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Line current. Wye inverter to Delta service

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    #16
    Originally posted by ggunn View Post
    I'm pretty sure that the current in the individual conductors from a given inverter to a service will be the same as the line current irrespective of whether the inverter is wye or delta connected; I don't know how to state it more simply than that. The OCPD on them is the same either way. Maybe that's not what you mean by phase current, hence semantics.
    Do we agree on the following? Three single phase inverters connected to a three phase system as in post #14. Say its a regular 208 service. Inverters are thus 208V, say 32 amps. That is 20KW total of inverters (208)(32)(3). Three phase power is W=(V)(I)(1.732) so current is 55.5 A or 1.732 times the inverter or phase current. The currents I am referring to as being different are the 32 amps and the 55.5 amps. (phase and line respectively). Are we each talking about different currents or points of measurement?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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      #17
      I made an Excel spreadsheet that did all the calculations in vector format for deriving line currents based on phase currents of delta connected inverters. I did it just to play around with unbalanced inverters in delta connections to see how the line currents and phase relationships change. I recommend doing it, very educational.

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        #18
        Originally posted by pv_n00b View Post
        I made an Excel spreadsheet that did all the calculations in vector format for deriving line currents based on phase currents of delta connected inverters. I did it just to play around with unbalanced inverters in delta connections to see how the line currents and phase relationships change. I recommend doing it, very educational.
        yes it gets a lot more complicated in the unbalanced case, I wasnt going to go there
        Ethan Brush - East West Electric. NY, WA. MA

        "You can't generalize"

        Comment


          #19
          Originally posted by ggunn View Post
          I'm pretty sure that the current in the individual conductors from a given inverter to a service will be the same as the line current irrespective of whether the inverter is wye or delta connected
          Say you have a group of 3 single phase inverters and a feeder from that group of inverters consisting of 3 ungrounded conductors and possibly a grounded conductor. The current in a feeder ungrounded conductor is the "line" current. The current through an inverter is the "phase" current.

          If the inverters are wye connected, then each feeder ungrounded conductor is connected to one inverter with no other connections. That means line current = phase current.

          If the inverters are delta connected, then each feeder ungrounded conductor is connected to two inverters. The line current on that feeder ungrounded conductor is the vectorial sum of the two phase currents, one from each connected inverter. If the inverters are 120 degrees out of phase, the magnitude of the line current will be sqrt(3) times the phase current.

          Cheers, Wayne


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            #20
            Originally posted by wwhitney View Post

            If the inverters are delta connected, then each feeder ungrounded conductor is connected to two inverters. The line current on that feeder ungrounded conductor is the vectorial sum of the two phase currents, one from each connected inverter. If the inverters are 120 degrees out of phase, the magnitude of the line current will be sqrt(3) times the phase current.
            And if the phase currents from two connected inverters are IPh1 and IPh2 with a phase angle Ø between them, then the resulting line current on the feeder conductor at that connection will be sqrt( IPh12 + IPh22 + 2 IPh1 IPh2 cos Ø ). If both of these two phase currents are defined as flowing into this connection, then Ø is 60 degrees (a180 flip from 120 degrees).
            So if the inverters were both 10 amps then the line current output is sqrt( 102 + 102 + 2 x 10 x 10 x cos(60) ) = sqrt(100 +100 + 2 x 10 x 10 x 0.5 ) = 17.32 amps = sqrt(3) x 10 amps. If the inverter currents are different from each other then you can substitute those in the formula.

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              #21
              Originally posted by electrofelon View Post

              Do we agree on the following? Three single phase inverters connected to a three phase system as in post #14. Say its a regular 208 service. Inverters are thus 208V, say 32 amps. That is 20KW total of inverters (208)(32)(3). Three phase power is W=(V)(I)(1.732) so current is 55.5 A or 1.732 times the inverter or phase current. The currents I am referring to as being different are the 32 amps and the 55.5 amps. (phase and line respectively). Are we each talking about different currents or points of measurement?
              Say you have two 100kW 3P inverters, one connected wye and the other connected delta, both running at capacity. You put your clamp ammeter around the output conductors (one at a time, of course) and take measurements. Do you see a difference in current between the conductors from the wye inverter and those from the delta inverter? I don't think you will. There are inverters that can be connected either way and they don't quote different output current or required OCPD for the different connections.

              It's why I mentioned semantics; the current in those conductors is what I know as "phase current" and it's always the same as line current for a balanced 3P circuit in the same way that the current in both conductors in single phase 240V is the same as the line current; maybe the term means something else to you.
              Last edited by ggunn; 10-11-19, 07:29 PM.

