A three-phase, 500-kVA, 4160/480-V transformer bank has R = 1.0% and X = 5%. Using Equation 2.15 or 2.18 with pu values, determine the % voltage rise in the secondary voltage on unloading from the following load conditions:

(1) 80% load at the unity power factor,

(2) Full load at 0.85 power factor lagging, and

(3) Full load at 0.90 pf leading. Assume that the secondary voltage was equal to the rated voltage in all load conditions.

Equation 2.15

Equation 2.18

Transcribed Image Text:

Vdrop = V₁ - V₁ = OA - V₁ = I x R cos 0 + 1x X sin 0 = I x (R cos 0 + X sin 0).