power quality reference guide

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PO ERQUALITY

Energy E ciency Re erenceVOLTAGE SAG

CURRENT SWELL

Time

Voltage

Current

LINE-NEUT VOLTAGE SAG

200V

100A

30.0A

AMPS

0A

125V

105V

0V20.0v/div vertical 2 sec/div horizontal

10.0A/div ver tical 2 sec/div hor izontal

LINE AMPS CURRENT SURGE

Time


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DISCLAIMER: Neither CEA echnologies Inc. (CEAauthors, nor any of the organizations providing funding

for this work (including any persons acting on the behaaforementioned) assume any liability or responsibility fodamages arising or resulting from the use of any informequipment, product, method or any other process whatsdisclosed or contained in this guide.

Te use of certified practitioners for the application of ttion contained herein is strongly recommended.

Tis guide was prepared by Energy @ Work for the CEnologies Inc. (CEAI) Customer Energy Solutions Int

(CESIG) with the sponsorship of the following utility cparticipants:

2007 CEA echnologies Inc (CEAI) All rights re


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TABLE OF CONTENTS

Chapter

1 The Scope of Power Quality

1.1 Defi nition of Power Quality

1.2 Voltage1.3 Why Knowledge of Power Q

Important

1.4 Major Factors Contributing to

Issues1.5 Supply vs. End Use Issues

1.6 Countering the Top 5 PQ Myt

1.7 Financial and Life Cycle Costs

2 Understanding Power Quality Concepts

2.1 The Electrical Distribution Syste

2.2 Basic Power Quality Concept

3 Power Quality Problems3.1 How Power Quality Problems

3.2 Power Quality Disturbances


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3.6 Related Topics

3.7 Three Power Quality Case Studies4 Solving and Mitigating Electrical Power Proble

4.1 Identifying the Root Cause and AsSymptoms

4.2 Improving Site Conditions4.3 Troubleshooting and Predictive Tip

5 Where to Go For Help

Web Resources

CSA Relevant Standards

CEATI Reference Documents


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FORWARD

Power Quality Guide FormatPower quality has become the term used to descrrange of electrical power measurement and operaOrganizations have become concerned with the iof power quality because of potential safety, opereconomic impacts.

Power quality is also a complex subject requiringterminology in order to properly describe situatio

issues. Understanding and solving problems becowith the correct information and interpretation.

Tis Power Quality Reference Guide is written tand practical guide to assist end-use customers ain the following sections:

Section 1: Scope of Power Quality

Provides an understanding that will hde-mystify power quality issues

Section 2: Understanding Power Quality ConcDefines power quality, and provides ccase study examples

Section 3: Power Quality Problems


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Section 4: Solving and Mitigating ElectricalPower Problems

Suggestions and advice on potential poweissues

Section 5: Where to go for Help

Power quality issues are often addressed reactively. Plmaintenance is more predictable and cost effective thunplanned, or reactive, maintenance if the right inforavailable. Power quality problems often go unnoticedbe avoided with regular planned maintenance and themitigating technologies.

Prevention is becoming more accepted as companies,particularly those with sensitive equipment, are recogmetering, monitoring and management is an effectiveto avoid unpleasant surprises. Metering technology h

improved and become cost effective in understandingavoiding problems.

Selecting the proper solution is best achieved by askinright question up front. In the field of power quality, question might best be addressed as:

What level of power quality is required for my elecsystem to operate in a satisfactory manner, given prand maintenance?


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thoroughly understand the root cause of the probthe problem and reviewing options will help secu

solution for the maximum return on investment


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1 The Scope o

1 THE SCOPE OF POWER Q

1.1 Defi nition of Power QualityTe Institute of Electrical and Electronic Enginedefines power quality as:

Te concept of powering and grounding electequipment in a manner that is suitable to thethat equipment and compatible with the premsystem and other connected equipment.1

Making sure that power and equipment are suitaother also means that there must be compatibilitelectrical system and the equipment it powers. Talso be compatibility between devices that share distribution space. Tis concept is called ElectromCompatibility (EMC) and is defined as:

the ability of an equipment or system to funcsatisfactorily in its electromagnetic environmintroducing intolerable electromagnetic disturanything in that environment.2

Te best measure of power quality is the ability oequipment to operate in a satisfactory manner, giand maintenance and without adversely affectingof other electrical equipment connected to the sy


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10


and 50 Hz in many other parts of the world. Tis frecalled the fundamental frequency.

1 Cycle

V

0

V

(1/60 second)

MaximPeak voRMS

Average voltage 0.637 Peak voltage

Effective ( 0.707typically 1electrical

Voltage

Figure 1: Pure Sinusoidal AC Voltage Waveor

Any variation to the voltage waveform, in magnitude

frequency, is called a power line deviation. However,power line deviations result in disturbances that can cproblems with the operation of electrical equipment.

1.2.1 Voltage Limits

Excessive or reduced voltage can cause wear or damagelectrical device. In order to provide standardization, mended voltage variation limits at service entrance pospecified by the electrical distributor or local utility A


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1 The Scope of

Rated voltage (V)* Voltage limits at point of delive

Marginal operating conditions

Normal operating conditionsSingle-phase circuits

120/240 106/212 110/220 125/250480 424 440 500

600 530 550 625Three-phase/four-wire circuits120/208 (Y)* 110/190 112/194 125/216277/480(Y) 245/424 254/440 288/500347/600 (Y) 306/530 318/550 360/625

Three-phase/three-wire circuits

240 212 220 250480 424 440 500600 530 550 625

Medium-voltage circuits

1,00050,000 - 6% - 6% + 6%

In addition to system limits, Electrical Codes spedrop constraints; for instance:

(1) Te voltage drop in an installation shall:

Be based upon the calculated demand lofeeder or branch circuit.Not exceed 5% from the supply side of t

i ( i l t) t th i t f t


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12


For voltages between 1000 V and 50 000 V, the maxilowable variation is typically 6% at the service entra

are no comparable limits for the utilization point. Teranges exclude fault and temporary heavy load conditexample of a temporary heavy load condition is the sta motor. Since motors draw more current when they when they are running at their operating speed, a vol

may be produced during the initial startup.VOLTAGE SAG

CURRENT SWELL

Time

Voltage

Current

LINE-NEUT VOLTAGE SAG

200V

100A

30.0A

AMPS

125V105V

0V

20.0v/div vertical 2 sec/div horizontal


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1 The Scope of

It is not technically feasible for a utility to deliveris free of disturbances at all times. If a disturbanc

waveform is required for the proper operation ofproduct, mitigation techniques should be employof utilization.

1.3 Why Knowledge of Power Qua

ImportantOwning or managing a concentration of electronlife-safety devices requires a familiarity with the electrical power quality.

Power quality diffi culties can produce significantsituations that include:

Important business applications (bankincontrol, process control)

Critical industrial processes (programma controls, safety systems, monitoring deviEssential public services (paramedics, hoair traffi c control)

Power quality problems in an electrical system ca

frequently be indicative of safety issues that may ate corrective action. Tis is especially true in thegrounding and bonding errors.

Y l l l d h ld b d d b


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14


1.4 Major Factors Contributing to Power

IssuesTe three major factors contributing to the problemsassociated with power quality are:

Use of Sensitive Electronic Loads

Te electric utility system is designed to provide reliaeffi cient, bulk power that is suitable for the very largeof electrical equipment. However, devices like compudigital controllers have been widely adopted by electrusers. Some of these devices can be susceptible to pow

disturbances or interactions with other nearby equipmTe Proximity of Disturbance-Producing Equipme

Higher power loads that produce disturbances equiusing solid state switching semiconductors, arc furnac

and electric variable speed drives may cause local poquality problems for sensitive loads.

Source of Supply

Increasing energy costs, price volatility and electricity

reliability issues are expected to continue for the forefuture. Businesses, institutions and consumers are becmore demanding and expect a more reliable and robucal supply, particularly with the installation of diversed C b l b


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1 The Scope of

by the regulator. Power quality issues on the custhe meter are the responsibility of the customer.

therefore, to understand the source of power quaand then address viable solutions.

