Electrical Surge-Protection Devices for Industrial … Surge-Protection Devices for Industrial ......

1 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 43, NO.1, JANUARY/FEBRUARY 2007

0093-9994/$25.00 © 2007 IEEE

Electrical Surge-Protection Devices for IndustrialFacilities—A Tutorial Review

Kostas Samaras, Member, IEEE, Chet Sandberg, Fellow, IEEE,

Chris J. Salmas, Member, IEEE, and Andreas Koulaxouzidis

Abstract—Industrial facilities are becoming more and moredependent on computer control of their processes, and as a con-sequence, require an increase in cleanliness and reliability ofthe electrical power supply system. Electromechanical subsys-tems are being replaced by electronic logic. Harmonic interference,welding, variable speed drives, and other “in plant” noise havereliable mitigation procedures. However, lightning and otherexternal sourced power disturbances rank high on the list of“uncontrollable” events that have shut down facilities in recentyears. This paper provides an overview of the causes of power-linesurges and their consequences for an industrial plant. The relevantinternational surge-protection standards will be briefly reviewed,and their differences will be analyzed. Different technologies uti-lized in the implementation of various commercially availablesurge-protection devices will be presented, followed by a compar-ative analysis. Finally, the latest trends and the most promisingtechnologies in surge-protection systems as well as their abilityto overcome the problems associated with conventional protectiondevices will be overviewed, and experimental data based on fieldtrials are reported.

Index Terms—Lightning protection, overvoltage protection,surge protection.

I. INTRODUCTION

HE TERM “surge” is used to describe a transient overvolt-age on a power line that has a duration of a few microsec-

onds. A transient overvoltage can exceed the insulation ratingof electrical equipment causing degradation of insulation andimmediate damage to the equipment. Relatively low-amplitudetransient overvoltages applied repetitively on the equipmentwill reduce its mean time before failure. The result will bethat equipment will have to be repaired more often, increasingoperating costs.

Every piece of electronic equipment found in an industrialenvironment is subjected to power surges generated on theutility grid either inside or outside of the plant and are trans-mitted to the equipment via incoming power lines. In order to

Paper PID-06-14, presented at the 2005 IEEE Petroleum and ChemicalIndustry Technical Conference, Denver, CO, September 12–14, and approvedfor publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS

by the Petroleum and Chemical Industry Committee of the IEEE IndustryApplications Society. Manuscript submitted for review September 15, 2005 andreleased for publication September 22, 2006.

K.Samaras and A. Koulaxouzidis are with Raycap Corporation, 151 24Athens, Greece (e-mail: [email protected]).

C. Sandberg is with Shell E&P, Palo Alto, CA 94303 USA (e-mail:[email protected]).

C. J. Salmas is with the Schlumberger Edmonton Product Center, Edmonton,AB T6B 2W9, Canada (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http:iieeexplore.ieee.org.

Digital Object Identifier 10.1 109/TIA.2006.887994

protect their equipment from surges, users are installing surge-protection devices (SPDs) either at the main circuit breakerfor the equipment or the branch circuit breaker depending onequipment ratings. There are several SPDs available, utilizingdifferent overvoltage-protection technologies and topologies.The commercially available SPDs significantly differ in termsof their surge handling capabilities and the level of protectionthey provide. Field experience has revealed serious safety issuesrelated to the SPD operation, particularly during its end-of-lifesituation.

Power surges can cause failure, permanent degradation, ortemporary malfunction of electronic devices and systems. Thedevelopment of an effective SPD is of paramount importanceto manufacturers and users of industrial electronic equipment.Electrical surges have been studied since the 1960s [1]; how-ever, during the last decade, the issue of surge protection forelectronic equipment is receiving more attention. Semiconductorintegrated circuits are much more vulnerable to failure byoverstresses compared to earlier electronic circuits.

Modern semiconductor technology has been widely usedin many industrial applications. Industrial control systems,variable-speed drives (VSDs), electronic measurement andprocess control systems are only a few examples where in-tegrated circuits (electronic switches, power-line carriers, mi-crocontrollers, memory chips, etc.) are now extensively used,replacing older technologies. These systems provide a betterperformance while offering additional features to the user. Onthe other hand, these systems can be damaged from powersurges, causing partial or complete disruption of an industrialprocess, eventually leading to increased maintenance costs andloss of revenue due to discontinuation of the process. Theoil and gas industry is a heavy user of sensitive electronicequipment; thus, the use of surge protection is of paramountimportance.

Almost all manufacturers of industrial-type SPDs use metal–oxide varistors (MOVs) in their design. MOVs are composed ofa thin disk wafer of material (metal–oxide) that has a knownvoltage breakdown characteristic. At low voltages, the MOVconducts very little current (microamperes). As the voltageapproaches breakdown, the MOV then begins to conduct current.At voltages slightly above the break down, large currents flow,effectively clamping the output voltage. This clamping featureallows the higher voltage levels to be shunted to ground,preventing overvoltages on equipment. Figs. 1 and 2 show thevoltage waveform before and after an ideal SPD.

