LEGRAND LE06499AE, Instructions For Installation, Use And Maintenance Manual

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5.6 Ventilation
The transformer during its operation generates losses due to the passage of current through the windings and the effect
on the core of the magnetizing current. The losses, the values of which are shown on the test report, are transformed into
heat that must be dissipated from the room in which the transformer is installed to comply with the conditions of normal
use and prevent over-temperature limits being exceeded.
The room must be equipped with an opening at the bottom part S, to ensure an adequate flow of fresh air and an aper-
ture S’ on the opposite wall in the high part, to extract the hot air that rises due to the chimney effect.
To determine the dimensions of the openings required use the following formulas ( valid for an annual average tempe-
rature to 20°C ).
S = 0.185 x (TL / radq(H);
S’ = S x 1.15 where:
S = net surface of entry in m2
S’ = net surface of exit in m2
TL = sum of no-load losses and load losses expressed in kW and indicated on the test report
H = height between two opening in meter
For transformer directly fixed to the floor without rollers, it is good that they are still lifted off the ground to allow air
circulation.
If provided with protective box, the transformers must be placed no closer than 0.2 m from the surrounding walls to allow
air circulation.
In the case in which the enclosure was undersized or poorly ventilated it is advisable to install a forced ventilation system
which can ensure a flow rate of 3.5 - 4 m3 of air per minute for each kW of losses.
If the transformer is equipped with ventilation bars please note that their useful life is approximately 20,000 hours and
that after that period must be replaced. It is also advisable to start them with temperatures above 90°C and switch off
when the temperature is stored at below 80°C.
5.7 Protection against overvoltages
To protect the transformer from overvoltage at power frequency or of atmospheric origin, adequate surge arresters must
be installed. They need to have technical characteristics depending on the level of insulation of the transformer and on
the characteristics of the HV distribution system.
Possible equipment for the correction of the power factor connected close to the transformer must be equipped with
limiters for the inrush current in order to prevent the generation of transient overvoltages.