What a dry type transformer is and why buyers care

A dry type transformer is a static electrical device that changes voltage levels without using liquid insulation or oil-based cooling. Instead of being submerged in mineral oil, the core and windings are cooled by air circulation, while insulation is provided by cast epoxy resin, vacuum pressure impregnated (VPI) materials, or high-grade insulating paper systems. With no oil tank, conservator, or combustible liquid, a dry type transformer is the default choice for indoor rooms, high-rise buildings, hospitals, data centres, metro and tunnel projects, and any site where fire load, leakage risk, or maintenance access is a real constraint.

For procurement teams the appeal is practical: a smaller footprint, no oil bunding or catch pit, simpler fire approval, and lighter long-term maintenance. The trade-off is a higher purchase price per kVA than an equivalent oil-immersed unit, plus greater sensitivity to ambient temperature and ventilation. Understanding that trade-off is what separates a low bid from a low total cost of ownership.

How a dry type transformer works in service

The working principle is the same as any transformer: an alternating current in the primary winding creates a magnetic flux in the laminated or wound core, which induces a voltage in the secondary winding according to the turns ratio. What differs is heat removal. Losses from the core (no-load loss) and windings (load loss) are carried away by natural air convection (AN) or, in higher-capacity units, by forced-air fans (AF) that can raise the output rating by roughly 20 to 40 percent. Because air is a weaker cooling medium than oil, dry type designs use larger conductor sections, higher insulation classes such as F or H, and precisely controlled resin casting to keep winding temperature rise within limits.

Common series you will see in a quotation

Model designations matter in evaluation, because they encode efficiency level and design generation rather than price alone.

• SCB10 dry type transformer – an earlier cast-resin generation still widely used in retrofits and budget-driven projects.
• SCB13 dry type transformer – a mainstream, energy-efficient choice for commercial buildings and distribution rooms.
• SCB14 dry type transformer – lower no-load loss, typically specified where electricity tariffs are high or duty cycles are long.
• SCB18 dry type transformer – a very high efficiency grade, usually selected for green building certification, data centres, and low-carbon projects.
• SGB10 – open or ventilated dry type designs used where cost and heat dissipation are prioritised.

Higher efficiency grades cost more up front but reduce no-load loss around the clock, which is why the payback calculation should be run over ten to twenty years, not on the quotation total.

Key specifications to lock down before ordering

• Rated capacity: from 30 kVA to 6300 kVA in standard distribution ranges; state the future load growth instead of sizing exactly to today's demand.
• Voltage class and ratio: 10 kV or 35 kV primary with 0.4 kV secondary is typical; confirm the actual system voltage and tap range (commonly ±2×2.5 percent).
• Vector group: Dyn11 for most distribution applications; Yyn0 or others for specific networks.
• Insulation class and temperature rise: class F (100 K) or class H (125 K) systems, with the temperature rise limit stated explicitly.
• Loss levels: specify no-load and load loss values, and reference the applicable national energy efficiency standard rather than a vague claim of being energy saving.
• Cooling and protection: AN or AN/AF, plus enclosure IP rating (IP20, IP23, or IP54 for dusty or outdoor-adjacent locations), and whether a temperature controller with fan and alarm contacts is included.
• Site conditions: ambient temperature, altitude above 1000 m, humidity, and seismic requirements all affect design and price.

Efficiency, losses, and where the money actually goes

Two cost curves run in opposite directions during procurement. The initial price rises as efficiency improves, while running costs fall. A quick evaluation method is to capitalise losses: multiply the no-load loss in kW by the annual hours of energisation and the local tariff, then do the same for load loss using an assumed load factor. For a 1000 kVA unit running continuously, the difference between two efficiency grades can add up to a meaningful annual saving, which often justifies the higher specification within a few years.

Installation and ventilation are not optional details

A dry type transformer needs an air path. The room should have adequate inlet and outlet openings, with cool air entering low and hot air leaving high, and clearances maintained around the enclosure for convection and inspection. Inadequate ventilation forces the transformer to run hotter, accelerates insulation ageing, and can derate the unit below its nameplate capacity. Protection coordination matters too: because dry type windings are exposed to dust and moisture at the surface, periodic cleaning and infrared scanning of terminations are the two maintenance tasks that deliver the most value.

A factory-direct procurement checklist

• Confirm the manufacturer's actual production scope, not just the trading company's catalogue.
• Request routine test reports, type test reports, and a certificate of conformity with the declared efficiency grade.
• Ask for the loss values in writing, and verify them against the test sheet after delivery.
• Check whether drawings, manuals, nameplate data, and lifelong quality tracking are included.
• Compare landed cost, lead time, and warranty terms together rather than unit price alone.

As a power transformer manufacturer with a comprehensive inventory, Runsheng Transformer Co., Ltd. supplies SCB10, SCB13, SCB14, SCB18, and SGB10 dry type transformers alongside oil-immersed and amorphous alloy units, delivering each order with manuals, inspection reports, and test certificates. For buyers who want a specification reviewed before issuing a purchase order, that kind of factory-direct conversation usually costs nothing and prevents the expensive mistake of underspecifying a unit that must run for twenty years.

Contact

Phone: +86 13406394988 | Email: runsheng@7813transformer.com | WhatsApp: 008613508930968