Oil Immersed Distribution & Medium Power Transformers

ELTAŞ A.Ş. manufactures:

  • Oil immersed distribution transformers. These transformers are used to decrease the medium voltage (3.3 -36 kV ) to low voltage level (≤ 1000 V)
  • Medium power transformers. These transformer ranges are mostly preferred at city transmission lines, industrial facilities and power plants.

Distribution and Medium Power Transformers can be ordered as single phase or three phased. Inhibited or uninhibited mineral oil are used as a cooling medium. If requested, non-flammable fluids can be used as well.

According to the customer request;

  • with ONAN, ONAF, ODAF , OFAF, OWAF cooling systems,
  • as open to atmosphere with conservator,
  • with off-load tap changers or on-load tap changers
  • with cable box or protection box,
  • with bushings with ceramic insulators or with resin type plug-in bushings.

The purpose of ELTAŞ A.Ş. is to fulfill customer’s requests completely and to provide highest quality. ELTAŞ A.Ş. manufactures distribution and medium power transformers according to customer requirement, contract requirements or technical standards such as TS 267 60076-1, IEC 60076-1, BS 171, DIN, ANSI, ENEL, ENDOSA, CSA. etc.

1 - Coil Winding

2 - Core Production

3 - Active Part Assembly

4 - Drying Ovens

5 - Quality Control & Testing

6 - Tank & Painting

Eco Design Transformers

With years of experience in the transformer sector, ELTAŞ supports the Eco Design Regulation. As a part of this, we design and manufacture our Oil Immersed Transformers according to Eco Design standards.

After the approval of the Kyoto protocol, the new environment-oriented and ambitious goal of the EU; to reduce greenhouse gas emissions by 20%.

The goals to be achieved in this scope include:

  • 20% decrease in energy consumption
  • Raising power generation from renewable sources to 20% of the total; and
  • 20% decrease in greenhouse gas emissions

To achieve success towards this goal we implemented the concept of “Eco Design Transformer.” The two main goals of this concept are:

  • Decrease in transformer losses and
  • Significant improvement in transformer performance.

For detailed dimensions and losses; You can send an e-mail to [email protected] .

Renewable Energy Transformers

Our SOLAR Transformers are design and produced;

  • with low losses,
  • Considering the harmonics,
  • with increased low voltage insulation level,
  • with additional static screen,
  • with short circuit and voltage fluctation resistivity

Our Wind Power Plant Transformers are design and produced;

  • suitable the door sizes of wind turbine,
  • Using insulating liquid resistant to high temperature (Slicone oil, synthetic or natural ester)
  • with compact dimensions (hermetically sealed, plug-in bushings)
  • with low losses,
  • Considering the harmonics,
  • with short circuit and voltage fluctation resistivity


For the low voltage coils, either copper or aluminum can be used as conductor material. The windings are made of foil or a flattened and paper or nomex insulated wire. If the coils are made of foil, the layers are insulated using a thermal upgraded paper as well as a covering made of DDP resin.

Depending on customer's requests, copper or aluminum conductors are used in high voltage windings. Coils are wound with fully automated computer-controlled machines. The layer insulation looks like a dagger, because of the stripped electrical insulation paper ( kraft or thermal-upgraded, diamond patterned ). The structure of this specially formed layer insulation increases the ability to withstand the impulse voltage. The layer insulation also helps in achieving another important goal: to produce a rigid coil without space. In other words a coil of excellent quality. The isolation class is generally "A". According to customer demand production at B, F, H or C isolation class is also available.


Cores of transformers are made of cold rolled grain oriented silicon steel. Cores are produced by using first class quality of steel. The choice of the material is made according to no-load values required by the customer. Cores are cut to length without burr by modern transformer lamination cut to length machines produced by GEORG and TUBOLY. Cores are produced as step-lap, over-lap, 90° cut with or 45° without holes.

Active Part and Cover

The assembly of core, coil and top cover are designed according to increase the resistance against short circuit forces. The top cover, including the active part of standard transformers, is mounted to the tank with bolts. Another application is direct assembly of active part to the tank. The connection of parts of the top cover, high voltage bushings and the arching horns are made of stainless materials or of materials covered by a special coating which is resistant to corrosion. The arrangement of the bushings, the accessories, the protection box or the cable box is done on the cover or the side of the transformer according to customer requests.


Tanks and top covers for transformers are made of mild steel. Cooling surfaces of distribution transformers are constructed with corrugated walls and they also form the lateral surfaces of the tank. Bottom plate, sides and frame are sealed by welding.

For transformers up to 4000 kVA , corrugated walls can be used as cooling surfaces. Also, it is possible to use radiators as cooling surfaces. Every transformer tank needs to pass an oil leakage test after welding. Therefore, each tank is taken under pressure after being produced. Finished tanks and top covers are sandblasted commensurate with DIN specifications. If the customer has specific requests or demands related to sandblasting, ELTAŞ A.Ş. has sufficient machinery to fulfill all these requirements. It is possible to enclose the bushings on the top cover into a protection box made of appropriate steel according to IEC 60144. According to BS 2562, the cable box can be installed to the sides of the tank.


Transformers are in the colour of RAL 7033 as a standard. Transformer tanks are painted by the method of dipping or spraying. Method of painting is chosen in accordance with customer requests and working conditions of the transformer. For example, Class C1 - C2 - C3 - C4 - C5-I - C5-M paints compliant with H2S can be used against corrosion. ELTAŞ A.Ş. can offer transformers with various applications (zinc coating), various film thicknesses or various colours according to customer demand. Also, if requested, hot dip galvanized tanks can be produced.

Dry and Filling

The active parts of transformers such as core and coils are dried under high vacuum in a furnace. The process of drying varies according to transformer’s type, power and voltage. Oil is filled under high vacuum.

1. Oil Level Indicator

Magnetic oil level gauges are used in order to follow and to control the oil level in the conservator of transformers. Oil level indicators give alarm and tripping signals in case of sudden changes of the oil level.

2. Air Dehumidifier

Air dehumidifier are utilized for transformers with oil conservator. It is connected to the oil conservator. Via silicagel, it removes moisture and dust coming into the conservator. The amount of Silicagel depends on the amount of oil inside the transformer

3. Oil Thermometer

Oil thermometers, which are located in thermometer pockets and welded on the top of the cover or on the side of the tank, follow and control the maximum temperature of the oil. It is available with maximum pointer, without electrical contact or with single or double electrical contact. If the temperature exceeds the estimated values, thermometers with contact give alarm or tripping signals

4. Buchholz ( Gas Collecting and Alarm) Relay

The Buchholz-Relay collects the gasses which are formed by discharges or arcs with low or high intensity inside of the transformer. It used for transformers with conservator. The relay can be with single or double contact. If certain amount of gas is collected on the Buchholz-Relay, both the alarm and tripping signals are activated. Moreover, Buchholz-Relay sends out an alarm signal in low level of oil. The Buchholz-Relay detects failures like overheating and prevents an increase of failure by signalling.

5. Pressure Relief Device

Even though hermetic protection relay is used in transformers, pressure relief device is used additionally. It helps to cover the pressure that expands inside of the transformer.

6.Hermetic Protection Relay

Hermetically sealed transformers equal and greater than 630 kVA are equipped with a Hermetic Protection Relay. It consists the functions of Oil Level Indicator, Temperature Indicator, Buchholz-Relay as well as Pressure Relay.

Besides, upon customer’s request, special accessories such as winding thermometer, digital thermometer, gas collecting unit can be used for oil immersed power transformers.