Dry-Type Transformer Installation and Ventilation Requirements
Dry-Type Transformer Installation and Ventilation Requirements (On photo dry-type transformer placed and connected)


Dry-type transformers should be installed over foundations that are properly leveled and capable to withstand their weight.

When a transformer is fitted with wheels, make sure the equipment will be equally supported on its base points in order to assure its stability and to prevent any deformation.

When installing the transformer, the following factors should be carefully taken in account:

1. There should be a minimum spacing of 0,5 m between one transformer and another, and between the transformer and any adjacent wall in order to facilitate the access for inspection and ventilation, depending, however, on the project dimensions and the voltages;

2. The room where the transformer will be installed should be well ventilated as to assure proper natural ventilation, since this is an essential parameter for a proper performance of a dry transformer.

In this regard, it is important that the air inlets are located at the front part of the transformer near the bottom and the air outlets are located at the back part of the transformer, with near the top openings large enough to allow for a circulation of approx. 2,5 cubic meters of air per minute/kW of loss. (See the example calculation below).

Proper ventilation in the transformer room will grant the expected useful life and stable operation either on continuous regime or under momentary overloads.

Natural transformer ventilation
Figure 1 – Natural transformer ventilation

As normally the natural ventilation is not sufficient, fans can be installed to increase the air flow i n the room according to Figure 2 or, preferably, adopt the refrigeration o f the room where the transformer will operate .

Danger! If the transformer room is going to be air conditioned, make sure the conditioned air will not be directly blown on the transformer, otherwise water condensation can be built on it and can result in the transformer’ s burning.
Forced transformer Room Ventilation
Figure 2 – Forced transformer Room Ventilation

To calculate the approximate size of the openings or the airflow necessary in the room the following expressions cab be used, considering a difference of 15ºC between the inlet air and the outlet air.

Approximate size of the openings or the airflow


Pt = total transformer losses sinked at 115°C [kW]
S = lower opening surface [m2]
S’ = upper opening surface [m2]
H = distance measured between the middle of the height of the transformer and the middle of the upper opening for air outlet [m]
V = cooling air volume[m3/min]

Example: Installation of two 2.000 kVA dry-type transformers

  • Typical total losses PT for 2 MVA dry-type transformer at 115ºC = 27kW
  • Distance H between the middle of the transformer height and the middle of the air upper outlet opening: 1,5m

Calculated area

From the calculated area we know that the installation of forced ventilation in the room will be necessary.

The minimum flow of the fans will be:

Minimum flow of the fans

This example does not consider the presence of a protection cabinet, wich would be put in questi on in the case of a proper room for the transformer installation.

Warning! If the transformer is fitted with protective cubicle, do not replace that Box with another because its ventilation might not be enough for a proper operation of the equipment.

Reference: Instruction Manual For Dry-type Transformers – WEG

About Author //


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on


    Jun 10, 2015

    Good Article!

  2. Behnam Khojir
    Aug 05, 2014

    Great Article, thanks for sharing. In your example the calculation for the fresh air volume it should be 2.5 x 27 x 2 according to the text in the installation section.

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