1.5 Supply vs. End Use IssuesMany studies and surveys have attempted to defi

percentage of power quality problems that occur anomalies inside a facility and how many are duethat arise on the utility grid. While the numbers agree, the preponderance of data suggests that mquality issues originate within a facility; however

an interactive effect between facilities on the systDoes this matter? After all, 100% of the issues thpower quality problems in your facility will causematter where they originate. If the majority of po

issues can be controlled in your own facility, thencan be addressed at lower cost and with greater cUnderstanding how your key operational processprotected will lead to cost savings.

Utilities base their operational quality on the num

minutes of uninterrupted service that are deliverecustomer. Te requirements are specific, public anthe regulator as part of their rate application (oftreferred to as the Distributors Handbook).

1 Th S f P Q l


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16


Most PQ issues are end-user issues

Most supply issues are related to utility reliabili

1.6 Countering the Top 5 PQ Myths1) Old Guidelines are NO the Best Guidelines

Guidelines like the Computer Business EquipmentManufacturers Association Curve (CBEMA, now caIIC Curve) and the Federal Information ProcessingPub94 (FIPS Pub94) are still frequently cited as beinpower quality guidelines.

Te IIC curve is a generic guideline for characterizielectronic loads typically respond to power disturbancFIPS Pub94 was a standard for powering large maincomputers.

Contrary to popular belief, the IIC curve is not useequipment or power supply designers, and was actualintended for design purposes. As for the FIPS Pub94released in 1983, was never revised, and ultimately wadrawn as a U.S. government standards publication in

1997. While some of the information in FIPS Pub9relevant, most of it is not and should therefore not bewithout expert assistance.

2) Power Factor Correction DOES NO Solve All

16

h f


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1 The Scope of

designed units have caused significant power quainteractions in buildings.

Te best advice for power factor correction is theadvice for solving power quality issues; properly uyour problem first. A common solution to powerproblems is to install capacitors; however, the optcan only be found when the root causes for the pproblems are properly diagnosed. Simply installincan often magnify problems or introduce new poproblems to a facility.

Power factor correction is an important part of re

cal costs and assisting the utility in providing a melectrical system. If power factor correction is noand maintained, other power quality problems melectrical system of any facility is not static. Propand compatible design will lead to peak effi cienc

power quality.3) Small Neutral to Ground Voltages DO NO

Power Quality Porblem

Some people confuse the term common mode n

measurement of a voltage between the neutral anof their power plug. A small voltage between neuon a working circuit indicates normalimpedance in the wire carrying the neutral curren

1 Th S f P Q lit


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18


4) Low Earth Resistance is NO MANDAORY f

Electronic Devices

Many control and measurement device manufacturermend independent or isolated grounding rods or systorder to provide a low reference earth resistance. Sumendations are often contrary to Electrical Codes an

make operational sense. Bear in mind that a solid conearth is not needed for advanced avionics or nautical

5) Uninterruptible Power Supplies (UPS) DO NO

Complete Power Quality Protection

Not all UPS technologies are the same and not all UPnologies provide the same level of power quality protfact, many lower priced UPS systems do not provide quality improvement or conditioning at all; they are mback-up power devices. If you require power quality p

like voltage regulation or surge protection from your make sure that the technology is built in to the devic

1.7 Financial and Life Cycle CostsTe financial and life cycle costs of power quality issu

fold;1.Te hidden cost of poor power quality. T

impact of power quality problems is often un

1 Th S f


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1 The Scope of

connections), to the expensive, such as pinstalling a large uninterruptible power

Evaluation of both costs should be included in thprocess to properly assess the value, risk and liquinvestment equally with other investments. Orgabasic financial analysis tools to examine the costsof their investments. Power quality improvementshould not be an exception; however, energy probevaluated using only one method, the Simple Paevaluation methods that can properly include theand cost of money are not used, e.g., Life Cycle C

Monetary savings resulting from decreased mainincreased reliability, improved effi ciency, and lowreduce overall operating costs. A decrease in cosan increase in profit, which increases the value oftion.

Regrettably, the energy industry has adopted thePayback as the most common financial method uPayback is admittedly the easiest, but does not cotant issues. o properly assess a capital improvemsuch as a solution to power quality, Life Cycle Cused. Both methods are described below.

1.7.1 Simple Payback



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As the name implies, the advantage of the Simple Pamethod is that it is simple to use. It is also used as an

of both liquidity and risk. Te cash spent for a projecthe amount of money available to the rest of the orga(a decrease in liquidity), but that cash is returned in tof reduced costs and higher net profit (an increase in Tus the speed at which the cash can be replaced is i

in evaluating the investment.Short payback also implies a project of lesser risk. Asrule, events in the short-term are more predictable thin the distant future. When evaluating an investmentin the distant future carries a higher risk, so shorter pperiods are preferable and more attractive.

A very simple payback analysis may ignore importantbenefits that result from the investment. Direct savinmay occur outside the immediate payback period, suc

incentive programs or tax relief, can often be overlook

1.7.2 Life Cycle Costing

Proper financial analysis of a project must address mojust first cost issues. By taking a very short-term persthe Simple Payback method undervalues the total finbenefit to the organization. Cost savings are ongoingcontinue to positively impact the bottom line of the clong after the project has been repaid

1 The Scope of


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1 The Scope of

value of money is an important part of the investSimply stated, money received in the future is les

money received today. When evaluating long-tercash gained in the future must therefore be discoits lower value than cash that could be gained tod

1.7.3 The Cost of Power Quality Problem

Te costs associated with power quality preventioincluded with the acquisition cost of sensitive eqthe equipment can be protected from disturbanccosts must also be factored into the purchase of acal product. Te design and commissioning of daspecific example. Te costs that should be consid

Site preparation (space requirements, air conInstallationMaintenanceOperating costs, considering effi ciency for acconditionsParts replacementAvailability of service on equipment

Consulting advice (if applicable)Mitigating equipment requirements

Te cost of purchasing any mitigating equipmen



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22


For very large electrical devices, even if no power qualityare experienced within the facility, steps should be taken t

the propagation of disturbances which may originate andback into the utility distribution system. Many jurisdictiothe compatibility of electrical loads in order to limit poweinteractions.

Section 4.0, Solving and Mitigating Electrical Power Pprovides suggestions.

2 Understanding Power Q


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2 UNDERSTANDING POWER

QUALITY CONCEPTS

2.1 The Electrical Distribution SysteOne of the keys to understanding power quality

understand how electrical power arrives at the sodistribution is such a critical issue.

Electrical power is derived from generation statioconvert another form of energy (coal, nuclear, oilmotion, wind power, etc.) to electricity. From theelectricity is transmitted over long distances at hivoltage through the bulktransmission system.

Power is taken from the bulk transmission systemtransmitted regionally via the regional supply sys

distributed locally through the distribution systemlocal utilities. Te voltage of the distribution systereduced to the appropriate level and supplied to tservice entrance.



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24

g w y p

TransformerStation

GeneratingStation

Bulk TransmissionSystem

Regional SupplySystem

TraSta

Electrical System

DistributionSystem

Customer

Figure 3: Electrical Transmission and Distribut

2.1.1 Voltage Levels and Confi gurations

Te power supplied to the customer by the utility wileither single-phase or three-phase power. Single-pha

is usually supplied to residences, farms, small offi ce ancommercial buildings. Te typical voltage level for sinpower is 120/240 V (volts).

LINE

Supply

fromUtilityLine

LINE

120V

120V

LINE

NEU



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LINE

Supplyfrom

Utility

LINE

LINE

Ground Line to NeutraLine to Line V

NEUTRAL

Figure 5: Typical 208 V Three-phase Wye Conne

ypical voltage levels for three phase power su

V/208 V, 277 V/480 V (in the United States an347 V/600 V (in Canada).

Rotating equipment such as large motors and othment require three-phase power to operate, but mrequire only single-phase power. Single-phase pofrom a three-phase system by connecting the loaphases or from one phase to a neutralconductor.



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26

g y p

NG

208V

480V600V

120V

277V347V

to N Voltage to Voltage

Figure 6: Grounded Wye Connection

2.1.2 Site DistributionElectrical power enters the customers premises via thentrance and then passes through the billing meter toboard (also referred to as the fuse box, breaker panIn most residential or commercial installations electri

will be run from this panel board.

