Introduction to Power Quality: Problems, Analysis & … to Power Quality: Problems, Analysis & Solutions Presented by: PowerCET® Corporation 3350 Scott Blvd., Bldg. 55 Unit 1 Santa

Introduction to Power Quality: Problems, Analysis & Solutions

Presented by:

PowerCET® Corporation3350 Scott Blvd., Bldg. 55 Unit 1Santa Clara, CA 95054 USA408/988-1346 | FAX 408/988-4869E-mail: [email protected]: [email protected] Page: http://www.powercet.com

Course: PQ103

© 2007 by PowerCET Corporation. All rights reserved. (070320)

PQ103 - Introduction to Power Quality: Problems, Analysis & Solutions

© 2007 by PowerCET Corporation. All rights reserved. (070320)1

Introduction to Power Quality: Problems, Analysis & SolutionsCourse: PQ103

ByPowerCET Corporation

2

The Electrical Environment & Power Quality• What is it? ...Quality or Reliability?• Why is it important?• How do we measure it?• Is it getting better?• Utility deregulation, what's going to happen?• Where do electrical problems come from?• What can we do about it?



3

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

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.



5

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

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.



7

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.

8

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

Air Traffic Control: Lost control at a major airport can cost $15,000-$50,000/minute

DuPont: Saved $75 million/annually by implementing PQ solutions. ($50,000 to $500,000 per event...additionally risk of accident and pollution.)

Compressor manufacturer: Sags and interruptions cost some $1,700,000/year. ($100,000 per event.)

Automotive Industry: Momentary interruptions cost some $10 million/year ($50,000 to $500,000 per event.)

Paper Industry: Billinton study determined cost of 2 second outage to be approximately $30,000

Source: EPRI Power Electronics Applications Center

The Cost of Poor Power Quality

10

Power Interruption Cost Calculator• Disturbance Statistics

– 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)

• Cost of Losses– 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)



11

Power Quality & Reliability

12

The "9s" of Reliable Power

Standby Generator

Multiple Redundancy UPS, Standby Generators

Mirrored Sites, Multiple Redundancy UPS, Standby Generators

30 MillisecondsOn-line Markets99.9999999%Nine 9s

32 SecondsBanks99.9999%Six 9s

5 MinutesHospitals, Airports99.999%Five 9s

59 MinutesFactories 99.99%Four 9s

9 HoursHomes99.9%Three 9s

Disruption Duration/YearApplicationsReliability

Source: Reliable Power Meters



13

Failing to "Look" Beyond the Traditional Power Quality Environment

PowerProblem

14

Looking Beyond Traditional Power Quality



15

Why is the Quality of the Environment Important?

Electrical

Environment

Infrastructure

Management

Equipment

Compatibility

Load

Sensitivity

Load

Sensitivity

Equipment

Compatibility

Infrastructure

Management

Electrical

Environment

RELIABILITY

PRODUCTIVITY

PROFITABILITY

16

T&D

Generation

Facility Wiring& Construction

TraditionalLoads

ElectronicLoads

Climatic & Geographic

What Determines Electrical Environment Quality?



17

U.S. Lightning Flash Density - 1989-98

18

Lightning Activity

• It is not a question of if, but when?



19

Electrical Loads

• Traditional– Lights– Motors

Electronic

LN

AC

DC

L

N

G

20

Sources of Electrical Problems

• External– Utility sources– Other utility customers– A.O.G.

• Internal– Wiring errors and poor

construction practices– Other loads– EMI / RFI



21

Evaluating the Changes Over the Past 30-Years• Equipment

characteristics

• Technology

• Environment

22

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



23

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...

24

The Environment• Past...

– Engineering, Construction & Maintenance

• Internal (Except for very large jobs or additions)

• Good records• Good infrastructure

management

• Present...– Limited internal engineering,

if any– Out-source most

construction– Deferred maintenance– Little internal control over

electrical environment– Installation by Folklore and

Tradition– Lack of understanding of the

Real World Environment



25

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

26

Increased Data Rates and Processor Speed

Data Rate (bps) Time Approximate Distance

60 16.7 mS 3100 Miles2400 417 uS 78 Miles1 M 1 uS 982 Feet10 M 100 nS 98 Feet

100 M 10 nS 10 Feet1 G 1 nS 1 Foot



27

Power Supply Technology

SMALL HF TRANSFORMER

SWITCH MODE D.C. POWER SUPPLY

L

PWM

VoN

LINEAR D.C. POWER SUPPLY

Vo

L

NLINEARREGULATOR

LARGE 60HzTRANSFORMER

N:1

28

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



29

The Electromagnetic Environment

FacilityLoads

(Harmonics)

