Wind Turbines From PEI 20100901 Sep 2010

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Wind Turbine Condition Monitoring

46 www.peimagazine.com September 2010 - PEi

G lobal demand or renewable energy is booming. The astestdeveloping sector is wind energy, currently expanding at around25 per cent per annum, with the number o installed turbines upby around 30 000 units each year. In Europe alone there are now 25 000wind arms and this number is orecast to double by 2015, while globallythe sector is expected to be worth some $109 billion by 2020.

These are phenomenal rates o growth by anybodys standards. Yet whilethe spotlight has largely been on the uture it is essential that we do not

orget the tens o thousands o turbines already in operation. Many othese have been installed or three years or more and, on both land and atsea, have had to operate or extended periods in some o the most hostileand arduous conditions. Perhaps more to the point, a growing number oturbines are now reaching the end o their manu acturers warranties butwill still be expected to unction reliably and at minimal operating cost orat least a urther ten to 15 years.

Industry analysts estimate that some 70 per cent to 80 per cent oturbines are still under their original manu acturers warranty but that within12 months this situation will change dramatically; indeed, by the end o2010 it is predicted that more turbines in North America will be operatingout o their original warranty than will be covered. Inevitably, this trend will

grow as the industry matures, making the challenge o maintenance andrepair an ever more critical issue or wind arm operators.

RUNNING COSTS

Based on existing industry fgures, it is generally considered that aroundten per cent o the annual cost o generating wind power can be directlyattributed to turbine maintenance and repair. As turbines age, however, thisfgure rises, approaching 35 per cent or turbines that are nearing the endo their operating li e.

The process o calculating operating and maintenance (O&M) costs israrely straight orward and is complicated by variables such as location,environment and actors that may have been un oreseen at the time odesign and installation.

For example, it is now recognized that the e ects o turbulence rom ttips o rotating blades can intensi y the loads on downwind turbines i thare positioned too close together; in turn, this can result in increased wearon gearbox and generator sha ts, bearings and seals. Similarly, the trendto produce ever larger rotors and towers is placing high levels o stresson internal and structural components leading to earlier than predicted

ailure rates.

Matt Fielder, Parker Hannifn, UK

Wind turbines: Off-warrantyshould not mean off-line

Matt Fielder, industrial market development manager or the Hydraulic Filter Division o ParkerHannifn, explores ways in which wind turbine operators can maintain reliability as installed turbinesgradually come o -warranty.

Although as many as 80 per cent o wind turbines are still covered by their manu acturers warranty this gure is set to plunge within the next 12 months, li ting maintenance and repair
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PEi - Septemberl 2010 www.peimagazine.com 47

Clearly, as more and more turbines come on-stream, and as growingnumbers reach the end o manu acturers warranties, the need or e ectivemaintenance and repair strategies or wind arm operators becomesincreasingly important.

As a result, there is a growing drive to ensure that critical systems are asrobust and long-lasting as possible, to minimize both ailure and wear ratesand to reduce the need or routine maintenance. For reasons o both coste fciency and health and sa ety, there is also a growing impetus to minimizemaintenance carried out at the top o turbine towers by modularizing keyoperational units and/or moving them to ground or sea level.

Be ore looking at ways in which the O&M costs o turbine systems can beminimized, it is important to understand some o the things that can a ectoperating costs, especially within the various hydraulic and associatedsystems that orm much o the operational systems in a typical turbine.

In particular, the logistical di fculties in carrying out regular routinemaintenance and emergency repairs on turbines located in remoteinaccessible locations, and increasingly at sea, continue to have asignifcant e ect on margins. Indeed, the task can be extremely di fcult,with skilled engineers needed to climb towers in order to carry out workthat, even with the attendant sa ety requirements, is a time-consuming,expensive and potentially risky exercise.

As a result, it is essential that wind turbines are developed that operateas e fciently as possible, with the minimum amount o manual intervention.Many turbine manu acturers are now achieving this goal by integrating thelatest generation o hydraulics technology into their products.

HYDRAULICS IN WIND TURBINES

The latest hydraulics technology, rom manu acturers such as ParkHannifn, can commonly be ound in the nacelle o a wind turbine to controthe pitch o the blades and the yaw o the nacelle, maximizing the turbinepower generating e fciency and protecting the equipment in high winds.Another use o this equipment is in low maintenance hydraulic gearboxethat are helping wind arm operators to reduce costs considerably.

In pitch control systems, the angle o the rotor blades is altered slowland precisely to achieve optimum generating output. The blades are eitherturned into the wind to increase rotational speed i the wind speed alls, oout o the wind i wind speed increases, causing the rotational speed othe blades to decrease in order to protect the turbine rom damage. This istypically achieved by installing three pitch control systems in the hub o thturbine, one or each blade. These systems employ hydraulic cylinders thavary the angle o the blades through a cam action.

