What is the best way to maintain a wind turbine?

Maintenance crews acknowledge that frequent lubrications with small amounts of grease extend the working life of bearings and seals. But long hours of hub crawling is physically and mentally demanding work. A useful idea is a centralized and automated lubrication system for wind turbines. One version for lubrication tasks in a nacelle can also handle main-shaft bearings. The equipment also reduces lubricant consumption. Most equipment of this sort makes refilling the grease pump simple and quick. Centralized lubrication systems are said to reduce turbine operating costs, increase operational reliability, and extend service intervals.

Another lubricator, a 24-Vdc electric-powered device, greases heavy-duty equipment without tapping into hydraulic or pneumatic lines. It is said to set up easily and fit directly onto a 5-gallon grease pail. It works with a hose reel and hand grease gun, and can be used stand-alone or with a centralized lubrication system. It weighs about 24 lbs. A metal follower plate has a wiping seal on its circumference. The follower plate works in straight or tapered pails, and ensures the complete removal of grease from a container. The pump can refill automated lubrication systems inside wind turbines or act as the driving pump behind the system. Its maximum discharge pressure of more than 4,000 psi is one of the industry’s highest. Discharge volume is 80 to 120 grams/min in continuous operation and 70 to 80 grams/min in 30-min periods. Operating temperatures range from 14 to 104°F.

Trends: Hydraulic-component companies are designing more complete lubrication-oil systems for wind-turbine gearboxes. These systems would come with filters, pumps, valves, coolers, and heaters as well as manifolds and piping to connect components. The advantage here is that the assemblies are probably more thoroughly tested and proven and carry the assurance of reliability from a qualified supplier.

Tools: The equipment used to maintain the machinery in a nacelle are much like those used by other technicians except they are fitted with tethers to prevent them from falling many feet to the ground. See the safety and bolting sections for additional discussions.

Cold weather filters: A recent element intended for wind turbines is said to ensure sufficient and effective filtration levels and prevent the filter from going into bypass mode, an event common to cold starts. Also, offline filters can remove water from oil. Existing systems on turbines can be upgraded with these capabilities.

A technician’s work is never done

Since it began commercial operation in 2002, Whitewater Hill Wind Farm in North Palm Springs, CA has helped supply 12,000 homes with clean power, displacing 130,000 tons of carbon dioxide (producing about 165 GWh annually). To help keep the 66-MW wind farm running properly, Whitewater Hill Wind Partners has awarded UpWind Solutions, Inc. a 5-year operations and maintenance agreement for post-warranty O&M services.

“Our commitment to continuous improvement is driving down operating costs while improving energy yield,” says Bo Thisted, President & Founder of UpWind. ”The result is a lower cost per KWh achieved by focusing on safety, quality, and performance. We are pleased our partners share this vision and have already achieved dramatic improvements in the project’s performance.”

As part of the company’s approach, UpWind technicians complete comprehensive training with the high EHS and safety standards. They are also trained and encouraged to find solutions that optimize wind turbine availability and performance for project owners, ensuring the highest return on their investment.

“We are excited to have this opportunity to work with Whitewater Hill Partners to optimize the performance of their wind project,” commented Marty Crotty, CEO of UpWind. “The long-term contract includes a comprehensive service offering and clearly aligns the interests of both parties.”

UpWind Solutions www.upwindsolutions.com

 

How to Keep Them Working 20 Years and Longer

Standard wind turbine gearbox warranties generally last two to three years, and when they expire, operations and maintenance professionals become responsible for keeping the turbines running for the remainder of their service lives. Considering that the average wind turbine is expected to operate for up to 20 years, maintenance professionals are challenged to maximize equipment performance and minimize maintenance.

Maintenance staffs are typically lean and must be as efficient as possible to complete the recommended maintenance in the proper intervals. Streamlined gearbox flushing and oil analysis strategies can help maintenance professionals prolong the life of a wind-turbine gearbox, minimize unscheduled repairs, and simplify maintenance procedures.

Technicians from COT-Puritech will winch the lubricant hose up tower so they can draining and refill the gearbox with fresh oil.

