BATTERIES: ALWAYS EXPECTED TO PERFORM BUT WHY DON'T THEY?

Copyright Material IEEEPaper No. PCIC-2006-16

Roger N. PocockMember, IEEE; CSISaft America, Inc3 Powdered Metal DriveNorth Haven, CT 06473USAroger. popcock@saftbatteries.com

E. Roy Hamilton, P.E.Member, IEEEChevron ETC/MEE3901 Briarpark Dr.Houston, TX 77042-5301USAerha@chevron.com

Abstract - DC back-up power is vital to most refinery and oilproduction processes. The environment associated with manyof these back-up supplies is usually aggressive. If the batterywere to fail, the results would be costly. This type of problem isavoidable through the application of an alternative class ofbattery. This is but one aspect for consideration when selectingbatteries. The authors will review real life scenarios of wrongchoices and offer alternative solutions. The intent of the Paperis to offer suggestion when selecting batteries so as to avoiddramatic repercussions.

Index Terms - Reliability; open circuit failures; thermalrunaway; sealed batteries (VRLA); nickel-cadmium (Ni-Cd);lead-acid; offshore platforms; battery maintenance.

I. INTRODUCTION

The paper will explore the causes of premature battery failureand the solutions. Examples of failures in the field will bereviewed, the impacts of these on production, together withsolutions that were offered to the operators. This paper willprovide information about battery differences, the importance ofthe location of the battery as well as the levels of reliability fromone type to another. The paper will review types of batteriesand when and where to use them. It endeavors to challengethe user to use life cycle costing when making decisions.

While the paper offers information and recommendations, thereaders are encouraged to inform themselves about batteriesand match them appropriately to their application. In thismanner, the costly failures may be reduced to a minimum infuture.

II. HISTORY AND BACKGROUND

A recent failure of a battery was attributed to the use of thewrong battery. The application was back up to a turbine threeyears' ago. The cost to the operator was in the millions ofdollars. The main reason for the battery selection was costdriven, with first cost being the driver. The operator elected toupgrade to a substantially more reliable battery, which would notfail open circuit, nor last less than 5 years. The operatorthought that his battery carried a 20-year warranty. It wasdiscovered that such a warranty has conditions.

Lower cost considerations drove the selection of replacementbattery banks for a 160,000-bbl/day offshore oil production'splatform power generation turbine starting motive power andturbine controller supply. The two original Ni-Cd battery banksfailed after 20 years of reliable service in a severe application

(high ambient temperatures of 100°F to 120°F, deep cycledischarge, and large number of discharges). A recommendationto replace the battery banks in kind was not taken, and insteadlower cost sealed lead-acid replacement battery banks werechosen based solely on cost. These batteries failed within 6months to a year of service.

In several major offshore oil and gas production platform UPSapplications, VRLA battery banks failed after 5 years of service;original expectations were for a 20-year service life. The batterytechnology was chosen solely for footprint and weightconsiderations and a 20 yr warranty. For these particularfacilities, the various battery rooms' ambient temperature couldnot reliably be held below a maximum of 78°F. This was aprimary cause that led to their premature failure. The failedbattery banks were replaced with a flooded cell battery bankwherever practical. Routine replacement was recommended forthose that could not be replaced with flooded cells.On a remote 6-wellhead oil production platform, a flooded

lead-acid battery bank exploded after three years of service.The battery bank provided power to the wellhead platform'sESD hydraulic power unit. The battery bank was located in abattery box on one corner of the wellhead platform deck. Peakinternal temperatures of similar battery box installations wererecorded at 140°F during the summer. A single stage batterycharger was also used for this application. Because of thenumber of installations in this offshore field, and the addedlogistics of reaching each installation by workboat, many of thebattery banks were not serviced in a timely fashion. Theelectrolyte level dropped enough to expose the plates in severalcells. An arc ignited the gas in the large vapor space of a batteryjar and the battery enclosure. The battery bank was totallydestroyed. Ni-Cd batteries were recommended as thereplacement, as well as a redesign of the battery enclosure, andinstallation of a multi-stage charger.

