VOLTAGE REGULATION OF POWER TRANSFORMERS BASICS
How To Compute The Voltage Regulation of Power Transformers?
The regulation that occurs at the secondary terminals of a transformer when a load is supplied consists, as previously mentioned, of voltage drops due to the resistance of the windings and voltage drops due to the leakage reactance between the windings.
These two voltage drops are in quadrature with one another, the resistance drop being in phase with the load current. The percentage regulation at unity power factor load may be calculated by means of the following expression:
(copper loss x 100/output) + [(percentage reactance) ²/200]
This value is always positive and indicates a voltage drop with load. The approximate percentage regulation for a current loading of a times rated full-load current and a power factor of cosΦ₂ is given by the following
expression:
percent regulation = a(Vr cosΦ₂ + Vx SinΦ₂) + (a²/200) (Vx cosΦ₂ - Vr SinΦ₂)²
where VR = percentage resistance voltage at full load
= copper loss x 100 / rated kva
At loads of low power factor the regulation becomes of serious consequence if the reactance is at all high on account of its quadrature phase relationship.
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