Pumps and Systems, May 2009
With the growth of wind farms, users are turning to condition monitoring and automatic lubrication systems for increased reliability.
The scope of this year's Windpower Conference & Exhibition emphasizes how far the wind industry has evolved in terms of technologies and impact. With the growth of wind farms, practical concerns turn to the requirements for sustained system reliability and effective maintenance processes.
An active business member of the American Wind Energy Association (AWEA), Kevin George shares his insight into how the industry can move toward a predictive maintenance model supported by proactive condition monitoring techniques.
Q: What are some of the fundamental challenges associated with wind turbine maintenance?
A:
Given the operating conditions a wind turbine experiences throughout a 20-year service life, maintenance problems are not a question of "if," but "when." Nevertheless, for many wind farms the number of maintenance technicians trying to delay the inevitable is limited and their deployment for service may be sporadic. When maintenance problems ultimately occur, farms face the downside of exorbitant crane mobilization costs, lost energy production, escalating costs per kilowatt-hour and limited supplies of spare parts due to intense industry demand for components. All these issues suggest the inherent benefits in detecting problems before they can escalate.
Q: What types of proactive maintenance activities can be applied to wind turbines for improved reliability?
A:
An integrated on-line condition monitoring system can serve as an effective tool for managing day-to-day maintenance routines for a wind turbine and consolidating risky, costly maintenance activities. By tracking component performance with condition monitoring technology, maintenance activities can be coordinated across the wind farm, service calls can be better planned and combined, and operators can take advantage of planned shutdowns to service several turbines at the same time, since machinery conditions are known from the monitoring. All factors help contribute economically and efficiently to wind farm operation.
Q: What types of operating faults can be detected with condition monitoring?
A:
By regularly measuring physical parameters and their variances, a variety of operating conditions can be targeted for early detection, diagnosis and remedial action. When implemented properly, condition monitoring can forecast trouble inside or outside the nacelle (see sidebar), including unbalanced turbine blades, misalignment, shaft deflections, mechanical looseness, foundation weakness, gear damage, blade or tower vibrations, inadequate lubrication and others.
Q: In general, how does a wind turbine condition monitoring system work?
A:
A system specially developed and dedicated for wind turbines allows for continuous monitoring of key turbine components by regularly measuring physical parameters such as vibration, temperature and lubrication particles. Mounted sensors and enabling software pinpoint the problems.
Systems have become quite sophisticated and some can handle any number of turbines and multiple data points for analysis. They can provide a maintenance-forecasting service by continuously recalculating fault frequencies and delivering accurate values based on reliable trends. This ability can facilitate the assigning of alarms at various speeds and loads, including low main shaft speeds, and form the basis for trend-based root cause failure analysis.
Wireless capabilities expand system potential by offering the capability to review data from any location with a computer or handheld device with Internet access. This can shorten lead-time from alarm to solution.
One system installed in hundreds of wind farms worldwide can fit every turbine's nacelle and includes an intelligent monitoring unit featuring 16 different channels that connects multiple measurement points. The typical wind turbine configuration incorporates the main bearing (one channel), gearbox (four channels), generator (two channels) and tachometer (one channel). In addition, other monitoring points may be added, including tower/structure vibration, blade vibration, oil temperature, oil pressure, oil quality and generator temperature.
This system integrates built-in hardware auto-diagnostics that continuously check all sensors, cabling and electronics for any faults, signal interruption, shorts or power failures. Any malfunctions trigger an alarm.
Q: What other technologies can help wind farms improve turbine reliability and reduce maintenance costs?
A:
Centralized automatic grease lubrication systems can aid sustained reliability. Systems engineered for bearings, pitch and yaw gears, and other locations in a wind turbine can efficiently and precisely deliver exact, clean quantities of the appropriate lubricant. The associated maintenance benefits from timely and effective lubrication include reduced wear, minimized lubricant consumption, maximized efficiency and less unscheduled downtime.
The automatic delivery of lubrication can be credited with lifting a heavy burden from the shoulders of the maintenance staff. According to industry averages, 10 to 20 percent of the time involved in servicing a turbine is spent on re-lubrication as technicians crawl in the cramped nacelle and hub to grease 10 to more than 80 lubrication points with several different greases in each turbine. As with conventional manual lubrication methods, over- or under-greasing is always an unwanted possibility, lubrication intervals may be sporadic or ill-timed, contaminants can inadvertently be introduced and equipment performance may be compromised.
Q: How is centralized lubrication performed?
A:
Every point receives the proper lubricant in the proper amount. Centralized lubrication systems can be applied to all bearings at a turbine's rotor shaft, blade pitch and azimuth positions, as well as non-rotating applications inside the turbine. Systems can be supplied as ready-to-install kits using block-type progressive feeders to supply lubricant from a central reservoir to the points inside a wind turbine.
Metered quantities of lubricant are fed progressively in predetermined ratios from master feeders to the lube points. The lubricant does not leave the respective feeder until the preceding one has discharged its volume. If a lube point does not receive any lubricant, regardless of the reason, or if a secondary feeder is blocked, the entire lubrication cycle is interrupted and the system will provide a signal to alert operators to the problem.
Advanced systems offer the capability to provide central monitoring of all feeder outlets, if desired, at relatively low cost, and can incorporate lubricant collectors attachable to open geared wheels and lubricated pinions for pitch and azimuth drive wheel.
Decision-making for the most appropriate system will generally depend on the application and a range of other parameters, including variations in the operating temperature and lubricant viscosity; accuracy requirements for lubricant quantities; turbine system geometry, including size, dimensions and symmetry and monitoring demands.
Properly executed predictive maintenance activities, beginning with effective condition monitoring and lubrication management programs, can equip wind farms with the tools and the knowledge to minimize costs, realize efficiencies, improve reliability and keep the blades turning toward profitability.
