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7/29/2019 Karady Voltage Sag Pserc Tele-seminar Feb2006
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IRA A. FULTON SCHOOL OF ENGINEERING
George G. Karady, Saurabh Saksena, Baozhuang Shi
Effects of Voltage Sags on
Household Loads
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IntroductionIntroduction Voltage sags is an important part of the
power quality problem Significant amount of research concentrated
on power quality issues
Detailed literature review was performed tostudy the effect of sags on power systemoperation, induction motors, synchronous
machines, and adjustable speed drives(ASDs)
The literature survey incorporated around 40
IEEE and other technical journal papers
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MotivationMotivation No significant and authentic data is available
to study the effect of sags on household loads Very few journal papers are published on the
effect of sags on residential loads, specially
on sensitive equipment The sensitivity of household equipment is
increasing because of increasing use of
electronics Due to the fast changing technology, the test
results performed few years ago have become
obsolete
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ObjectivesObjectives To present an experimental study of the effect of
voltage sags on household loads such as airconditioners, lighting loads, DVD players, televisions
and other sensitive equipment
To design Computer Business EquipmentManufacturers Association (CBEMA) curves for loads
that stalled/ switched off due to sags, and comparewith the standard CBEMA curves
To create a prediction table for the effect of sags on a
single apartment unit To discuss financial implications of sags on
customers and utilities
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Experiments on HouseholdExperiments on Household
LoadsLoads
Contactors and Circuit Breakers Motor loads eg. Air conditioners Lighting loads eg. Fluorescent and Helium
Lamps Sensitive equipment9 Computers9 Microwave Ovens9 Televisions9 DVD and VCR players, digital radio clocks
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What are voltage sags???What are voltage sags???A sag or dip, as defined by IEEE Standard1159, IEEE Recommended Practice forMonitoring Electric Power Quality, is
a decrease in root mean square (rms) voltageat the power frequency for durations from 0.5cycles to 1 minute, reported as the remaining
voltage
Typical values of sags are between 0.1 pu and
0.9 pu.
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Terminology usedTerminology used
The terminology used to describevoltage sag is confusing
Sag of 20% means a voltage drop, V
of 20% from its initial voltage level
20% sag depth represents that the
remaining voltage is 20% of theoriginal line voltage
Terminology used
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Voltage Sag: A Pictorial ViewVoltage Sag: A Pictorial View
-200
-150
-100
-50
0
50
100
150
200
0 500 1000 1500 2000 2500
voltage
cycles
Voltage sag showing 50% sag depth, 20 cycle duration
Sag depth of 50% which
depicts the remaining
voltage in%
Sag period of 20 cycles
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Experimental ConfigurationExperimental Configuration
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Experimental ConfigurationExperimental Configuration The sags are created using the EPRI Process
RideThrough Evaluation System (PRTES) which isa portable voltage sag generator with built in dataacquisition system
Salt River Project (SRP) lent the voltage saggenerator
The sag generator supplied directly the test object.
