Oil-Immersed Medium Power Transformer

ELTAS Medium Power Transformers are produced  from 5000 KVA  to 40 MVA up to 110 KV.  These transformer ranges are  mostly preferred at city transmission lines, industrial facilities and power plants . 

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 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.


Our transformer are designed according to “ core type” design. Slitting and cutting of core is done “ in house”. Core are manufactured from high quality standards also high quality cold – rolled grain oriented silicon steel laminations, which are coated with carlite.



All winding are of the circular type, since this type has the highest resistance against short circuits. Depending on the specific design criteria, layer, helical, disc, partly interleaved or fully interleaved winding are also used.


Active part and Cover

The assembly of core,coil and designed 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 the direct assembly of active part to the  tank. The connection parts of the top cover, the 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 bushing, the accessories, the protection box or the cable box is done on the top or the side of the transformer according to customer requests.



Tank design is competely done by 3-D CAD on computer, which determines the optimum size and the number and location of needed supports, which makes handling, assembely and instalation easier for customer.

  • All welds are tested, ensuring 100% leak proof seams and maximum mechanical strength.


Cooling system

  • All transformer are equiped with detachable panel radiators, which are connected to top and bottom headers.
  • Most commonly natural air/ forced air cooling is used to accelerate the cooling process (NAN/NAF).
  • Other cooling methods such as forced oil/ forced air (OFAF), Directed oil / forced air (ODAF), forced oil / forced water (OFWF), directed oil / forced water (ODWF) are also available if required.



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. ELTAŞ A.Ş. offers different applications, different thickness of film or transformers with different colours as per customer requests. Also, if requested, hot dip galvanized tanks can be produced.


The following accessories are mainly used to protect transformers:

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.