ServiceEntrance

BillingMeter



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g

BillingMeter

Panel Board

Pane

Pane

Ci

Figure 8: Service with Branch Panel Bo

A transformer is used if a different voltage or isothe rest of the distribution system is required. Teffectively creates a new power supply system (carately derived power source) and a new groundinneutral.

Transformer

208V480V



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28

2.2 Basic Power Quality Concepts

2.2.1 Grounding and BondingGrounding

Grounding is one of the most important aspects of anelectrical distribution system but often the least unde

Your Electrical Code sets out the legal requirements jurisdiction for safety standards in electrical installati

For instance, the Code may specify requirements in tfollowing areas:

(a) Te protection of life from the danger of electricproperty from damage by bonding to ground nocarrying metal systems;

(b) Te limiting of voltage on a circuit when exposvoltages than that for which it is designed;

(c) Te limiting of ac circuit voltage-to-ground to aon interior wiring systems;

(d) Instructions for facilitating the operation of eleapparatus

(e) Limits to the voltage on a circuit that is exposedning.

In order to serve Code requirements effective ground



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also helps prevent the build-up of potentially dancharge in a facility.

Te grounding electrode is most commonly a conelectrically conductive underground water pipe rthe premises. Where this is not available the Elecdescribe other acceptable grounding electrodes.

Grounding resistances as low as reasonably achiereduce voltage rise during system upsets and therimproved protection to personnel that may be in

Connection of the electrical distribution system ing electrode occurs at the service entrance. Te

neutral of the distribution system is connected toservice entrance. Te neutral and ground are alsotogether at the secondary of transformers in the system. Connection of the neutral and ground wother points in the system, either intentionally or

ally, is both unsafe (i.e., it is an Electrical Code vpower quality problem.

Equipment Bonding

Equipment bonding effectively interconnects all

carrying conductive surfaces such as equipment eraceways and conduits to the system ground.

Te purpose of equipment bonding is:



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30

120V appeenclosure pa hazard to

LOAD

Short to Enclosure Enclosure

Ground

15A Breaker

120V

Figure 10: Equipment without Proper Equipment B

Fault currentthrough safeand breakerNo voltage aenclosure. Nhazard.

LOAD

Short to Enclosure Enclosure

Ground

15A Breaker Opens

Fault CurrentSafety Ground

120V

Figure 11: Equipment with Proper Equipment Bo

If the equipment were properly bonded and groundedequipment enclosure would present no shock hazard ground fault current would effectively operate the ovedevice.

3 Power Q


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3 POWER QUALITY PROBLEM

3.1 How Power Quality Problems DTree elements are needed to produce a problemdisturbance:

A sourceA coupling channelA receptor

If a receptor that is adversely affected by a poweris not present, no power quality problem is exper

Disturbance

Source

Coupling

Channel

Figure 12: Elements o a Power Quality P

Te primary coupling methods are:

1. Conductive couplingA disturbance is conducted through the powerequipment.

3 Power Quality Problems


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operation of arc welders, intermittent switching ofcontacts, lightning and/or by intentional radiation

broadcast antennas and radar transmitters. When tcouples through the air it does so either capacitivelinductively. If it leads to the improper operation ofit is known as Electromagnetic Interference (EMIFrequency Interference (RFI). Unshielded power c

act like receiving antennas.Once a disturbance is coupled into a system as a vodeviation it can be transported to a receptor in twoways:

1) A normal or transverse mode disturbance is aunwanted potential difference between two ccarrying circuit conductors. In a single-phaseoccurs between the phase or hot conductorneutral conductor.

2) A common mode disturbance is an unwanteddifference between all of the current-carryingtors and the grounding conductor. Commondisturbances include impulses and EMI/RFIwith respect to ground.

Te switch mode power supplies in computers and anequipment can also be a source of power quality prob

Te severity of any power line disturbance depends o

3 Power Q


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3.2 Power Quality DisturbancesCategory Typical Spectral Cintent Typical Duration

1 .0 Transients

1.1 Impulsive Transient1.1.1 Nanosecond 5 ns rise 1 ms

1.2 Oscillatory Transient1.2.1 Low Frequency 1 min 3.2 Under-voltages >1 min 3.3 Over voltages >1 min

4.0 Voltage Imbalance Steady State5.0 Waveorm Distortion

5.1 DC Offset 0-100th Harmonic Steady State5.2 Harmonics 0-6 KHz Steady State

5.3 Inter-harmonics Steady Stateh



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34

disturbance and the f requency of occurrence. Tese cltions are shown in the previous table.

3.3 Load Sensitivity: Electrical Loads thAffected by Poor Power Quality

3.3.1 Digital Electronics

Digital electronics, computers and other microprocesequipment may be more sensitive to power linedisturbances than other electrical equipment dependiquality of their power supply and how they are intercTe circuits in this equipment operate on directcurrent (DC) power. Te source is an internal DC powhich converts, or rectifies, the AC power supplied bto the various DC voltage levels required. A computesupply is astatic converterof power. Variations in the

supply can therefore cause power quality anomalies iners.

Te Computer Business Equipment Manufacturers ACurve (CBEMA, now called the IIC Curve) publisIEEE Orange Book is intended to

illustrate a suggested computer susceptibility profile tvoltage variations. Te IIC curve is based on generaassumptions, is not an industry standard and is not in

t d i N IIC b

3 Power Q


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ITI (CBEMA) Curve(Revised 2000)

Prohibited Re

No Interruption In Function Region

No Damag

Perce

nto

fNomina

lVoltage(RMSorPea

kEquiva

lent)

Voltage Tolerance EnvelopeApplicable to Single-Phase120-Volt Equipment

500

400

300

200

140

120

100

8070

40

0

1us.001 c 0.01 c

1 ms 3 ms 20 ms 0.5 s

Duration in Cycles (c) and Seconds (

1 c 10 c 100

Figure 13: Computer Susceptibility Profle to L



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36

Te susceptibility profile implies that computers can slow variations from -13% to + 5.8%, and greater am

disturbances can be tolerated as their durations becomIn fact, many computers can run indefinitely at 80% onominal supply voltage; however, such operation doepremature wear of the power supply.

While the operating characteristics of computer perip

may at one time have been more dependent on the typower supply designs and components used, generalizinfer that computers are highly sensitive to small devpower quality are no longer true.

Tere is also no validity in the contention that, as thespeed of a computer increases, so does its sensitivity tvariations. I equipment sensitivity is due to the manwhich its power supply components interact with theAC power.

3.3.2 Lighting

Tere are three major effects of voltage deviations on1. Reduced lifespan2. Change of intensity or output (voltage flicker)

3. Short deviations leading to lighting shutdownturn-on times

For incandescent lights the product life varies inverse

3 Power Q


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Information on lighting is available from the comlighting reference guide that can be easily foun

various internet web search engines.

3.3.3 Motors

Voltages above the motors rated value, as well asimbalance, can cause increased starting current a

ing. Reduced voltages cause increased full-load teand reduced starting torques.

3.4 Types and Sources of Power QProblems

3.4.1 Transients, Short Duration and LongVariations

A general class of power quality variations (summ

the following charts) are instantaneous variationssubdivided as:

ransients (Impulsive and Oscillatory; up to Short-Duration (0.5 cycles to 1 minute)

Long-Duration (>1 minute but not a steady enon)Generally, instantaneous variations are unplanneshort-term effects that may originate on the utili



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3 Power Q


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Power Line Disturbances Summary



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40

Power Line Disturbances Summary (1 of 4)

DISTURBANCES SYMPTOMS POSSIBLE CAUSES POSSIBLE

Po


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high amptitude, shortduration voltagedisturbances

can occur incommon andnormal mode

switching inductive loads on or off(motors, relays, transformers,x-ray equipment, lighting ballasts)

operation of older UPS/SPSsystems may cause notching

arcing grounds lighting capacitor switching fault clearing

electronic interfer microprocessor ba

errors

hardware damagequipment

current limiting fu

High frequencyoscillations (from a fewhundred Hz to 500 kHz)that decay to zero withina few milliseconds

Impulsive Non-Periodic

Impulsive Periodic

Oscillatory

Non-periodic impulseswhich increaseinstantaneous voltage

Periodic impulses whichincrease or decrease theinstantaneous voltage

TRA

N

SIEN

TS

Duration typically , 0.5 cycles

Coupling Mechanism

conductive, electromagneticDuration

impulsive oscillatory



DISTURBANCES SYMPTOMS POSSIBLE CAUSES POSSIBLE RESU


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42


SH

O

RTD

U

RATIO

N

D

ISTU

RBA

N

CES

Low voltage in one ormore phases

starting large loads (motors,air conditioners, electric furnaces,etc)

overloaded wiring and incorrectfuse rating

fuse and breaker clearing

lightning (indirect cause due toeffects of lightning arresters) ground faults utility switching/equipment failure utility reclosing activity

related computer systemfailures

hardware damage unlike ickering of lights motor stalling reduced life of motors an

driven equipment digital clock ashing

Sag

Duration 0.5s - 1min.