The current of the test object and the voltageacross the terminals was measured and recorded
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Data acquisition system
Voltage sag generator Laptop interface
Contactor under test
Experimental ConfigurationExperimental Configuration
EPRI PRTES system portable sag generator and built-in data
acquisition system
Tap setting for
Changing sag depths
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Test ProcedureTest Procedure The sag depths are varied in steps of 10%
starting from 90% and going to 50% usingthe tap setting
At each sag depth the sag duration was
varied from 5, 10, 20 60 cycles. (10 Cyclesteps)
The voltage and current wave shapes weremeasured and recorded in an excel file
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Experiments on AirExperiments on Air--
Conditioner CompressorsConditioner Compressors
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Experiments on AirExperiments on Air--ConditionerConditionerCompressorsCompressors
Three window unit air conditioners were
tested:
Air conditioner A, 2kW, 9A full load Air conditioner B, 1kW, 7.4A full load
Air conditioner C, 670W, 6.1 A full load
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Experiments on AirExperiments on Air--ConditionerConditionerCompressorsCompressorsSpecifications of air conditioner compressor A
120 V ac single phase thermally protected
Full load amperes: 7.4 A
Locked rotor amperes: 35.7 A
Measured operating current: 6.7 A
Peak value of starting current of thecompressor before subjected to sags: 48 A
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-2 0 0
-1 5 0
-1 0 0
-5 0
0
5 0
10 0
15 0
20 0
0 500 1000 1500 2000 2500
voltage
cycles
Voltage sag (60% depth, 20 cycles)
-4 0
-3 0
-2 0
-1 0
0
1 0
2 0
3 0
0 500 1000 1500 2000 2500
Current
Responding motor current
cycles
Non stalling condition for compressor A
Experiments on air-conditioner
compressors
IEEE PES Meeting, San Francisco, Jun 12- Jun 17, 2005
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Experiments on air-conditionercompressors
-200
-150
-100
-5 0
0
5 0
10 0
15 0
20 0
0 500 1000 1500 2000 2500
volta
ge
Voltage sag (50% depth, 20 cycles)
cycles
Stalling condition for compressor A
- 5 0
- 4 0
- 3 0
- 2 0
- 1 0
0
1 0
2 0
3 0
4 0
5 0
0 500 1000 1500 2000 2500
curre
nt
cycles
Responding motor current
IEEE PES Meeting, San Francisco, Jun 12- Jun 17, 2005
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Experiments on Air-Conditioners
- 5 0
- 4 0
- 3 0
- 2 0
- 1 0
0
1 0
2 0
3 0
4 0
5 0
0 5 0 0 1 00 0 1 5 0 0 2 0 00 2 5 0 0
cur
rent
cycles
Responding motor current for stalling condition for
compressor A
Momentary
transient
period
Point of sag initiation
1.5 times normal current
after transient period
Gradual increase in
current
Sag period
Post sag period
High current
greater than
locked rotor
current signifyingstalling condition
(A)
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Experiments on air-conditioner
compressors
N: Non- stalling condition Y: Stalling condition
Results of stalling conditions for
different sag depths and durations for compressor A
For a sag of50% depth
and
duration 60
cycles,
compressor
A stalls
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Experiments on AirExperiments on Air--ConditionersConditionersThree window unit air conditioners were tested
Results of stalling conditions for air-conditioners
N no effect on speed of compressor
SR speed reduction due to sag
S air-conditioner stalls
Sag Depth (%)
5 10 20 30 40 60
90 N N N N N N
80 SR SR SR SR SR SR
70 SR SR SR SR SR SR
60 SR SR SR SR S S
50 SR SR S S S S
Sag Duration (cycles)
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Conclusions
Air conditioners stall for sags of 60% depthand 40 - cycle and 60 - cycle duration, andsags of 50% depth and duration greater than
10 cycles; thermal protection causes thecompressor to stall
The motor current can rise to as high as 4.7
pu during sag
Initiation phase of the sag has no obviouseffect on the performance of the motor
Experiments on Air-Conditioners
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Experiments on AirExperiments on Air--ConditionerConditioner
CompressorsCompressorsImpact of sag initiation phase on motor recovery current
0
1
2
3
4
5
6
0 90 180 270 360
Phase (Degree)
Motorrecoverycurr
ent(p.u.)
50%10Cycle
50%20Cycle
40%10Cycle
40%45Cycle
Motor recovery
current in per unit
Sags represent voltage
drop in this case
Stalling cases; no effectof sag initiation phase
on recovery current
Non-stalling cases;
recovery current forsags initiated at 0
and 180 deg. Is
greater than that for
90 and 270 deg.
