A slip ring from UEA is designed to withstand the harsh environments in wind turbines, and uses solid brushes and rings stacked in a manner that saves space. UEA has built more than 15,000 slip rings for large wind turbines in the last few years.
Wind turbines require reliable transmission of power and data signals from the nacelle to the control system for the rotary blades, and this is where slip ring functions are required. A slip ring is used to transfer electric current from a stationary to a rotating unit. Slip rings are small components compared to gearbox bearings or generators, but the devices perform an important task. Similar to other turbine components, defects or failures in the devices can make or break the performance of a turbine.
If a slip ring fails, power and communication data cannot pass through to pitch mechanisms and other controls in the hub and top box, which may cause a wind turbine to shut down. This is why manufacturers have devoted engineering time developing slip rings specifically for wind turbines that last longer and require less maintenance.
Regardless of the design, it is important to consider the quality of the materials used, the annual maintenance required, and the overall life expectancy when selecting slip rings for wind turbines.
A wide selection of circuitry is available depending on the power requirements, with many combinations of amperage and voltage (ac or dc). Today’s advanced designs can transfer higher wattage with decreasing power loss. For example, UEA slip rings have handled over 55 kW for pitch control motor use with circuits rated over 100 amps and 690 VAC.
Wattage transfer capacity and power losses may be affected by various factors, which is why custom designed slip rings are often recommended for wind-turbine applications to ensure proper capacity and function.
Material considerations are also important for reducing O&M (operations and maintenance). In a hostile environment, such as that common to remote wind turbine locations, high-grade slip ring materials are important to reduce surface degradation. Some wire-brush slip rings wear down their gold plating, resulting in lost conductivity and transfer capacity.
Most wind-turbine operators would agree that the fewer up-tower maintenance trips the better. Replacing slip ring brushes is time-consuming and costly, so extended maintenance intervals are ideal. However, traditional slip rings need frequent maintenance to avoid degradation of the rotating electrical connection caused by regular wear and debris. Manual cleaning and lubrication are essentially eliminated with solid metal brush slip rings. A higher spring pressure than that on conventional slip rings can help clean the ring as it rotates.
Fortunately, there are more advanced designs that allow for slip ring assemblies to go 100+ million revolutions before brush replacement. These designs typically come with built-in, lifelong lubrication, which means these components only require about five minutes of maintenance per year — and some turbine operators say that they have eliminated annual maintenance altogether.