Re: Promotion Test
This whole problem can be done graphically. To go one step further than Ed carried it, this can be laid out on a piece of graph and a protractor and a compass.
The Given: 25kva Transformer Real power is 1200 watts and the pf of .6 lagging.
By marking off 25 kw on the horizontal (X) axis which is the Real power, set the compass to this length, and strike an arc from the origin and 25 kw point to the vertical axis (Y) this will give the limits of the transformer. The power triangle will now fit within this arc. Whenever the hypoteneuse( of the power triangle) is equal to the radius of the arc you will be at full load or 25kva/kw of the transformer(depending on the powerfactor) as long as you know the power factor or an assumed power factor you can plot any parameter of that transformer.
And as long as the S side (kva) is not equal the the distance from the origin to the 25(or whatever size is used) kva arc you will be able to add to the current load on the transformer.
The answer in question will be as accurate as how accurate you lay out the graph, in other words accurate to 1/2 the least count.
WOC