Fluke 434 Series Ii Application Note

2015-09-09

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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.
2 Fluke Corporation Saving energy through load balancing and load scheduling
Technicians use one of two
methods to determine an unbal-
ance 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.
While this process should be
one of the first steps when
troubleshooting an identified
unbalance problem, it will not
provide for an accurate analysis
over time as loads cycle on and
off. This requires trending or
power logging.
The Fluke power quality ana-
lyzers and power loggers utilize
a mathematical tool called the
“method of symmetrical com-
ponents” to analyze unbalance.
This method not only simplifies
the voltage imbalance concept
by providing a graphical repre-
sentation of unbalance in vector
format, but also provides accu-
rate and detailed information to
be used for analysis. Fortunately,
the Fluke analyzers and record-
ers automatically perform the
calculations for us—technicians
only need to read the results!
The instruments split each
phase voltage and current into
three separate components:
the positive sequence, the
negative sequence and the
zero sequence. The positive
sequence component represents
the normal voltage or current in
a balanced three-phase system.
The negative sequence volt-
age or current is created by an
unbalance in the system and
results in overheating in induc-
tive loads such as motors and
transformers. This component
is also responsible for reduc-
ing motor torque and can affect
speed. The zero sequence
component represents the
unbalanced current that flows in
the neutral of the three-phase,
four-wire system. This results in
energy losses in the form of heat
in conductors and transformers.
The EN50160 power qual-
ity standard sets the maximum
unbalance at 2 % at the point of
common coupling. The analyzer
or power logger displays and
records the percentage. This
percentage is the ratio of the
negative sequence component
to the positive sequence com-
ponent, or the zero sequence
component to the positive
sequence component.
Technicians will be relieved
to find out they must not memo-
rize the theory but, only learn to
operate the equipment and read
the results. When checking for
unbalance, select “Unbalance”
on the power quality analyzer
menu. Then, simply read the
ratios on the meter screen. Nei-
ther the Vneg” nor the “Vzero”
values should exceed 2 %. (See
Figure 1, Unbalance.) If these
limits are exceeded, isolate and
correct the source of the problem
or energy losses could become
substantial.
Since the meter screen on
the power quality analyzer
updates constantly, the analyzer
meter function is best suited
for checking for unbalance at a
particular point in time. Select
Trend” when in the Unbalance
mode to observe both negative
sequence and zero sequence
voltages over time. After record-
ing has stopped, use the cursor
to determine at what time the
unbalance occurred and its
severity. (See Figure 2, Unbal-
ance Trend.)
After a power logging session,
download the data to a PC and
analyze using the Power Log
software. This software analyzes
voltage unbalance recordings
from several different types of
recording instruments including
the Fluke 345 and 435.
Technicians must also con-
sider the options available when
setting a recorder instrument to
log voltage unbalance situations.
The Power Log software allows
for plotting of the following val-
ues if they are present in the
recorded data:
Frequency
Unbalance Vneg %
Unbalance Aneg %
Voltage: positive, negative and
zero sequence
Amperes: positive, negative
and zero sequence
Figure 2. Unbalance Trend. This is the Trend function of the Fluke 435 meter screen in
Figure 1. By selecting Cursor “ON” and then moving the cursor along the signatures, the
amount of unbalance can be identified at different times. These trends should then be
compared to operation of single-phase equipment during these times to determine the
source of the unbalance.
Placing cursor
at this point
would indicate
acceptable
limits of:
Vn 1.8 %
Vz 1.0 %
Placing cursor at this point would
indicate unacceptable limits of:
Vn 9.2 %
Vz 8.2 %
Negative
sequence
voltage
Zero
sequence
voltage
3 Fluke Corporation Saving energy through load balancing and load scheduling
The more data available to
analyze, the more likely you are
to come up with energy sav-
ing 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 check-
ing 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 graphi-
cally by selecting the minimum,
maximum or average value of
each desired set of informa-
tion. (See Figure 3, Power Log
Frequency/Unbalance Tab). For
further analysis of the data,
export the data to a spread-
sheet by selecting “Export data”
under the File tab. You can then
compare the exact dates, times
and voltage unbalance values
to other plant data. Savvy engi-
neers and technicians, armed
with knowledge of what single-