Likewise, the yaw, or rotational position o the nacelle is continuallyadjusted to obtain maximum e fciency rom the turbine. In the same wathat output is optimized by tilting the angle o the blades so that they are

acing into the wind, the nacelle too must be rotated horizontally about theaxis o the tower in response to the changing wind direction. Hydraulicallypowered yaw control systems are able to o er a simple, compact directdrive, reducing the requency o maintenance required in comparison wit

other methods, such as electromechanical control.While these systems are enabling the e fciency o wind turbines to be

increased signifcantly, the hydraulics must be protected rom potentiaparticulate and water contamination, the primary cause o ailure inlubricated and hydraulic equipment. Indeed, a range o e ective fltratioand condition monitoring solutions should be used i consistently reliaboperation, and there ore minimized operating costs, are to be achieved.

INLINE FILTRATION

E ective inline fltration technology is an essential element to captuparticles be ore they reach sensitive components in all large capacityturbines; including those that have alternative methods o pitch and yaw

control such as electromechanics. Gearbox problems typically accountor the majority o unplanned maintenance requirements, and with turbingearboxes required to gear up the low speed input sha t to provide a highspeed output or the turbine, the fltration o both lubricating and hydraul

uids is crucial.Where hydraulic control systems are used, e ective fltration technolog

is especially important, extending maintenance intervals and increasing thereliability o pitch and yaw systems. A comprehensive range o fltratiotechnology has been developed specifcally or fltering out particulate andwater contamination rom hydraulic uid to just a ew microns.

Without this technology, precision engineered system components suchas cylinders, accumulators and valves can su er rom reduced per ormanlevels and premature ailure, ultimately reducing the e fciency o thwind turbine and raising costs or operators. However, the design andspecifcation o fltration systems require considerable care to preventrestriction to the uid ow and, thus, lower e fciency o a hydraulic circuI they are not properly designed or sized, pressure loss across flters cansignifcantly reduce the per ormance o hydraulic systems, increasinenergy consumption and the associated challenges o heat management.

As well as machine per ormance, correct flter selection must allow ooverall operating conditions. By their nature, flters will require periodic

Source: Parker Hannifn
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48 www.peimagazine.com September 2010 - PEi

cleaning and replacement to ensure e fcient operation o equipment.Filter packages should be sized to ensure that the required requency ointervention matches that o the overall equipment maintenance strategy inorder to minimize the cost and disruption associated with flter care.

In answer to this, the leading designers and manu acturers o fltrationsystems or wind turbine hydraulic machinery are constantly refning thedesign o their equipment in order to maximize per ormance and minimizethe associated drawbacks.

In addition, recent advances in flter materials modi y the compositionand construction o standard glass fbre materials to improve their strengthand dirt-holding capacity while also reducing resistance to ow. ParkersMicroglass lll material, or example, can reduce dynamic pressure across

the flter by 8 per cent while typically improving contamination loading by15 per cent, compared with conventional flter material.

While this uid fltration technology e ectively removes contaminanthat fnd their way into a hydraulic system, contamination levels alsoneed to be recorded and analyzed in order or essential maintenanceto be scheduled be ore problems occur. However, taking samples rom ahydraulic system in a wind turbine to a laboratory or testing is extremeimpractical, which is why many wind arm operators are now using thelatest particle counting technology, such as that developed by ParkerHannifn, as a real-time, on-site solution.

CONDITION MONITORING

Particle counters or portable analyzers, such as Parkers IcountPD, o erast and accurate measurement o contamination levels in hydraulic uid

using a process called light obscuration, light blockage or light extinction.Essentially, the shadow o any particles suspended in a uid passing acrossa light source causes a voltage drop across a light sensitive diode; thesignal generated as a result o the shadow is dependent on the size o theparticle and the speed at which it passes across the light.

The IcountPD can also be built into the hydraulic system, including thlubrication or power transmission circuit, along with remote monitorindevices to provide end users with a real-time look at solid contamination

levels in accordance with ISO cleanliness codes. Indeed, thishigh-per ormance device can identi y particles down to 4 m in size

Leading designers and manu acturers o fltration systems or wind turbine hydraulic

machinery are constantly refning the designo their equipment in order to maximize

per ormance and minimize the associated drawbacks

________
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PEi - September 2010 www.peimagazine.com 49

providing an early warning o wear and potential component ailure,as well as the option or an integral moisture sensor to detect watercontamination without requiring a separate stand-alone unit.

Furthermore, the latest generation o particle counters eature robustconstructions, making them ideal or use in the hostile environments inwhich wind turbines are typically located. The counters compact, portablenature makes these devices ideal or feld use, while their power ul internalcomputer o ers results that are consistently accurate, thereby removingthe subjectivity that was associated with manual, laboratory-basedtesting methods.

FULFILLING WIND POWERS POTENTIAL

While the latest hydraulics technology is o ering an e ective and reliablemethod o optimizing the e fciency o wind turbines, in order or thetechnology to ulfl its ull potential it is essential that e ective fltration andcondition monitoring devices are also considered and included rom thedesign stage.

By accurately monitoring contamination levels, and ensuring that anycontaminants that do enter the system are fltered out, operators canbeneft rom turbine control systems with long, low-maintenance service

lives, ultimately increasing the power generating capacity o turbines andreducing operating costs considerably. The IcountPD gauges contamination levels in hydraulic fuids by measuring light obscuration

________

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Wind Turbines From PEI 20100901 Sep 2010