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Kapp regulation diagram

Stan Zurek, Kapp regulation diagram, Encyclopedia Magnetica,
reviewed by Jeanete Leicht, 2014-02-01

Kapp regulation diagram (or in short Kapp diagram) - a graphical method of determining the voltage regulation in a transformer caused by changes in load and power factor.1)

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Kapp regulation diagram2)

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 reduction 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.3)

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 Φ2 to OL such that cos(Φ2) is the power factor of the load
  3. Draw phasor LM (where I2·R02 is the voltage drop on resistance referred to the secondary side) parallel to OX, and then MN (where I2·X02 is the 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 a given secondary current the locus of N is the 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 OS (joining the three points OQS) should be drawn at at angle Φ to OX. If the impedance triangle is drawn at the position UQT then OU = OS. The length of QS represents the sought-after voltage drop.

See also


kapp_regulation_diagram.txt · Last modified: 2021/04/17 10:49 by stan_zurek

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