phase equipment was operating
at what time and, with an up-
to-date one-line diagram of the
distribution system, can now
isolate loads and equalize them
across all three phases to correct
the unbalance problem.
Load scheduling
In addition to reducing energy
costs through load balancing,
technicians and engineers can
also create immediate energy
savings through load schedul-
ing. Load scheduling is the part
of energy load management that
minimizes demand.
Electric utilities charge large
commercial and industrial cus-
tomers a peak demand penalty.”
This peak demand penalty is
in addition to the total usage
of electricity over the billing
period. “Maximum Demand” is
the maximum amount of elec-
tricity used by a customer at any
point in time. The utility must
be capable of supplying this
load, must size its distribution
equipment accordingly, and will
therefore charge the customer
to be able to meet this need.
This maximum electrical energy
usage, or demand, is averaged
over a 15 minute period, (typi-
cal), and determines the rate
schedule at which a customer
will be charged. Peak demand
is usually caused by a spike in
power consumption, most often
when multiple loads come on
simultaneously. These addi-
tional penalties can be high and
add significantly to the cost of
electrical energy. It only makes
sense to minimize the amount of
peak power being used, if at all
possible. Power logging provides
this opportunity.
If you are attempting to more
effectively schedule load opera-
tion, conduct power logging
recording sessions to measure
energy usage over time and
identify large loads that oper-
ate concurrently. Use one-line
diagrams to determine the
energy demand of various loads
and compare them to operating
needs. Do not look for just one
particular load to be causing the
problem. Quite often you must
work with operations personnel
and adjust a process by stagger-
ing cycling times, or complete
certain processes during off-
peak hours to reduce demand.
Engineers and operations man-
agement must work together
to review the electrical energy
bill and compare it to collected
power logging data to aid in
making the best plant opera-
tions and energy cost savings
decisions.
Figure 3. Power Log Frequency/Unbalance Tab. By selecting the various checkboxes at the
top of the Power Log software Frequency/Unbalance Tab the various sequence components
can be compared. In this comparison the negative sequence voltage component and its effect
upon amperage are plotted.
Unbalance
Aneg %
Unbalance
Vneg %
Date Time Unbalance An Avg Unbalance An Max Unbalance Vpos Min
10/9/2008 21:47:16 909ms 8.79 8.79 159.46
10/9/2008 21:47:26 909ms 8.79 8.8 159.46
10/9/2008 21:47:36 909m s 13.28 15.64 139.09
10/9/2008 21:47:46 909ms 15.63 15.64 139.09
10/9/2008 21:47:56 909ms 15.63 15.64 139.09
10/9/2008 21:48:06 909ms 15.63 15.64 139.09
10/9/2008 21:48:16 909ms 15.63 15.64 139.09
Data can be easily exported to a spreadsheet program for further analysis.
4 Fluke Corporation Saving energy through load balancing and load scheduling
You should always begin mon-
itoring 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 averag-
ing 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 con-
sumption requirements change.
Import the data to the PC upon
completion of the logging ses-
sion and use the “Powertab
and the “Energy” tab to search
for periods where energy usage
exceeds desired limits. Identify
the equipment creating the peak
demand charges by observing
Fluke Corporation
PO Box 9090, Everett, WA 98206 U.S.A.
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PO Box 1186, 5602 BD
Eindhoven, The Netherlands
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Web access: http://www.fluke.com
©2008 Fluke Corporation.
Specifications subject to change without notice.
Printed in U.S.A. 11/2008 3399303 A-EN-N Rev A
Modification of this document is not permitted
without written permission from Fluke Corporation.
Fluke. Keeping your world
up and running.®
Figure 4. Power Log Power Tab. The Power Log Power tab plots total power values
including kW, kVA, kVAR and power factor against time. Determining power usage at
specific points in time is the first step in controlling demand.
excessive uses of “Active Power
(kW) on the Power tab. (See
Figure 4, Power Log Power Tab.)
Adjust plant operations and
processes as necessary, to mini-
mize demand charges. Do not
be intimidated by the amount of
data. Spend some time breaking
the data down into manageable
time frames and use the check-
boxes at the top of the menu to
indicate only one or two param-
eters at a time on your graph.
Engineers, electricians and
technicians play a large role in
reducing plant energy costs. If
you will set up a power qual-
ity instrument to record needed
voltage and power values, and
use software to analyze the
recorded data, you can reap the
benefits of significant energy
savings through proper load bal-
ancing and load scheduling.

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