ElectricalService

Configuration

ElectricUtility

Reliability

FacilityWiring,

Grounding &Construction

TelcoInterface

& Protection

Mission CriticalEqpt & Sys

NetworkFacilities

Dist & Prot

EMI&

RFI

ElectrostaticDischarge

(ESD)Control

30

The Future of Power Quality

• The Utility• The Mitigation Equipment Supplier• The Consulting Engineer• The Electrical Contractor• The User



31

The California Experience

32

Electric Utility Deregulation



33

Electric Utility Deregulation

Generation

Transmission

Distribution

Customer Service

Power Producers(GENCOs or IPPs)

Regional Transmission Network Operators (TRNSCOs)

Bulk Power Trader(POWERCOs)

Distribution System Operators(DISTCOs)

Retail Power Marketers(RETAILCOs)

Energy Service Companies (ESCOs)

Deregulated& Industry

Restructuring

Vertically Integrated Electric Utility

Deregulated Electric Utility Industry

34

Power Quality and the Utility

• Reliability and quality will decrease with deregulation

• Increased monitoring and performance measurement requirements

• Most will offer enhanced and/or contract services (SEFI&O)

• Stability of the utility power industry will be a problem, at least in the short-term

• Displaced workforce as competition and deregulation become a reality



35

PQ and the Mitigation/Protection Equipment Supplier• Market segmentation• Suppressors• Filters• UPS equipment• Margins continue to

erode -- commodity pricing

• Push vs. Pull• Direct vs. Indirect• Market channels• Positioning and

product differentiation• Vertical market

segments• F.U.D.

36

Monitoring Equipment Suppliers

• New competitors will continue to enter the market

• More permanently installed monitoring & control systems

• Equipment will evolve slowly providing an opportunity for additional competition

• New low cost monitoring equipment will do well in this market as long as complex programming or setup is not required



37

PQ and the Consulting Engineer

• Work will become more competitive and less profitable

• Larger firms will dominate• Some will offer PQ services as a method of

maintaining customer/account control• Some will probably have a sales operation

for protection/mitigation products or a relationship with suppliers (additional revenue source)

38

PQ and the Electrical Contractor

• Increased awareness of Power Quality opportunity– TEGG

• Most will have some "bad" experiences with PQ• Some contracting operations (medium size, 10 to

50 employees) will develop PQ capabilities in an effort to– Increase revenue and – Differentiate themselves from the competition



39

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!

You Never Have a Problem...

Until You Plug it IN!


© 2007 by PowerCET Corporation. All rights reserved. (070320)1-1

I The Electric Utility System

2

The Consumers View of the Utility



3

Managing the Electric Utility Grid

4

The US National Grid

• Transmission level interconnections

• Evolving mission from backup to power transfer

• Three major interconnections



5

Electric Utility Energy Sources

6

Electric Utility Customers & Usage



7

The Utility

8

Power Quality & Utility Reliability



9

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

10

Std. Nominal System VoltagesVoltage Class 2-wire 3-wire 4-wire

Low Voltage (LV)120* 120/240*

480600

240/120208Y/120480Y/277

Medium Voltage (MV)

2400416048006900

1380023000345004600069000

4160Y/24008320Y/4800

12000Y/693012470Y/720013200Y/762013800Y/7970

24940Y/1440034500Y/19920

High Voltage (HV)115000138000161000230000

Extra High Voltage (EHV)

345000500000765000

1100000



11

Power Quality and the Utility

• Transformers– Transmission &

distribution– Service

• wye• delta• open delta• red-leg (high-leg) delta

OR

12

Service Transformers

• Single phase • Three phase



13

Pad mount3-phase pole mount3-phase red-leg delta

Service Transformers

14

Protective apparatus

• Fuses and circuit breakers• Lightning arresters and suppressors• Insulators, conductors and switches



15

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

16

Reclosure



17

Customer Impact of Utility Faults

• Faults on adjacent feeders and circuits generally result in voltage sags

• Faults on serving feeder results in sag followed by interruption

Circuit Breakers

1 3 42

Transmission

Distribution

13.8k

230k

480 V

To HV Transmission &

Power Generation

A B

Customers

Customer

= Single line-to-ground fault (SLGF)

18

Utility Fault Clearing: Reclosure Operation



19

Utility Reclosure Operation

• Utility fault on customer feeder

V & I = Source

20

Utility Reclosure Operation

• Fault on adjacent feeder

V & I = Source



21

Utility Reclosure Operation / Lightning

22

Sag Correcting Devices

• SoftswitchingTechnologies

Dip Proofing Technologies, Inc.



