September 2011

The cost of energy plays an increasingly important role in today’s world. This applies to all different types of energy production. Since wind energy is one of the most important sources for renewable energy production nowadays, it is closely monitored regarding the cost of energy and wind energy’s potential for a high return on investment.

The factors that influence the energy production costs of a wind turbine are the lifecycle costs, which include costs for the overall wind turbine construction, maintenance, and service costs, as well as the output generated during the lifecycle. Therefore reliability, serviceability, and high efficiency—as well as a compact wind turbine design—are the key requirements for wind turbines. Since the drivetrain is the “heart” of a wind turbine, during the design phase all those aspects have to be especially considered. Figure 1

The conventional drivetrain design consisting of a three-stage gearbox, coupling, and generator is a very reliable concept and is the standard drivetrain for wind turbines, which has a track record of almost 150 GW globally installed base. New concepts, like the HybridDrive are especially designed to meet these requirements for compact design, high efficiency, and great serviceability. Every concept has its own advantages, so it is not possible to talk about the “perfect” drivetrain design. But, each drivetrain meets the specific requirements of a single customer so that he/she has the choice of which concept should be employed in its wind turbines. In the following article the HybridDrive concept is introduced and the major advantages explained.
 
Compact and Efficient
The main focus of the HybridDrive is its compact design. A two-stage gearbox is directly connected to a permanent-magnet-operated generator, which means that the length of the drivetrain can be shortened by about 35 percent. Although the HybridDrive has an extremely compact design, it has a very high efficiency. If the efficiency of the HybridDrive is compared with other technologies that are available, it has a peak value of more than 94 percent. This means that it achieves the best annual efficiency of all the existing technologies. Figure 2

Its compact dimensions present various advantages for the design of a wind turbine. If the HybridDrive is used to replace an existing wind turbine design, it is possible to utilize the space that has been saved for the converter and transformer instead of locating these in the tower. This choice of location for the transformers reduces the low-voltage cable (energy) losses, which improves efficiency. If the objective of the wind turbine manufacturer is to construct the nacelle to be as compact as possible, this can also be achieved with the HybridDrive. Any configuration is possible with the HybridDrive, whether it is positioned with ust one bearing, a dual-bearing rotor shaft, or with a converter and transformer in the tower.

Depending on the concept, the costs for the tower can be reduced as a result of the reduced weight of the nacelle; not only this, transportation is easier as the nacelle dimensions have been reduced. The customer is free to choose which concept he/she wants to focus on. Figure 3
 
Modular Design
A well thought out maintenance concept was already taken into account in the early design phase of the HybridDrive. Despite its compactness, the HybridDrive has a modular design, which enables individual parts to be disassembled or replaced for maintenance purposes. The benefit of this is active risk management. For example, the service crane of the nacelle can lift the individual modules, so that even when large-scale service is necessary, there is no need for an external crane. This considerably reduces service and maintenance costs. The reliability and quality of the HybridDrive is optimized, as there is only one supplier involved who is responsible for the design and quality assurance of the core of the wind turbine: its drivetrain.

The advantage of the HybridDrive concept over directly-driven wind turbines is that it only uses 20 percent of the quantity of rare earth materials that are required for a direct drive. As a consequence, dependency on one particular raw material is considerably lower, and costs can be more easily calculated over the long term. Since the sourcing and production of rare earth material is currently still under discussion, it is also possible to design the HybridDrive without any permanent magnets at all. Figure 4

The first prototype of the HybridDrive has an output of 3MW and is intended for use in an offshore turbine. The concept can also be easily implemented for the 6-7MW power range.
 
Teaming Up for Technology
Winergy introduced the HybridDrive drivetrain concept as a new member of its product family this year at Hannover Fair and at AWEA WINDPOWER 2011. The HybridDrive will be employed for the first time in the Fuhrländer FL 3000 wind turbine system. The project is the result of a long-term partnership between Winergy AG, Fuhrländer AG, and W2E Wind to Energy GmbH, and is to be completed within one year. As described, the HybridDrive sets itself apart as a result of its compact dimensions and the combination of a two-stage planetary gearbox and a medium-speed synchronous generator in one unit. The drivetrain is supplemented by a frequency converter.

The new FL 3000 wind turbine uses the “Larus Compact” drivetrain concept already proven in the FL 2500. This concept integrates components in order to maximize security and technical availability. The wind turbine will have a rotor diameter of 120 m and a rated power output of 3MW. The wind turbine system is suitable for use up to wind class IEC 2a. Table 1
 
Conclusion
The new HybridDrive is an exciting and competitive drivetrain design. Both the conventional drivetrain and the HybridDrive have their advantages, as each offers the opportunity to reduce the cost of energy, when employed for the right application. Ultimately, the customer must decide which concept fits his/her requirements best. 

The standard gear oil textbook has been ripped up and rewritten following recent advances in wind turbine technology. The loads on the lubricant are now so great, the operating conditions are so harsh, and the need for reliability is so vital that the lubricants—like other aspects of wind turbine technology—have become increasingly sophisticated. The development of these fluids is pushing at the boundaries of known science.

At Shell we can offer a unique insight into the challenges of developing a lubricant that meets the requirements of the wind turbine industry. Creating a next-generation gear oil can take up to five years at a cost of millions of dollars. It has to undergo more than 300 separate laboratory and rig tests before it is even considered for a field trial. These tests measure a multitude of parameters such as wear protection, load carrying capability, shear stability, resistance to foaming, filterability, and micropitting protection. Figure 1

Clearly, developing a lubricant that meets the exacting standards of the wind turbine equipment manufacturers is a substantial challenge, but it has led to a wide range of highly advanced lubricants that are used across other industrial sectors. The technological advances we make in developing these lubricants are ultimately benefiting users in sectors such as mining and manufacturing. When a customer selects a lubricant for their operations that they know meet the requirements of the wind turbine industry, they can be sure that it will deliver value to their operations, whatever the challenges.

The wind turbine sector is effectively the space race of the power sector, with innovations and advances appearing at an astonishing rate. The lubricants are an integral part of this development cycle.

Wind: The Fastest Growing Power Generator
The wind turbine industry is the world’s fastest-growing option for power generation. The annual growth rate is at some 25 percent through the on- and offshore developments being pursued all over the world. Europe and Asia are driving this growth along with the United States, where wind power contributes 42 percent of all new generating capacity. Global wind power capacity is expected to more than double between 2008 and 2013.

