ptonsparky
Tom
- Occupation
- EC - retired
How does altitude affect VFD operation? Cooling?
Yes, cooling. The VSDs we usually used were rated to 1000 metres.How does altitude affect VFD operation? Cooling?
Yes. A fan blows a more-or-less constant volume of air, but the density of air decreases as altitude increases. At higher altitudes, there are fewer air molecules available to pass over a heat sink and extract heat.
https://en.wikipedia.org/wiki/International_Standard_Atmosphere
https://www.engineeringtoolbox.com/standard-atmosphere-d_604.html
The thinner air also makes high-voltage electrical apparatus more prone to corona and flashover, but that's not significant unless there are thousands of volts available.
Yes, cooling. The VSDs we usually used were rated to 1000 metres.
Ben Nevis is 1,345 metres. We did a few ski lift drives. But let that pass.With (per Wikipedia) the highest point in UK being 978 metres, not a problem for your local jobs, was it ... ?
With (per Wikipedia) the highest point in UK being 978 metres, not a problem for your local jobs, was it ... ?
Where did you get the 978 metres from?
He used the highest point in England (Scafell Pike, 978 meters), the wretched Sassenach.
Did you ask for UK or England?Ignorant South Carolinian here trusted Wikipedia when I asked for the highest point in UK ... I deserve a flogging.
mea culpa
And Brits too.Did you ask for UK or England?
Often confused by furriners.
Did you ask for UK or England?
Often confused by furriners.
And Brits too.
Did you ask for UK or England?
Often confused by furriners.
Most if not all VFD mfrs provide an altitude de-rating formula for their drives, usually buried in the technical information somewhere. For A-B drives for example they tell you to de-rate the output current by 10% for every 3,300ft (1,000m) above the 3,300ft baseline, or looked at another way, 1% for each 330ft above 3,300ft.
So for 10,000ft elevation, that's 6,700ft over the baseline, / 330ft = 20% de-rate.
It's certainly better than not derating at all, but I wouldn't say it's "conservative", just adequate. At 3000 m altitude, there are 26% fewer air molecules in a given volume of air than at sea level.... In my opinion, 20% de-rate for 3000m (10000 ft) is a good conservative number. ...