This paper describes in brief the power-line surges and theirimpact on industrial facilities with concentration on gas and

T

SAMARAS et al.: ELECTRICAL SURGE-PROTECTION DEVICES FOR INDUSTRIAL FACILITIES—TUTORIAL REVIEW 2

Fig. 2. Voltage waveform after an ideal SPD.

oil facilities. It provides an overview of the commerciallyavailable surge-protection technologies designed for industrialapplications, emphasizing their principle of operation followedby a comparative analysis among different technologies. Abrief description of the relevant international standards is alsoprovided. Some representative examples of hardware failuredue to surges as well as SPD failures will be described. Finally,the latest technologies in SPDs and their advantages comparedto conventional protection devices will be overviewed, and thedata collected from field trials are provided.

II. CAUSES OF POWER-LINE SURGES

Power surges and transient overvoltages are due to the sud-den change in the electrical conditions of a circuit and therelease of large amounts of energy stored in the inductance andcapacitance elements of the system. Sources of power surgescan be external or internal to the facility. External sources oftransient overvoltages can be [1] the following:

1) lightning;

2) switching (on/off) of capacitor banks, for power coeffi-cient correction;

3) power-line disconnection and reconnection;4) transformer switching on/off;

5) electrostatic discharges;6) power utility load switching;7) poor quality of power transmission and distribution grids.

Internal surges are caused by the operation of the followingdevices:

1) circuit breakers or fuses;

2) electric motors, i.e., elevators;3) air conditioners;4) VSDs generators.Fig. 3. Simplified relationships between voltage,

duration, rate of change, and their effects on equipment.

III. INTERNATIONAL SPD STANDARDS OVERVIEW

In this section, we briefly describe the standards which areapplicable to the evaluation of SPD performance and safety.The following aspects are covered in general:

1) location of the SPD installation, classification accordingto the estimated surge exposure level at a particularlocation, and the surge withstand capability of the device;

2) determination of the voltage and current waveforms to beused for testing;

3) recommendation of the test equipment and the testprocedures;

4) safety of SPDs.

Every SPD must be tested according to the recommendationsof the following standards.

IEEE C62.41.1-2002—This standard forms a guide on thesurge environment in low-voltage ac power circuits. The surgesconsidered in this standard do not exceed one half cycle of thenormal mains waveform (fundamental frequency) in duration[2]. They can be periodic or random events and can appearin any combination of line, neutral, or grounding conductors.Their amplitude, durations, or rates of change can be sufficientto cause equipment damage or operational upset, as presented inthe general diagram shown in Fig. 3. While SPDs acting primarilyon the amplitude of the voltage or current are often applied todivert the damaging surges, the upsetting surges might requireother remedies, as for example, voltage regulators.

This standard also includes a comprehensive reference listof documents supporting the fundamental concepts adoptedby the standard. Finally, the standard extensively presents thelimitations and resulting assumptions or simplifications madeto develop a definition of a representative generic environment.

IEEE C62.41.2-2002—This standard describes the conceptof the location categories and determines the test waveformsand amplitudes of the voltage and current that best approximatepower-line surges at each location category [3].

Fig. 1. Voltage waveform before SPD.


TABLE IEQUATIONS FOR STANDARD SURGE TEST WAVEFORMS

According to the location category concept, LocationCategory A applies to the parts of the installation at somedistance from the service entrance—the main distribution panelof an electrical installation of a building. Location Category Capplies to the external part of a structure. Location Category Bextends between Location Categories C and A. Because thereality of surge propagation is a continuous situation, separatingthe categories by sharp conceptual boundaries would be anarbitrary and debatable process. Instead, the concept of locationcategories recognizes the existence of transition bands thatconnect the categories by overlapping.

Three representative surge waveforms are described in thisstandard. These are the “Combination Wave,” the “100-kHz

Ring Wave,” and the “10-/1000-us Long Wave” which arebriefly described here. The mathematical equations for thecombination wave and the ring wave are given in Table I.

Combination wave—The combination wave is delivered by

a generator that can apply a 1.2-/50-us voltage across an open

circuit and an 8-/20-us current wave into a short circuit. Theexact waveform that is delivered is determined by the generatorand impedance of the SPD under test. A plot of the nominalopen-circuit voltage is shown in Fig. 4, and a plot of the nominalshort-circuit current is shown in Fig. 5. The open-circuit voltage

waveform has a front time equal to 1.2 us and duration equal

to 50 us. The front time is defined as 1.67 x (t90 -

t30),

where t90and t

30 are the times of the 90% and the 30%amplitudes on the leading edge of the waveform. The durationis defined as the time between the virtual origin and the 50%amplitude point of the tail. The virtual origin is the point wherethe straight line between the 30% and 90% points on the leading

edge of the waveform intersects the V = 0 line.

Fig. 4. Combination wave open-circuit voltage.

Fig. 5. Combination wave short-circuit current.

Fig. 6. 100-kHz ring wave voltage waveform.

