Transcript
Introduction to Power Quality: Problems, Analysis & Solutions Course: PQ103
Presented by:
PowerCET® Corporation 3350 Scott Blvd., Bldg. 55 Unit 1 Santa Clara, CA 95054 USA 408/988-1346 | FAX 408/988-4869 E-mail:
[email protected] E-mail:
[email protected] Web Page: http://www.powercet.com
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317)
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Introduction to Power Quality: Problems, Analysis & Solutions Course: PQ103 By PowerCET Corporation
Introduction to PQ Sections Introduction I. The Utility II. The Facility III. Harmonics IV. Ground / Grounding V. Power Problems VI. Power Conditioning / Mitigation Equipment VII. Network Protection VIII. Safety IX. Planning & Performing a PQ Survey 2
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
The Electrical Environment & Power Quality • • • • • •
What is it? ...Quality or Reliability? Why is it important? How do we measure it? Is it getting better? Where do electrical problems come from? What can we do about it?
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Power Quality (def.) • "Poor Power Quality" generally mean there is sufficient deviation in the power (electrical) supply to cause equipment/process mis-operation or failure. • "Good Power Quality" means that the power (electrical) supply is sufficient for the equipment/process to operate satisfactorily. • Equipment design is a major determinant between good and bad power quality. 4
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Quality & Reliability • Power Reliability is the presence of sufficient voltage at the meter. • Power Quality is the value of the voltage (and other electrical parameters) as a percent of nominal at the meter.
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Power Quality - Translated • If you can achieve what you want--making widgets, etc.--in the existing electrical environment then power quality would be considered good! • If you can not achieve the desired results in the existing electrical environment then power quality would be considered bad! • It can change from good to bad in an instant! 6
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Some Additional PQ Observations • 95% of the PQ problems are on the customer side of the meter. • 80% of the $$$ losses are caused by the 5% of the problems from the utility side of the meter. • The vast majority of the problems from the utility are voltage sags.
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Sources of Power Quality Problems in Order of Frequency of Occurrence • • • • • •
User loads User electrical distribution and grounding Weather related...lightning, wind, rain, etc. Utility distribution. Utility transmission. Utility generation.
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
The Cost of Poor Power Quality • Various studies (annual costs to U.S. business).... – Clemmensen (1993) $25.6 Billion – EPRI (1995) $400 Billion – Swaminathan and Sen (1998) $150 Billion – Douglas (2000) $50 Billion
• The truth is no one really knows...our cost accounting systems just do not capture the data to provide an accurate indication of the true cost of poor power quality
• . 9
The Cost of Poor Power Quality Compressor manufacturer: Sags and interruptions cost some $1,700,000/year. ($100,000 per event.)
DuPont: Saved $75 million/annually by implementing PQ solutions. ($50,000 to $500,000 per event...additionally risk of accident and pollution.)
Paper Industry: Billinton study determined cost of 2 second outage to be approximately $30,000
Automotive Industry: Momentary interruptions cost some $10 million/year ($50,000 to $500,000 per event.)
Air Traffic Control: Lost control at a major airport can cost $15,000-$50,000/minute
Source: EPRI Power Electronics Applications Center
10
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Interruption Cost Calculator • Disturbance Statistics – – – – – – – – –
• Cost of Losses
Downtime duration (Hrs.) Recovery time (Hrs.) Number of idled personnel Average hourly rate ($/Hr) Number of recovery personnel Average hourly rate ($/Hr) Payroll overhead & benefits ($/Hr) Scrap material (units) Scrap material unit cost ($/unit)
– Other lost material value ($) – Canceled orders – Late delivery / performance penalty payments – Lost customer confidence
• Recovery Costs – Equipment repair/replacement costs – Software / restarting costs (labor & material)
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The "9s" of Reliable Power Applications
Disruption Duration/Year
99.9%
Homes
9 Hours
99.99%
Factories
59 Minutes
Reliability Three 9s Four 9s
Standby Generator Five 9s
99.999%
Hospitals, Airports
5 Minutes
Multiple Redundancy UPS, Standby Generators Six 9s
99.9999%
Banks
32 Seconds
Mirrored Sites, Multiple Redundancy UPS, Standby Generators Nine 9s
99.9999999%
On-line Markets
30 Milliseconds
Source: Reliable Power Meters
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Failing to "Look" Beyond the Traditional Power Quality Environment
Power Problem
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Looking Beyond Traditional Power Quality
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Why is the Quality of the Environment Important? Load
Electrical
Sensitivity
Environment Load RELIABILITY
Electrical
Environment
Sensitivity
PRODUCTIVITY Infrastructure Equipment
PROFITABILITY
Management Compatibility Infrastructure
Equipment
Management
Compatibility
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What Determines Electrical Environment Quality?
Generation
Climatic & Geographic
T&D
Facility Wiring & Construction
Traditional Loads
Electronic Loads 16
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Electrical Loads • Traditional – Lights – Motors L N
Electronic
L N
AC DC
G 17
Sources of Electrical Problems • External – Utility sources – Other utility customers – A.O.G.
• Internal – Wiring errors and poor construction practices – Other loads – EMI / RFI
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Evaluating the Changes Over the Past 30Years • Equipment characteristics
• Technology
• Environment
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Equipment Characteristics • Past... – Inefficient power supply, voltage regulation generally required. – Large physical size – Increasing applications – Limited networking (stand alone systems)
• Present... – Compact, high efficiency design – More sensitive to high frequency electrical noise – Increased temperature sensitivity – Voltage regulation generally not required – Increasing networking applications 20
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
The Technology • Past... – Discrete components -relatively robust, high power logic – Slow data rates and processor cycle times
• Present... – Increasing IC densities – Increasing processor speed and data rates – Switch mode & PFC power supplies – Increasing network applications – New technology • Wireless , Cellular, Power line networks... 21
The Environment • Past... • Present... – Engineering, – Limited internal engineering, Construction & if any Maintenance – Out-source most • Internal (Except for construction very large jobs or – Deferred maintenance additions) – Little internal control over • Good records electrical environment • Good infrastructure – Installation by Folklore and management Tradition – Lack of understanding of the Real World Environment 22
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
The Future... • • • • •
Increasing complex applications Component technology continues to evolve Increasing operating speeds and data rates Increased networking applications Power supplies--CE Mark complications / harmonic limits – Decreased filter capacitors to reduce harmonics also decreases effective ride-through...voltage regulation??? – Application of "choppers" to provide sinusoidal current draw results in increased low frequency emissions and voltage source interactions 23
Increased Data Rates and Processor Speed
Data Rate (bps)
Time
60 2400 1M 10 M 100 M 1G
16.7 mS 417 uS 1 uS 100 nS 10 nS 1 nS
Approximate Distance 3100 Miles 78 Miles 982 Feet 98 Feet 10 Feet 1 Foot 24
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Supply Technology LINEAR D.C. POWER SUPPLY LARGE 60Hz TRANSFORMER L LINEAR REGULATOR
N
Vo
N:1
L
SMALL HF TRANSFORMER
N
Vo
SWITCH MODE D.C. POWER SUPPLY
PWM 25
The Changing Electrical Environment • Changing electrical loads (SCRs) – Variable speed drives (ac & dc) – Frequency modulators – Large UPS systems • Loss of control over the internal electrical environment • Decreased infrastructure management and control • Changing residential electrical environment
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
The Electromagnetic Environment Electrical Service Configuration
Telco Interface & Protection
Network Facilities Dist & Prot
Electric Utility Reliability
Mission Critical Eqpt & Sys
EMI & RFI
Facility Wiring, Grounding & Construction
Facility Loads (Harmonics)
Electrostatic Discharge (ESD) Control 27
The Future of Power Quality • • • • •
The Utility The Mitigation Equipment Supplier The Consulting Engineer The Electrical Contractor The User
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
The California Experience
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Electric Utility Deregulation
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Electric Utility Deregulation Deregulated Electric Utility Industry Power Producers (GENCOs or IPPs) Regional Transmission Network Operators (TRNSCOs)
Vertically Integrated Electric Utility Generation Transmission Distribution
Deregulated & Industry Restructuring
Customer Service
Bulk Power Trader (POWERCOs) Distribution System Operators (DISTCOs) Retail Power Marketers (RETAILCOs) Energy Service Companies (ESCOs) 31
PQ and the User • • • •
Will become more demanding Will increase reliance on electrical energy Will have a greater variety of loads May, in some instances, make Power Quality a PRIORITY!
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
You Never Have a Problem...
Until You Plug it IN!
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
I The Electric Utility System
The US National Grid • Transmission level interconnections • Evolving mission from backup to power transfer • Three major interconnections
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Electric Utility Energy Sources
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Electric Utility Customers & Usage
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Quality & Utility Reliability
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Electrical Conditions that can Disrupt a Process. • Voltage sags, i.e., 90% of nominal for 6-12 cycles • Single phasing, i.e., loss of one of three phase sources • Voltage interruption of several cycles caused by a utility reclosure operation • Complete extended power outage • Transients caused by: – Lightning – Utility grid and capacitor switching – Non-linear loads 6
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Std. Nominal System Voltages Voltage Class
2-wire 120*
Low Voltage (LV)
Medium Voltage (MV)
High Voltage (HV)
Extra High Voltage (EHV)
3-wire 120/240* 480 600 2400 4160 4800 6900 13800 23000 34500 46000 69000 115000 138000 161000 230000 345000 500000 765000 1100000
4-wire 240/120 208Y/120 480Y/277 4160Y/2400 8320Y/4800 12000Y/6930 12470Y/7200 13200Y/7620 13800Y/7970 24940Y/14400 34500Y/19920
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Power Quality and the Utility • Transformers – Transmission & distribution – Service • • • •
wye delta open delta red-leg (high-leg) delta OR
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Service Transformers • Single phase
• Three phase
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Service Transformers Pad mount 3-phase pole mount 3-phase red-leg delta
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Protective apparatus • Fuses and circuit breakers • Lightning arresters and suppressors • Insulators, conductors and switches
11
Circuit Breakers / Reclosure • 5 to 6 Cycles for operation after application of the fault condition – Customer experiences a sag during this interval
• Open duration from 20 cycles to 2 to 5 seconds – Actual duration depends on location of fault and local utility practices
• Multiple operations (typically 3) may be experiences if the fault does not clear during initial operations 12
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Reclosure
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Utility Fault Clearing: Reclosure Operation
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Utility Reclosure Operation • Utility fault on customer feeder
V & I = Source
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Utility Reclosure Operation • Fault on adjacent feeder
V & I = Source
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Utility Reclosure Operation / Lightning
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Sag Correcting Devices • Softswitching Technologies
Dip Proofing Technologies, Inc.
