Application Note

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Application Note

Saving energy through

load balancing and

load scheduling

From the Fluke Digital Library @ www.fluke.com/library

Engineers, electricians and technicians

can find significant energy saving oppor-

tunities through load balancing and load

scheduling when using power logging test

tools. Whether conducting an energy audit

While analysis of each param-

eter is important in the overall

scheme of reducing energy costs,

in this article we will focus on

how to reduce your energy bill

by balancing loads across a

three-phase distribution system

and, scheduling the operation of

certain loads to reduce energy

demand. Therefore, we will

concentrate on taking voltage

and current unbalance read-

ings to determine load balancing

issues and on taking power and

related events to identify load

scheduling issues. Correct load

balancing and scheduling is a

good, quick way to reduce elec-

trical energy usage.

Load balancing

System designers and electri-

cians usually balance loads

across a three-phase distribu-

tion system during installation.

Loads are calculated in accor-

dance with Article 220 of the

National Electrical Code

based

on their volt-amperes (VA) or

kilovolt-amperes (kVA), rather

than watts or kilowatts (kW).

This provides an accurate analy-

sis of the ampere values that

will flow in the circuit. Even

though non-inductive load rat-

ings are expressed in watts or

kilowatts, these wattage rat-

ings can be considered the

equivalent of the same rating

or troubleshooting to find energy losses,

a typical power logging session should

record several factors including: voltage,

current, power trends, transients and

event logs.

in volt-amperes or kilovolt-

amperes. Understanding this

concept of how loads are calcu-

lated and the associated units of

measurement allows for proper

power quality instrument setup,

results interpretation and correc-

tive action decisions.

Electricians install equipment

and divide kVA between phases

such that each phase will carry

an equal amount of load. This

concept, however, holds true

in theory only. In the practical

world, the three-phase system is

rarely “perfectly” balanced. Load

unbalance (imbalance) mani-

fests as a voltage and current

unbalance. Therefore, techni-

cians must be sure to monitor

and record both voltage and cur-

rent to determine the extent of

the load imbalance in a system.

Figure 1. Unbalance. In this example the Vneg

of 9.2 % indicates expected overheating of three-

phase motors and transformers and reductions

of motor torque and speed. The Vzero of 8.2 %

indicates excessive current ﬂow in the neutral

due to the unbalance with expected overheating

of conductors and transformers.

Summary of content (4 pages)

PAGE 1
Saving energy through load balancing and load scheduling Application Note Engineers, electricians and technicians can find significant energy saving opportunities through load balancing and load scheduling when using power logging test tools.
PAGE 2
Technicians use one of two methods to determine an unbalance situation. The first, which may be referred to as the IEEE or NEMA method, utilizes a digital multimeter (DMM) to take spot voltage readings. To use this method, measure the three phase-to-phase voltage readings (AB, AC, BC). Sum their values and divide by three to obtain the average voltage. Any phase voltage reading that deviates by more than 1 % from the average value warrants corrective action.
PAGE 3
The more data available to analyze, the more likely you are to come up with energy saving ideas. However, do not be overwhelmed with data. In the Power Log software, select only the specific set of data you wish to analyze at one time by checking the appropriate checkboxes on the top menu. Once the data is downloaded to the PC, select the “Frequency/ Unbalance Tab” in the Power Log software. View data graphically by selecting the minimum, maximum or average value of each desired set of information.
PAGE 4
You should always begin monitoring at the service entrance to determine total energy usage. Set the averaging time in the power logger to 15 minutes if that is the time used by your utility. Consult with your utility to determine the actual averaging time as 30 minutes may also be used. Also, monitor power for an entire billing cycle of thirty days; that will provide the most comprehensive information. Consider repeating this on a seasonal basis, as power consumption requirements change.