Wind-Electric System Maintenance: Page 3 of 4

On the Tower

Safety on towers requires knowing how to climb safely, and having the right equipment. There is no substitute for tower climbing experience, so if you’re new at it, find a mentor and get some practice. Climb the fixed tower, lower a tilt-up tower or use a lift (see Access for articles on tower styles and tower safety).

Tower Mechanical

• Look for missing or loose bolts, nuts, and lock nuts. Carry several sizes and types of spare hardware with you so you can inspect and repair or replace hardware in the same visit.
• Check for proper torque. A good manual will have the manufacturer’s recommended torque specifications and hardware sizes so you can throw the appropriate sockets and wrenches in your climber’s tool bag. While the majority of tower hardware can be tightened with a torque wrench that goes up to 250 foot-pounds, some tower hardware may require 350 foot-pounds or higher—plan accordingly.
• Down-tower wiring. Check cable and conduit integrity and verify that it’s properly secured. This will range from a Kellums-type hanger for jacketed multiconductor cable to various types of clamps for conduit, and even wire ties for flexible metallic-sheathed cable assemblies.
• Inspect tower-mounted data equipment, such as the boom, anemometer, and wind vane mounting hardware. Also check their wire integrity and tie-downs. The anemometer is another manufactured item that has moving parts. They do not last forever and may need to be replaced.
• On the way down, wire-brush rusted tower parts and apply cold-galvanizing spray or paint.

Wind Generator

• Turbine mechanical: Bearing problems may be difficult to spot, so learning to read the telltale signs of bearing failure—such as rust streaks—is essential. This is caused by moisture entering then exiting the bearing, which usually leaves a very distinctive, rust-colored residue behind. This is especially true for rotor bearings, where the streaks may be seen artfully arranged on one side of the blades.
• Where moisture has not been a factor, a fine black powder may be seen around the bearing race or on nearby surfaces. This is most often found in protected areas, such as the rear rotor and the yaw bearings inside the turbine nacelle. Grease/oil where it shouldn’t be is a sure sign that sealed bearings are no longer sealed.
• Loose hardware can leave similar signs, where vibration and movement have worn away protective coatings and allowed oxidation to occur.
• Inspect turbine-to-tower mounting hardware and check for proper torque. Look for cracking or other signs of stress on the mainframe welds.
• Verify blade mounting integrity, including loose blades and loose or missing hardware.
• Check the blades for structural integrity: cracks, pits, erosion, leading edge wear, or damaged/missing leading edge tape. If excessive movement is found, egging of mounting holes or other damage may be present.
• Slowly spin the rotor, listening for unusual noise or feeling for resistance to turning, which can be caused by grit on the magnets, dry bearings, too much play, or magnets rubbing on the stator. Check for bearing slop by lifting upward on the rotor.
• Inspect all bearing and pivot points, which typically include rotor and yaw bearings, furling bearings or pivot, furling or brake assembly, and friction areas. On furling turbines, the tail pivot bushings are a high wear point, especially at turbulent wind sites. If the upper pivot bushing lets go, the tail can swing downward into the blades, destroying both.
• Inspect the governor assembly if applicable (for example, with Jacobs and Kestrel turbines). There are lots of moving parts in there that need loving attention!
• On turbines such as the Endurance S-250, check the brake pads for wear. Inspect the condition of the flexible hoses in the air brake system and check the color of the desiccant. The color changes as moisture is absorbed to indicate when replacement is needed.
• Check out the slip-ring and brush assembly. Look for pitting or roughness (signs of arcing), and uneven wear on slip rings. Brushes can jump track or track unevenly, causing excessive slip-ring and brush wear, arcing, and premature failure of the assembly. Inside this assembly is another place to look for black dust, metal shavings, or excessive grease from bearing failure, which can cause electrical problems by interfering with brush contact with the slip rings.
• Inspect the turbine wire connections. Look for wear and loose terminals from vibration, evidence of arcing, and conductor insulation breakdown. Corrosion from moisture may be present yet unseen inside terminal blocks or other connectors.

Lubrication

• Some sealed bearings can be greased with a needle-type grease gun attachment. Any grease seal openings created during this process should be carefully and thoroughly sealed to keep out moisture. Small, handheld tubes of RTV sealant serve this purpose well.
• Where applicable, grease all fittings, and change gearbox oil (i.e., on Endurance and Jacobs turbines) according to manufacturer’s recommendations.
• Watch where the oil goes when performing an oil change. An unplanned coating of oil on the tower will not make for a pleasant tower descent!