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Factor Correction Capacitors
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Corrective apparatus • Voltage regulating equipment • Power factor correction capacitors
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Factor Capacitor Switching • Zero Voltage Sensing Control--before & after
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Utility Fault – Time Plot Data Timeplot
300
Volts
275 250 225 200 A Vrms
1500
B Vrms
C Vrms
B Irms
C Irms
1250
Amps
1000 750 500 250 0 00:00 05/13/2008 Tuesday
A Irms 03:00
06:00
09:00
12:00
15:00
18:00
21:00
00:00 05/14/2008 Wednesday
Event #104 at 05/13/2008 08:13:16.450 CV Mild Bipol Trans Neg 1/4 Cyc
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Utility Fault – Sag Event Details/Waveforms
Volts
400 200 0 -200 -400 AV
BV
CV
Volts
300 280 260 240
Amps Amps
A Vrms (val) 750 500 250 0 -250 -500 -750 500 450 400 350 300 250 200
AI
A Irms (val) 08:13:16.4 05/13/2008 Tuesday
08:13:16.5
B Vrms (val)
BI
CI
B Irms (val)
C Vrms (val)
DI
C Irms (val) 08:13:16.6
08:13:16.7
Event #104 at 05/13/2008 08:13:16.450 CV Mild Bipol Trans Neg 1/4 Cyc
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Utility Fault – Single Phasing
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
II Building & Facility Wiring
Service Entrance • Main disconnect and overcurrent protection (circuit breakers). • Building electrical system earth reference (neutralto-ground bond). • Earth grounding system. • Equipment grounding system. • Wiring errors and electrical code violations (NEC Article 250).
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Building (Facility) Wiring BUILDING SERVICE TRANSFORMER
MAIN ELECTRICAL SERVICE PANEL
FEEDER
SUB-PANEL
G
N-G BOND
PLUG/ RECEPTACLE
G EARTH GROUNDING SYSTEM
UTILIZATION EQUIPMENT
N
NEUTRAL BUS
N
BRANCH CIRCUIT
GROUND BUS
EQUIPMENT GROUNDING SYSTEM (GREEN WIRE)
EARTH GROUND
3
Ground Fault Circuit Interrupt Protection for personnel: NEC 210-8 [1996 - 2005] –32 separate references in the 2002 code & 39 references in 2005 code. –Receptacles, portable devices, bathrooms, etc. y5mA response level
SHUNT TRIP
GFI SENSE TEST
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Facility Ground Fault Protection Service entrance •Protection for switchgear yNEC 230-95 [1996 - 2005] y>1000 ampere & >150V L-G yMaximum response levels: 1200 amperes & 1 second ySlowest and highest response levels at service entrance
Exceptions –Service entrances with multiple input breakers (six or less) none of which have ampacities equal to or greater than 1000 amperes. –Continuous industrial services where the interupption of power poses more hazard than relying upon normal overcurrent interruption –Services with high impedance grounded neutral systems.
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Ground Fault Interrupt (GFI) • Required for all 480V services rated at 1000A or more.
• GFI problems – Excessive current from voltage sag or load operation. – Harmonic distortion confuses current summing circuitry. – Electrical noise (interference) confuses the GFI controller
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Ground Fault Interrupt 1 Polyphase -- single CT GFI -- "zero sequence"
SHUNT TRIP
GFI SENSE
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Ground Fault Interrupt 2 Polyphase -- Multiple CT GFI -- "residual"
SHUNT TRIP
GFI SENSE
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Ground Fault Interrupt 3 Neutral-to-ground bond detect - "source"
SHUNT TRIP
GFI SENSE
9
GFI Problems Magnetic pickup from adjacent circuits Voltage and current harmonics vs CT response EMI/RFI sensitivity Trips settings too low for the application GFI on primary of N/G bond in wye-to-wye systems Neutral return current flow through N/G bond CT in multiple grounding systems
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Ground Fault Interrupt (GFI) Troubleshooting • Monitor neutral-to-ground bond to determine if tripping is the result of a fault or wiring errors. • Monitor for distortion levels. • Monitor service voltage levels. • Have GFI circuitry tested and calibrated. • Do not disable GFI equipment or adjust threshold limits to their maximum range.
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Distribution Transformer Uses • Isolation • Voltage transformation (step-up/step-down). • Limit neutral-to-ground voltage differentials. • Limit and control undesirable neutral return currents (delta-to-wye
Line
Voltage Transformation
Neutral Ground Neutral-to-Ground Voltage Differential = Near Zero
ØA
ØA
ØB
ØB
ØC
ØC
Neutral Eqpt Grounding Conductor
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Other Transformer Considerations • Separately derived systems must be grounded as outlined in NEC Article 250 or 645. • Transformers 1000VA and larger must be grounded to the nearest grounding electrode (NEC Article 250). • Health care facilities have special requirements.
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Separately Derived Sources • Neutral continuity is the key determinant. If the neutral is interrupted or switched then the source is probably separately derived. • If separately derived then the source must be bonded to the building grounding electrode system (BGES). • Autotransformers (voltage changers) are not separately derived.
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Panelboards (sub-panels) •
1, 2. Incoming Hot wires. There is 240 volts between these wires, or 120 volts between either wire and the neutral line.
•
3. Neutral wire. This is at the same electrical potential as the ground. At the main breaker only, the neutral is connected to ground.
•
4. Ground Bus Bar. This strip of metal has a row of screws for connecting the ground wires of the various circuits.
•
5, 6, 7. Neutral Bus Bars. This panel has 3 short bus bars for neutral wire connections. Some panels have only one long bar.
•
8. Circuit Breakers. Each single-pole breaker connects to one of the two hot bus bars. Each double-pole breaker connects to both of the bus bars (thus providing 240 volts between hot wires).
•
9. The last available space in this panel. Our new breaker will go here.
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Neutral to Ground Bonds • Only ONE allowed! • Extra bonds are common through mis-wiring & equipment problems • Use separate neutral & ground buses • Monitor circuit and ground conductors
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Overcurrent Protection: "Do's & Don'ts" • Circuit breakers must be ganged for poly-phase circuits. • Avoid using fuses in feeders as supplemental protection in poly-phase circuits unless phase loss detection is installed. • Overcurrent devices can only be loaded to 80% of their rated capacity.
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More: "Do's & Don'ts" • Inspect panelboards for loose, noisy or excessively hot circuit breakers (IR or Ultra-sonic scans). • Inrush (nuisance) tripping -- replace older breakers. • Excessive voltage drop across circuit breaker -replace (it will be the HOT one).
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Ultrasonic Detectors (Translators)
45KHz
In
Amp
Mixer
Amp
Out
5KHz
40KHz Osc
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Mechanical Connections • Conduit instead of grounding conductor – – – –
Screw thread Clamp Compression sleeve Flexible
• Wiring termination practices – Mixed wires & double-lugging – Solid vs stranded – Copper vs aluminum
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Feeders & Branch Circuits • Recommended voltage drops – Feeders 3% – Branch circuits 3% – Overall 5%
• Methods to decrease voltage drop – Increase wire size – Decrease load – Decrease length of circuit
• Shared Neutral Circuits (Feeders)
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Shared Neutral Facilities • Multi-wire circuits and non-linear loads • Non-canceling neutral return currents • Symptoms of high impedance (open) shared neutral conductors – High incidence of power supply failure – Erratic equipment operation – Load interaction
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
High Impedance Neutral Medium Load
Heavy Load
Light Load
A B C N G VOLTAGE L-N L-G N-G
PHASE A 143 122 54
PHASE B 73 122 54
PHASE C 166 123 54 23
Results of an Open Neutral • High Impedance Neutral
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Neutral Current - Sinusoidal Loads • No Imbalance – Phase currents offset
• Phase Imbalance – Imbalance = neutral
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Neutral Current and Computer Loads • Current pulses do not offset • Current in neutral can reach 1.73 times the size of individual phase currents • Frequency of current is 3x fundamental
A B C N G
– 150 Hz for 50 Hz – 180 Hz for 60 Hz
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Solutions for Multiwire Problems • Delta-wye transformers • Eliminate shared facilities / oversize neutral conductors • Filtering • Equipment redesign • Managing the environment
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Receptacles (NEMA Notation)
CONTACT TYPE "L" denotes locking type; nothing denotes straight blade.
TYPE OF CONNECTOR "R" denotes receptacle, or female. "P" denotes plug, or male.
L21-30R VOLTAGE TYPE 5 = 120V 6 = 240V, 208V 14 = 240/120V, 208V 21 = 208/120V, 3-Phase
CURRENT CAPACITY 15 Amps 20 Amps 30 Amps
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Standard & IG Receptacles
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IG Receptacle Construction
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
IG Applications • IG passes back through panels to service origin. • With separately derived source the IG must terminate within the derived service. • Grounding wire size must increase to match ampacity of panels it passes through.
