Power Quality
Monitoring
Textbook:
Power Quality in Electrical System: Chapter 14
Electrical Power Systems Quality:
Section 11.1, 11.3.1 ~ 11.3.9, 11.4
1
Power quality monitoring
⚫ PQ monitoring is the process of gathering, analyzing and
interpreting raw measurement data into useful information.
⚫ Gathering – continuous measurement of voltage and current over an
extended period.
⚫ Analysis, interpretation –traditionally performed manually, now
possible to be implemented by intelligent systems.
⚫ PQ monitoring programs are driven by the demand for improving the
performance.
⚫ Customers with sensitive loads
⚫ Computer networking and telecommunication facilities, semiconductor and
electronics manufacturing facilities, biotechnology laboratories, and financial
data-processing centers.
2
Contents
⚫ Monitoring Considerations
⚫ Instruments
⚫ Assessment of Power Quality Measurement
Data
⚫ Case Study
3
Monitoring objectives
⚫ Objectives determine the choice of monitoring equipment,
triggering thresholds, methods for data acquisition and storage,
analysis and interpretation requirements.
⚫ Common objectives
⚫ Characterize system performance –proactive approach
⚫ Characterize specific problems – reactive
⚫ Monitoring as part of an enhanced power quality service
⚫ Monitoring as part of predictive or just-in-time maintenance.
4
Monitoring as part of a facility site
survey
⚫ Site survey – evaluate power quality and equipment
performance throughout a facility
⚫ Inspect wiring and grounding concerns
⚫ Equipment connections,
⚫ Voltage and current characteristics (RMS, THD…)
⚫ Initial site survey – obtain information from customer
⚫ Nature of the problems (data loss, nuisance trips, component failures,
control system malfunctions, etc.)
⚫ Problems experienced by sensitive equipment
⚫ The times at which problem occur
⚫ Coincident problems or know operation (capacitor switching)
⚫ Possible sources (motor starting, power electronics equipment)
⚫ Existing PQ conditioner
⚫ Electrical system data (diagram, transformer size…)
5
Determine what to monitor
⚫ A wide variety of PQ disturbance
⚫ Monitoring equipment performance
⚫ Transients: high frequency sampling rate
⚫ RMS, THD, time-duration
⚫ Data collection requirements
⚫ Communication
⚫ Data management
⚫ Report preparation
http://www.dranetz-
bmi.com/images/ellen4_sag.bmp
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http://www.kjt.com/technical-overview.php
Choose monitoring locations
⚫ Customer service entrance locations
⚫ Characterize customer load current variation
⚫ Harmonic distortion level
⚫ Reduce transducer costs
⚫ Indicate the origin of the disturbances
⚫ Utility or customer side
⚫ Characterize specific PQ problem – locate as
close as possible to the equipment affected
7
Options for PQ monitoring equipment
⚫ Digital fault recorder (DFRs)
⚫ Not designed for PQ monitoring
⚫ Trigger on fault events
⚫ Record voltage and current event
⚫ Example: DFR from GE
⚫ Other options are listed in the textbook
8
Setting monitor thresholds
⚫ Best approach: select that match the specifications
of the equipment
⚫ Alternative approach:
⚫ Set thresholds fairly tight for a period of time
⚫ Select appropriate threshold for longer-duration
monitoring
⚫ Some equipment has fixed setting.
⚫ Some let you choose among several widely-used
standards.
9
Quantities and duration to measure
⚫ Voltage:
⚫ Quality of power being delivered
⚫ System response to harmonics
⚫ Current:
⚫ Harmonic – individual load, a group of loads, entire facility
⚫ Duration:
⚫ Sag: a significant length of time
⚫ Problem involves capacitor switching: a couple days
⚫ Harmonic, flicker: at least 1 week
10
Finding the source of disturbance
⚫ Correlate the disturbance waveform with possible
causes (terms)
⚫ General guidelines
⚫ High frequency voltage variations limit to locations
close to the source of disturbance.
⚫ Power interruption close to the monitoring location
cause a very abrupt change in the voltage
⚫ The highest voltage distortion levels occur close to
capacitors that cause resonance problem.
