0435\u043c\u0438\u0443\u043c<\/th>\n<\/tr>\n<\/thead>\n
100 \u043a\u0412\u0410<\/td>\n$2,500\u2013$6,000<\/td>\n$4,000\u2013$9,000<\/td>\n+40\u201360%<\/td>\n<\/tr>\n
250 \u043a\u0412\u0410<\/td>\n$4,500\u2013$11,000<\/td>\n$7,000\u2013$16,000<\/td>\n+45\u201355%<\/td>\n<\/tr>\n
500 \u043a\u0412\u0410<\/td>\n$8,000\u2013$16,000<\/td>\n$12,000\u2013$24,000<\/td>\n+50%<\/td>\n<\/tr>\n
1,000 \u043a\u0412\u0410<\/td>\n$15,000\u2013$32,000<\/td>\n$22,000\u2013$46,000<\/td>\n+45\u201360%<\/td>\n<\/tr>\n
2,500 \u043a\u0412\u0410<\/td>\n$38,000\u2013$75,000<\/td>\n$58,000\u2013$110,000<\/td>\n+50\u201370%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The prices are estimates and depend on specifications, manufacturers, and geographic locations. As the power increases, the differences between oil units narrow, as opposed to when they use an ester fluid that is fireproof. In the case of the hospital, the additional charge of $10,000 originally included in the price of the dry-type unit turned out to be misleading, as when the vault, containment pit, and fire-fighting system of the oil power system were included, it was found out that it was more expensive to install the “cheap” solution.<\/p>\n

Performance: Overload, Efficiency, and Life<\/h2>\n

Oil-immersed transformers stand out when it comes to overload performance. The oil heats up while the transformer is in use, which allows it, in accordance with IEC 60076-7 standards, to work while carrying 1.3 to 1.5 of recommended load for several hours after previous use. As for dry-type transformers, they are only able to carry slightly more than their rated capacity (typically 1.1) because they have little thermal capacity.<\/p>\n

Speaking of efficiency, state-of-the-art transformers have similar performance, though it must be noted that amorphous-core oil-immersed transformers have the least level of no-load losses \u2014 it serves well where transformers are working around the clock. Lifetime-wise, both types are designed for 20 to 30 years, but lifetimes will depend on insulation temperature. Moisture in oil, sludge formation, and gases dissolved in oil are sources of maintaining oil-based units; while dry-type transformers have their own issues as they do not get affected by oil-based problems but are under the threat posed by dust accumulation on windings and by the start of partial discharge in humid conditions.<\/p>\n\n\n\n\n\n\n\n\n\n
Performance Metric<\/th>\n\u041c\u0430\u0441\u043b\u043e-\u0438\u043c\u043c\u0435\u0440\u0441\u0438\u043e\u043d\u043d\u044b\u0435<\/th>\n\u0421\u0443\u0445\u043e\u0439 \u0442\u0438\u043f<\/th>\n<\/tr>\n<\/thead>\n
Short-term overload (IEC 60076-7)<\/td>\n1.3\u20131.5\u00d7 for hours<\/td>\n~1.1\u00d7 briefly<\/td>\n<\/tr>\n
Temperature rise (rating)<\/td>\n55\u201365 K<\/td>\n100 K<\/td>\n<\/tr>\n
Typical efficiency (500 kVA)<\/td>\n98.2\u201398.8%<\/td>\n98.0\u201398.6%<\/td>\n<\/tr>\n
Insulation life target<\/td>\n20\u201330 years<\/td>\n20\u201330 years<\/td>\n<\/tr>\n
Main failure mode<\/td>\nOil degradation, moisture, DGA events<\/td>\nPartial discharge, dust tracking<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Installation and Space Requirements<\/h2>\n

Space and civil work selection normally takes place before pricing. For an oil type of transformer inside a building, a fire-rated vault will be needed (at the very least, with two hour resistant walls); also, an oil containment pit will be necessary that will be able to contain the full volume of the oil plus 10 % of the fire-fighting water, as well as ventilation be provided in compliance with the regulations with a required minimum flow.<\/p>\n

