Hawkins Electrical Guide v. 05 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

From the table cos 30° = .866, hence

true watts = 200 × 1,000 × .866 = 173.2 kw.

Fig. 1,359.—Diagram for obtaining the active component of the current in a circuit having a current of 200 amperes and angle of lag of 30°.

EXAMPLE II.—If in an alternating current circuit, the voltmeter and ammeter readings be 110 and 20 and the angle of lag 45°, what is the apparent power and true power?

The apparent power is simply the product of the current and pressure readings or

apparent power = 20 × 110 = 2,200 watts

The true power is the product of the apparent power multiplied by the cosine of the angle of lag. Cos 45° = .707, hence

true power = 2,200 × .707 = 1,555.4 watts.