23

Corrective apparatus

• Voltage regulating equipment• Power factor correction capacitors

24

Power Factor Correction Capacitors



25

Power Factor Correction Capacitors

26

Power Factor Capacitor Switching

• Zero Voltage Sensing Control--before & after



27

Utility Fault

28

V & I = Source

Utility Transient

Source related transient



II Building & Facility Wiring

2

Service Entrance

• Main disconnect and overcurrent protection (circuit breakers).

• Building electrical system earth reference (neutral-to-ground bond).

• Earth grounding system.• Equipment grounding system.• Wiring errors and electrical code violations

(NEC Article 250).



3

Building (Facility) Wiring

SUB-PANEL

NPLUG/

RECEPTACLE

BUILDINGSERVICE

TRANSFORMER FEEDERBRANCHCIRCUIT

UTILIZATIONEQUIPMENT

N-GBOND

G

G

MAINELECTRICAL

SERVICEPANEL

N

EARTHGROUNDING

SYSTEM

EQUIPMENT GROUNDINGSYSTEM (GREEN WIRE)GROUND

BUS

EARTHGROUND

NEUTRALBUS

4

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



5

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.

6

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

Ground

Neutral

Voltage Transformation

Neutral-to-Ground Voltage Differential = Near Zero

ØC

ØB

ØA

Eqpt Grounding Conductor

Neutral

ØA

ØB

ØC



7

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.

8

Panelboards (sub-panels)

• Configuration– 1-phase, 3-wire– 3-phase, 4-wire

Ampere Ratings of Mains– 12 to 42 pole positions– 100 to 400 Amp typical



9

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.

10

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



11

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.

12

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).



13

Amp AmpMixer

Osc

In Out 5KHz45KHz

40KHz

Ultrasonic Detectors (Translators)

14

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



15

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)

16

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



17

ABCNG

MediumLoad

HeavyLoad

LightLoad

VOLTAGE PHASE A PHASE B PHASE CL-N 143 73 166L-G 122 122 123N-G 54 54 54

High Impedance Neutral

18

Results of an Open Neutral

• High Impedance Neutral



19

Neutral Current - Sinusoidal Loads

• No Imbalance– Phase currents offset

• Phase Imbalance– Imbalance = neutral

20

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 – 150 Hz for 50 Hz– 180 Hz for 60 Hz

A

B

C

N

G



21

Solutions for Multiwire Problems

• Delta-wye transformers• Eliminate shared facilities / oversize neutral

conductors• Filtering• Equipment redesign• Managing the environment

22

Receptacles (NEMA Notation)

L21-30R

CONTACT TYPE"L" denotes locking type; nothing denotes straight blade.

VOLTAGE TYPE5 = 120V6 = 240V, 208V14 = 240/120V, 208V21 = 208/120V, 3-Phase

TYPE OF CONNECTOR"R" denotes receptacle, or female."P" denotes plug, or male.

CURRENT CAPACITY15 Amps20 Amps30 Amps



23

Standard & IG Receptacles

24

IG Receptacle Construction



1

lll Harmonics

2

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



3

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

4

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



5

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/Triacloads

6

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 #

Harmonic Sequence

3 Pulse &L/N Loads 6 Pulse 12 Pulse 18 Pulse 24 Pulse

3 0 x5 - x x7 + x x9 0 x

11 - x x x13 + x x x15 0 x17 - x x x19 + x x x21 0 x23 - x x x x25 + x x x x27 0 x29 - x x31 + x x33 0 x35 - x x x x37 + x x x x39 0 x41 - x x43 + x x45 0 x47 - x x x x49 + x x x



7

Power FactorDisplacement Distortion

Power Factor• Power Factor (PF)

– PF = Watts / Volt*Ampere• Displacement Factor (f)

– Cosine of angle (E & I)• Distortion Factor (d)

– d = Afund / Arms

8

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

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 Mean PowerFundamental 121.8 87 32.75 103 3,832

3 12.1 48 14.1 306 -355 2.8 264 8.3 167 -39 1.7 52 1.6 0 2

Total 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 d = 0.89• Displacement PF = cos(ffun) = cos16 = 0.96

12

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

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...

