113055 reliability and power quality brochure

Electric Service:Reliability and Power Qualityat CenterPoint Energy

CenterPointEnergy.com Rev. 12-06

CenterPointEnergy.com 1

Why do we care?At CenterPoint Energy we understand that our customers demandboth reliable and high-quality electric service. Dependableelectricity is essential to the bottom line of industrial andcommercial businesses, as well as a necessity for the productivityand comfort of our residential customers. As a result, CenterPointEnergy strives to make reliable power delivery a top priority.

In this report, we will explain the origin of reliability and powerquality events. In addition, we’ll explain how the electric deliverysystem works, as well as what to expect from your CenterPointEnergy delivery service in terms of reliability and power quality. We will also identify possible solutions that may help relieveundesired events.

Electricity is critical to thelivelihood of almost everyoneand essential for companiesto conduct business as usual.That’s why CenterPoint Energystrives to maintain a safe andreliable electric deliverysystem.


What is going on here?Are you experiencing problems with your appliances or equipment,or have you noticed any of these occurrences?

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• Upon coming home, you see your digital clocks flashing “12:00.”

• The ground-fault circuit-interrupter (GFCI) receptacle in your bathroomkeeps tripping for no apparent reason.

• You have experienced frequent failures of home entertainmentequipment, which you suspect to be caused by “power surges.”

• The incandescent light bulbs in your home seem to requirereplacement more often than what you consider normal.

• Every time your air conditioner turns on, the lights flicker.

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• The chillers at your facility frequently trip off-line.

• The Variable Frequency Drives (VFD) in your facility trip off-line at thesame time every day.

• The motors in your plant trip off-line when there is a “power blip.”

• The Uninterruptible Power Supply (UPS) for your computer hasfrequently been beeping and switching to battery.

• What you consider to be excessively frequent power interruptions areimpairing production.

If so, then you’re not alone. Many of the more than two million customersthat receive electric delivery service from CenterPoint Energy have similarconcerns. Why is this? Well, events like these are possibly the result ofeither reliability or power quality related issues. These occurrences maybe caused by conditions originating from the utility system, from withinyour home or facility, or even from the affected equipment itself.

In order to determine the most appropriate solutions to your reliability andpower quality problems, it is best to first understand how electrical poweris delivered from the utility system to your appliances or equipment.

What is a PowerSurge?The term “power surge” hasno official definition and, assuch, is not recommendedterminology. What manycustomers refer to as “powersurges” are in fact eithermomentary interruptions,voltage sags or voltagetransients. IEEE Standard1100 (Emerald Book) containsthe technical definitions ofpower quality terms and is anexcellent source ofinformation on power quality.


How does CenterPoint Energydeliver electricity?The electricity delivered to your home or business is typicallygenerated in large centralized power plants as illustrated in thefigure below. Power then travels over long distances via highvoltage transmission lines, which are interconnected in a grid ornetwork configuration. From the transmission system, powertravels to distribution substations. From these substations,distribution lines, operating at lower voltage levels, disperse thepower throughout cities and neighborhoods. For safety reasons,each distribution line is protected by a circuit breaker in thesubstation.

What is reliability andpower qualityexactly?• Reliability refers to the

continuity of electricdelivery as described by thenumber and duration ofpower outages.

• Power Quality describesthe characteristics ofpower fluctuations, such asmomentary interruptions,voltage sags or swells,flickering lights, transients,harmonic distortion andelectrical noise.

TransmissionLines

Step-UpTransformer Power Plant

PowerTransformer

CircuitBreaker

ServiceTransformer

DistributionLines

ServiceTranformer

CustomerSubstation

Fig. 1


CenterPoint Energy maintainsmore than 3,600 miles oftransmission lines and 28,600miles of distribution lines.With the advent of electricityderegulation in Texas in 2002,wholesale electric powercompanies and retail electricproviders are allowed todeliver electricity overCenterPoint Energy’s powerlines. (12-31-05 data)

CenterPoint Energy deliverselectricity to more than twomillion customers in a 5,000-square-mile area includingHouston, the nation’s fourthlargest city.

