Technical guidance: Ups systems

Po erfuldri ersfor maintenanceA Ups system is the central building block of a Power Continuity Plan in medical facilities, butsuch equipment requires careful maintenance to continue fulfilling its vital role in deliveringpower resilience, and avoid catastrophic downtime, and potentially tens of thousands of poundsin costs to rectify the issues caused by poor maintenance. In our latest technical guidancearticle, Steve Mason, MD at Bender UK, one of the leading providers of isolated power supplies,theatre control panels, Ups systems, and Steris surgical products, and a turnkey provider ofsolutions for safe handling of electrical power and advanced provision of critical care products,examines some of the issue surrounding Ups maintenance

he sophistication and complexity ofa Power Continuity Plan will dependupon the business/clinical risk

assessment, the level of resilience required,the size of loads to protect, futureexpansion, and the budget available.In terms of resilience, a Power ContinuityPlan is concerned with the use of multiplepower paths to ensure AC supply continuityeven during maintenance, the ability of thepower protection systems to clear faultconditions, and achievement of the lowestpossible number of single points-of-failure.

A Ups (Uninterruptible Power System) isthe primary building block around whichthe plan is designed. Dualinput suppliesand static transfer switches are riotconsidered viable options for this role,but can provide useful support functions toimprove overall system design. A numberof Ups configurations are available,including single, parallel, and seriesredundant systems - each offering adifferent level of resilience, Mean TimeBetween Failure (MTBF), and availability.

Ups failure curveFailure rates for Ups, in common withother sensitive electronic devices, followa 'Bath Tub curve' through three distinctperiods.

'Infant mortality' failures: These earlyfailures are due to component ormanufacturing defects, or installation

Random failures: during normal working,the rate of these is low, and fairlyconstant.

Wearoutfailures: at the end of theequipment's working life, or due to poor

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Benderservice contract personneltestihg Ups equly7ment.

maintenance and monitoring of thesystem and its operational conditions.Battery problems are common, and canaccountfor over 98% of Ups failures at

this stage

Issues

Temperature is overwhelming Iy the singlebiggest factor in Ups battery failures, andhigh ambienttemperatures can causebatteries to breakdown, casings to meltand weld together into an immovablemass, and internal cabling insulation tobecome brittle and fail. Other consumable

items that require monitoring includecapacitors and fans which, of course,takes you back to temperature - the bigthreat to Ups batteries.

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Health Estate JournalOctober 2013

installation faults, or immediatecomponent failure, fallinto the categoryof 'not my problem'. Legacy issues of thiskind can, however, come back to bite you.For example, while a Ups system may gooperational during the commissioningphase, it may be that systems such as theventilation or airconditioning required tomaintain ambienttemperatures in theplantroom are not put to work for somemonths. During that pre-handover period,damaging Iy high temperatures coulddevelop which could seriously impacton the life of the batteries years later.An earlier errorthen becomes the problemof the maintenance team.

The standard design life for healthcareUps installations is 10 years at 20-25'C(BS6290 part 4). In other systems thisdesign life may be only five years, butfor medical systems 10 years is nowthe norm.

Not our problem?Maintenance teams operating in hospitalsand medical facilities may consider that'Infant Mortality' issues relating to

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ypical' Ups installationBatteries are typically 12 volt cells -usually alongside the Ups, and consist ofa string of 10 x 12 volt batteries - 120 voltsacross the single string. If a cell fails and'goes open circuit' then it can render thewhole string in operative. An installationin a medical facility will therefore oftenincorporate a parallel string for greaterresilience of supply.

The most common battery rating isthe Amp-Hour Rating. This is a unit ofmeasurement for battery capacity,obtained by multiplying a current flowin amperes by the time in hours ofdischarge. The ampere hour ratingdetermines how much current is suppliedfor how long. For example, in a typicalinstallation. to deliver one hour autonomythe consulting engineer may specify twobattery strings, each providing 30 minutesof power in the event of a mains failure.If one fails and goes open circuit, then theother string can take up the slack andmaintain supply. This type of multi-stringarrangement means maintenance teamscan isolate one string for maintenancepurposes and still maintain Ups integrity

HTM 06-01Most in-house maintenance at medical

installations is governed by the standard,HTM 06-01, Electrical Services Supply andDistribution: Part B - Operationalmanagement relating to UninterruptiblePower Supplies, inverters, and batteries

The HTM recommendation for Ups

autonomy is 30 to 60 minutes, dependingon an assessment of business risk andspatial constraints to accommodate thebatteries. However, the latest electricalwiring regulations state that Upsinstallations should offer a minimum ofthree hours' life - unless there is a back-

up supply available within 15 secondswith sufficient fuel for 24 hours - in other

words, a generator. If a generator isavailable, three hours' autonomy canbe reduced down to one

Whatever system a medicalestablishment may have in place currentlyto protect critical services, futureinstallations will almost certainly requiremore batteries, because the autonomyrequirement is Increasing. Certainty inthe duration of their performance, andmaintaining that performance, are thuscrucial.