Wind turbine installations and structures are increasing in size to maximize power generation capacities: the turbines can stand up to 150m high and have a rotor span of 100m. In 1996 the average turbine rating was 600kW, but this is increasing rapidly and most new ones are about 2–3MW, with some at 5MW. Several companies and research programmes are even planning or investigating wind turbines of up to 10MW output or more. Figure 2

Such developments will help to maximize returns on investment and reduce the cost of producing electricity from wind power. However, this expansion in generating capacity introduces various challenges for the turbine and component manufacturers, wind farm operators, and service companies that need to ensure that the equipment works reliably and requires minimal maintenance. A modern wind turbine is expected to generate electricity continuously when wind speed is available, to operate unattended, and to have extremely low maintenance requirements.

This is a complex technical challenge. The wind turbines sit on top of high columns, and many installed units have to be robust enough to withstand both very high and very low temperatures, from sub-Arctic cold to blistering desert heat, as well as salt-laden winds and rain. The rotors can also be static for periods of time, all of which place specific challenges on the lubricants. Figure 3

Designed to Meet Challenges
The main gearbox, which drives the generator and is the heart of most wind turbines, comes under enormous strain. Reliability is imperative. A major reliability concern is gearbox micropitting, which results from factors such as case hardening and the surface roughness of the gear teeth, as well as inappropriate lubricant selection and application.

Given the gearbox’s size, the lubricant’s short recirculation times and the potential for air entrainment in the system, good air-release and anti-foaming characteristics are vital properties for the gear oil. Excessive foaming can cause the oil level to rise above the maximum, which may result in unplanned turbine shutdown and loss of power to the grid. Figure 4

To deal with these challenges Shell Lubricants has developed Shell Omala S4 GX 320, a synthetic gear oil that provides excellent performance in the areas requiring added protection against common failure modes, including micropitting and bearing wear. The product offers distinct advantages over conventional gear oils, particularly for product life. Field trials have shown it has up to four times the oil life of conventional mineral oil-based products, which enables the intervals between maintenance to be extended. The lubricant also gives excellent wear protection and is designed to reduce micropitting wear on gear teeth, which helps to extend the life of gearbox components and prolong operation.

Shell Omala oils have delivered value to customers across a wide range of industries. For instance, one customer in an industrial application reports virtually eliminating gearbox failures and saving over $50,000 a year by switching to Shell Omala S4 GX. The oils have also extended oil-drain intervals: some equipment manufacturers approve Shell Omala S4 GX for four-year drain intervals, and some customers have extended their oil-drain intervals by up to five times.

However, a wind turbine’s lubricant-related challenges are not limited to the gearbox. The massive blades of a wind turbine are supported using grease-lubricated blade bearings that, if insufficiently lubricated, can fail through fretting and false brinelling. Again, the lubricant must be able to operate at temperature extremes and have corrosion-protection qualities. Figure 5

As a result, Shell formulated Shell Rhodina BBZ grease using experience gained from developing greases for helicopter rotors. This is designed to protect bearings against fretting corrosion, moisture contamination, and false brinelling at temperatures as low as –55ºC.

Shell Rhodina BBZ is establishing a track record with both customers and major wind turbine manufacturers. It is lubricating the blade bearings of many wind turbines globally through our listings with leading blade bearing suppliers such as IMO, Liebherr, Rollix and Rothe Erde, and wind turbine manufacturers including Vestas, Acciona, Gamesa, Dongfang New Energy Equipment, Sinovel Wind Group, and Siemens Wind Power.

Operating in Extreme Conditions
For wind turbines that operate in ultra-low temperatures, Shell Tellus S4 VX is recommended for the hydraulic systems. Through its specially selected base fluids, it has the widest operating temperature range in the Shell Tellus range, so it can be used in wind turbines that operate in extreme climates.

Operators that need to run hydraulic equipment in extreme cold have benefited from using Shell Tellus S4 VX because it can help to deliver high levels of equipment availability. Start-up is easy, and maintenance requirements are reduced. Crucially, it also helps to improve efficiency because the energy losses through pumping hydraulic fluid at low temperatures are controlled. The product is recommended or listed by Svendborg Brakes and by wind turbine manufacturers including GE Wind Energy, Voith Turbo, Vestas, Dongfang Wind Turbines, Sinovel, REpower, Nordex, and DHI.

The yaw gear, which is mounted on the tower and enables the nacelle to rotate, is also subjected to huge forces. For these applications Shell developed Omala S4 WE, an advanced, synthetic industrial-gear lubricant formulated using specially selected polyalkylene glycol base fluids and additives. Shell Omala S4 WE offers outstanding lubrication performance under severe operating conditions, including improved energy efficiency in comparison to mineral-based products, long service life, and high resistance to micropitting. Figure 6

Accelerating Innovation
A recent report by the International Energy Agency (IEA) suggested a target of 12 percent of global electricity from wind power by 2050, and said that there is no fundamental barrier to achieving or even exceeding this goal. It expects investment costs to continue decreasing: by 23 percent for onshore installations and 38 percent for offshore projects by 2050.

Nevertheless, the IEA counsels that increased efforts in wind technology research and development are essential. That is why Shell is working hard to develop lubricants that will meet the industry’s challenges, and it is not working in isolation. It collaborates with leading wind turbine manufacturers, component suppliers, and industry associations to understand emerging lubrication needs, the rapidly changing industry, and manufacturers’ specifications.

Every component in a wind turbine is technically challenged, pushed to the limits and operating on the edge of known science, and the lubricant is no different. Equipment design and the lubricant’s capability will be key to the larger, more-reliable units that the industry is striving for. Shell is committed to facilitating this by advancing the state of the art in lubricant technology. 

Equipment lubrication is the lifeblood of any electrical system, from the large-scale wind farm to the small single-pole 20-amp circuit breaker in our homes. Whether the lubrication is in the form of grease, oil, or powder the proper selection and application is huge, and the consequences of not correctly applying and maintaining lubrication through the life of the electrical system can be disastrous.

Considering all of the related training seminars, certifications, application tools, manufacturers’ published data, and the overall industry awareness about the importance of lubrication, the failure of rotating machines should be rare and unheard of. But the truth is that lubrication-related failures happen every day, and with a high cost to production, reliability, and worst of all to safety. This article will explain some of the common terms and best practices that an owner/operator of a wind farm can use to keep his or her equipment properly lubricated so they don’t get burned by failures and downtime.

Learning the Lingo
Understanding “lubrication lingo” is important when dealing with electrical equipment. Think about the physical properties of lubrication with these terms and how they can apply to electrically driven mechanical devices.

Lubrication: The process or technique employed to reduce wear of one or all surfaces in close proximity and moving relative to each another by interposing a substance called lubricant between the surfaces to carry or to help carry the load (pressure generated) between the opposing surfaces.

Elastohydrodynamic lubrication: Opposing surfaces are separated by just a few microns of lubrication, but there is interaction between the raised solid features called asperities, and there is an elastic deformation on the contacting surface, enlarging the load-bearing area whereby the viscous resistance of the lubricant becomes capable of supporting the load.