The power then travels from the distribution line through a servicetransformer located in close proximity to your home or business.Electricity enters the facility either through overhead orunderground service entrance conductors (wires) which connectto the meter. CenterPoint Energy reads this meter on a monthlybasis and reports the information gathered to your retail energyprovider (i.e. Reliant Energy, TXU, etc.) Typically, ownership andresponsibility of the service entrance conductors are transferredfrom CenterPoint Energy to the customer near the meter. Thelocation where this transfer of ownership takes place is referred toas the point of service.

From the meter, or point of service, power flows along conductorsto the main panel which contains the main breaker. The mainbreaker’s duty is to provide protection for the entire facility. Inhomes, the main panel may also contain additional circuitbreakers which provide protection for each individual branchcircuit. These branch circuits deliver power for lights, appliancesand electric outlets within the residence.

In industrial or commercial facilities (see fig. 2 on page 5), themain panel may also be the point of origin for circuits providingheating, ventilation, and air conditioning, as well as lighting.Furthermore, the main panel may supply feeder circuits for subpanels and dry-type transformers. The dry-type transformers stepthe voltage down to lower levels for branch circuits, which supplyconvenience receptacles throughout the facility.


The following figure helps illustrate the paths traveled within acommercial facility.

In figures 1 and 2, you can see the long and complex pathelectricity takes from the centralized generating plant all the wayto an appliance, piece of equipment or receptacle. Unfortunately,due to the length of this path, numerous opportunities exist forevents to happen, which can interrupt the flow of power or degradeits quality as it travels to a particular destination.

Main Panel(480/277 V)

ServiceTransformer

Meter

LightingFixtures(277 V)

Branch Circuits(120 V)

Receptacles (120 V)

Sub Panel(208/120 V)

Dry-TypeTransformer

(08/120 V)

ChillerCompressor

(480 V)

Fig. 2

What are SensitiveLoads?In general, modern equipmentand appliances haveincorporated electronics andmicroprocessors, whichimprove performancecapability but are also moresensitive to common powerquality and reliabilityproblems. Examples ofsensitive loads include:

• Digital Computers

• Variable Frequency MotorDrives

• Programmable LogicControllers

• Computer NumericalControl (CNC) Equipment

• Automated Systems andProcesses

• Consumer Electronics

• Digital Clocks


Before examining reliabilityand power quality in detail,we should discussCenterPoint Energy’sresponsibility for electricservice delivery. As aninvestor owned utility,CenterPoint Energy isregulated by the Public UtilityCommission of Texas (PUCT).In an effort to ensure qualityelectric service at anaffordable rate, the PUCTrequires CenterPoint Energyto adhere to its Tariff forRetail Delivery Service aswell as Chapter 25 of theSubstantive Rules.

What is CenterPoint Energy’sresponsibility regardingreliability and power quality?In terms of reliability and power quality, two sections in Chapter5 of the PUCT-approved CenterPoint Energy Tariff are especiallyimportant:

• Section 5.2.1 (Liability Between Company and RetailCustomers) states CenterPoint Energy will make reasonableprovisions to supply steady and continuous delivery service,but does not guarantee against fluctuations or interruptions.

• Section 5.5.3 (Equipment Sensitive to Voltage andWaveforms) states customers with equipment that may beadversely impacted by voltage fluctuations are responsiblefor installing the necessary protective equipment to limit theaffect of those events.

Section 5.2.1 requires CenterPoint Energy to make reasonableefforts to provide reliable service, while Section 5.5.3 states it isthe customer’s responsibility to install protective equipment forsensitive loads. In addition to the Tariff, the PUCT has two specificSubstantive Rules addressing reliability and power quality:

• Substantive Rule 25.51 (Power Quality) covers such issuesas voltage and frequency variations, harmonics, powerquality monitoring and voltage surveys. This rule requiresCenterPoint Energy to provide steady-state supply voltage incompliance with the American National Standards Institute(ANSI) Standard C84.1.

• Substantive Rule 25.52 (Reliability and Continuity ofService) is similar to Section 5.2.1 of the PUCT-approvedCenterPoint Energy Tariff. It states CenterPoint Energy willmake reasonable efforts to maintain electric delivery service.In the event of an interruption, CenterPoint Energy shallreestablish service as quickly as possible.


The Tap WaterAnalogyThe electricity supplied alongpower lines is much like thewater coming out of yourfaucet. It is perfectly safe fornormal use; however, it doescontain minor impurities.Should you desire entirelypure water, then filtering outthese impurities is left up toyou. Electricity works in thesame manner. Even thoughCenterPoint Energy isdedicated to providingreliable and high qualityelectric service, it is notpossible to provide a perfectpower supply that is steadyand continuous withoutoccasional interruptions orfluctuations. Items to obtain“pure” electricity will bediscussed later.