11
Contents
⚫ Monitoring Considerations
⚫ Instruments
⚫ Assessment of Power Quality Measurement
Data
⚫ Case Study
12
Power quality measuring
instruments
⚫ Wiring and grounding test devices
⚫ Multimeters
⚫ Oscilloscopes
⚫ Disturbances analyzers
⚫ Harmonic analyzers and spectrum analyzers
⚫ Combination disturbance and harmonic analyzers
⚫ Flicker meters
⚫ Energy monitors
13
Market of PQ instruments
⚫ North American power quality test and measurement market.
⚫ More than 50% of those revenue will come from permanently
installed monitors and instruments.
The global power quality meter
market is estimated to have a
market size of USD 870.5
Million in 2016, and is projected
to grow from 2016 to 2021, to
reach USD 1,252.0 million by
2021.
ecmweb.com/mag/electric_protect_system_pq/
14
http://www.marketsandmarkets.com/Market-Reports/power-quality-meter-market-34696492.html
Power Monitoring Market
Power Monitoring Market Size, Share & Market Forecast - 2024 | MarketsandMarkets
15
PQ instruments
⚫ Factors considered when selecting instruments
⚫ Number of channels (voltage and/or current)
⚫ Temperature specifications of the instrument
⚫ Ruggedness of the instrument
⚫ Input voltage range (e.g. 0 to 600V)
⚫ Power requirements
⚫ Input isolation
⚫ Ability to measure currents
⚫ Housing of the instruments (portable, rack-mount, etc)
⚫ Ease of use (user interface, graphics capability)
⚫ Documentation
⚫ Communication capability (modem, network interface)
⚫ Analysis software
16
Wiring and grounding test device
⚫ Megger ET3/2Earth resistance tester. 3 or 4 wire test of
ground resistance. Hand crank generator. (Price: USD 350)
http://www.equiptek.com/000.htm
⚫ Easy-to-use mains wiring tester
Price: USD 14
www.kewtechnik.co.uk/press/plug_top.php
17
Multimeters
⚫ Quick checks of the voltage and/or current levels
with a facility.
⚫ Overloading of circuits
⚫ Undervoltage and overvoltage
⚫ Unbalances
⚫ Method for calculate RMS value
⚫ Peak method, average method, true rms
⚫ Same for pure sinusoidal wave
⚫ Different for distorted waveform
18
Comparison of methods for
measuring RMS
http://upload.ecvv.com/upload/Info/200801/C20061128100225388851_Multimeter_YX_961TR.jpg
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http://i127.photobucket.com/albums/p129/majesticmodifications/multimeter.jpg
Digital Cameras
⚫ Photographs are extremely useful for
documentation purposes.
⚫ Human memory is unreliable
⚫ Nameplates of transformers, motors, etc.
⚫ Instrumentation setups
⚫ Transducer and probe connections
⚫ Key waveform displays from instruments
⚫ Substations, switchgear arrangements, arrester positions,
etc.
⚫ Dimensions of key electrical components
20
Oscilloscopes
⚫ Valuable for performing real-time tests
⚫ Waveforms of voltage and current
⚫ High voltage differential probe
⚫ Bandwidth: 100MHz
⚫ Differential voltage: 5000V
⚫ Common-mode voltage: 2000V
⚫ Some digital oscilloscope
⚫ Data storage
⚫ Analysis waveform
⚫ communications
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http://www.eeproductcenter.com/test-measure/review/showArticle.jhtml?articleID=51202441
Current Probes
⚫ Hall effect current probes detect all the way down to DC.
⚫ Generate an output voltage in response to a magnetic field
created by a current.
⚫ Prone to drift and should be calibrated prior to use
⚫ Current transformers (CTs)
⚫ Do not give an DC output
⚫ Conversion ratio when terminated in the proper resistance
22
Disturbance analyzers
⚫ Developed specifically for power quality measurements.
⚫ Short-duration disturbances
⚫ Long-duration disturbances.
⚫ Thresholds can be set
⚫ Left unattended to record disturbances over a period of time.
