Troubleshoot PQ

8/2/2019 Troubleshoot PQ

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Consumer Power Quality Problems:Troubleshooting by Telephone

Reprint of handbook edited and published by NRECA, 1999Text by Franois D. Martzloff, National Institute of Standards and Technology

Graphics by Susan Spangler

SignificancePart 6: Tutorials, textbooks and reviews

This is a handbook developed for use by NRECA service representatives when dealing with

customers making complaints over the telephone about power quality of their service, with a set of

questions work sheets that could help diagnose the problem without requiring distant travel by

service technicians, or to get them better prepared to do so.

The National Rural Electric Cooperative Association (NRECA) is the national service organization

of more than 900 rural electric systems. These cooperatively owned utilities own and operate

about 44% of the miles of distribution lines in the nation to provide power to less than 10% of the

consumers. NREC A is the national service nation's people, primarily in the sparsely populated,

rural areas of 46 states. NREC A was founded in 1942 to unite rural electric systems in a way that

would permit them to develop the services and support needed to properly serve rural America.

NRECA is on of the largest, rural-oriented cooperative organizations in the United States.


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Prepared byNation al Rural Electr ic

Cooperat ive Assoc iat ionCoopera t ive Research Ne tw ork

4301 Wi lson BoulevardAr l ington, V i rg in ia 2220 3-1 8 60

a n dF r a n ~ o i s . Mar tz l o f f

Nat ion al Ins t i tu te o f Standards andTechnology

10 0 Bureau Dr iveGai thersburg, Mary land 20899

C&N@C O O P E R A T I V E R E S E A R C H N E T W O R K


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The National rural Electric Cooperative Association (NRECA) is the national service organization of more than 900 rural electricsystems. These cooperatively owned utilities own and operate about 44% of the miles of distribution lines in the nation to pro-vide power to less than 10% of the nation's people, primarily in the sparsely populated, rural areas of 46 states.

NRECA was founded in 1942 to unite rural electric systems in a way that would permit them to develop the servlces andsupport needed to properly serve rural America. NRECA is on of the largest, rural-oriented cooperative organizations in theUnited States.

The Cooperative Research Network, a service of NRECA that was used to support this project, was created to conduct studiesand carry out research of special interest to rural electric systems and thelr consumers.


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Contents - v

Section 1

Section 2

Disturbances and RemediesIntroductionThe Nature of DisturbancesToo Much VoltageNo t Enough VoltageOther Power-Line DisturbancesSystem Interactions

Questions t o AskCustomer-Owned OffendersHow to Use the WorksheetsIdentifying Residential and Commercial Appliance CategoriesWorksheet EDE: Electronic, dual, externalWorksheet EDI: Electronic, dual , internalWorksheet ES: Electronic, simpleWorksheet HE: Heat, elec tron~cWorksheet HM : Heat, mechanicalWorksheet ME: Motor, electronicWorksheet MM: Motor, mechanicalWorksheet PLC: Power line conditioning


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v i - I l l u s t r a t i ons

I L L U S T R A T I O N SFIGURE PAGE

1.1 Sine wave of an AC voltage supply. 2

1.2 A surge induced by lightning on an AC voltage. 3

1.3. Typical voltage on a distribution bus during capacitor bank energizing. 4

1.4: Example of a customer's bus voltage during utility capacitor switching. 5

1.5 A lamp and a rabbit-ear TV are examples of single-port appliances. 6A computer with a telephone modem connection is an exampleof a two-port appliance. An ordinary house offers many examplesof both single-port and multiple-port appliances.

1.6 A typical WSS with power and telephone protection. 7

1.7 A meter-base arrester installed by the utility. 71. 8 Relative energy deposited in the suppressor by a typical high-energy 9

surge for various combinations of 250-volt (H), 150-volt (M), and130-volt (L) ratings, as a function of separation distance.

Division of surge current in a cascade of two 150-volt devices: I,is the current in a 40-rnm-diameter arrester and I, is the current ina 20-mm-diameter suppressor, with 10-meter separation for thesame 3000-ampere surge as in Figure 1.8.

1.10 A voltage swell lasting eight cycles. 10

1.11 Unequal line voltages caused by an open neutral. 11

1.12 A very brief outage (top) and a very long outage (bottom). 13

1.13 A sag lasting 10 cycles with the line voltage reduced to 55% of normal. 13

1.14 The original CBEMA curve (top) and the updated ITIC curve (bottom). 15

1-15 Noise superimposed on an AC voltage. 16


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I l l u s t r a t i o n s - v i i

FIGURE PAGE- - -- . -.1.16 An AC voltage distorted by harmonics. 16

1.17 Commutation no tches o n an AC voltage. 17

Power and telephone services enter the house at opposite ends.A personal computer is connected across the two systems.Voltage and current recorded with telephone and power services 19entering at opposite ends of the house.

1.20 Mitigation obtained by inserting a surge reference equalizer inboth the power line a nd the telephone line.

1.21 Shifting reference potential can be remedied by inserting a surge 21reference equalizer on the communications and po wer lines (here,the appliance is a TV and the communications line 1s a TV cable,but a PC with a telephone modem connection presents the sameproblem). In the ideal situation, the commun~cations nd power linesenter the house on the same side, and the SRE is most effective.


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v i i i - T a b l e s

TABLE PAGE

2.1 Home-Based Disturbances, Causes, and Remedies 23-2 . 2 Categories of Equipment Victims 25


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F o r w a r d - x

F O R E W O R DCustomer service representatives have a toughtask when they have to respond to calls fromconsumers who are having problems with anappliance. "My television won't work. What'swrong?" "My computer lost its memory. Whatdid the co-op do to cause this?" Complaints maybe couched in vague terms, and the caller maytend to blame the electric cooperative.

This manual was commissioned by theCooperative Research Network to address thesekinds of complaints. Written with the help ofan expert in household and small-business elec-tricity problems, it provides a series of work-sheets that guide representatives through aquestion-and-answer session with a caller, lead-ing the caller from the general to the specificwith the goal of finding the exact source of theproblem (which often is not attributable to thecooperative).

Senrice representatives can use the work-sheets in conjunction with the manual's simpleexplanations of the nature of disturbances andhow to prevent or cure their effects to diagnosespecific problems. On the basis of the diagnosis,the representative can tell the consumer what todo or can call in the cooperative's repair serviceto handle the problem. If the cause of a particu-lar problem proves elusive, the representativecan refer ir to a specialist.

The manual should help representatives workmore effectively and efficiently. It should helpcooperatives avoid unnecessary service calls. Andit should help consumers get quick solutions totheir problems, whether utility-related or not.

Martin E. Gordon, PE .Senior Program ManagerCooperative Research ivetwork


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E x e c u t i v e Su r n r n a r v - x i

E X E C U T I V E S U M M A R YWhen an electricity consllmer has a problemwith an appliance-a light bulb that flickers, atelevision that "burns out," a motor that over-heats, for example-a natural tendency is tocomplain to the electric utility. In actuality.many such problems are not the fault of theelectric utility, and indeed may be beyond thecontrol of the electric utility.

How does an electric cooperative, with limit-ed customer-service resources, handle suchcomplaints? How can it efficiently separate prob-lems that it can fix from [hose that are beyondits control, and perhaps recommend cures orpreventive measures to consumers for the latterproblems? This manual suggests a way: It pro-vides worksheets for customer service represen-tatives to guide them through a dialogue with acustomer calling for help. By following the guid-ance, a representative can ask the right ques-tions, get at the root of a problem, and thendecide on an appropriate action: send a repaircrew, tell the customer how to fix the problem,or, for a problem that resists immediate solution,call in an expert in the field.

The manual is organized in two parts:Part1 eviews the nature of disturbancesthat can occur in the power supply to cus-tomers--disturbances such as voltage surges,lightning strokes, voltage swells, outages,brownouts, voltage sags, noise, harmonics,unbalanced phases, and interaction betweenthe power system and a telephone or cableTV system. A customer service representativecan learn in this part how the disturbancesoriginate, how they affect electrical equip-ment, and what can be done about them.Part 2 helps the customer service representa-tive troubleshoot over the telephone. It

contains worksheets, eight in all, covering themajor categories of equipment-heaters,motors, and electronics of various types. Eachworksheet is a blueprint for a question-and-answer session with a customer, designedto arrive at the cause of the customer's prob-lem and a possible cure. By applying the sim-ple theory in Part 1 and following the step-by-step instructions, the representative shouldbe able to diagnose many problems anddecide whether intervention by the coopera-tive is warranted.The manual stresses a crucial fact: that prob-

lems with equipment connected to both an elec-tric power system and a communication sys-tem-televisions with cable connections or per-sonal computers with modem hookups, forexample-can be caused by ezther system. Suchproblems are compounded when the two ser-vices enter at opposite ends of the building;physical separation of the entry point magnifiesthe disturbances. Such disturbances shouldnever be blindly attributed to "power linesurges"; often the communication link can be atfault, especially when it is improperly installed,as sometimes happens with cable connections.

Scattered throughout Part 1 are short case his-tories drawn from ordinary experiences-achandelier that inexplicably flickers, motor con-trollers that shut down when the electric utilityadjusts its power factor. With such experiencesand simple electrical theory as background, cus-tomer service representatives should be able toanalyze many of the problems posed by distur-bances and find a solution for the consumer, orknow when to call in expert help.


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D i s t u r b a n c e s a n d R e r n e d ~ e s 1

Disturbances and Remedies

In Thls Section:Introduction; the nature of disturbances; too much voltage; not enough voltage;other power-line disturbances; system interactions

lnlroductlon Many people believe that upsets or damage toelectrical equipment can be blamed on distur-bances caused by the power distribution systemor by lightning. However, such a belief is anincorrect generalization; many times the problemis in the equipment itself, not the power system.This manual can help cooperatives' customerservice representatives distinguish betweenequipment-related and system-related problems,and either suggest a solution the customer oralert the dispatcher that the cooperative's assis-tance is needed. The manual presents in simpleterms the principles underlying unwanted upsetsand damage and offers remedies for them.

