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What is the meaning of the term natural convection and forced convection in the data sheet under environment for the Altivar Process drives?

Issue: 
What is the power dissipation in Watts for natural convection and forced convection?

Product Line:
Variable Speed Drives.

Environment:
Altivar Process, ATV630, ATV650 and ATV930.

Cause:
How to understand the difference between the natural convection and forced convection.

Resolution:

The table for ATV630 fits ATV650 and ATV930 as well. As you know the difference between ATV630 and ATV650 is an enclosure and the switch on ATV650 body (option). But the losses generated by ATV630 and ATV650 are the same.
Regarding the forced cooled area and natural cooled area the situation is following:
Every ATV630, 650 and 930 has internal cooling fan. The heat generated by ATV can be transferred to the ambient environment thru two ways:
1. via the forced ventilation - it means internal fans blow the air thru ATV power parts and this forced air removes heat from ATV (mostly form power parts)
2. via natural heat transfer. Every part of ATV that has greater temperature than ambient environment causes heat transfer.
The reason we provide two parts of heat losses is following:
- If you install ATV630 in the cabinet, then calculate total losses as forced losses + natural losses if you want to design ventilation of the cabinet
- If you use kit for flush mounting, then forced air is blown outside the enclosure (the air can be with dust) while all electronic circuits are naturally cooled from the air inside the cabinet. That is why you have to design cooling of enclosure only for natural losses (because forced losses are outside)

As you can notice, high power drives show forced losses much greater than natural losses. It is because IGBT losses increases directly with the current, while losses from electronic circuit does not increases proportionally to motor current.
Use this link to download a copy of the ATV630, ATV650 Installation Manual
https://www.schneider-electric.com/en/download/document/EAV64301/
 
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