EXAMPLE.—An alternator delivers current at 800 volts pressure at a frequency of 60, to a circuit of which the resistance is 75 ohms and .25 henry.
Determine: a, the value of the current, b, angle of lag, c, apparent watts, d, power factor, e, true power.
a. Value of current
| pressure | E | |||
| current | = | = | ||
| impedance | √(R2 + (2πfL)2) | |||
| 800 | ||||
| = | = | 6.7 amperes | ||
| √(752 + (2 × 3.1416 × 60 × .25)2) |
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. |