I was given in class a problem about power transform but I don't understand which current is used in a stage of the resolution. It is asked to find the efficiency of a transformer in a period of a day (24 hours) given that;

  • \$S_{N}=110kVA\$
  • \$2200V/110V\$
  • \$ 60~ Hz\$
  • \$R_{1}=.22\Omega\$
  • \$R_{2}=.5m\Omega\$
  • \$X_{1}=2\Omega\$
  • \$X_{2}=5m\Omega\$
  • \$R_{c}=5.5k\Omega\$
  • \$X_{m}=1.1k\Omega\$ with this power cycle
  • 4 hrs with no load
  • 8 hrs at 1/4 full load and pf .8
  • 8 hrs at 1/2 at pf 1
  • 4 hrs at full load and pf 1
  • Constant core loss of 1.346 kW Both in the resolution given and my idea is to make this fraction


then the core loss is
and finally the ohmic losses in the windings

  • 8 hrs at .25 full load
  • 4hrs at .5 full load
  • 8hrs at full load

but I don't understand why 14.1, 26.6 and 51.7, isn't supposed to be the nominal current on the high voltage side \$I_{1N}=\frac{110000}{2200}=50A\$?

and that would be

  • 8 hrs at .25 full load
  • 4hrs at .5 full load
  • 8hrs at full load

If not then which current is this and how to calculate?

the total ohmic loss will be 53.17kWh and then

But I still don't get how the 14.1...and respective currents are calculated

  • 2
    \$\begingroup\$ What exactly are you asking? Why you should include the magnetizing current in the I^2*R loss calculations? Or why it has that specific value? (The details you gave are fine, but pretty much meaningless without the equivalent model they refer to) \$\endgroup\$ – Brian Drummond Mar 13 '18 at 18:05
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    \$\begingroup\$ Rated voltage is done at full load, you are assuming Vout at no load So kVA rating= Ploss + Pload for R loads and effic = Ploss/kVA \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 13 '18 at 18:05
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    \$\begingroup\$ How many circuits could be made from 3 resistors and 3 inductors? \$\endgroup\$ – Andy aka Mar 13 '18 at 18:59
  • \$\begingroup\$ @BrianDrummond, what are the 14.1, 26.6 and 51.7 values? what current does stand for? \$\endgroup\$ – riccs_0x Mar 13 '18 at 22:19
  • 1
    \$\begingroup\$ Primary current. Your second set of figures only accounts for the current delivered in the secondary, omitting the magnetizing current and any due to power factor considerations. \$\endgroup\$ – Brian Drummond Mar 13 '18 at 22:21

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