What should I expect? Most power outages and disturbances can be attributed to factorsbeyond the control of a utility. CenterPoint Energy’s system isexposed to environmental influences and normal operationalconditions, which can create both power quality and reliabilitydisturbances. Common sources of disturbances include thefollowing and are illustrated in the figure below:

1. Lightning 6. Trees and Vegetation

2. Insulator Flashovers 7. Strong Winds

3. Dig-ins on Underground Lines 8. Vandalism

4. Automobile Collisions 9. Equipment Failures

5. Birds and Other Wildlife 10. Switching and Maintenance

TransmissionLines

Power Plant

CircuitBreaker

DistributionLines

House

Substation

Business

1

2 3

4

78

9

9

910

10

6

5

Fig. 3


Reliability IndexesThe most widely usedreliability indexes are SAIFI,CAIDI and SAIDI.

• SAIFI stands for SystemAverage InterruptionFrequency Index and isdefined to be the averagenumber of outages for thesystem over a specifiedtime period.

• CAIDI stands for CustomerAverage InterruptionDuration Index and isdefined to be the averageduration of a single outageevent.

• SAIDI stands for the SystemAverage InterruptionDuration Index and isdefined to be the averageoutage duration for thesystem over a specifiedtime period.

Also, the indexes aremathematically related asfollows:

SAIDI = (SAIFI) x (CAIDI)

Average Reliability CenterPoint Energy maintains statistics of outage frequencies anddurations for each distribution circuit and for the electric systemas a whole. While there is some variation from year to year, theaverage figures that customers may experience are as follows:

Duration of Sustained Outages = 3 hours per year

Number of Sustained Outages = 2 per year

Average Power Quality As for power quality events, CenterPoint Energy also maintainsstatistics of momentary outage frequencies for each distributioncircuit and for the system as a whole. While there is some variationfrom year to year, the average figure that customers mayexperience is as follows:

Number of Momentary Outages = 10 per year

Besides momentary outages, instantaneous voltage sags are themost common type of utility-related power quality event thatadversely affects our customers. While CenterPoint Energy doesnot keep statistics on voltage sags, it did participate in a nationalpower quality survey that accurately reflects what typicalcustomers can experience:

Number of Sags Below 90% of Nominal Voltage = 70 per year

Of these 70 sags, 23 will dip below 70% of nominal voltage, which isgenerally considered the threshold for causing motors and othersensitive equipment to drop off-line.


CenterPoint Energy’s Tariff forRetail Delivery Service stateswhile reasonable provisionsare made to delivercontinuous and steadyservice, there is no guaranteeagainst interruptions orfluctuations. In fact, BulkPower not only containsreliability-related eventssuch as sustained outages ofservice but also containscommonly occurring powerquality events such as flicker,momentary interruptions,voltage sags, swells,transients, harmonic distortionand electrical noise.

Bulk Power vs. Premium PowerBulk power is a term used to describe the electricity delivered bythe utility system in a well-established manner allowing forsatisfactory performance of conventional lighting and motor loads.Utility systems providing bulk power are designed to minimizecosts while maintaining reasonable levels of reliability. As a result,bulk power is often referred to as “utility-grade” power and isdescribed in the tap water analogy on page 7. Bulk power alsorefers to the power supplied inside customer-owned facilities,which contains internally created power quality disturbances andproblems. In fact, studies done by the Electric Power ResearchInstitute (EPRI) indicate that four out of five power qualityproblems are due to faulty wiring and grounding inside customer-owned facilities.

In contrast, premium power is used to describe the electricitydelivered to sensitive electronic loads requiring higher reliabilityand power quality than conventional loads. Premium power can becustomized to match the operating requirements of the equipmentin question and is commonly referred to as “computer-grade”power. Ideally, premium power will consist of continuous,regulated voltage free from disturbances.

In general, CenterPoint Energy cannot provide premium power. Inorder to obtain this level of service, customers must enhance orupgrade their existing electrical facilities by installing powerconditioners and applying other power quality solutionsspecifically selected to meet their requirements.

