Fluke 434 Series Ii Application Note

: Fluke Fluke-434-Series-Ii-Application-Note-808982 fluke-434-series-ii-application-note-808982 fluke pdf

Open the PDF directly: View PDF .
Page Count: 4

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 “Power” tab

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.

Fluke Europe B.V.

PO Box 1186, 5602 BD

Eindhoven, The Netherlands

For more information call:

In the U.S.A. (800) 443-5853 or

Fax (425) 446-5116

In Europe/M-East/Africa +31 (0) 40 2675 200 or

Fax +31 (0) 40 2675 222

In Canada (800)-36-FLUKE or

Fax (905) 890-6866

From other countries +1 (425) 446-5500 or

Fax +1 (425) 446-5116

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.