Design Technology in Wind Turbines: "Smart Yaw" - the new concept in load reduction |
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MHI has completed development of "Smart Yaw" - a unique safety design concept that will reduce the design loading on wind turbines. In strong winds and electric power outages, which can simultaneously occur in typhoons, the Smart Yaw manages the gale force winds by preventing excessive loads being applied to the blades and tower. As a result, MHI has managed to cut 15% off the weight of the blades and tower. ("Smart Yaw" is a registered trademark of MHI Patent pending.)
Usually in strong winds, wind turbines cease operations, face upwind and go into standby mode so as to minimize the loading caused by the wind. However, if there is a power failure caused by the typhoon knocking down power poles and cutting the transmission lines, the loss of pulse power makes the yaw controls inoperable. (The yaw controls are the controls that swivel the nacelle.) Under these circumstances, a wind from diagonally in front or directly from the side can exert an astonishingly excessive load causing the tower to collapse, the blades to be sent flying or other such devastation (Fig 1).
Fig1. Relationship between wind direction and bending moment
The Smart Yaw utilizes properties similar to weather vanes which naturally face down wind. If there is a strong wind, the nacelle rotates to face down wind, thereby alleviating the load (Fig 2).
Fig2. Operational principle of the SmartYaw ®
The operational principle of the Smart Yaw is described below (Fig 3, 4 and 5).
Fig3. Flowchart of SmartYaw ®
Fig4. Operational principle of SmartYaw ® (during normal operation)
Fig5. Operational principle of SmartYaw ® (SmartYaw applied)
| (1) |
In winds exceeding 25m/s (averaged over 10 minutes), the blades turn with the wind (known as "feathering") and the turbine cuts out. |
| (2) |
If the winds pick up to more than 28m/s (averaged over 10 minutes), they are considered to be gale force winds, such as in a typhoon, and the rotor swivels downwind. |
| (3) |
The hydraulic yaw brake is disengaged and the yaw motor break is partially applied. |
| (4) |
The yaw is free to swivel in strong winds, and so automatically faces downwind.
The Smart Yaw is powered purely by wind force, and as a result, electrical power is unnecessary. It is a particularly effective system, even during power outages in typhoons. |
With the Smart Yaw, the loading on the blades and tower is reduced by 25% and 30% respectively. Consequently, MHI has been successful in reducing the weight of the blades and tower by approximately 15% (Fig 6).
Fig6. Effect of reducing load and weight by SmartYaw ®
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