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Soft-starts at high altitudes


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#1 boomer

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Posted 28 June 2004 - 09:38 AM

Hi, is there anyone who has ever used a softstarter at altitudes higher than 2000m.
The specifications of the soft-starters I know of are rated as follows: "above 1000m derate linearly by 1% unit of full load current per 100m to a maximum altitude of 2000m."

Does the derating change above 2000m or it is impossible to use it at those altitudes?

#2 marke

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Posted 28 June 2004 - 11:28 AM

Hello boomer

Welcome to the forum.
Yes it is very possible to operate soft starters at higher than 2000M. I have done with not problems.
The issue is that the air get less dense with altitude and therfore the cooling efficiency drops.
Standard rules are used, but are not correct. You really need to calculate the rating based on the altitude and starting conditions.
Companies like AuCom Electronics, NHP and Danfoss have software that will allow these calculations.

I suggest that you contact your supplier and see if they can help. If not, find a supplier that can.

Best regards,

#3 Guest__*

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Posted 01 July 2004 - 09:46 PM

Hi. Im a little confussed about the power factor of a motor during a soft start. ive read in some pages that when the soft start is being performed, the power factor is very high. But what happens when the motor is working at full speed? Then the power factor is corrected by capacitors or the microprocessor still works?

#4 marke

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Posted 04 July 2004 - 07:28 PM

The power factor of a motor operating under very high slip, is very low. As the slip is reduced, the power factor increases up to a maximum at almost full speed. At full speed and light load, the power factor drops.
The soft starter does not change the power factor of the motor during start.
Best regards,

#5 jraef

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Posted 03 August 2004 - 08:38 PM

Back to the altitude issue, another important concern above 2000m is voltage derating as well. The rarified air has a lower dielectric and as a result, some spacings may become inadequate for the design voltage. This is usually not a problem with low voltage designs since most are built with 600V or 690V spacings and are used at lower voltages anyway, but the original post did not mention working voltage.

At 2000m, rated equipment voltage must be lowered by 11.5%, so if it was a 600V design, the maximum voltage is still 531V. If operating at say 380V this is not a problem. However if it is a max. 415V design it gets derated to only 367V.
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