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Experiments on Air-
Conditioner Compressors
Conclusions
Compressor A stalls for sags of depths60% and more and duration greater than
40 cycles
Compressor B stalls for sags of depths60% and more and duration greater than20 cycles
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Experiments on Air-
Conditioner CompressorsConclusions (Generalized)
Test results of 2 motors show that motor stallsfor sags deeper than 60% and longer than 20cycles
The motor current can rise to as high as 4.7 puduring sag
Initiation phase of the sag has no obviouseffect on the performance of the motor.
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Experiments on AirExperiments on Air--
Conditioner CompressorsConditioner Compressors
The gradual increase of sag and sagduration leads to the stalling of the motor
The motor stops and current increases to
the starting current
The large current activates the thermal
protection in the winding
The motor is re-started manually
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Experiments on LightingLoads
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Experiments on Lighting Loads Experiments were conducted on
fluorescent lamps and
helium lamps
Lamps were subjected to sags ofdifferent depths, durations and
initiation phases
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Experiments on Lighting LoadsFluorescent lamps
Specifications of Fluorescent Lamp Tested
GE/Philips SP35 32W Canada
110VAC/32Watt Regular size (4 feet) fluorescent lamp
120V, RMS value of operation current is 0.33 A.
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Experiments on Lighting Loads The sag produces a sudden reduction of light
intensity
The current becomes zero at the beginning ofsag for two cycles
Subsequently, current increases to a value,which is proportional to the sag voltage
When sag ends, a current spike occurs and
then current returns to its normal
During the current spike the light intensityincreases sharply
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Experiments on Lighting Loads
- 4
- 3 . 5
- 3
- 2 . 5
- 2
- 1 . 5
- 1
- 0 . 5
0
0 . 5
1
1 . 5
0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0
c
u
rr
e
cycles
Typical responding current signal for florescent lamp (40% depth, 10 cycles)
Point of sag initiation
Zero current indicating
beginning of sag
Sag period where current
becomes proportional to applied voltage
Current spike indicating
end of sag
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Experiments on Lighting LoadsHelium Lamps
Specifications of Helium Lamp Tested
GE Helium Lamp 120V AC/ 750 Watts
Measured operating current: 6.19 A
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Experiments on Lighting Loads
Conclusions Light dims during sags in helium lamps
Lamp current is proportional to sag depth
Dimness of light is dependent on sag depth and isindependent of sag duration
At the end of the sag, a current surge occursresulting in a sharp increase in the intensity of light.
This may reduce the life of the lamps
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Experiments on Computers
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Experiments on ComputersSpecifications of the tested computers
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Experiments on Computers
-20
-15
-10
-5
0
5
10
15
20
0 500 1000 1500 2000 2500 3000 3500 4000
Cur
rent(A)
IEEE PES Meeting, San Francisco, Jun 12- Jun 17, 2005
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 500 1000 1500 2000 2500 3000 3500
Cur
rent(A)
Current for 60%/ 20 ~ No loading/ Restart Current for 50%/ 30 ~ loading/ Restart
Loading refers to the case when the hard disk is loading data
High current surges of the order of 7-10 times the normal current
indicating end of sag
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Experiments on ComputersEffect of voltage sag on computer As restarting and data loading
Experiments were conducted considering two cases: when the hard disk is loading
data and one when it is functioning normally without loading data
For a sag of depth 40%,
duration of 15 cycles or
less and when hard disk is
not loading data, there is
no effect on computer A
For a sag of depth 50%,
duration of 8 cycles or
more and when hard disk
is loading data, computerA restarts
C
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Experiments on Computers
If the sag duration is shorter than 7 cycles,sags do not cause the restart of a computer
and the loss of data
If the depth of voltage sag is larger than 30%
and duration is longer than 8 cycles, voltagesag may cause a computer to start
Voltage sags have more severe effect on
computers restarting if the computer powersupply is driving more devices such as harddisk, CD R, etc
E i C
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Experiments on Computers
Voltage sag is normally not a hugeproblem to single computers unlessthey are used as servers or mainframecomputers.