Phase A

Phase B

Phase C

16

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

Phase A

Phase B

Phase C



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

Power Monitor & Harmonic Analysis



19

THD Graphical Displays

Vthd

Ithd

Wthd

20

(Blank)

CHA Volts (%FND)

CHA Amps (%FND)

CHA kWatts (%FND)

CHA Volts Phase(Deg)

CHA Amps Phase(Deg)

THD 3.73 29.21 -0.304 0 0FND 0.00 0.00 0.000 90 105H02 0.04 0.27 -0.000 142 9H03 1.32 21.46 0.024 11 286H04 0.00 0.06 0.000 50 98H05 2.69 18.59 -0.319 262 134H06 0.05 0.17 -0.000 55 202H07 1.32 5.18 -0.007 88 352H08 0.09 0.11 0.000 107 190H09 0.23 1.41 -0.002 331 206H10 0.08 0.17 0.000 189 114H11 1.31 3.29 -0.003 271 177H12 0.05 0.11 0.000 312 257H13 0.18 0.39 -0.001 328 158H14 0.20 0.32 0.000 37 336H15 0.31 0.66 -0.000 39 302

Harmonic Flow -- Power Monitor



21

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

22

K-Factor Calculations• Low-Impedance Power

Source– K-Factor = 9.43 – Voltage = 117.8 V rms.,

162.2 V pk, 1.38 CF– Current = 4.38 A rms., 11.2

A pk, 2.55 CF• High-Impedance Power

Source– K-Factor = 3.73 – Voltage = 114.1 V rms.,

145.2 V pk, 1.27 CF– Current = 3.83 A rms., 7.9 A

pk, 2.06 CF



23

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

24

Power Supply W/O Power Factor Correction



25

Power Supply With Power Factor Correction

26

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.



27

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...)

28

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



29

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

30

IEEE 519

V harmonic

I harmonic

PCC



31

IEEE 519 Harmonics Standard• Utility responsibility

– Limit overall voltage distortion

– General limit 5% THD at PCC

– Maximum single harmonic 3% of fundamental

• Voltage distortion reflects– User-injected harmonic

currents– Utility system impedance

• Customer responsibility– 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!

32

ISC / IL <11 11 ≤ h < 17 17 ≤ h < 23 23 ≤ h < 35 35 ≤ h TDD<20* 4.0 2.0 1.5 0.6 0.3 5.0

20<50 7.0 3.5 2.5 1.0 0.5 8.050<100 10.0 4.5 4.0 1.5 0.7 12.0

100<1000 12.0 5.5 5.0 2.0 1.0 15.0>1000 15.0 7.0 6.0 2.5 1.4 20.0

Maximum Harmonic Current Distortion in Percent of ILIndividual Harmonic Order (Odd Harmonics)

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 .whereIsc = maximum short-circuit current at PCCIL = maximum demand load current (fundamental frequency component) at PCC.

IEEE519 Current Distortion Limits (120V Through 69000V)



IV Grounding

2

Grounding Considerations• Safety grounding

("earthing")– Low frequency currents– Personnel safety– Reference the power

system ground– Requires low resistance

paths

• Signal & performance grounding– High frequency currents– Equipment

performance– Reference is local

equipment chassis– Low impedance paths

• Low inductance• High capacitance



3

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-to-

ground bond– Must be run in same conduit

as phase/neutral conductors– May use conduit– Connected to electronics dc

& logic reference

4

Earth Grounding System



5

Facility Grounding• 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

6

Facility Grounding – Ground Rods



7

Lightning Protection System Grounding

8

Resistance Measurements• 3-Point Fall of

Potential• Single Point

Measurement



9

Soil Type Average ResistivityOhms per CM

5/8" x 10' Driven Rod Ohms Resistance

Well graded gravel, gravel-sand 60,000 -- 100,000 180 -- 300

Loose gravel, gravel-sand 100,000 -- 250,000 300 -- 750Clayey gravel, sand-clay 20,000 -- 40,000 60 -- 120Silty sands, sand-silts mixtures 10,000 -- 50,000 30 -- 150