Coupling Mechanism

conductive sags swells interruptions

Swell

Voltage Flicker Repetitive

High RMS voltagedisturbance on one ormore phases

open neutral connection insulation breakdown sudden load reduction improper wiring, which restricts

the amount of current availablefor loads

fault on one line causing voltagerise on other phases

open conductor fault

light icker degradation of electrical

Repetitive sags or swellsin the voltage

large cyclic loads such as spotwelders, induction arc furnaces,and motors when cycled

light icker

Po




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LO

N

G

D

U

RATIO

N

D

ISTU

RBA

N

CES

Voltage DeviationsDuration:

>120 cycles (2 sec)

Coupling Mechanism: conductive

Undervoltage Any long-term changeabove (overvoltages) orbelow (undervoltages) theprescribed input voltagerange for a given piece ofequipment. (undervoltages)the prescribed input voltagerange for a given piece ofequipment.

overloaded customer wiringloose or corroded connections

unbalanced phase loadingconditions

faulty connections or wiringoverloaded distribution system

incorrect tap setting reclosing activity

errors of sensitive low efciency and

of electrical equipsome motors, hea

lengthens processinfrared and resistprocesses

hardware damage dimming of incan

and problems in tuorescent lightsBrownouts A type of voltage uctua-

tion. Usually a 3-5% voltagereduction.

poor wiring or connections high power demand within building

or local area intentional utility voltage reduction

to reduce load under emergencysystem conditions

planned utility testing

Overvoltage improper application of power

factor correction capacitors incorrect tap setting

overheating and electrical equipme

blistering of infra





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44


LO

N

G

D

U

RATIO

N

D

ISTU

RBA

N

CES

Power InterruptionsDuration:

momentary interruptions: , 3 s

sustained interruptions:.

1 minCoupling Mechanism: conductive

Power Interruptions Total loss of input voltage.Often referred to as ablackout or failurefor events of a few cyclesor more, or dropoutor glitch for failures ofshorter duration.

operation of protective devices inresponse to faults that occur dueto acts of nature or accidents

malfunction of customer equip-ment

fault at main fuse box trippingsupply

loss of computer/controlmemory

equipment shutdown/fa hardware damage product loss

3 Power Q

3 4 2 St d St t Di t b


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3.4.2 Steady State Disturbances

3.4.2.1 Waveform Distortion and HarmonicsHarmonics are currents and voltages with frequewhole-number multiples of the fundamental powquency (which is 60 Hz in North America). Harthe supplied 60 Hz voltage and current waveform

normal sinusoidal shapes.Each harmonic is expressed in terms of its order.the second, third, and fourth order harmonics haof 120 Hz, 180 Hz, and 240 Hz, respectively. As therefore frequency, of the harmonics increases, tnormally decreases. Terefore, lower order harmothe fifth and seventh, have the most effect on theDue to the nature of power conversion techniquebered harmonics are usually the only frequencieswhen dealing with harmonic problems. Te preselevels of even harmonics in a system requires expadvice from a power quality professional.

Te effect of a given harmonic on the power systby superimposing the harmonic on the fundamen

to obtain a composite:



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46

Initially In-Phase

0

0

sin (x)

sin (x) + .33 sin(3x)

.33 sin(3x)

Vo

ltage

Voltage

Figure 14: Superposition o Harmonic on Fundam

Initially In-Phase

In this example, the two waveforms begin in-phase wother, and produce a distorted waveform with a flatteTe composite waveform can be changed by adding t

harmonic, initially out-of-phase with the fundamentaa peaked effect:

3 Power Q


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Initially Out-Of-Phase

0

0

sin (x)

sin (x) .33 sin(3

.33 s

Vo

ltage

Voltage

Figure 15: Superposition o Harmonic on Fun

Initially Out-o-Phase

Harmonics can be differentiated from transients that transients are not periodic and are not stead

nomena.Production and ransmission

M t h i lt f th ti f


C S f H i


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48

Common Sources of Harmonics

Sector Sources Common Pro

Industrial Variable speed drives welders, largeUPS systems, lighting system

Overheating and fuse power factor correction c

Overheating of supply

Tripping of overcurrent

Commercial Computers, electronic officeequipment, lighting

Overheating of neutraltransformers

Interference

Residential Personal computers, lighting,electronic devices

Generally not a proble

However, high densityloads could cause overhetransformers

Figure 16: Main Sources o Harmonics

Harmonics are caused by any device or equipment whnonlinear voltage-current characteristics. For exampleproduced in electrical systems by solid state power cosuch as rectifiers that conduct the current in only a poeach cycle. Silicon Controlled Rectifiers (SCRs) or thare examples of this type of power conversion device.

Te levels of harmonic current flowing across the syspedance (which varies with frequency) determine thevoltage distortion levels

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200 V/div vertical

1000 V

1000 V

0 V

5.0 ms/div h

PH BNEUT INITIAL WAVE SHTime

Voltage

Figure 17: Harmonics Produced by Three

Controlled Loads

(Reproduced with Permission of Basic Measuring Instruments, from HandSignatures, A. McEachern,1988)

Aside from solid state power converters, loads mharmonics if they have nonlinear characteristics, the impedance of the device changes with the ap

Examples include saturated transformers and gaslighting, such as fluorescent, mercury arc and higsodium lights.


Tird harmonic currents are usually most apparent in


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50

Tird harmonic currents are usually most apparent inneutral line. Tese occur due to the operation of singl

nonlinear loads, such as power supplies for electronicment, computers and lighting equipment.

As lighting equipment has been a cause of many neuproblems adequate precaution must be taken to mitigharmonic emission of lighting equipment, in particul

of re-lamping. Tese harmonic currents occur due to tion of single-phase nonlinear loads, such as power sufor electronic equipment and computers. Te third haproduced on each phase by these loads adds in the nesome cases, the neutral current can be larger than the

currents due to these third harmonics.

Effects of Harmonics

In many cases, harmonics will not have detrimental eequipment operation. If the harmonics are very severhowever, or if loads are highly sensitive, a number ofproblems may arise. Te addition of power factor corrcapacitors to harmonic producing loads can worsen thtion, if they have parallel resonance with the inductanpower system. Tis results in amplifying the harmoniproducing high harmonic voltages.

Harmonics may show up at distant points from theirthus causing problems for neighbouring electrical end

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EQUIPMENT HARMONIC EFFECTS RESULT


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EQUIPMENT HARMONIC EFFECTS RESULT

Capacitors (all; not just those

for power factor correction)

capacitor impedance

decreases with increasingfrequency, so capacitors actas sinks where harmonicsconverge; capacitors donot, however, generateharmonics

supply system inductancecan resonate with capacitorsat some harmonic frequencycausing large currents andvoltages to develop

dry capacitors cannotdissipate heat very well,and are therefore moresusceptible to damage fromharmonics

breakdown of dielectricmaterial

capacitors used incomputers are particularlysusceptible, since they are

often unprotected by fusesor relays

heati

increa

short

fuse f

capac

Transformers current harmonics causehigher transformer losses

transf

d


In addition to electrical conduction, harmonics can b


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52

,inductively or capacitively, thus causing interference o

telecommunication systems. For example, humming ophones can be caused by induced harmonic distortion

A power harmonic analysis can be used to compare dlevels against limits of acceptable distortion. In additioperation of some solid state devices will produce a n

effect on the voltage waveform.

