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    5kV Motor Termination

    One of the engineers in my company posted an email asking the following question. I have no answer myself, so I thought I would see if we can get some assistance from the forum members. Here is the situation:

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    I have a 5kV termination challenge that I was wondering if anyone might be able to provide some ideas on.

    I have a 2500HP chiller motor compressor that has shown up on the job site with (2) #2/0 leads per phase off the motor into the motor terminal box. Our designed feeder to the compressor motor terminal box is a single 350 shielded conductor per phase.

    Is anyone aware of a termination/splice kit that can take a single shielded feeder conductor and splice it to two motor conductors?

    We previously were going to use a 3M 5380 Series Pigtail Splice Kit, but even at the largest size, the internal diameter of the boot is not large enough to accommodate the total size of the three conductors and appropriate lugs.

    Short of revising our incoming feeder, does anyone have any experiences or ideas that might work?

    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

    #2
    I don't know why 5 KV motor terminations always seem to be a sore point,the motors come onto the job site with j-boxes to small for stress cone make up or termination options that are untenable because they were not discussed.The motor manufacturers/sales people don't dig into the requiements and that is normally the specifying engineers fault or his designated Vendor Drawing approval sign off guys error or fault.

    Pigtails,bushings,bus bars are all available,,,,,,,,of course you know all that.I realize this doesn't answer the question,I'm just venting.

    A possible option does come to mind tho,,,,,,,,it may be possible for the manufacturer to come aboard and retro fit an approved termination parameter that construction can live with, another would be if the construction schedule will allow it is do a complete motor change out and lastly put the motor in plant stores for a future project/spare and reorder one that fits the bill.

    dick

    Comment


      #3
      Originally posted by dicklaxt View Post
      I don't know why 5 KV motor terminations always seem to be a sore point,the motors come onto the job site with j-boxes to small for stress cone make up or termination options that are untenable because they were not discussed.The motor manufacturers/sales people don't dig into the requiements and that is normally the specifying engineers fault or his designated Vendor Drawing approval sign off guys error or fault.

      Pigtails,bushings,bus bars are all available,,,,,,,,of course you know all that.I realize this doesn't answer the question,I'm just venting.

      A possible option does come to mind tho,,,,,,,,it may be possible for the manufacturer to come aboard and retro fit an approved termination parameter that construction can live with, another would be if the construction schedule will allow it is do a complete motor change out and lastly put the motor in plant stores for a future project/spare and reorder one that fits the bill.

      dick
      I copy your venting....seems mechanical and electrical never coordinate the motor terminal box size and it always comes in to small.

      We have removed the TB that came with the motor and purchased a bigger TB with bus bars and insulators.

      But I was thinking instead of a pigtail termination, make it an inline splice. Perhaps use a compression to 4 hole connector on the field cable and install the stress cone as required. The motor leads would be terminated with compression to one or two hole connectors. the connectors would be bolted together ( washers, belville washers). The exposed section of the bolted connectors and the barrel on the motor leads can be tapped and shrink wrapped. This method would take up more room than a pigtail.

      Comment


        #4
        Originally posted by charlie b View Post
        One of the engineers in my company posted an email asking the following question. I have no answer myself, so I thought I would see if we can get some assistance from the forum members. Here is the situation:

        - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

        I have a 5kV termination challenge that I was wondering if anyone might be able to provide some ideas on.

        I have a 2500HP chiller motor compressor that has shown up on the job site with (2) #2/0 leads per phase off the motor into the motor terminal box. Our designed feeder to the compressor motor terminal box is a single 350 shielded conductor per phase.

        Is anyone aware of a termination/splice kit that can take a single shielded feeder conductor and splice it to two motor conductors?

        We previously were going to use a 3M 5380 Series Pigtail Splice Kit, but even at the largest size, the internal diameter of the boot is not large enough to accommodate the total size of the three conductors and appropriate lugs.

        Short of revising our incoming feeder, does anyone have any experiences or ideas that might work?
        The pigtail usually do not require stress control, so just use standard end terminator on the feeder cable with stress control, single hole compression lug on all three ends and bolt the pigtails to the feeder lug from bothesides with a throughbolt. Tape or heatshrink each connection without stress control, but make sure they are equally spaced and from each other and the peckerhead walls.

        I might be missing your concern..

        Comment


          #5
          300.40 says you need to stress reduction on the shielded cable terminations, stress cones is one of the approved methods for sure,,,,,,, I have never seen a general requirement other than that in the code,we have had clients who said 2.4 KV did not need to be relieved and I think that was do to the length of time it would take to deteriorate,,,,,,,,,,,

          What are some other methods of stress reduction,maybe distance alone.

          dick

          Comment


            #6
            Originally posted by dicklaxt View Post
            300.40 says you need to stress reduction on the shielded cable terminations...
            As Laszlo said, the motor leads are not shielded cable, therefore they do not need stress relief.

            There was a period of time when the NEC did not require stress relief for 5KV, or less, systems. Many people, including manufacturers, live in the past.
            Just because you can, doesn't mean you should.