Clayey sands, sand-clay mixtures

5,000 -- 20,000 15 -- 60

Silty or clayey fine sands w/plasticity

3,000 -- 8,000 9 -- 24

Fine sandy or silty soils, elastic silts

8,000 -- 30,000 24 -- 90

Gravelly clays, sandy clays, silty clays, lean clays

2,500 -- 6,000 (moisture related) 17 -- 18 (moisture related)

Inorganic clays, high plasticity 1,000 -- 5500 (moisture related) 3 -- 16 (moisture related)

Soil Type vs. Resistivity(IEEE Std. 142-1991Grounding of Industrial and Commercial Power Systems)

10

1020

3040

5060

7080

Temperature in F

10

100

1,000

10,000

Ohm

s

8' Ground Rod Resistance

05

1015

2025

30

% Moisture Content by Weight

10

100

1,000

Ohm

s

8' Ground Rod Resistance

Effects of Soil Moisture & Temperature

• Soil temperature • Moisture content



11

Optimal Facility Grounding Means• Building Footer

– Ufer Ground• Ground ring & rods

– Bonded at corners

12

Enhanced Conductivity Concrete



13

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]

14

Floated ServiceResistance GroundingGround Fault Interrupt

Mains Grounding Variations



15

Mains Grounding Variations• 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

• Impedance Grounded Service– 480/277Vac service– No neutral connected loads– Creates ground referenced voltage during faults

16

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



17

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

18

Low Frequency Ground Current - 1

LINE

NEUTRAL

GROUND

BUILDINGELECTRICAL

SERVICETRANSFORMER

N-GBOND

GROUND

GROUND

EARTH GROUND(MAIN BUILDING ELECTRICAL GROUND)

SUB-PANEL

SUB-PANEL

BC

A

LEGEND:LOAD CURRENT

NEUTRAL RETURN CURRENT

1

D

2

UTILIZATION

EQUIPMENT



19

LINE

NEUTRAL

GROUND

BUILDINGELECTRICAL

SERVICETRANSFORMER

GROUND

GROUND


SUB-PANEL

SUB-PANEL

A

BC

N-GBOND

LEGEND:LOAD CURRENT


D

2

1

UTILIZATION

EQUIPMENT


20

LINE

NEUTRAL

GROUND

BUILDINGELECTRICAL

SERVICETRANSFORMER

N-GBOND

GROUND

GROUND

"ISOLATED" GROUND,GROUND ROD, COLD

WATER PIPE, ETC..


SUB-PANEL

SUB-PANEL

A

BC D

E

LEGEND:LOAD CURRENT


1

2

F

UTILIZATION

EQUIPMENT




21

LINE

NEUTRAL

GROUND

BUILDINGELECTRICAL

SERVICETRANSFORMER

N-GBOND

GROUND

GROUND

"ISOLATED" GROUND,GROUND ROD, COLD

WATER PIPE, ETC..


SUB-PANEL

SUB-PANEL

A

BC D

E

LEGEND:LOAD CURRENT


1

2

F

UTILIZATION

EQUIPMENT


22

High Frequency Ground Current• Sources

– Transients from lightning and switching

– Electromagnetic interference

– Radio frequency interference



23

High Frequency Interference Current - 2 (RS-422 Interference)

24

Signal Reference Grid -- EricoA very good reference grid



25

Safety Ground Vs Reference Grid

26

Connections to Reference Grid• Short flat straps best• Metal braid OK• Bond at opposite

corners of equipment• Bond all equipment

within room



27

Transient

Arrives here first

Problem of Networked Computers --Differential ground voltage

28

Differential Ground Voltage Solutions• Reference grid (computer rooms)• Fiber optic networks• Twisted pair networks (10baseT)• Ferrite cores• Over-voltage protectors• Grounding Inductance



29

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

30

Controlling Network Interference• OVP Protectors (SAD)• Filters (ferrite cores -- shunt capacitors)



31

Ferrite Cores• Ferrous metal baked in

ceramic fixture• Functions by creating

high frequency losses• Inductive & resistive

characteristics

32

Filter Pin Connector• Normally use capacitive elements internally• Specify desired level of capacitance• Some designs add series inductance



33

Data Cable Protectors• Silicon Avalanche

Diodes

• MOV Components

34

5 Pin Protector (Classic)• Gas tube OVP• Sneak current coils• Protects

– Tip to ground– Ring to ground



35

5 Pin Telco Protectors (Variations)

36

5 Pin Hybrid Protector• Gas tube• Silicon Avalanche diode & low capacitance diodes• Capacitors



37

High Frequency Interference Measurement

`

38

High Frequency Monitoring



39

High Frequency Monitoring / Scatter Plot

40

High Frequency Interference Current (facility ground interference)



41

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

42

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



43

Shield Grounding• 1kV ESD Pulse --

Shield Grounded (normal conditions)

• 1kV ESD Pulse -- 2" Shield Pigtail (shield drainwire)

44

AC POWER TELCO

CATV

Very Bad!