This first part of the manual gives anoverview of the disturbances that can occur inthe power supply to the customer. It brieflydescribes the origins of the disturbances andexplains which disturbances are avoidable,which are unavoidable, wh ch are predictable,and which are entirely random occurrences. Thefirst part is organized in four sections. The firsttwo are concerned with the most frequent butbrief disturbances-too much or not enoughvoltage (energy). The third section addressesless frequent disturbances that are almost per-manent, such as noise, harmonics, notches, andvoltage unbalance. The fourth and last section

describes the possible interaction between thepower system and a communications system,which is believed to be the cause of many Fail-ures that are often misinterpreted as caused by a"power line surge."The second part of the manual is formatted asa collection of worksheets that suggest interac-tions between the customer service representa-tive and the customer reporting a problem.

An important fact is that upset or damage toequipment that involves a communications sys-tem can also be caused by disturbances on thecommunications system and should not blindlybe attributed to "power line surges." Ways toprevent this kind of upset or damage do exist,but some are beyond the control of the cus-tomer and the distributing utility. It is a matter ofrecognizing the situation and selecting a techni-cally correct and cost-effective remedy. Theremay be cases where the risk or consequences ofsuch damage or upset might be low, comparedto the cost of prevention. Therefore, the choiceof protecting or not protecting should be madethoughthlly, not left to neglect or ignorance.Armed with thls knowledge, customer servicerepresentatives as well as customers will be .guided toward a satisfactory resolution.


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2 - S e c t ~ o n n e

The Nature of Electric power is delivered to custonlers in theform of an alternating-current (AC) voltage thatthe utility strives to keep as constant as possible(Figure 1.1).However, disturbances can and willoccur in this voltage, in the form of either toomuch or not enough. In turn, the energy con-sumed by the load-what the utility sells-isrelated to the voltage at which it is delivered.The AC voltage follows a sinusoidal pattern,with a complete cycle occurring 60 times per

second-engineers call that a 60-hertz (Hz) ACvoltage. This smooth waveform can be distortedunder steady-state conditions, or have a tran-slent overvoltage or undervoltage.

Some disturbances are brief-from millionthsof a second (microseconds) to thousandths of asecond (milliseconds). Other disturbances canbe long, lasting from seconds to hours in theworst cases of service interruption.

FIGURE 1.1: Sine wave of an AC voltage supply.

Too Much Too much voltage can be the result of a normalVoltage or abnormal utility operation, or the effect of anexternal influence. Under normal operating con-ditions, the steady-state voltage is controlled bythe utility withm a narrow band. Deviations fromthis band are rare, and the utility can readilycorrect them, if informed of their occurrence, byacting on voltage regulators and tap changers.

On the other hand, there are momentary(transient) disturbances that occur under thetypical operating conditions of a power system.There are two types of transient excessive volt-age that can occur under normal circumstances,although by themselves they would be describedas "abnormal":

1. A surge is an overvoltage that can reachthousands of volts, lasting less than onecycle of the power frequency, that is, lessthan 16milliseconds.

2. A swell is longer, up to a few seconds, butdoes not exceed about twice the normalline voltage.

A third type of excessive voltage, a temporaryoven/oltage, is not a part of normal operation,but is associated with a fault in the power sys-tem. Temporary overvoltages can last a muchlonger time, and generally do not disappearuntil the fault is cleared.SURGESTypes and Origins o f SurgesSurges have been blamed as the cause of equip-ment upsets or damage under many names:power surges, spikes, glitches, impulses, and soforth. In this report, the term surge is used, withthe understanding that it means events lastingless than one cycle of the power frequency.

The two major causes of surges areLightninean obvious and well recognizedevent (Figure 1.2)Load sw it ch in ea type of event that includesmajor power system operations as well assimple and seemingly benign switching bythe customer


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D i s t u r b a n c e s and R e m e d i e s - 3

Next to outages, surges are thetype of disturbance most fre-quently perceived by customersas the source of [heir problems,and therefore merit a detailedexamination.Lightning Surges. There are fourtypes of lightning surges,described here in order of severi-FIGURE 1.2: A surge induced by ty. The first, rare but traumatic, islightning on an AC voltage. a direct lightning stroke to thebuilding. Unless special protec-tion systems have been provided

(lightning rods in plain language, air term~nalsnprotection jargon) with proper down-conductorsand grounding, damage to the structure andequipment can be substantial. Of course, suchan event cannot be blamed on the utility. Fewresidential customers go to the expense ofinstalling a lightning protection system. Instead,they make an intuitive risk analysis:A typicallightning protection system can cost thousandsof dollars, while the probability of a directstroke (outside of known areas of high lightningactivity) is about once every 200 years for adetached home.

The second type of lightning surge occurswhen a nearby stroke, and the resulting flow ofcurrent in the earth, elevates the potential of theground references of the building, including thepower system neutral that is bonded to groundat the service entrance. This situation is calledground potential rise. Meanwhile, the powersupply phase conductors, which are referred toground through the secondary winding of thedistant distribution transformer (whose neutral isgrounded there) remain essentially at theground potential of that distant transformer. Alarge difference of potential can then occurbetween the neutral and the phase conductorsat the service entrance of the building. That dif-ference of potential appears to be a surge deliv-ered by the utility connection, but has nothingto d o with the utility operations.

The third type of lightning surge is producedby the radiationof electromagnetic fields asso-ciated with a lightning strike at some distancefrom the building. Such a surge involves low

energy but can still produce upsets and evendamage in sensitive electronic circuits. Theseverity of these surges depends mostly on dis-tance. Nearby strikes are rare but may havesevere effects, distant strikes are more frequent(increasing with the area of collection, that is,with the square of the distance) but less severe.Again, these surges cannot be blamed on theutility, but some customers might believe thatthey came from the utility connection andattempt to place the responsibility on the utility.

The fourth and last type of lightning surge isone that actually arrives on the service drop ofthe utility, as a result of a direct stroke to someelement of the distribution system. A surgeinduced in the utility distribution circuits by anearby stroke, just like the third type discussedabove, can also appear at the service entrance. Incontrast to the first three types, this fourth type istruly an excessive voltage delivered by the utilityto customers. However, the general practiceamong utilities is to provide surge arresters ontheir systems, so that the residual surge that canappear at a customer's service entrance is some-what limited. The rare exception would be adirect stroke to the pole or service drop, wherethe utility surge arrester would not intervenebefore a surge heads for the service entrance.Switching Surges. There are two types ofswitching surges:

Those that result from normal switching of aload on or off by a customer or the utilityThose that are incidental to an intended oper-ation aimed at clearing a fault-a short circuitor severe overload.

Switching Surgesfrom Normal Operations.The first type of switching surge ("normal"surge) occurs whenever a load-any type ofload-is being switched, either within the distrib-ution system or w i t h the customer's installation.Therefore, these can occur quite frequently. ,Those associated with the switching of a localload, especially if it is an inductive load such asa motor, are generally short (a few microsec-onds) and do not involve a large amount ofenergy. However, there is another source of


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4 - S e c t i o n O n e

potentially large switching surges when capaci-tor banks are switched for power-factor correc-tion. These can occur at random if the power-factor correction bank is controlled by theinstantaneous state of the system, or they canoccur at fiied times in the day if the capacitor

Capacitor Switching SurgesCapacitor banks have long been accepted as anecessary part of efficient electric power sys-tens . Switching capacitor banks on and off isgenerally considered a no rm 1 operation for 3utility system, and the transients associatedwith switching are generally not a problem forutility equipment. The low-frequency transients,however! can be magnified in a customer'sfacility (if the customer has !ow-voltagepower-factor correction capacitors) or result inthe nuisance tripping of power-electronicdevices such as adjustable-speed drives.Actually. capacitor energizing is just one of themany switching events that can cause transientson a utility system, but? because of their regu-larity and impact on power system equipment.they quite oFten receive special attention.

There are a number of transient-related con-cerns that are genemlly evaluated when distri-bution shunt capacitor banksare applied to a power system.However, these considerationsare related to the system designrather than its operation, andthe customer has no controlover them. Remedies will essen-tially be to learn how to livewith these unavoidable tran-sients. When they originate fromthe switching of a large capaci-tor bank, it is unrealistic toexpect that the typical surgesuppressor has the energy-han-ding capability to absorb them.CharacteristicsofEnergizingan IsolatedCapacitorBank.Energizing a capacitor bankresults in an inunediate drop insystem voltage toward zero.

bank is switched on and off by a timer.Capacitor switching surges from the utility havebeen found troublesome in installations wherethe customer also has some power-factor correc-tion capacitors: Magnification of the surges canoccur. (See box, "Capacitor Switching Surges.")

followed by an oscillating transient voltagesuperimposed on the fundamental power fre-quency waveform. The peak voltage magnitudedepends on the instantaneous system voltageat the instant of energization, and can rise to 2times the normal system voltage under worst-case conditions.

Ordinarily, though, other components of thesystem help to keep the voltage rise to 1.2 to1.8 imes the normal value, and the transientoscillates at frequencies from 300 to 1,000,000Hz. igure 1.3 shows an example. recorded inthe field, of a transient created by energizing acapacitor bank.

Tsdnsient overvoItages caused by capacitorswitching are generally not a problem for utili-ties because their peak magnitudes are usuallyjust below the level at which surge protectivedevices (SPDs) begin to operate. However,these transients will often be coupled through

-1 .5 ' I I I I I I0 10 20 30 40 50 60 70Time (milliseconds) -RE 1.3: ~ y p i c x o l t a g e n a distribution bus duringcapacitor bank energizing.


