Oil Immersed Transformer



Based on know-how accumulated over several years, Hyosung's oil-immersed transformers have been supplied to various industries including semiconductor, steel work, and petrochemical. Further, as an outstanding and comprehensive solution provider, we respond to the demanding requirements of our customers by developing and manufacturing both eco-friendly and high-efficiency transformers.


  • Excellent short-circuit resistance

  • Satisfies the various load conditions required by customers

  • Low-loss step lap laminated core

  • Uses latest insulation material with high short-circuit strength to realize high thermal capacity

  • Cold steel sheet is used for radiating pipe to ensure a sufficient cooling effect and aesthetic exterior

  • Compact, light, and low-noise transformer with standard efficiency and noise level which can be easily installed even in a small indoor or outdoor area

Panel type

50,000kVA or below, 66kV OR below
  • Radiating Structure

  • Manufactured with the thin, cold-rolled steel sheets containing a vertical oil path, where insulation oil can circulate; each radiating pipe is constructed of two cole-rolled steel sheets, which are parallel and have equal length.

  • The length of the radiating pipe is determined by the tank's height. It is divided into a separate or all-in-one type depending on the welding method used.

  • Customized design is available by combining the radiating sheet in a variety of ways; the radiator can be separated for transportation.

General Cast Resin Transformer

  • 01

    General Cast Resin Transformer


Our cast resin transformers are certified by ISO and CESI, an international certification authority. In 2008, we obtained the coveted seismic and vibration test(Q-Class) certificate, proving once more that our quality management and technical competence are unmatched.


  • Self-extinguishing characteristics of epoxy significantly reduces the spread and effect of a fire, and the possibility of explosion is nearly non- existent

  • Easy transportation and installation with simple structure

  • No toxic substance (oil or gas) discharged

Extended lifetime

  • Adopts a higher class epoxy resin

  • Epoxy Resin; uses H class epoxy resin, which is higher than the standard F class, as the main insulation material of the mold transformer to control thermal aging and extend the overall lifetime of the transformer by three-folds.

High stability and durability with strict quality management

  • Winding structure: when the radial build (RB) of the high-pressure winding is large, the temperature difference between the center and the surface of the winding gets higher, then crack in the winding may cause a partial discharge. Therefore, when the RB is large, an air duct is inserted making the RB thinner, then the temperature difference between the center and the surface is reduced and cracking is prevented.

  • When the air duct is inserted, the electric field distribution of the high-pressure winding becomes stable and the withstanding voltage becomes more resilient against external surge.

  • Casting process quality management: By strengthening quality management and interim examination of the casting by batch is checked (*Testing is required for checking how high the temperature is required to be for transiting from the solid glass-like elasticity of the solid polymer to the flexible rubber-like elasticity as well as checking the chemical combination status of the epoxy resin and process stability.)

  • By adopting the latest analysis technique, the transformer can be operated under severe conditions.

  • Satisfies the customers by resolving various failures and anomalies, which may occur in operation on site, through technical analysis and visiting the site when customers request after-service.

Transformer for special load: Inverter, converter, UPS system, electric are furnace, variable transmission drive, electric welding device, industrial process control

Installation Site

Where the installation condition is limited

Where fire prevention is required (Flame Retardancy)

where customers request reliability

Transformer for special load: Inverter, converter, UPS system, electric are furnace, variable transmission drive, electric welding device, industrial process control

Where the eco-friendly and environment-resistance is necessary

  • Common and public facilities: Condominiums, hotels, studio apartments, shopping malls, hospitals, and other public facilities

  • Manufacturing factories:Automobile factories, semiconductor factories, and chemical factories

  • Special areas: Power plants(nucler, water, fire, wind, and tidal), airports, subways, container cranes, and tunnel excavation work


Classification Description
Instalation Area Indoor
Rated Voltage (KV) 1st Voltage and
Tap Voltage
23.6F-22.9R-21.9-19.9 6.9F-6.6R-6.3~6.0~5.7
2nd Voltage 6.6/3.3 0.38-0.22 0.22-0.11 0.38-0.22
Phase 3ph 3ph 1ph 3ph
Standard Wiring △-△ △-Y 1ph, 3-wiring △-Y
Rated Capacity(kVA) 75 75 75
100 100 100
150 150 150
200 200 200
300 300 300
500 500 500
750 750 750
1000 1000 1000
1500 1500 1500
2000 2000 2000
3000 3000 3000
4000 4000 4000
5000 5000 5000
Frequency 60Hz, 50Hz
Insulation Class Primary : F,B Secondary
Increase in Winding Temperature Primary : 100℃, 80℃ Secondary : 100℃, 80℃
Dielectric Strength Voltage class 20kV 6kV 3kV 0.4kV or below
Power Frequency Withstand Voltage 50kV 20kV 10kV 3kV
Impulse Withstand Voltage(BIL) 95/125kV 60kV 40kV -
  • 02

    High Efficiency Cast Resin Transformer


Our high-efficiency and low-noise cast resin transformer uses domain refinement silicon steel instead of conventional grain-oriented (CGO) silicon steel for the core. In addition, minimizing the no load loss for high efficiency ratings delivers an economical effect and improves the site, usage environment, and the electrical characteristics.


  • Improves the noise level by 8~11dB or more compared to the KS standard

  • More advantageous to use special loads by securing harmonic characteristics

  • Secures about 15% of continuous overload capability

  • 30% of electricity charge is saved per year, compared to the general cast resin transformers, thus reducing costs over the long run.