Boundary lubrication (also called boundary film lubrication): The bodies come into closer contact at their asperities; the heat developed by the local pressures causes a condition which is called stick-slip, and some asperities break off. At the elevated temperature and pressure conditions, chemically reactive portions of the lubricant react with the contact surface forming a resistant layer or film on the moving solid surfaces (boundary film) which is capable of supporting the load and major wear or breakdown is avoided.

Oil viscosity: Viscosity is the capacity of a fluid to provide resistance, and thus friction, to an opposite laminar movement of two adjacent layers. If you have high viscosity there is a high resistance to flow, whereas a low viscosity is a thin fluid. Viscosity should be appropriate for the load and speed of the application at operating temperature. This will help to insure maximum protection and component life.

Grease consistency: The consistency of grease is one of its most visible characteristics, and the consistency of grease should be appropriate to the application as it affects the ability to reach the areas to be lubricated. An NLGI (National Association of Lubricating Grease Manufacturers) grade 2 grease is the most commonly used grease in electric motor and generator applications.

Oxidization resistance: Oxidation resistance is a behavior of lubricant greases that are exposed under static (in-service) conditions and influenced by the atmosphere for a prolonged period of time. Electric motor greases should have outstanding resistance to oxidation, as this extends the life of bearings running at high speeds and high temperatures, such as greases with a high ASTM D 3336 oxidation life.

Anti-wear and extreme pressure additives: Anti-wear or AW additives are for lubricants that help prevent metal-to-metal contact between parts of gears and bushings and usually contain zinc or phosphorous compounds. Extreme pressure (EP) additives are commonly used in applications such as gearboxes or where there is a thrust load on bearings. AW additives are used with lighter loads such as hydraulic and automotive engines. EP additives can shorten the life of the grease and should not be used where they are not needed.

Dropping point: The dropping point of lubricating grease is the temperature at which it passes from a semi-solid to a liquid state. It is used in combination with other testable properties to determine the suitability of greases for specific applications. It is applicable only to grease that contains soap thickeners made of fatty acids or metallic salts.

So what does it all mean? In layman’s terms, “lubrication” really means reducing the surface friction between two components with oil or grease that creates a small amount of pressure to keep the two components equally apart. Lubricants also act as a coolant to contact areas and can assist in the removal of wear products. While carrying out these functions the lubricant is constantly replaced from the contact areas either by the relative movement (hydrodynamics) or by externally induced forces. Without lubrication you will likely have equipment seizures that are similar to the welding together of components… or even get burned, literally and physically!

Keeping it Lubed
The average gearbox takes a lot of abuse, and when applied to wind it is actually an extreme engineering challenge due to the difficulty in properly assessing the loads—in particular the non-torsional loads that pass through the gearbox—and how these affect bearings and gears. A gearbox absorbs additional loads introduced by the rotor such as shaft bending through a single bearing assembly and deflections of the bedplate and main bearing, not to mention alignment issues. This makes for a nasty mess that could propagate additional points of failure due to lubrication contamination. These contaminants create issues like micro-pitting, which can lead to wearing and changes in gear teeth shape and reducing gear accuracy, increasing vibrations, noise, and eventual misalignment and failure. Most gearbox manufacturers utilize a special gearbox oil filter, which helps ensure maximum oil cleanliness. This is a key factor in environments where dust and debris can get into gearboxes and eventually lead to contact fatigue failures.

Many motor and generator bearings are lubricated with an automatic greasing system. These auto lubrication systems promote improved operating times and longer maintenance intervals, typically one year or longer. Additional benefits are lower costs for repairs, spare parts, and lubricant, and greater bearing life from regular, exact amounts of lubrication. This system minimizes or eliminates safety risks associated with hard to reach lubrication points, increases corrosion protection from the elements, and significantly reduces the amount of wasted lubrication.

Lubrication issues on a circuit breaker can cause catastrophic results. The overall safety of the electrical worker has become a higher priority at the wind farm, and we cannot forget about what the lack of lubricant, and hardened lubrication, can do to an overcurrent protective device such as a circuit breaker. In 2007 The International Electrical Testing Association (NETA) performed a study of overcurrent protective devices tested on a normal and routine basis. This data was supplied by its member companies and analyzed a cross section of electrical equipment in North America. The survey yielded data about the average condition of electrical equipment currently in service throughout the United States. Of the defective devices found in the survey, 51.4 percent had lubrication issues with the breaker mechanism or operator.

Circuit breakers create a huge lubrication challenge since most of them remain static in the closed position and do not operate for months or even years at a time. When these protective devices are called on to operate and interrupt faults they may be slow, sluggish, or may not operate at all due to the factory lubrication drying out and/or hardening over time. This creates a coordination nightmare, and it increases arc duration and incident energy exposure. This situation can render the best electrical safety program, training, and PPE less effective, it can affect the results of the arc flash study, and worst of all it can lead to an electrical worker getting burned.

Getting Burned
It can be said that many of the lubrication issues that face the wind industry are very similar to those that exist in general industry. As a third party insulating oil and lubricant testing laboratory, many lubrication pitfalls are noted while analyzing wind generator oil and grease samples.

Lubrication quantity: An insufficient amount of grease and oil will lead to excessive wear and overheating, eventually leading to catastrophic failure. Excessive amounts of grease allow the rollers to slide in the journal, causing heating and scoring. Conversely, large amounts of grease can migrate into the generator windings creating potential contamination and electrical insulation issues.

Lubrication storage: Humidity, moisture, sand, and other contaminants are typically found in many samples. A drum of oil stored in the sun and allowed to cool during the night can collect as much as a gallon of water within a few weeks of being stored in such conditions. These same conditions will occur within lubricated systems like hydraulic reservoirs and gear cases. In these conditions, water-absorbing filtration systems should be considered.

Lubricant corrosion: Red/brown areas on balls, raceways, cages, or bands of ball bearings are symptoms of corrosion. This condition results from exposing bearings to corrosive fluids or a corrosive atmosphere. In extreme cases, corrosion can initiate early fatigue failures.

Lubrication sampling/trending: Contamination of lubricants by dirt, wear metals, water, or other particulate matter cause over 70 percent of lubrication related equipment failures.

Lubricant incompatibility: Incompatibility can be caused by something as simple as mixing two different greases or oils to the same lubricated component. Incompatible greases may be indicated when the oil in the grease begins to leak past the bearing seal within minutes of regreasing a bearing. Incompatible gear oils may cause oil seals to soften, shrink, or harden, resulting in a leak. Excessive foaming in a hydraulic reservoir may be the result of mixing two incompatible hydraulic oils.