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Technical guidance: Ups systems

7:9chnici^ns carrying out maintenance checks on Ups equtoment and batteries.

Rap' battery age gThe most importantfactorfor batteryageing is temperature. Highertemperatures can actually improveimmediate performance, but cause rapidageing and early failure. A temperatureof 20'C is the optimum batterytemperature, although most systems willtolerate between 18'C and 24'C. Lower

temperatures are not normally an issue,but high temperatures certainly are

At 30'C the battery design life is halvedControlling temperature is vital to avoidpremature, and potentially very costly,replacement, which will invariably leadto system downtime if not caught earlyenough. It could cause a complete systemfailure, which often becomes evident onlywhen the battery set is placed under loadduring a mains power supply failure

Heat lossUps units generate heat loss, and thisincreases as the Ups is put under load.Batteries also generate heat whencharging, and together the Ups and thebatteries can generate a significant heatloss, which can be a big factor whentrying to maintain an optimumtemperature of 18-24'C. The locationof the Ups relative to the batteries istherefore an important consideration,and ifthey are in same room, then airconditioning may be required to maintaina safe operating temperature.

How the batteries are arranged can alsoaffect how they perform. If they are tightlypacked into a barely adequate space,there will not be sufficient room for case

expansion and heat dissipation - and sofailures are likely to occur. Maintenanceteams should be aware of these issues,and take appropriate action before theybecome critical.

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opened, the maintenance team discoveredthat batteries had swollen and burst.

Battery casings had melted into a massof lead, and distorted plastic, and wereleaking acid gel. The batteries werecrammed into the compartment, and ittook a team wearing full PPE because ofthe presence of hazardous materials twodays to prise them out. The lead time toacquire replacement batteries meantfurther downtime and costs.

By-pass switchingMany installations also have a wraparoundisolation or by-pass switch which allowsa by-pass of the whole Ups - putting theload solely onto the mains power supplyMost Ups installations come with an

external by-pass switch arrangementIt is prudent for any operations managerto know how it is arranged, and how toput the load onto the mains, in the eventof a Ups problem

Standard maintena coproceduresThe standard, HTM 06-01, ElectricalServices Supply and Distribution: Part B- Operational management relating toUninterruptible Power Supplies, inverters,and batteries, lays down specific guidancefor maintenance of Ups systems.

The maintenance team is normallyresponsible for the non-intrusive visualinspection of uninterruptible powersupplies (Upss), inverters, and batteries,which should be considered as a frequentmaintenance task to be carried out at

least once a month. The non-intrusive

visual inspection should include a visualcheck that no alarms have been activated,and that rooms are apparently at designcondition.

Failing to act on amingsA worst case scenario with battery failurecan costtens of thousands of pounds torectify, and lead to extensive downtime.In a recent incident, the site operatorsat a UK hospital failed to act on warningsabouttemperature issues, and thebatteries failed. When the cabinet was

Full service maintenance checksWhere the Ups, inverter, or battery,includes self-monitoring or data-loggingfacilities, visual inspection should includea printout of these facilities. In this way, a

These batteries, damaged byexcessive heat, are swollen andj;alled.They will need replacing - a costlyand di^ruptiVe procedure.

Health Estate JournalOctober 90/3

Technical guidance: Ups systems

condition-based maintenance system canbe initiated for full-service maintenance

checks. The cleaning of ventilation grilleson the Ups should be carried out at the

same time - because blocked ventilation

grilles again lead to higher temperatures.In addition, the room's generalenvironmental conditions should be noted,and most particularly its temperature;as a general rule maintenance crewsshould follow their instincts - so if a room

appears to be warm, or even hat, thenyou may have a problem, and it shouldbe investigated.

Six-monthly frequencyForthe medical sector, Bender UKadvocates six-monthly service checks onUps installations in line with the

recommendations of HTM 06-01 Part B.

Some suppliers claim that annual checksare sufficient, but every six months is themost prudent maintenance frequency tosafeguard systems, and avoidunscheduled downtime.

