Inverter sizing mystery

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  • GCE
    Platinum Member

    • Jun 2017
    • 1473

    #16
    No closer , have spoken to numerous people that are involved with designing including supply and always the same answer - Can't be possible

    Config would be star and there is nowhere else that power can be coming from

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    • Derlyn
      Platinum Member

      • Mar 2019
      • 1748

      #17
      Still working on this "mystery".

      I dont know 3 phase inverters.
      Dave mentioned that a 12Kw 3phase inverter consists of 3 single phase 4Kw inverters.

      Now the question is, what is the phase voltage of each 4 Kw inverter ? 220v or 380v ?

      Comment

      • Derlyn
        Platinum Member

        • Mar 2019
        • 1748

        #18
        I somehow don't think there's a problem with your physical current readings.

        The "mystery" is somewhere in the power calculation in my opinion. Now to find it.

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        • GCE
          Platinum Member

          • Jun 2017
          • 1473

          #19
          Originally posted by Derlyn
          Still working on this "mystery".

          I dont know 3 phase inverters.
          Dave mentioned that a 12Kw 3phase inverter consists of 3 single phase 4Kw inverters.

          Now the question is, what is the phase voltage of each 4 Kw inverter ? 220v or 380v ?
          It is 3 phase inverter but you can draw single phase supplies of each phase and if balanced then 4kw on each phase , most allow up to 70% imbalance on the phases

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          • Dave A
            Site Caretaker

            • May 2006
            • 22810

            #20
            Originally posted by GCE
            These are 2 pics of the inverter screen running on grid in parallel
            On the load side under one with a tong tester I get 25amps and on the other 14 amps

            [ATTACH=CONFIG]8933[/ATTACH]
            [ATTACH=CONFIG]8934[/ATTACH]
            I'm not sure why, but those images are not available.
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            • GCE
              Platinum Member

              • Jun 2017
              • 1473

              #21
              Resized - might have been the problem

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              • Derlyn
                Platinum Member

                • Mar 2019
                • 1748

                #22
                How is it possible that the load power can be higher than the grid power ? I would have expected the grid to be slightly higher than the load on all 3 phases..

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                • Dave A
                  Site Caretaker

                  • May 2006
                  • 22810

                  #23
                  Originally posted by Derlyn
                  How is it possible that the load power can be higher than the grid power ? I would have expected the grid to be slightly higher than the load on all 3 phases..
                  The grid power consumption is slightly higher than the load power consumption.

                  One curiosity is the power draw is similar on both inverters, but the current on one is nearly double the current reported on the other.
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                  • GCE
                    Platinum Member

                    • Jun 2017
                    • 1473

                    #24
                    Originally posted by Dave A
                    The grid power consumption is slightly higher than the load power consumption.

                    One curiosity is the power draw is similar on both inverters, but the current on one is nearly double the current reported on the other.
                    Slightly ? - grid shows 25Amp on one inverter which should be around 5Kw and yet it show +/-1 and the 2nd inverter 14 Amps which should show +/-3Kw yet both show 1 Kw

                    I thought CT's were in wrong position but when we ran off grid it started the confusion

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                    • Dave A
                      Site Caretaker

                      • May 2006
                      • 22810

                      #25
                      Originally posted by GCE
                      Resized - might have been the problem

                      [ATTACH=CONFIG]8937[/ATTACH]
                      [ATTACH=CONFIG]8938[/ATTACH]
                      Originally posted by GCE
                      Slightly ? - grid shows 25Amp on one inverter which should be around 5Kw and yet it show +/-1 and the 2nd inverter 14 Amps which should show +/-3Kw yet both show 1 Kw

                      I thought CT's were in wrong position but when we ran off grid it started the confusion
                      I was looking at the on-grid-supply power numbers. Looks like there's a 100w overhead on each inverter according to the power report.

                      I agree the current reports raises red flags - properly.
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                      • GCE
                        Platinum Member

                        • Jun 2017
                        • 1473

                        #26
                        Originally posted by Dave A
                        I was looking at the on-grid-supply power numbers. Looks like there's a 100w overhead on each inverter according to the power report.

                        I agree the current reports raises red flags - properly.
                        Yip and that is where I come back to the KW readings on inverter not matching actual draw
                        The inverter picks up the current, total , at +/-38 amps which is what I get on the combined load

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                        • Derlyn
                          Platinum Member

                          • Mar 2019
                          • 1748

                          #27
                          The total grid power( 3 pases added together) is higher than the load, but there are individual phases where the load power exceeds the grid power. That's what I was referring to.

                          Another question. You said there are 4 escalators if I'm not mistaken. Does each inverter feed 2 escalators or do both inverters , in parrallel, feed all 4 escalators ?

                          Comment

                          • GCE
                            Platinum Member

                            • Jun 2017
                            • 1473

                            #28
                            Originally posted by Derlyn
                            The total grid power( 3 pases added together) is higher than the load, but there are individual phases where the load power exceeds the grid power. That's what I was referring to.

                            Another question. You said there are 4 escalators if I'm not mistaken. Does each inverter feed 2 escalators or do both inverters , in parrallel, feed all 4 escalators ?
                            Inverters are in Parallel and supply all 4
                            Discrepancy on phases can be motor loads and power sharing between phases - You often find 1 phase on a motor drawing less and that is generally due to incoming powerfactor - Can be as much as 10% in extreme cases

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                            • Dave A
                              Site Caretaker

                              • May 2006
                              • 22810

                              #29
                              How about the phases on the one inverter (the one with the high current readings) are wired incorrectly?

                              My read is the evidence suggests the power draw readings are the most likely to be reasonably accurate. (DC draws off the battery - both in current and SOC after a couple of hours, one inverter fairly close to 3kW across all measures).
                              So what could cause a massive current discrepancy in a star supply to delta load situation?
                              In a rig installed by an IT guy.
                              On a supply with a phase rotation that runs the wrong way (compared to the rest of the country).
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                              • GCE
                                Platinum Member

                                • Jun 2017
                                • 1473

                                #30
                                The mains supply is a star config and transformer is 20m away so I don't see any reason that there should be a change

                                The phase rotation - don't see that making any difference

                                Can only think that it is PF of the motors and incoming PF

                                On the incoming there is a power factor correction panel that is working and keeping PF at 0.98

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