Question

A 60-Hz 220-V-rms source supplies power to a load consisting of a resistance in series with an inductance. The real power is 1500 W, and the apparent power is 4600 VA.
a. Determine the value of the resistance.
b. Determine the value of the inductance.

Answer 1

Answer:

(a) The value of the resistance is 3.431 Ω

(b) The value of the inductance is 0.0264 H

Explanation:

Given;

frequency of the source, f = 60 Hz

rms voltage, V-rms = 220 V

real power, Pr = 1500 W

apparent power, Pa = 4600 VA

(a). Determine the value of the resistance

$P_r = I_{rms}^2R$

where;

R is resistance

$I_{rms} = \frac{Apparent \ Power}{V_{rms}} \\\\I_{rms} = \frac{P_a}{V_{rms}}\\\\I_{rms}= \frac{4600}{220} \\\\I_{rms}= 20.91 \ A$

Resistance is calculated as;

$R = \frac{P_r}{I_{rms}^2} \\\\R = \frac{1500}{(20.91)^2} \\\\R = 3.431 \ ohms$

(b). Determine the value of the inductance.

$Q_L = I_{rms}^2 X_L$

where;

$Q_L$ is reactive power

$X_L$ is inductive reactance

$Apparent \ power = \sqrt{Q_L^2 + P_r^2} \\\\P_a^2 = Q_L^2 + P_r^2\\\\Q_L^2 = P_a^2 - P_r^2\\\\Q_L^2 = 4600^2 - 1500^2\\\\Q_L^2 = 18910000\\\\Q_L = \sqrt{18910000}\\\\Q_L = 4348.56 \ VA$

inductive reactance is calculated as;

$X_L = \frac{Q_L}{I_{rms}^2} \\\\X_L = \frac{4348.56}{(20.91)^2} \\\\X_L = 9.95 \ ohms$

inductance is calculated as;

$X_L = \omega L\\\\X_L = 2\pi f L\\\\L = \frac{X_L}{2\pi f} \\\\L = \frac{9.95}{2\pi *60} \\\\L = 0.0264 \ H\\\\L = 26.4 \ mH$