The short-circuit current waveform has a front time of 8 us

and duration of 20 us. The front time in this case is defined as

1 .25 x (t90 -

t10)

wheret90

and t10 are times of the 90% and

10% points on the leading edge of the waveform.100-kHz ring wave—This waveform is used to simulate

oscillatory phenomena related to direct lightning strikes. Noshort-circuit current waveform is specified for the 100-kHzring wave. The peak short-circuit current amplitude is selectedaccording to the location category of the SPD. The waveformof the 100-kHz ring wave is plotted in Fig. 6.


Fig. 7. 10-/1000-µs long wave.

10-/1000-us long wave—The long duration of the 10-/1000-us long wave plotted in Fig. 7 has a front time of 10 usand duration of 1000 us. The long duration of this waveformreduces the effect of wiring inductance of the power lines.

IEEE C62.45-2002—This standard focuses on test procedurefor SPDs used in low-voltage ac circuits, by applying the rep-resentative surge waveforms described previously. It providesspecifications of the test equipment, its calibration procedure,and practical guidance on the way the test is performed [4].

The above three standards are widely known as the“Trilogy” concerning the occurrence, characterization, andtesting of surges in low-voltage ac power circuits.

NEMA LS-1—This international standard provides a uniformspecification for evaluating the performance of SPDs for low-voltage (less than 1000 Vrms) transient surge environment. Thedocument presents a comprehensive description of thespecification parameters like the maximum continuous oper-ating voltage, the maximum surge current, and the clampingvoltage. It also provides the methodology of determining thesespecification parameters [5].

IEC 61643-1—This part of IEC 61643 is applicable tolow-voltage SPD devices for surge protection against indirectand direct effects of lightning or other transient overvoltages.Performance characteristics and standard methods for testingand ratings are established for these devices. According to thestandard, SPDs are divided into three classes depending on theirperformance [6].

1) Class I devices are tested using a current waveform de-fined by its peak current value and the charge transferredfrom the surge generator to the device under test. Theexact shape of the current waveform is not specified;however, the 10-/350-us waveform is commonly used tocharacterize class I products.

2) Class II and Class III devices are tested using the1.2-/50–8-/20-us combination wave, as it is defined inIEEE C62.41.2-2002. Devices tested at open-circuit voltageand short-circuit current lower or equal to 20 and 10kA, respectively, are characterized as Class III products.Above these values, SPDs are characterized as Class IIproducts.

The above standards are widely used by manufacturers toevaluate the performance of their SPDs. They also serve asthereference tools to assist the users of the SPDs to compare dif-

ferent technologies and to select the most appropriate productfor a particular application.

Even though all the above standards are valid worldwide,there is a preference depending on the geographic region. IEEEstandards are mostly used in the North-American region, whileEurope shows a preference to IEC standards. The reason behindthis is that different technologies of SPDs are accepted in thesetwo main market regions. The use of voltage switching-typeSPDs (also called “crowbar type” devices), like spark gapsand gas tubes, are allowed to be used as low-voltage SPDs inEurope. In North America on the other hand, voltage-limiting-type devices (varistors and diodes, also called “clamping-type”devices) are only allowed to be used at the low-voltage serviceentrance of sensitive electronic equipment. The North Americanmarket has excluded “crowbar” devices from protecting sensitiveelectronic equipment due to the proven harmful interference thatcrowbar devices induce during their conducting stage on theelectronic equipment that they intend to protect.

When an SPD operates during a transient surge, high current(tens or hundreds of kiloampere) is passing through the deviceheading to ground. Even though the internal resistance of theSPD is generally low during the conduction stage, it is still largeenough to generate large amount of thermal energy inside thedevice. Catastrophic failure of SPDs can also occur as the resultof abnormal overvoltage. Abnormal overvoltages occur due tofaults in the power-line network. For example, loss of neutralline, line-to-neutral short circuit, or primary to secondary faultin a medium voltage transformer. All conditions describedabove can lead to a catastrophic thermal breakdown of an SPD,turning it into a potential hazard for personnel and equipmentin close proximity of the device. Some examples of catastrophicSPD failures will be presented later in this paper.

The safety issues related to the use of SPD products areaddressed by Underwriters Laboratories (UL), an independentsafety organization. The standard related to SPD products isthe UL 1449 2nd edition. This standard recommends testingprocedures for both the mechanical and the electrical char-acteristics of the device. Every SPD is required to complywith this standard. In 1998, the UL 1449 2nd edition standardbecame effective with special provisions to address the “slowburn” or “thermal runaway” failure mode of SPDs, responsiblefor catastrophic events which could compromise the safety ofelectrical installations. One of the key tests required by UL1449 2nd edition is the limited current abnormal overvoltagetest. This test examines the end-of-life condition of the SPDat relatively low short-circuit currents. During this test, therms voltage applied on the SPD terminals is regulated so thata constant current of 5-A rms is passing through the device.The test requires that the SPD withstands the heat generatedinside the device for 7 h without emitting fire or smoke [7]. Themajority of the SPDs include thermal disconnect mechanismsto isolate the SPD from the power supply before the SPD isdamaged.