Lubricant color: As oils age in service, it is normal for them to thicken and become darker in color. If an industrial oil becomes thicker and turns brown or almost black in color in an abnormally short period of time, however, the cause is almost always temperature related. Excessive operating temperatures will cause the oil to oxidize prematurely causing the viscosity to increase and the color to darken. Greases can also oxidize if a bearing is continually over greased.

Lubricant failure: Discolored (blue/brown) ball tracks and balls are symptoms of lubricant failure. Excessive wear of balls, rings, and cages will follow, resulting in overheating and subsequent catastrophic failure. Ball bearings depend on the continuous presence of a very thin (millionths of an inch) film of lubricant between balls and races and between the cage, bearing rings, and balls. Failures are typically caused by restricted lubricant flow or excessive temperatures that degrade the lubricant’s properties.

Lubricant contamination: Many of the gearbox and generator manufacturers utilize epoxies and specialty glues to attach bearing covers, inspection ports, and filler caps. Many times trace to large amounts of these substances are found in grease and oil samples, or worse implicated in bearing failures of gearboxes and generators. The largest majority of sample data has shown that high ferrous and ferrous particles are usually present. Large amounts of sand and epoxies contribute to excessive wear, overloading, and overheating that eventually leading to catastrophic bearing failure.

To-Do List
To maintain reliable systems, during the uptower inspection process you should have or develop an inspection, testing, and sampling route for the gearbox main shaft bearings and yaw/pitch gears. Typical time frames for the inspection process are:

• Monthly—visual inspection of the machines anchorage, alignment, oil levels, filters, pumps, valves, coolers, heaters, manifolds, and piping to connect components, as well as vibration sampling and analysis on the rolling elements.
• Quarterly—monitor the condition of the lubricating fluids through sampling and testing to determine wear and contamination levels for metals, viscosity, particle count, water/moisture, total acid number and oxidization/nitration through sampling and trending of gearbox oils and generator greases. If contamination is an ongoing issue, routine weekly sample cycles can help predict failure allowing for a pre-planned outage window for component repair/replacement.
• Every four to six months—perform lubricating oil filter changes, apply grease to gear teeth and slew bearings. Check and top off oil lubricants in yaw/pitch gears.
• Annually—inspect contact and wear patterns of gears and bearings on the rolling element with the use of borescope/videoscope cameras.

When maintaining collector substation and circuit breakers, develop electrical maintenance programs that employ a lubrication component as part of the program. You should develop the program based on national consensus standards (see references). Adopting a complete maintenance and lubrication plan will significantly reduce the risk of catastrophic equipment failure. With the high growth rate of wind power, understanding the impact of proper lubrication on high stress equipment is essential to achieve a high availability. Lubricating materials, procedures, and test methods are continually improving, providing invaluable tools for maintenance personnel that improve the operation and safety of wind power generators. So keep it lubed, and it will keep you from getting burned.

Conclusion
In spite of the high lightning risk that wind power system installations are exposed to, they can be protected by the application of Surge Protection Devices and Lightning Protection Systems. Regarding SPDs, one must give thoughtful and careful consideration to the placement of the SPD on the system and what they are intended to protect, the connection from the system to the SPDs, and the proper bonding of all grounded members and the ground system. Also check for the adequate discharge rating of the SPD, the voltage protection level the SPD provides, the suitability of the SPD for the system it is applied to, and consideration to failure mode of SPDs and status indication. Also be mindful of local and remote status indication and easily replaceable modules, and the suitability of SPDs on systems so as not to affect normal system function, specifically on non-power systems. 

References:
1) IEEE STD 902-1998 (Yellow Book) Guide for Maintenance, Operation and Safety of Industrial and Commercial Power Systems.
2) NFPA 70B, Recommended Practice for Electrical Equipment Maintenance.
3) International Electrical Testing Association (NETA) ANSI/NETA MTS-2011 Standard for Maintenance 1) Testing Specifications for Electrical Power Distribution Equipment and Systems.

Wireless technology was once limited by inadequate bandwidth, early integrated circuit design, and insufficient power management technology. Improvements to today’s wireless networks allow robust monitoring and control, even in remote and harsh applications or classified areas.

Bidirectional communications, fully-acknowledged data transfer, and configurable default output conditions now make remote and field-based monitoring and critical control a reality. Low power systems and high capacity battery packs provide a lower cost and more reliable solution than previous technology. These alternative power options have increased the usability of sensor networks because the systems are no longer limited only to locations wired for power. New systems enable cost-effective monitoring that is scalable down to a single point.

Today these improvements to RF technology make wireless an ideal solution for a wide variety of applications including field-based agribusiness, remote power generation, and water management systems. Process measurements such as operational status, temperature, rotational counts, and other crucial information can now be easily monitored and controlled remotely, even in locations not wired for data transfer or power.

Remote I/O Monitoring in the Past
Historically, wireless remote terminal unit (RTU) systems incorporated a number of different components, including an RTU, radio, solar panel, and rechargeable battery pack, as well as input and output terminals. Once all these devices were selected users still had to purchase an outdoor enclosure and integrate the disparate components into a single, cohesive system. These older systems were difficult to purchase and install in part because of the number of components and vendors required to complete the monitoring system. Figure 1

Older monitoring systems were complicated to maintain over time. They required large solar panels and batteries to operate because of the diverse power requirements of the components, making these monitoring systems too expensive, or too large, for small, single-point monitoring systems. To be cost effective, installing these systems required wiring as many I/O points as possible back to each remote node. Ironically, it required a significant amount of conduit wire and time to connect a dozen or more I/O points to the traditional large wireless RTU panel. Once they were set up, these systems could not be easily relocated if the application location changed.

Remote I/O Monitoring and Control Today
Today, many remote monitoring solutions are available that offer more reliable wireless communication while integrating many of these components into a single, palm-sized, inexpensive unit. A radio and I/O terminal contained within a single housing rated for outdoor use eliminates the need for an additional enclosure. These new wireless industrial I/O devices are easy to install and then move to a new location as requirements change.

With the radio, power controller, I/O terminals, and RTU components included within a single, water-resistant housing, fewer mechanical and wiring issues need to be incorporated into a maintenance schedule, resulting in valuable time and cost savings without sacrificing capabilities. A single wireless I/O device can collect both digital and analog sensor readings and forward this data to a central collection point for analysis. This ability to log and track data across a wide area creates new opportunities for operators to identify trends that need an immediate response.

Evolution of RF Technology
Just as packaging improvements have made wireless monitoring systems easier to install, radio communication technologies including Frequency Hopping Spread Spectrum (FHSS) have improved network reliability. When using FHSS as a communication method, the frequency range is split into several channels. Data packets are transmitted using these channels randomly in a pattern known only to the master device, or gateway, and the nodes. If interference is detected on one channel, both radios hop to the next channel and resend the data packet, minimizing unsuccessful transmissions in high interference environments.

