Kapp regulation diagram



Kapp regulation diagram - a graphical method of determining the voltage regulation in a transformer caused by changes in load and power factor.

The output voltage of a mains power transformer when loaded reduces for inductive load (power factor lagging) and increases for capacitive load (power factor is leading).

The Kapp diagram is helpful in finding the voltage drop or increase (voltage regulation). The main disadvantage is that the voltage regulation phasors are much smaller than the radii of the main circles, so the diagram has to be drawn on a very large scale to get sufficiently accurate results.

Drawing algorithm
In order to create the diagram it is necessary to know the equivalent reactance X02 and resistance R02 of the transformer as referred to the secondary side. The following algorithm should be used:
 * 1) Draw phasor OL representing secondary terminal voltage V2 on load
 * 2) Draw OX representing the phase of the secondary current at an angle &Phi;2 to OL such that cos&Phi;2 is the power factor of the load
 * 3) Draw phasor LM (I2 R02 - voltage drop on resistance referred to the secondary side) parallel to OX, and then MN (I2 X02 - voltage drop on reactance referred to the secondary side). The resulting NL is the total voltage drop.
 * 4) Transfer the impedance triangle NLM to OO'P which gives O'L = ON = 0V2. Therefore, for given secondary current the locus of N is a circle with centre O and radius 0V2, while the locus of L has the same radius but with the centre O'
 * 5) To find the voltage drop on full load at any power factor the radius OQS should be drawn at at angle  &Phi; to OX. If the impedance triangle is drawn in position UQT then OU = OS. The length of QS represents the voltage drop.