Do more than change the oil

The main gearbox drives the generator marking it a critical piece of equipment. Advanced designs and overall  importance to system performance makes gearboxes costly to repair or replace after the warranty expires. For example, replacing a gearbox in a 1.5-MW turbine can cost a company more than $500,000 when you add in the price of a new gearbox, labor, crane rental, and lost revenue from turbine downtime.

To minimize the chance of a premature gearbox failure, OEMs recommend routine, scheduled maintenance,  oil-circulation equipment, and an oil analysis.  Although the maintenance staff traditionally changes the oil, there are  many physical and logistical challenges, including the climb up-tower, remote turbine locations, weather extremes,  limited available utilities, numerous trips lugging down used oil, hefting 85 gallons of new lubricant up a 60-m tower, and finally pouring it into a gearbox. Following established OEM procedures, the oil change for a wind turbine gearbox  generally takes about eight hours and requires three maintenance technicians.

Industry averages suggest a 1.5-MW turbine generates roughly $1,200 worth of electricity every 24 hours. Thus,  halting a turbine for an oil change costs a wind-plant operator $400 in revenue and may drive additional expenses for  the use of outsourced maintenance crews to handle general maintenance activities and troubleshoot more pressing  issues while the internal maintenance  personnel change the gearbox oil.

To make matters worse, field experience indicates that routine oil-change procedures remove only about 70% of the  used oil. When adding the new wind-turbine gear lubricant to the system, it mixes with the 30% residual used oil, which  contains contaminants and wear metals. Mixing contaminated oil with new oil shortens the life of the new oil and could  also lead to premature component wear and potential equipment breakdown.

To address these issues and help wind  companies maximize turbine output, outsourced maintenance companies are starting to offer gearbox-oil-change  services. The best of these service providers use a proprietary protocol and specialized equipment. This specialized  equipment moves oil safely up and down the turbine using high pressure pumps and hoses. This equipment also assists  in removing up to 97% of the used oil from the gearbox,  while helping to remove contaminants and cleaning critical  gearbox components.

The new wind-turbine gear lubricant then delivers better equipment protection than contaminated oil, thereby  extending oil life and reducing lubricant expenditures. What’s more, the entire oil change, flushing, and cleaning also  takes about half of the time it would take for a maintenance staff to perform a conventional oil change, and gets a turbine back to work sooner. This service makes minimal demands on the time of maintenance staffs and lets them  focus on routine maintenance protocols. Considering the cost analysis, the expense of employing an outsourced partner to perform a gearbox oil change is quickly recouped in the cost-saving benefits of extended gear-oil drain intervals for wind turbines and it potentially extends wind-turbine gearbox life.

After filling the gearbox with fresh oil, it is imperative for maintenance personnel to monitor it. Routine oil analysis is  one of the most widely used proactive maintenance strategies for wind turbines and employs a slate of tests to evaluate  the condition of the in-service lubricant and help evaluate the condition of internal hardware. Routine oil analysis as  part of a preventive maintenance program lets maintenance staffs extend the useful lives of the gear oil and gearbox by detecting and acting on early warning signs such as contamination or increasing wear metals.

For the greatest benefit from oil analysis, it is imperative to work with an expert lubricant manufacturer and conduct an oil analysis every three to six months. Identifying trends in the data will help maintenance personnel make more informed oil-suitability decisions. When analyzing oil samples from the wind-turbine gearbox, the maintenance staff  must test for viscosity, iron wear, total acid number, water contamination, and oil cleanliness. Each deserves more  discussion.

Viscosity

It measures a lubricant’s resistance to flow. This variable is the most critical parameter for most applications and can  change over time, more quickly in equipment that sees extreme temperatures or high pressures or high speeds. Ensure  that lubricant viscosity is within its targeted range. Doing so minimizes wear between critical equipment components.

Typically wind-turbine gearboxes require a viscosity around 320 cSt (centiStokes) but it can be higher based on service with variable temperature, speed, and loads. When viscosity changes by ±15% of its original value, monitor the oil  more frequently. Equipment can perform normally if the lubricant is outside of this range, but it should be watched  more closely because it usually indicates changes are needed. If oil temperature significantly varies, particularly trending higher, it is recommended to review the ISO grade of the oil to ensure it provides an appropriate film thickness  for efficient wear-free performance.