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D i s t u r b a n c e s a n d R e m e d i e s - 5

step-don-n tr.insfonners to c u , ~ x n e roails The 5ize o f the utilit! 's 5n-itched capacitor(Figuse I.+). \vhere they can ~1ifec.t oner- Ixunk is more thnn 10 times larger than t l ~ equality-sensitive custonler ecluipment. i~rch c~~strxncr'sustomer haik.:IS cumputers. The frequrnc! of the energizing oscillation

If the customer uses c:ipacitors for the cor- is close to the resonant freq~~enc!- f therection of pon-er factor nn lhe lov-voltage circuit fol-medhk- the step-clorvn trans-side, higher transient or-ervoltages can rise former and the customer's porver-hctore\ en higher. This effect-"\ oltagr inagnifica- correction capacitor Ixlnk.tion"+xcurs when a tmnsient oscillation. ini- The customer's load has relatively littletiated by the energization of a urilih cqxacitor resistance (this is t).pical of industrial p1:ltvsbank, excites a resonmt circuit in the l o w %-heremotors represent the major part ofvoltage system (the circuit is a combination of the load).the inductance of the ste p-d onn transformerand the capacitance of the customer's power- Orclinarily. these transient switching or-en.olt-factor correction bnnk). The result is a higher ages might simply clamage lo w- en er n surge-oven-oltage at the lon-er voltage bus. The protective devices or cause a nuisance trip ofworst ~nagnification ccurs wl ~e nhe follon-ing power-electronic equipment. Nevertheless.conditions exist: mcidents have been repor ted of complete

failure of end-user equipment.I

I5 10 15 20 25 30 35 40 45 50

Time (milliseconds)FIGURE 1.4: Example of a customer's bus voltage during utility capacitor switching.

Switching Surgesfrom Fault-Clearing. The sec- voltage, and their duration ranges from hun-ond type of switching surge, far less frequent, dreds of microseconds to a few milliseconds.occurs when a system fault is cleared, either bythe opening of a circuit breaker or the operation Effect of Surges on Equipmentof a fuse. The latter can generate high surges if UpsetversusDamage. Surges impinging onthe fuse is located at the end of a long cable, in equipment can cause upsets or permanentwhich the fault current can store substantial damage, with consequences ranging from barelyenergy in the cable inductance. noticeable to total destruction or consequential

The magnitude of these fault-clearing surges damage.can reach several times the normal system Among upsets, there are several possibilities:


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6 - S e c t i o n O n e

Barely noticeable, with self-recovery: a clickin a sound system or a flash on a video screenPern~anen t nd noticeable, requiring manualreset: blinking clocks and VCRsPermanent but not readily noticeable:data corruptionThere are also several kinds of damage:Damaged components, repairable at aservice shopDamaged components that are too costlyto repairObvious and irreparable damage requiringcomplete replacement of the equipmentDamage such as internal equipment fire thatcould set other objects afireInsurance statistics provide information on the

relative frequency of damage among insuredappliances. It is significant that video equipmentis at the top of the list, and the discussion ofmultiple-port equipment damage under "SystemInteractions" at the end of Part 1 will explainwhy. A potit is a connection between a piece ofequipment and the outside world. The line cordof an appliance is a powerpolst.The modulartelephone jack on a fax machine, or the UHFconnector at the back of a W set is a communi-cationsport. In the modern home, both one-portand multiple-porc appliances abound (Figure 1.51,and the same situation exists in commercial andindustrial installations. When the rime comes tounderstand the origin of the surge suspected to

FIGURE 1.5: A lamp and a rabbi-ea rN re examples of single-portappliances. A computer with a telephon e modem connection is an exampleoffers many examples of both

have causecl damage to an appliance, it isimposcant to determine if the appl~ance s a sin-gle-port or a multiple-post type.

Many appliances are still single-port equip-ment, in spite of the trend to provicle sophisti-cated controls: a simple kitchen range is asingle-port appliance, but a range controlled bya smart-house computer system is a two-portappliance. A TV set with rabbit-ear antenna is asingle-port appliance, but the same set with aroof antenna or cable TV connection becomes atwo-port appliance.Multiple-Port Equipment. More and more elec-tronic equipment in homes and businessesrequires a communications link, hence a com-munications port in addition to the usual powersupply connection, the power port. Examples ofsuch two-port appliances include fax machines,telephone answering machines, personal com-puters with modem or printer connections, andcable-connected TV eceivers and VCRs.

A possible problem is tknt although each ofthe power and communications systems mayinclude a scheme for protection against surges,the surge current flowing in the surged systemcauses a shift in the voltage of its referencepoint while the other, nonsurged, system refer-ence point remains unchanged. The differenceof voltage between the two reference pointsappears across the two ports. Depending on thenature OF the appliance and its immunity, thisdifference of voltage may have some upsettingor damaging consequences. The problem is soimportant that it is discussed in more detail in"System Interactions" at the end of Part 1.Remedies against SurgesGeneral Approach. At first glance, ~twouldseem that if surges could be prevented fromhappening, many problems could be prevented.However, lightning cannot be eliminated. (Thereare some yet unproved schemes to dissipate thecharges in a cloud and thus prevent lightningstrokes.) Similarly, switching surges that occur inthe utility system cannot be eliminated by thetime they arrive at a customer's service entrance.Therefore, the general remedy is to install(insert) surge-protective devices at one or morepoints of a customer's installation.


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Dis tu rbances and Remed ies - 7

Surge-ProtectiveDevices:What's in a Name?The devices that can protect against surges arecalled surge-protectiue cleuices, or SPDs, by engi-neers, but that might sound too much like jar-gon to most customers. The name that seems tostick in the general public is surge suppressot:which many manufacturers use for their tradedesignation, with a variety of catchy trade-marked names The Underwriters Laboratorieschose to call them transient uoltage sulge sup-pressors (TVSSs), and that name or acronymgenerally appears next to the UL sign on theproduct. In the utility industry, the generic nameused in the transmission and distribution parts ofthe system is surge arrester:

Actually a surge cannot be suppressed norarrested; the correct word to describe what hap-pens is diverted. What these protective devicesdo 1s simply divert a surge to ground, where itcan do no harm. So a name that makes sensewould be surge divertel*,but it was not pickedThe consumer industry has settled on TVSS,while the utilities stay with the long-used wordawester and use it for the more rugged devicesthat a utility installs a1 the service entrance.

The surge protection schemes for residentialcustomers are these:

Insert a TVSS for each sensitive appliance(Figure 1.6)Accept the offer (if made) fl-onl the utility toprovide "whole-house protection" (Figure 1.7)Wholehouse protection consists of a protec-

tive device at the service entrance complement-ed by TVSSs for sensitive appliances within thehouse. The service entrance protection is anadapter inserted by the utility between the rev-enue meter and its base. Variations exist, such asa separate box connected to the meter base box.

With whole-house protection-that is, anarrester at the service entrance and one or moreTVSSs inside the building-the issue of .'cascadecoordination" arises. The concern is that, if thevarious protective devices are not selected withdue consideration, h e stress of incoming surgesmay not be shared according to the capability ofeach device. (See box, "Cascade Coordination.")This is a concept that the residential customershould not be expected to assess; it 1s the utili-ty's responsibility to consider it and offer anintegrated, coordinated package of serviceentrance protection and TVSSs.

FIGURE 1.6: A typicalNSS with power andtelephone protection. FIGURE 1.7: A meter-base arrester installed by the utility.


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8 - Sect ton O n e

Cascade Coordinationcisc:~ding s~lrge-protectiw le\-ice is :I con-cept n.herehy two (or n~o se ) rotectix e &\-icesare connectecl :I[ tn-o (or 1nore1differentpoints of a pon-er sy tem . The "upstrran~"device (the one closest to h e utility's distribu-tion system) is the first line o f defene: it isdesigned to divert the I I L I I I < of an impingingsurge. The "don-nstrealn" cle\.ices (those clos-est to the equipment to be protected) areintended 2s a final stage. cli\wting any remain-ing surges, including those generateil withinthe customer's wiring.

Successful coordination of cascaded cle\.icesis achieved when the hea\-v-du~-pstreamdevice does indeed divert the bulk of thesurge. instead of letting the don-nstreamdevices attempt to divert an excessive amo~intof the surge current. In keeping n-it11 the ter-minology of this manual. the ~ipstseam ie7-icen-ill be referred to as an armrer , while thelighter du v. don-nstream devices n-ill bereferred to as s~lpprrssors.The basic and criti-CJI parameters for successful coordination ofthe arrester suppressor cascade include therelative voltage clamping of the devices, theirelectrical separation through n-iring induc-tance. and the actual waveform of the imping-ing surge

A w-ell-designedcascade arrangement maxi-mizes the benefit of surge protection n-ith aminimum expenditure of hard%-are.Anotherbenefit of a cascade is the diversion of largesurge currents at the service entrmce. so thatthey do not flow in the building, and sideeffects are thus avoided.

It is one thing to design a cascade based onoptimurn coordination where all the parame-ters are under the control of the designer.Such an opportunity exists in utiliy systemsimplemented under centralized engineering. Itis an altogether different challenge to attempt,after the fact, coordinating the operation ofsurge-protective devices connected to thepower system by diverse and uncoordinated(and uninformed) users.

Promoting a coordinated approach maycome too late for the de facto sitiration in

which millions of suppressors are in s e ~ ~ i c en-ith a relati\dy lo\\. clampin3 voltage. Thissituarion will impose an upper limit to theclamping voltqe of a candidate retrofittedarrester. Therefore. close attention must I xpaid to the selection of the relative clamping\-oltage of the devices. in \-ien-of the contlict-ing requirenlents for performance undrr surgeconditions-a successful cascade-and reliabl?n.ithstanding temporary power-frequencyoven.olrnges. Nevertheless. coordination stillIIYJ!- he possible if die arailable t~~ cleoffsreunderstood. In the filrure. m-ell-informed userscoulcl avoid the pitfalls of poor coordination01. he disappointment of implenlenting protec-tion schemes that cannot pro\-ide the hoped-for results.