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Common IG Errors • NEC violations – IG run separately from current carrying conductors – IG does not terminate at the derived service – IG grounding is separate from facility grounding. – Supplemental grounding at IG cannot serve as the sole grounding
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Automatic Transfer Switches
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Generator – ATS Setup 1 Continuous neutral Not separately derived 3 Pole ATS –Automatic transfer switch
GES –Grounding electrode system –Bonds to generator chassis
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Generator - ATS Setup 2 Separately derived Neutral interrupted 4 Pole ATS –Automatic transfer switch
GES –Grounding electrode system –Bonds to generator neutral and chassis
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Multiple Redundant System Isolation breaker between feeders Dual feeders - N+1 redundancy Fast acting transfer switch to power loads from A or B side Maximum load on any UPS is 25% N/G Bond???
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
ATS Configurations Break before make
Make before break
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Synchronizing Waveforms Synchronizing rate -- A / (A-B) –A frequency = utility; B frequency = generator –3 Hz delta @ 60 Hz = 20 cycles & 18° per cycle –0.1 Hz delta @ 60 Hz = 600 cycles @ 0.6° per cycle
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Make Before Break Transfer Sources paralleled and synchronized Phase offset at moment of transfer - 15° Preferred offset - 7° or less
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Non-Synchronous Transfers Flux opposing
Flux aiding
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Short Decay Time Transfer Decay time –Less than 2 cycles Common problem with some ATS Inrush Current –Almost 5kA inrush Waveform Instability –Following transfer
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Transformer: Out-of-Phase Transfer 200kVA transformer: 5% impedance 3mS break during transfer between sources
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Phase Position Vs Rotation
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
lll
Harmonics 1
Harmonics • Harmonics – Integer multiples of a fundamental -- added to fundamental create distorted sinusoidal or non-sinusoidal waveform – Harmonics are caused by Non-linear load currents & Non-linear voltage sources – Measurements of harmonic content does not always indicate the presence of problems
2
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Effects of Harmonics • Current – Current flow without work (low power factor) – Transformer & wiring losses – Negative sequence currents that reduce torque in motors – Excessive neutral current
• Voltage – – – –
Peak voltage loss and "ride-through” reduction Phase voltage imbalance Motor plugging or cogging Zero voltage cross distortion and frequency errors 3
Odd Harmonics • Symmetrical – 90°, 180°, 270° – Leading/trailing edge – Positive/negative cycle
• Single phase loads – 3rd, 5th, 7th, 9th...
• Polyphase loads – Frequency doublets – 5th & 7th, 11th & 13th
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Even Order Harmonics • Asymmetrical – 90°, 180°, 270° – Can shift the position of the fundamental causing loss of 120° phase shift between phases – Can cause dc bias problems in motors and transformers – Can cause phase control problems for SCR/Triac loads
5
Harmonic Order • Balanced harmonics – Frequency doublets: 6n +/- 1 – 5, 7; 11, 13; 17, 19; 23, 25 ... – Positive & negative sequence
• Zero Sequence Harmonics – Triplens: 6n-3 (odd multiples of 150/180 Hz) – Ground referenced (neutral)
• Even order harmonics – Conduction angle differences – Diode failure – 3 pulse rectifiers -- IEEE519
Harmonic # 3
Harmonic 3 Pulse & Sequence L/N Loads
6 Pulse
12 Pulse
18 Pulse
24 Pulse
0
x
5
-
x
x
7
+
x
x
9
0
x
11
-
x
x
x
13
+
x
x
x
15
0
x
17
-
x
x
x
19
+
x
x
x
21
0
x
23
-
x
x
x
x
25
+
x
x
x
x
27
0
x
29
-
x
x
31
+
x
x
33
0
x
35
-
x
x
x
x
37
+
x
x
x
x
39
0
x
41
-
x
x
43
+
x
x
45
0
x
47
-
x
x
49
+
x
x
x
x x
6
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-3
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Factor • Power Factor (PF): PF = Watts / Volt*Ampere • Displacement Factor (θ): Cosine of angle (E & I) • Distortion Factor (δ): δ = Afund / Arms
Displacement
Power Factor
Distortion
7
Power Factor • Power Factor (PF) – PF = Watts/Volt*Ampere
• Displacement Factor (θ) – Cosine of angle (EFND & IFND)
• Distortion Factor (δ) δ = AFND / Arms
8
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-4
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Distorted Voltage Waveform • High impedance distribution system – Load currents interact with impedance – Peak voltage loss and extended voltage waveform – Dominant harmonics third, fifth and ninth
9
Computer Load Current • Load current developed by computers • Dominant harmonic currents: – Third, fifth and ninth
10
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-5
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Calculations • Fundamental and harmonic contributions to power – Power = E * I * cosine of angle between E & I
• Phase angle affects power contribution – 0° to 90° (+) : 90° (0) : 91° to 180° (-) : 180 (-1) – 181° to 270° (-) : 270° (0) : 271° to 360° (+) Harmonic
Voltage
Phase
Current
Phase
Fundamental
121.8
87
32.75
103
Mean Power 3,832
3
12.1
48
14.1
306
-35
5 9 Total
2.8 1.7
264 52
8.3 1.6
167 0
-3 2 3,796 11
Power Factor Determination • • • • • • •
Mean power delivered = 3,796 watts RMS voltage = 122.6 volts RMS current = 36.7 amps Apparent power = 122.6*36.7 = 4,499 VA Power factor = 3,796/4,499 =0.84 Distortion factor δ = 0.89 Displacement PF = cos(θfun) = cos16 = 0.96
12
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-6
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Single Phase Angle Control Loads • Light dimmers and heater controls • Odd order harmonics dominant • Power factor and THD depend upon phase angle • Even order harmonics present when firing angle varies
13
Full Wave Power Supply • Computer loads • Harmonics – Odd orders dominant • 3rd, 5th, 7th, 9th, 11th... • Zero sequence harmonics • Triplens - 3rd, 9th, 15, 21st...
• THD can exceed 100% – Referenced to fundamental
• Power factor typically 0.7
14
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-7
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Half Wave Power Supply • Half cycle pulsed current – Asymmetrical current – DC bias
• Power Factor – 0.5 true power factor – Displacement power factor if load is inductive
• Harmonics – Odds - 3rd, 5th, 7th, 9th... – Evens - 2nd, 4th, 6th, 8th... – Source of zero sequence harmonics (triplens) - 3rd, 9th, 15, 21st... 15
6 Pulse Voltage Fed Load Each half cycle Double pulsed current Symmetrical current
Power Factor 0.8 true power factor - typical No displacement power factor
Harmonics Odd harmonics Frequency doublets (6n +/- 1) 5th, 7th; 11th, 13th...
16
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-8
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
6 Pulse Current Fed Load Pulsed current each half cycle Asymmetrical current due to
commutation differences
Power Factor 0.6 to 0.8 true power factor Displacement power factor due to
motor load
Harmonics Odd harmonics Doublets (6n +/- 1) 5th, 7th; 11th, 13th... Even harmonics - limited amounts
17
12 Pulse Current (UPS) • Top trace -- 100kVA UPS Normal operation • Bottom trace -- 100kVA UPS with problems – Input SCRs failed -- even order distortion about 40%
18
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-9
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Monitor & Harmonic Analysis
19
VTHD Graphical Display Waveform harmonics
% 1.50
1.25
1.00
0.75
0.50
0.25
0.00 THD
H02 DC
H04 H03
H06 H05
H08 H07
H10 H09
H12 H11
A VHarm AV RMS 287.16 FND 100.00 DC -0.00 THD 1.47
BV 286.20 100.00 -0.49 1.40
CV 286.59 100.00 0.46 1.39
DV 0.05 100.00 -188.19 663.44
H14 H13
B VHarm A-BV 495.95 100.00 0.28 1.46
B-CV 495.54 100.00 -0.55 1.35
H16 H15
H18 H17
H20 H19
H22 H21
H24 H23
H25
C VHarm C-AV 497.98 100.00 0.27 1.44
AI 396.46 100.00 0.03 11.41
BI 413.42 100.00 -0.41 11.74
CI 441.19 100.00 0.49 12.21
DI 41.28 100.00 -6.25 81.50
20
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-10
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
ITHD Graphical Display Waveform harmonics
% 12.5
10.0
7.5
5.0
2.5
0.0 THD
H02 DC
H04 H03
H06 H05
H08 H07