Harmonic Prevention and Reduction

It is very important when designing an electrical systor retrofitting an existing one, to take as many precauas necessary to minimize possible harmonic problemrequires advanced planning and, potentially, additionTe complete electrical environment must be conside

Filters

Harmonic filters can be used to reduce the amplitudemore harmonic currents or voltages. Filters may eitheto protect specific pieces of equipment, or to eliminatics at the source. Since harmonic filters are relatively

requirements may have to be budgeted for.In some situations, improperly tuned filters may shiftresonant frequencies close to the characteristic harmoh T f h hi h h i ld

3 Power Q

high-amplitude low order harmonics. A similar e


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g pwith pulse width modulated converters.

Method Advantages D

Change the size of thecapacitor bank to shift theresonant point away from themajor harmonic

vulnechang

relatively lowincremental cost

ease of tuning

Place an inductor in serieswith the capacitor bank, andtune their series resonancebelow the major harmonics

better ability to minimizeharmonics

flexibility for changing loadconditions

series fundamfrequecapacihigher

be req

elephone Line Interference

elephone interference can be reduced by the afoprevention and reduction methods, by rerouting

lines, improved shielding and balance of telephoncompatible grounding of telephone cables, or by harmonic levels on the power line. Te degree of interference can be expressed in terms of the eleference Factor (IF).

Harmonic Study

Single calculation of resonant f requencies, transil i d di it l i l ti th t


Equipment Specifications


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54

Consider the effect on your power system when orde

harmonic producing equipment. Large projects may ra pre-installation harmonic study. Be prepared for filtrequirements if necessary to ensure compatibility witpower system. If a harmonic filter is required, a descrthe power system should be considered in its design,

including:Fault level at the service entranceRating and impedance of transformers between tentrance and the input to the power conditioning

mentDetails of all capacitor banks in the facility.Where a choice is available, consider using equipmenharmonic emission characteristics. Tis should be exstated in the manufacturers literature. Where Variabl

Drives (VSDs) will be deployed, active front end desgenerate lower harmonic levels and have a power factto unity. Variable Speed Drives are also the same equAdjustable Speed Drives (ASDs); Variable Frequency(VFDs); Adjustable Frequency Drives (AFDs), etc.

3.4.2.2 Flicker

Flicker is the impact a voltage fluctuation has on the lui t it f l d fl t t b h th t th

3 Power Q

House Pumps Single Elevator Arc Furnaces


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5

4

3

2

1

1 12 2 3 4 610 1020 2030 30 6

0

Border Linesof Visibility

Border Linesof Irritation

Solid Lines composite curvGeneral Electric company. Kansas City Power & L igh1934: T&D Committee, EDetroit Edison Company: WPublic Service Company o

Dotted Lines voltage flickeElectrical World November

%V

oltageFluctuation

Fluctuations Per Hour

House PumpsSump Pumps

A/C EquipmentTheatrical Lighting

Domestic RefrigeratorsOil Burners

Single ElevatorHoistsCranes

Y-Delta Changes on

Elevator-Motor-Generator SetsX-Ray Equipment

Arc FurnacesFlashing SignsArc-Welders

Drop Hammers

SawsGroup Elevators

Fluctuations Per Minute

Figure 19: Flicker Curve IEEE 519-19

3.4.3 Distribution and Wiring Problems

Many power quality problems are due to improp

electrical distribution wiring and/or grounding wcustomers site.

Grounding and distribution problems can result following:

Improper application of grounding electrodedevising alternate grounds or grounding sysHigh impedances in the neutral current retur


Electrical Safety Code to ensure the safety of personnAll l l


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56

proper equipment operation. All electrical equipmentbe approved by the applicable authority, such as the CUL, or inspected by the local authority in order to enregulatory minimum safety standards have been achie

3.4.3.1 Fault Protection in Utility Distribution System

Faults resulting in overvoltages and over-currents min the utility system, typically due to lightning, constraccidents, high winds, icing, tree contact or animal inwith wires.4 Tese faults are normally detected byover-current relays which initiate the operation of fau

clearing by equipment.Faults may be classified as temporary or permanent. faults may be caused by momentary contact with treelightning flashover, and animal contact. Permanent fathose which result in repairs,

maintenance or equipment replacement before voltagbe restored. Protection and control equipment automdisconnects the faulted portion of a system to minimnumber of customers affected.

Te utility distribution system includes a number of dsuch as circuit breakers, automatic circuit re-closers acutouts which clear faults. Automatic re-closers and rbreakers restore power immediately after temporary f

3 Power Q

and assist in locating a fault, thereby decreasing thi t ti


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interruptions.

Automatic reclosers and reclosing breakers open over-current to prevent any further current flow, aafter a short period of time. If a fault does not disone reclosure operation, additional opening/reclooccur.

FaultPersists

CircuitOpen

CircuitClosed

FaultStart

t t

CircuitRecloses

CircuitOpens;

First ReclosureInitiated

CircuitReopens;

Second ReclosureInitiated

CircuitReopens

Third ReclosInitiated

FaultPersists

Figure 20: Example o a Repetitive Reclosure

Normally a few seconds are required to clear a fauthe appropriate circuitry for a reclosure. Te reclofor a recloser is the open circ it time bet een an a


200 V


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58

125 V

105 V

0 V20.0 V/div vertical 2 sec./div

LINENEUT VOLTAGE SAG

Voltage

Time

Figure 21: Eect o Multiple Reclosure Operation on

(Reproduced with Permission of Basic Measuring Instruments, from Handbook oSignatures, A. McEachern,1988)

Reclosing Interval (Seconds)

Type of Control t1

t2

3 Power Q

constant in the detection circuitry results in the gIn this figure small voltage rises indicate when re


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In this figure, small voltage rises indicate when reattempted unsuccessfully due to the persistence o

If a fault persists, the recloser or breaker may locka fuse or sectionalizer will operate. An autoreclosfeeder that is faulted can produce a disturbance tneighbouring feeders.

Customers frequently mistake the effects of a tem- 2s) interruption, such as the loss of time-keepindigital clocks, as evidence of a sustained power inTe fact that most High Intensity Discharge (HIwhich is frequently used in industrial settings, caminutes to come back on after a fault has clearedexample of an apparent power supply problem threpresents normal operation of the utility distribuTe lengthy period of time before light is restorethe characteristics of the lighting system. Althousystems are available that eliminate this problemrepresent the majority that are currently used.

3.4.4 Voltage Unbalance

A voltage unbalance is a condition in a three-phawhich the measured r.m.s. values of the phase vophase angles between consecutive phases are not age unbalance is a significant concern for users th


its operation although the motor does not operate at efficiency and power factor Voltage unbalance may al


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effi ciency and power factor. Voltage unbalance may alan impact on AC variable speed drive systems unless output of the drive rectifier is well filtered.

Tere are two major sources of voltage unbalance:

1) the unbalance of load currents, which can be contrmaking sure load currents are balanced to within 1

2) high impedance or open neutrals, which representwiring fault that needs to be corrected by your elec

3.5 Relative Frequency of Occurrence

Frequently, the source of a disturbance originates witcustomers plant or building. Some pre-existing data conducted in the United States indicate that as manyof the origins of power quality problems originate wicustomers or a neighbours facility. Many of these dis

are due to the use of disturbance producingequipment, improper wiring and grounding, or the mtion of mitigating equipment.

Some disturbances are caused by normal utility operatfault clearing, capacitor switching, and line switching. Afewer in number than those generated within a facilityevents can cause great diffi culty for customers that havment incompatible with these normal operations.

3 Power Q

100


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RelativePercent ofOccurrence(%)

100

8060

40

20

0 Sags

Volta e Disturbance

Impulses OPowerInterruptions

Figure 23: Relative Occurrence o Disturbance

Systems Supplying Computers

Source: Goldstein and Speranza, The Quality of U.S. Commercial AC Powe

INTELEC Conference, 1982.

In 1991 and 2000, the Canadian Electrical Assoctook major studies of power quality in Canada

Power Quality Survey . Utilities from across the performed monitoring at hundreds of sites. By coprimary and secondary metered sites, the survey the average power quality provided by Canadian good, and the average quality experienced by cus

Tere are considerable differences in the state of between sites or locations. Tis is because of the of factors involved, such as customer equipment


that changes in voltage can be very significant when othese loads is turned on or off Frequently customers


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62

these loads is turned on or off. Frequently, customers ingly cause their own power quality problems by operdisturbance-producing process equipment in the samas electronic control devices.