In a large onshore gas plant, the UPS system's VRLAbatteries were equalized as part of a routine preventivemaintenance program. After three years of service, the batterybank failed open circuited during a controlled load test. Thewater in many of the cells had been "driven off". The OEM triedunsuccessfully to revive the battery banks by adding water tothe cells. The battery banks were eventually replaced with somewarranty concession.

In a major onshore oil production facility, the majority of thebattery banks for the UPS and station service are VRLAbatteries. This type of battery bank technology was chosenbecause of low maintenance requirements. Several batterybanks have failed after approximately 5 to 6 years of service.The failed battery bank strings were discovered to be open

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circuited when they were required to supply power. The batterybanks are being replaced in kind due to space limitations. Asurvey of the installed battery banks indicated thatapproximately half of the battery banks have not been servicedsince their original installation. A routine replacement program isbeing recommended.These few cases are examples of experience being ignored,

wrong selections of battery types and inadequate management.These lead to higher than first recognized costs of ownershipand loss of production and revenues.

III. BATTERY RELIABILITY

To understand how, why and if batteries fail suddenly, it isnecessary to look at the basic electrochemistry of both lead-acidbatteries and nickel-cadmium batteries. Formula 1 in theAppendix section shows the basic internal reactions of batteries.In reliability terms, the impact is that lead batteries fail relativelysuddenly. In turn, flooded lead-acid batteries fail short circuit,and valve-regulated lead-acid batteries fail open circuit due todry out. Due to the chemistry, the Ni-Cd cell is more reliablethan the flooded lead-acid battery as it does not suddenly fail.Combine these facts with expected life of batteries and then it

becomes clearer that reliability factors vary. The valve-regulated lead-acid type typically lasts 3-10 yrs whereas theflooded counterpart will last 12-17 yrs. The Ni-Cd cell will last25 yrs or more. Thus, the cost of ownership and life cyclecosting should be included in the evaluation and selectionprocesses.The environment has a significant impact on both

performance and life on batteries and again, to differingdegrees. Temperature compounds the potential problems thatbatteries face. Low temperatures require added capacitycompensation for lead-acid and Ni-Cds to varying degrees andtemperatures over 90 Fahrenheit will reduce the life of lead-acidfar more than Ni-Cd, which accounts for the field scenariosdescribed in the previous section. See Appendix for a thermalrunaway 24 Vdc battery.

Electrical abuse will likewise reduce battery lives in differingdegrees. There is often a misconception by uses thatmaintenance-free batteries require absolutely no maintenance.These battery banks may be installed and left unchecked until apower outage requires their operation. A maintenance-freebattery bank under these circumstances may or may notfunction as intended. The authors have experienced numerousfailed battery installations with this type of battery technology.The reliability of this type of battery bank is primarily dependentupon several factors including ambient temperature, chargingconditions, type and number of discharge cycles, and routinevisual inspection of terminal conditions and tightness, and celljar condition. On an offshore production platform, it may bemore difficult to maintain the proper battery room environmentfor the VRLA battery technology. As these facilities age, theHVAC systems may not operate as efficiently as initiallyinstalled, the battery rooms may not seal as adequately as theinitial installation as well. These factors may allow the batteryroom to maintain an elevated room temperature that couldadversely affect the life of the battery bank. Extended platformpower outages (especially in a summer environment) may alsoallow the battery bank to operate in a high ambient temperature.These factors have a detrimental affect on the battery bank'sreliability. Many of the VRLA manufacturers have well published

data on the detrimental effects of continuous elevatedtemperatures on the life of the battery bank. Life of a batterybank will go down exponentially when operated continuously atelevated temperatures. The cell may also be subject to thermalrunaway and drying out of the cell's water. If enough water isdriven out of a cell, the cell will open circuit. Only one cell failureis required to fail open circuit to fail the entire battery bank.Frequent equalization of the battery bank will also detrimentallyaffect the reliability and life of the battery bank. The internal heatgenerated in the cell may dry out the cell as with operating in anelevated ambient. Equalization should be performed only asrecommended by the battery manufacturer. Monitoring of thecell's internal impedance will help to monitor the cell's conditionand help to avoid the sudden death failure often experiencedwith VRLA technology. A battery impedance monitoring systemrequires an initial installed cost that may not be consideredduring the selection of this type of battery technology. It alsorequires a proactive approach to battery maintenance by thefacility personnel to ensure that the battery will operate asintended. Terminal tightness and condition should be checkedas part of a battery maintenance program. The cell jars shouldbe inspected for bulging, which indicates plate growth, or forcracking/splitting, and leakage. In extremely critical applications,where plant and man safety are dependent upon the batterybank operating as intended, it may be prudent to implement aroutine VRLA battery bank replacement program to ensure thereliable operability (availability) of the battery bank.