.%I illusrmtion of [he effect of the relativevolrages and device separation on the enerRsharing bern;een two devices appears inFiglire 1.8. The fig~lre hows 3 plot of the per-centage of the total energy dissipated in thesuppressor, as a function of the distance sepa-rxing the nvo devices. for \-arious co rn bi ~~a-tions of clamping voltages. In the plot. H. h1.and L correspond respectively to a high (250V). medium (150 V). and Ion- (130 V) voltagerating, in a 120-V rms circuit application. Inthe designations H-H. H-M. H-L. etc., the firstletter is the rating of the arrester and the sec-ond letter is the rating of the suppressor.

Figure 1.9 shows an example of a coordi-mt ed scheme where the current in the sup-pressor is indeed small compared to the cur-rent in the arrester. This encouraging resultcan sen.e as the basis for the selection of thetwo devices in a schenle that a utility can offerto its customers as an integrated package.

The active element in most surge protectivedevices is one or several disks of metal oxidevaristor (MOV) that perforn~he current diver-sion function. The surge diversion capability ofarresters and suppressors increases with theirdiameter. A typical cascade might consist of a40-millimeter-diameter arrester and a 20-mil-linieter-diameter suppressor, described as a40-mn1/20-mm cascade.


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D i s t u r b a n c e s a n d R e m e d i e s - 9

Distance between arresterand suppressor (meters)

FIGURE 1.8: Relative energy deposited in the suppressorby a typical high-energy surge for various combinationsof 250-volt (H), 150-volt (M),and 130-volt (1) atings, asa function of separation distance.

. - \ i t l ios~~iie rcnlit! of Ixl\ ing n u n )millions or 130-\ ok suppressorsin ~ td l c i l n 12o-\-oltsystelns makes ;I\T ell-coorilinatetl casc:tde difficdt o rpuhaps ~un;~itninalAc.t least in thenr;u future. n cooperative can stilltake ce mi n steps lo i~npr o\.e oorcli-nation in a protection sr-stem..is acompromise. :I cascade n ~ t h qu:il\ oltage nting s 6 s he arrester and thesuppressor can offer successfi~l oor-clinution. if the impinging ssurges :Irerel:~ti\.ely hort. The coordination of :Isimple cascade of a n arrester and :Is u p p x s o r of equal voltage rating.hoth connected line-to-neutral. 1sslightly improwd b!- the larger diame-ter of the arrester. Mon-el-er.an unfd-voralAe ccimhinxtion of rt~ lera nce s orthe two devices c a n wipe out theimpro\.ement-for exa mp le, if thearresrer clamping voltage is at theupper end of the tolennce band andthe suppressor is at the Ion-er end ofthe tolerance band. effecti\.ely makingthe suppressor t l ~ rower devicehence the one that mill have to divestInoa of the surge.

-1 0000 10 20 30 40 5 0 60 70 80 90 100Time (microseconds)-FIGURE 1.9: Division of surge current in a cascade of tw o 150-volt devices: I , is the currentin a 40-mm-diameter arrester and I , is the curre nt in a 20-mm-diameter suppressor, wi th10-meter sepa ration for the same 3000-ampere surge as i n Figure 1.8.


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10 - S e c t i o n One

In large business or industrial installationswith internal feeders, suhpanels , and fairly longbranch circuits, the question of cascade coorcii-nation is more complex than for a simple resi-dence. It should be assessed by the specialistresponsible for the electrical installation.SWELLSOrigins of SwellsThe disturbance called a swell is a brief increasein the line voltage, typically less than 20 or 30%,associated with load rejections and sluggishvoltage regulation response. The AC voltagesine wave remains essentially undistorted, but ~ t samplitude is increased for a few cycles or a fewseconds (Figure 1.10).

FIGURE 1.10:A voltage s we ll lasting eight cycies. IEffect of Swells on EquipmentSwells lasting only a few cycles are unlikely tocause any damage, and only the most sensitiveelectronic equipment might experience amomentary disturbance. On the other hand,swells lasting more than a few cycles can causea trip-out of protective circuitry in some power-electronic systems. Variable-frequency drives(also called adjustable-speed drives) ofteninclude an overvoltage sensor in their electroniccontrol, which can cause a trip of the system,with or without restart. The safety issue of auto-matic restart versus mandated manual-onlyrestart is well known among plant engineers.Remedies against SwellsFor the residential consumer, there is no con-cern about damage and only a small likelihoodof some upset of an electronic appliance. A user

of variable-speed drives (these are beginning toappear in residenrial heating and air-condition-ing systems) might experience a trip-out duringa swell. That possibility raises the question ofability to withstand swells, to be taken up withthe vendor of the variable-speed drive.

There is no device that can suppress a swellthe way a suppressor "suppresses" a surge; theremedy must be inherent immunity of theequipment. Thus, there is little that the user-residential or industrial-can do short ofrequesting the vendor to provide appropriatedesigns for the equipment.TEMPORARY OVERVOLTAGESTypes and Origins of Temporary Ov ervoltagesTemporary overvoltages are abnormal distur-bances, at the power frequency, that occurunder the usual (normal or abnormal) operatingconditions of a distribution system. The princi-pal causes are system faults over which the utili-ty has little or no control (animals, storms, vehi-cle collisions) and a troublesome situation of alost (open) neutral connection in the servicedrop to customers, in particular the residential120/240-V three-wire systems.Distribution SystemFaults. Overvoltages on thedistribution system originate from a variety ofsystem faults such as line-to-ground insulationfailure within the distribution transformer.Overvoltages caused by system faults can reach2.5 times the normal voltage. Depending on thesettings of the protective schemes, it can take aslong as 5 seconds to clear the circuits.

A rare but possible system fault occurs whenthe same pole carries two systems at differentvoltages and a collision, high wind, or ice causesone set OF conductors to fall onto the other. Thisscenario will produce overvoltages proportionalto the difference of the two system voltages.Open Neutral. An open neutral situation canoccur as a result of corrosion in undergroundservice drops, falling branches or ice onthree-conductor overhead service drops, andeven a loose connection of the neutral in a ser-vice panel. Service drops with aluminum neutralconductors are more prone to this type of fault.


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D i s t u r b a n c e s a n d R e m e d i e s - 1 1

Utility engineers can report many anecdotesabout that type of disturbance.

As the box "When a Neutral Opens" explains,what happens is that if the loads on the two

When a Neutral OpensOpen neutral connection. in 120 1-to-\. CLI.;-t0111er i l l d t ; i ~ [ : ~ t i O l l ~an occur under wwral cir-cumstance.;. including:

W ~ e norrosion of ;un aluminum under-ground s cn ke re~cheb n acute Stag!\Yhen the neutral n k e of n .;cparLlre-c.cx-ductor sen ic c drop is brnlien h!- Gilinghranches or icing\Yl~en n intermittent loow connectionexists in the service n:~nel

(Note that all of the :~ ho \e re .'\\-lien"C ~ ~ I L I S -es-not "if and n.hen"-hecause ;dl of thesec i r c u ~ ~ ~ s t a n c e ~re som cnh ~ tikel!. ro occur :itsome point: it is onl!- a marlel- of pldxlxlir !and frequency of nccurl-ence.

In 0-pica1 installations. the t \ \o hal\.es ofthe pon-er suppl!.. on e ~ c hide of rlie center-tap neutral connecrion, are d c i om exactl!-I~alanceci. nd

sides of the 120/240-V custonier installation arenot balanced. the side w~ t hhe lightest loadexperiences a large increase from 120 V, theoret-ically almost up to the full 240 V

(se e Figure 1 . 1 1 ) . l' he on[! remaining connei,-tion is the r \ \ c lines. L l :ind 1.1. x.ross \\ hic.11-the full 2tO-\- supply is niaintainccl.

' [he putenlial xt the midpoint Iwt\veen thctn-o Ioatls %, :mil Z2 \ \ - i l l be w ~ ~ i e \ \ ~ I ~ e r ei>et\\-em1 hc potential o i L I kind L1 , in in\-ersc.proportion to thc \-alucs oi Zl mil Z2. If , forinstance. Z2 i \ r n ~ ~ c hOU el- than TI. a ' l l SSconnectecl on the L1 side \\-ill experience ase\.ere o\ .en oltagt. (a s \xi11 the equip~ne ntep-resented I>).Z I , Hone\ -e r. ~h i l e osL equip-men1 h:is some toieranc'e h r 3 moilemre o\ w -\ c k ~ g e . YShs. in prticul;i~-hose that claiminn clamping \ ollnge. are quite wnsit il-e to thatcondition. Tlii:. sir~utions prol,.,il>l!. the causeof most reported catastrophic Failures of T\-SSs.

Some p~~ldicationsn powt.1- qualit!- includean illustration of n scren driver (presumalAyintended to tighten loose connections i n-it11 3caption that reads -'the most useful power-qiua li~ ool"!

Effects of Temporary Overvoltages on EquipmentOvervoltages, whether a result of distributionsystem faults or open neutrals, can be quitedestructive for equipment if allowed to last morethan a few cycles ( ~ n hich case they might fallin the category of swells). Power equipment isdesigned to survive these overvoltages: trans-formers are likely to saturate, providing some

sometimes are

voltage reduction on the secondary. Distributionarresters are generally selected for their ability tosurvive temporary overvoltages. However, many .consumer-type n S S s are likely to fail during atemporary overvoltage [see box, "Lower Is Not(Necessarily) Better"]. In Fact, the major cause ofTVSS failures is a temporary overvoltage, ratherthan an unusually large surge.

highly unbalanced.I f the insral1:lrionneutl-al beconic sclisconnectecl fromthe utilih. neutral.voltages and I >appear on eachside of the non--disconnected

Line

240 ,, Neutral1p u n dyX voltagesI ~ O neutral v2

Lineinst:tllation I I C L ~ X I FIGURE 1.1 1: Unequal line voltages caused by an open neutral.


