CONCEPTS OF METERING ELECTRICITY
1. INTRODUCTION. To effectively manage or participate in electric energy
management programs, a basic knowledge of electricity and meters is highly
beneficial. A course in electricity and meters is beyond the scope of this
manual. The material presented here acquaints individuals with fundamental
electrical units and phenomena specifically related to meters. The major
emphasis is to show how information obtained from electrical meters is
applicable to management programs. There is some mathematical and technical
discussion, but it has been kept to a basic level.
2. COMMON METERING TERMS. The following definitions provide the means for a
basic application of metering data.
Unit of current or rate of flow of electricity.
Blondel's Theorem: The power/energy in a circuit of N lines can be
metered by N single-phase watt/watthour meters with the potential circuits
connected from each line to any common point. If the common point is on one
of the lines, the power/energy can be metered by N-1 watt/watthour meters.
Demand Analysis: Demand analysis is the critical examination of demand
profiles obtained from a power survey recorder (PSR), or compiled from data
collected using kilowatthour meters, rate schedules, demand registers, and
other instruments. One of its purposes is to locate peaks and valleys in a
demand profile to evaluate the possibility of load shifting to level out the
profile and to reduce demand charges.
Demand Factor: Ratio of maximum demand to the total connected load.
Demand Peaks: Although demand billing procedures are not uniform,
time-dependent demand charges are typical. One method uses onpeak, midpeak,
and offpeak hours to assess demand charges. Although hours may vary between
summer and winter months, a typical summer schedule is: onpeak-demand--l:00
PM to 7:00 PM, weekdays; midpeak-demand--9:00AM to 1:00 PM and 7:00 PM to
11:00 PM, weekdays; offpeak-demand--all other hours including holidays.
Highest charges are assessed for onpeak-demand with proportional cost
reductions for midpeak and offpeak periods.
Demand Profile: A demand profile is a graphic representation of
electrical demand made on a system during a given period. The profile
illustrates the relationship between demand, in kilowatt, and time of day
demand occurred. When graphing, place demand on y-axis and time on x-axis.
Diversity Factor: Ratio of the sum of individual maximum demands of
various subdivisions of a system to the maximum demand of the whole system.
Horsepower (hp): Measure of time rate of doing work; equivalent to
raising 33,000 lbs, one ft in one minute; 746 watts.