UL 1449 2nd edition also evaluates the end-of-life conditionof the SPDs when exposed to high short-circuit currents. Thistest is known as the short-circuit current abnormal overvoltagetest. During this test, the overvoltage is applied on the SPD


for 7 h. The short-circuit current is not limited; therefore, thefull available short-circuit current can pass through the SPDdevice. The test is considered successful if the SPD becomesdisconnected from the ac supply by an overcurrent disconnectiondevice, preventing a catastrophic failure of the SPD.

In 2005, UL revised this standard after receiving reportson catastrophic failure of UL listed or recognized SPD products.The revised version of UL 1449 2nd edition standard becomeseffective in February 2007. This revised standard extends thecurrent range of the abnormal overvoltage testing to includenot only the low short-circuit current range (up to 5 A) andthe high short-circuit current range (from 25000 up to 200 000A), but also to include intermediate short-circuit currents (100,500, and 1000 A). All UL listed or recognized SPDs sold in themarket must meet these revised safety requirements of the newUL 1449 2nd edition standard.

IV. OVERVIEW OF SPD TECHNOLOGIES

A. SPD Technologies

There are three basic types of components: the gas dischargetube (GDT), the silicon avalanche diode (SAD), and theMOV. These components have significant differences in termsof the principle of operation, the performance characteristics,and the ability to handle high transient currents. In thissection, we present the main advantages and disadvantages ofeach of the above technologies with particular focus ontheir suitability as surge protectors for low-voltage industrialcontrol systems.

The GDT uses specially designed electrodes fitted insidea tube filled with one or more gases under pressure. Theyare rugged, relatively inexpensive, and have a small shuntcapacitance; therefore, they do not limit the bandwidth of high-frequency circuits as much as other nonlinear components.However, there are three major drawbacks that prohibit theiruse in low-voltage industrial applications involving sensitiveequipment.

1) They can be slow to conduct. The conduction thresholddepends on the rate of change of the transient voltage,which is usually in the order of several hundreds of volts.This level of protection is inadequate to prevent damagein sensitive electronic systems like VSDs.

2) In some situations, they are difficult to turn off after thetransient has ended. This phenomenon is described as thefollow current. The presence of follow current results intemporary disconnection of the power to the equipmentto be protected for as long as the follow current lasts.

3) The spark, which is developed between the electrodes ina GDT, is a violent effect. When the GDT switches fromthe insulating state to the conduction state, the high value

of dI/dt can cause problems to the equipment close tothe GDT.

SADs are semiconductor devices that can respond rapidly toa transient voltage surge. They clamp the transient overvoltageat a relatively low residual voltage. On the other hand, theysuffer from low energy withstand capability. To overcome this

problem, SPD manufacturers combine several SAD compo-nents in order to equally share the energy of a surge event withinthe rated parameters of the SAD device. However, installationsin locations, where frequent as well as high energy transientsoccur, have revealed the inability of SAD-type SPDs to with-stand high energy transients without failing, while effectivelyprotecting the equipment.

MOV-type surge suppressors can withstand high transientsurges, at the same time maintaining sufficiently low clampingvoltages to protect the equipment. For this reason, MOV-basedSPD systems are considered to be the most effective protectiontechnology for industrial applications.

There are two types of MOV-based SPDs available forindustrial environments. The first one utilizes a combina-tion of parallel MOVs, while the second type uses a singleMOV disk.

The first type uses commercial-type small-diameter MOVs,which are primarily designed to protect individual electronicPCBs. Individual commercial-type MOVs do not have therequired energy handling capability to protect an electronicequipment from intense surges. They typically consist of anMOV disk with a diameter of up to 20 mm coated with resinto prevent moisture ingress, which deteriorates the performanceand shortens the life of the product. To overcome this problem,several MOVs are connected in parallel to increase the surgecurrent capacity of the SPD. The vast majority of SPD manu-facturers are using parallel MOV technology. The differencesbetween all these products are mainly focused on the diameterand the number of the MOVs and the casing. They are designedto be installed in power distribution panels (DIN-rail mounteddevices), or as a stand-alone permanently connected SPDdevice.

The application of these devices for protection of industrialequipment revealed several problems regarding their perfor-mance and safety which will be described in Section V.

The second type of surge protection is based on the use of asingle MOV disk capable of adequately handling the energy ofthe surge event. This is achieved by utilizing an industrial gradeMOV material and by increasing the disk diameter to 80 mm.Resin coating has been replaced with an aluminum housingwhich also acts as a heat sink to the MOV. This type of SPDtechnology will be described in detail in Section VI.

B. Modes of Protection

A typical single phase configuration of the power serviceincludes one phase wire and one neutral wire, which sometimesis grounded at the service entrance of an installation. There arethree modes of protection.

1) Line-to-neutral (L-N)—An SPD module installed betweenthe line and the neutral protects the equipment from surgesoriginated mainly from disturbances generated on thedistribution grid. It can be caused by capacitor bankswitching, operation of transfer switches, or by the switchingon/off of nearby equipment (air conditioners, elevators,motors, generators, etc.).


Fig. 9. Exploded multiple-MOV-based SPD module.

Fig. 8. Multiple-MOV-based SPD.

2) Neutral-to-ground (N-G)—It protects from surges devel-oped between the neutral conductor and the ground.

