80%* of bearing failures are as a result of lubrication issues.

Wind Turbines have experienced gearbox failures since the first one in the United States was built in Cleveland, Ohio by Charles F Brush in 1888.

Since gearboxes are one of the most expensive components of a wind turbine, the higher-than-expected failure rates are adding significantly to the cost of wind-generated energy. In addition the future uncertainty of gearbox life expectancy is adding to the cost escalation. Observations over a considerable period of time have concluded the following:

• Most problems with gearboxes are generic and not due to a specific manufacturer of model.
• Most gearbox failures do not begin as gear failures or gear teeth design deficiencies.
• The majority of gearbox failures appeared to begin in the bearings.

The wind energy generation industry has reached a point where the best design practices for gearboxes do not result in sufficient lifespan. The down-time for gearbox repairs is the longest of all components repairs. This is obstructing future forward progress. Some operating problems such as stand-still damage and debris damage and abrasive wear continue.

One predominant fact has been experienced, which is that no gear box can survive without clean oil. Over 15% of bearings that failed in the first five years and often sooner are:

• Manufacturing defects in bearing of gearbox,
• Stand-still damage,
• Lubricant starvation or overheating,
• Lubricant contamination.

Many bearings failing in that period for the second time are:

• Planetary bearings,
• Intermediate bearings,
• Accumulated debris damage.

Lubrication

Continuous on-line monitoring is essential for insuring the gearbox is good operating condition. For this purpose, Allen Filters, Inc. provides various models of the AGB system. This system is compact by design and is completely enclosed in a weather-proof steel cabinet, suitable for outdoor operations in all climate conditions.

An added feature of the AGB systems is the Allen Remote Monitoring System (ARMS). This software system gathers the signals from multiple sensors located in various parts of the AGB and displays this information to a central location via a web browser. ARMS is designed to send alerts based on rules setup by the end users. When an event triggers the alert, ARMS will send an email or a text messgae which can be viewd via a laptop, an IPad™ or a cellular telephone. The system provides the ability to trend the parameters and create a permanent record of turbine performance.

ARMS provides a two-dimensional representation, combining condition monitoring parameters with operational conditions. This provides the ability for interpreting real-time condition monitoring signals through relating operating parameters such as vibration or particle count with specific operating parameters such as load and cumulative energy production.

This allows detection of impending problems, such as significant increases in amplitude and variance in vibration signals that could presage an incipient bearing fault.

This representation for instance can show the effect of load variations on particle count and wear debris and relate this information to specific operational parameters such as power and energy production.

The AGB system itself can be supplied with several options such as:

• Dual filter vessels with automatic changeover in case of plugging of one filter.,
• Installation at ground level or internal platform,
• Ability to draw an oil sample at the oil pump for further analysis,
• Ability to drain or fill gearbox oil using the reversible oil pump,
• Ability to monitor all parameters by a technician simply passing each wind turbine,
• Continuous, on-line data transmission and reporting capability available anywhere at anytime.

The basic model of the AGB oil purification system is shown above. The available options are:

• All parameters are controlled by a Programmable Logic Controller (PLC),
• The ARMS remote Monitoring System, software included,
• Multiple filters with automatic switch-over,
• Reversible oil pump for filling or positive draining of the oil from the gear box,
• Sample tap to withdraw oil samples for laboratory analysis,
• Powerful pump allows installation at ground level or internal platform for weasy access,
• Removal of particulates large than 5-microns,
• Removal of moisture and acids,
• Removal of varnish particles,
• Internal weatherproof steel cabinet has controlled temperature and fan to remove condensation,
• Insect screens,
• Various pumping capacities available,
• Simple construction and reliable proven performance.

References

1. Kittiwake Monitoring innovation, 2009.www.kittywake.com
2. NREL Conference paper NREL CP-500-41548
3. Puigcorde, J and de Beaumont, A July 3, 2010, London

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