Another method of ensuring successful data transmission is by using Time Division Multiple Access (TDMA), which divides communication time into specific time slots for each node and guarantees all devices within a radio network have time to transmit and receive data packets. When multiple radios are not trying to communicate with the master device at the same time, data collisions and radio interference are minimized. Using TDMA to avoid data collisions also prevents wasted power resources in resending data packets.

Bidirectional transceivers on both ends of a communications link ensure fully acknowledged data transmissions on both ends of the wireless link. Polling and site survey capabilities monitor communication integrity either at the radio master device (gateway) or locally at each radio node. A site survey is a signal strength analysis conducted by the gateway to determine the reliability of the radio signal received by the node. If a site survey is conducted before installing the devices, the test ensures each node is positioned at an optimal location. New industrial wireless solutions have site survey capabilities built into every device, ensuring the wireless communication link can be monitored even while application data is being exchanged. Figure 2

Gateways poll their nodes at specific intervals to verify the radio communications are operating. If a gateway identifies a radio link that is not operational based on an unsuccessful poll, these new systems are capable of reacting deterministically. Deterministic response capabilities drive specific outputs to a user-defined state when wireless links temporarily fail, ensuring control over the network and system responses.

Power Management Systems
To accommodate remote monitoring needs in locations without power, optimized wireless I/O devices using advanced power management technology can operate from a single battery pack for several years. State of the art power management systems can now be configured to extend battery life up to 10 years. This extended life span is achieved by putting the entire system in a low-power mode that consumes very little power.

The power management system can be configured to periodically sample the sensor and report data at defined intervals. These intervals can be configured from a few samples per second to a few samples per hour with the longer sampling intervals corresponding to longer battery life. Typically, a five to 10 year battery life is achieved by optimizing the sensor’s sample rate while preserving power to provide constant radio communication.

Integrated power management systems are also beneficial when using solar power. Typically the entire solar panel system can be significantly smaller, less expensive, and easier to install. With power options that include solar panels or battery packs, radio devices can now be installed over a wide geographical area, extending the range of data collected over many miles.

A growing class of power-managed sensors, including temperature, relative humidity, ultrasonic, and others take advantage of independent power sources to operate for years without replacing batteries. These sensors and their radios can even operate using wired power in ideal conditions and then switch to a battery module if the wired power fails.

Cost Effective Scalability
Now multiple sensors can be connected to a single radio node, and dozens of radio nodes can exist within a single radio network. Hundreds of sensor readings can be aggregated into a single gateway device before being forwarded to a host-controlled system, such as an HMI or PLC, for analysis.

Further extending a wireless I/O network are serial data radios, backhaul devices that receive serial data from another data radio and forward that data to another serial device miles away. Chaining data radios can expand a wireless I/O network indefinitely. This backhaul architecture enables limitless scaling for everything from single-point data collection to 10,000 data point applications while retaining the cost advantage associated with minimal wiring for power or I/O transmission.

Today’s wireless technology enables remote monitoring solutions that were previously unaffordable or impractical to install. Compact, reliable, inexpensive wireless I/O monitoring devices can now be installed in isolated, low-signal count locations for data collection. These compact devices can be easily relocated as the application changes.

Remote Monitoring Applications
The new generation of wireless remote I/O is particularly suitable for small, single-point measurements such as monitoring motor temperatures in isolated locations. While previous remote monitoring technology was too expensive or too bulky to use for low-signal count applications, current technology makes these applications easy to install and use regardless of scale. For example, a single wireless I/O device and power-optimized temperature sensor can reliably monitor motor temperatures and report the measurements back to a central location. The “peel and stick” installation allows this device to be easily moved and reinstalled depending on the requirements of the application.

Because these devices are more compact than past systems and are certified for a wide variety of environments, they are easy to retrofit into existing applications, particularly on mobile assets such as trucks or boats that must enter and exit hazardous locations or areas rated to require intrinsically safe equipment. These devices can be installed in a broad range of environmental conditions ranging from outdoor installations exposed to weather to applications within hazardous or explosive locations.

In the case of wind turbines, a common predictive maintenance application involves monitoring bearings, gearboxes, shafts, and generators for excessive vibration. When excessive vibration is detected, repair crews can be scheduled to correct the problem before a complete failure occurs, saving time and money. In many wind turbine installations there are already sensors installed on the turbine to detect blade pitch, strain, and load. Using wireless technology to gather and transmit this information eliminates the need for costly, maintenance-intensive slip rings.

Data from accelerometers can be collected from up to 48 wireless nodes on a wind farm and wirelessly transmitted back to a central control point for logging and analysis. Depending on the distance the data needs to travel, MultiHop data radios may be integrated into a data collection network to extend the reach of the wireless network, or the data may be pushed up to a satellite or cell modem. Today’s wireless technology makes retrofitting existing installations quick and easy.

Conclusion
Whether an application needs to be a cost-effective solution for single-point monitoring or scalable up to 10,000 data points, the new generation of wireless products and sensors offer reduced installation time, multi-year battery life, reliable radio communications, and simple integration into existing plant-wide control systems. These new wireless networks offer a simple solution to increase productivity and reduce labor costs without sacrificing ease of use. 

The White Creek Wind I and Harvest Wind farms are owned by four consumer-owned utilities and operated by the NAES Corporation. NAES plant staff investigated solutions to upgrade the existing communications system at these facilities located in south central Washington State, selecting Bergelectric—one of the nation’s top electrical contractors—to develop and install a state of the art Internet-over-fiber solution. This communications solution provides an example of how to outfit a wind station with outstanding and cost effective safety and communications capabilities. Bergelectric designed the VoIP (Voice over Internet Protocol) system, partnering with IndustrialENET for its resilient industrial network solution and experience in the wind industry. IndustrialENET has developed communications solutions for the wind industry since 1997, including supplying Ethernet switches for more than 10,000 wind turbines.

As with many wind farms, the White Creek Wind I and Harvest Wind facilities are constructed over a large geographical area, in this case approximately 40 square miles. In order to find a site with large enough parcels, and with lower property costs, these two sites were developed in a remote area void of cellular or hardwired phone service.

At the White Creek Wind I site, and magnified with the addition of the Harvest Wind Project site, there was concern with the poor coverage for site communications. Both sites used two-way radios with the signal amplified by a single radio repeater. For maximum coverage, the repeater was installed in a wind turbine that had a battery backup system to maintain communications during grid outages. Even with selecting a turbine that provided maximum “line of sight” coverage, however, there were holes where radio contact could not be maintained.

