Understanding Power Quality IIEE CSC UST
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Transcript of Understanding Power Quality IIEE CSC UST
1
Understanding Power Understanding Power
QualityQuality
February 7, 2007
University of Sta. Tomas
Marvin Ryan G. Bathan
Power Quality Team
Power Services / MERALCO
ObjectivesObjectives
• To understand the concept of EMC and what specifically becomes a power quality problem
• To establish collaboration among involved parties in dealing with PQ problems
ObjectivesObjectives
• To have a common understanding of power quality and its attendant terminology
• To be acquainted with the typical causes and solutions to specific power quality problem
2
Power QualityPower Quality
Power Quality - the quality of the voltage, including its frequency and the resulting current that are measured in the Grid, Distribution System, or any User System
Quality?Quality?
Quality is a relative term
Power Quality is relative to the sensitivity of a device, equipment, or system
Power Quality ProblemPower Quality Problem
"Any power problem manifested involtage, current, or frequency deviation that results in failure or mis-operation of
utility or end-user equipment."
3
PQ Problem IllustratedPQ Problem Illustrated
NormalNormal
Failure
Failure
Power Quality IssuesPower Quality Issues
Power quality issues may be viewed
from three different perspectives:
2 End-user
2 Utility2 Equipment Manufacturer
PQ Problem Solution: PQ Problem Solution:
A joint effortA joint effort
• Solution to PQ problems is not the responsibility of only one party.
• The solution is a concerted effort between the power supplier, the electricity user, and equipment manufacturer.
4
MERALCO Power Quality TeamMERALCO Power Quality Team
Profile:
PEE – 1
REE – 5
RME – 1
MBA – 1
Trainings:
Attended various PQ conferences/trainings here and abroad
Seminars conducted:
Regular speaker in PQ seminars and lectures
PQ ServicesPQ Services
PQ ServicesPQ Services
5
PQ ServicesPQ Services
PQ ServicesPQ Services
Voltage Sag ProblemVoltage Sag Problem
Voltage Unbalance ProblemVoltage Unbalance Problem
TransientTransient
HarmonicsHarmonics
InterestingInteresting
CC
AA
SS
EE
SS
TT
UU
DD
YY
6
BackgroundBackground
• series of compressor breakdowns
• 5 replacements since the installation of their 3 compressors
• Refrigeration experts says that the power supply caused the breakdown
• Customer requested for technical assistance in characterizing their power supply
Simplified Schematic DiagramSimplified Schematic Diagram
S1
S2
S3
R1
R2
R3
• Compressor - 230Vac, 3-phase, 60Hz
• Contactors - 240 Vac, 75 FLA, 450 LRA
Current Voltage
Compressor S1 S2 S3 R1 R2 R3 L1 –L2 L2 –L3 L3 –L1
1 44.8 44.1 43.5 46.7 41.0 48.0
2 31.5 35.2 34.6 31.5 35.9 35.2
3 39.7 39.7 38.0 36.7 40.0 37.9
228.3 232.8 228.3
64% FLA
Voltage ProtectionVoltage Protection
• Programmable Voltage Monitor
• ±10% over and under voltage set-point
• 5% voltage unbalance set-point
7
Compressor 3 Inrush Compressor 3 Inrush
CurrentCurrent
760 Amperes.
Compressor #3 was
started.
180 Amperes.
Represents the
current drawn by
the AHU,
condenser, and
compressor.
80 Amperes.
Loads running
were the AHU
and condenser.
Compressor 1 Inrush Compressor 1 Inrush
CurrentCurrent
32 A
320 A
60 A
Compressor 1 Inrush Compressor 1 Inrush
CurrentCurrent
30 A
350 A
70 A
8
RMS Voltage VariationRMS Voltage Variation
RMS Voltage Profile
215
225
235
245
255
265
275
8/3
0/0
4 1
5:0
0
8/3
1/0
4 1
2:0
0
9/1
/04 9
:00
9/2
/04 6
:00
9/3
/04 3
:00
9/4
/04 1
:00
9/4
/04 2
2:0
0
9/5
/04 1
9:0
0
9/6
/04 1
5:3
3
9/7
/04 1
2:3
3
9/8
/04 9
:33
9/9
/04 6
:33
9/1
0/0
4 3
:33
9/1
1/0
4 1
:33
9/1
1/0
4 2
2:2
3
9/1
2/0
4 1
9:2
3
9/1
3/0
4 1
6:2
3
9/1
4/0
4 1
3:2
3
9/1
5/0
4 1
0:2
3
9/1
6/0
4 7
:23
Date & Time
Vo
ltag
e
V RM S AB (V)
V RM S BC (V)
V RM S CA (V)
Transformer tap
change.Overvoltage
incidents.
