# Derating for altitude?



## erics37 (May 7, 2009)

te12co2w said:


> I was looking for a drive for a single phase 7.5hp centrifugal irrigation pump. A square d rep told me they could supply one that would act as a phase converter and a soft start. I called my distributor and had him check it out to get me the right thing. He called back and said that at my elevation SQD would not guarantee the drive. This was an Altivar 61. He said they are tested for 3000'. They didn't have one to do the same thing after derating for altitude. This got me to wondering what is in one of these things that would need to be adjusted for altitude? I know internal combustion motors need to be adjusted because of thinner air at higher altitudes. Also baseboard heater elements. But why would altitude affect coils, capacitors, and electronic components? Can't dissipate enough heat? Thanks in advance.


I never gave that any thought before! Most of the work I do is pretty close to sea level  Your heat dissipation idea sounds plausible, though. But I don't see how altitude would effect the actual flow of current (besides the heat thing). I mean, satellites have electrical stuff and they work in space.


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## te12co2w (Jun 3, 2007)

I know. I just can't see the problem. I don't think altitude makes motors draw more current. I've bought and installed plenty of motors and never have I seen them draw more current than nameplate amperage.


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## drsparky (Nov 13, 2008)

Ask square D.


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## Bob Badger (Apr 19, 2009)

Motors do not use more current at higher altitudes but they will run hotter and may need to be derated as well.

When the air is less dense the amount of cooling it will provide is reduced.

So basically the equipment will run hotter as the altitude increases.


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## cdnelectrician (Mar 14, 2008)

I remember reading something about ABB drives and operating them at higher altitudes...I'll dig out my book on them and see if it explains anything.


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## Bob Badger (Apr 19, 2009)

From an EC&M article about VFDs




> Altitude affects the heat dissipation capability of the heat sink and units in locations at 3300 ft (1000 m) above sea level must be derated. A common rule of thumb is a 2% derating for every 1000 ft above the 3300 ft altitude level.



http://ecmweb.com/mag/electric_understanding_variable_speed_2/


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## drsparky (Nov 13, 2008)

Cool, I will find a place in the back of my hat rack to store that for future reference.


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## John Valdes (May 17, 2007)

How can an AC drive (inverter) operate a single phase motor? It can't. Single phase in and three phase out, yes. You mean you have a three phase motor right?


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## InControl (Mar 20, 2007)

John Valdes said:


> How can an AC drive (inverter) operate a single phase motor? It can't.



Thats a strong statement. Do you wish to retract?


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## acmax (Apr 20, 2009)

John Valdes said:


> How can an AC drive (inverter) operate a single phase motor? It can't. Single phase in and three phase out, yes. You mean you have a three phase motor right?


:blink:


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## 5volts (Jan 11, 2008)

John Valdes said:


> How can an AC drive (inverter) operate a single phase motor? It can't. Single phase in and three phase out, yes. You mean you have a three phase motor right?


AC inverter drives for single phase operation exist. They either change the frequency of the line voltage a single phase motor sees or change the voltage seen by the motor.http://www.freesmileys.org​


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