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Phase Converters - 240/1 to 208/3

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    Phase Converters - 240/1 to 208/3

    Good morning.
    We have an upcoming application (restaurant reno and expansion) where the existing service is 240/1. There is a planned service upgrade to 208/3. But, that upgrade will take place maybe 6 months AFTER the completion of the reno/expansion. So...I think that the HVAC equipment (the only stuff that needs 3-phase) will need to run from Phase Converters before the upgrade. There will be 3 AHUs and 3 Condensing Units. I think 10 tons each.
    I plan on designing the new Elec equipment with 3-phase distribution and using only two phases in this interim period.
    This gets a little tricky, but I think we can make it happen.
    I've not specified Phase Converters before, and am looking for a little guidance. Anyone have preferred manufacturers? Anyone ever RENTED them for 6 months? Rotary? Static? One for each piece of HVAC equip?

    Thanks In Advance for any insight/advice.

    #2
    My experience with rotary and static converters is there is unbalance voltage and current in most instances - not so much of a problem if motors are oversized, but if running a motor near it's full load rating or even into service factor can be a problem. Problem is worse if the motor load varies as it is hard to compensate for changes in load on the fly. Rotary might be better, in such cases but will still have some of this issue. Static converters are best suited for steady loads as you fine tune them by adjusting taps in the capacitors to achieve as optimal balance as possible, but a change in load needs re tuning to get optimal balance again.

    Keep in mind you will not have 120 volts to neutral in either case on your derived phase.
    I live for today, I'm just a day behind.

    Comment


      #3
      Seems like an expensive way of doing things. If you can spend the same amount of money* and get the new service now, I'd do that. Is only the building's service equipment single-phase and the 3-phase just needs to be run down a pole or does the PoCo need to install transformers/etc?

      * buy, install, and remove the converters, plus whatever would be spent on the new service equipment.

      Comment


        #4
        building is served (underground) from a 1 phase transformer on a nearby pole. So the utility (PG&E, this is in San Fran) has some work to do. All would LOVE to get a new service now, but, need to wait for the utility to do their work first.
        And, our client does not wish to wait (sound familiar?).
        So I need to find a way to get them up and running on 1 phase.
        And, just for kix, I also need to make sure that there is adequate kw capacity in this guy....HVAC guys think they need a lot.

        Comment


          #5
          and, fortunately, there is 3-phase on the nearby pole line

          Comment


            #6
            Can you use vfd's or perhaps the equip already has them?
            they need oversized by ~sqrt 3

            Comment


              #7
              Originally posted by Ingenieur View Post
              Can you use vfd's or perhaps the equip already has them?
              they need oversized by ~sqrt 3
              I don't know what rating the OP needs (or I missed it) but there are a number of mainstream drive companies that do single phase in, three phase out.
              Si hoc legere scis nimium eruditionis habes.

              Comment


                #8
                Originally posted by Besoeker View Post
                I don't know what rating the OP needs (or I missed it) but ...
                A typical 10-ton HVAC package or condensing unit would need about 12 kVA.

                Now, he says these are split systems, so in addition to the condensing units, we have three air handlers that also need power. A 10-ton air handler will probably be 3-phase equipment as well, about 2 kVA each.

                Air handlers might complicated the matter greatly because whereas condensers are often located near one another and fed from the same panel, it is quite common that air handlers will be close to the space they condition, and are often fed from their nearest panel.
                Last edited by MAC702; 10-05-17, 01:27 PM.

                Comment


                  #9
                  10 ton Splits. And TWO systems, not Three, as I had previously thought.
                  CUs are 45 MCA, 208/3 (16kw)
                  AHUs are 67 MCA, 208/3 (24kw), which includes 10 kw each for elec heat.
                  Totals about 80 kw.

                  Comment


                    #10
                    Originally posted by raberding View Post
                    ...AHUs are 67 MCA, 208/3 (24kw), which includes 10 kw each for elec heat...
                    I'm assuming these are heat pumps with auxiliary electric heating? If so, you may be able to get by for the hopefully-only-six-months without needing the auxiliary heating strips. This would reduce your AHU requirement drastically.

                    Comment


                      #11
                      Originally posted by MAC702 View Post
                      A typical 10-ton HVAC package or condensing unit would need about 12 kVA.

                      Now, he says these are split systems, so in addition to the condensing units, we have three air handlers that also need power. A 10-ton air handler will probably be 3-phase equipment as well, about 2 kVA each.

                      Air handlers might complicated the matter greatly because whereas condensers are often located near one another and fed from the same panel, it is quite common that air handlers will be close to the space they condition, and are often fed from their nearest panel.
                      Thank you for the information, sir.
                      Si hoc legere scis nimium eruditionis habes.

                      Comment


                        #12
                        Do the units have basic across the line started compressors?

                        Air handlers very well may be single phase even though the compressors are three phase.

                        Why will it take so long to get three phase service if there is already three phase primary on the pole?

                        Is the existing single phase transformer large enough to handle the load? If not you may have to wait for POCO regardless.
                        I live for today, I'm just a day behind.

                        Comment


                          #13
                          ...re Why will it take so long...? Dunno. It's PG&E. In San Francisco.

                          The Existing service is 400A at 240/1. We are looking at ways of reducing some of our load. Like using only One of the splits (temporarily sharing ducts) if we can do it during a temperate season.

                          Comment


                            #14
                            Phase Converters - 240/1 to 208/3

                            This is going to get pricey real fast. Rotary Phase converters have come a long way in the last ten years. Having a 240 1P feed and a 208 3P need complicates things. Lots of the Rotary Phase Converters are listed in Horsepower not in VA, Amps, Watts, etc but usually have a Badge Plate with HP and Amperage Info. The Horsepower is typically the rating of the Motor being used as a rotating Transformer to come up with the missing phase. So a 60 Horsepower range is close to what you are after for a 50 Amp need but I believe you will have an issue with obtaining 208 Volts; it will most likely be 240 3P.
                            I would suggest looking at some of the YouTube videos to come up with some of the better Builders / Manufacturers and contact them for the ability to purchase a System that will take the incoming power and deliver a different base output. Worst case would be to temporarily install a Transformer to drop it down to 208 3P in the proper configuration so everything you are expecting from the final POCO drop exists now.
                            If the Refrigeration Compressors can operate on 240 3P, you pretty much have it made with Rotary Phase Converters. You will need to compare the economics of 1 large Rotary Phase converter versus one for each of the Refrigeration Compressor units.
                            JimO

                            Comment


                              #15
                              Originally posted by jimo144 View Post
                              ...If the Refrigeration Compressors can operate on 240 3P...
                              Don't know what equipment he's getting, but 10-ton condensers are definitely out there that operate on both 208 and 230 (240) nominal 3Ø voltages. Perhaps even most of them.

                              Comment

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