RMS Voltage VariationRMS Voltage Variation
Monitoring Site Minimum Average Maximum Count
Compressor 3 95.67% 103.79% 112.31% 264
Compressor 1 96.42% 101.80% 106.61% 141
Voltage UnbalanceVoltage Unbalance
Monitoring Site Minimum Average Maximum Count
Compressor 3 0.08% 0.62% 1.09% 264
Compressor 1 0.16% 0.50% 0.98% 141
9
Voltage & Current HarmonicsVoltage & Current Harmonics
• Maximum Voltage THD » 3.88%
• Average Voltage THD » 2.06%
• Maximum Current TDD » 10.72%
• Average Current TDD » 1.97%
Compressor CyclingCompressor Cycling
Compressor 3
DateNumber of
Starts
30-Aug-04* 6
31-Aug-04 20
1-Sep-04 20
2-Sep-04 4
3-Sep-04 1
4-Sep-04 1
5-Sep-04 0
6-Sep-04 1
7-Sep-04 2
8-Sep-04 1
9-Sep-04 3
10-Sep-04** 2
*Started at 3:30 PM **Ended at 3:48 PM
The number of start and stops the compressor makes could be greaterthat those listed in the table!
Compressor CyclingCompressor Cycling
Compressor 1
Date Number of Starts
10-Sep-04* 7
11-Sep-04 10
12-Sep-04 0
13-Sep-04 30
14-Sep-04 35
15-Sep-04 31
16-Sep-04** 18
*Started at 3:48 PM **Ended at 1:08 PM
10
Causes of Intermittent CyclingCauses of Intermittent Cycling
• Too sensitive Voltage protection
• Erratic operation of low pressure switch
• Insufficient refrigerant
• Closed suction service valve
Causes of Intermittent CyclingCauses of Intermittent Cycling
• Partially open discharge valve
• Insufficient fluid flowing through the
condenser
• Presence of air in the system
ConclusionConclusion
• Power supply characteristics conforms
with the PDC recommended limits and therefore could not have caused the compressor breakdowns.
• It is the intermittent cycling of the compressors that lead to its premature failure.
11
RecommendationRecommendation
Coordinate closely with your supplier to address the intermittent cycling of the
compressors.
General PQ Evaluation General PQ Evaluation
ProcedureProcedure
Ξ Problem Category Identification
Ξ Power Measurements & Data Collection
Ξ Solution Range Identification
Ξ Solution Evaluation
Ξ Optimum Solution
Solution Range IdentificationSolution Range Identification
� Equipment Design/Specification
� Customer Systems
� Utility Distribution System
� Utility Transmission System
12
Good Day!Good Day!
For your comments / suggestions / questionsFor your comments / suggestions / questions
MARVIN RYAN G. BATHANMARVIN RYAN G. BATHAN
[email protected]@yahoo.com
1622-3591
Voltage UnbalanceVoltage Unbalance
Maximum deviation from the average of the three-phase voltages divided by the average of the three-phase voltages, usually expressed in percent
t
•Unbalanced distribution of single phase loads•Unstable system neutral•One-phase out power supply
BackgroundBackground
Customer business is lead recycling
Customer complained of frequent breakdown of 3-phase motors
13
Profile of Voltage UnbalanceProfile of Voltage UnbalanceVoltage Unbalance Trend
0
1
2
3
4
5
6
7
8
9
10:1
1
3:1
1
20:1
1
13:1
1
5:4
5
22:4
5
15:4
5
9:4
5
2:4
5
19:4
5
12:4
5
5:4
5
22:4
5
15:4
5
8:4
5
1:4
5
19:4
5
12:4
5
5:4
5
22:4
5
15:4
5
8:4
5
1:4
5
18:4
5
11:4
5
4:4
5
22:4
5
Time
Vo
ltage U
nb
ala
nce (%
)
SolutionSolution
Redistribution of single-phase welding machines
Voltage SagVoltage Sag
A decrease in RMS voltage between 10% to 90% of the nominal value for duration from half cycle to 1 minute
1 minute
or less
Starting of electric motorsSwitching “on” of large loadsFault on either distribution, transmission, or generation systems
14
Voltage SagVoltage Sag
410
420
430
440
450
460
0.000 0.025 0.050 0.075 0.100 0.125 0.150
PerkinElmer Main - 6/3/2004 14:50:13.142
EPRI/Electrotek PQView®
RM
S V
olta
ge
(V
)
Time (s)
V RMS AB V RMS BC V RMS CA
• Nominal Voltage: 460V• Magnitude: 88.41%• Duration: 4 cycles• Cause: Fault on the
adjacent substation
Susceptibility Susceptibility
CurveCurve
Information Technology Industry Council (ITIC) curve was developed to accurately reflect the performance of computer-type equipment.