From 1992 to 1995, the Electrical Power Research In(EPRI) collected data at 300 sites in the U.S. to asses

power quality at the distribution level. A report* indithat sites experienced an average of 9 voltage sag or inruption events per year. In addition, the data indicatevoltage HD (otal Harmonic Distortion) peaked dafternoon and evening periods. For residential feeder

is consistent with past experience, since this is where sources such as television sets are the predominant losystem.

3 Power Q

Individual Voltage Harmonic Statistics fo


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Individual Voltage Harmonic Statistics foEach column represents a mean average of a given statisti

2.5

2.0

1.5

1.0

.5

0.0THD 2 3 4 5 6 7 8 9

%

ofFundamental

Figure 24: Individual Voltage Harmonic Statist

DPQ Sites rom 6/1/93 to 6/1/94

(Reproduced with Permission of EPRI, from * Preliminary Results For EighMonitoring from the EPRI Distribution Power Quality Project, D. Sabin, T. 1994)

3.6 Related Topics3.6.1 Electromagnetic Compatibility (EM

Electromagnetic compatibility is the term given and creation of electrical equipment that has botbility and transmission of electromagnetic noise ramount of reduction may be regulated by governmay be required to meet a certain operational req


3) Radiated noise from power wires (solved witrouting, shielding or filtering)


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64

u g, g g)

4) Generation of harmonics by electrical loads with filtering or re-design of the circuitry).

Electromagnetic Compatibility is a more involved ancomplex subject than can be adequately addressed in Te international technical community has provided ization activity under the IEC EMC committees (seewww.iec.ch/zone/emc for more information).

3.7 Three Power Quality Case Studies

3.7.1 Case Study: Meter, Monitor & Managproactive response to power quality

Te site in question is located in a multi-story offi ce Te top four floors of the building have been designa

Business Recovery Center (BRC) of a large financiation. Te function of the center is to provide backup, support services for the companys business units. If aor operational disaster occurred, many of the businesscould be temporarily routed to this center. As a result

contains a significant concentration of computing resthat need to be available at any time. Workstation comrequirements are based on the actual working systemline personnel

3 Power Q

tions and servers that may be brought to the site to the on-set of a recovery situation and added to


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ycomplement of business equipment. Tis could reover-loading at some points in the distribution nthe modern context of loading, harmonic currentattention, thus a real time monitoring system waprovide harmonic and true loading of the centergrid.

As was pointed out to the BRC personnel and enfor only a small additional cost, a total power quasystem could be installed that would provide builinformation along with distribution point data w

envelope. Te BRC utilizes a 600 V base buildingsystem. BRC business equipment transformers aone of two bus risers, whilemechanical equipment is fed from a separate 600In the event of a total loss of utility power these

be fed by two diesel generators that have an extencapability.

Te following requirements were developed bothrequests and expert input from the various stakeh

Each dry-type transformer in the BRC was t in order to provide current and harmonic loaand voltage distortion, voltage unbalance, ancurrent readings in real time


All meters must be fully networked utilizing opennetworking architectures and protocols


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66

g p

One of the key decisions that was made at this site onbasis of data viewed from the power quality componemeters was with regard to Uninterruptible Power Sup(UPS). wo issues arose that lead to cost savings. Tethese concerned the need for a large on-site UPS syst

was advocated by some. While servers require the ridof the UPS, management determined that the impacttransfer switching, while annoying for some is acceptthat most workstations did not need the protection os of ride through afforded by the UPS. Data from mo

generator tests revealed however that transfer switch anomalies were impacting the servers, leading to somanomalies. Te UPSs in use at the site were of a hybrthat allowed transient and switching noise to pass thrUPS. UPSs were also subjected to excessive battery w

on waveform data captured during testing, a decisionto switch to an on-line UPS design and to institute aUPS management system.

Within 8 months of operation, an increased voltage uwas noted on a non-K-rated dry-type transformer. N

this would indicate a high impedance neutral to groubond which, if left undetected, would lead to overheaequipment failure. A check of the meter revealed how

3 Power Q

Information is available at all times that can factors for key processes


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Reporting is available that shows the size, sh tion of building envelope power quality anomTe money invested in the monitoring system hagreat returns in terms of the impact power qualiton equipment purchase and utilization since inst

3.7.2 Case Study: High Demand Load inAssembly Facility

A pulsed laser system used by an aircraft manufato number and identify wires on each and every ptured. Te unit was malfunctioning and would stfor short durations. Te cost to the operation invtime of staff and equipment but, more importantwire marking presented a massive safety liability.

Te machine operated at 20 Hz supplied from a V, 60 Hz single phase branch circuit. Te systemeffective transfer of peak power from the power slaser. Anything less than the peak power during ptions resulted in reduced laser intensity with a co

of quality in the process. Further investigation requality of voltage at the site was distorted by 4.5%peaks of the voltage waveform were flattening ou


delivered to the laser was over 25% less than what waProduct marking during this cycle was substandard.


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68

Facility electricians were instructed to wire up a tempsource close to the laser load which had a lower impehigher capacity. Tis solution provided a healthier situthe internal workings of the power supply, since capafull charge and more power was available for the laser

Why was the capacity of the source increased? Nomiunit operated on a 20 A breaker at 120 V giving us a capacity rating of 2400 VA. Te system required largecurrents to power its laser, and therefore a source of 5120V, 6000 VA, was needed. It is not unusual to havesource requirements considerably for loads of this typ

3.7.3 Case Study C: Motor Drive and TransIncompatibility in a Commercial Building

Tis case study looks at a commercial offi ce building utilizes two banks of AC motors with variable speed (VSDs) to control Heating, Ventilating and Air Con(HVAC) functions. Each of the banks is serviced by ikVA transformer; the only loads on these transforme

AC drives. Te figure below shows a rather innocuousnapshot. Te variable speed drives are rather like largmode power supplies whichd d k t ft hi k lt

3 Power Q

Site 4 - Phase B-Neut. Snapshot 10:25:45 AM


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200150100500

50

100150200

Vo

lts

Site 4 - Neut-Gnd Snapshot 10:25:45 AM

5

3

1

1

3

5

Vo

lts

Te major problem at this site was the intense heservice transformers. Te problem became especi

h h d fl l i d b


What was discovered was that the load on the transfowas at least 5 kVA over their nominal de-rated capac

d f h h B h f


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70

accounted for the severe heating. Both transformers woperating just above their maximum designed temperwhich will lead to premature insulation failure. Whatshown here, and was required to obtain the results is data analysis from the power quality instrument that the RMS and peak currents.

Te solution for this site was new K-rated transformedrive bank. Given the isolated nature of the drives anneutral to ground voltage, there was no need for phastransformers or special neutral current limiting devic

4 Solving and Mitigating Electrical P

4 SOLVING AND MITIGATINELECTRICAL POWER PROBLE


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ELECTRICAL POWER PROBLE

4.1 Identifying the Root Cause andSymptoms

Power quality technologists employ technical insTis instrumentation can range from simple digitering through to sophisticated waveform analysirue power quality monitoring requires full-timeso that steady state effects can be trended and inf

can be captured as they occur. A variety of electronow available for permanent monitoring that offfeatures at moderate prices.

A trained PQ specialist can also employ a portabor groups of instruments, to diagnose power qual

periods of time. It should be emphasized that pomonitoring is a highly technical and potentially dskill; even many trained electricians are completewith the details of how power quality measuremecarried out.

Do not attempt to undertake a power quality mexercise without the help of a professional practfield

4 Solving and Mitigating Electrical Power Problems

Some of the elements that might be tracked by a PQsional are:


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RMS (Root - Mean - Square) MeasurementsAverage MeasurementsPeak MeasurementsHarmonic Analysis

Power Line Event Logging

4.2 Improving Site ConditionsConsideration of disturbance sources external to the

should only be considered after the internal electricalment has been thoroughly checked.

4.2.1 Mitigating Effects

Te key elements to mitigate power quality problems

Proper grounding and wiringEffective mitigating equipment (if required)

4.2.2 Mitigating Equipment

A wide variety of products are available that can helpgate power line disturbances. Care should be taken toselect effective mitigating equipment. Improper appli


effective may fail to protect sensitive equipment change has occurred.