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12 - S e c t i o n One

Not EnoughVoltage

Lower Is Not (Necessarily) Better!The funclanienral purpose of a surgc-protectlwdevice is to reduce tlie stress imposed on loadequipment n k n surges occur on the :\Cpower system. Surge protective de\.ices (SPDs)do this by di~wtinghe current of an imping-ing surge to gro~indhrough a low impedance.The effect is a subsrantial reduction of theimpinging voltage surge..bSPD is a volrage divider in n-hich the

vo1t;lge on its low side (the side connected t othe load) becomes lower as the surge currentincreases. "cla~nping"he ~olragelnpressed onthe load.

Before the proliferation of SPDs. made pos-sible by the development of metal-oxide varis-tors (MOVs). the perception existed that thethreat of surges was the voltage they candevelop at the terminals of a load. Thus.people thought that clamping that voltageto a Ion- lexd was desirable and, intuitixdybut erroneously. the lower the better. Thisperception was reinforced by the decision ofthe Underwriters Laboratories to require man-ufacturers of TVSSs (UL Standard 1449) toshow tlie clamping voltage of their producton the package. picking fi-om a List of discretesteps starting with 330 V for 120-V applica-tions. This UL requirement triggered a

Remedies against Temporary OvervoltagesThe nature of temporary overvoltages makes itdifficult if not impossible to prevent them, andtherefore they must be accepted as a probable,but hopefully rare, event. Surges can be divertedbecause the energy levels to be absorbed in the

OUTAGESOutages represent the worst type of disturbancefor the operations of a customer. They can havea duration as short as a few cycles, the typicalsituation when the breaker of a feeder trips outon a fault and the fault is cleared, with automat-ic reclosing (Figure 1.12). Other outages can bemuch longer, as when the distribution equip-ment suffers a major fault (downed lines, cata-strophic failure of transformers or switchgear).

tiown\~ard ,auction' among mnnufacrurerswho xwnced to be in the 330-V categor?.overlooking the undesirable side effects ofsuch a tight clamping.

Actually. most load equipment is morerobust to surges than Tb5S manufacturersimply by offering these low clanlping \.olrages.For instance, a 500-V clamping voltage wouldbe quite adequate for protecting equipment.Furthermore-the point of the axiom ,'Lower isnot better!"-a n;SS clamping at 500 V wouldnor respond to most swells or temporary over-voltages, a characteristic that is highly desir-able. Such a passix.e sinration would help inretarding the aging process of MO\'s. Moreimportant, it certainly would reduce the inci-dence of the catastrophic failures that are peri-odically reported in trade magazines.

Some manufacturers have responded to theargument by offering guarantees or no-ques-tions-asked replacement. Nevertheless, failureof a WSS from a temporary ovenoltage mightstill be a traumatic experience for a homeown-er. Those few manufacturers who subscribeto the "Lower is not better" philosophy shouldbe rewarded by being chosen when con-sumers go through the q u a n d a ~f @.ing toselect from the multitude of WSSs offered onthe shelves.

diversion are limited. In contrast, a temporaryovervoltage involves the full power of the sys-tem, and no device can absorb that level ofenergy. As noted above, some equipment canbe designed to withstand the overvoltages, butthat decision is beyond the control of a utility.

Outages rarely damage equipment directly.Indirectly, of course, industrial processing equip-ment (for metals, plastics, textiles, semiconductordevices, and so forth) shut down by anunscheduled outage can suffer damage. Thematerial under process is not only mined butcan also jam the equipment, with painful andtime-consuming cleanup operations.Less dramatic consequences or cessation ofoperation can range from inconvenience to loss


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D i s t u r b a n c e s a n d R e m e d i e s - 1 3

FIGURE 1.12: A very brief outage (top) and a very long outage (bottom).

of revenue. Individual consumers also can sufferfrom loss of power needed for heating, air con-ditioning, and food refrigeration. One utility,with a mixture of seriousness and facetiousness,used to describe the severity of outages by thenumber of claims filed for spoiled freezer loadsof frozen raspberries!

The obvious remedy against outages at thecustomer level is to provide a standby source ofpower, either a storage battery or an engine-generator set. The battery-power approach, gen-erally called an unintemptiblepower supply(UPS), is a very popular remedy. It is applied atall power levels, from the small package favoredby reliability-conscious computer users, to abuilding-wide system where loads are segregat-ed into essential and nonessential. There arevarious types of UPS offered by manufacturersin a highly competitive market, each with per-formance characteristics aimed at minimizing oravoiding altogether the momentary disturbancewhen power is transferred from the utility to thestandby source.

For large industrialloads, schemes of dualfeeders with an automatictransfer switch have beenapplied successfully bymutual agreementbetween the customerand the utility. Such anapproach is justifiedwhen the financial and

operational cost of an outage justifies the invest-ment in a dual feeder system. Pessimists havenoted, however, that when an installationdepends on two feeders, it might be subjectedto twice as many sags because each feeder car-ries a likel~hood f sags.SAGSPower quality engineers call "sag" an eventwhen the line voltage is reduced for a fewcycles to a level of less than 80% of the normalvoltage (Figure 1.13).This type of disturbancecan trigger upset or shutdown of control circuits.Sags rarely cause equipment damage but are thecause of many complaints of malfunction.

Sags have their source in faults in a feeder thatcause a large current to be drawn in the feeder,hence a voltage drop in the bus from whichother feeders draw power. Many power qualityengineers consider sags as the major cause ofequipment malfunctions-but rarely, if at all, ofdamage. Upsets affect primarily the informationtechnology equipment. Also affected are simplepower devices controlled by a magnetic motorstarter, which can drop out and stop a process.

Field studies of sag-related disturbances in pro-cessing equipment have revealed that the sourceof the problem can be a simple relay in the con-trol system, rather than a major disturbance in thepower equipment. In such cases, a very effectiveremedy is to provide the control system with aUPS, or even with a simple constant-voltagetransformer that can ride through most sags.BROWNOUTSIn periods of hlgh demand where the systemcapacity is reached and would be exceeded, util-ities reson to the scheme of deliberately reducingthe voltage by a few percent. The effect is a

FIGURE 1.13: A sag lasting 10 cycles with the line voltage reduced to55% of normal.


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1 4 - S e c t o n O n e

reduction of the power co nsun~ed y most loads,with some exceptions in the case of process con-trols that include a voltage regulating schemethat defeats the objectwe of the brownout.SUSTAINED UNDERVOLTAGESA very severe brownout might cause overheat-ing of compressor motors, and some peoplebelieve that domestic refrigerators thereforeshould be disconnected when the lights are verydim. This perception needs clarification, and util-ity engineers should quantfy the risks involved.

Another damaging consequence might be thefailure of some electronic voltage regulators builtinto computer-based equipment (genericallycalled "information technology" equipment).Such equipment has an intermediate regulatingstage that can become overloaded and overheatwhen attempting to compensate for the voltagereduction. Anecdotes have been circulated, andthe phenomenon has been demonstrated in thelaboratory, but is confined to isolated cases. Itis recounted here as a yet another hint thatequipment failures should not blindly be attrib-uted to surges.CHARACTERISTIC CURVESThe information technology industry has devel-oped a characteristic curve describing the toler-ance of equipment to undervoltages (mostlysags) and overvoltages (mostly surges). That

curve, n ell known to power-quality speclalistsas the CBfibk4 curve, has recently been updatedancl IS now called the Z77C cwv e (for theInforniatlon Technology Industry Council). Seebox. 'The CBMA Curve."FLICKERWhen light sources (mostly incandescent butalso some fluorescent) are supplied from apower line in which repetitive sags occur, aflickering effect is produced that h~unansindannoying. The correct term to describe the

The Case of the Flickering ChandelierIn one nnecclote. a customer comphined o ftlickering lights to the electric utilit!-. \\ liichinstalled a strip-cl~itr~ecortlcr :kt 111c sen iceentrance in response (:IS if that coulcl cletecrsmall tli~crualions!). f course. none \yerecletected. I t turned our 111x1 he customer l~atlleft a n enipt!. electric skillet on \vhile suppel-n.ns k i n g enjoyed in the dining room. 111that \.int:tge-era house. the sliillet ( 1500 n atrson a =l-+.\KG wire) nnd the chandeliern-ere on the same Ixtnch circwit. The flickern-as cnusrtl h!. the thermostat of the skilletcycling o n and off. Flickering cmdles on thedining room tahle ma\. be ro~ixintic. ut :Iflickering chandelier is declared :innoying.

The CBMA Curve111 the 1:lre 19'0s. computer mnnuf;~cti~rersnd usersreached a consensus on the pawn quality (use of the termha d just sta~~ed)hat woulcl he necess:u.)- to ensure ~indis-turbecl operation of computers. The concept-as a designgod . not a specification-\~:ts first proposed as relev:~nt omainfi:~me compurers and presented in the form of a cloii-hle cun.e showing a l o ~ w rimit : I I ~ n upper limit foracceprahle mains \.oltage. or. in other n-orcls. the clesi~.ahlrrolel.ance of e q~ ~i pm en to p o n w supply rariations. This~ I X I I T became known :IS the CBEALI curve and n-:IS oonconsiclererl-perhaps nor an appropriate extension-as,~pplicahleo some eleclronic equipment other than com-puters. ancl n.as cited in sever:ll stand:ircls. The origin:llcun.e nxs a ch:tlIenging consensus-building effort. I t was:I committee agreement on what people thoi~ght he

equipinent could stand. It was not rhoroughly tested or vet-ifiecl zit t1i:lt time. Although the ponw-supply ~echnologiesof husiness equipment have improwcl. some m:tnuf~~cturers:[re still reluctant to incorporate them into thcir procli~ctshecause o f competitive market constlxints.

