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H61 H59 20kV(15kV) Hermetical Oil Immersed Distribution Transformer

ENGELEC Oil immersed Distribution Transformer with oil conservator is equipped with an expansion tank or conservator mounted above the main tank. The expansion of the insulating liquid is compensated inside the conservator by the raising of the oil level. In the conservator the top of the oil is in contact with the air which must remain dry to avoid any oxidation. This is achieved by admitting the outside air in the conservator through a desiccating device containing silica-gel crystals. The HV and LV coil is continuously winded around the core with good concentricity and compact winding. Our product has advantages of low consumption and low noise pollution by combining new generation of technology good performance and energy saving. It is widely used in power distribution system.
  • SM


  • SM2


20kV (15kV) Hermetical Oil Immersed Distribution Transformer SM Series

We generally manufacture distribution transformers in this power range, mainly in two different types:

  1. Transformer with conservator tank (S),

  2. Hermetically sealed type (SM),

Below table will help to engineers to select the best option according to environmental conditions which transformer works in:

High Environmental TemperatureHigh AltitudeRural NetworkHigh HumidityOver Load ConditionsUnstable Loading

Meanwhile here is the advantage-disadvantage of the S/SM types:

  • In SM type, tank pressure is more than S type. S type generally works under low pressure due to its open to atmosphere,

  • In SM type, cooling/insulation oil does not contact to the air (theoretically). Therefore oil maintenance period is longer than S type,

  • SM type transformers and their related parts generally work under higher temperature (If we evaluate S/SM work under same conditions).

♦ Hermetically Sealed Type:

Oil type distribution transformers can change the input and output voltages up to 36 kV voltage levels with a capacity of 5000kVa power in desired ratios. The heat generated during operation is maintained and cooled at the normal temperature level with transformer oil. This type of transformer can be examined under two main headings as hermetic and conservator tank:

They are produced in a range of 25 – 5000 kVA, up to 36 kV high voltage level, with three or single phase, oiled, naturally cooled (ONAN), idle tap changer, or automatic on-load tap changer, both externally and indoors. Hermetic oil type distribution transformers are manufactured by filling the oil under a vacuum by balancing the oil pressure and atmospheric pressure at the desired temperature and not allowing the cooling oil to come into contact with the atmosphere.

As a result of changing oil pressure due to thermal changes in hermetic oil type distribution transformers, the internal heat is controlled by a natural conservator and contraction of boiler wave walls. Mechanical design and manufacturing are made to withstand these effects.

Hermetic oil type distribution transformers are shorter in length than a conservator tank transformer”. Therefore, it can be used in smaller areas.

Since the oil does not come into contact with the atmosphere in hermetic transformers, it does not require oil change in certain periods as in a transformer with a conservator tank.

20kV (15kV) Three phase hermetical oil immersed distribution transformer, SM series

Main Technical Parameters
Rated capacity(kVA)Primary voltage
H.V. tap range (%)Secondary voltage(V)Connection groupNo-load loss

Load loss


No-load current (%)Short circuit impedance (%)











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