Spectrum/Harmonic analyzers
⚫ Compute fast Fourier transform
23
Combination disturbance and
harmonic analyzers
⚫ Modern Power Quality Analyzer
⚫ Smart Power Quality monitors
24
Flicker meters
⚫ IEEE standard 141-1993 and 519-1992 both
contain flicker curves
⚫ IEC Standard 61000-4-15
⚫ Guides for evaluate the severity of flicker
25
http://www.conformity.com/artman/publish/printer_128.shtml
Contents
⚫ Monitoring Considerations
⚫ Instruments
⚫ Assessment of Power Quality Measurement
Data
⚫ Case Study
26
Assessment of PQ data
⚫ Power Quality monitoring
⚫ Install monitor system
⚫ Data management, analysis and interpretation
⚫ Off-line analyses
⚫ Perform at central processing location
⚫ On-line analyses
⚫ Perform within instrument
27
Off-line PQ data assessment
⚫ Off-line assessment is carried out separately from the
monitoring instruments.
⚫ Off-line PW data assessment software:
⚫ Viewing of individual disturbance events
⚫ RMS variation analysis
⚫ Steady-state analysis
⚫ Harmonic analysis
⚫ Transient analysis
⚫ Standardized power quality reports
⚫ ……
28
On-line PQ data assessment
⚫ Analyze data as they are captured
⚫ More complex than off-line software
⚫ Advantage: provide instant message to notify user of
specific events of interest.
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Contents
⚫ Monitoring Considerations
⚫ Instruments
⚫ Assessment of Power Quality Measurement
Data
⚫ Case Study
30
Monitoring results of different sites
in UM
Site Computer FST K.C.Wong Library Gymnasium
Current Center (N102) Office Building Building Site
Average RMS A 125.41A 6.53A 11.01A 52.13A 7.943A
Average RMS B 31.88A 6.14A 5.52A 25.76A 2.213A
Average RMS C 24.45A 3.206A 6.13A 10.24A
Average RMS N 49.69A 5.701A 13.34A 13.80A
THD Min A 13.14% 31.06% 2.24% 3.49% 7.14%
THD Min B 29.73% 53.55% 3.74% 4.64% 14.09%
THD Min C 14.16% 20.27% 3.32% 4.31%
THD Min N 33.80% 110.70% 12.40% 3.61%
THD Max A 41.35% 91.50% 141.60% 51.18% 26.52%
THD Max B 50.73% 145.00% 859.00% 20.59% 37.81%
THD Max C 48.71% 50.54% 64.76% 23.13%
THD Max N 367.60% 1716% 539.40% 30.19%
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The blank cell is caused by limitations met during the monitoring
Detailed monitoring results of New
Academic Building
Three phase unbalance
Day Mon Tue Wed Thu Fri Sat
Average RMS
127.9A 122.2A 131.0A 123.1A 118.2A 126.8A
A
Average RMS
29.87A 31.29A 29.88A 36.44A 32.94A 31.91A
B
Average RMS
20.98A 19.82A 20.44A 28.62A 33.51A Neutral
Large 25.70Acurrent
C
Average RMS
52.13A 50.54A 52.82A 46.97A 43.98A 49.96A
N
THD Min A 13.14% 14.30% 14.24% 14.17% 16.55% 14.23%
THD Min B 34.39% 29.73% 30.43% 30.43% 30.23% 30.30%
THD Min C 27.99% 22.45% 19.08% 20.84% 14.16% 22.69%
THD Min N 39.49% 40.52% 39.48% 43.20% 53.01% 40.94%
THD Max A 41.30% 41.35% 34.18% 35.41% 33.80%Serious Harmonics
35.27%
THD Max B 45.45% 50.73% 48.25% 41.82% 50.04% 46.59%
THD Max C 47.75% 44.53% 48.71% 37.62% 30.78% 46.06%
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THD Max N 305.70% 367.60% 135.40% 269.30% 209.80% 187.00%
Measured Power Quality Results in UM
See Current Waveforms in New Academic Building of UM
i-c
i-b i-a
i-neutral
R.M.S Values: 33
i-a ➔ 46.09A , i-b ➔ 27.03A , i-c ➔ 43.85A , i-neutral ➔ 45.64A
Measured Results in UM
Measured Power Quality Results in UM
See THD of Current in New Academic Building of UM
i-neutral
i-a i-b i-c
34
Harmonic spectrum of
Neutral Current
Harmonic spectrum of neurtral current
100
80
60
40
20
0
1 3 5 7 9 11 13 15 17
Fundamental frequency Triple harmonics is caused
component is caused by by phase current harmonic
three phase unbalance components
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The End!
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