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When selecting equipment that has an operationas indicated by an effi ciency rating, provision shofor adequate cooling of the equipment, especiallylocated in a computer room.

4.2.1.1 Dedicated CircuitsA dedicated circuit is a single circuit with one loarelatively inexpensive distribution technique thatload interaction. Te ability of a dedicated circuitquality problems depends on its location, impeda

factors. o achieve the lowest possible impedancethe load of the circuit should be as close as possibbuilding service entrance. However, this could agsituation if transients are a problem, since they comore freely through the system. For improved op

circuit, the neutral and the ground wires should bas the current-carrying conductor.

ips and Cautions

Dedicated circuits will solve local problems only.installed dedicated circuits obviate the need for iing circuits.


tant to note that transient suppressors do not provideregulation or isolation.


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4.2.1.3 Lightning ArrestersTe lightning arrester is designed to remove large oveand associated high energy levels. Tis is accomplishean overvoltage by short-circuiting the line to ground

referred to as a crowbar effect of energy diversion. Ttion of energy to ground will cease when the current zero. Te response time for this technology is relativeTese products are used as primary arresters on mainfeeders.

4.2.1.4 End-User SPDs

Faster-acting SPDs that use Metal Oxide Varistors (Msilicon avalanche diodes (SADs) can be used for lowetransient attenuation. Tey act by clamping line volta

specific value and conducting any excess impulse eneground, regardless of frequency. Te energy shunting of a line clamp is expressed by its joulerating, which determines the amount of energy the dhandle. It is important to realize that these units are o

good as the ground wiring that they are connected totransient energy to ground may result in the mis-opesome devices. In addition, they are quite susceptible td i l hi h l d hi


183V

transient clamped at 18


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0V

183V

170V

183V

Voltage

transient clamped at 183V peak

transient: +400V peak

transient: 250V pea

170V

Figure 25: Eect o Line Clamp on Transient

120 Volt System

0V

183V

Voltage

transient:50V peak

170V


4.2.1.5 Power Line Filters

Filter design is a complex topic and needs to be prop


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76

addressed by a qualified power quality practitioner.Linear Passive Filter

Design and Operation

A linear filter is composed of linear components, suchinductors and capacitors. It passes the basic power fre(60 Hz) and attenuates other frequencies which are iof electrical noise and harmonics.

Some filters are tuned circuits, which means they add

small range of frequencies. Examples of filters that artuned are the simple low pass filter, and the simple hifilter (next page).

Uses

Simple low pass filters attenuate high frequencies, anthe general characteristics most desired in filters for ipower quality and noise attenuation.

Simple high pass filters attenuate low frequencies.

uned shunt filters are not used for general power quapplications.

Special designs are used to attenuate harmonics. A sh


L


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COutput

Produces

Produces

Produces

Produces

OutputC

R

C

C

L

R

Output

CutoFreque

Output

h l d h

Fr

Low Pass Filter Design and Characteristics


Examples of Harmonic Filters

Equipment which is either sensitive to electrical nois


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78

creates it, is often designed with linear filters for protequipment. For instance, all power supplies contain efilters. For harmonics, multi-staged shunt filters are meffective for mitigation of lower order harmonics.

Disadvantages

Common mode noise is not necessarily eliminateuse of linear filters.Low pass series filters are seldom used for harmoation since they must be rated for full line curren

them relatively expensive.Shunt filters applied at individual loads can oftenoverloaded by harmonics produced by nearby loadat other customer sites.

4.2.1.6 Isolation Transformers


Isolation transformers consist of two coils (primary aary) intentionally coupled together, on a magnetic co

Tey have two primary functions:

a) Tey provide isolation between two circuits, by


primary and secondary sides, while increasing thto ground. Isolation transformers have no direct between primary and secondary windings. Tis fe


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p y y g

characteristic of an auto-transformer, and therefotransformer cannot be used as an isolation transf

Unshielded isolation transformers can only attenfrequency common mode noise.

High frequency normal mode noise can be attenspecially designed and shielded isolation transforalthough it is not frequently required (consult wielectrical system expert).

AdvantagesIsolation transformers are used to attenuate cnoise.Tey provide a new neutral to ground referen

Tey can be used to break ground loops. Isolation transformers can reduce higher ordbut will not eliminate harmonic distortion ornotching.Isolation transformers may be combined with

ment such as transient suppressors and circuiform complex circuits known as Power Distr(PDUs).


Te ability of an enhanced isolation transformer tate normal mode noise varies, depending on the l


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4.2.1.7 Line Voltage Regulators


A line voltage regulator is a device that maintains a rconstant voltage output within a specified range, rega

input voltage variations. Some kinds of line voltage recan regulate, but not condition, the power. Tey are frequently used, and include the ferroresonant transfotap switching transformer, the variable ratio transformmagnetically coupled voltage regulator, the induction

and the saturable reactor. Te ferroresonant transformswitcher are discussed in more detail within this secti

Auto-transformers are frequently used in voltage regudevices. If an auto-transformer is used as the variable

element, it develops a variable voltage which is addedincoming AC line voltage. A sample of the input voltrectified, filtered and compared to a DC reference voTe difference is then used to offset the input voltageAuto-transformers are also used in Silicon Controlled

regulators. In this case, the primaryvoltage of the autotransformer is varied by phase con

Uses


Disadvantages

Voltage regulators do not have noise suppress


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ties.Tose with switching power supplies actuallynoise in the input line.

4.2.1.8 Ferroresonant Transformers

In contrast to a typical isolation transformer, the transformer is designed to operate at saturation. Tnant transformer provides the same functions as isolation transformer, but also provides instantanvoltage regulation, as well as ride-through capabi

A ferroresonant transformer has a relatively simpno moving parts; however this mitigation device for older, linear electrical loads. A ferroresonant toften incompatible with modern electronic loadsbe used with caution on high demand loads. Ferrtransformers usually have higheroperating temperatures that can lead to very warmenclosure temperatures. It is therefore recommentransformers be safely guarded from accidental cpersonnel.

4.2.1.9 Tap Switching Transformers


continuously, but in steps. Switching occurs when linpasses through zero, so transients are not created.


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Te tap switcher can react in one or two cycles. Either peak or RMS voltage detectors may be useaps may either be on the primary or secondary s

Uses

Where voltage fluctuation is the primary concern.Disadvantages

Voltage output changes are not continuous. Better vocontinuity is achieved by using more taps.

If auto-transformers are used, no isolation is provided

4.2.1.10 Power Conditioners

Devices marketed as power conditioners are often co

of the above-mentioned mitigation devices. Tey oftetransient voltage surge suppression, noise filters, and transformers or voltage regulators. Careful consideratproduct specifications and the intended use are requirto determine if they will be effective.

4.2.1.11 UPS Systems

UPS means uninterruptible power supply. A UPS s


A UPS does not necessarily provide protection aenergy impulses.


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A properly selected UPS system is the only proda generating unit, that can protect critical loads ainterruptions exceeding 0.5 seconds and which cactive regulated power.

Some inexpensive UPS systems with low power

produce a square wave output, causing some loadmalfunction. Tis characteristic is particularly truUPS systems. Te problem can be avoided byselecting a UPS system with a synthesized sine w

Disagreement often arises as to the preferred typrotary or static. Rotary systems are often criticizeregular maintenance they require, whereas static criticized for the frequency of failed componentspointed out that regular maintenance and parts r

rotary systems helps to prevent componentfailures, whereas static systems can run for a signperiod of time without maintenance before failurminimal downtime. No matter what system is seshould expect that some type of maintenance or

replacement will eventually be required. Multiplecan be used for redundancy in critical applicationarranged in parallel, in which case they normally in isolation so that each UPS supplies a


designed small UPS systems (


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84

mounted in a cabinet, and the whole system can be pcomputer room. Care should be taken to ensure that battery life is available for these systems.

Battery Design and Selection

A battery is an electrochemical device that converts schemical energy into electrical energy.