The sag typically restarts the computer,which results in loss of data
This may cause financial losses totrading and telecommunication offices
E i t C t
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Experiments on Computers
The obtained numbers (which representsag depths and sag duration) were put
in the CBEMA curve and were seen tocomply with the experimental values.
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Experiments onExperiments onMicrowave OvensMicrowave Ovens
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Experiments on Microwave OvensExperiments on Microwave Ovens
-30
-20
-10
0
10
20
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Time (sec)
Current(A)
Load current for 50% sag depth and 30-cycle sag duration
Current decreasing to almost
zero signifying switching off
condition
Decrease in current signifying
flickering inside the oven
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Experiments on Microwave OvensExperiments on Microwave Ovens
Sag Depth (%)
5 10 20 30 40 60
90 V V V V V D
80 V V V V V D
70 V V V V V D
60 V V V S S S
50 V S S S S S
Sag Duration (cycles)
Two microwave ovens were tested
V: oven does not switch off, only visible effects such as flickering
D: oven does not switch off, visible effects such as flickering andmomentary stopping of digital clock
S: oven switches off without getting damaged
Summary of performance of microwave oven A due to sags
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Conclusions
No microwave oven was damaged dueto sags of varying depths and duration
Microwave oven A switched off for 60%depth/ 30 cycle duration and 50%
depth/ 10 cycle duration
Microwave oven B showed only visible
effects of sags such as flickering
Experiments on Microwave OvensExperiments on Microwave Ovens
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Experiments on TelevisionsExperiments on Televisions
Current waveform for 50%, 60-cycle sag (television turns off)
Point of sag initiation
Period marked by
blinking and shrinkingof image
Television switches
off automatically
End of sag marked by
sharp surge; television
turns on automatically
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Experiments on TelevisionsExperiments on TelevisionsTwo televisions were tested
N: television has no effect of sag
V: television does not switch off; only visible effect such as
blinking and shrinking of image S: television switches off without getting damaged
Summary of performance of televisions due to sags
Sag Depth (%)
5 10 20 30 40 60
90 N N N N V V80 N N V V V V
70 V V V V V V
60 V V V V V V
50 V V V S S S
Sag Duration (cycles)
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Conclusions
No television was damaged due to sags ofvarying depths and duration because ofinternal protection circuitry
The televisions switched off for 50% depthand duration greater than 20 cycles
The end of sag was marked by a surge; at
this instant the television switches onautomatically
The cause of the surge is Switch Mode
Power Supply (SMPS) inside the television
Experiments on TelevisionsExperiments on Televisions
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Experiments on DVD/VHS PlayersExperiments on DVD/VHS PlayersThree VHS/DVD players were tested
N: VHS/DVD has no effect of sag
V: VHS/DVD does not switch off; only visible effect such asblinking of electronic timer
D: VHS/DVD does not switch off; electronic timer stopsmomentarily
Summary of performance of DVD/ VHS players due to sags
Sag Depth (%)
5 10 20 30 40 60
90 N N N N N N80 N N N N N N
70 N N N V V V
60 N N N V V V
50 V V D D D D
Sag Duration (cycles)
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Experiments on DVD/VHS PlayersExperiments on DVD/VHS Players
Point of sag initiation
Current waveform for 70%, 50-cycle sag (flickering in timer)
Momentary current zero
signifying flickering of the
timer
Surge marking the end
of sag; surge due to
SMPS
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Conclusions
No VHS/DVD player was damaged due tosags of varying depths and duration
The only effect of sags is the visible effecttermed as flickering of the electronic timer
The end of sag was marked by a surge
The cause of the surge is Switch ModePower Supply (SMPS) inside the players
Experiments on VHS/DVD PlayersExperiments on VHS/DVD Players
E i Di i l Cl k R diE i t Di it l Cl k R di
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Experiments on Digital Clock RadiosExperiments on Digital Clock RadiosTwo FM/AM digital clock radios were tested