Flooded lead-acid cells are more robust than the VRLAtechnology, but their reliability is contingent upon properinstallation and maintenance as well. A conditioned battery roomis required to ensure the proper operating ambient temperature,adequate ventilation, and proper conditions to handle acid. Theflooded lead-acid cell is also adversely affected by continuousoperation in elevated temperatures. The reliability and life of thistype of battery technology will also decay exponentially ifoperated at elevated temperatures. The battery room alsorequires proper ventilation to remove the hydrogen that evolvesduring the charging of the cells. The flooded cell batterytechnology offers the option of significantly more parametersthat can be monitored to determine the condition of theindividual cell. This is a consideration for reliability that is oftenforsaken for the maintenance-free convenience of VRLAtechnology. For flooded cells, the electrolyte level can be clearlyseen through the often transparent cell jar. Markings providedby the battery manufacturer on the side of the battery jar clearlyshow the acceptable maximum and minimum electrolyte levelsfor the cell. Maintenance personnel can easily take specificgravity of the electrolyte during routine inspections. The specificgravity of the electrolyte is an indication of the cell's charge. Theindividual cell temperature can be monitored. Plate conditionssuch as sulfate build-up and adverse plate growth can be clearlyseen through the transparent jar. This type of battery can beroutinely equalized to ensure that the plates avoid excessivesulfate build-up and all cells are maintained at equal potential.The lead-acid flooded cell typically fails in a short-circuitedcondition. The sudden death condition experienced with theflooded cell bank is not as typical as with VRLA technology. Thereliability of flooded cell battery banks can be verified by thewider range of measurable parameters, but they do require ahigher degree of maintenance.The Ni-Cd flooded cell battery is one of the most robust and

reliable industrial cell technologies available. The Ni-Cd cell can

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handle continuous operation in greatly elevated ambienttemperatures while maintaining a 20-year life. They are alsocapable of deep cycle discharge without adverse affect to theoverall life of the battery bank as with VRLA and to a lesserextent lead-acid flooded cells. The Ni-Cd cell is not prone to thesudden death failure condition as with VRLA. As with the lead-acid flooded cell the condition of the cell can be monitored morethan with the VRLA technology, but not to the extent of the lead-acid flooded cell.

IV. CHOSING THE OPTIMUM DC SOURCE

In an operating oil and gas production facility, battery banksare often placed in mission critical applications. These includethe D.C. tripping power for switchgear circuit breakers, UPSD.C. inverter supply for plant DCS and PLC control systems,D.C power for emergency shutdown systems (ESD), and D.C.supply to provide autonomous operation of remote control orRTU systems that are normally supplied by photovoltaic arrays.The choice of the DC supply should depend on reliability, cost

of failure, the environment, downtime, real life performance aswell as the designed life of the equipment associated with thebattery.

In selecting a battery technology, operating companies aredrawn to certain features that initially seem to outrank many ofthe considerations stated above. Typically these are thephysical size of the battery bank (footprint), weight of the batterybank, maintenance requirements, and perceived lower initialinstallation costs. This is particularly true for applications that arelogistically difficult to access such as offshore platforms, facilitiesthat may have less skilled maintenance staff, or a minimallystaffed skilled workforce. The operating company's personnel ortheir selected Engineering Design Contractor may not take allnecessary factors into account when selecting the appropriatebattery technology. The user must be aware of thecharacteristics of each battery technology and their individuallimitations.The user is encouraged to consider the following in selection

of the appropriate battery bank:* Environmental considerations (ambient operating

conditions, conditioned battery room versus outdoorbattery enclosure)