Further, the radio system provided communication between radios only; that is, crew to crew, or between the crew and the O&M building. During periods of limited staffing, such as when on-call crews must respond to an issue on a Sunday, offsite communication was not available. In the event of an emergency, a technician could not call for emergency services using the radio system. Cell phone coverage, which was also very limited, did not provide a suitable alternative form of communication. Plant staff had to ensure that there was always a staff member at the O&M building whenever crews were working—a rather inefficient use of plant labor.

Investigating Alternatives
For the past year NAES plant staff studied solutions to address the communication coverage, including technologies that provided additional benefits such as Wi-Fi routers in the towers, cell phone repeaters mounted on the met tower, radio repeaters, satellite phones, and others. Two viable technologies were investigated further.

First was an improved radio system that provides minimum coverage from a safety standpoint. This system involves installing a second repeater to provide coverage over the entire site, along with a link to allow for simultaneous use of multiple repeaters. With the addition of a phone switch, the radios can also be used as a telephone allowing for offsite communication during emergencies or for technical support. As with any radio system, however, multiple conversations cannot occur simultaneously. If a technician is on a support call, which could easily last 30 minutes or more, no other onsite (two-way radio) or offsite (emergency) calls can be made.

The second technology that was investigated provided Internet access over fiber optic cabling to meet not only the minimum coverage for safety, but also to provide significant benefits for technician tools and turbine monitoring. This system makes use of two spare fiber optic cables already in place at the base of each tower, extends those fibers up the tower into the nacelle, and terminates them in a fiber-Ethernet switch that includes a VoIP phone and an Ethernet port (fig. 1). The phone allows for communication between towers, the O&M building, and offsite. The Ethernet port allows technicians to access the site servers providing instant access to electronic manuals, the SCADA system, turbine work history, the Computerized Maintenance Management System (CMMS), and more. Further, with a static IP (Internet protocol) address in each tower, any Internet-based electronics such as cameras, vibration monitors, and sensors can be easily installed and then accessed from any Web-based interface.

In the final analysis the enhanced radio system met the minimum requirements for safety coverage, yet failed to provide the capability to conduct multiple simultaneous conversations. The Internet-over-fiber solution, though significantly more expensive than the enhanced radio option, met not only the minimum safety coverage, but also provided technicians with access to all pertinent manuals, history, and operational programs, as well as providing a platform for future monitoring needs. The Internet-over-fiber option was the final recommendation.

Designing the System
The communications infrastructure at wind farms typically utilizes fiber optic cabling connections amongst the wind turbine generators, and in most cases, between the O&M facility and substation as well. In some cases wireless capabilities are also built into the communications system. When designing the technical requirements for the communications system many key factors need to be considered, including enhanced 911 (E911) calling features, availability, quality of service, ambient conditions, open standards, security, and system vulnerabilities.

It is also good design practice to provide multiple Ethernet ports to allow connectivity to other edge devices, such as cameras, laptops, Wi-Fi devices, and perhaps even IP-enabled testing equipment and instruments.

Crucial Features
Enhanced 911 (E911) is paramount in cost justification and is an important component to the system. Features should include user definable CALLER ID of 911 calls by location, automated call recording of all 911 calls, and notification of 911 calls in progress to all operator group members, including the extension that made the 911 call.

The call should be recorded in Call Data Recording (CDR) format and generate a “syslog event” as well. With proper set up on a syslog server, this event can be emailed to the appropriate emergency services as soon as the call is made. Syslog is a standard for logging program messages that separates the software that generates the messages from the system that stores them and the software that reports and analyzes them. It also provides devices that would otherwise be unable to communicate a means to notify administrators of problems or performance. Syslog can be used for computer system management and security auditing, as well as generalized informational, analysis, and debugging messages. It is supported by a wide variety of devices like printers, routers, and receivers across multiple platforms. Because of this, syslog can be used to integrate log data from many different types of systems into a central repository.

Redundancy Important
A failure in the communications system can sever the very link needed to communicate an emergency. Knowing when there is a single point or multiple points of failure is important so that corrective action can be taken immediately. This is possible only if the network is composed of managed switches with robust redundancy protocol/s enabled, and with the fiber media constructed into a ring since folded rings are common in the wind industry.

When wireless is used, the system needs to include two radios on each side of the communications link, with one radio configured as the primary link and the other as the backup link. In this case, the Rapid Spanning Tree Protocol (RSTP) is common.

Redundancy and link failures need to be alarmed back to a network management system that is capable of notifying staff, either by continuous monitoring or via email, if there is a link failure between the switches, radios or an edge device, such as the telephone. The first backbone link failure will go unnoticed until a second failure occurs, by which time either a portion or all of the network will have been severed, possibly resulting in the inability to make a call. Refer to Figure 1 when considering the following:

1) Each nacelle includes a VoIP telephone and managed Ethernet switch located in a water tight enclosure with a clear door, as well as one FX multi-mode port and three TX RJ45 ports (FX = Fast Ethernet over optical fiber, and multi-mode fiber is typically used for distances less than 6 miles and is less expensive than single mode fiber, which is typically used for distances greater than 6 miles);
2) If desired, a down tower managed switch can include two FX single-mode ports, one FX multi-mode port, and six TX RJ45 ports;
3) Managed switch configured as the redundancy manager, located in an IT room or substation and connected to the nacelle system via both a standard link and a redundant link;
4) The connection to the telephone company/service provider includes the Telco Connectivity Appliance, a VoIP IP PBX Gateway, a Syslog Server that supports E911, and a Layer 3 (preferred) managed switch;
5) IP camera mounted with a spring clamp and connected with 20 foot Cat 5e cable;
6) Edge devices (laptop computers, etc.) can be connected to allow access to system manuals and Internet connectivity.

Industrial Communications Equipment
To avoid equipment failure at the turbines, use only robust industrial rated communications equipment that can survive the ambient conditions, shock, vibration, and equipment line power anomalies at the site. Deploy only industrial-rated Ethernet switches that follow industry standard practices and approvals. The same requirements should apply to all the devices, whether located in the turbine or in any harsh environment, such as in the substation or elsewhere.

Planning the VoIP System
The VoIP system is composed of a gateway—which is a computer or a network that allows or controls access to another computer or network—connecting the telephone service to the local area network (LAN), and in most cases the wide area network (WAN) as well. It is very desirable that the gateway will support the VoIP Session Initiation Protocol (SIP), which is an IEEE Open Standard. This way, you can choose from a number of different suppliers when selecting the telephones. The telephones can either plug directly into an Ethernet switch or be wireless, as in the case of also including a Wi-Fi cloud over the site. A good gateway architecture that includes redundancy from the Telco (telephone company) side is recommended, along with using a combination of any two of the following services: Plain Old Telephone System (POTS) lines, T1, PR1, DSL, and an Internet Telephony Service Providers (ITSP) SIP trunk. Keep in mind that the lower the power requirements for these options, the better. Back up both the VoIP gateway and the syslog server with a UPS (uninterruptible power supply) system designed to keep the system up and running for a predetermined amount of time, typically several hours. How long might an emergency last?