3) Line-to-ground (L-G)—It protects from surges developedbetween the line and the ground.

It is essential that an SPD protects from all the above modes.In a typical three phase WYE configuration system, whichincludes three line wires and one neutral wire, the SPD mustprovide seven modes of protection: three for L-N, one for N-G,and three for L-G.

V. EXISTING PROBLEMS WITH SPD DEVICES

A. Poor Design and Assumptions in Design

It is a common practice in the surge-protection industry toinstall protection devices in parallel to achieve a higher ratingthan just one device. A typical example of a conventional SPDusing parallel MOV technology is shown in Fig. 8. This practiceapplies whatever the technology is in use. It is also commonlyassumed that the surge performance of a number of devicesis a simple multiplication of the performance of an individualdevice. This is not the case both electrically and mechanically[1]. Even semiconductor devices fabricated on the same slicevary in performance due to the minor defects and/or impuritiesin the lattice of the semiconductor material.

Differences in mechanical design can lead to one individualMOV always having to handle more current than its neighbors.As a rule, an electrical transient takes the shortest most con-ductive path, and when it goes around the corners, it exertsforces on the current carrying conductors (Lorentz forces). Thenet result is that for large transient currents, such as thoseproduced by lightning, SPDs often explode as a result of theseforces and energies dissipated in one device rather than themany. An example is shown in Fig. 9. This picture was takenfrom an actual installation. This device shows a catastrophicfailure even though it has been tested to comply with UL1449 2nd edition. Another example of catastrophic failure isgiven in Fig. 10.

Several SPD designs exist that attempt to achieve equal pathlengths for the devices placed in parallel. These designs do leadto an increased resistance to transient events but tend to sufferfrom longer events as the characteristics of the devices areaffected by temperature and by no means do all the devices in

Fig. 10. SPD internal fire.

one of these designs have the same ability to dissipate thermalenergy equally.

B. Fusing

Thermal fuses are known to have reliability issues and ageover a period of a few years usually accentuated by thermalcycling. Conventional and thermal fuses also suffer aging frommechanical shock. Mechanical shock can be delivered duringoperation of the SPD by the transients. Martzloff [8] showedthat fuses are progressively weakened by transient currents. Inother words, the reliability of the protector is reduced as a resultof including a device that is present to protect the protector orpresent to protect you from the protector. Obviously, when afuse opens, the protector is rendered totally ineffective, leavingthe equipment unprotected to subsequent surges.

C. Emission of Smoke and Fire

The photograph in Fig. 11 shows an SPD that has suffereda varistor fire. The SPD modules are protected by 30-A fastblow fuses. These fuses were intact and still providing powerto the unit. Investigation showed that the cause of the firewas thermal runaway of the surge protector modules insidethe SPD. No raised system voltages were detected, and it isbelieved that the device was wrongly sized for its exposure totransients in a high lightning area and simply wore out fromoverstress. Consider that a 30-A fuse can carry 20 A for aconsiderable time, certainly greater than 1000 h, and during thistime on a 120-V system, 2400 W could be dissipated inside theindividual SPD.


Fig. 11. SPD internal fire.

VI. INTEGRATION OF SPDS

There are two methodologies that can be employed to protectindustrial equipment. One method is to connect the SPD externalto a power distribution panel. This method of installation doesnot provide a sufficient level of protection to the equipment athigh surge currents, as will be explained in the next section. Thesecond method is to integrate the SPD devices withinpanelboards, switchboards, switchgear, motor control centers,VSDs, or other electrical equipment. Integration of SPDdevices ensures the lowest clamping voltage, thus the highestlevel of protection to the equipment.

Important items to consider in the selection of SPDs for anintegrated application are the following.

1) The location of the SPD should achieve the best electricalconnection with respect to the phase, neutral, and groundbuses in the electrical distribution equipment to effec-tively suppress the transient overvoltages to a voltagelevel which is lower than the immunity level of theequipment. The use of long lead wires as well as wirebending should ideally be eliminated.

2) An SPD must be compatible with the available short-circuit current of the power distribution system and havethe appropriate ratings and listings.

The system design engineers must ensure that the SPDs havebeen listed as UL recognized components and have successfullypassed all the safety tests described in the UL 1449 2nd editionstandard, including the recent changes effective February 2007,before approving the SPDs for integration. In particular, it isessential that when SPDs are to be integrated into an industrialsystem, the SPD must sustain the available fault current of thepower system for a period of at least three complete cycles ofthe sinusoidal current waveform without a catastrophic failure.This test is known as three-cycle testing. This test ensures thatthe SPD will withstand a fault condition for sufficiently longtime to allow the upstream circuit breaker to disconnect andclear the fault. Failure to comply with this test may result ina catastrophic failure of the SPD before the operation of theovercurrent protection device and constitute a safety hazardfor the personnel and the adjacent equipment. A typical avail-able short-circuit current value for VSD industrial applicationsis 65-kA rms symmetrical.

