Electrical Power Systems Technology

Power Measurement Equipment 71

Sample Problem:

Given: an industry uses 5000 kW peak power and 3880 kW average

power over a 24-hour period.

Find: the industry’s demand factor over the 24-hour period.

Solution:

Peak Power

Demand = ——————

Avg. Power

5000kW

= ————

3800kW

Demand = 1.31

This ratio is important since it indicates the amount above the aver-

age power consumption that a utility company must supply to an industry.

Power demand is usually calculated over a 15-, 30-, or 60-minute interval,

and then converted into figures that represent longer periods of time.

Industries may be penalized by a utility company if their peak power

demand far exceeds their average demand. Power-demand monitors help in-

dustries to better utilize their electrical power. A high peak demand means

that the equipment for an industrial power-distribution system must be

rated higher. The closer that the peak demand approaches the value of

the average demand, the more efficient the industrial power system is in

terms of power utilization.

FREQUENCY MEASUREMENT

Another power measurement that is very important is frequency.

The frequency of the power source must remain stable, or the operation of

many types of equipment can be affected. Frequency refers to the number

Figure 3-9. Schematic diagram of a

power factor meter circuit