What Exactly Is a Dry Type Transformer?

A dry type transformer is a voltage conversion device that uses air and solid insulation instead of insulating oil. Its core and windings are cooled by natural or forced air, while the windings are protected by cast epoxy resin, resin-impregnated fiberglass or high-strength insulating materials. Because there is no oil tank, no oil conservator and no liquid that can leak, a dry type transformer is the preferred solution for indoor substations, basements, high-rise buildings, tunnels and any site where fire safety and maintenance cost really matter.

Put simply: if you see a transformer running quietly inside a building - in a hospital, a subway station, a data center or a shopping mall - it is very likely a dry type transformer.

How a Dry Type Transformer Works

The basic principle is the same as any other transformer: alternating current in the primary winding creates an alternating magnetic flux in the iron core, and that flux induces a voltage in the secondary winding. What makes the dry type transformer different is how heat and insulation are managed.

• Iron core: built from high-grade cold-rolled grain-oriented silicon steel laminations, stacked and clamped to reduce no-load loss, noise and vibration. Amorphous alloy strip is used in higher-efficiency designs.
• Windings: copper or aluminium conductors wound as foil or wire, then cast under vacuum in epoxy resin or impregnated with insulating varnish to form a solid, sealed insulation structure.
• Insulation system: normally Class F (155 °C) or Class H (180 °C), which gives better overload capability and a longer thermal life than conventional oil-immersed designs.
• Cooling: AN (natural air) for normal duty and AF (forced air) with cooling fans for peak load. Forced cooling can raise usable capacity noticeably when temporary overload occurs.

Common Dry Type Transformer Series Explained

Model codes are not random letters - they tell you the phase, the insulation structure and the loss level of the unit you are buying.

• SCB10, SCB13, SCB14, SCB18: three-phase cast-resin dry type transformers in progressively higher efficiency classes. SCB10 is an earlier, higher-loss design, while SCB13, SCB14 and SCB18 reduce no-load and load losses step by step, which lowers long-term electricity cost and helps meet modern energy-efficiency requirements.
• SGB10: a resin-impregnated, open-wound dry type transformer that is lighter, more compact and often more economical where space and budget are tight.
• SCBH15: an amorphous alloy dry type transformer with very low no-load loss, ideal for distribution duty where the unit stays energized around the clock.

Choosing between them is mostly a calculation: higher efficiency classes cost a little more up front but pay the difference back through lower losses over years of operation.

Dry Type vs. Oil-Immersed: A Quick Comparison

• Fire and safety: a dry type transformer contains no combustible oil, so it suits indoor, underground and densely occupied buildings; oil-immersed units are usually installed outdoors or in separate oil-proof chambers.
• Maintenance: no oil sampling, no oil filtration and no leakage risk - routine work is largely limited to cleaning and checking connections and fans.
• Footprint: a dry type transformer needs no oil pit, fire wall or oil-retaining facility, which simplifies civil works.
• Environment: no oil means no risk of soil or water contamination, which is why hospitals, tunnels, ports and renewable energy projects often specify dry type units.
• Cost balance: oil-immersed transformers generally cost less per kVA at large capacities; dry type units win on total installed cost in indoor and safety-critical projects.

Key Parameters to Confirm Before You Order

An accurate specification sheet prevents expensive rework after delivery. Check at least the following:

• Rated capacity, from small distribution sizes up to several thousand kVA, matched to your real load profile rather than a rough guess.
• Rated voltage and tapping range, typically 10 kV, 20 kV or 35 kV on the high-voltage side with plus or minus 5 percent tappings.
• Vector group and phase connection, such as Dyn11 or Yyn0, to match your existing switchgear and protection scheme.
• Impedance voltage, no-load loss and load loss, since these directly affect parallel operation and running cost.
• Insulation class, temperature rise limit, cooling method (AN or AF) and enclosure protection class (for example IP20 or IP23).
• Compliance with recognized standards such as GB/T 1094.11 and IEC 60076-11, plus factory routine tests: ratio, resistance, no-load loss, load loss, insulation and withstand voltage tests.

Where Dry Type Transformers Are Used

• Commercial buildings, hotels, shopping malls and office towers with indoor substations.
• Hospitals, laboratories and cleanrooms where fire risk must be minimized.
• Metro stations, tunnels, airports and underground utility rooms.
• Data centers and telecom facilities with continuous, stable load.
• Solar, wind and energy-storage projects that need compact, low-maintenance step-up or auxiliary transformers.
• Industrial plants - especially where a mining transformer, rectifier transformer or custom special transformer is required for a specific process.

Factory-Direct Buying: Save Money Without Losing Quality

Price differences between quotations for the same capacity often come from hidden gaps: thinner conductor, lower-grade silicon steel, a lower efficiency class, or missing type tests. A reliable way to control both cost and risk is to buy directly from the manufacturer and compare technical data sheet by data sheet, not price by price alone. As a transformer manufacturer with a comprehensive inventory, Runsheng Transformer Co., Ltd. supplies SCB10, SCB13, SCB14 and SCB18 dry type transformers alongside S11, S13, S20 and S22 oil-immersed transformers, SH15 and SCBH15 amorphous alloy units, and 35 kV preassembled substations. Every unit is delivered with manuals, inspection reports, test certificates and lifelong quality tracking.

Before placing an order, use this short checklist:

• Confirm capacity, voltage ratio, vector group and impedance in writing.
• Ask which efficiency class and loss values are guaranteed, and request the routine test report.
• Verify the insulation class, temperature rise and cooling arrangement for your ambient conditions.
• Check enclosure protection class, cable entry direction and installation dimensions.
• Confirm delivery scope, spare parts, documentation and after-sales response time.

Final Thoughts

A dry type transformer is a long-life asset, not a one-off purchase. Understanding its structure, series naming and key parameters lets you specify correctly the first time, avoid overspending on unnecessary options, and secure a unit that runs efficiently for decades. Whether you need a standard SCB series distribution unit or a custom special transformer for an unusual load, working directly with the source factory keeps quality, documentation and price fully transparent.

Contact us for a quotation or technical consultation: phone +86 13406394988, e-mail runsheng@7813transformer.com, WhatsApp 008613508930968.