A. Problems With Conventional SPD Technologies

Electronic VSDs are extensively utilized by the oil industryfor the speed control of electric motors used in several steps ofthe oil extraction process. VSDs are connected to the utility gridand powered by a three-phase three-wire low-voltage system.They include semiconductor components which are sensitive tosurges coming through the power wires. Many years of fieldexperience has shown that power surge is the most frequentreason for VSD failures whether as a result of a serious transientevent or a multiple of events over time which compromisesthe insulating levels of components. This results in a loss ofproduction, which results in increased maintenance costs and asignificant revenue loss.

To overcome this problem, VSD users have tried to protecttheir equipment using conventional SPDs based on fused multipleMOV technology. Fig. 12 shows the interconnection diagram of aconventional SPD device installed in VSDs used to controlESPs. The SPD, which is located outside the VSD cabinet, isconnected to the power wires via a fused three-wire powercable.

Field application of this protection scheme has shown thefollowing problems.

1) Conventional SPDs are using fuses to disconnect thedevice and protect it from fire or explosion. This unavoid-ably leaves the VSD unprotected to a subsequent surgewhen fuses are blown.

2) Repetitive high energy surges may result in a catastrophicfailure of the SPD. An example is shown in Fig. 13.

3) The conventional SPD requires the use of leads and fusingto connect in parallel to the line side of the breakerand cannot be mounted inside the equipment due tothe catastrophic failure condition of the device in caseof a high energy event. The length of the leads addsimpedance to the circuit and increases the residual voltage.

The residual voltage is increased by L × (dI/dt) + I ×R, where L is the self-inductance of the leads, dI/dt is

the rate of change of the surge current, and R is theresistance of the lead wire. This results in residual voltagesthat are higher than desired, potentially leading toequipment damage. Assuming that the inductance of the

wire is 0.255 µH/m, its resistivity is 1 mΩ/m, then, for atotal conductor leads length of 1 m and for surge current10 kA (8/20 waveform), the residual voltage is increasedby approximately 115 V.

Fig. 12. Protection of VSD equipment using conventional SPD technologies.

VII. APPLICATION OF SPDS IN VSDS FOR USE WITH

ELECTRICAL SUBMERSIBLE PUMPS (ESPS)


Fig. 13. Failure of conventional SPD.

Fig. 14. Single-MOV-based SPD module.

B. Solution: Single MOV Technology

As part of the quality health safety and environment policies,the upmost importance is placed on ensuring human health,operational safety, and protection of equipment, hence thepush to evaluate an alternative SPD technology for theprotection of VSD from power surges. This technology is basedon the use of a single MOV disk capable of adequatelyhandling the energy of the surge event, while keeping at thesame time the residual voltage at a level lower than theovervoltage immunity level of the equipment. Thistechnology has been widely used for the protection of criticaltelecommunication and power utility equipment worldwide,particularly in locations highly exposed to lightning surges.

This technology utilizes one industrial grade MOV diskwhich is encapsulated into an aluminum casing which sealsthe MOV from moisture and acts as a heat sink. The aluminumelectrodes contact the entire surface of the MOV providing aneven distribution of the surge current over the total area of theMOV. This design, contrary to the majority of other SPDtechnologies, does not incorporate a thermal disconnectmechanism, and it is proven to comply the UL 1449 2ndedition. The single MOV-based SPD is illustrated in Fig.14.

Fig. 16. Protection of VSD equipment using single-MOV protection modulesinstalled “in-line.”

Due to its robust construction and the absence of flammablematerials in its housing, this design enabled the installation ofthe SPD inside the VSD cabinet, as shown in Fig. 15. Fur-thermore, the absence of fuse enables the “in-line” installationof the SPDs. They are connected directly on the load sideof the breaker, eliminating the need for long lead wires. Ageneral diagram of the “in-line” connection is illustrated inFig. 16.

A key advantage of this innovative method of protection isthe ability to protect the equipment under any surge condition.In the rare event of extremely high energy surges, the SPDfails in a short-circuit mode, thus enabling the breaker to tripand disconnect power from the equipment, thus protecting theequipment from subsequent surges.

Laboratory tests have proven the ability of the single MOV-based SPD to handle extremely large amounts of thermal en-ergy. The amount of energy that an SPD can handle is described

by its I2t parameter, which is measured to be greater than500 MA2s for the device illustrated in Fig. 14.

VIII. EXPERIMENTAL RESULTS

In this paragraph, we report the results from experimentaltesting done both in actual field installations as well as in thelaboratory environment. These results demonstrate the funda-mental differences in performance between devices based ondifferent technologies.

Fig. 15. Single-MOV protection modules installed “in-line” inside a 815-kVAsine wave drive.


Fig. 17. Power-line transient overvoltages measured in a 24-h period beforeinstalling single-MOV-based SPD (Site A).

Fig. 18. Power-line surges measured in a 24-h period after installing thesingle-MOV-based SPDs (Site A).

A. Results From a Field Trial

For the purposes of this paper and in order to evaluate theperformance of the single MOV-based module versus conven-tional surge-protection modules, two installation sites of thesame type of VSD, with rich history of severe power surgeproblems, were selected for the trial installation.

Site A: Protection of the VSD using the single-MOV-basedSPD device.

Site B: Protection of the VSD using a conventional parallelMOV-based-SPD device.

