What Is a dry type transformer? A Straightforward Definition

A dry type transformer is a static electrical device that transfers electrical energy between circuits through electromagnetic induction, with one important difference from a conventional distribution transformer: its core and windings are cooled by air rather than by insulating oil. There is no liquid dielectric anywhere in the unit, which is exactly why it is called "dry type".

Every dry type transformer is built from three essential elements: a magnetic core made of grain-oriented silicon steel or amorphous alloy, high and low voltage windings wound in copper or aluminium, and a solid insulation system. That insulation system is usually either epoxy resin cast under vacuum (cast resin) or a vacuum pressure impregnated (VPI) resin structure. These materials determine the unit's temperature class, its short-circuit withstand and its service life.

How a dry type transformer Works in Practice

Alternating current flowing through the primary winding creates an alternating magnetic flux in the core. The core channels that flux into the secondary winding, where it induces a voltage at a level suitable for the load. Because the windings and core generate heat, dry-type units rely on two cooling methods:

• AN (air natural): passive convection cooling, the standard configuration for most indoor installations.
• AF (air forced): fans increase airflow and can raise the continuous rating by roughly 25-40% when demand peaks.

Typical insulation classes are class F (155 degrees C) and class H (180 degrees C), with standard temperature rise of 80K or 100K. This thermal headroom is what makes a well-built dry type transformer resistant to short-term overload and voltage fluctuation.

The Main Types of dry type transformer You Will See on the Market

Series designations are not marketing labels - the digits indicate loss levels and energy efficiency. A lower no-load loss figure means lower electricity bills over the unit's 20-30 year life, which is why efficiency grade matters far more than purchase price in a lifetime cost calculation.

• SCB10 dry-type transformer: entry-level cast resin design, still widely used in general distribution.
• SCB13 dry-type transformer: reduced no-load and load losses, a common workhorse for commercial buildings.
• SCB14 dry-type transformer: lower loss still, often specified for projects with efficiency requirements.
• SCB18 dry-type transformer: the highest efficiency cast resin grade in the series, ideal for data centres and high-utilisation loads.
• SGB10 dry-type transformer: open-wound, non-encapsulated construction for dry, clean indoor environments.
• SCBH15 and SH15 series: amorphous alloy versions that cut no-load loss dramatically - valuable for renewable energy transformer duties where the unit sits energised for long hours.

Key Technical Parameters to Verify Before Ordering

Procurement mistakes almost always trace back to an incomplete specification. Confirm these items in writing on every quotation:

• Rated capacity - standard dry-type ranges cover 30-6300 kVA, with 35 kV and below voltage classes the most common.
• Voltage ratio and vector group, for example 10/0.4 kV, Dyn11.
• Impedance voltage (usually 6% for distribution duty) - it governs short-circuit current and voltage regulation.
• No-load loss and load loss values, referenced to a stated efficiency standard.
• Insulation class, temperature rise, cooling method (AN or AN/AF).
• Enclosure protection, typically IP20, IP23 or IP30, matching the environment.
• Compliance with IEC 60076-11 or the equivalent national standard, plus routine test reports and, where required, type test certificates.

dry type transformer vs Oil-Immersed Transformer

Choosing between technologies is a question of environment and duty:

• Fire and safety: a dry type transformer contains no flammable oil, so it needs no fire pit, oil bund or blast wall - a decisive advantage indoors, underground and inside high-rise buildings.
• Maintenance: no oil sampling, filtration or leak repair; routine checks are largely visual and thermal.
• Footprint and cost: oil-immersed units are generally cheaper per kVA and tolerate higher overload, while dry-type units cost more upfront but simplify civil works and approvals.
• Environment: extended rating works best for dry-type units in sealed, air-conditioned spaces; in high-humidity or dusty plants, adequate ventilation and IP protection are essential.

Where dry type transformer Units Are Used

Because they are quiet, non-flammable and maintenance-light, dry-type units dominate commercial and critical-power applications: hospitals, shopping malls and office towers, data centres, metro and airport projects, semiconductor and food plants, ships and offshore platforms, plus solar and wind farms where a renewable energy transformer must operate indoors or in enclosures.

How to Avoid Overpaying for a dry type transformer

Buyer beware is real in this market. Watch for these common traps:

• Efficiency downgrade: an SCB13 dry-type transformer quoted at an SCB18 dry-type transformer specification but delivered at a higher loss level. Insist on loss test data.
• Aluminium sold as copper: aluminium windings are legitimate, but they must be priced and rated as such.
• Missing test documents: a credible unit ships with a manual, routine inspection report and test certificate.
• Under-specified enclosures: an IP20 unit installed in a dusty workshop will fail early.
• Hidden middlemen: each trading layer adds margin without adding engineering value.

What Actually Drives dry type transformer Price

Four factors explain most of the price difference between quotations: winding material and conductor cross-section, cast resin versus VPI insulation, efficiency grade (SCB10 through SCB18), and capacity or voltage class. Enclosure type, forced-air cooling and third-party testing also move the number. When two quotes differ by 30%, the difference is almost never the factory - it is the specification or the supply chain.

Why Factory-Direct Supply Matters

As a power transformer manufacturer, Runsheng Transformer Co., Ltd. produces SCB10, SCB13, SCB14 and SCB18 dry-type transformers, SGB10 units, SH15 amorphous alloy transformers, S11/S13/S20/S22 oil-immersed transformers, mining and rectifier transformers, plus 35 kV preassembled substation equipment and high/low voltage switchgear. Because units ship directly from the production line, buyers avoid distributor mark-ups, and every order is delivered with manuals, inspection reports, test certificates and lifelong quality tracking.

The practical takeaway for procurement teams is simple: fix the efficiency grade and loss figures first, compare like-for-like specifications second, and only then compare price. Bought that way, a factory-direct dry type transformer typically lands 20-30% below list-channel pricing while still meeting IEC and national standards.

Frequently Asked Questions

• Is a dry type transformer suitable outdoors? Yes, with an appropriate IP-rated enclosure and sun/rain protection it can be installed outdoors.
• How long does one last? With correct loading and ventilation, 20-30 years is normal.
• Can it be customised? Yes - voltage ratio, impedance, temperature rise, dimensions and special duties such as mining or rectifier service can all be engineered to order.

For specifications, drawings or a factory-direct quotation, contact Runsheng Transformer Co., Ltd. by phone at +86 13406394988, e-mail runsheng@7813transformer.com, or WhatsApp 008613508930968.