H10 H09
H12 H11
A IHarm AV RMS 287.16 FND 100.00 DC -0.00 THD 1.47
BV 286.20 100.00 -0.49 1.40
CV 286.59 100.00 0.46 1.39
DV 0.05 100.00 -188.19 663.44
H14 H13
H15
B IHarm A-BV 495.95 100.00 0.28 1.46
H16
H18 H17
H20 H19
H22 H21
H24 H23
H25
C IHarm
B-CV 495.54 100.00 -0.55 1.35
C-AV 497.98 100.00 0.27 1.44
AI 396.46 100.00 0.03 11.41
BI 413.42 100.00 -0.41 11.74
CI 441.19 100.00 0.49 12.21
DI 41.28 100.00 -6.25 81.50
21
ITHDNeutral Graphical Display Waveform harmonics
% 80 70 60 50 40 30 20 10 0 THD
H02 DC
H04 H03
H06 H05
H08 H07
H10
H12
H09
H11
DV 0.05 100.00 -188.19 663.44
A-BV 495.95 100.00 0.28 1.46
H14 H13
H16 H15
H18 H17
H20 H19
H22 H21
H24 H23
H25
D IHarm AV RMS 287.16 FND 100.00 DC -0.00 THD 1.47
BV 286.20 100.00 -0.49 1.40
CV 286.59 100.00 0.46 1.39
B-CV 495.54 100.00 -0.55 1.35
C-AV 497.98 100.00 0.27 1.44
AI 396.46 100.00 0.03 11.41
BI 413.42 100.00 -0.41 11.74
CI 441.19 100.00 0.49 12.21
DI 41.28 100.00 -6.25 81.50
22
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-11
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
PowerTHD Graphical Display Waveform harmonics
%
0.00
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07 THD
H02 DC
H04 H03
H06 H05
H08 H07
H10 H09
H12 H11
A PHarm AV RMS 287.16 FND 100.00 DC -0.00 THD 1.47
BV 286.20 100.00 -0.49 1.40
CV 286.59 100.00 0.46 1.39
DV 0.05 100.00 -188.19 663.44
H14 H13
B PHarm A-BV 495.95 100.00 0.28 1.46
B-CV 495.54 100.00 -0.55 1.35
H16 H15
H18 H17
H20 H19
H22 H21
H24 H23
H25
C PHarm C-AV 497.98 100.00 0.27 1.44
AI 396.46 100.00 0.03 11.41
BI 413.42 100.00 -0.41 11.74
CI 441.19 100.00 0.49 12.21
DI 41.28 100.00 -6.25 81.50
23
Harmonic Flow -- Power Monitor Harm
AV Harm [%]
THD
1.47
AV Harm [Deg]
AI Harm [%]
AI Harm [Deg]
AP Harm [%]
AP Harm [Deg]
11.41 0
0.00
0
Ө [Deg]
COS Ө
0
1.00
180
(1.00)
(0.00)
180
0.03
H02
0.51
270
0.45
300
0.00
22
31
0.86
H03
0.15
250
1.47
141
(0.00)
69
109
(0.32)
H04
0.19
270
0.28
283
0.00
9
13
0.98
H05
1.12
253
10.63
132
(0.07)
59
121
(0.52)
H06
0.15
271
0.27
167
(0.00)
55
104
(0.24)
H07
0.43
168
3.40
346
(0.02)
358
178
(1.00)
H08
0.10
260
0.13
236
0.00
3
23
0.92
H09
0.19
266
0.42
239
0.00
336
27
0.89
H10
0.10
262
0.10
208
0.00
358
54
0.59
H11
0.38
113
0.59
326
(0.00)
33
213
(0.84)
H12
0.07
261
0.12
261
0.00
1
1
1.00
H13
0.19
83
0.67
258
(0.00)
355
175
(1.00)
H14
0.04
260
0.15
281
0.00
17
21
0.93
H15
0.12
202
0.32
148
0.00
311
54
0.59 24
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-12
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Transformer Sizing • De-rating – ANSI C57.110-1986 – Standard ignores harmonic voltages and even orders
• K-factor – – – – –
Based upon UL1561 K-factor affected by source impedance Calculated number may be low Allow for increased transformer impedance Avoid the “Goldilocks” approach
25
K-Factor Calculations • Low-Impedance Source – K-Factor = 9.43 – Voltage rms = 117.8; Voltage peak = 162.2; Voltage crest factor = 1.38 – Current rms = 4.38; Current peak = 11.2; Current crest factor = 2.55
• High-Impedance Source – K-Factor = 3.73 – Voltage rms = 114.1; Voltage peak = 145.2; Voltage crest factor = 1.27 – Current rms = 3.83; Current peak = 7.9; Current crest factor = 2.06
26
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-13
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
K-Factor Correction • Compensation process – Vthd is <2% the K number is OK – Vthd is >2% and <6% then K+1 – Vthd is >5% then K+2
• Rule of thumb K rating – Standard K-Factors: 4, 9, 13, 20, 30, 40 & 50. – At service with load diversity • K = 4 or 9 – At load • K = 13 or 20
27
Power Supply W/O Power Factor Correction
28
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-14
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Supply With Power Factor Correction
29
Neutral Current • Old style switch mode power supplies – Draw current in unique pulses – Ratio of neutral vs. phase current can reach 1.73:1 • New style supplies with PFC – Power supplies with power factor correction circuitry (PFC) draw current in a more sinusoidal form. – Concentrations of PFC corrected supplies will offset and not contribute to neutral current. – Ratio of neutral vs. phase current may be less then 1 : 1. • The need to double neutral conductor size may decrease with PFC corrected equipment. • The need to double the neutral conductor size for theaters is a code requirement. 30
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-15
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Harmonic Propagation • Harmonic effects increase with load/source interaction • Odd harmonics develop naturally with rectangular waveforms • Even harmonics develop with asymmetrical waveforms – Asymmetry results in direct voltages and currents (dc) – DC conditions can adversely affect magnetic devices – Even harmonics often indicate load problems • Harmonic content normally decreases with increased frequency (1/3 of the third, 1/5 of the fifth...)
31
Harmonic Problems Summary • Overheated, noisy transformers • Overloaded or burned (hot) neutrals • Timing errors in logic controlled equipment • Blown SCRs • Capacitor failure • Variable speed drive (VSD) dropout
• Drift or hunting in electronic controls • Rapid motor failure or insufficient torque • Insufficient distribution capacity • Power factor or harmonic rate penalties
32
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-16
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Harmonics and Power Factor • Mitigation methods – Delta-wye transformers – Eliminate shared neutrals – Filtering – Phase angle blending for control of harmonics – Equipment redesign (linearize) – Management of the environment
• Displacement Factor = Power Factor – Correction capacitors should work
• Distortion Factor = Power Factor – Harmonic filters or phase shifting required
• Displacement & Distortion Present – Proceed with caution 33
IEEE 519
V harmonic
PCC I harmonic
34
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-17
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
IEEE 519 Harmonics Standard • Utility responsibility
• Customer responsibility
– Limit overall voltage distortion – General limit 5% THD at PCC – Maximum single harmonic 3% of fundamental
– Limit current injection into utility – Limits based on short-circuit capacity and maximum demand – Limits based on total demand distortion – Individual harmonics limited – Even harmonics limited to 25% of odd – No half-wave converters!
• Voltage distortion reflects – User-injected harmonic currents – Utility system impedance
35
IEEE519 Current Distortion Limits (120V Through 69000V) Maximum Harmonic Current Distortion in Percent of IL Individual Harmonic Order (Odd Harmonics) ISC / IL
<11
11 ≤ h < 17
17 ≤ h < 23
23 ≤ h < 35
35 ≤ h
TDD
<20* 20<50 50<100 100<1000 >1000
4.0 7.0 10.0 12.0 15.0
2.0 3.5 4.5 5.5 7.0
1.5 2.5 4.0 5.0 6.0
0.6 1.0 1.5 2.0 2.5
0.3 0.5 0.7 1.0 1.4
5.0 8.0 12.0 15.0 20.0
Even harmonics are limited to 25% of the odd harmonic limits above. Current distortions that result in a dc offset, e.g., half-wave converters, are not allowed. *All power generation equipment is limited to these values of current distortion, regardless of actual Isc / IL . where Isc = maximum short-circuit current at PCC IL = maximum demand load current (fundamental frequency component) at PCC. 36
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 3-18
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
IV Grounding
Origins For Grounding Concepts • Electrical code – Single point grounding – Fault path to electrical service • Telecommunications grounding – Traditional DC grounding practices – Ground start & signaling • RF grounding – Antenna grounding • Isolated grounding – U.S. practice 2
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-1
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Grounding • Earthing – Establishing a bond to earth at the facility service entrance for the electrical distribution system • Grounding (U.S. Convention) – Establishing fault clearing paths within a facility for the electrical distribution system and for equipment within the facility. • Referencing – Establishing a chassis contact to an external point to limit voltage rise. Magic Grounding
Vs
Science Grounding 3
Facility Grounding Considerations • Safety grounding ("earthing") – Reference the power system • Low frequency currents • Requires low resistance paths
– Personnel safety • Remove touch potential • Prevent unacceptable voltage rise
– Lightning protection • Provide discharge path for lightning currents.
