b. The angle of lag
| reactance | 2πfL | 2 × 3.1416 × 60 × .25 | ||||||
| tan φ | = | = | = | = | 1.25 | |||
| resistance | R | 75 | ||||||
| φ | = | angle of lag | = | 51° 15´ | (from table, page 451). | |||
c. The apparent power
| apparent power | = | volts × amperes | = | 800 × 6.7 | = | 5,360 watts |
| = | 5.36 kva. |
d. The power factor
| power factor | = | cosine of the angle of lag | ||
| = | cos 51° 15´ | = | .626. |
e. The true power
| true power | = | apparent power | × | power factor | ||
| = | 5,360 | × | .626 | = | 3,355 watts. |
Fig. 1,369.—Wattmeter method of three phase power measurement. Two wattmeters are required in unbalanced systems as shown in the illustration. The total power transmitted is then the algebraic sum of the readings of the two wattmeters. If the power factor be greater than .5, the power is the arithmetical sum, and if it be less than .5, the power is the arithmetical difference of the readings.