Encrypted Connection
A Linux operating system running on the VoIP gateway is a better choice than using an Open Source Architecture, such as Windows. This way, there is a greatly reduced risk to vulnerabilities and hacker attacks.

The Secure Shell (SSH) allows a secure remote channel to be opened between the gateway and any remote programming station. SSH uses encryption to provide a secure connection to the gateway over an unsecured network, such as the Internet. This secure level of support is highly desirable when provisioning SIP trunks and performing troubleshooting and maintenance.

Ensuring Voice Quality
Quality of service is very important when using VoIP, as packet loss and delays can make the voice transmissions useless. Therefore the network system of switches and/or appliances should support prioritization, especially if the network is intended to share other media such as video and Internet connectivity.

With prioritization, you can select which data packets are sent first over the system, ideally the VoIP has the highest priority. If a large amount of video data is to be transmitted over the network, then implementation of an IEEE 802.1Q VLAN (Virtual Local Area Network) is recommended to virtually separate the video traffic from the VoIP traffic. VLAN architecture can also be used to secure the VoIP network from the network ports intended for the edge devices (laptop computers, etc.) and that traffic.

Internet-over-Fiber Solution
Between July 19 and December 2, 2010, NAES plant staff worked with Bergelectric to install Internet access in the 132 wind turbines at the White Creek Wind I and Harvest Wind facilities, as well as a telephone equipped with the Enhanced 911 (E911) technology. Each nacelle is now equipped with a NEMA 4 box that includes the fiber-to-Ethernet switch, a VoIP telephone, a power supply, and a surge protector. The box also doubles as a laptop stand.

The project is already showing the potential to lower insurance premiums and labor services costs. The E911-enabled phone and IP connection for various devices such as computers, cameras, and sensors are not only increasing safety for maintenance personnel, but are also enabling them to be more efficient. Technicians can now access electronic work instructions, contact technical support, access manuals and diagrams, and operate the SCADA system, all while at the top of a wind turbine, eliminating the time consuming up-and-down process to climb the tower or the use of a radio-to-phone middleman.  

More than a decade ago Castrol Optigear® Synthetic A 320 (OGSA 320) was developed to meet specific criteria developed by the National Renewable Energy Lab (NREL) for use in wind turbine gearboxes. OGSA 320 was submitted along with products from other major lubricant suppliers. The gear oils were tested against specific criterion that included operating temperature range, protection against micropitting wear, and the ability to last up to 20 years in the gearbox.

Castrol Optigear Synthetic A 320 outperformed all other oils in the micropitting resistance tests due to its unique Microflux-Trans® (MFT) anti-wear and anti-scuffing additive system. Under extreme loads the organo-metallic additives in the MFT system enhance the gear surfaces by plastic deformation. This smoothing of the surfaces increases the load bearing surface area, thereby reducing wear and lowering friction.

Visual evidence of MFT’s surface smoothing effect can be seen in Figure 1 and Figure 2. Figure 1 shows a highly magnified wear scar surface from an SRV wear test with a conventional gear oil. Figure 2 show the SRV test surface using MFT surface-active technology.

Castrol Optigear Synthetic A 320 quickly became the industry standard for wind turbine gear oils and gained approval from many of the wind turbine OEMs for first fill, in large part due to its superior micropitting protection. OGSA 320 has been operating successfully in over 17,000 turbines worldwide.

Performance Issues Arise
With the original goal of a 20-year life set forth by NREL—note that the current gearbox lifespan is expected to be 10 years—the anti-wear and anti-scuffing MFT additives were formulated in robust proportions. It is known that the MFT additive package is somewhat hygroscopic and will take up certain amounts of water. This was not an issue in the field until wind farms began to expand from arid climates to more-humid locations such as the Midwest and Upper Midwest regions of the United States.

In a very small percentage of turbines filled with OGSA 320, water content became an issue. Where water determination by Karl Fischer results showed greater than 500 ppm water, some turbines experienced precipitation of the additives. The resulting additive fallout residue caused premature filter loading, and in some cases false low oil level alarms due to interference with the low oil level sensor. Even with this additive fallout, however, levels in the oil remained above the minimum specifications and wear protection of the gears and bearings were never compromised. Additionally, oil life did not appear to be negatively affected.

In an attempt to mitigate and respond to these issues caused by high water content, Castrol Detergen® System Cleaner (DSC) was added to the gear oil in small percentages in several turbines. DSC has been in the Castrol product line for more than 20 years and is an oil-based cleaner containing detergents and dispersants. It dissolves sludge residues and is routinely used for cleaning industrial gearboxes and hydraulic systems prior to oil changes. After it was added to the problematic wind turbine gearboxes, improvements were quickly noted: additive residues were eliminated from the filters, and false low oil level alarms stopped.

Laboratory Testing Verification of Water Effect
The additive precipitation described above, and reduced additive levels also presented in a small percentage of field cases. In early 2010 Castrol performed extensive laboratory testing to validate the effects of water on OGSA 320, and to verify positive field experience that DSC can reduce the negative effect water engress has on the additive system.

Water Effect on Optigear Synthetic A 320 Additive System
Four samples were prepared: 1) control sample new OGSA 320; 2) OGSA 320 with 500 ppm water; 3) OGSA 320 with 750 ppm water; and 4) OGSA 320 with 1,000 ppm water. Visual inspection confirmed that there is no additive fallout in the OGSA 320 control sample without water. However, in the water-contaminated samples the field experience was confirmed and certain additives were seen to precipitate out and cause a residue. Figure 3 shows the sample with 750 ppm water, and a light brown sludge can be seen at the bottom of the cylinder.

The Optigear Synthetic A 320  additive system consists of magnesium (Mg), molybdenum (Mo), zinc (Zn), and phosporus (P) typically in levels ranging from 1,200-1,800 ppm for new oil, with minimum limits on used oil from 400-3,000 ppm. Spectrographic analysis of the top and bottom layers of the oil samples found approximately 2X the levels of Mg and Mo on the bottom as compared to the top layers of the sample with 750 ppm water. This confirmed that the residue was indeed additive fallout. Of the three, the sample with 750 ppm had the most dramatic difference between the top and bottom layers. Based on this testing, the following conclusions can be made regarding the water effect on the OGSA 320 additive system:

• OGSA 320 with no water added is stable with no additive precipitation;
• At water levels over 500 ppm, additive precipitation and fallout can occur;
• With 750 ppm water added, OGSA 320 can form additive fallout residue, particularly of the Mg and Mo components of the additive system;
• Water at these levels does not have a significant impact on P and Zn.

