Contact Material Of Wind Turbine Slip Ring
As the rise of wind energy, although a small part of the total cost and the design of wind turbines is negligible, but the slip ring running plays a key role. Slip ring installed in the nacelle of the wind turbine, the electrical signal is typically used to transfer power and signal. Slip ring via the rotation interface transporting electrical power and signal.
Operating principle: the sliding contacts via the slip ring assembly in the rotary interface to transmit electrical signals and energy. That is to say, to ensure the correct electrical signal transmission, the need for "metal to metal contact" between the stationary and rotating brushes of the slip ring. Fiber brush slip rings capable of providing the working life of at least 100 million times a turn for the wind turbine owners without maintenance, which means that technical staff may only need to replace them after 20 years. But is not all the slip ring can meet this requirement. In fact, to understand the design and construction of slip ring assemblies to assess their maintenance needs.
About 10% of the market for wind turbine slip ring is a fiber brush, this kind of slip ring which requires only a small amount of maintenance. Most (about 60%) slip ring is made of a composite metal brush, generally metal and graphite sintering conductive block. Even if the composite metal brush slip ring manufacturer as they have claimed up to 75 million transfer times working life, but they need frequent maintenance. The remaining 30% of the wind turbine slip ring using a single line of precious metal brush (typically made of gold). The amount of maintenance of composite metal brush and single line brushes required are far greater than the fiber brush slip rings.
The reason: Composite brushes facing three challenges:
1. The debris generated by an electrically conductive, abrasive, in powder form, to be cleaned regularly;
2. Such brush material is very sensitive to humidity, if the relative humidity is below 15% or higher than 85%, which will result in uneven wear;
3. When circuits for signal level, which will occupy a lot of space composite brushes.
Single metal brush slip ring brushes advantage over complex design, the first is less wear debris, the other is used for signal circuits when higher capacity. But singlet metal brush system there are also disadvantages:
1. Single brush relatively small size lead to limited current-carrying capacity;
2. For example: Most contact between gold and gold require lubrication, and always maintain adequate lubrication is very difficult.
The market began to appear in the power circuit using graphite / metal brush, signal circuits using gold monofilament brush slip ring design. In the slip ring assembly applications requiring low number of revolutions, this "mix" to achieve good results. But the mix "graphite / metal" and "gold contacts gold" in the same assembly of the brush will make wind turbines run unreliable. Graphite / metal debris would contaminate the gold signal contacts, and produce abrasive metal powder, especially if there is a signal circuit can cause premature failure of the lubricating oil when the contact.
Fiber brush is designed to have a plurality of metal filaments bundled into a dense multi-fiber "brush". In general, these fibers are precious metal materials, and conductive ring is also plated precious metals. The use of a precious metal prevents the generation of oxide layer and cover layer in the contact point, while ensuring a minimal contact force. Small contact force reduces wear rate, and thus the brush debris generated almost negligible. And a plurality of metal fibers to provide superior conductivity and high current densities.
The composite metal brush slip rings and single brush slip ring replacement is very simple, and the fiber brush slip ring is more reliable. But some owners of wind turbines with respect to whether or not to replace the existing fiber brush slip ring, because they harbor "try new technologies to bear risk" idea. The people who have carefully examined over fiber brush slip ring technology, they will find choose a part which almost no maintenance, in fact, have eliminated the risk and does not require maintenance.