The purpose of this field experiment was to record the leveland the amount of surges on the VSD (over a period of 24 h)without protection and also after the installation of the protec-tion devices to examine the efficiency of the protection devicesin alleviating those surges. Since the observation period wasrather limited, we have carefully selected two sites in an areaof the plant where several failures had been recorded in thepast. This selection maximizes the likelihood of recording asignificant amount of surges. Most of those surges are dueto switching and operations inside the plant and not due tolightning. In both sites, the electrical configuration was iden-tical, a three-wire 240-/415-V three-phase system. In the caseof Site A, three single-MOV modules were installed betweeneach of the three power lines and the ground/protected earth.Fig. 15 illustrates the type of configuration used to connectthe SPDs on the load side of the VSD breaker. In Site B,the parallel MOV-based TVSS system was installed externallyto the drive cabinet due to space limitations inside the drive.

A power-line monitoring device (Powertronics, PQR-2020)was installed prior to the installation of the SPD modules.The device was set to record every transient overvoltage witha peak amplitude of at least 50 V higher than the nominalline to ground voltage of 240 Vrms and a duration of atleast 05 /is. Therefore, the device was essentially recordingsurges of amplitude higher than 290 V. The time and peakamplitude of the overvoltages, recorded for a period of 24 h,

Fig. 19. Power-line transient overvoltages measured in a 24-h period before

installing conventional SPD (Site B).

are shown in Fig. 17, for Site A—prior to the installationof the SPD. This diagram shows surges recorded on allthree phases of the system. Only the overvoltage level above240 V is shown, i.e., for a point of this diagram with avalue of 100 V, the actual overvoltage corresponding to itwas 340 V. A significant number of surges have beenrecorded having peak amplitude voltages up to 652 V. Thesame monitoring setup was used after the installation of thethree single MOV SPDs, and measurements were recordedfor a period of 24 h again. The results are shown in Fig.18, and as it is clear, the situation was drastically improved.

In Site B, we followed exactly the same procedure as above,for Site A. Measurements were recorded before and afterthe installation of the parallel MOV SPDs. The distributionof the surges’ magnitude as a function of time, before andafter the installation of the SPD, is given in Figs. 19 and 20,respectively.

Examining the results plotted in Figs. 17–20, it becomesapparent that the protection of VSD from power-line surges isabsolutely necessary. The installation of the single MOV-basedSPD has drastically reduced the frequency that surges appear.Furthermore, the peak amplitude of the surges has been reducedto a maximum of 215 V, thus ensuring a sufficient protection of


Fig. 20. Power-line surges measured in a 24-h period after installing aconventional parallel-MOV-based TVSS (Site B).

TABLE IISURGE STATISTICS IN 24-h PERIODS

the VSD. Table II summarizes the results obtained from sites Aand B. The use of the single MOV-based SPD reduced the totalnumber of surges encountered by the equipment in the 24-h testperiod by 84%.

The parallel MOV-based device on the other hand failed toprovide a sufficient protection to the equipment. The averagepeak amplitude of the surges was reduced only by 18.5%,allowing the peak amplitude of eight surges to exceed 500 Vin the 24-h test period.

B. Laboratory Tests

In addition to the results from the field installation describedin the previous paragraph, we have conducted a series oftests in a laboratory environment, using different surge wave-forms. In those tests, we try to simulate the effects of agingon SPDs. In several field installations, we have beenencountering situations where the protected equipment wasfailing without failure of the SPDs. With the tests de-scribed below, we prove that certain devices demonstratea nonconsistent level of protection over time, i.e., when aparallel-MOV device is exposed to consecutive surges, its

Fig. 21. Residual voltage and surge current through a parallel-MOV deviceduring successive strikes.

performance characteristics do not remain constant and dete-riorate over time.

1) Residual Voltage: In the first test, a parallel-MOV devicewas exposed to a series of surge events while monitoringthe residual voltage and the actual current through the de-vice after every surge hit. Ten surges were applied to thedevice, each of them having an amplitude of approximately9 kA. The waveform used was the typical 8/20 waveformas described in IEEE C62.41. Between successive surges,we allowed for 1-min delay in order to allow the deviceto cool down. The residual voltage and the current throughthe device are plotted on the same graph in Fig. 21 for allten hits.

As shown in the above diagram, we have observed a sig-nificant change in the values of the residual voltage and thelet-through current as a function of time. The initial residualvoltage recorded during the first hit was 1484 V, while duringthe tenth hit, the residual voltage was increased to 3335 V.This represents a variation of 125%, which is translated intosignificantly reduced protection level offered to the equipmentwhich may have been connected downstream from the SPD. Atthe same time, the current through the device was reduced toapproximately 8000 A—starting from 9000 A during the firstsurge event.

In a similar test setup, we have exposed a single MOVdevice to a series of 2000 surges of 8/20 waveform withamplitude of approximately 20 kA. We allowed for a 1-mindelay between successive surges. We measured the let-throughvoltage during the first surge, and it was found 810 V. We alsomeasured the let-through voltage during the last surge, and itwas found 822 V, showing a variation in its performance ofless than 1.5%.