Castrol Detergen System Cleaner Effect on Additive Precipitation
Laboratory testing and field experience clearly indicate that certain additives, primarily Mg and Mo, can precipitate out of solution and form residue when OGSA 320 is exposed water contamination in excess of 500 ppm. To investigate the effect DSC can have on mitigating this issue, 2- and 5-percent dosages were added to the samples with 500 and 750 ppm of water and fallout present. After the DSC was added, the samples were agitated and allowed to cure for 48 hours. The DSC immediately cleaned up the residue fallout in both samples. Figure 4 shows the sample with 750 ppm water and 5 percent DSC with no fallout present.

Spectrographic analysis of the top and bottom layers of the oil samples confirmed that the additives went back into solution. The amounts of Mg and Mo in both layers were approximately equal and back to normal. This supported the visual conclusion that the fallout residue became soluble back into the oil. Based on testing, the following conclusions can be made regarding the effect of DSC on additive precipitation:

• DSC caused the precipitated additive components to go back into solution;
• OGSA 320 that had additive fall out residue in the presence of 750 ppm water appeared clear with no distinct layers after the addition of 5 percent DSC;
• At 5 percent DSC added, the amounts of Mg and Mo in both the top and bottom of the oil sample layers became approximately equal;
• DSC does not have a significant impact on P and Zn.

Castrol Detergen System Cleaner Effect on Wear Protection, Foaming, and Filter Life
After it was determined by lab testing that the addition of DSC had the desired positive impact, further testing was performed to see what effect the DSC would have on other key performance properties of OGSA 320. For all of these tests, three samples were used: 1) control sample new OGSX 320; 2) OGSX 320 with 750 ppm water and 2 percent DSC; and 3) OGSX 320 with 750 ppm water and 5 percent DSC.

SRV wear tests were performed on the three samples. The addition of 2 or 5 percent of DSC did not have any significant effect on either wear scar diameters or the coefficient of friction of OGSA 320 as compared to the control sample. In fact, a scar diameter of 0.44 mm was reported for the DSC and water containing samples, which is lower than the 0.50 mm scar diameter for new OGSA 320.

ASTM D-892 foam test was performed on the three samples. All of the samples (without DSC added) were placed in a 60 C oven for two weeks and tested. As expected, the control sample exhibited excellent anti-foaming properties in all sequences of the test. The presence of 750 ppm of water greatly increased foaming, especially at the elevated temperature of sequence II. The two samples with 750 ppm water were then dosed with 2 and 5 percent DSC, and all samples were placed back in a 60⁰ C oven for two weeks. The sample with 2 percent DSC with 750 ppm water reduced foaming by one half, versus the sample without DSC. At 5 percent DSC level foaming was practically eliminated in both the sample with 750 ppm water and the control sample.

Filter life is impacted by many variables that are not related to the oil, such as external contamination. However, filterability of the oil as measured in the amount of oil-generated particles remaining on the filter media also impacts filter life. To test this, 25 mLs of each sample was filtered through a 2.7 micron filter. The filter papers were carefully weighed before and after filtering and after being dried, and the results reported in percentage of mass change. Mass change of the filter is directly related to the amount of additive precipitation. With 750 ppm water in OGSA 320 and without DSC, the percentage of mass increased by 2.6 times due to the additive fallout. With 2 percent DSC added to the sample with 750 ppm water, the percentage of mass change is about equal to a new OGSA 320 sample without water or DSC. With 5 percent DSC added the percentage of mass change was reduced more than 10 times versus the sample with 750 ppm water and no DSC, and five times lower than the new OGSA 320 sample without water or DSC. Laboratory testing conclusions showed that:

• Certain additives, especially Mg and Mo, can precipitate and fall out of solution from OGSA 320 in the presence of 500 to 1,000 ppm water;
• The addition of low concentrations of DSC has no adverse effect on SRV friction or wear properties;
• With DSC added, OGSA 320 easily passed all foam tests and outperformed new oil (without water or DSC);
• Filterability is significantly improved with DSC even better than clean oil with no DSC;
• Any negative effects due to water contamination are completely mitigated by a low dosage treatment of Castrol DSC.

Field Experience with DSC
Subsequent to the laboratory testing, DSC has been added to more than 140 turbines filled with OGSA 320 and operated for three to six months. Since oil sample intervals are generally six months, we have only been able to review about 40 recent samples to compare the results to samples prior to the addition of DSC. The results have been good. Molybdenum levels are all well above the minimum requirements, and they have stabilized nicely. Cleanliness levels are good, and there have been no reports of any residue in the filters and filter housings that have been inspected. Neither have any issues concerning shortened filter life, or false oil level alarms caused by residue, been reported. A gear inspection of one turbine which had been in operation for three years using OGSA 320, and had 5 percent DSC added 90 days prior, showed clean gear tooth surfaces with no signs of pitting or wear (Figure 5).

Even in high humidity areas, a reduction in water content has been documented in many cases. In one controlled study of 10 GE 1.5MW wind turbines located in the upper Midwest, a 28 percent average reduction in water was reported after 60 days of adding DSC.

Conclusion
The addition of 5 percent Detergen System Cleaner to water-exposed Optigear Synthetic A 320 provides a safe, long-term solution to all known issues involving the precipitation of gear oil additives and resulting sludge formation. This solution does not impair the performance of the oil and will potentially extend the life of Optigear Synthetic A 320 fluid and system filters, while maintaining optimum wear protection. Currently the effect of the DSC as a long-term solution has only been tested with OGSA 320.

Where issues concerning water contamination of OGSA 320 are present, the addition of a small amount of DSC will enhance the performance of the oil and potentially extend its useful life. Wind farm owners can realize significant cost savings by extending the life of the oil by one or more years, and avoiding costly oil changeouts, while at the same time being confident that their wind turbine gearbox components are being protected from wear.

Next Generation Gear Oil
Being cognizant of the issues with OGSA 320, Castrol has developed the next generation in wind turbine gear oil: the Castrol Optigear Synthetic X 320. It has higher resistance to micropitting than its leading competitors, can provide greater protection to gearbox components, and extend the life of the gearbox. This product is more tolerant of water and performs exceptionally well in the most adverse conditions in any part of the country, with better filterability. Optigear Synthetic X 320 has several OEM first fill approvals for wind turbine gearboxes and is a great choice for a second fill gear oil to maximize the life of the gearbox and reduce total cost of ownership. Optigear Synthetic X 320 can last up to seven years before an oil change, resulting in a potential savings of up to $250,000 versus a typical competitor’s oil, which could need an oil change in this time.