N: digital clock radio has no effect of sag
V: only visible effect such as flickering of the electronic timer
A: loss of audio for few cycles
Summary of performance of digital clock radios due to sags
Sag Depth (%)
5 10 20 30 40 60
90N N N N N N
80 N N N N V V
70 V V V V V V
60 V V V V A A
50 V V V A A A
Sag Duration (cycles)
E i t T tE i t T t
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Experiments on ToastersExperiments on ToastersTwo toasters were tested
N: toaster has no effect of sag
V: only visible effect such as blinking of the coils
S: toaster switches off; to be restarted manually
Summary of performance of toasters due to sags
Sag Depth (%)
5 10 20 30 40 60
90N N N N N N
80 N N N N N N
70 N N N N N N
60 V V V V V S/V
50 V V V V S/V S/V
Sag Duration (cycles)
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Conclusions
No toaster was damaged due to sags ofvarying depths and duration
For the case when toaster has just begun
operation, toaster switches off automaticallyfor 60% depth/60 cycle and 50% depth/40cycle,60 cycle duration; it is restarted
manually For the case when toaster is already
operational, there is no effect of sag except
blinking of red hot coils
Experiments on ToastersExperiments on Toasters
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CBEMA Curve AnalysisCBEMA Curve Analysis
CBEMA Curve AnalysisCBEMA Curve Analysis
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CBEMA curve defines the envelope withinwhich the equipment should continue tofunction without interruption
It plots the depth of voltage sags inpercentage on the vertical axis against theduration of voltage sags on the horizontalaxis
Curves have been created for all theappliances that were switched off or stalleddue to voltage sags air conditioners,computers, microwave ovens, andtelevisions
CBEMA Curve AnalysisCBEMA Curve Analysis
CBEMA Curve AnalysisCBEMA Curve Analysis - MethodologyMethodology
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The CBEMA curves are plotted using theresults of the experiments performed on the
various appliances The CBEMA curve for the appliance is
created by looking at the voltage sag depth
and duration for which the appliance isaffected by the sag
For a particular sag depth, if the appliance is
affected by several sag durations, then theminimum sag duration for which theequipment stalled is taken as the boundary
point
CBEMA Curve AnalysisCBEMA Curve Analysis -- MethodologyMethodology
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CBEMA Curve AnalysisCBEMA Curve Analysis--MethodologyMethodology
A percentage level of 40% is used to provide
zero level for the CBEMA curve
The corresponding sag duration for 40% sagdepth is chosen as duration which is less than
the x coordinate of the boundary point
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CBEMA Curve AnalysisCBEMA Curve Analysis--MethodologyMethodologySag Depth (%)
5 10 20 30 40 60
90 N N N N N N
80 N N N N N N
70 N N N N N N
60 N N N Y Y Y50 N Y Y Y Y Y
Sag Duration (cycles)
1 10 100Duration in (60 Hz) cycles
40
50
60
70
80
90
Magnitude
inPercent
Standard CBEMA curve
Microwave oven switches off
No effect of voltage sags
Ove
nsw
itch
esoff
ITIC
CBEMA Curve AnalysisCBEMA Curve Analysis
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CBEMA Curve AnalysisCBEMA Curve Analysis
1 10 100Duration in (60 Hz) cycles
40
60
80
100
Mag
nitudeinPercent
Standard CBEMA curve
ITIC
Air-conditioner compressorsLighting LoadsMicrowave OvensTelevisionsComputers
The obtainedCBEMA curves areconservative in
comparison tostandard CBEMA/ITIC curves
These curvesprovide the utilitiesand themanufacturers with
the informationabout thesensitivity of theequipment to
voltage sags
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Survey of ResidentialSurvey of Residential
ComplexesComplexes
Survey of Residential Complexes
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The survey of electric loads is performed
for an apartment complex to identify themost common electric loads present ineach unit
Two apartment complexes were surveyed Tempe Terrace and University Crossroads
The common loads are the air-conditioningmotors, fan motors, refrigerators,
microwave ovens, bulbs, crushers, andtelevisions
Survey of Residential ComplexesSurvey of Residential Complexes
Creation of Prediction Table for aCreation of Prediction Table for a