When a lubricant’s viscosity increases, there is a chance it has been contaminated by oil with a higher viscosity or has  started to oxidize. However, when viscosity decreases, inspect the oil filter for wear debris, monitor the box for higher operating temperatures, and check for other lubricant contamination.

Iron wear

Steel is used in nearly every piece of equipment, especially wind turbine gearboxes, so it is imperative to monitor its presence. Don’t be overly alarmed  when elevated levels of iron appear in the oil analysis at the beginning of the gearboxes’ service life. This is typical during “break in” periods for new equipment and should reach a steady state over  a few months.

Two tests can identify iron content in oil: ICP spectrography and a PQ Index. ICP spectrography  identifies iron particles in oil ranging up from about 10μ (micron). For comparison, a human hair has about a 40μ diameter. Hence, the smaller particles could pass through an oil filter and potentially be a precursor to increased gear  wear.

The PQ Index test quantifies the size of ferrous material in the oil sample. For the most accurate assessment of the oil’s condition, it is recommended that maintenance personnel monitor the Index over time and compare it to ICP analysis. When the PQ Index is lower than ICP analysis, it indicates the presence ferrous particles smaller than 5 micron. If the PQ  Index exceeds the ICP analysis, that could indicate that the ferrous particles are larger and a chance that wear has  accelerated.

When high iron-particle readings coincide with high silicon readings, the oil has become contaminated with dirt. The oil  does not necessarily need a change at this point. It can be filtered. However if contaminant levels are not reduced or  stabilized, change the oil and make sure to flush the bearings of wear debris that collects in oil pockets.

Total acid  number

This number, called the TAN, indicates a thermal stability, oxidation rate, and amount of acidic material  generated in the oil.  Oxidation is the reaction of oxygen with the hydrocarbon molecules in the gear oil. The rate of   oxidation increases exponentially as temperature rises and with the presence of metallic contaminants. An oil  temperature increase of 10 Celsius degrees effectively doubles the oxidation rate. Copper, bronze, brass, and iron  contaminants are typical materials that catalyze the oxidation reaction. Oxidation is typically the main contributor to  sludge and varnish formation in gearboxes. Based on a turbine’s normal operating conditions, when the TAN is below 2.0, oxidation is occurring at a slower rate unless there is a mechanical problem such as plugged coolers, or bearing or  seal failures.

PAO-based (polyalphaolefin) synthetic oils resist oxidation longer than their mineral-oil counterparts, but if the TAN is  two points higher than its starting point, change the oil immediately.

Water contamination

Water and oil do not readily  mix. Water tends to lead to reduced viscosity, an increased oxidation rate, and causes additives to drop out of the  lubricant, potentially leading to component failure. Higher-performing oils are engineered to not hold water so  contamination by it should not be an issue. However, if oil analysis indicates water levels above 200 ppm (parts per  million), check all sources including oil for a contamination source. Oil containing as little as 200 ppm water can reduce bearing-fatigue life by up to 20%. An improperly stored drum of oil will breathe as temperatures change during the day and night, drawing standing water past the bung seals and into the drum. Store drums indoors, under cover, or tilt  drums so that bungs are at 9:00 and 3:00 o’clock positions and water cannot collect on the top of the drum.

Oil  cleanliness

This measures insoluble dirt and hard particles in fresh or in-service oil. Several factors impact a lubricant’s  cleanliness, most notably contamination and harsh operating conditions, such as, extremely high temperatures,  press-ures, and operating speeds. Oil cleanliness is typically determined using a laser particle counter which can detect water and air bubbles in oil, even particles in sampling bottles. Hence, reported values can be higher than an oil’s actual  cleanliness level. So, if oil samples come back as dirty with low wear rates, check the water content and then resample to confirm the results.

Under ISO 4406, an ISO code is determined by measuring and grouping particles into three ranges based on their size in microns (> 4μ, >6μ, and >14μ). From these results, oil is given an ISO classification  between 00 and 24. The typical target oil cleanliness for gear oil is an ISO 16/13.

The long haul

Wind turbine gearboxes  are one of the most challenging applications in the modern industrial world, and require proactive maintenance  strategies to promote enhanced performance. The streamlined protocol presented here lets maintenance professionals prolong wind turbine gearbox performance, minimize unscheduled repairs, and simplify maintenance procedures long  after a warranty expires.