AC POWER TELCO

CATV

Code compliant,but still bad!

AC POWER

TELCO

CATV

Single point is the preferred application

NEC 2002250.56, 800.40 & 830.40

AC & Communications Grounding



45

Concluding Statements• Current Flows in Paths

– Kirchhoff's Laws Prevail• Ground is a path not a terminus• Understanding the paths is the key to good

grounding• Electrical Codes cannot be compromised by

grounding practices



V Power Problems

2

"Power Hit"

Surge

Sag

Impulse

Event

Glitch

Swell

Distortion

Outage

Glitch

Transient

Notching

Blink

Anomaly

Confusion???

Terms for Power Problems



3

Voltage Tolerance Curves

4

Voltage Tolerance Curves



5

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.

6

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



7

Power Problems

• Source – Internal or external– Utility or load

• Coupling– Direct– Induced

• Characteristics– Low Frequency– High Frequency

8

Power Problems - Coupling

• Directly conducted• Electromagnetically coupled or induced



9

Power Problems: Low Frequency

• Variation of amplitude near power system frequency

• Important Characteristics– Magnitude, Duration

and Source

• Types of event:– Swells (surges)– Sags & brownouts– Dropouts & outages– Frequency variation

10

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 multi-

cycle sample



11

Typical RMS Voltage Disturbances

12

Power Problems: Utility

• Power factor correction capacitor switching

• Circuit breaker operation and grid switching

• Arcs and line fault clearance

• Lightning and storms



13

Storm-Related Problems - Lightning

14

Storm Related Event



15

Facility Exposure to Lightning

16

Power Problems: Facility

• Loose connections• Overloaded circuits

and transformers• Wiring errors• Ground loops (low and

high frequency)



17

Facility Power Problems

• Breaker trip & fuses blow on motor start-up

18

Facility Power Problems-2

• ATS operation during motor start-up



19


ATS Re-transfer to preferred source

20


Good Start-up!



21


ATS Wiring Error!!!!

22

Power Problems: Equipment

• Equipment turn on/off• Equipment current

distortion• Phase-angle controlled

loads• Low immunity to

disturbances



23

V & I = Load

Load Related Events - 1

Load related event--load "turn-on"

24

Load Related Events - 2



25

Load Related Events (Harmonic Eval.)

26

Induction Motor Response to Outage



27

Equipment Response to Notch

28

Sub-cycle and Other Disturbances



29

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– Between physically

separated grounds

• One mode often converts to another through:– Circuit voltage drop– Capacitive coupling– Mutual inductive

coupling

30

Measurement Techniques

Normal Mode Common Mode Longitudinal Mode

Voltage Differential

Line-to Neutral or Phase-to-Phase

Neutral-to-Ground Imbalance between conductors or another reference point

Current Phase or Neutral Current

Line & Neutral Summation or Ground Current

Multiple Conductor Summation

L

N

G

L

N

G

L

N

G

v

v

v

Interference Modes



31

Power Problems: High Frequency - 1

• Important characteristics– Peak voltage, current &

energy– Rise time (dv/dt, di/dt)– Phase angle– Frequency of

occurrence

32

Transients

• Transient sources include– Lightning– Utility

• Power factor correction capacitors

• Switching

– User• load switching• Equipment operation• ESD



33

Transient Effects

• Damage– AC power supplies– Data, telephone and

communications interfaces

• Disruption– Data loss– System crash

• Degradation– Minor damage which

surfaces later

34

Transients

• Transient Propagation– Obeys circuit laws– Current flows in circuit– Capacitance may

complete circuit• Transient Protection

Basics– Current block

• Series high impedance– Current divert

• Parallel low impedance

Transient generator Load

Transient generator Load

Block



35

Meter

20'

6'

Line

Neutral

Placement of Surge Suppressor

36

Let throughAt the suppressorWith 6' of wireWith 20' of wire

6' of Wire

20' of Wire

Surge Suppressor Performance



37

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

38

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



39

ACTIVITY LOW (<20%) HUMIDITY

HIGH (>65%) HUMIDITY

Walking across carpet 35,000 V 1,500 VWalking 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