It is generally applicable to other equipment containing solid-state devices.
Voltage Sag ProblemVoltage Sag Problem
• Mall somewhere in the north
• 3 transformers, 1.5MVA each, 34.5kV / 230V
• Mall tenants are complaining of power “fluctuations” that causes equipment
shutdown
• Mall pumps and fans shutdown on power “fluctuations”
15
Monitoring ResultsMonitoring Results
Within
RecommendedLimits
2.5% 1.85%1.02%0.38%Voltage Unbalance
Vca – 3.94%
5%13.59%Vbc – 4.37%0.66%Outside
RecommendedLimits
Vab – 3.63%Current Total DemandDistortion
Vca – 1.18%
5%2.50%Vbc – 1.20%0.31%
WithinRecommended
Limits
Vab – 1.16%Voltage
HarmonicDistortion
Vca – 101.15%
±10%105.83%Vbc – 103.32%99.83%RMS VoltageWithin
RecommendedLimits
Vab – 102.37%
CommentLimitsMaximumAverageMinimumParameter
Voltage SagsVoltage Sags
Transient1 cyc89.41%14:108/17/05
Transient5 cyc69.09%14:108/17/05
No data1 cyc81.87%11:008/15/05
ShutdownNo data4 cyc70.11%10:238/11/05
Transient13 cyc88.02%16:488/6/05
ShutdownTransient5 cyc71.39%16:468/2/05
Lightning4 cyc88.32%18:338/1/05
line trip2 cyc88.77%12:517/31/05
NPC 230kV3 cyc82.86%12:517/31/05
Transient2 cyc87.67%13:277/30/05
7 cyc36.12%18:427/26/05
9 cyc34.79%18:417/26/05
8 cyc36.67%18:407/26/05ShutdownEquipment Failure
9 cyc38.75%18:367/26/05
Effect on
Customer
Coincident DataDurationMagnitudeTimeDate
Findings / RecommendationFindings / Recommendation
• Voltage regulation, unbalance, and voltage harmonics are within prescribed limits
• Adjust the -5% under-voltage relay setting to -10% and include 1 sec delay
• Holding coils could be installed to increase voltage sag ride-through
• Reduce ITDD levels to within limit
16
Customer FacilityCustomer Facility
• High rise residential building
• 2 - 53 story buildings with 396 semi-furnished units
• each unit is equipped with two refrigerators and two freezers
(personal-size)
Supplier InvestigationSupplier Investigation
“Cause of motor-compressor failure is due to low voltage”
Monitoring EquipmentMonitoring Equipment
17
Monitoring ResultsMonitoring ResultsPhase AB, BC and CA RMS Voltage Chart
220
225
230
235
240
245
15:3
5:0
0
17:3
5:0
0
19:3
5:0
0
21:3
5:0
0
23:3
5:0
0
1:3
5:0
0
3:3
5:0
0
5:3
5:0
0
7:3
5:0
0
9:3
5:0
0
11:3
5:0
0
13:3
5:0
0
15:3
5:0
0
17:3
5:0
0
19:3
5:0
0
21:3
5:0
0
23:3
5:0
0
1:3
5:0
0
3:3
5:0
0
5:3
5:0
0
7:3
5:0
0
9:3
5:0
0
11:3
5:0
0
13:3
5:0
0
15:3
5:0
0
17:3
5:0
0
19:3
5:0
0
21:3
5:0
0
23:3
5:0
0
1:3
5:0
0
3:3
5:0
0
5:3
5:0
0
7:3
5:0
0
9:3
5:0
0
11:3
5:0
0
13:3
5:0
0
15:3
5:0
0
Time
Volt
224
226
228
230
232
234
236
238
240
242
244
4 days monitoring
Monitoring ResultsMonitoring Results
VAB VBC VCA
Maximum 238.4 239.9242.7
(+5.52%)
Minimum227.0
(-1.3%)229.6 231.1
Nominal Voltage: 230V
Most Probable CauseMost Probable Cause
• Voltage sags and short duration interruptions can contribute to the degradation and eventually failure of the motors.
• If the motor-compressors were running prior to an interruption, large inrush current will be imposed on the motor winding as it tries to restart when power is restored.
