3 phase transformer on 1 phase

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "J. B. Weazle McCreath by way of Terry Fritz <twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>


Hello Greg and coilers,

Here's the scoop on how to wire up a 3 phase transformer to
work on single phase power as promised.  This method was
shown to me by an electrical engineer friend and I have
personally made use of it successfully.

73, Weazle


       USING A THREE PHASE TRANSFORMER ON SINGLE PHASE
       ===============================================

          I = Iron core of transformer
          W = Windings on each leg of core (numbered)
          S = Start terminal of windings
          F = Finish terminal of windings


                IIIIIIIIIIIIIIIIIIIIIIIIIIIII
                IIIIIIIIIIIIIIIIIIIIIIIIIIIII
              SWWWWWWW    SWWWWWWW    SWWWWWWW
               WWWWWWW     WWWWWWW     WWWWWWW
               WW 1 WW     WW 2 WW     WW 3 WW
               WWWWWWW     WWWWWWW     WWWWWWW
               WWWWWWWF    WWWWWWWF    WWWWWWWF
                IIIIIIIIIIIIIIIIIIIIIIIIIIIII
                IIIIIIIIIIIIIIIIIIIIIIIIIIIII

   Only the windings on the outer legs are used, the windings
   on the middle leg (No. 2) are not used.  The principle of
   the hookup is that you want the phasing of the outer legs
   to be such that at a given moment the magnetic flux will
   be north at the top of the left hand windings while it is
   south at the top of the right hand windings.  You'll see
   that the two fluxes created by the outer leg windings add
   together in the outside legs and horizontal parts of the
   core, but they cancel each other out on the middle leg. 

   I'm assuming that the transformer has high voltage windings
   in the 10,000 to 15,000 volt range and low voltage windings
   of 240 volt or 120/208 volt.  The connections are as below:

   1) Locate and identify the start and finish of each winding.
      There will be a primary and a secondary winding on each
      of the three legs of the core.  Determine which terminals
      are the primary connections and which terminals are the 
      secondary connections.  The high voltage terminals are 
      usually labeled H1, H2, and H3, while those of the low
      voltage are labeled X1, X2, and X3. Also, the low voltage
      terminals will have much heavier gauge wire coming from
      the windings than the high voltage terminals.

      You will likely find that the finish terminals of all of
      the primary windings are connected together.  You'll also
      likely find that the finish terminals of the secondary
      windings are connected together. If this is the case, it
      indicates a Wye connection configuration and it can be
      left that way.  If not, proceed with the next steps.
 
   2) Connect together the finish terminals of the low voltage
      windings 1 and 3. If the finish terminal of low voltage
      winding 2 is also connected, you can leave it that way,
      or you can disconnect it.  Connect together the finish
      terminals of high voltage windings 1 and 3.  If you find
      that the finish terminals of high voltage winding 2 is
      also connected, remove that connection.
   
   3) Apply 120 volts AC by connecting one lead to the start
      terminal of high voltage winding 1 and the other lead
      to the start terminal of high voltage winding 3.

   4) Measure the voltage between the start terminal of low
      voltage winding 1 and the start terminal of low voltage
      winding 3.  You'll measure a low voltage, with it being
      in respect to the transformer ratio.  For instance, if
      the primary is 12,000 volt and the secondary is 240 volt,
      the ratio is 50:1 so you should measure about 2.4 volts.

   5) A final test is to measure for voltage at the terminals
      of windings 2, which should be very low or nil if things
      are connected properly.

   6) Once the tests are completed successfully, it can then
      be connected into the circuit the right way around.