Recharge time is typically 8-10 times the discharge tiselecting a UPS battery, the cell size, cell life, required

reliability, weight/space and manufacturers warranty considered. It is also important to note that battery dtime as a function of load is not a linear relationship. types of batteries that are used for UPS systems are leand Valve Regulated Lead Acid (VRLA). Carefully c

the minimum amount of battery time that is necessarto reduce capital and maintenance costs in the system

Rotary UPS

A state-of-the-art, on-line rotary UPS is one of the m

effective but more costly types of UPS systems. Althonumber of designs are available, they include motor-gwith battery backups and fly-wheel systems.


nal to the first panelboard where it is connected tbus. Bonding of the conduit, boxes, etc. of the cirplished by ordinary means, i.e., conduit or a sepa


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wire. Te two grounds are connected only at the Many years ago, this arrangement was implemencommon-mode noise problems. Common-modeattenuated at each device in the system and is in

filtered at the input of modern electronic devicesTe IEEE Emerald Book states that:

Tis type of equipment grounding configuratiointended to be used for reducing common-mode on the electronic load equipment circuit as descri

NEC.It has no other purpose and its effects arcontroversial.

Isolated grounding receptacles are no longer recofor installation in any situation. Te effects they a

to solve can be more easily and cheaply mitigatedelectrical system design.

4.2.3 Preventative Measures

4.2.3.1 Distribution System Considerations for

Te quality of the power supplying sensitive loadinfluenced by other loads within a customers faciare heavy loads such as motors or heating venti


108V


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86

600V 208Y/120V

187V

12V dropalong feed

Supply

Transformer

Figure 28: Motor and Sensitive Loads Supplie

rom the Same Feeder

If the feeder has a resistance of 0.075 ohms, during astart the voltage drop along the feeder is:V = IR= 160A x 0.075 = 12V

Voltage at the sensitive loads is 120 -12 =108VVoltage at the motors is 208 - ( 3 x 12) =187V

If the motor is a 10 HP motor, it will draw an inrushthe order of 160 A for a short period of time when

starting.Te impedance of the feeders to the distribution pansupplying the motor and sensitive loads will cause a v


higher than the normal starting current. Tis will84 V feeding the sensitive loads during this time

If h l d d h l d


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If the motor load and the sensitive loads are supseparate feeders then the voltage drop does notfeeder supplying the sensitive loads.

Negligible drop

12V drop

208Y/120V

600V

120V

187V

Figure 29: Motor and Computer Loads Su

rom Separate Feeder

An even better approach is to effectively create a system for the sensitive loads by using a transformto a separate feeder


C

1


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88

208Y/120V600V

187V

Figure 30: Isolation Transormer Added to

Computer Feeder SupplyA transformer establishes a separately derived power Te transformer can be of the step-down type to redusupply voltage to the utilization voltage of the equipman isolation transformer if the supply voltage is alread

appropriate voltage.ypical voltages for computer equipment are 120 voltphase and 120/208 volts three-phase wye. If the sensiloads are susceptible to some form of RFI (radio fre

interference), the transformer may utilize a shield thelectrical and magnetic noise coupling from the prithe secondary of the transformer. Tis shield is conn

T


harmonic). Computers and microprocessor contrment operate at high frequencies (in the 100s of control devices and well into the GHz region for

)


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communications equipment).I equipment transfers data between various piecment at very high frequencies utilizing low signathe past, where these signal levels were referenced

ground system, they were susceptible to electricalinterference. Examples of the types of interfaces tfrom noise coupling problems were the RS-232 ithe Centronics printer interface. Grounded intercstandards like these have been largely superceded

higher speed connections like Ethernet, fibre optWhere older analog communications systems and dstandards are still used, these types of equipment nmeans of grounding for both low and high frequenceffective approach is to eliminate all ground-refere

cation interfaces in a facility with newer, higher spimmune interfaces.

Effects of Frequency on Conductors

Wiring systems used within a building generally

impedance at low frequency, but as the frequencyimpedance increases. Real wiring can be modelwith resistance and inductance and stray capacita


good equipment ground, is a less reliable high frequeground.

I d i f b h i di d id h b d h ld b


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90

In order to satisfy both equipment grounding and siggrounding requirements, a hybrid system should be eTis system is a combination of the parallel path groucombined with a multipoint ground for good high frperformance.

One such method, described in IEEE 1100-1999, TBook, is a signal reference structure.

Typical Conductor

Equivalent

Circuit

Resistanceof Wire Inductanceof Wire

Stray Capacitanceof Wire

Figure 31: Equivalent Circuit o a Wire

Signal Reference Structure

A ground plane is a conducting surface that has low iover a range of frequencies. Te ideal situation wouldll i i i l d d


bonded interconnection of equipment racks and intervals also creates a SRG effect.

Common grounding point at point of

penetration of the electrical conductors


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Computer Roompenetration of the electrical conductorsto computer room.

Equipment bondedto reference grid vshort conductors.

Ground viaElectricalDistributionSystem.

Zero signalreference gridgrounded toelectricalsystem atthe commongrounding

point.

Figure 32: Signal Reerence Structure or

Te grid is grounded to the electrical system groupoint where the supply enters the room. All powis also grounded at this point making the equipm


4.3 Troubleshooting and Predictive Tip

4.3.1 Tips


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Distribution Wiring and Grounding

Check that the electrical contractor is reputable, tices proper grounding and wiring techniques. Tinstallation should be tested with instruments to compliance to Codes and equipment requiremenwiring inspected.Electrically separate highly sensitive loads from oTis may involve using separate buses, or separate

tion transformers. Te Code generally does not alseparate AC services to be used in a facility.Ensure that all equipment is CSA certified for sareasons. Before purchasing mitigating equipmentthat all distribution and grounding problems hav

identified and corrected. Ten identify any problerequire mitigating equipment.Ensure that all components of interconnected Iare bonded to the same grounding system.For the purposes of signal grounding, never assumtwo physically separated points of a ground systemat the same potential. Use isolation techniques ortransmitters for physically separated equipment


When purchasing electrical products, ensure effectively perform the functions that are requminimal degradation of the power system. It

to req est a demonstration of the eq ipment


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to request a demonstration of the equipmentplant, when possible, especially for mitigatingFollowing installation of mitigating equipmethe problem is solved.Always identify any equipment sensitivity reqsuch as sensitivity to voltage fluctuations, in Consider the interaction between mitigating the load. For instance, if the mitigating equiphigh impedance, and the load has high inrush

perhaps, to the starting of large motors), a voresultTe noise suppression capabilities of some prspecified in terms of peak attenuation, whichpropriate for some applications. In addition, i

to know the conditions under which the attenmeasured.Proper installation of electrical equipment is and yet often overlooked. For example, manytransformers and power conditioners are imp

installed due to incorrectly sized primary conbreakers.


Determine the load operating voltage, currenVA from the nameplate rating.Sum all individual VA ratings of the loads. an estimate of the power consumed by the lo


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an estimate of the power consumed by the lois the real power in watts, calculate:Real Power = VA x Power Factor.Many nameplate ratings assume a power facunity. If this is not a good assumption, factorSome units are rated in Primary Power ratinthis is the case then the sum of all secondaryloads will have to be divided by the effi ciencyunit in order to obtain the Primary Power raespecially important to obtain the power reqfor sensitive loads from the manufacturer.

Best Practices

Reduce the number of disturbance sources.

Maintain a malfunction log. Customers should be aware of the level of harmoare producing. If a customer is exceeding the accelimits of the distribution system, they may be reqshut down their facility.

o minimize problems related to voltage sags usevoltage starters on motorsIf i t lli i l ti t f th t


taken to troubleshoot the problem. Te key is a pelimination. Reputable consultants may be contacustomer to assist the process:

Define the type of disturbance frequency1 -


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Define the type of disturbance, frequency 1 -and magnitude of the problem.

Determine which power conductors -- ho2 -ground -- have problems; this is critical, since s

tion techniques only address problems with a stor. For grounding problems, the source of the be fixed; no mitigating equipment will provide

Check wiring for loose connections.3 -

4. Check that proposed solutions actually 4 -follow-up.



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5 WHERE TO GO FOR HELP

Web Resources

5 Where


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Web ResourcesIEEE Standards Information

Home of the IEEE standards; in particular 4(Te Emerald Book, considered the key IEon power quality); 1159; 1250 and 1346.

Copper.org

A site by the Copper Development Organiz

responsible