4
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-2
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Equipment Grounding Considerations • Fault currents and leakage currents – Low impedance path to derived source • Touch potential and chassis potential – Low 60Hz impedance path to derived source • Signal & performance grounding – High frequency currents – Equipment performance – Reference is local equipment chassis – Low impedance paths • Low inductance • High capacitance
5
Grounding System • Earth grounding system – Grounding electrode conductor – Grounding electrode(s) • • • •
Driven rod(s) Metal buried water pipe Structural steel Concrete encased electrode (Ufer) • Buried ring or linear conductor
• Equipment grounding (conductor) system – Grounds exposed metal and cabinets – Starts at the neutral-toground bond – Must be run in same conduit as phase/neutral conductors – May use conduit – Connected to electronics dc & logic reference 6
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-3
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Essential Grounding References
7
The Roles of Grounding • General requirements – NEC 250.4 [2002 & 2005] – Establish voltage reference – Limit touch potential – Clear electrical faults – Carry lightning currents • Performance issues – Provide equipment reference – Provide RF/ESD discharge path
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-4
8
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Grounding Electrode System (GES) - 1 • National Electrical Code Article 250 – Electrical service entrance bonding • NEC 250-5 [1996] & NEC 250-20 [1999 - 2005] • Incoming utility neutral or internal facility neutral
9
Grounding Electrode System (GES) -2 • National Electrical Code Article 250 (cont.) – Grounding electrode system - NEC 250.50 • Structural steel where effectively grounded • "All grounding electrodes as described in 250.51(A)(1) through (A)(6) that are present at each building or structure served shall be bonded together to form the grounding electrode system." – – – – – –
Ufer grounds (concrete encased electrode) Building footings if designed as Ufer grounds Water pipes Ground ring Plate electrodes Driven grounding rods
10
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-5
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Earth Grounding System (GES)
11
Grounding Electrode System • • • •
Driven Ground Water Pipe Bond Structural Steel Bond Metering – Must not impede grounding path – NEC 250-50(a)(1)[1999] • Underground gas pipes – Not part of GES – NEC 250-51(a) [1999] • Gas pipes inside facility – Bonding after shutoff valve – NEC 250-104(b)[1999]
12
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-6
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Facility Grounding Standards • NEC – 25 Ohms or supplement – NEC 250-56 [2002] • Health Care – IEEE Std. 602-1996 (White) – Section (10.4.5.2) – No more than 10 ohms – 5 Ohms or less preferred • Industrial Plants – ANSI/IEEE Std. 141-1986 (R1999) (RED) – Section 7.5.2 – 1 ohm or less for substations – 5 ohms or less for industrial plants • Sphere of influence – Radius equals length of buried rod 13
Facility Grounding – Ground Rods
14
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-7
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Resistance Measurements • 3-Point Fall of Potential
• Single Point Measurement
15
Effects of Soil Moisture & Temperature
8' Ground Rod Resistance
8' Ground Rod Resistance 1,000
10,000
Ohms
Ohms
1,000
100
100
10
10
0
10
30 20
50 40
70 60
10 5
80
20 15
30 25
% Moisture Content by Weight
Temperature in F
16
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-8
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Ground Ring • Ground ring – NEC 250-81 [1996] – NEC 250-50(d) [1999] – NEC 250.52(A)(4) [2002 - 2005] • Buried at least 2.5' (762mm) • At least 20' long • No smaller than No. 2 gauge
• Augmented ring – Driven rods – Surface radials – Bond to structural steel • At corners • At regular intervals 17
Concrete Encased Electrode Concrete encased electrode Ufer Ground Ground rod in foundation (GRIF) –Encased in at least 2 inches (50.8mm) of concrete –Reinforcing bar may be bonded together by the usual steel tie wires –At least 20 feet (6.1m) of zinc galvanized conductor or steel reinforcing bar not less than 1/2 inch or 20 feet of bare No. 4 copper conductor –NEC 250-81-1996 & NEC 250-50(d) [1999] & NEC 250.52(A)(3) [2002-2005]
Required use - NEC 250.50 [2005] 18
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-9
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Ground Rod in Foundation
19
Electrically Conductive Concrete • Conductive components – Carbonaceous particles & metallic compounds • Uses – Deicing & snow melting of roadways & bridges – Ground plane effects in data centers & barns – Reducing electrolysis in grounding systems – Reducing earth resistance in grounding systems – Increasing surge current capabilities – Enhanced screen room control (Tempest) 20
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-10
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
San Earth Enhanced Concrete
21
Common Facility Power Systems Single phase 240/120
Three phase 480/277 & 208/120
22
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-11
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power/Grounding Variations Floated wye –Ground referenced voltages vary with leakage currents
Floated delta-delta –Ground referenced voltages vary with leakage currents
Corner grounded delta –One leg at earth potential, others at phase-to-phase potential
23
Wye Service Grounding Variations • Ground fault protected – >150 volts to ground – >1000A • Resistance grounded – Resistance or impedance – Chosen to protect against an arcing ground fault
24
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-12
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Impedance Grounded Service • 480/277Vac service – Greater than 150 volts to ground & more than 1000A • No neutral connected loads • Maximum response is 1200A and 1 second
– Ground referenced voltage during faults
25
Delta/Delta Service • Floated Delta Service – Absence of solid ground reference allows ground referenced voltage fluctuations • Load related fluctuations usually within voltage envelope of service • Utility related fluctuations reflect primary voltages • Lightning transients create severe dv/dt
26
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-13
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Common & Problematic Service Three phase delta voltages (240 delta) Single phase voltages (240/120) High leg delta (crazy leg, red leg etc.)
27
Hi-Leg Measurements
28
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-14
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Phase-to-Neutral & Phase-to-Phase
29
Safety Grounding System • Equipment grounding conductor – Grounds exposed metal and cabinets – Starts at the neutral-to-ground bond – Must be run in same conduit as phase/neutral conductors – May use conduit – Connected to electronics dc & logic reference
30
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-15
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Grounding Issues • Grounding conductor size – Is bigger better? • Transformer grounding • Ground loops • "Isolated" grounds
• Conduit instead of grounding conductor – Screw thread – Clamp – Compression sleeve – Flexible
31
Low Frequency Ground Current - 1 LEGEND: LOAD CURRENT
1 A
NEUTRAL RETURN CURRENT GROUND
SUB-PANEL UTILIZATION BUILDING ELECTRICAL SERVICE TRANSFORMER
EQUIPMENT
LINE 2 NEUTRAL GROUND
GROUND N-G BOND
C
B
D
SUB-PANEL
EARTH GROUND (MAIN BUILDING ELECTRICAL GROUND)
32
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-16
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Low Frequency Ground Current - 2 LEGEND: LOAD CURRENT
1 A
NEUTRAL RETURN CURRENT GROUND SUB-PANEL UTILIZATION BUILDING ELECTRICAL SERVICE TRANSFORMER
EQUIPMENT
LINE 2 NEUTRAL GROUND
GROUND
N-G BOND C
B
D
SUB-PANEL
EARTH GROUND (MAIN BUILDING ELECTRICAL GROUND)
33
Low Frequency Ground Current - 3 LEGEND: LOAD CURRENT
1
A
NEUTRAL RETURN CURRENT GROUND SUB-PANEL BUILDING ELECTRICAL SERVICE TRANSFORMER
UTILIZATION EQUIPMENT
LINE 2 NEUTRAL
N-G BOND
GROUND
GROUND C
B
D
SUB-PANEL F
EARTH GROUND (MAIN BUILDING ELECTRICAL GROUND)
E
"ISOLATED" GROUND, GROUND ROD, COLD WATER PIPE, ETC..
34
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-17
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Low Frequency Ground Current - 4 LEGEND: LOAD CURRENT
1
A
NEUTRAL RETURN CURRENT GROUND SUB-PANEL BUILDING ELECTRICAL SERVICE TRANSFORMER
UTILIZATION EQUIPMENT
LINE 2 NEUTRAL
N-G BOND
GROUND
GROUND C
B
D
SUB-PANEL F
EARTH GROUND (MAIN BUILDING ELECTRICAL GROUND)
E
"ISOLATED" GROUND, GROUND ROD, COLD WATER PIPE, ETC..
35
Neutral-to-Ground Voltage
NEC fine print note 210.19(a) FPN No.4 Branch circuits sized for maximum 3% drop with total 5% drop for feeder and branch circuit.
120 Vac 5% drop = 6 volts 3 volts lost in supply and 3 volts lost in return per phase Polyphase systems N/G can reach 5 volts (3*1.73 = 5.2) 36
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-18
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
High Frequency Ground Currents • Sources – Transients from load switching – Surge voltages and current from lightning – Electromagnetic interference – Radio frequency interference 37
High Frequency Interference Current - 2 • Interference caused by refrigeration motor • Affected RS-422/485 circuit and upset POS system
38
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-19
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Facility Exposure to Lightning
39
ANSI/IEEE C62.41-1991 Location C –>10kV –>10kA
Location B –6kV Impulse or Ring –3kA Impulse –500A Ring
Location A –6kV Ring –200A Ring 40
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-20
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Storm Problems - Lightning
41
Facility Grounding & Lightning Lightning treatment –Bond ground terminals to GES yNEC 250-106 [1999 - 2005]
–Air terminal conductors and ground terminals are not to be used in lieu of intended GES yNEC 250.60 [2005]
–250.106 FPN 2 y6' (1.83m) clear air spacing to conductive metalwork or 3' (0.92m spacing through wood, concrete or brick)
–NFPA 780-2004 (4.21.2) provides calculation for clearance from down conductors due to high voltage & ionization 42
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-21
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Lightning Protection System Grounding
43
Referencing Issues
44
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-22
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Separately Derived Sources • Neutral continuity is the key determinant. If the neutral is interrupted or switched then the source is probably separately derived. • If separately derived then the source must be bonded to the building grounding electrode system (BGES). • Autotransformers (voltage changers) are not separately derived.
45
Bonding Dual Power Sources • Dual power sources used to ensure redundancy. • Dual sources can be affected by “ground skew.” Ground skew refers to voltage differences between sources. • Bonding the sources together as well as bonding to the BGES helps reduce ground loop currents through equipment powered from the dual sources. 46
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-23
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
AC & DC Sources • AC & DC sources must also be bonded to the BGES to reduce common mode potentials in equipment powered from the sources. • Supplemental DC return bonds to ground cannot be placed at equipment. This causes unwanted DC current flow throughout the facility.
47
DC Bus Grounding • A = Isolated grounding – DC return grounded independently – Voltage differential possible between AC power and dc system
• B = Contiguous grounding – DC bonded to ac grounding means
48
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-24
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Common Mode Problems • AC reference? • DC reference? • Potential between systems?
49
Separate DC Grounding Conductor • DC grounding tied to main facilty grounding • DC grounding conductor run independent of ac conductors • Attempt to prevent crosstalk between ac and dc conductors
50
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-25
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Multiple DC Reference • Extra dc reference points turns grounding into a dc path • DC current flows everywhere (inversely proportional to the dc resistance values).
51
Signal Reference Ground & DC Systems
52
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Signal Reference Ground & AC Systems
53
Misapplied Signal Reference Grid • Attempt to reference equipment independently of facility grounding. • Violates NEC. – SRG not bonded to BGES per NEC 645. – SRG serves as sole grounding means independent of SRG.
54
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 4-27
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
V Power Problems
Terms for Power Problems Confusion ???
ulse
Surge
t en Ev
Glitch Im p
e tag Ou
Blink rtion Disto
Sag
Swell ng hi tc No
Transient
Glitch "Power Hit"
Anomaly
2
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-1
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Voltage Tolerance Curves
3
Voltage Tolerance Curves
4
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Problems • Events are anomalies – Event recording is dependent on the threshold settings of the monitoring equipment and the nature of the electrical environment.
• Disturbances are undesirable consequences of events – Correlation establishes the relationship between EVENTS and equipment DISTURBANCES. Single correlation is not conclusive -- it may be "coincidence!"
