UEA Tech Talk

Slip Rings in Off-Shore Wind Turbines

Slip Rings in Off-Shore Wind Turbines

Standard wind turbines have proven to be a harsh and rugged environment for electrical slip rings.  However designing slip rings for off-shore wind turbines is an even tougher challenge.  Not only are we dealing with gearbox oil, dirt and vibrations, but now we are aslo exposed to salt water and salt air.

The salt environment can cause a few different problems for a slip ring if not properly designed.  First of all, the outer housing and hardware must be suited for slat air. Even if a rusty enclosure and screws don’t change the performance of the slip ring, no turbine manufacture wants to install a rusty component on a multimillion dollar machine.  United Equipment Accessories uses all stainless steel hardware if possible which also makes maintenance much easier.  As for the housing, aluminum is generally used among all slip ring suppliers as it is durable and light weight, but it's not the most corrosion resistant material.  Because of this, UEA has standardized to have aluminum components anodized if being used in a salt air environment.

No matter how well a slip ring enclosure is sealed it seems the salt air still finds it way inside.  This can cause brass rings to corrode at a much more accelerated rate.   The biggest challenge is to keep the rings from starting to corrode before they are put to use.  A lot of the slip rings will sit for months before they are actually being used.  If they are sitting in a salt environment, some type of protection is needed.   UEA uses a type of electrical protection spray that coats the rings and stops them from corroding, but the biggest benefit that UEA offers over most competitors is the self cleaning brushes.  We run a very high brush pressure compared to most manufactures, so if some corrosion on the ring does occur, the brushes will clean the rings as they begin to rotate.

These are just a couple of the issues that we take into consideration when designing slip rings for the off-shore environment.  As the wind industry progresses I have a feeling we will be seeing a lot more of these applications.

-Jesse Shearer, Design Engineer

UEA Slip Ring Assemblies

 

The fact that UEA slip ring assemblies are known for their dependable service in a wide variety of environments stems from their original design to operate in the rugged and dirty world of construction equipment.  The first UEA slip rings were designed and built when UEA founder, Vern Iserman, was unable to locate or purchase a slip ring design that would stand up to the environments encountered by the electro-pneumatic remote control packages he was building and installing on small truck mounted cranes and draglines for the Shield Bantam Co.  The patented brush assembly design included two brush contacts, each radiused to match the OD of the ring contact, with paralleling insulated brush shunt between the contacts.   The contacts are each riveted to an insulating brush arm with the contact allowed to pivot around the rivet.  The brush arms are stacked over a stainless steel stud, with the arms also allowed to pivot on the stud, and the two arms in each pair tied to each other with an extension spring.  This design with three pivot points, including the brush contacts and the brush retention post, allows the UEA brush to maintain contact even with a considerable amount of misalignment or oscillation as the equipment and bearings wear.  The brush design, with the spring insulated from the actual circuit, precludes the possibility of the spring losing tension due to overheating, etc. when the spring serves dual-duty as both the brush arm and conductor as used on many other slip ring brush designs.  Operating with the high contact force of 15-18 lbs./sq. in. the UEA brush contacts not only provide very good cleaning action to wipe the rings as the brushes rotate but a very high resistance to contact bounce as the equipment vibrates.  Another unanticipated advantage at the time of their design of the high contact pressure at the brush contact to ring interface is that the very low contact resistance permits the use of lower level signals such as video and audio even on some of the standard circuits with copper graphite contacts and brass rings. 

      Using variations of both contact and ring materials has allowed the basic double-contact UEA design from the 1960's to be used in a wide variety of applications and environments around the world nearly 50 years later.  Using that same basic brush design the UEA slip ring line has been expanded to meet through-bore slip ring needs from 0.50" to 14.00" in inside diameter.

Slip ring for wind turbine

 

Wind Turbine Slip Rings

The hub slip ring in large wind turbines has proved to be a difficult application for a lot of slip ring manufacturers.

There are 2 types of hub slip rings for large wind turbines; one used for powering the electric pitch motors and the other for controlling the hydraulic pitch system.  They are both used for the same reason, powering/controlling the pitch of the blades to control the speed of the gearbox/generator.  For the most part each presents the same challenges in designing a slip ring.  However, the slip rings for controlling the hydraulic systems are much smaller since there is no need for power circuits.

The main challenge with these slip rings is the environment.  Depending on the type of turbine and location the environmental conditions can be very wide spread.  The design of the slip ring must take into account rain, salt air, oil from other components and a lot of vibrations.  The one condition that nearly all wind turbine slip rings must handle is cold air.  Depending on the style of ring a heater may be require to withstand these below zero conditions.

Another challenge is the fact there  are so many different wind turbine designs.  It's hard to relate data from a slip ring in one manufacture to another because of the difference in the overall turbine design.  The pitch system determines the need of circuits within the slip ring which intern determines the overall size.  The larger the slip ring the more rugged it needs to be to handle its own weight.  Other differences between turbines range from vibrations, leaking gear box oil and size limitations. 

UEA has a long history of supplying to very rugged applications such as rough terrain cranes and boom trucks.  These applications deal with the weather of all four seasons, dirt, oil, road salt, and vibrations much the same as a wind turbine. These challenging conditions are why UEA has been a good fit as a wind turbine slip ring supplier. 

Wind turbine slip ring trip

Customer service at United Equipment Accessories is one way we set ourselves apart from our competitors.  I have been with the company for about 5 years now as a design engineer and I still am amazed by the effort that UEA puts forth to provide outstanding customer service. 

Just recently we had a wind turbine customer in Wyoming with a concern regarding the operation and maintenance of a slip ring.  After discussing the situation over the phone it was determined it would be beneficial to both the customer and UEA to meet face to face and examine the ring in operation.  Within 2 weeks myself and Kent Davis, another design engineer, visited the Wyoming wind farm.  What made this trip so challenging was the fact that the slip ring in operation is located 300ft above ground in the nacelle part of the wind turbine. 

In the past couple of years I have had the opportunity to climb 2 other wind turbines in the Midwest.    However, I came to conclusion that climbing a turbine in the Midwest was much different than climbing at 7000 feet above sea level in Wyoming.  It definitely took a little longer to get to the top, but we managed to make it and gather the information we came for.  It is very important to us to have our slip ring customers know we care about them enough to make the trip.

By UEA sending two engineers to address the customers' concerns, we were able gather information that will help us provide better products and services not just to this customer, but to all our customers.   This is just one example showing that UEA is dedicated to providing outstanding customer service no matter what the situation may be or how high we have to climb.  

Jesse Shearer

Design Engineer

 

A view from the TOP!!