Gas Turbine Efficiency - overcoming your power problems

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LOADBANK TESTINGWhat is loadbank testing -and how does it work?Alan LuscombeAlan Luscombe, Sales & Marketing Director of Uninterruptible Power Supplies Ltd,explains the technicalities behind testing the power protection system under loadconditions without risking the supply to the protected loads.AUPS (uninterruptible power supply)sits between an alternative sourceof power - such as a standby dieselgenerator - and protected loads. Most UPSare designed to power connected loadscontinuously via their inverter, which alsoenables conditioning of mains supplyvoltage and insurance of a break-freesupply of electrical energy in the even ofa mains failure. In most applications, UPSare considered critical to businesscontinuity without which loads would notbe able to operate during a power outage.For this reason, loadbank testing isimplemented to ensure UPS can meet therequirements of their intended functionwhen most needed.Loadbank testing is a way of validatingthe correct operational performance andbattery autonomy of the UPS system. Ittests the UPS and generator under loadconditions. It is most often carried outduring preventative maintenance.As a UPS battery set is only as strong asits weakest battery cell, loadbank testingcan also be used to ascertain thecondition of UPS batteries and batterysets (or 'strings' as they are also known) toindicate if any individual cells areapproaching the end of their working lifeGood preventative maintenance isessential, says Alan Luscombe.and not holding a chargeor about to fail. Thisenables them to bereplaced in advance ofcritical application.Loadbank testing isoffered as a service bysuppliers of powerprotection equipment.Some suppliers offer loadbanktesting as part ofthe UPS commissioningprocess but caution mustbe exercised: ideally it should be carriedout at least one week after the UPS hasbeen commissioned to permit the voltageacross the battery blocks to equalise andbatteries to be fully charged. Loadbanktesting prior to this will not yield accurateresults, or give a true picture of how thesystem is running, and thus be a waste oftime and money.Suppliers of loadbank testing normallycarry their own small loadbanks (typically100kW or less) and will hire in largerdummy sets to test larger UPS systems asrequired. These loadbanks are typicallyresistive (neither inductive nor capacitiveand with no initial switch-on surge).Current rises immediately to a steadystate. Loadbanks like these are availablefor either ac or dc systems.An ac loadbank is used to test entire UPSsystems, whereas a dc loadbank will beused to test batteries. Reactive loadbanksare also available (typically with a laggingpower factor 0.8) but they tend to belarger and heavier in design.The point is to test the power protectionsystem (and component parts) under loadconditions but without risking supply toprotected loads. A loadbank should besupplied with suitably-rated cables, whichenable it to be placed no more than 20UPS system and battery systems.metres from the UPS terminals or outputpower distribution unit (PDU).A loadbank test will provide timelyidentification of problems with thegenerator and UPS and an indication ofremedial actions that should be taken.In the case of a standby generator, aloadbank test will indicate the engine'sability to provide the required power; thealternator's capability to provide therequired voltage stability; stablefrequency; efficiency of control systemsunder varying conditions of load;performance of the whole system; oil andfuel pressure. It will also help removedeposits from pistons, engine castings andexhausts, identify potential weaknessesand record results and any work required.Loadbank testing costs include the hireof the equipment (for larger systems)where applicable, engineer time andtemporary cable provision andconnection.Loadbank testing itself should be carriedout prudently and with caution as it canreduce system resilience, dischargebatteries and may, in that case, placeconnected loads at risk.WIPInternet linkwww.upspower.co.uk22MARCH 2010 • WORLDWIDE I NDEPENDENT P OWER
WORLDWIDE LOADBANK SPECIALISTSCrestchic loadbanks maximum powerwhen you really need it■SALES ■ RENTAL ■When power generation is vital, when backupsystems must be fully tested to make surethey’re up to the job - you need a stable,continuous and variable power generationtest to imitate real loads, in real time. Youneed a load test solution you can rely on.No other company specialises in worldwideload test solutions like Crestchic.Manufacturing loadbanks for sale and rentalfor over 20 years, we have delivered reliableand effective test solutions to all sevencontinents.Crestchic Tailor-made load testsolutions from 30kW to 100MVAWhy look anywhere else?For more information, contact us on(+44) 01283 531645Or find us on the Internet at www.crestchic.co.ukYou can also email us: sales@crestchic.co.ukor hires@crestchic.co.uk
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