20,000 V 1,200 V

Movements on urethane padded chair

18,000 V 1,500 V

Electrostatic Voltages

40

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



VI Power Conditioning

2

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



3

Cascaded Protection

• Uses multiple shunt protectors• Uses blocking impedance

– Power system wiring– Power system transformers– Filter or transformer power conditioners

4

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



5

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

6

Arresters & Shunt Suppressors

• Use non-linear shunt elements– Varistor– Spark gap or gas tube– Silicon-controlled

rectifier (SCR)– Suppression diode

stacks



7

Voltage

Current

System

Clamping

Non-Linear Shunt Elements

• High "off" impedance• Low "on" impedance• Rapid transition

between states• Low to moderate

"headroom"

8

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



9

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

10

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



11

Component Service Life

• Service Component Damage– Caused by thermal

overstress:• Exceeding surge energy

rating• Exceeding rated voltage

– AC overvoltage• Wiring errors• Accidents• Utility problems

• Service Degradation– Varistors & diodes:

• Small change in leakage current

• Not limiting service factor

– Gas Tubes:• Electrode erosion• Rupture

12

120 VOLTS 114 VOLTS

3 VOLTS0 VOLTS

LOAD

UTILITY

HOT

NEUTRAL

GROUND

IR IR

IRIR

ELECTRICALSERVICE

TRANSFORMER

Dedicated Circuit



13

Surge Suppressor Specs ("Standards")

• Underwriters Laboratories (UL) Std. 1449• Commercial Item Descriptions (CIDs)

– Performance– Endurance (reliability)– Application– Safety– Certification

14

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



15

Filters

• Normally adds LC components to TVSS

• May or may not have sine tracking

• N/G usually weaker performance

• Adds RF attenuation to clamping

16

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– Inductance and load determine

attenuation • Common mode attenuation via

coupling capacitance– Shields or screens improve

attenuation

Line Load



17

Ferroresonant Voltage Regulators• Transformer operates in

saturated mode• LC filter produces

sinusoidal output voltage• Shielding may improve

common mode performance

PrimaryWinding

OutputWinding

ResonatingWinding

MagneticShunt

Primary Section of Core

Secondary Section of Core

Air Gap

18

Tap Switching Voltage Regulators

• Control of voltage taps– SCR– Triac– Relay

• 0.5 cycle response time

• Continual tap changing

Line

Ground

Electronic ControlTap Selection

Load



19

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

20

Motor-Generator

• Isolates load mechanically

• Provides some dropout ride-through



21

Uninterruptible Power Supplies

• Provide backup AC power from storage batteries

• Automatically power load on loss of utility source

• May also suppress and condition power

22

UPS

UTILITY

LOAD

Ideal UPS

• Source Input:– Disturbed (transients &

switching)– Discontinuous – Unregulated – < 100% reliable

• UPS Output:– Undisturbed

(suppressed & no switching)

– Continuous – Regulated– 100% reliability



23

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

24

PSEUDO-SINE

RECTANGULAR

SINUSOIDAL

UPS Output Waveforms



25

HOT

NEUTRAL

GROUND

UTILITY LOAD

HOT

NEUTRAL

GROUND

RECTIFIER INVERTER

AC DC DC AC

+-

BYPASS

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

26

HOT

NEUTRAL

GROUND

UTILITY LOAD

HOT

NEUTRAL

GROUND

RECTIFIER INVERTER

AC DC DC AC

+-

TRANSFERSWITCH

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



27

HOT

NEUTRAL

GROUND

UTILITY LOAD

HOT

NEUTRAL

GROUND

+-

INVERTER

DC AC

RECTIFIER

AC DC

TRANSFERSWITCH

UPS Modes of Operation - 3

• Line interactive– Inverter on but unloaded– Output suppressed, conditioned and regulated– Output may be transformer isolated

28

Inertial and Flywheel UPS



29

Diesel UPS

30

Diesel Generator



31

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

32

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



33

Make Before Break Transfer

• Sources paralleled and synchronized• Phase offset at moment of transfer - 15°• Preferred offset - 7° or less

34

UPS -- ATS Problems• Site symptoms

– Burned contacts on automatic transfer switch (ATS)

– Blown fuses and tripped breakers at utility

– Synchronizing option added to ATS

– UPS static transfer failed and UPS transfers to bypass

– Problem worst with transfers from generator to utility

– Very large current inrush into UPS



35

Transfer to Utility - Sync cycle

36

Transfer -- Open Transition



37

Transfer -- Closing Transition

38

Transfer Complete -- Inrush Current



39

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.

