What a Dry Cast Resin Transformer Really Is

A dry cast resin transformer is a power distribution transformer whose high-voltage and low-voltage windings are encapsulated in epoxy resin under vacuum, so the unit contains no insulating oil whatsoever. Instead of relying on oil for dielectric strength and cooling, the coils are cast into solid resin cylinders that insulate the winding, protect it mechanically and dissipate heat through air circulation around the coil surface. That single design decision is what creates the two advantages buyers care about most: no fire risk from flammable liquid and almost no routine maintenance.

Cast resin units are built to the same electrical logic as any distribution transformer — they step 10kV or 35kV down to 400V for a plant, building or substation — but they are deployed wherever oil is unwelcome: inside buildings, in basements, on rooftops, in tunnels, hospitals, data centres and shopping malls.

How the Vacuum Casting Process Works

The manufacturing sequence is what separates a reliable dry cast resin transformer from a cheap imitation, so it is worth knowing before you sign a purchase order.

• Winding: Copper or aluminium foil and wire are wound on a precision former with insulation layers placed between turns.
• Vacuum casting: The winding is placed in a mould and epoxy resin is drawn in under vacuum, then cured under pressure. Vacuum removes trapped air, which is what keeps partial discharge low.
• Curing and demoulding: The resin is cured on a controlled temperature curve so it does not crack under thermal cycling.
• Core assembly: The cast coils are married to a laminated silicon-steel core, assembled with the clamping structure.
• Testing: Routine tests cover winding resistance, ratio, no-load and load loss, insulation resistance, power-frequency withstand and partial discharge.

A genuine dry cast resin transformer should show partial discharge levels held to roughly 10 pC or below on routine test. If a supplier cannot produce that record, the casting process is not under control.

Dry Cast Resin Transformer vs Oil-Immersed Transformer

• Fire and safety: Cast resin units are self-extinguishing and contain no oil, so they suit indoor and fire-sensitive locations; oil-immersed units need oil pits, fire separation and bunding.
• Maintenance: Oil-immersed transformers require oil sampling, filter changes and leakage inspection. A dry cast resin transformer is essentially maintenance-free apart from cleaning and connection checks.
• Installation: No oil handling, no conservator, no bushings exposed to oil leaks — installation is faster and the footprint can be smaller.
• Cost trade-off: Oil-immersed units are usually cheaper per kVA at large ratings; cast resin units win on lifetime cost in indoor and high-humidity applications.
• Environment: No oil means no spill risk, and the resin coils can often be recycled as part of the copper recovery stream.

Standard Models and Typical Specifications

Most projects specify one of the standard SCB or SGB families. The model number is not decoration — it signals the loss level and energy performance of the design.

• SCB10: A widely used earlier generation, still found in existing installations.
• SCB13: Improved no-load loss over SCB10, a common retrofit and new-build choice.
• SCB14: Lower losses again, meeting current energy-efficiency expectations for new projects.
• SCB18: The highest-efficiency cast resin family in the SCB line, chosen where running cost and utility approval matter most.
• SGB10: A related three-phase cast resin family for specific low-voltage requirements.

Typical ratings run from 30 kVA to 2500 kVA with 10kV or 35kV primary voltage, insulation class F or H, temperature rise around 100K for air-natural (AN) cooling and 125K with forced-air (AF) cooling, and protection degrees from IP00 open design through IP20 and IP23 enclosures. Ratings up to 6300 kVA and custom special transformers are available for mining, rectifier and renewable-energy duty.

Where Dry Cast Resin Transformers Are Used

The dry cast resin transformer has become the default choice in several sectors because its limitations are rarely a problem there and its safety is a real benefit.

• Commercial buildings, hotels, hospitals and shopping centres
• Data centres and telecom rooms with strict fire rules
• Metro stations, tunnels and underground substations
• Prefabricated and compact substations, often paired with high and low voltage switchgear
• Wind and solar generation, where no oil leakage is allowed near equipment
• Chemical plants, mines and other sites with dust or humidity exposure

How to Choose: A Practical Buyer's Checklist

1. Load profile: Size for your real demand plus a sensible growth margin; oversizing wastes money and raises no-load loss.
2. Loss level: Compare no-load and load loss, not just purchase price. A cheaper transformer with higher losses can cost more over ten years of operation.
3. Loss evaluation: Ask for the guaranteed loss values in writing and how they are tested.
4. Insulation and temperature rise: Confirm class F or H and the rated temperature rise for your ambient conditions.
5. Enclosure: Indoor open design, or IP20/IP23 for dust and moisture protection.
6. Test documentation: Factory test report, inspection certificate and partial discharge record should travel with the unit.
7. Winding material: Copper and aluminium are both valid, but the price difference must be reflected honestly in the quotation.

Price: What Actually Drives the Cost

Buyers usually ask for a cast resin transformer price first and specifications second, which is the wrong order. Cost is determined by rating, winding material, loss class, copper market price, enclosure rating and whether the unit is standard or customised. A 1000 kVA SCB14 with aluminium windings and a 1000 kVA SCB18 with copper windings are not comparable products, so any quote that does not state the model, loss level and winding material is not a real quote.

The biggest avoidable cost is not the manufacturing cost at all — it is the distribution chain. Trading companies, agents and resellers add margin without adding engineering value. Purchasing from the manufacturer removes that layer.

Why Factory-Direct Supply Cuts Your Total Cost

Runsheng Transformer Co., Ltd. manufactures oil-immersed and dry-type transformer ranges including SCB10, SCB13, SCB14, SCB18 and SGB10 cast resin units, alongside S11, S13, S20 and S22 oil-immersed transformers, SH15 amorphous alloy transformers, mining and rectifier transformers, plus 35kV and below preassembled substations, compact substations and high and low voltage switchgear. Buying from the production floor means factory-direct pricing, documented testing and lifelong quality tracking rather than a markup for a middleman's phone call.

Maintenance and Service Life

A properly installed dry cast resin transformer is one of the least demanding assets in a substation. Practical care is limited to keeping the coil surfaces and cooling ducts dust-free, checking terminal torque annually, monitoring the temperature controller and watching for unusual noise or vibration. In clean, well-ventilated rooms, a quality unit commonly serves 20 to 30 years.

If you are comparing quotations for an upcoming project, request the full technical data sheet, the loss values and the routine test report before comparing prices — then compare total cost of ownership. Runsheng Transformer Co., Ltd. can supply complete documentation with every unit.
Phone: +86 13406394988 | E-mail: runsheng@7813transformer.com | WhatsApp: 008613508930968