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The identification of the common loads throughsurveys resulted in the creation of predictiontable for a single apartment
It predicts the effect of voltage sags on a single
apartment as a function of sag depth andduration
The maximum effects of voltage sags to the
residential customers occur during a sag depthof 50% and duration greater than 10 cycles. Mostof the single phase electric motors stall, themicrowave switches off, lamps get blown off and
the television switches off
Single Apartment UnitSingle Apartment Unit
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Sample Prediction TableSample Prediction Table
50%
Non-Stalling
AC
motor
stalls,
Microw
ave
ovens
switches
off
automati
cally
AC
motor
stalls,
Microw
ave
ovens
switches
off
automati
cally
AC motor
stalls,Microwave
ovens
switches off
automaticall
y, television
switches off
automaticall
y and turns
on
automaticall
y after thesag
AC motor
stalls,Microwave
ovens
switches off
automatically,
television
switches off
automatically
and turns on
automatically
after the sag,
toasterswitches off
In the case of DVD/VHS
players, for 30-cycle duration
and greater, the timer stops for2-3 seconds and resets itself
once the sag is over, in the
case of digital clock radios
audio is lost for duration of 50
and 60 cycles and takes few
cycles after the sag is over to
recover, in the case of stereo
players song being played is
stopped accompanied by a
scratching noise, song restarts
few cycles after the sag is over,Toaster switches off for
duration of 40 cycles or more
5~ 10~ 20~ 30~ 40~ 60~
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Financial Implication ofFinancial Implication of
Voltage SagsVoltage Sags
Financial Implication of Voltage SagsFinancial Implication of Voltage Sags
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Voltage sags do not damage any householdequipment. Hence, residential customers have
minimal or no cost of voltage sags incurred onthem
Electric utilities might incur financial losses ifvoltage sags cause feeders to go out ofoperation.
This scenario is possible if all the air-conditionercompressors in an apartment complex are stalledfor sag of 50% depth and duration greater than 30
cycles and restarted simultaneously
Financial Implication of Voltage SagsFinancial Implication of Voltage Sags
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Overall ConclusionsOverall Conclusions
Overall ConclusionsOverall Conclusions
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Overall ConclusionsOverall Conclusions
The most severely effected is the computer assag can cause loss of data
No damage occurred on any of the loads
The sag may stop the air conditioners in the
residential areas due to sags The restart can produce over load if all air-
conditioners are started simultaneously and
further sags can occur.
In residential areas, the sag has minimal financial
consequences to the owners
Contribution of the ProjectContribution of the Project
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Has provided the utilities and the customers withthe information that voltage sags are not a
serious cause of concern in residential areas Has provided the utilities and the manufacturers
of sensitive equipment with CBEMA curves which
will inform them about the sensitivity of theequipment
Has provided the utilities with a prediction table
of a single apartment which will help in predictingthe performance of loads on being subjected tovoltage sags
Contribution of the ProjectContribution of the Project
PublicationsPublications
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S. Saksena, B. Shi, G. Karady, Effects of voltagesags on household loads, IEEE Power
Engineering Society, San Francisco, June 2005
S. Saksena, G. Karady, Effects of voltage sags
on sensitive equipment in residentialcomplexes, IEEE Transaction on Power Delivery,to be submitted
S. Saksena, G. Karady, Designing CBEMAcurves for household appliances affected byvoltage sags, IEEE Transaction Letter, to be
submitted
PublicationsPublications
AcknowledgementsAcknowledgements
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AcknowledgementsAcknowledgements
Sincere acknowledgement to PowerSystem Engineering Research Center(PSERC) for sponsoring the research
Special thanks to Dr. Baj Agrawal,Arizona Public Service for key inputs
Special thanks to Salt River Project for
lending us the Voltage Sag Generator