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Ungrounded 480x240 delta to delta 3ph 3w voltage to ground reading

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    #16
    I agree the ungrounded system is not for this application.

    As for faults, at first discovery the system was ungrounded. One breaker continued tripping. Measuring one leg to ground with voltage on several disconnects. (using wiggy type meter)
    Turned off all the disconnects isolated the disconnect to that breaker, as soon as it was turned on the breaker would trip, removed the wiring from the breaker and disconnect and the voltage to ground was gone.

    All welders are dual voltage and are all production use, it is common to see 2 or 3 welders running on one disconnect. Figure the breaker trips when all are simultaneously in use, this also could be causing the receptacles to begin melting.

    Fuses were blowing some time ago, only the breakers have been tripping. Checked disconnects, fuses have been replaced with 60A FRN-R-60 time delay fuses. Some are wired with #8 and some #6.

    So, the breaker is doing as it should, just going bad from constant over-current usage. Using dedicated fused disconnects, correctly sized breakers and install new receptacles, should correct this.

    Load for the welders needing 230v is very low going to a smaller KVA would work, nothing needs the 240v.

    480 service is fine, three of the larger welders are hard wired to dedicated disconnects running fine.
    Moving to 480 from the 600A panel may be best.

    Cost compared moving to 480 or to use the ungrounded system, both require additional induvial disconnects. Cost for a detection system or corner grounding.

    To use the 240 system, you indicate new panel and breakers; can you explain further. The 3-phase panel has straight voltage 240v breakers.

    I may need further advice on the plan for 480 600A panel, with the 200A disconnect bussed, probably should post under electrical calculations.

    Thank you for all your support.

    Comment


      #17
      Niiice.

      To refeed from the utility 480, most likely I would be considering 1 1/4" or 2" conduit run to a new 480 panel board close to the load. There is also the consideration of reusing as much of the existing distribution wiring in an economical manner.

      So you would already have a 480 V feed at the 240 delta transformer location. You may be able to reuse that feed, even if the neutral was not carried to it. That may be one location for a new 480 V panel board and breakers, refeed the existing load out from there with some reuse of the existing branch circuits tied on after the old transformer, but now refed out at 480, which will give you a lot more current and kVA per existing circuit.

      Most likely the existing load had no neutral and the reconfig to 480 will not take a neutral either, but care and following the manufacturer's instruction are necessary for this. It's may be possible to refeed most of the dual voltage load without a neutral, from where the 112 kVA tranny is now.

      So one new 480 panel at the old tranny location and one new 480 feeder and panel board close to the load.

      I mentioned new panel board and breakers earlier because it is a lot cheaper to buy a new panel board fully loaded with breakers as a package, than it is to buy or have the panel already but add breakers one by one.

      Still lot of money to spend. You can put together plan A, plan B and looks at each costs. I would see only plan A at this point with plan B possibly retaining the 240 delta. Some money needs to be spent to get from B to A. But it sounds like they got all they could out of the existing system and it is going to cost them money one way or the other.

      You could try to justify some costs savings in efficiency gains eliminating the dog 240 delta idling losses and shifting them to the utility side.

      For me, the new protective devices and updated outlets and connectors is where I would tell them they are saving money. They can do it right the first time or pay for it ten times over in downtime, injuries, rework, and repeated fixing of the same things like clockwork going forward. Improvements considered here should be extremely reliable, safer, and lower cost over time.

      Would only take one OHSA complaint to make the entire upgrade bid look cheap.

      Retaining the existing 240 delta with corners grounding, the new panel board would be loaded with 1 and 2 pole breakers for single and three phase, but a very substantial type of properly rated breaker.
      Lasciate ogne speranza, voi ch'intrate

      Comment


        #18
        I am thinking you may be able to tap the existing transformer feeder to power the new 480 panel. New panel location likely adjacent to the existing tranny load side panel board.

        With both systems powered at the same time you would be able to make the load side changes one at a time, each equipment reconfig to 480 V will take skill and time.

        Having both systems powered and running gives the schedule a huge competitive advantage, makes the job doable within some civilized and necessary time frame,

        Still I know how hard it is to pry money out of the customer's (accountant's) pocket. They all want to run their men and equipment as hard as they can (costing more over time).

