Announcement

Collapse
No announcement yet.

Fault current calculation for 69KV Instrument Transformer

Collapse
This topic is closed.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Fault current calculation for 69KV Instrument Transformer

    Hi, I am trying to do a basic fault calculation of a 69KV to 120V transformer and am finding GE specs on the unit confusing. This is not something I have a great deal of experience with so some advice would be great.

    The unit is the JVT350. If you are interested a spec sheet is easily located by searching on that model.

    Specs:
    Primary: 69KV
    Secondary 120V
    Ratio: 600:1
    Thermal rating: 4.5KV
    BIL: 350KV
    And something I do not understand:
    "ANSI Accuracy, Burden Per ANSI, W,X,M,Y = 0.3"

    What do I use as the impedance for the fault calculation?

    Also, just to confirm, thermal VA is the rated secondary output maximum while maintaining accuracy?

    thanks!

    #2
    Max Secondary Current

    Page 19-6 of the GE Buylog says the max current is 4500 amps.

    http://www.geindustrial.com/catalog/buylog/18_BL.pdf

    now I have to hit the books and see what all this means.

    Comment


      #3
      Originally posted by friendlyfire View Post
      Hi, I am trying to do a basic fault calculation of a 69KV to 120V transformer and am finding GE specs on the unit confusing. This is not something I have a great deal of experience with so some advice would be great.

      The unit is the JVT350. If you are interested a spec sheet is easily located by searching on that model.

      Specs:
      Primary: 69KV
      Secondary 120V
      Ratio: 600:1
      Thermal rating: 4.5KV
      BIL: 350KV
      And something I do not understand:
      "ANSI Accuracy, Burden Per ANSI, W,X,M,Y = 0.3"
      What do I use as the impedance for the fault calculation?
      Also, just to confirm, thermal VA is the rated secondary output maximum while maintaining accuracy?
      thanks!
      0.3% accuracy will be attained at rated voltage and frequency.
      Type JVT350 has a rating of 400VA (ZZ designation). So, your impedance is = 120^2/400 VA = 36 ohms.
      Thermal rating is the rating that should not be exceeded to prevent damage to VT. The VT burden is the max load on the VT that the unit remains accurate (to 0.3% in your case).

      Comment


        #4
        Originally posted by topgone View Post
        0.3% accuracy will be attained at rated voltage and frequency.
        Type JVT350 has a rating of 400VA (ZZ designation). So, your impedance is = 120^2/400 VA = 36 ohms.
        Thermal rating is the rating that should not be exceeded to prevent damage to VT. The VT burden is the max load on the VT that the unit remains accurate (to 0.3% in your case).
        This will give the load impedance that loads the VT to its thermal rating. You need the tested impedance of the VT to calculate the fault current.

        Comment


          #5
          hey, thanks for the responses.
          topgone: what does it mean ZZ designation, and where did the 400VA come from? I do not see that figure anywhere in the spec sheet.

          jghrist: I think you are correct, but the tested impedance seems to be lacking in the spec sheet. It seems to me that my next step is to bug GE for that info.

          Comment


            #6
            VT Burden Based on Designation Letter/s


            If you doubt the attached data, you can Google it yourself using key phrases "Standard Burdens for Voltage Transformers"

            Please take note:
            VA = IE = E^2/Z or Z = E^2/VA = 120^2/400 = 36 ohms.
            and:
            R = E^2 X PF/ VA = 120^2 X 0.85/400 = 30.6 ohms
            Last edited by topgone; 07-29-10, 11:12 AM. Reason: wrong formula

            Comment


              #7
              Originally posted by friendlyfire View Post
              topgone: what does it mean ZZ designation, and where did the 400VA come from?
              As shown in the chart, the ZZ designation means the VT will be within accuracy specifications when it is supplying loads up to 400VA at 0.85 power factor.

              I have never seen an impedance value given for a VT, but I never looked explicitly for one either.

              I am curious as to why you are trying to calculate the short circuit current on the 120V side of the VT?
              Bob Wilson

              Comment


                #8
                Hi,
                The reason for this investigation is to determine appropriate ratings and arc flash labeling required of a service rated panel to be connected to the output of the transformer. Application is an unmetered highway sign in the middle of nowhere. The only source of power is a 69kV transmission line.
                Last edited by friendlyfire; 07-29-10, 01:00 PM.

                Comment


                  #9
                  Originally posted by BJ Conner View Post
                  Page 19-6 of the GE Buylog says the max current is 4500 amps.

                  http://www.geindustrial.com/catalog/buylog/18_BL.pdf

                  now I have to hit the books and see what all this means.
                  I think that is the thermal rating in VA, see http://www.gedigitalenergy.com/produ...cs/JVS_JVT.pdf

                  Comment


                    #10
                    I would just label it HRC 1 with a 4 foot boundary per the tables. No study is required here.

                    Comment

                    Working...
                    X