• Power Problems are a consequence of disturbances -- a set or class of disturbances. 5
Power Problems Depend On: • Nature and source of event – External (source) – Internal (load)
• Susceptibility of load to the event – Load does not react...no problem – Load reacts...activity / process interruption
• Effect on process or activity – Stops the activity / process – Easy "work around"
• Cost sensitivity to this effect – BIG $$$ – No real identifiable costs...can not justify $$$ to mitigate problem 6
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-3
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Problems • Source – Internal or external – Utility or load
• Coupling – Direct – Induced
• Characteristics – Low Frequency – High Frequency 7
Power Problems - Coupling • Directly conducted • Electromagnetically coupled or induced
8
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-4
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Problems: Low Frequency • Variation of amplitude near power system frequency • Important Characteristics
• Types of event: – – – –
Swells (surges) Sags & brownouts Dropouts & outages Frequency variation
– Magnitude, Duration and Source
9
Power Problems: Frequency • Not usually a problem with utility - a "stiff" source • Typical problem sources: – Engine generators – UPS systems – Small, remote or isolated power systems
• How do power monitors measure frequency? – Cycle-by-cycle – Averaged over a multicycle sample
10
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Typical RMS Voltage Disturbances
11
Power Problems: Utility • Power factor correction capacitor switching • Circuit breaker operation and grid switching • Arcs and line fault clearance • Lightning and storms 12
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Storm-Related Problems - Lightning
13
Storm Related Event
14
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Problems: Facility • Loose connections • Overloaded circuits and transformers • Wiring errors • Ground loops (low and high frequency)
15
Facility Power Problems • Breaker trip & fuses blow on motor start-up
16
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Facility Power Problems-2 • ATS operation during motor start-up
17
Facility Power Problems-3 ATS Re-transfer to preferred source
18
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Facility Power Problems-4 Good Start-up!
19
Facility Power Problems-5 ATS Wiring Error!!!!
20
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Problems: Equipment • Equipment turn on/off • Equipment current distortion • Phase-angle controlled loads • Low immunity to disturbances
21
Load Related Events - 1 Load related event-load "turn-on"
V & I = Load
22
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Load Related Events - 2
23
Load Related Events (Harmonic Eval.)
24
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Induction Motor Response to Outage
25
Equipment Response to Notch
26
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Sub-cycle and Other Disturbances
27
Transient modes • Normal mode – AC line to line – AC line to neutral – Telco tip to ring
• Common mode – Any line to local ground
• Differential ground mode
• One mode often converts to another through: – Circuit voltage drop – Capacitive coupling – Mutual inductive coupling
– Between physically separated grounds 28
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-14
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Interference Modes L N
L v
G
L
N G
N v
G v
Measurement Techniques Voltage Differential
Current
Normal Mode
Common Mode
Longitudinal Mode
Line-to Neutral or Phase-to-Phase
Neutral-to-Ground Imbalance between conductors or another reference point
Phase or Neutral Current
Line & Neutral Summation or Ground Current
Multiple Conductor Summation 29
Power Problems: High Frequency - 1 • Important characteristics – Peak voltage, current & energy – Rise time (dv/dt, di/dt) – Phase angle – Frequency of occurrence
30
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Transients • Transient sources include – Lightning – Utility • Power factor correction capacitors • Switching
– User • load switching • Equipment operation • ESD 31
Transient Effects • Damage – AC power supplies – Data, telephone and communications interfaces
• Disruption – Data loss – System crash
• Degradation – Minor damage which surfaces later 32
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Transients • Transient Propagation – Obeys circuit laws – Current flows in circuit – Capacitance may complete circuit
Load
Transient generator
• Transient Protection Basics Block
– Current block Transient generator
• Series high impedance
– Current divert
Load
• Parallel low impedance 33
Placement of Surge Suppressor Line
Meter Neutral
6' 20'
34
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-17
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Surge Suppressor Performance Let through At the suppressor With 6' of wire With 20' of wire
6' of Wire
20' of Wire
35
Common Electrical Problems • Wiring errors – Electrical system – Data, telecommunications & network
• Overloaded circuits – Lack of power management – Harmonics
• Ground loops – Leakage – Neutral/ground bonds
• Transients – Switching – Lightning – Electrostatic discharge
36
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-18
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Electrostatic Discharge • Causes: – Triboelectric (rubbing) effects – Separation and accumulation of charge
• Results: – High voltages (up to 50 kV) – Spark discharges – High dV/dt and dI/dt
37
Electrostatic Voltages ACTIVITY Walking across carpet
LOW (<20%) HUMIDITY 35,000 V
HIGH (>65%) HUMIDITY 1,500 V
Walking over vinyl floor
12,000 V
250 V
Worker at bench
6,000 V
100 V
Handling vinyl envelopes
7,000 V
600 V
Picking up poly bags from bench Movements on urethane padded chair
20,000 V
1,200 V
18,000 V
1,500 V 38
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-19
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Electrostatic Discharge • Avoidance & control: – High humidity (>50%) – Conductive materials and flooring – Protective clothing and straps – Ionizers
• Equipment immunity & hardening – Keyboards, mice & human interface – Ground, shield & suppress – AC suppression rarely effective 39
Gaussmeter Measures flux density –Gauss or Teslas yMilligauss & MicroTeslas
Problems arising from flux density –CRT waver –Induced current flow in data cables
Easy to use –Single axis vs triaxial
40
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-20
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Solutions for EMF Problems Correct the source –Attenuate harmonic currents –Fix wiring errors
Move the affected equipment Shield the source or the receiver –Mumetal –Steel sheets –NoRad flux control systems –Change affected equipment –Change CRT scan rate 41
Diverting Magnetic Fields
TA2
TA2
STRAY FLUX
STEEL SHEET 42
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 5-21
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
VI
Power Conditioning
Power Conditioning • Provides improved power quality to load by: – Separating circuits of sensitive loads – Establishing controlled reference grounds – Conditioning power with a treatment device – Providing alternative source of electrical energy
2
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-1
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Cascaded Protection • Uses multiple shunt protectors • Uses blocking impedance – Power system wiring – Power system transformers – Filter or transformer power conditioners
3
Power Treatment Devices • Voltage regulators – Ferroresonant – Tap switching
• Surge protective devices – Lightning arresters & surge suppressors
• Filters • Motor generators
• Transformers – Isolation – Low impedance conditioner – Ferroresonant
• Uninterruptible power sources (UPS) – On-line – Off-line – Line interactive 4
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Surge Protection • Lightning arresters – Primary and secondary devices – Applied on utility up to PCC (watt-hour meter)
• Surge suppressors – Applied in facility beyond PCC – Service entrance • Incorrect installation may detract from performance
– Distribution system – Point-of-use 5
Arresters & Shunt Suppressors • Use non-linear shunt elements – Varistor – Spark gap or gas tube – Silicon-controlled rectifier (SCR) – Suppression diode stacks
6
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-3
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Non-Linear Shunt Elements • High "off" impedance • Low "on" impedance • Rapid transition between states • Low to moderate "headroom"
Clamping
Voltage
System
Current
7
Metal Oxide Varistor • Best overall modern device • Strengths: – Good clamping and headroom – Excellent durability – Sub-nanosecond switching
• Weakness: – Low voltage devices not effective – High capacitance
8
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-4
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Suppression Diodes • Applications: special power and data protection • Strengths: – Excellent clamping and headroom – Moderate to good durability – Sub-nanosecond switching
• Weaknesses: – Low voltage devices most effective – High capacitance
9
Gas Tubes • Good choice for special data protection applications • Strengths: – – – –
Excellent clamping Good to excellent durability Microsecond switching Low capacitance
• Weaknesses: – Overshoot on fast wavefronts – Not auto-resetting 10
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Component Service Life • Service Component Damage – Caused by thermal overstress: • Exceeding surge energy rating • Exceeding rated voltage
– AC overvoltage
• Service Degradation – Varistors & diodes: • Small change in leakage current • Not limiting service factor
– Gas Tubes: • Electrode erosion • Rupture
• Wiring errors • Accidents • Utility problems
11
Dedicated Circuit ELECTRICAL SERVICE TRANSFORMER U T HOT I L I NEUTRAL T Y GROUND
IR
IR
120 VOLTS IR 0 VOLTS
114 VOLTS
L O A D
IR 3 VOLTS
12
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-6
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Surge Suppressor Specs ("Standards") • Underwriters Laboratories (UL) Std. 1449 • Commercial Item Descriptions (CIDs) – Performance – Endurance (reliability) – Application – Safety – Certification
13
Surge Suppressors (TVSS) • Nonlinear response to excessive voltage • Clamping depends upon energy handling • Device configuration determines protection mode • Response time based upon MOV or SAD 14
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-7
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Filters • Normally adds LC components to TVSS • May or may not have sine tracking • N/G usually weaker performance • Adds RF attenuation to clamping
15
Isolation Transformers • Isolate common-mode only • Common-mode coupled by inter-winding capacitance • Capacitance may be reduced by design • Normal-mode couples magnetically • Limited normal mode attenuation
Line
Load
– Inductance and load determine attenuation
• Common mode attenuation via coupling capacitance – Shields or screens improve attenuation 16
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-8
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Ferroresonant Voltage Regulators • Transformer operates in saturated mode • LC filter produces sinusoidal output voltage • Shielding may improve common mode performance
Primary Section of Core
Primary Winding
Magnetic Shunt Air Gap Output Winding
Secondary Section of Core
Resonating Winding
17
Tap Switching Voltage Regulators • Control of voltage taps – SCR – Triac – Relay
• 0.5 cycle response time • Continual tap changing
Electronic Control Tap Selection
Line
Load
Ground
18
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Low Impedance Conditioner • Uses low-impedance isolation transformer • Varistor suppression on primary • Filtration on secondary • N-G bond controls common-mode isolation transformer • Sine-tracking output filters -- low pass filter • Ground Impedance
Line
Load
Ground
19
Motor-Generator • Isolates load mechanically • Provides some dropout ride-through
20
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Uninterruptible Power Supplies • Provide backup AC power from storage batteries • Automatically power load on loss of utility source • May also suppress and condition power
21
Ideal UPS • Source Input:
• UPS Output:
– Disturbed (transients & switching) – Discontinuous – Unregulated – < 100% reliable
– Undisturbed (suppressed & no switching) – Continuous – Regulated – 100% reliability
UTILITY
UPS
LOAD 22
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-11
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Real UPS • Reliability <100% (MTBF) • Discontinuous – Off-line switch output transfer
• • • •
On-line switch bypass Non-sinusoidal output Poor or no regulation Poor or no suppression 23
UPS Modes of Operation - 1 • On-line (Static UPS) – – – – –
Inverter drives the load, rectifier/charger powered by utility Load switched to utility bypass on inverter overload Output usually filtered, conditioned and regulated Output usually transformer isolated Bypass possible source of problems
BYPASS
UTILITY
HOT NEUTRAL GROUND
RECTIFIER AC
DC
INVERTER
+ -
DC
AC
LOAD
HOT NEUTRAL GROUND
24
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-12
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
UPS Modes of Operation - 2 • Off-line (standby) – – – – – –
Inverter normally off Utility supplies load Load source switched when utility lost Output may be suppressed but not conditioned Output not usually transformer isolated Transfer switch possible source of problems
UTILITY
LOAD
HOT
HOT TRANSFER SWITCH
NEUTRAL GROUND
NEUTRAL GROUND
RECTIFIER AC
INVERTER
+ -
DC
DC
AC
25
UPS Modes of Operation - 3 • Line interactive – Inverter on but unloaded – Output suppressed, conditioned and regulated – Output may be transformer isolated UTILITY
LOAD HOT
HOT TRANSFER SWITCH
NEUTRAL GROUND
NEUTRAL GROUND
RECTIFIER
+
INVERTER
AC
DC
DC
AC 26
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Inertial and Flywheel UPS
27
Diesel UPS
28
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-14
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Diesel Generator
29
UPS Issues
30
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-15
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Separately Derived UPS Gear • Continuous neutral bonded to the output of the UPS eliminates the need for grounding/bonding to the building grounding electrode system (BGES). • The ganged bypass in which both the hot and neutral are switched makes the UPS separately derived in both normal mode and inverter mode and the output must be bonded to the BGES.