In the 1990s. incrr:ising intcrcst in solving ponw qualityprohlems led to c.xtensive resr:trcli in thc tol e~ in ce f vari-ou s cclurpment to power supply clisturlxmcrs, in particular.;;igs. Changing technolog!- in computer equipment-non.classified as infomiation technology equiplnent (ITE) alsoled ro >I revision of the lin~its, nel :I re\-isedcurie x i sissued in 1996 17). the Information Technology I n c l i ~ s t ~ ~Council IITIC). together with an qq>lication note (FigureI . 14) .

Cpdxez to this information may he found ;tt the x'eh sirehttp: w-~\~.chenla.orgtic sire-map inclcs.lltml


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Disturbances and Remedies - 1 5

breakdown concern106%

100% tolerance envelopeLack of stored energy ~nsome manufactures'-equipment . 0%

0 9 6 0 0 0 ~ o b iI I 1 I I I

0 1 0 5 1 0 6 1 0 30 1001 1000Time in cycles (60 Hz) seconds

500 - ----- 1

120 L --*Voltage tolerance - + - I- envelope

'O . t-- - -r I"& ' ' i t , i ' I d "" % ' ' I & ' .'i'doo' d o c

l m s 3 m s M rn s 0 5 s 10 s StearTwo scales on horizontal axis:1. Duration in cycles2. Elapsed time

behavior of the power supply is uoltngejlt ictun-tioiz, but jlickeriizg is often used to describe thequality of the power, even though it is only theeffect, not the cause.

Voltage fluctuations can be considered repeti-tive sags OF low amplitude (the human eye candetect light output variations caused by a frac-tion of a percent fluctuation in the voltage,when the fluctuations occur at rates rangingfrom a few seconds to about 20 per second).Typical sources are arc furnaces (not too manyaround) and welding machines (arc and resis-tance spot welding).

There is no remedy that the customer canapply when the fluctuations come from an inter-mittent load of a neighbor. (Be sure that the skil-let or flat-iron is not on!) If the complaint soundsserious, the only remedy is for the utility toinvestigate where the intermittent load is, andnegotiate a solution with the offender. Powerquality specialists are acquainted with a variety ofsolutions, but each is to be applied case by case.

FIGURE 1.14: The original CBEMA curve (top) and the updated lTlCcurve (bottom).


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1 6 - Sect ion O ne

Other Other disturbances, less frequent than the "too- -Powelcline much" and "not enough" lust described, can alsooccur as the result of the operation of the distrl-Disturbances bution system and interactions wlth customelloads. ~h e s e isturbances include noise, har-monics, notches, unbalance, and carrier signals.NOISEThe term noise is loosely used to describe smalldisturbances (a few volts at most) at high fre-quencies (note the plural). See Figure 115 . Thesources of noise include chattering relays (ashort-duration event) and coupling of radio fre-quencies from a nearby broadcast antenna (aquasi-permanent situation).

FIGURE 1.15: Noise superimposed on an AC voltage.In keeping with Federal Communications

Commission (FCC) requirements, most domesticequipment has a filter in the power cord thatlimits the emission of high frequencies backinto the power cord. Industrial equipment hassimilar FCC requirements, but less stringent. Byreciprocity, this filter also limits the penetrationof line-conducted noise into equipment; thisfact is worth keeping in mind when consideringthe purchase of a TVSS making claims ofadding noise filtering to its prime mission ofsurge protection.HARMONICSHarmonics are currentsand voltages at frequen-cies that are multiples ofthe fundamental 60-Hzwaveform (Figure 1.16).They are the result ofnormal operation of cer-tain loads, called non-linear because their

Impedance is not constant or because they drawcurrents that are not proportional to theirimpedance. This type of load is becoming morewidespread as consumer electronics proliferateand as new-, sophisticated power-controlschemes aimed at improving efficiency are builtinto some major appliances. The presence oflarge harmonics is readily visible in the voltagewaveform. Small, but potentially objectionable,harmonics require a more sophisticated instni-ment, such as a power-quality monitor, to detectand quantlfy them.Effect of Harmonics on EquipmentAs a result of the increase in occurrence of har-monics, the subject has become a hot topic (punintended) because the effect on equipment canbe severe overheating. The problem startsbecause nonlinear customer loads generate cur-rents at harmon~c requencies. (In the jargon ofthe applicable standards, this is called harmonic

& .

emission.)There are several undesirable resultsfrom this situation:1. Effective (root mean square, or RiiS) cur-

rents in conductors are increased, in par-ticular in the neutral of three-phase sys-tems. These increased currents can causeoverheating because the wiring installa-tion, done in accordance with earlier ver-sions of the National Electrical Code(NECm, rademark of the National FireProtection Association), made no provi-sion for that situation.

2. The harmonic currents clrculate in thedeltz-connected secondary of wye-deltatransformers but not in the primary side,therefore primary overcurrent protectionis not effective and the secondary can beseverely overheated.

FIGURE 1 l6:An AC voltage distorted by harmonics.


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D i s t u r b a n c e s a n d R e m e d ~ e s 1 7

3. If the harmonic currents are not filtered include the providing filters as a retrofit option.out or canceled at the point of common As of 2001, the issues are still the subject ofcoupling (as they are in 2 above), the much debate, and should be reviewed bycurrents flow in the utility distribution sys- power-quality specialists before expensivetem and cause a voltage distortion in the and possibly counterproductive measuressupply of adjacent loads, proportional to are implemented.the current and the utility system imped-ance. In other words, systems with rela- NOTCHEStively low available short circuit capacity "Notches" can be created in the supply voltagewill experience more voltage distortion when large power-electronic drives in adjacentfor a given nonlinear load than systems loads cause a momentary short circuit betweenwith high capacity. the phases that power the drive, each in turn.

These are called commz~tation otches and occa-Remedies against Harmonics sionally cause some interference with otherRemedies against harmonics are essentially com- loads that use the 60-Hz power frequency as apromises in a range of extremes. One such com- controlling signal (Figure 1.17).promise is to control harmonic emission by In a sense , notches may be considered as amandating limits for each and every piece of special case of harmonic emission, and theequipment, the approach presently taken by remedies, if interference is noted, are similar tosome European countries. Another approach, those mentioned for harmonics in general.which has gained accep-tance in the United States,is a voluntary compromisewhere limits for harmonicemissions at the point ofcommon coupling areonly recommended.

Consumers have practi-cally no control over theharmonics that their

' , ' ,

FIGURE 1.17: Commutation notches on an AC voltage.equipment can generate,but the perception in theUnited States is that, for the moment, they donot pose problems. This laissez-faire attitude UNBALANCEmlght change if harmonic-generating loads such Voltage unbalance between phases occurs whenas electronic ballasts and variable frequency dri- a three-phase system supplies single-phase loadsves for heating and air conditioning were to that draw unequal currents. Three-phase loadsbecome a larger portion of the total consumer supplied under those conditions can be adverse-load. ly affected, with overheating of motors in partic-

In commercial and office buildings with older ular as a symptom. Variable-frequency drive sys-wiring and a large amount of information tech- tems have a tendency to magnify the problemnology equipment, supplied single-phase from a by skipping some OF the six half-cycles that arethree-phase system with shared neutral, harmon- expected, each in turn, to deliver power to theics can cause overheating problems. Later ver- drive. Thus, a severe current unbalance can ,sions of the NEC recognized the problem and result from a moderate voltage unbalance.have mandated larger ampacity For shared-neu- The remedy for this situation is under thetral conductors. control of the end user and is simply to reassess

Industrial customers are more concerned the allocation of single-phase loads from theabout harmonics because some of their loads three-phase system.can have a significant emission. Remedies


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1 8 - Sec t i o n O n e

CARRIER SIGNALS These are isolated cases for which case-by-Occurrences of interference fro111 carrier case remedies have been developed by power-signals have been described in anecdotes. quality specialists.

System THE PROBLEMInteractions A special kind of surge problem is that of aninteraction between the power system and acommunications system, as briefly mentioned inthe beginning section of this part, "Surges." Thiscase merits special attention because it can bemisinterpreted as being caused by the utility

Shifting Reference PotentialsTo illustsate the problem of shifting referencepotentials. a lal>orato~)-eplica of a residentialwiring system xvas used to malie nleas~11-e-ments during surge events produced hy inject-ing a surge into the wiring. In Figure 1.18. 11modern-equipped PC is connected 11). itspon-er porr to a lhranch circuit. and by ~ t stnocleni port to the telephone service of thehouse. For a worst-case scenario. the powerancl telephone s e ~ ~ i c e snter the house atopposite ends.

.inopen loop is formed by the copper pipeor ground concluctor used as a bonding cotl-d~ictor.he eq~~ipm entrouncling concluctor ofthe branch circuit feeding the PC. and the tele-phone wires from the netn ork interhce device(KID) to rhe PC. I f a surge impinges on theexternal telephone plant. it isdiverted by the TID via thecopper pipe to the cornmongrounding point of the house.:1t the pox er s eni ce entrance.The surge current in the cop-per pipe creates a changingmagnetic t lus around the pipe.which induces a voltage in theloop. This voltage xvill appearbenveen the m-o IC posts ifthey are separated by a highimpetlance (of unknon-n surge

power supply. Furthermore, the problem canarise even if both of the systems have been pro-vided with surge protection, leaving a customerthus afflicted puzzled or disappointed. The effectof this interaction is to shift the reference poten-tials of the two ports during a surge, as explainedin the box *'ShiftingReference Potentials."

pip-n-l~icli can be espected in residenlialn.iring-a large loop is formed. embracing thefl~lx roduced by the surge current in the cop-per pipe.