2) Long-Duration Surges: As mentioned before, not allsurges happening in the field are following the typical8/20 model which accurately describes short-term high-intensity surge events mainly due to lightning. In reality andin most industrial environments (especially in geographic areaswhere lightning is not a major concern), surges are mainlydue to load switching, capacitor switching, etc. These surgestend to have significantly lower intensity but at the same timesignificantly larger duration. IEEE C62. 11 describes a wave-form which is regarded as describing such events. This is a


Fig. 22. Measured residual voltages of single-MOV and multiple-MOV SPDs.

rectangular (square) waveform of duration 2 ms and magnitudein the order of 500–1000 A. The occurrence of surges likethose in industrial environments is associated with what is knownas failure due to the accumulated events. The intensity of thosesurges is not that high to cause an immediate failure of theSPD as may have happened during a lightning strike, but theydo carry significant amounts of energy (due to their longerduration) which cause degradation in the material of the SPD.The result is that after a number of exposures to such events,devices fail.

We have exposed a parallel MOV device to a number ofsquare waveform surges, and we have recorded its performance.During the first surge at 913 A, we did not observe anyvisible damage to the device. During the second 2-ms surgeat 931 A, the device emitted heavy smoke, but it did notfail. During the third surge, the device got on fire and someof the MOVs exploded/disintegrated—this is regarded as afailure. The residual voltage measured during the first surgewas 700 V. During the second surge, the residual voltage was1890 V, and during the third surge, it was measured at 3360 V,a 380% degradation.

In a similar test setup, we have exposed a single MOVdevice to a series of 250 square waveform surges of amplitude1030 A. We allowed for a 1-min delay between successivesurges. We measured the let-through voltage during the firstsurge, and it was found 335 V. We also measured the let-through voltage during the last surge, and it was found 339 V.No visible damage or smoke emission or fire was observedduring the test.

3) Slope Resistance: The comparison of slope resistancefor a single MOV and a parallel MOV device is shown inFig. 20. To obtain these measurements, the standard 8/20 surgewaveforms were used at the levels indicated on the graph.In particular, the diagram shown in Fig. 22 is a plot of themeasured residual voltage as a function of the surge currentpassing through the device, for single MOV and parallel MOVSPDs. The graph shows that single MOV devices exhibit lowslope resistance which results in lower residual voltages atintermediate and high surge currents compared to the residual

voltage of the multiple MOV-based products.

IX. COMPARISON OF MULTIPLE MOV AND SINGLE MOVSPD TECHNOLOGIES

In Section V of this paper, the drawbacks of conventionalmultiple MOV-based low-voltage SPD devices were presented.The idea of an SPD design based on the use of a singleMOV was developed a few years ago in order to overcomethose problems. The main advantages of this design com-pared to the multiple MOV-based devices are summarizedbelow.

1) No need for thermal disconnect mechanism to protectthe SPD. This is due to the material and design of itshousing. The absence of a disconnect mechanism ensuresthat the equipment will never be left unprotected duringa surge event. Furthermore, disconnect mechanisms areresponsible for increased residual voltage across the SPDterminals.

2) The use of just one industrial grade epoxy free MOVeliminates the problems related to multiple MOV designswhich were discussed in detail in Section V.

3) The metallic casing of the design as well as the absence offlammable materials allows the device to dissipate largeamount of thermal energy, resulting in an increased surgecurrent capability.

X. CONCLUSION

In this paper, we have provided a tutorial overview of thecritical issue of overvoltage protection for industrial electronicapplications with primary focus on the Oil/Gas/Mining indus-tries. We have presented the available technologies utilizedfor the implementation of surge-protection systems, and wehave outlined their basic advantages and disadvantages. A de-tailed description and references to the international standardsare provided. Finally, we have described a new technologicalconcept currently under extended trials worldwide as well asresults from its application. Field trial results as well as mea-surements in lab environment are provided. Strong indicationsexist to prove that this new technology can provide superiorperformance and complete protection to critical industrial plants.

REFERENCES

[1]R. B. Standler, Protection of Electronic Circuits From Overvoltages.New York: Dover, 2002.

[2]IEEE Guide on the Surge Environment in Low Voltage (1000 Vor Less) ACPower Circuits, IEEE C62.41.1-2002.

[3]IEEE Recommended Practice on Characterization of Surges in Low-Voltage (1000 or Less) AC Power Circuits, IEEE C62.41.2-2002.

[4]IEEE Recommended Practice on Surge Testing for Equipment Connectedto Low-Voltage (1000 or Less) AC Power Circuits, IEEE C62.45-2002.

[5]Surge Protective Devices Connected to Low-Voltage Power DistributionSystems, IEC 61643-1.

[6]Transient Voltage Surge Suppressors, UL 1449, 2nd ed., 2005.[7]Low Voltage Surge Protection Devices, NEMA LS-1-1992. Nat. Elect.

Manuf. Assoc.[8]F. D. Martzloff, “Matching surge protective devices to their envi-

ronment,” IEEE Trans. Ind. Appl., vol. IA-21, no. 1, pp. 99–106,Jan./Feb. 1985.

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