What would happen if I apply a voltage (same phase as primary) to a tertiary winding wound over the transformer core? Would the mutual flux change or would the primary draw a different value of current so as to oppose the change in flux?

(In short, would this tertiary winding act as another primary winding (injecting flux) or would it act similar to the secondary winding (seen as a load by primary))


1 Answer 1


If both windings have the same number of turns and are driven with the same voltage then both will contribute equal amounts of flux to the core i.e. they will each produce a flux that is half the flux produced when just the primary was driven. Two halves make a whole.

If the turns are different and the voltages are scaled proportionately then this will also mean both windings contribute the same.

Anything else means the likelihood of an excessive current being taken and that current will not be related to core flux so, if you are trying to control core flux this way, it won't happen.

  • \$\begingroup\$ I want to control the flux of a distribution transformer (11kV/433V) so as to achieve essentially constant voltage at secondary. The reason being that at high loads, the primary voltage goes down to (say) 10.5 kV and hence the flux reduces. Correspondingly, the secondary voltage also changes. Is there some way by which I can "inject" flux so as to bring back the flux value to same and hence get almost the same secondary voltage (nearly 433 V). Please note that I don't want to use tap changers since they are costly, give only discrete voltage values and arcing is involved with their use. \$\endgroup\$
    – user172541
    Commented May 16, 2018 at 12:43
  • 1
    \$\begingroup\$ @Pranjal I read your original question and no, unfortunately I don't think that this can be done in the manner you wish. \$\endgroup\$
    – Andy aka
    Commented May 16, 2018 at 13:09
  • \$\begingroup\$ Good grief! Who put this guy in charge of anything 11 kV? \$\endgroup\$
    – winny
    Commented May 16, 2018 at 14:04
  • \$\begingroup\$ @winny Don't worry as I am not in charge of any 11kV line! Just an EE student attempting to achieve voltage stabilization possibly by flux control in the above manner ... \$\endgroup\$
    – user172541
    Commented May 16, 2018 at 14:27
  • \$\begingroup\$ I sense XY problem! \$\endgroup\$
    – winny
    Commented May 16, 2018 at 14:42

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