Figure I 19 s11on.s the recording olh~aineclin the laboratory replica of residential wiring.For a rate of change in the surge current of -5.A )IS (amperes per microaeconcl). typical ofstandard test wiveforms a peak of i . 3 k\. isinduced in the loop and appears betn-een them'o ports.

.\ relatively simple retrofit solution is tocq~lalize he difference of voltage bemeen thetwo systems by 3 device designed for the pus-pose and inserted in both communications anclpon-er links j~lsrbefore they enter [he nppli-ance. This device, defined in IEEE Standard1100-1992 as a "surge reference equalizer." is

y old water ppedevice

--volrage withstand capacity). FIGURE 1.18: Pow er and telephone services enter the houseWt h the telephone wires rout- a t opposite ends. A personal computer is connected acrossed avay from the copper the tw o systems.


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D ~ s t u r b a n c e s n d R e m e d e s - 2 1

REMEDIES AGAINST SYSTEM INTERACTIONSFort~inately. n du sq ha recogi~~zeilhe prob-lem and offen 3 line of devices spec~all!-designed to pl-ocect against rliose spe c~ al . utpre\ alent. surge pl-ohlems. Tlxs t> pe of deucecan be recognized easdy because it lm i 11 mi n p ~ ~ tine cord with output ponei ieceptaclesand (2 1 mo telephone modular i;icIis (o r \.ideacoax connectors) to insert In the telepllone con-nectlon (o r video cable connection) The PI-ope1engineering term for this ilev~ceS .iii/::e I-efev-euce eqz~n l i zevSRE) . but here again, popularusage has not 3dopted the eng~neerlngargon

.sz~ppressoi-wirh added \\.ords to ciran- attentionto the mo-port system.

To place the operation of 3 surge equalizer inperspeitlve, visualize the m-o po~ rs f theequipment and their ground rekre nces, as InF~g~ire.21.During a surge event on one sys-tem. there 1s a transient unhd r~nce etn.een them-o input references. wlhich c m be made worsen hen thc seivice entrances a]-e at opposite ends .Inaer tq an SRE lust behind the T'v' set almostre-establishes a balance between the m-o portsThe ideal sltuation wo~~ lc le to first ha w them;o sen-lces on the same sd e . and as 3 finlsl-iing

and rlie device is often called slmpl>- sz~ige toach still provide an SRE

Power YideoV ideo

Bad Better Best

FIGURE 1.21: Shifting refe rence poten tial can be remedied by inserting a surge reference equalizer on the comm unications andpowe r lines (here, the appliance is a TV and the comm unications line is a TV cable, but a PC wi th a telephone m odem connectionpresents the same problem). I n the idea l situation, the com mun ications and power lines enter the house on the same side, andthe SRE is m ost effective .


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Q u e s t ~ o n s o A s k - 2 3

In This Section Customer-owned offenders; how to use the worksheets; identiFying residentialand commercial appliance categories; Worksheet EDE: electronic, dual, external; Worksheet EDI:electronic, dual, internal; Worksheet ES: electronic, simple; Worksheet HE: heat, electronic;Worksheet HM: heat, mechanical; Worksheet ME: motor, electronic; Worksheet MM: motor,mechanical; Worksheet PLC: Power line conditioning

This part of the manual is intended to facilitatethe interactions between a customer and a coop-erative's service representative in tracking downthe cause of malfunction or damage and offeringremedies when possible. Hopefully, this proce-dure will serve the common interests of bothparties, but, as a note of caution, not all prob-lems can be solved over the telephone, and insome cases it might be necessary to call in apower quality specialist to study the problemand identify possible solutions, just as somemedical problems can be described over thetelephone to the family doctor and a suitableprescription be picked up at the local pharmacy,

but other problems require a visit to the doctor'soffice and even a referral to a specialist.While the main thrust of the manual is the

effect of the utility supply on equipment-withthe equipment characterized as "victim"-thereare also cases of disturbed equipment that areassociated with the customer's own operationswhere some other equipment can be character-ized as a troublemaker or "offender." Theseoffenders are listed in Table 2.1, for a quickcheck that the reported problem does not fall inthat category, so that the dialogue can thenfocus on the suspected interaction between theutility power supply and the equipment problem.

CustomerOwned some appliances generate distur-Offenders bances that can cause a malfunc-tion of other appliances in the

same installation, or even inneighbors' installations. Thesedisturbances are not attributableto the utility, but an uninformedcustomer might still make it asubject of complaint to the utili-ty . Table 2 .1 describes typicaldisturbances, their causes, andpossible remedies.

TABLE 2.1: Home-Based Disturbances, Causes, and Remedies

TV remote disabledwhen lamp is onFi~ckermgamps

Remedyisturbance CauseInterference fromfluorescent lampsLoad cycling [electricskillet, laser ~rinter)

Change type of lamp

Plug loads in o therbranch circuits


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24 - S e c t i o n Two

HOW to Usethe WorksheetsThe procedure of troubleshooting consists ofthe following steps:

1. Obtain from the customer a descriptionof the victim equipment, and categorizethe type, using Table 2.2, a list of appli-ances likely to be found in residentialand small-business installations.

2. Turn to the diagnostic worksheets corre-sponding to the type of victim equipmentidentified in step 1.The worksheets arestructured in three parts:a) History and symptomsb) Tentative diagnostics and remediesC) Disposition of case

Identifying For the purpose of narrowing the tentative diag-Residential andCommercialAppliance

nosis, Table 2.2 lists several categories of equip-ment victims. To allow good understandingbetween the customer and the service representa-tive, it will be useful to pin down, early in the d m

Categories logue, what is the specific appliance category tobe discussed. When the category is thus pinneddown, the "script" for the dialogue can be foundin one the the eight work sheets at rhe end of themanual. The customer representative should pho-tocopy blank work sheets and keep a supply ofthem to be filled in as the dialogue progresses,then file them for future reference or additionalreview. For easy reference to the correspondingwork sheet, the categories identified by the tableare associated with a code that appears in boldtype on the top right comer of the work sheet.MOTOR-DRIVEN APPLIANCES AND HEATINGAPPLIANCESFor each category (motor-driven or heating),there can be two or more types, depending onthe type of control used:

Mechanical control (on-off, rotary, etc.-no sophisticated keypad or other electroniccontrol)Electronic control (keypad, display, etc.)

These different controls influence the tentativediagnosis. Consequently, motor-driven and heat-ing appliances are divided into four kinds, with

3. Obtain from the customer as much back-ground information as possible, usingPart A of the worksheet as a script forthe dialogue.

4. Reviewing the information thus obtained,ask further questions as appropriateaccording to Part B of the work sheet.

5 . Present to the customer a tentative diag-nostic and possible remedy (some prob-lems might be beyond simple remedies).

the following codes in Table 2.2 .1. Motor, mechanical MM2. Motor, electronic: ME3. Heat, mechanical: HM4. Heat, electronic: HE

ELECTRONIC (COMMUNICATIONS) APPLIANCESThis generic category includes telephones, audioand video equipment, and personal computers.Here again, two types must be recognized:

1. Appliances with a simple, one-link con-nection to a power system (or to a tele-phone system for simple sets).

2. Appliances with a dual connection to bothpower and communication. Such appliancescan be subdivided further into two types:a) Appliances that are powered as well as

linked to an external communicationsystem such as telephone line, rooftopantenna, cable TV, or satellite dish. Theexposure of this type of appliance issignificant because surges of externalorigin can come in through either thepower line or the communication link.They can be caused by system distur-bances or by remote lightning strokes.

b) Appliances that are powered as well aslinked to an internal communicationsystem, such a garage door opener,burglar alarm, intercom, thermostat, or


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Qu e s t i o n s t o A s k - 25

computer-controlled appliance. Theexposure of this type of appliance,even though it involves two systems, islower than that OF systems with exter-nal links. Disturbance or damage asso-ciated with the internal communicationlinks is limited to the rare case of avery close lightning stroke Inducing avoltage in those internal links.

The absence of a communication link, or thetype is a link is present, will influence the diag-nosis. The types of electronic appliances can beassigned these codes in Table 2.2:

Electronic, simple: ESElectronic, dual, external: EDE* Electronic, dual, internal: ED1POWER LINE CONDITIONING EQUIPMENTSurge suppressors and un~nterruptiblepowersupplies are given the code PLC in Table 2.2.

rABLE 2.2: Categories of Equipment VictimsCodes:

EDE = electron~c, ual, external HM = heat, mechanicalED1 = electronic, dual, internal ME = motor, electronicES = electronic, simple M M = motor, mechan~calHE = heat, elec tron ~c PLC = power line conditioning

Appliance I Category as victim I Work sheet

Burolar alarm, indeoendent 1 Electronic dual, internal 1 ED1

Air conditioner, central, conventionalAir conditioner, central, variable speed

Air conditioner, windowAntenna rotating systemAttic fan, thermostat controlled

Automatic lawn sprinklerBoom boxBurqlar alarm, telephone link

Clothes dryer

Motor, mechanicalMotor, mechanicalElectronic, dual, internalMotor, mechanicalElectronic, dual. externalMotor, mechanicalElectronic, dual, externalElectronic dual, externalElectron~c, impleElectronc dual, external

--Cell phone chargerCentral computer for businessCentrex telephone systemClock radio

Motor, mechanical or electronicHeat, mechanical or electronic

M MM MED1M MEDEM MED IEDEESEDE

Coffee maker I Heat, mechanical

Electronic, simpleElectronic, dual, externalElectronic, dual, externalElectronic, dual, simple

ESEDEEDEES

Computerized the rmostat system 1 Electronic, dual, internal I ED1I I

ED1 or EDEomputer network

DehumidifierDesktop publishing system

Electronic, dual, externa l only or internal

Motor, mechanicalElectronic, dual, internal only or external

M MED1 or EDE


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2 6 - S e c t i o n Two

Digital video disk player I Electronic, simple 1 ES I

TABLE 2.2: Categories of Equipment Victims (Cont.)

