Question

An iron-cored choking coil takes 5 A when connected to a 20-V d.c. supply and takes 5 A at 100 V a.c. and consumes 250 W. Determine (a) impedance (b) the power factor (c) the iron loss (d) inductance of the coil.

Answer 1

(a) Z = 100/5 = 20 Ω

(b) P = VI cos φ or 250 = 100 × 5 × cos φ

∴ cos φ = 250/500 = 0.5

(c) Total loss = loss in resistance + iron loss

∴ 250 = 20 × 5 + Pi

∴ Pi = 250 − 100 = 150 W

(d) Effective resistance of the choke is P/I2 = 250/25 = 10Ω

∴ XL = √(Z2 - R2) = √(400 - 100) = 17.32Ω