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    Altitude

    How does altitude affect VFD operation? Cooling?
    Tom
    TBLO

    #2
    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/Intern...ard_Atmosphere
    https://www.engineeringtoolbox.com/s...ere-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.
    Last edited by drcampbell; 05-29-19, 07:57 AM.

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      #3
      De-rate or additional fans would be the options. Not to difficult for my state but what or how much to change for 10,000 feet? Is it strictly a matter of monitoring the temperature of the VFD and adding fans as the temp increases?
      Tom
      TBLO

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        #4
        I don't have a simple answer. The problem should be reviewed by someone with a flair for mechanical engineering.

        It's a significant-enough problem that Los Alamos National Lab had a standard boilerplate paragraph in their purchase orders and RFQs reminding people that the lab is at a 7000-foot elevation and vendors are expected to assure that their equipment will work there.

        Doing design work after the fact ("adding fans as the temperature increases") is rarely a recipe for success.

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          #5
          Originally posted by ptonsparky View Post
          How does altitude affect VFD operation? Cooling?
          Yes, cooling. The VSDs we usually used were rated to 1000 metres.

          Comment


            #6
            Correct

            Originally posted by drcampbell View Post
            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/Intern...ard_Atmosphere
            https://www.engineeringtoolbox.com/s...ere-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.
            This is absolutely correct, and noted in Air Cooled Refrigeration condensers which are less efficient at elevation. I have noted this for sure at 4500 Ft.
            Microwave Radiation Dangers should be openly discussed

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              #7
              Another consideration though is that at 10,000 feet the outdoor ambient temp is likely lower than many other places. This same aspect applies to anything that you may be trying to sink heat away from and into the air though.
              I live for today, I'm just a day behind.

              Comment


                #8
                Originally posted by Besoeker3 View Post
                Yes, cooling. The VSDs we usually used were rated to 1000 metres.
                With (per Wikipedia) the highest point in UK being 978 metres, not a problem for your local jobs, was it ... ?

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                  #9
                  Originally posted by GeorgeB View Post
                  With (per Wikipedia) the highest point in UK being 978 metres, not a problem for your local jobs, was it ... ?
                  Ben Nevis is 1,345 metres. We did a few ski lift drives. But let that pass.
                  We did drives for gold mines in the Highveld around Johannesburg, elevation close to 2,000 metres. With that and the high ambient temperatures, we fitted fans with higher flow rates.

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                    #10
                    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.
                    __________________________________________________ ____________________________
                    Many people are shocked when they discover I am not a good electrician...

                    I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

                    Comment


                      #11
                      Originally posted by GeorgeB View Post
                      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?

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                        #12
                        Originally posted by Besoeker3 View Post
                        Where did you get the 978 metres from?
                        He used the highest point in England (Scafell Pike, 978 meters), the wretched Sassenach.

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                          #13
                          Originally posted by gadfly56 View Post
                          He used the highest point in England (Scafell Pike, 978 meters), the wretched Sassenach.
                          Ignorant South Carolinian here trusted Wikipedia when I asked for the highest point in UK ... I deserve a flogging.

                          mea culpa

                          Comment


                            #14
                            Originally posted by GeorgeB View Post
                            Ignorant South Carolinian here trusted Wikipedia when I asked for the highest point in UK ... I deserve a flogging.

                            mea culpa
                            Did you ask for UK or England?
                            Often confused by furriners.

                            Comment


                              #15
                              Originally posted by Besoeker3 View Post
                              Did you ask for UK or England?
                              Often confused by furriners.
                              And Brits too.

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