CenterPoint Energy’s Tariff states it is the customer’sresponsibility to install the necessary protective equipment tolimit the adverse effects to equipment from voltage fluctuations,waveform distortion and single-phasing events. The concepts ofbulk power and premium power help provide an explanation of theresponsibilities and obligations for both the utility and itscustomers.


Most power quality problemsare due to a lack of compati-bility between customer-owned equipment and thepower supply. This includesnot only outages andfluctuations emanating fromthe utility system but alsopower quality disturbancesand problems created insidecustomer-owned electricalfacilities. Therefore, bothCenterPoint Energy and itscustomers have a critical roleto play in resolving powerquality problems.

As a consumer of electricity,what are you responsible for?As noted before, customer-owned electrical facilities can be thesource of a significant percentage of power quality problems. Inaccordance with the CenterPoint Energy Tariff, customers havethe responsibility to install necessary protective equipment tolimit the adverse affect of power quality problems. In fact, existingcodes and standards provide a wealth of information on how toimprove the performance of customer-owned electrical facilities. Ifa customer desires “pure” power, or a higher quality of service thanCenterPoint Energy is able to supply, it is his/her responsibility tosupply that level of service.

Items to improve or betterendure your current situationProtective equipment able to enhance electric service is readilyavailable in the power quality market place. Examples of thesedevices and methods are as follows:

• Transient Voltage Surge Suppressor (TVSS)

• Constant Voltage (Ferroresonant) Transformer

• Magnetic Synthesizer

• Dip Proofing Inverter

• Lightning Protection System

• Dynamic Sag Corrector

• Static VAR Compensator

• High Speed Transfer Switch

• Battery UPS

• Rotary UPS

• Proper Maintenance of Electrical Facilities

• Dedicated Branch Circuit


Who can help?CenterPoint Energy strongly recommends that the services of aprofessional engineer or qualified power quality consultant beutilized to evaluate various solution options based upon safety,performance and economic pay-back criteria.

An excellent source of information to improve the power quality ofcustomer-owned facilities is the set of standards created by theInstitute of Electrical and Electronics Engineers (IEEE). The IEEEis a nonprofit technical professional organization with over 360,000members that creates consensus standards for industrial andcommercial power systems. Among the various IEEE publications,which may help improve power quality-related issues are:

• Standard 1100 (Emerald Book) – IEEE Recommended Practice forPowering and Grounding Electronic Equipment

• Standard 446 (Orange Book) – IEEE Recommended Practice forEmergency and Standby Power Systems for Industrial and CommercialApplications

• Standard 493 (Gold Book) – IEEE Recommended Practice for theDesign of Reliable Industrial and Commercial Power Systems

• Standard 519 – IEEE Recommended Practices and Requirements forHarmonic Control in Electrical Power Systems

According to EPRI, poorpower quality and reliabilityare estimated to be costingthe United States economy$56 billion per year. Inresponse, the power qualityequipment and servicesmarket offers a myriad ofsolutions. However, it isimperative that the powerquality problem be clearlydefined in order to make thebest decision whenevaluating the possiblesolution options. The servicesof a professional engineer orqualified consultant canprovide the knowledge andexperience necessary toinsure success.


CenterPoint Energy’scommitment to improvingreliability and power qualityReliable electricity is critical to the daily life of almost everyone.From the lights in their homes to the computers at their offices orthe large equipment within their plants, a safe and reliable supplyof power is essential. The New York blackout in August, 2003,reminded everyone how crucial it is for utility companies tocontinually strive to maintain a reliable system. Many factors play arole in maintaining the safe and reliable operation of the electrictransmission and distribution network.

CenterPoint Energy prides itself with traditions of quality andcommitment – traditions we have developed during more than 130years of energy delivery service. In addition to honoring thesetraditions, we are excited about establishing new traditions ofservice and operational excellence by providing our customers withelectric delivery service that is characterized by both highreliability and power quality. Therefore, CenterPoint Energyemployees are always there to maintain the reliability and powerquality of the electrical delivery system as well as quickly restorepower after outages.

Furthermore, CenterPoint Energy hopes to help customersunderstand their retail electrical service. Should you desire to discussreliability and power quality in greater detail than what is covered inthis brochure, please ccoonnttaacctt ccuussttoommeerr sseerrvviiccee aatt 771133--220077--22222222 foranswers on the spot.

CenterPoint Energy. Always There.

113055 reliability and power quality brochure

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