* Discharge (float service versus deep cycledischarge)

* Number of cycles (frequent versus occasional)* Load Profile* Accessibility for routine maintenance* Battery monitoring system availability* Routine replacement versus longevity of initial

installation* Life cycle costs versus initial installed costs* Weight of the battery bank

Cost alone should never be the deciding factor in selection ofthe appropriate battery technology. In many installations, theselection of VRLA technology is chosen because of lowerperceived lifecycle costs (simpler battery room, little or nomaintenance, lighter weight, and an expected 20 year life). Inpractical application, the authors have generally experienced formost applications an average life of approximately 5 years for aVRLA battery bank. Over a twenty year life, the user can expectto replace the VRLA battery bank on the order of 4 times. For

extremely critical applications (man safety/plant safety) a morefrequent cycle of replacement should be considered (e.g. threeyears). This would increase the number of times the batterybank may need to be replaced to a minimum of six times.Typical life based on battery technology and an estimatednumber of life cycle replacements can be summarized asfollows:

Battery Avg Life (yrs) (1) No. of Life CycleTechnology Replacements

VRLA (non (2)5 4critical)VRLA (critical) 3 6-7Flooded Lead 10-17 1-2acidNi-Cd 20+ 0Ni M Hydride (6)20+ 0

(1)

(2)

(3)

No. of replacements that may be experienced over a typical industrial lifecycle of 20 yrs.The Avg. life of VRLA battery banks is based on experience in air-conditioned battery rooms.Metal hydride technology is still relatively new and data is estimated.

In addition to the replacement cycle (particularly for VRLAs),an additional cost that may or may not be considered is for abattery monitoring system. A battery monitoring system thatlooks at internal cell impedance is highly recommended for avalve regulated battery bank. The monitoring system will alertthe user to cells that may be heading for a sudden death failure(which can be experienced with VRLA technology).

Environmental conditions can figure prominently in theselection of a proper battery technology. The most significantfactor that can detrimentally affect a battery's life is temperature.Valve regulated lead-acid cells must be maintained in anambient that is maintained at a maximum of 78°F or less. Well-published longevity versus temperature curves show that the lifeof VRLA cells decay exponentially with increasing maintainedambient temperatures.

Referring to IEEE450-2002, appendix H, the reader will beable to calculate the impact of high temperature on reduced lifefor all Lead acid batteries. Suffice it to say, for every 15 degreesrise above 77 °F, there is a 50% reduction in life.

For Nickel-Cadmium batteries, the factor is 18-20%shortening of life for each 15 degrees rise.

Flooded lead acid cells are similarly affected by temperature(though not as drastically as VRLA). VRLA battery technology isgenerally favored for applications that have limited space andweight restrictions such as offshore production platforms. Asstated previously, this type of battery should never be selectedfor use in an ambient environment above the manufacturersrecommended maximum (typically 78°F). In offshoreenvironments, especially on older platforms, the battery roomenvironments may be difficult to maintain below the 78°Fmaximum. This may be due to air leaks through penetrations inthe building walls, doors left open or not well sealed,modifications to the facility that may not have accounted foradditional load to the HVAC system, improperly maintainedHVAC systems, or improperly balanced HVAC systems. Thisbecomes even more problematic for unmanned platforms. Onsmaller wellhead platforms, battery systems are often employedto provide the critical power for emergency shutdown systems(ESDs). If these types of platforms are not electrified, the battery