            Comment


              #7
              Yes I know but how do we know the NEC was talking about the pigtail and not the feeder,,,,,,,,,,,,,,,if the insulation fails on the pigtail then I would think the manufacturer would be liable but if the insulation failed on the feeder that nelongs to the owner..............I wouldn't take it to court but it seems something is amiss.

              dick

              Comment


                #8
                Originally posted by dicklaxt View Post
                Yes I know but how do we know the NEC was talking about the pigtail and not the feeder,,,,,,,,,,,,,,,if the insulation fails on the pigtail then I would think the manufacturer would be liable but if the insulation failed on the feeder that nelongs to the owner..............I wouldn't take it to court but it seems something is amiss.

                dick
                NEC is not intended to cover equipment design, so they would not be talking about the pigtail. Nothing seem to be amiss to me....

                Comment


                  #9
                  Originally posted by dicklaxt View Post
                  Yes I know but how do we know the NEC was talking about the pigtail and not the feeder,,,,,,,,,,,,,,,if the insulation fails on the pigtail then I would think the manufacturer would be liable but if the insulation failed on the feeder that nelongs to the owner..............I wouldn't take it to court but it seems something is amiss.

                  dick
                  Originally posted by weressl View Post
                  The pigtail usually do not require stress control, so just [COLOR=red]use standard end terminator on the feeder cable with stress control[/COLOR], single hole compression lug on all three ends and bolt the pigtails to the feeder lug from bothesides with a throughbolt. Tape or heatshrink each connection without stress control, but make sure they are equally spaced and from each other and the peckerhead walls.

                  I might be missing your concern..
                  We use Raychem MCK-5V kits for our motors. The specs I have don't indicate an internal ID of the boot and I don't have a kit handy to check. They do have stub kits available that handle up to 750kcmil whereas the largest 3M 5380 kit is for 500kcmil, may be worth a call to Raychem to get an internal ID. I know tape seems to be a thing of the past but that is always an option.
                  Last edited by eric9822; 07-28-10, 06:15 PM. Reason: Fat fingered spelling corrected.

                  Comment


                    #10
                    Right on Eric thanks for pointing that out,,,I need to read these statements and answers closer but thats why we discuss.

                    dick

                    Comment


                      #11
                      So are we saying that because the feeder cable is shielded it must have a stress kit termination however since the motor leads are not shielded they dont require stress relief?

                      So is the pigtail a connector that has stress relief on one end but not the other, or is the pigtail something that goes on the motor leads and then bolts to a termination piece on the feeder cable that has stress relief?

                      I also believe that the NEC requries any cable over 1000V to be shielded. Is this correct?

                      Comment


                        #12
                        Originally posted by PhaseShift View Post
                        So are we saying that because the feeder cable is shielded it must have a stress kit termination however since the motor leads are not shielded they dont require stress relief?

                        So is the pigtail a connector that has stress relief on one end but not the other, or is the pigtail something that goes on the motor leads and then bolts to a termination piece on the feeder cable that has stress relief?

                        I also believe that the NEC requries any cable over 1000V to be shielded. Is this correct?
                        The 'pigtail' is what motor leads are called in electrician's slang. They are UNSHIELDED, therefore they do not require stress relief of the shielding transition. (The 'penciling' of this insulation will provide a gradual dissipation of the dielectric 'stress' that occur at sharp edges. It avoids corona formation on the edge of the 90* cut that forms ozone, which in turn deteriorates the insualting material. Note that the requirement is for corona resistance, not corona 'proof' which indicates that all dielectrics are subject to the effects of corona, some to greater, some to lesser degree.)

                        NEC, which has authority over the feeder, requires that:

                        310.6 Shielding.
                        Solid dielectric insulated conductors operated above 2000 volts in permanent installations shall have ozone-resistant insulation and shall be shielded. .......

                        Exception No. 1: Nonshielded insulated conductors listed by a qualified testing laboratory shall be permitted for use up to 2400 volts under the following conditions:
                        (a) Conductors shall have insulation resistant to electric discharge and surface tracking, or the insulated conductor(s) shall be covered with a material resistant to ozone, electric discharge, and surface tracking.
                        (b) Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.
                        (c) Insulation and jacket thicknesses shall be in accordance with Table 310.13(D).

                        Exception No. 2: Where permitted in 310.7, Exception No. 2.

                        Comment


                          #13
                          Originally posted by weressl View Post
                          The 'pigtail' is what motor leads are called in electrician's slang. They are UNSHIELDED, therefore they do not require stress relief of the shielding transition. (The 'penciling' of this insulation will provide a gradual dissipation of the dielectric 'stress' that occur at sharp edges. It avoids corona formation on the edge of the 90* cut that forms ozone, which in turn deteriorates the insualting material. Note that the requirement is for corona resistance, not corona 'proof' which indicates that all dielectrics are subject to the effects of corona, some to greater, some to lesser degree.)
                          So does this mean that there is no strees relief required for the feeder cable? Or is there stress relief required on feeder cable but not pigtail?

                          Comment


                            #14
                            I have a facility full of 4160V motors that were put in over the last 50 years - none with shielded cable. Ahh for the old days when life was simpler. Any new installtions will have to be installed with the new shielded cable. In prep for that, I've been talking to my vendors and have identified the Raychem GelCap-8-S motor termination as my most likely solution. I had the vendor in to demo it for me and it looks good. It's made for 5KV shielded cable motor terminations and they have a size for 4/0-500 cable that will probably work in your application. Take a look at it.

                            Comment


                              #15
                              Originally posted by PhaseShift View Post
                              So does this mean that there is no strees relief required for the feeder cable? Or is there stress relief required on feeder cable but not pigtail?
                              Would you please re-read my original response?!

                              Comment

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