40

CONTROLS

MOTORS

OTHERLOADS

INCREASING COST

1

4

2

3

Feeder orGroup ofMachines

UtilitySource

1 - EquipmentSpecifications

4 - Utility Solutions

3 - Overall Protection Inside Plant

2 - ControlsProtection

Customer Solutions

Source: Electrotek Concepts, Inc.

The Cost of Power Quality Solutions


© 2007 by PowerCET Corporation. All rights reserved. (070320)7- 1

VII Safety

2

WARNING #1Performing 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.



3

WARNING #2• Follow all appropriate safety rules and

procedures– Company– NFPA / NEC– OSHA– Appropriate state and local work rules

4

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



5

Safety Equipment / Apparel• Rubber gloves rated at

600v/20kv• Leather protectors• Hard hat• Hearing protection (when

appropriate)• Safety face or eye protection

(UV rating)• Long-sleeved shirts (Nomex or

Indura flame-resistant clothing) worn while working on or near 0-600 volts

• Specialized safety equipment for high voltage and other hazardous environments

6

Never Assume a Circuit is Dead



7

Jewelry / Surroundings / Conductor / Neutral

8

Typical Body Current Paths



9

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 contraction1mA: Threshold of perception; tingling.

Applied to Myocardium (Microshock)100uA: Ventricular fibrillation.10uA: Recommended maximum leakage current.

Effects of Electric Shock

10

(Blank)



VIII Planning & Performing a Power Quality Survey

2

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!"



3

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

4

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



5

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

6

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.



7

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.

8

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



9

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)

10

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



11

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.

12

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?



13

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



15

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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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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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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3Ø Monitoring Instruments / $2K to $6K

• Ideal Model 805

• Summit Technologies Power Sight 4000

• LEM Analyst 3Q

• AEMC PowerPad 3945

• Fluke 430-Series

• Dranetz-BMI PowerGuide 4400 & PowerVisa 440

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LEMTopaz 10000

RPM (Fluke)PowerRecorder

Dranetz-BMIPowerXplorerPX5 (PX5-400 for 400Hz apps.)

Hioki 3196

Portable 3Ø Power Quality Monitors / $7K to $15K



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PML ION77 Dranetz-BMI Signature System

PowerLogic CM4000T RPM (Fluke) Multipoint Dranetz-BMI Encore

Electro Ind. NEXUS 1250

Permanent Power Monitors / $2K to $4K + Installation & Software

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Laptop CPU / Controller

e/w HS Modem

Energy Analyzer

High Speed DSO

Power Quality Analyzer

Spectrum Analyzer

Monitoring Systems



25

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

26

Review the Electrical Service

• Service entrance -- single or multiple?• How are the service entrances grounded?• Building Grounding Electrode System?• Transformer isolation?• Ground Fault Interrupt?



27

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



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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



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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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• 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



33

XX

XX

XXEvent Log#2

Event Log#3

Event Log#1 XXX

X

Summary Info w/Event Log Correlation

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Key Event



35

Symptom Possible CauseI/O port failure Longitudinal CMIProcessor lockup Software / RF / ESDKeyboard controller failure ESDPower supply failure Surge-transient / ESDSystem crash Surge-transient (voltage)Wavy screen EMFClock/date reset Battery / conducted RFOpen door/cabinet halt Radiated RF


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Writing the Report - Software Tools• AiPower (Kreiss-Johnson

AI based report generator, supports multiple manufacturers)

• Dranetz-BMI Technologies– DranView Versions 4, 5 & 6

• Fluke / RPM– PAS & Scenario w/Report

Writer– EN50160 Report Writer– Flukeview



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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

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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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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

– Too little, too late for too much

• Monitor on an ongoing basis

• Be part of the solution• Provide ROI• Manage the facility

infrastructure

ANALYZEDATA

EVALUATESOLUTIONS

GATHERDATA

IMPLEMENTSOLUTIONS



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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!!!

Documents

Introduction to Power Quality: Problems, Analysis & … to Power Quality: Problems, Analysis & Solutions Presented by: PowerCET® Corporation 3350 Scott Blvd., Bldg. 55 Unit 1 Santa