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banks must survive the ambient environmental temperature forthe location. Both VRLA and traditional flooded cell technologyare problematic in applications such as this. Conditioned batteryrooms may not be available - only unconditioned batteryenclosures. The life of these battery banks will be severelyreduced. Routine replacement of these battery banks willbecome necessary, but may or may not be practical from aneconomic or physical aspect. This is because these locationsare often accessible only by workboat. The logistics ofdismantling a battery bank and bringing in a replacement can bea great challenge, especially if a field has a large number ofinstalled battery banks. Ni-Cd battery banks are a betterselection for high ambient environments. A recombinant Ni-Cdtechnology is ideal for the remote wellhead platform applicationthat may see minimal maintenance. This type of battery bankholds up well in high temperature environments and has minimalwatering requirements (depending upon the load cycle andactual ambient temperature, topping may be only be necessaryonce every 5 - 10 years).The lifecycle replacement costs of the VRLA and flooded cell

lead-acid battery banks would need to include inflation of thereplacement battery bank, labor costs to physically remove theexisting battery bank and to install a new battery bank, boatcosts to ferry the new and old battery banks to and from theplatform, and recycle costs of the old battery bank. These costsmay significantly outweigh the higher initial installed costs for Ni-Cd or recombinant Ni-Cd batteries.Most important of all, the user must consider the impact that abattery bank failure will have on their facility's equipment andproduction. The implications of a failed battery bank arepersonnel safety, damaged/destroyed electrical equipment,damaged/destroyed production equipment, and lost profitopportunities. These costs are generally difficult to assess priorto an actual event. In general, an estimate may include severalpossible failure scenarios, one would consider the costs toreplace electrical equipment that could be damaged by loss ofD.C. tripping power, and another may examine the loss profitopportunities of shutting an entire facility down for several hoursto several days. The cost of a properly selected batterytechnology and proper installation are incidental in relation tothese costs. The costs of a failed D.C. system are againcompounded by the logistics of repair/replacement for facilitiesthat may be difficult to readily access with equipment andpersonnel.

V. CONCLUSIONS

The owner/operator is to be encouraged to educate him orherself on the differences of the various battery technologiesand to select a corporate policy regarding the type of batterytechnologies their company should employ. They should writestrong corporate specifications to avoid less than adequateproduct from being installed for their applications. He or she isalso recommended to establish experts should this position notalready exist in the company.The battery industry should be encouraged to step away from

warranties and devote more time to educate the end usersabout battery limitations and expectations. Reliability needs tobe re-reviewed with respect to the cost of failure while first costshould be given greater attention along with life cycle costanalysis. Habits are hard to change but unexpected failures areharder to accept or dismiss as being unlikely to happen again

too soon. Over the long term, it is anticipated that the batteryindustry will be charging to recycle even lead batteries, whichwill be reflected by higher costs to cover this. The Cadmium inmost industrial Ni-Cd cells is 99% recycled which does presenta very environmentally responsible battery.The production environment is comprised of diverse battery

applications and can pose a significant challenge to the enduser. A reliable DC system can be obtained but it does requirea cooperative effort between the battery OEM, the EDC, and theoperating company. The OEMs are encouraged to provideeducation to the EDC and the operating company about theirparticular battery technologies and the EDCs and operatingcompanies are encouraged to seek education from severalbattery OEMs to ensure themselves that the proper batterytechnologies are being proposed for their particular applications.Among the emerging new technologies, the Lithium Ion may

be valuable in that space is small, maintenance is zero and lifeis estimated at 12+ years even at elevated temperatures.

In closure, knowledge is paramount in both understandingwhat may be expected from a DC back-up system so that evenUPS systems employ longer living and more reliable batteries.

VI. ACKNOWLEDGEMENTS

A special thank you goes to Mr. Paul Hamer, IEEE Fellow, forthe opportunity to work on this presentation.

VII. REFERENCES

[1] IEEE 1187 Recommended Practice for Installation andDesign of Valve-Regulated Lead-Acid Batteries (VRLA)Storage Batteries for Stationary Applications.

[2] IEEE 1188 Recommended Practice for Maintenance,Testing and replacement of Valve-Regulated Lead-AcidBatteries (VRLA) for Stationary Applications.

[3] IEEE 1189 Guide for Selection of Valve-Regulated Lead-Acid Batteries (VRLA) for Stationary Applications.

[4] IEEE 485 Recommended Practice for SizingLead-Acid Batteries for Storage Applications

[5] IEEE 484 Recommended Practice for InstallationDesign and Installation of Vented Lead-Acid Batteries forStorage Applications.

[6] IEEE 450 Recommended Practice for Maintenance,Testing and Replacement of Vented Lead-Acid Batteriesfor Stationary Applications.