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                #22
                Originally posted by ggunn View Post

                Say you have two 100kW 3P inverters, one connected wye and the other connected delta, both running at capacity. You put your clamp ammeter around the output conductors (one at a time, of course) and take measurements. Do you see a difference in current between the conductors from the wye inverter and those from the delta inverter? I don't think you will. There are inverters that can be connected either way and they don't quote different output current or required OCPD for the different connections.

                It's why I mentioned semantics; the current in those conductors is what I know as "phase current" and it's always the same as line current for a balanced 3P circuit in the same way that the current in both conductors in single phase 240V is the same as the line current; maybe the term means something else to you.
                Ahh ok I think I see where the misunderstanding is. For the purpose of this thread when we are talking about "delta connected" or "wye connected" we are NOT referring to the type of three phase system that the inverters are interconnecting to. We are talking about connecting three single phase inverters in a delta or wye configuration (mostly delta, forming a wye connection from three single phase inverters would be odd and maybe not even work).

                Regarding "phase" vs "line" values, again these are well established and not semantic. I believe you are incorrect to interchange phase and line (although in a wye connection line current is the same as phase current but not in a delta). I think if you google a few articles or look at a text you will see what I mean.

                https://www.allaboutcircuits.com/tex...onfigurations/

                Edit: perhaps reread my post #16. That example has the different phase and line currents.
                Ethan Brush - East West Electric. NY, WA. MA

                "You can't generalize"

                Comment


                  #23
                  Originally posted by electrofelon View Post
                  ...forming a wye connection from three single phase inverters would be odd and maybe not even work.
                  It does work, or at least it did with the old style transformer coupled inverters. I did it several times back in the day. Not lately, though; there are a lot more smaller 3P inverters available now than there used to be. Granted, I haven't tried it with transformerless inverters, but I did build a system that way with (42) 6000W Sunny Boys - fourteen of them per phase connected phase to neutral on a 480v 3P service.

                  And if you will reread the OP, he was talking about a single inverter, not three single phase inverters. The output current from a single three phase inverter is the same per phase conductor and the same as the line current whether it is connected to a delta or wye service. I think that was his question.
                  Last edited by ggunn; 10-11-19, 08:32 PM.

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                    #24
                    Nobody wants to make a diagram?

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                      #25
                      Originally posted by ggunn View Post



                      And if you will reread the OP, he was talking about a single inverter, not three single phase inverters. [color=red]The output current from a single three phase inverter is the same per phase conductor and the same as the line current whether it is connected to a delta or wye service [/color]. I think that was his question.
                      Yes I absolutely agree with the red. Most of the confusion here comes from using "delta" and "wye" in different contexts. One use is the type of electrical service, specifically the transformer connection serving the service. The second is the connecting of three single phase sources/loads/inverters into delta and wye configurations and the resulting current and voltages "seen" by the single phase components. The latter is what I was talking about during out back and forth and for that topic "Phase" and "line" have specific meanings. For the former, say, a three phase feeder, "phase current" vs "line current" are essentially synonyms. For a three phase plus neutral circuit, (from a wye) "phase voltage" probably technically means the line to neutral voltage but as far as i know no one really says that and I wouldnt use it. That is my analysis anyway.

                      It does work, or at least it did with the old style transformer coupled inverters. I did it several times back in the day. Not lately, though; there are a lot more smaller 3P inverters available now than there used to be. Granted, I haven't tried it with transformerless inverters, but I did build a system that way with (42) 6000W Sunny Boys - fourteen of them per phase connected phase to neutral on a 480v 3P service.
                      Ok cool. But for some reason when I said "wye connected" I was thinking of a three inverters wye connected with only the three phases connected and the star point isolated. That is what I was questioning as to whether it would work. Connecting single phase inverters line to neutral to a three phase system is fine other than the voltages that would be required, 120V or 277 volts and I am not aware of any currently that have that voltage options.
                      Ethan Brush - East West Electric. NY, WA. MA

                      "You can't generalize"

                      Comment


                        #26
                        Originally posted by electrofelon View Post

                        Yes I absolutely agree with the red. Most of the confusion here comes from using "delta" and "wye" in different contexts. One use is the type of electrical service, specifically the transformer connection serving the service. The second is the connecting of three single phase sources/loads/inverters into delta and wye configurations and the resulting current and voltages "seen" by the single phase components. The latter is what I was talking about during out back and forth and for that topic "Phase" and "line" have specific meanings. For the former, say, a three phase feeder, "phase current" vs "line current" are essentially synonyms. For a three phase plus neutral circuit, (from a wye) "phase voltage" probably technically means the line to neutral voltage but as far as i know no one really says that and I wouldnt use it. That is my analysis anyway.
                        You see? We agreed all along.

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                          #27
                          Originally posted by jaggedben View Post
                          Nobody wants to make a diagram?
                          I just drew one on my computer screen with a Sharpie. Can't you see it?

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