I Doorbell, sophisticated I Electronic, dual, internal I ED1 1

ApplianceDigital clock, electronicDigital clock, mech anical

I Fax machine 1 Electronic, dual, external 1 EDE 1

Category as victimElectronic, simpleMotor, mechan~cal

Distributed home entertainment systemElectric car battery chargerExercise equipm ent

Work sheetESM M

I Fluorescent ligh t~n g ystem ( Electronc, dual, internal I ED1 I

Electronic, dual, internal and externalElectronic, simpleMotor , mechanical or electronic

Fire alarm system-Fluorescent lamp, compa ctFluorescent liqht, maqnetic ballast

I Fluorescent light, electro n~c allast, single I Electronic, simple 1 ES I

01 and EDEESM M or ES

Electronic, dual, internal and externalElectronic, simpleHeat, mechanical (eauivalent to ]

1 Garage door opener 1 Electronic, dual, internal 1 ED1 1

EDE and ED1ESH M

Food mixerFreezerFurnace

I Heat pump / Motor, mech anical or electronic I M M o r M E I

Motor, mechanicalMotor, mechanicalMotor, mechanical or electronic

Ground-fault circuit interrupter, receptacleGround-fault crrcuit interrupter, service panelHam radio, transmitter w ~ t hntennaHam radio, receiver with out externalantenna

MMM MM M o r ME

I Hot water heater, isolated I Heat, mechanical 1 MA

Electronic, simpleElectronic, simpleElectronic, dual, externalElectronic, simple

Hi-fi system, concentratedHi-fi system, distributedHome security system, telephone link

ESESEDEES

( Instant hot water for beverages I Heat, mec han~cal 1 H M I

Electronic, simpleElectronic, dual, internal and externalElectronic, dual, external

Hot water heater, computer controlled

HumidifierHVAC (heating, ventilating, andair conditioninq) controls

1 Intercom system 1 Electronic, dual, internal I ED1 I

ESED1 and EDEEDE

Heat, mechanicalElectronic, dual, internalMotor, mechanicalElectronic, dual, internal

HMED1M MED1

Llght bulb, incandescent Heat, mechanical M H


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Clues ti ons t o Ask - 2 7

rABLE 2.2: Categories of Equipment Victims (Cont.)Appliance I Category as victim I Worksheet

Light d~mrner / Electronic, s~rnple I ESMicrowave oven I Electronic, simple I ESPersonal computer, isolated I Electronic, simple I ESPersonal computer, telephone modem 1 Electronic, dual, external I EDE

Motion-detection lightng I Electronic, simple I ES

Personal computer, cable modemPoint-of-sale cash registerPower tool

Rechargeable flashlight/emergency Ig htin g I Electronic, simple I ES

Electronic, dual, externalElectronic, dual, externalMotor, mechanical

Sump pump 1 Motor, mech an~ca l r electron ~c I M M o r M E

EDEED1M M

Range, k~t che nRefrigeratorSatellite dish receiverSink disposal

Surge suppressor, permanent connection 1 Power line conditioner I PLC

Heat, mechan~ca l r electronicMotor, mechanicalElectronic, dual, externalMotor, mechanical

Telephone desk set, powere d I Electron~c,dual, external 1 EDE

HM or HEM MEDEMM

Surge suppressor, plug-inSurge suppressor, service entranceSurveillance camera systemTelephone answering machine

Telephone desk set, simple / Electronic, simple I ESTelevision receiver, cable input I Electronc, dual, external I EDE

Power line conditone rPower line cond~tonerElectronic, dual, externalElectronic, dual, external

PLCPLCEDEEDE

TVSS, permanently connected I Power line conditioner I PLC

Televis~on eceiver, ra bb t earTelevision receiver, satellite inputTrash com ~ac tor

WSS, plug-in I Power lhne conditioner I PLCWSS, surge reference equalizer

Electronic, simpleElectronic, dual, externalMotor, mechanical

Power line conditionerElectronic, dual, external

ESEDEMM

PLCI EDE

Videocassette recorder, cable input I Electronic, dual, external 1 EDE

Uninterruptible p ower supplyVacuum cleanerVacuum cleaner, central system

Videocassette recorder, satellite input

Power line conditionerMotor, mechanicalMotor, mechanicalElectronic, dual, internalElectronic, dual, external

PLCM MM M

EDE


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2 8 - S e c t i o n T w o

I Video conferencing I Electronic, dual, externa l I EDETABLE 2.2: Categories of Equipment Victims (Cont.)

I Washer, dishesAppliance 1 Category as victim

Motor, mechanical or electronicHeat, mechanical or electronic

Work sheet

/ Water well pump, indoor, aboveground 1 Motor, mechanical or electronic 1 M M o r ME

Washer, clothesWater well pump, submersed

Motor, mechanical or electronicMotor, mechanical or electronicElectronic, dual, externa l

HM or HEM M or MEEDE


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Q u e s t i o n s t o A s k - 29

EDEWorksheet EDE

Electronic, dual, externalA. HISTORY AND SYMPTOMSAppliance identity

Name of customerAppliance in question

C]Where located in building?Approximate a g e ? y e a r sSymptomsQuit working during normal operation -C]Would not start when turned on -Smoke came out -Acrid smell -Blinking displays -Other -

Has that condition happened before?Previous repair history -Did not report it -

] Reported it but no action -Suggested action failed -Don't knowWeather at the time of the problemBlue sky -High winds -Ice storm -Distant thunder -Local lightning -

C] Don't know -B. TENTATIVE DIAGNOSIS AND REMEDY

Similar problem in neighbor's home?0 es -0 o -

on't know -Power system conditions

Apparently normal -Problem occurred in conjunction with:A utility outage?Other incident? -Describe:

Don't know -System interaction

Proper bonding of power system andcommunications system? (Y/N) -Surge reference equalizerinstalled? (Y/N) -

Other information and remarks by customer:

I Diagnosis / RemedyI System interaction [most likely). See under A. I Install surge reference equalizer.

I Temporan/ overvoltage I Repair if appliance is expensive, or replace.

End-of-life burnout. (How old is equipment?)Mechanical switc h failureSurge on the power line

C. DISPOSITION OF CASE

Replace.RepairWas there a surge reference equalizer? If yes, a tem por ayovervoltane is likelv. If no, install surse reference esualizer.


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3 0 - Se c t r o n T wo

Worksheet ED1Electronic, dual, internal

A. HISTORY AND SYMPTOMSAppliance identity Similar problem in neighbor's home?

Name of customer 0 es -No -

ppliance in question Don't know -Where located in building? Power system conditionsApproximate a g e ? y e a r s Apparently normal -Symptoms Problem occurred in conjunction with:Quit working during normal operation - A utility outage? -

ould not start when turned on - Other incident? -Smoke came outAcrid smell

- Describe:-linking displays - Don't know

OtherHas that condition happened before?

Previous repair historyDid not report itReported it but no actionSuggested action failedDon't know

Weather at the time of the problemBlue skyHigh windsIce storm

17 Distant thunderLocal lightningDon't know

Other information and remarks by customer:How extensive are the communication links- (garage antenna, intrusion switches, thermo-stat controls, etc.)?

( End-of-life burnout. (How old is equipment?) / Replace.

B. TENTATIVE DIAGNOSIS AND REMEDY

I Mechanical swi tch failure I RepairDiagnosis

Surge on the power line

Remedy

- ~pWas there a surge reference equalizer? If yes, a temporaryovervoltage is likely. If no, install surge reference equalizer.

Temporary overvoltage I Repair if appliance is expensive, or replace.C. DISPOSITION OF CASE


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L l u e s ti o n s t o A s k - 31

Worksheet ESElectronic, simple

A. HISTORY AND SYMPTOMSAppliance identity

Name of customerAppliance in questionWhere located in building?Approximate a g e ? y e a r sSymptomsQuit working during normal operation -Would not start when turned on -Smoke came out -Acrid smell -Blinking displays -Other -

Has that condition happened before?Previous repair history -Did not report it -Reported it but no action -Suggested action failed -Don't know -eather at the time of the problemBlue sky -High winds -

l"-J Ice storm -Distant thunder -Local lightning -Don't know -


Similar problem in neighbor's home?0 es -

No -on't know -

Power system conditionsApparently normal -Problem occurred in conjunction with:A utility outage?Other incident? -Describe:

Don't know -Other information and remarks by customer:

DiagnosisEnd-of-life burnout, (How old i s equ~pment?)Mechanical sw itch failure

Temporary overvoltage I Repair if appliance is expenwe, or replace.C. DISPOSITION OF CASE

RemedyReplace.Repair

Surge on the power line Was there a surge reference equalizer? If yes, a temporaryovervoltage is likely. If no, install surge reference equalizer.


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3 2 - S e c t i o n T w o

Worksheet HEHeat, electronic

A. HISTORY AND SYMPTO MSAppliance identity

Name of customerAppliance in questlonWhere located in building?Approximate a g e ? y e a r s

SymptomsQuit working during normal operation -Would not start when turned on -Smoke came out -Acrid smell -Blinking displays -Other -

Has that condition happened before?[7 Previous repair history -

Did not report it -eported it but no action -uggested action Failed -Don't know -Wea ther a t the time of the problem

Blue sky -High winds -Ice storm -Distant thunder -Local lightning -Don't know -


Similar problem in neighbor's home?0 es -

No -] Don't know -

Power system conditionsApparently normal -Problem occurred in conjunction with:A utility outage? -Other incident? -

Describe:

Don't know -Other information and rem arks by customer:

C. DISPOSITION OF CASE

DiagnosisEnd-of-life burnout. (

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