A dry‑type transformer is a power transformer that uses air or solid insulation (such as epoxy resin) instead of liquid insulating oil. Unlike traditional oil‑immersed transformers, the core and windings are not submerged in oil – they are cooled by natural air circulation or forced air fans. This “oil‑free” design is the key differentiator.
Since the first cast‑resin dry‑type transformer (400kVA/20kV) was developed by AEG in 1964, dry‑type technology has evolved dramatically. Today, in countries like the US, Germany, and Japan, dry‑type transformers account for over 20% of distribution transformer production – and in compact substations, that figure reaches 80‑90%. China is now the world’s largest producer and consumer of dry‑type transformers, and their share in 10kV distribution networks keeps rising.
Xinhong Electrical is a professional manufacturer dedicated to high‑quality epoxy cast‑resin dry‑type transformers. Our product line spans from 30kVA to 2500kVA, serving commercial buildings, industrial plants, hospitals, data centers, and more.
Dry‑type transformers operate on electromagnetic induction. When AC current flows through the primary winding, it creates a varying magnetic flux in the core. This flux induces a voltage in the secondary winding, thereby transforming the voltage level. Xinhong Electrical uses high‑grade silicon steel laminations to reduce hysteresis and eddy current losses, delivering superior efficiency.
Core: Made of cold‑rolled, grain‑oriented silicon steel sheets, stacked to provide an efficient flux path and minimize no‑load loss.
Windings: HV and LV windings are wound around the core. Xinhong Electrical adopts foil‑type windings for the low‑voltage side and a stepped, segmented layer structure for the high‑voltage side – this significantly improves impulse voltage distribution.
Insulation system: HV coils are vacuum‑cast with epoxy resin, forming a solid, durable insulation layer. Insulating cylinders are placed between HV and LV windings to enhance dielectric strength.
Structural support: Cushions and anti‑vibration fasteners keep coils firmly in place, ensuring long‑term reliability.
Typical dry‑type transformers range from 30kVA to several MVA, with voltage ratings of 6kV, 10kV, 20kV and above. Xinhong Electrical units deliver: rated capacity 30‑2500kVA, connection group Dyn11 or Yyn0, short‑circuit impedance 4% or 6%, no‑load current below 1.5‑2.1%, fully compliant with GB/T 1094.11.
Natural air cooling (AN): Heat dissipates by natural convection – the transformer can run continuously at rated load.
Forced air cooling (AF): Fans force air over the windings, boosting output capacity by up to 50% – ideal for intermittent overloads or emergency conditions.
Note: Overload operation increases load losses and impedance voltage; it is not economical for sustained periods.
HV windings are vacuum‑cast with epoxy resin, fully encapsulating the coils. This provides exceptional fire resistance and environmental robustness.
Xinhong Electrical’s epoxy cast‑resin series – our flagship product – uses premium epoxy resin in a vacuum casting process. The fully encapsulated coils offer fire retardancy, moisture resistance, dust protection, and chemical corrosion resistance. Ideal for high‑risk environments: high‑rise buildings, hospitals, chemical plants, etc. Capacity: 30‑2500kVA; voltage classes: 6kV, 10kV, 20kV, and custom options.
This type uses Nomex® paper‑based insulation, delivering excellent electrical and mechanical performance over a long service life. Usually Class H insulation (180°C), it performs well in well‑ventilated spaces.
Other variations include vacuum pressure impregnated (VPI) and open‑wound designs. VPI impregnates windings with resin under vacuum, offering superior moisture protection.
| Aspect | Dry‑Type Transformer | Oil‑Immersed Transformer |
|---|---|---|
| Safety | Oil‑free, zero fire/explosion risk, flame‑retardant materials | Risk of oil leaks, fire, and explosion |
| Maintenance | Minimal – no oil changes or oil testing | Requires regular oil monitoring, changes, and disposal |
| Environmental impact | No oil leaks, no hazardous vapors, eco‑friendly | Used oil requires special disposal; pollution risk |
| Installation location | Indoor, crowded spaces, fire‑sensitive areas | Outdoor or substations with oil containment |
| Initial cost | Higher (especially cast‑resin) | Lower |
| Life‑cycle cost | Lower maintenance, better long‑term economy | Ongoing oil‑related costs |
| Size & weight | Lighter, easier to transport and install | Heavier, more demanding installation |
| Overload capacity | +50% with forced air cooling | Naturally high, good for sustained heavy loads |
Xinhong Electrical recommends dry‑type transformers when safety, indoor installation, and environmental compliance are top priorities.
No flammable oil – all insulation materials are self‑extinguishing. This makes dry‑type transformers the standard for high‑rise buildings, hospitals, subways, and other densely occupied places.
No oil changes, no oil quality tests, no circulation system maintenance. This greatly reduces operating and management costs over the transformer’s life.
Zero risk of oil leakage, no toxic byproducts from aging oil. This reduces environmental liability and simplifies regulatory compliance.
No need for fire pits or firewalls. Dry‑type transformers can be placed directly inside electrical rooms, saving valuable floor space. Their lighter weight also makes transport and rigging easier.