For example, a battery which is notconnected to a power system for charging- perhaps due to a fuse blowing or someother minor system failure, will retain itscharge for up to six months, and thereforeis still available for service. Beyond sixmonths, however, it will almost certainlynot be available when required

Non-intrusive functional testsBender UK therefore recommends that

non-intrusive functional tests of Ups

installations, inverters, and batteries, becarried out every six months by dedicatedservice personnel.

These functional tests should include

a physical test of any connected automaticor visual alarms. The tests should also

verify that the inverter input would changefrom the rectifier output to battery outputwithin 0.5 seconds. Similarly, the staticswitch should operate within 0.5 secondsfollowing any fault condition of theinverter unit.

In the same way, the full service of Upssystems, inverters, and batteries, shouldbe considered as a maintenance task

every six months, to improve the likelihoodof a successful outcome when the

batteries are called uponIndustry guidelines suggest that Ups

systems above 80 kVA may have self-diagnostic test facilities for batterycondition, and that these can be usedto safeguard the system. However, inpractice these self-diagnostic test facilitiesare very rarely specified or installed,and battery testing therefore generallyfalls to the Ups service engineer.

Holding theI chargeFull service tests should demonstrate

that the batteries can hold their fullycharged state while the Ups is onbypass. Secondly, the batteries and Ups

should be tested online (with the mainsdisconnected). The battery dischargevoltage and current should be monitoredover a 10-minute period. Following this,the battery voltage and current-rechargeconditions must be observed, and anyadverse conditions corrected.

The test should also verify the conditionof the rectifier and inverter components,including the static switch and all bypassswitches, and inverter input and outputwaveforms should be checked and verified.

All cable and component connectionsshould be tightened as required

ServicertesVrecorddocumentationA simple single-line diagram of theUps/inverter arrangement, indicating howthe units are connected Into the electrical

infrastructure, should be maintained aspart of the operational and maintenancemanual and site logbook.

The site logbook should contain fulldetails of the Ups, inverter, and batteryunits, including:. Battery autonomy. Ups rating (kVA).. Rectifier type (six or 12 pulse). Mode of operation (single/double

conversion, on/offline).. Single or dual supply.. Date of installation

. Manufacturer

. Service contract details

Other third party changeover devicesare developed primarily for non-medical,industrial applications, where the intrinsiclevel of device safety and reliability is setagainst the continuity of an industrialprocess, not the support of human life

ATICS is, in our view, rapidly becomingthe industry standard for resilient IPSspecifications, and is the only device ofits kind that specifically meets the needsof the healthcare market.

Changeover solutionsThe increased use of parallel powersources operating as back-up orredundancy solutions provide furtherresilience for medical power infrastructureMany healthcare installations areinstituting high integrity changeoversystems to bring in power from anotherboard or source.

The ATICS unitfrom Bender UK is the

only changeover solution purpose-designed for medical applications withpatient safety at the very core of itsconception and development. Central tothe ATICS design is the incorporation ofpermanent self-testing across all criticalcomponents, bringing increased peaceof mind over other products that aresusceptible to failure without priorwarning.

ATICS has the unique distinction ofachieving independent eruV) accreditationto the Safety Integrity Level (Sit) Level 2standard, and compliance with BS76712008 (2001),

It removes the single-point-of-failurethreat to power resilience inherent inthe traditional single supply cable, byenabling supply from two different sources.The primary supply maintains normaloperation, but, in the event of failure, ATICstransfers over to the secondary supplywithin 05 seconds to comply withHTM 06-01.

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eveSteve Mason was appointed managingdirector of Bender UK in 2010. Since

then, the turnover of this subsidiaryof the 'global technology leader' hasgro n Largo per cent yearon-year, andthe workforce has almost doubled.

He has always been fascinated byelectrical systems, and reckons titsnatural aptitude is inherited from hisfamily of electrical engineers. As a boylie spent weekends helping his fatherto carry out electrical fitting andmaintenance work etbusinesses andengineering companies around theFumess area. He served an electricalcraft apprenticeship at the Vickersshipyard in Barrow, and progressedthrough a series of contracting jobs togain wider experience, before joiningBender in 2003

He quickly identified that changes inelectrical regulations had created aneed to use unearthed power supplieswithin critical healthcare applications,which created new opportunities forBender equipment in the giant hospitaldevelopments being built at the time viathe 'Private Finance Initiative revolution'.

Bender UK became known as the

authority on protection for thesophisticated electrical systemsrequired by the new healthcare facilities.Steve Mason and his team worked hard

to extend their knowledge of securepower infrastructure for hospitals,and expanded their offering to includeuninterruptible power systems (Ups).As a result, the company grew rapidly

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20Health Estate JournalOctober 2013