[7] IEEE 1115 Recommended Practice for Sizing Nickel-Cadmium Batteries for Stationary Applications

[8] IEEE 1106 Recommended Practice Installation,Maintenance, Testing, and Replacement of Vented Nickel-Cadmium Batteries Stationary Applications.

[9] NFPA 111 Standard on Stored Electrical EnergyEmergency and Standby Power Systems.

[10] D.O. Feder "Performance measurement and reliability ofVRLA batteries".International Telecommunications Conference (INTELEC1995)

[11] G.W. Vidal. Storage Batteries. Published by Wiley Press.[12] H.Bode. LeadAcidBatteries. Published byWileyPress.[13] NMAC/EPRI Stationary Battery Guide

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Vill. APPENDIX

Battery ReliabilityIn Formula 1, the two types of reactions are presented. In

the case of the lead-acid battery, the acid, sulfuric acid orH2SO4, reacts continuously with both the positive and negativeplates. Eventually, the plates degenerate to the point of notaffording the generation of electrons or current. In the case ofthe valve-regulated lead-cad battery where there is no access toreplenish lost water, the battery eventually dries out and mayeven experience a thermal runaway, leading to a fire.The second equation for nickel-cadmium battery, there is no

reaction between the electrolyte and the plates. In fact, theelectrolyte protects the plates, the opposite of the lead-acidoperation. The impact of this is that the plates do not fail andthere is no sudden failure, simply a steady decline over time ofperformance.

With the above knowledge gained above, the issue ofreliability between cells may be reviewed. A string of cellscontaining cells that may fail open circuit will never be as reliableas a string of cells, which fail short circuit. Compound this factwith the impact of operating cell voltage, then the reliability of alead-acid cell is less than that of a nickel-cadmium cell. Thetypical cell voltage of a flooded lead-acid cell is 2.17 to 2.25whereas that of the Ni-Cd is 1.37 to 1.40. In a 1 30Vdc battery,it will have 60 cells of a lead-acid cell type versus 94 or 95 cellsof a Ni-Cd.

FORMULA 1

THERMAL RUNAWAY6-month-old Abused Battery

BATTERY TECHNOLOGY COMPARISONS

ViIII. VITAE

E. Roy Hamilton received his undergraduate degree inElectrical Engineering from the Georgia Institute of Technologyin 1980. He has worked as an electrical design engineer for theTennessee Valley Authority, as an l&E project engineer for E. I.

DuPont and the former Amoco Oil Company. He also served asan electrical operations engineer for nine years in SaudiAramco's Northern Area Producing Department. Currently, he isworking in Chevron's Engineering Technology Center as anelectrical engineering power systems specialist.He is a member of the IEEE and IEEE IAS.

Roger N. Pocock received his degree in Chemistry atNottingham University, UK and has over 30 years experiencewith Texas Instruments, Schlumberger and Saft in engineering,sales and marketing in semiconductors, instruments andcontrols products and batteries. He has been with Saft Americafor 12 years and is now responsible for working exclusively withthe consulting engineering firms of North America.He is a member of the 7X24Exchange, CSI and IEEE

organizations. He is a past Board Member of the ElectricalGenerating Systems Association & rewrote Chapter 27,"Batteries and Chargers" of the EGSA publication "On-SitePower: A Reference Book".

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+++ PROS +++ TECHNOLOGY --- CONS ---Small size VRLA 3-10 yrsLow 1St cost Sudden death olc12- 15yrs Pasted Plate LA Rapid death at

end of life25+ yrs Plante High 1St cost25+ yrs Ni-Cd High lst costNo sudden failureV small space Lithium Ion High 1st costMaintenance free

Lead-acid Battery OperationPb02 + Pb + H2SO4 = PbSO4 + PbSO4 + H20+ve plate - plate acid + plate - plateBoth Plates react all the time with the acid (H2SO4)

Nickel-Cadmium Battery Operation2NiO.OH + Cd + 2H20 = 2Ni(OH)2 + Cd(OH)2Plates do not react with the electrolyte (KOH)