31
Isolated UPS Systems • Isolated bypass or isolated output make the UPS systems separately derived in both normal and battery powered operation.
32
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-16
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Sinusoidal Output Waveform quality affected by output filter network Inverter stability affected by stored energy and dc transfer
33
PWM Inverter Output Pulsed Voltage LC Filter Integrates pulsed voltage into
sinusoidal voltage.
Capacitor maintenance –Annual checks for filter balance
with individual replacements as required. –After 5-7 years of service capacitors should be replaced. –Voltage stress and pulsed current are leading causes of capacitor failures. 34
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-17
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Load Demand Effects Current pulls UPS inverter output
filter out of tune Current magnitude limited by
inverter/filter
35
Load Harmonic Effects • 6 pulse current from load interacts with UPS inverter output impedance • 5th order harmonics in load current cause peak output voltage waveform • Increase in peak voltage leads to increase in RMS voltage levels.
36
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-18
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
UPS Input Current Harmonics Light Load Distortion too high ATS will not function 500kVA UPS –27kVA; 24kW –0.7 PF (W/VA) Current –28° leading Harmonic distortion –61% THD –7th order = 54% THD
37
UPS Input Current Harmonics Moderate Load Same UPS - more load 500 kVA UPS 126kVA; 119kW 0.92PF (W/VA) Current 22° lagging Harmonic distortion 12% THD 7th order = 7% THD
38
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Factor Correction (PFC)
39
PFC Startup & Run Current AC Wall Outlet Top figure - equipment startup Bottom figure - normal operation
Start-UP Oscillation 85 amperes peak-to-peak 7.7kHz Some Loads wake up in a bad
mood! This is one of the reasons that many data centers do not allow any work during prime hours.
40
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-20
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
PFC & UPS Interaction 2 Voltage THD = 14%; Current THD = 147% Current transitions from about 5 amps to over 20 amps Severe oscillation due to PFC interaction with UPS
41
UPS & PF Corrected Data Center 1 • 500kVA UPS • 480 volt output feeds transformer based PDU throughout data center • Data center load is all IBM file servers with the same power supply • If load current stays near or below 300 amperes then the output remains stable
42
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-21
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
UPS & PF Corrected Data Center 2 • When load current increases above 300 amperes then the output become unstable with pronounced oscillation • Problem caused by time base interaction of the UPS and the data center equipment. • More load diversity throughout the data center would be beneficial. • UPS manufacturer changed voltage regulation response to solve the problem
43
Inverter Output Noise • Problem: Shields of output transformer bolted to varnished surfaces • Shield grounding problem allows inverter pulse-widthmodulation noise into output • Correcting shield grounding reduces output noise – Blue trace – after shield grounding – Red trace – original
44
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-22
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
24 Volt & Pseudo sine Standby UPS • Normal operation shows small waveform breakup & transient voltage • UPS inverter operation shows large ringing transients at end of each voltage pulse.
45
UPS Considerations • Specifications – Input (distortion & power factor) – Output (waveform & filtering) – Reliability (MTBF) and reparability – Holdup time – Suppression & conditioning – Acceptance testing
• Maintenance – Battery testing, monitoring & alarm – Battery replacement & servicing – Management & supervision
46
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-23
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
PQ Solutions Do Not Have to be Expensive • Determine your equipment's sensitivity to various power events and the impact on your operation. • Is the sensitivity of the equipment associated with the entire unit or just a subsystem. – In many cases it may be possible to add an inexpensive device to increase the hold-up time for the line relays. – Drop-out or time delay relays can protect 3-phase loads from single phasing
• Understanding the problem that you are trying to resolve is key to implementing cost effective solutions. 47
The Cost of Power Quality Solutions INCREASING COST Customer Solutions 4 - Utility Solutions
3 - Overall Protection Inside Plant Feeder or Group of Machines
Utility Source
4
3
2 - Controls Protection
1 - Equipment Specifications
1 2
CONTROLS
MOTORS
OTHER LOADS
Source: Electrotek Concepts, Inc. 48
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 6-24
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
VII Network Protection
Problem of Networked Computers -Differential ground voltage
Transient Arrives here first
2
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 7-1
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Differential Ground Voltage Solutions • • • • • •
Reference grid (computer rooms) Fiber optic networks Twisted pair networks (10baseT) Ferrite cores Over-voltage protectors Grounding Inductance
3
High Frequency Interference Measurement • • • • • •
Signal voltages small and mingled with noise Voltage probe insertion may hurt signals Currents much larger, easier to measure Couple using high-frequency transformer Measure using digital storage oscilloscope Some applications, use spectrum analyzer
4
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 7-2
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Controlling Network Interference • OVP Protectors (SAD) • Filters (ferrite cores -- shunt capacitors)
5
Ferrite Cores • Ferrous metal baked in ceramic fixture • Functions by creating high frequency losses • Inductive & resistive characteristics
6
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Filter Pin Connector • Normally use capacitive elements internally • Specify desired level of capacitance • Some designs add series inductance
7
Data Cable Protectors • Silicon Avalanche Diodes
• MOV Components
8
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
5 Pin Protector (Classic) • Gas tube OVP • Sneak current coils • Protects – Tip to ground – Ring to ground
9
5 Pin Telco Protectors (Variations)
10
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
5 Pin Hybrid Protector • Gas tube • Silicon Avalanche diode & low capacitance diodes • Capacitors
11
High Frequency Interference Measurement
`
12
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
High Frequency Monitoring
13
High Frequency Monitoring / Scatter Plot
14
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PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
High Frequency Interference Current (facility ground interference)
15
Communications Media Sensitivity • Most sensitive: RS- 232, Thinnet & similar single-ended unbalanced systems • Less sensitive: RS 422 & similar balanced systems • Better still: Signal transformer or opto-isolated systems (10 Base-T) • Best: Non-conducting media, fiber-optic and radio
16
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 7-8
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Data Line Shielding • Shields effectively conduct high frequency current • Shields do not effectively limit effects of low frequency current • Must be grounded BOTH ends – Or - ungrounded ends MUST be protected • Suppression may also be needed
• Electrical Code Data Line Safety Issues – On entering building: • Shields require grounding • Listed protectors must be used
– Where there is: • Exposure to lightning • Exposure to power lines
17
Shield Grounding • 1kV ESD Pulse -- Shield Grounded (normal conditions)
• 1kV ESD Pulse -- 2" Shield Pigtail (shield drainwire)
18
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 7-9
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
AC & Communications Grounding Very Bad!
yNEC 2002 y250.56, 800.40 & 830.40
AC POWER
TELCO
CATV
Single point is the preferred application TELCO
Code compliant, but still bad! AC POWER
TELCO
AC POWER CATV
CATV
19
20
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 7-10
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
VIII Safety
WARNING #1 Performing power quality investigations in and around energized equipment, exposed electrical buss work , and inside confined spaces can be dangerous. Testing and inspection of energized equipment should only be performed by qualified individuals familiar with proper safe work-practices.
2
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 8- 1
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
WARNING #2 • Follow all appropriate safety rules and procedures – – – –
Company NFPA / NEC OSHA Appropriate state and local work rules
3
Potential Safety Hazards • Follow applicable safe work practices and lockout procedures • Familiarity with application, installation and operation of various diagnostic equipment • Use approved clothing and protective equipment • Ensure that all tools and equipment are in proper working order and condition
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 8- 2
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Safety Equipment / Apparel • • • •
Rubber gloves rated at 600v/20kv Leather protectors Hard hat Hearing protection
•
Safety face or eye protection
•
Long-sleeved shirts (Nomex or Indura flame-resistant clothing) worn while working on or near 0600 volts Specialized safety equipment for high voltage and other hazardous environments
– when appropriate – UV rating
•
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Never Assume a Circuit is Dead
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 8- 3
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Jewelry / Surroundings / Conductor / Neutral
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Typical Body Current Paths
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 8- 4
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Effects of Electric Shock Applied to skin (Macroshock) 6+ Amps: Sustained myocardial contraction followed by normal rhythm. Temporary respiratory paralysis. Burns, if small area of contact. 100 - 300 mA: Ventricular fibrillation. Respiratory center intact. 50mA: Pail, fainting, exhaustion, mechanical injury. Heart and respiratory function intact. 16mA: "Let go" current, muscle contraction 1mA: Threshold of perception; tingling. Applied to Myocardium (Microshock) 100uA: Ventricular fibrillation. 10uA: Recommended maximum leakage current.