Commercial & high‑rise buildings – Offices, malls, hotels (fire safety priority)
Medical facilities – Hospitals require absolute reliability and fire safety (operating rooms, ICUs, imaging equipment)
Data centers & telecom – Sensitive to power quality and fire risk
Industrial manufacturing – CNC machines, automated lines, large motors
Transportation infrastructure – Airports, ports, subway stations, high‑speed rail stations
Renewable energy – Solar farms, wind farms (oil‑free design suits outdoor use)
Calculate total connected load and allow for future expansion. Common sizes: 30, 50, 100, 200, 315, 500, 630, 800, 1250, 1600kVA. Xinhong Electrical covers 30‑2500kVA and offers custom capacities.
Based on grid access and load requirements. Typical: 6kV, 10kV, 20kV, 35kV primary; 400V (3‑phase) or 230V (1‑phase) secondary.
Dyn11 (delta HV) is preferred – better third‑harmonic suppression. Yyn0 is also available.
Indoor or outdoor? Need enclosure (IP20, IP23, or higher)?
Ambient temperature ≤40°C, altitude ≤1000m standard.
For corrosive or dusty environments, choose higher protection ratings.
High‑efficiency dry‑type transformers reduce long‑term operating costs. The global energy‑efficient dry‑type transformer market is projected to grow from $8.07 billion (2025) to $13.74 billion (2032), CAGR 7.9%.
Xinhong Electrical designs exceed national efficiency standards – low no‑load and load losses.
Ventilation: Ensure free air flow around the transformer; cooling paths must not be blocked.
Foundation: Level and strong enough to support the weight.
Wiring: Follow the diagram strictly; ground connection must be secure.
Temperature control: Install temperature controllers and fan control systems.
Clean regularly – Remove dust from core and windings to prevent insulation degradation.
Check fasteners – Ensure bolts and clamps are tight.
Monitor insulation resistance – Measure periodically; act on any drop.
Check temperature system – Verify sensors and fans work properly.
| Symptom | Possible Cause | Remedy |
|---|---|---|
| Short circuit (winding‑to‑winding or to ground) | Conductive debris, moisture, dust | Clean, improve environment, replace windings if needed |
| Low insulation resistance | Overall moisture ingress | Field drying |
| Spark discharge on energization | Poor grounding, sharp edges, dust | Check grounding, clean, smooth burrs |
| Winding deformation or burn | Short‑circuit impact, prolonged overload | Replace damaged windings, adjust operation |
Always cut power before any inspection or repair.
Q1: Can a dry‑type transformer be installed outdoors?
Yes, but with an enclosure rated IP23 or higher (weatherproof). For permanent outdoor use, consult Xinhong Electrical for a specially designed outdoor model.
Q2: What is the typical service life?
20‑30 years under normal use and maintenance. Cast‑resin types age slowly; a good environment can extend life even further.
Q3: What is a K‑factor transformer?
A dry‑type transformer designed to handle high harmonic content from non‑linear loads (UPS, VFDs, LED lighting). Recommended for projects with many switching power supplies.
Q4: How noisy are dry‑type transformers?
They produce some electromagnetic noise due to core magnetostriction. Xinhong Electricaldesigns minimize noise through optimized core geometry and damping – well within national and international standards.
Q5: How do I get a quote or technical support from Xinhong Electrical?
Visit our official website for product catalogs and technical data. Submit your project requirements (capacity, voltage, protection level) – our engineering team will provide custom solutions and accurate quotes.
The global dry‑type transformer market is expected to grow at ~6.7% CAGR from 2026 to 2033, driven by urbanization, industrialization, and stricter fire safety regulations.
Key trends:
Higher efficiency – Stricter energy standards push losses lower
Smart monitoring – Built‑in sensors, remote diagnostics, predictive maintenance
New insulating materials – Even better environmental and thermal performance
Compact design – Smaller footprint, easier installation
Xinhong Electrical continues to innovate, delivering safe, efficient, and eco‑friendly dry‑type transformers to global customers.
Xinhong Electrical (Jiangsu Xinhong Electrical Equipment Co., Ltd.) is headquartered in Xuzhou, Jiangsu, China, specializing in the R&D, manufacturing, and sales of dry‑type and distribution transformers.
Our strengths:
Wide range – 30kVA to 2500kVA, fully customizable
Proven technology – Epoxy resin vacuum casting, fully encapsulated coils, excellent fire resistance
Certifications – ISO9001, CCC (China Compulsory Certification)
Supply capacity – Reliable delivery for 30‑2500kVA series epoxy cast‑resin dry‑type distribution transformers
Whether you are designing a high‑rise building, expanding an industrial facility, or upgrading a data center power supply, Xinhong Electrical delivers safety, reliability, and efficiency.
This guide is a technical reference for electrical engineers and procurement professionals. Reproduction or quotation must credit the source and retain the original integrity.
References:
Baidu Baike – Dry‑Type Transformer
GB/T 1094.11-2022 Power transformers – Part 11: Dry‑type transformers
IEEE C57.94-2025 Guide for Installation, Application, Operation, and Maintenance of Dry‑Type Distribution and Power Transformers
Global Dry‑Type Transformer Market Research Report
