Electrical Power Systems Technology

Alternating Current Power Systems 155

VNL – VFL

VR = ————— × 100

VFL

122.5 – 120 × 100

= ———————— × 100

120

VR = 0.02 = 2%

GENERATOR EFFICIENCY

Generator efficiency is the ratio of the power output in watts to the pow-

er input in horsepower. The efficiency of a generator may be expressed as:

Pout

Efficiency (%) = —— × 100

Pin

where:

Pin = the power input in horsepower, and

Pout = the power output in watts.

Sample Problem:

Given: a three-phase alternator has a power output of 22 MW and a

power input of 35,000 horsepower.

Find: efficiency of the alternator.

Solution:

Pout

= (%) Eff = —— × 100

Pin

22,000,000 W

= ——————— × 100

35,000 hp × 746

%Eff = 84%

To convert horsepower to watts, remember that 1 horsepower = 746

watts. The efficiency of a generator usually ranges from 70 percent to 85

percent.