However, outside the situation reverses \u2013 while oil transformers are normal since a simple lined pad is required for them, you can hardly expect to find a dry-type transformer outside without affecting its price and having the risk of overheating. There is noise as well: while oil transformers are quiet since the tank absorbs the core vibration, dry-types are noisier not less than by 5-10 dB(A) due to the same power rating (according to IEC 60076-10 sound level measurement standards).<\/p>\n\n\n\n\n\n\n\n\n\n
Installation Aspect<\/th>\n\u041c\u0430\u0441\u043b\u043e-\u0438\u043c\u043c\u0435\u0440\u0441\u0438\u043e\u043d\u043d\u044b\u0435<\/th>\n\u0421\u0443\u0445\u043e\u0439 \u0442\u0438\u043f<\/th>\n<\/tr>\n<\/thead>\n
Indoor clearance<\/td>\nVault + oil pit + fire rating<\/td>\n300\u2013600 mm air clearance<\/td>\n<\/tr>\n
Outdoor weatherproofing<\/td>\nIntegral (tank sealed)<\/td>\nNeeds enclosure (IP54+)<\/td>\n<\/tr>\n
Foundation<\/td>\nContainment liner, heavier base<\/td>\nFlat pad, lighter<\/td>\n<\/tr>\n
Noise at 1 m (500 kVA)<\/td>\n~55\u201362 dB(A)<\/td>\n~60\u201370 dB(A)<\/td>\n<\/tr>\n
Floor loading<\/td>\nHigher (tank + oil)<\/td>\nLower<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Maintenance and Total Cost of Ownership<\/h2>\n

When it comes to transformers that involve oil, maintenance is undeniably a real and ongoing requirement, which consists of yearly inspections, the sampling of the oil (every 1 to 3 years in accordance with how critical the transformer is), checking of the oil level and temperature, the completion of a replacement of the silica gel in the breather, and eventually filtering of the oil. Dry transformers need virtually no maintenance when indoors and have only minimal dust cleaning and thermal checks. However, because of a higher initial cost, dry-type transformers tend to be more problematic as they may end up leading you to get a higher capacity than you require.<\/p>\n

In terms of the total costs of ownership over a period of twenty years, oil transformers may cost less initially, but they would involve ongoing costs associated with oil maintenance (around $150-600 per year) unlike dry transformers that have a high initial cost (around 40-80% higher) and almost no operational costs. This means that with a device installed, both solutions will be getting very close to each other in terms of the costs, with the difference being not more than 10-20%. Consequently, decisions must be made according to impossible conditions (where it will be located, fire code, overload characteristics, etc.) rather than the cost.<\/p>\n

Side-by-Side Comparison Table<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n
\u0420\u0430\u0437\u043c\u0435\u0440\u043d\u043e\u0441\u0442\u044c<\/th>\n\u041c\u0430\u0441\u043b\u043e-\u0438\u043c\u043c\u0435\u0440\u0441\u0438\u043e\u043d\u043d\u044b\u0435<\/th>\n\u0421\u0443\u0445\u043e\u0439 \u0442\u0438\u043f<\/th>\n<\/tr>\n<\/thead>\n
Best location<\/td>\nOutdoor, substations, industrial<\/td>\nIndoor, buildings, tunnels<\/td>\n<\/tr>\n
\u041f\u043e\u0436\u0430\u0440\u043d\u0430\u044f \u0431\u0435\u0437\u043e\u043f\u0430\u0441\u043d\u043e\u0441\u0442\u044c<\/td>\nNeeds vault\/containment<\/td>\nSelf-extinguishing<\/td>\n<\/tr>\n
Price (500 kVA)<\/td>\n$8,000\u2013$16,000<\/td>\n$12,000\u2013$24,000<\/td>\n<\/tr>\n
Overload tolerance<\/td>\n1.3\u20131.5\u00d7 for hours<\/td>\n~1.1\u00d7 briefly<\/td>\n<\/tr>\n
\u041e\u0431\u0441\u043b\u0443\u0436\u0438\u0432\u0430\u043d\u0438\u0435<\/td>\nOil, DGA, inspections<\/td>\nMinimal<\/td>\n<\/tr>\n
\u0428\u0443\u043c<\/td>\nLower (55\u201362 dB)<\/td>\nHigher (60\u201370 dB)<\/td>\n<\/tr>\n
Environmental risk<\/td>\nOil spill containment<\/td>\n\u041d\u0438\u0447\u0435\u0433\u043e<\/td>\n<\/tr>\n
Indoor code compliance<\/td>\nRestricted<\/td>\n\u0421\u0442\u0430\u043d\u0434\u0430\u0440\u0442<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

For starters, please refer to this table: if the row shows “indoor building” you can proceed to dry-type; if it mentions “outdoor substation” then you will require oil. After this, most of the projects have the direction confirmed from the fire code and overload profile.<\/p>\n

\"A<\/p>\n

A Decision Framework for Your Project<\/h2>\n

Follow these five questions in order \u2014 the first question that dictates the responses to the following:<\/p>\n