        Lasciate ogne speranza, voi ch'intrate

        Comment


          #19
          I've not followed all the details of this thread, but could a grounding transformer such as a zig-zag be an option instead of corner grounding the delta? It would offer some advantages but the costs would have to be considered.

          Comment


            #20
            Originally posted by synchro View Post
            I've not followed all the details of this thread, but could a grounding transformer such as a zig-zag be an option instead of corner grounding the delta? It would offer some advantages but the costs would have to be considered.
            My concern would be, most of the people encountering the system would have no understanding of it exactly as its parts. They would only have some guess that it is like all the others and at some level, has the engineering controls like breakers that trip when they have to.

            Consider the environment. The workforce probably does not have their own electrician or EE on staff. But they run 100kW of production welders. They are guys who like to make sparks with electricity. They have hand held guns that can pop studs into the I beam webbing for poured concrete applications.

            They have no idea how it works but the guys who do that job like that gun. They need just a copy of some standard (extremely reliable) system that their equipment manufacturer specifies. If you try anything non standard, no one will understand its operation and it will be the first thing chopped out when they have trouble.

            They make their living melting stuff with that 112 kVA 240 floating delta.
            Last edited by __dan; 08-15-19, 02:02 PM.
            Lasciate ogne speranza, voi ch'intrate

            Comment


              #21
              Agreed with most of what was said. But here’s another potential issue even if you fix the ground faults. An intermittent (arcing) ground fault on an ungrounded system acts like a charge pump. It jacks up the fault voltage until it finds the weakest insulation anywhere in the system. I mean anywhere. This is the only thing that keeps the voltage from going infinitely high. Typically something burns up at 6 to 8 times system voltage so around 1500-2000 V in your case. I suspect this might be what is burning up everything even without double ground faults. This is typically what happens. Once you fix this, expect electrical issues to drop to about 25% of what you are experiencing now.

              Comment


                #22
                A brief intro of this application history.
                Information provided, this application was working fine and we had many more welders running so what’s the problem now.
                Issues:
                Fuses blowing, breakers tripping & failing, melting plugs, receptacles, extension cord connectors and wiring at disconnects.
                Cause:
                Someone just didn’t do it right, could be just like a loose wire.
                Request:
                Add more welder receptacles also fix plugs, receptacles and extension cords.

                Observation:
                Stress from the magnitude of welders running on the same overamped circuits. With two and three welders running on the same disconnects with oversized fuses, and so many running at the same time. Possibility of an unbalanced load on one phase at the panels causing failure to one leg on 3-pole breakers. Exceeding the load on the panel, transformer and only a primary breaker.
                Suggested Solution:
                Wiring from the 240v panel to the disconnects needs to be tested for faults
                Removal of the delta xmfr and install a smaller wye to provide necessary 230v single phase for only three welders all other welders are a dual voltage. Install 480V 3Ph MLO panelboard adjacent to location of welders.
                All of the manufacture’s manuals show individual disconnect adjacent to the welders. Art. 630 also indicates disconnection means for each welder. Plan to install the 480 panel within 50’ of all welders and add safety switches to comply with 630.13.

                Thank you all for the support

                Comment


                  #23
                  Sounds good. They have to spend something substantial just to repair and get back where they were. Moving the 480 loads to 480 will have a lot of advantages, new breakers and connectors being just one. Reliability and safety would be the big one, especially if they did not know how to care for the floating delta.

                  Once some of the load moves, you may end up with more good used spares from the old 240 V connectors and disconnects.

                  The 112 kVA delta secondary is a big monster. But other than the larger idling losses, I don't see any driving need to change it. Idling loss would be the number I would want to know, If the idling losses will pay for a new properly sized transformer, it may be justified. If the idling losses are never going to pay for a new transformer, I would certainly be planning on keeping it. Adding the corner ground to the delta and repairing the reduced size 240 V distribution system with spare parts from the converted loads, is only a small bit of work from where they are now.

                  If they are going to continue as a production welding shop, reducing and adding load to the 240 V (corner grounded) delta could happen routinely.They may have load now and in the future for it.
                  Lasciate ogne speranza, voi ch'intrate

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