Dear all

Recently, my boss give me a interesting question for wind turbine on-situ balancing. Does anyone can provide any information of this topic.

For my view, since wind turbine is very low speed machine, i think the unbalance force is quit low due to w^2*r. is it right ?

thanks and best regards,

Jazz

Hello JazzChan, all rotor designs tend to utilize laws of physics as much as possible. The wind rotors usually have a fixed speed (newer have variable) and one of the limiting factors is the tip speed. Same issues appy to a helicopter rotor. So in relation to the design, the balancing is an important issue for both. I would apply the same rules for balancing limits as for any rotor with consideration taken to the speed. If you study a few mills in a row, you will notice how most can stop in any position when wind is getting to zero but one or two always stops in a certain position. Unbalance is large enough to overcome frictions and decides the position at rest.

Now, at what level should you balance? Depends on design really. Somewhat also if already trimmed well or not. Most turbine´s hub have provisions for trim weights, some blades have tip and/or root pockets. To find the requirement for your case, I would refer to the designer. A rule of thumb is that you should get to the same unbalance quality as for a fan. The procedure is in any case identical to any rotor balancing. With some patience, you can take readings in normal operations and only change weighs during calm weather to avoid taking an operation loss.

A strong incentive to trim as an ongoing routine work is that you will soon have a good feeling for the behaviour of the individual rotor and can find tendencies to crack developments very precisely. Older mills have an age risk factor to develop cracks that costs a bundle to detect with an NDT testing, but knowing the development of the unbalance over time, you can point out a suspect rotor well in advance so that NDT testing can be avoided when not directly motivated. This approach is identical for that being used a lot in steam turbines with cracking risks. Regards Arne