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(Blank)
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 8- 5
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
IX Planning & Performing a Power Quality Survey
What is a PQ Survey? • A forensic activity (investigation). • It is much like investigating the scene of a crime. – – – – – –
Gather evidence Interview witnesses Surveillance (monitoring) Review the evidence and surveillance data Present your findings "Arrest the guilty!"
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 1
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Reasons for a PQ Survey • Normal reason is a loose forensic activity (problem investigation) • Estimating effects of electrical changes – New equipment or changes to the distribution system – Effects of Harmonics
• Governmental regulations • Baseline and maintenance • ISO9000 Compliance procedures 3
Survey Justification • Money, Manpower & Test Equipment – Labor required to perform the survey – Use of expensive equipment – Disruption of normal activities
• Survey must provide a ROI – Immediate problem resolution – Energy management cost reduction
• Management participation in survey goals
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 2
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
The Six Steps to a Successful PQ Survey • • • • •
1 - Plan / Prepare 2 - Inspect (Survey) 3 - Monitor 4 - Data Analysis 5 - Key Findings & Recommendations (the Solution) • 6 - Implementation & Verification
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Why have a Written Survey Plan? • Some surveys have continued for months without tangible results because they were not well planned. • Complex facilities, multiple monitors and data collection systems require a formal plan for the activity to be brought to a successful completion.
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 3
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
When a Written Survey Plan May Not be Needed Simple uncomplicated monitoring activities may not require a formal written plan, but all the same steps will need to be considered (at least informally) for the activity to reach a satisfactory conclusion.
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Survey Objectives • What are the objectives for the activity? – What is to be accomplished? – Is it measurable? (Deliverables)
• Objectives must be clear, well defined and most importantly: accepted by the individual (organization) requesting the survey
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 4
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Examples of Survey Objectives • • • • • •
Solve an equipment performance problem Identify and correct sources of interference Determine overall electrical environmental quality Determine capacity for a facility Predict the impact of harmonic loads (IEEE519) Establish an electrical environment "baseline" for a facility (ISO9000)
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Determinants of the Scope of Activities • Size of the facility • Complexity of electrical system and equipment • Quantity of monitoring equipment • Duration of monitoring program • Quantity and complexity of monitor data
• Number and length of event logs • Access to restricted areas or equipment • Specialized options (RF, current, temperature, humidity, etc.) • Involvement of staff and administrative support
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 5
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Power Monitor Placement • Classic placement – Service Entrance(s) – Transformers – Distribution -- feeders and panelboards – Point of use -- branch circuits, equipment
• Multiple monitors – Improves quality of data – Speeds-up the investigative process. • Service entrance, load center, utilization equipment
– Additional monitors can be rented for between $500 and $1000 / month. 11
Verify Survey Plan • Is the objective clear and measurable? • Is the quantity and placement of monitoring equipment clear? • Are personnel and responsibilities assigned? • Is the length of the survey established? • Is the data collection system (event logs) defined and ready for testing?
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 6
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Equipment Event Logs • Things to include in the EVENT LOG – – – –
Operator / Location / Activity Record of normal operating cycles Record of equipment anomalies Record of environmental anomalies
• Design log to make the data collection as easy as possible. • Use alarm relays, control switches to aid in time stamping events.
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Preparing for the Survey • Documentation and data collection – Site history – Equipment/activity event log(s) – Service/repair history
• Tools and equipment
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 7
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Site History • Has the system or equipment ever worked satisfactorily? – When did the problems start?
• Time of occurrence for recurrent problems – Look for patterns
• Failure symptoms or hardware failures – Someone somewhere knows what parts were replaced
• Electrical service and configuration – wye-wye or delta-wye
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Site History - 2 • Inventory of major loads in the facility – Operating cycles for major loads in the facility
• Recent equipment changes • Renovations in the facility • Telecommunications/data-network facilities and equipment – Recent implementation of wireless technology
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 8
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Monitoring Tools & Equipment • Power quality • Power quantity • High frequency – DSO – Spectrum analyzer
• ESD meters • Multi-meters (True RMS) • Thermographic recorders
• ELF & VLF field strength meters • Ultrasonic meter • Video camera • Ground resistance meter • Current probes – Current transformer – Hall Effect (d-c)
• Circuit tester
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ESD & ELF Meters
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 9
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Popular 1Ø Phase Monitoring Instruments • Fluke 43B – Power quality analyzer
• Fluke 41B – Harmonics & energy
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Flexible AC Current Probes
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 10
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
3Ø Monitoring Instruments / $2K to $6K • Ideal Model 805 • Summit Technologies Power Sight 4000 • AEMC PowerPad 3945 • Fluke 430-Series • Dranetz-BMI PowerGuide 4400 & PowerVisa 440 21
Portable 3Ø Power Quality Monitors / $7K to $15K Fluke 1760 Three Phase PQ Recorder
Hioki 3196
Fluke 1750 Three Phase Power Recorder
Dranetz-BMI PowerXplorer PX5 (PX5-400 for 400Hz apps.)
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 11
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Permanent Power Monitors / $2K to $4K + Installation & Software
PML ION 7700
Electro Ind. NEXUS 1250
PMI Eagle Class Recorders
Dranetz-BMI Encore
PowerLogic CM4000T
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Monitoring Systems
Power Quality Analyzer
Spectrum Analyzer
Laptop CPU / Controller e/w HS Modem Energy Analyzer
High Speed DSO 24
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 12
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Inspecting the Site - Visual/External • Type of electrical service (underground, aerial, low or high voltage?) • Utility power factor correction capacitor installations • Neighboring facilities • Utility substation in the immediate vicinity • Physical location of building (exposure) • Lightning protection system • Building construction
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Review the Electrical Service • • • • •
Service entrance -- single or multiple? How are the service entrances grounded? Building Grounding Electrode System? Transformer isolation? Ground Fault Interrupt?
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 13
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Inspecting the Site -- Internal • Review major facility loads and how they are controlled – – – – – – – –
Large photocopiers Variable speed drives UPS Elevators / escalators Lighting systems Welders Battery chargers Air conditioning compressors, chillers and air handlers
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Inspecting the Site - 1 • Look for obvious problems – – – – – –
Broken or corroded conduits Transformers which are hot or noisy Electrical panels with hot or loose circuit breakers Loose connections -- EMT without grounding wires Conduits which are hot and buzzing Transformers or conduits near CRTs with screen "wiggle" – Coffee pots plugged in with file servers – Power cord plug/connectors showing signs of excessive wear -- check for warm spots 28
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 14
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Inspecting the Site - 2 • Talk with the equipment/system operators and users – Management's perception of the problem may be quite different from the people using the equipment. – Listen! Listen! Listen! • Most people want to tell you about the problem. • Learn to translate the information into appropriate terminology.
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Monitoring • Power monitoring configurations – Match the configuration of the load – Monitor neutral-to-ground to record "common mode" events – Use current probes to record phase, neutral or ground currents.
• Use multiple monitors - service entrance, distribution center, utilization equipment • Monitor threshold settings - sensitive, normal or tolerant 30
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 15
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Identifying Problems - 1 • Review monitor data – Look for events which occurred during periods of equipment malfunction (event log entries) – Identify severe events.
• Identify events that exceed equipment performance parameters • Correlate problems found during the physical inspection with equipment symptoms.
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Identifying Problems - 2 • Review site history and event logs • Plot monitor event summaries – Look for trends
• Compare event summaries to equipment event logs – Single Event Correlation is not conclusive
• Compare event data to equipment performance specifications • Select key events 32
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 16
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Summary Info w/Event Log Correlation
Event Log#1
X
Event Log#2
XX
Event Log#3
X
X
X
X
X
X
X
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Key Event
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 17
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Identifying Problems - 3 Symptom I/O port failure Processor lockup Keyboard controller failure Power supply failure System crash
Possible Cause Longitudinal CMI Software / RF / ESD ESD Surge-transient / ESD Surge-transient (voltage)
Wavy screen
EMF
Clock/date reset
Battery / conducted RF
Open door/cabinet halt
Radiated RF
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Writing the Report - Software Tools • Dranetz-BMI Technologies – DranView Versions 4, 5 & 6
• Fluke / RPM – PAS & Scenario w/Report Writer – EN50160 Report Writer – Flukeview
• Hioki – HiView
• AEMC – DataView 36
© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 18
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
PQ Survey Report Organization • Executive Summary – Written last after the main report is completed – Never more than 2-pages
• • • • • •
Overview/Background Methodology Key findings Recommendations Summary Appendices 37
PQ Survey Report Content • Quality information NOT quantity! – The purpose of the report is to identify and present the significant information, not bury the reader in paper.
• Use summary information – Easier for people to understand
• Use waveform data (graphics) sparingly to add emphasis and support recommendations – Do not include every waveform recorded as it tends to lessen the value of the data
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 19
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Be Wary and Watchful • Never assume a single cause – Peel the onion
• • • •
Know your instrumentation Don't become part of the measurement Use equipment symptoms as a guide Never assume the equipment is without guilt
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Make Solutions A Priority • Inaction is costly • Reaction is costly
GATHER DATA
– Too little, too late for too much
• Monitor on an ongoing basis • Be part of the solution • Provide ROI • Manage the facility infrastructure
ANALYZE DATA
EVALUATE SOLUTIONS
IMPLEMENT SOLUTIONS
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 20
PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions
Summary • Apply the TEST OF REASONABLENESS to all data and information. • Know the limitations of monitoring and test equipment. • Look for the OBVIOUS. • Don't become the victim of ANALYSIS PARALYSIS. • Do the simple thing first.
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If All Fails...Call an Expert!!!
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© 2007-2009 by PowerCET Corporation. All rights reserved. (090317) 9- 21