• Results to over-heating and additional motor stress
18
RecommendationsRecommendations
• Installation of time delay switch. This will provide ample time for pressure equalization in the compressor and thus lower the motor load.
• Installation of a thermal protector on the motor-compressor. This will prevent burning of the motor winding due to overloading / overheating.
What is the best solution?What is the best solution?
1
3
EquipmentSpecification
ControlProtection
Over-all
ProtectionInsidePlant
4
Utility
Solution
Increasing Cost
Controls
Motors
Other Loads
2
Think about it….Think about it….
19
End of PresentationEnd of Presentation
Good day!
BackgroundBackground
An electrical service contractor offered Company X installation of additional capacitor banks to improve pf and avail of the pf discount
• Several days after the installation of the new capacitor banks, the existing old capacitor bank failed.
• The electrical service contractor sought the help of MERLACO PQ Team to determine the feasibility of installing a 1800 kVar capacitor at the high voltage feeder in place of the existing capacitor banks.
BackgroundBackground
20
Single Line DiagramSingle Line Diagram
Requirements for Requirements for
evaluationevaluation
• Magnitude of harmonic currents
• Equivalent circuit model
Channel Average Max im um
ITDD A 17.85% 25 .21%
ITDD B 17.17% 23 .87%
ITDD C 18.08% 24 .20%
Current TDDCurrent TDD
Measured using Dranetz-BMI 7100 PQ Node
21
Harmonic CurrentHarmonic Current
Statistical Summary of Current TDD and Harmonics
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
TD
D 3 5 7 9
11
13
15
17
19
21
23
25
TDD and Individual Harmonics
% o
f B
as
e C
urr
en
t
CP05
Average
CP95
PQView®
• Equivalent circuit for nth harmonic frequency
• Equivalent circuit for fundamental frequency
Equivalent CircuitEquivalent Circuit
• XT0 - tx impedance at fund. freq. ω0, 0.0649 pu
• XS0 - source impedance at fund. freq. ω0, 0.021189 pu
• XC0 - capacitor impedance at fund. Freq. ω0, 1.94 pu
• VCh - hth harmonic component of voltage across the
capacitor
• Vh - hth harmonic component of the voltage at
transformer secondary
• Ich - hth harmonic component of the current through
the capacitor
• Ih - hth harmonic current generated by the load
Variable DefinitionsVariable Definitions
22
• Determine hr
Let,
Which results to
h
C
S
C
S
Ch I
X
Xh
X
Xh
I
−
−
=
0
02
0
02
1
012
=−
C0
S0r
X
Xh
57.9021189.
94.1
0
0===
S
Cr
X
Xh
Resonant FrequencyResonant Frequency
Determine the effect of resonance to the capacitor current and voltage, and the load voltage
h
r
rCh I
h
h
h
h
I
−
−
=
2
2
2
2
1
−
=
2
2
1r
rhSCh
h
h
h
h
IjXV
−
+=
2
20
1r
rSThh
h
h
h
h
XhXjIV
Effect of ResonanceEffect of Resonance
Equations for equivalent
circuit for fundamental
frequency
00
0.1
CS
ChXX
I−
=
00
0
CS
CCh
XX
XV
−
−=
00
0
CS
Ch
XX
XV
−
−=
Effect of ResonanceEffect of Resonance
23
h Ih Ic Vc Vh
1 -1.00000* -0.51011* -0.95038* -0.92472*
3 0.02760 -0.00301 0.17814 0.00732
5 0.20403 -0.07664 2.72252 0.09594
7 0.05450 -0.06275 1.59227 0.04215
9 0.01023 -0.07852 1.54958 0.02290
11 0.03950 0.16233 -2.62120 -0.00043
13 0.01907 0.04161 -0.56850 0.00988
15 0.01060 0.01787 -0.21164 0.00801
17 0.04940 0.07231 -0.75549 0.04625
19 0.03610 0.04837 -0.45215 0.03958
21 0.01393 0.01758 -0.14873 0.01737
23 0.01300 0.01572 -0.12141 0.01808
25 0.00753 0.00883 -0.06271 0.01154
Effective voltage across the capacitor will
reach as high as 460% of nominal voltage!
Harmonic Current & Voltage Harmonic Current & Voltage
MagnitudeMagnitude
RecommendationRecommendation
Installation of the capacitor at the high
voltage feeder should be complemented with preventive measure/s to prevent harmonic resonance. This could be
through:
– installation of reactors at the capacitor for harmonic de-tuning or
– filtering of the harmonics at the harmonic generating load.