Yaw shaft

Types of Yaw Shafts

A yaw shaft transfers torque from the yaw motor to the yaw gear or yaw ring. It is combined with other components that rotate the entire wind turbine nacelle to align it with the wind direction.

• Yaw Bearing Shaft

  The yaw bearing shaft connects the yaw motor and gear. The gearbox has been renamed the yaw gear. When the yaw motor rotates the yaw bearing shaft, the complete gear also rotates thereby allowing the nacelle to turn in the required direction.

• Short Yaw Shaft

  A short yaw shaft links the yaw motor to the yaw bearing shaft. It does this by going through the tower of the wind turbine. It is also called a yaw drive shaft. The yaw motor turns the short shaft which then rotates the yaw bearing shaft.

• Long Yaw Shaft

  Available in both single and double shafts, the long yaw shaft transfers motion from the yaw gearbox or yaw gear to the yaw bearing. This shaft is very common in wind turbines with a tower height of around 100 meters or more. Such turbines usually have a geared drive train.

• Double Yaw Shaft

  In some wind turbine designs, there is a double yaw shaft that connects the yaw motor and the yaw gear. This yaw motor may have pinion gears at one end. It is usually present in large wind turbine towers with a height of around 150 meters.

Every yaw shaft has its own dimensions and is made of materials like carbon steel, stainless steel, or alloy steel. Materials with very good anti-corrosion properties are used if there are any yaw shaft components that may corrode in any way during use.

The design of every yaw shaft also depends upon the yaw system of the wind turbine. Normally, a flange coupling is used to connect the yaw shaft sections. The flange coupling has two flanges, one attached to each shaft section. The yaw coupling is connected to a shrink disc. It is a type of mechanical device that connects two rotating parts to transmit torque.

Yaw shaft specifications and maintenance

The specifications for a typical yaw drive shaft are as follows. Note that depending on the manufacturer, some may vary or have additional features.

• Length: The length of the yaw shaft varies depending on the feature it is connecting. However, it can range from a few feet to several meters long. Some designs have a segmented shaft that connects through a different coupling to extend its length.
• Diameter: The diameter of the yaw shaft varies depending on the size and capacity of the wind turbine. The diameter ranges from 100 to 200 mm. The dimension affects the torque and the yawing speed.
• Materials: Most yaw shafts are made of stainless steel or carbon steel. The steel has a high tensile strength, allowing the yaw shafts to function well and last for many years.
• Connection mechanism: Most yaw shafts use clamping mechanisms, splines, or couplings to connect yaw gears or yaw motors.
• Load capacity: Yaw shafts bear axial and radial loads depending on the weight of the wind turbine and its design.
• Yaw speed: The yaw speed refers to the rotational speed of the yaw shaft when it is aligning the turbine to the oncoming wind. The speed varies depending on the motor connected to the shaft. However, the typical speed ranges from 0.2 to 2 degrees per second.

Yaw shaft maintenance

Maintaining a yaw shaft is critical to prolonging its lifespan and ensuring it performs well. Here are a few tips on maintenance.

• Regular inspection: Carry out a regular inspection of the yaw shaft. Look for signs of wear and tear, such as cracks or deformations. Also, check the components that connect the yaw shaft, like the yaw bearings and yaw drive gears. Swiftly attending to any faults will prevent considerable damage from occurring.
• Lubrication: Lubricate the yaw with grease or any other suitable lubricant. Lubrication minimizes friction and lowers the chance of wear and tear. It also prolongs the life of the yaw shaft and connected components.
• Cleaning: Dirt build-up can easily damage a yaw shaft. The dirt can act as an abrasive, damaging the bearings and gear. Regular cleaning will prevent dirt build-up and damage.
• Maintain alignment: Misalignment can cause uneven distribution of weight and add tension to the yaw shaft. Ensure all the yaw components are aligned correctly and connected securely to avoid imbalance.

Uses of yaw shafts

The main application of a ^yaw shaft is to transmit working forces between a yaw motor and a yaw bearing. There are, however, several other uses of yaw shafts in different turbines, such as:

• Facilitate Yaw Motion: Yaw shafts are designed to link the yaw motor and the yaw gear. They transfer the motor's torque and rotation to the yaw gear, which enables the turbine nacelle to rotate, thereby aligning the wind turbine with the wind direction, facilitating yaw motion.
• Transmit Torque and Rotation: Yaw shafts are engineered to transmit torque and rotation, not just from the yaw motor to the yaw gear. In some turbines where dual motors are applied for yaw control, they relay the yawing force from one yaw shaft to another.
• Structural Support: Besides transmitting forces and motions, the yaw shafts play a structural support role by holding different components of the yaw system in a fixed position.
• Facilitating Maintenance and Repair: Yaw shafts facilitate maintenance and repair operations by providing a means of disconnecting the yaw drive system from the nacelle if necessary. This feature enables technicians to handle issues that may arise from the yaw drive system, like motor failures or gear wear, thereby simplifying turbine maintenance.
• Absorbing and Damping Loads: Yaw shafts, especially those with a tubular shape, absorb and dampen dynamic loads and shocks arising from yawing motions. They reduce the transmission of such shocks to the delayed gear and yaw motor, protecting these components and enhancing their durability.
• Allowing for Misalignment Compensation: Due to factors like thermal expansion, manufacturing tolerances, and site conditions, some misalignment may occur between the yaw motor and gear. Yaw shafts, particularly those coupled with flexible couplings, compensate for such misalignments, thereby reducing stress on the yaw motor and gear.

How to choose a yaw shaft

When choosing a yaw shaft, a few things need to be considered. First and foremost, it's crucial to take the measurements of the turbine. Along with measuring the length and diameter of the turbine's tube, it's also essential to look at the turbine's gear ratio. This will help determine which kind of yaw shaft would work best with the turbine in question. Once the measurements have been taken, it's time to explore the various types of yaw shafts available on the market.

Operators can narrow down their options by determining which types of yaw shafts are commonly used in conjunction with the yaw system. Once this has been identified, a compatibility test should be performed to see if the yaw shaft being considered works with the yaw drive and gearbox. Suppose the yaw bearing supports or the alignment are not compatible. In that case, the yaw shaft should not be considered an option, as it is likely to create operational issues when installed.

Before making a purchasing decision, consult with the vendors who are providing the potential yaw shafts. Inquire about their installation services and the warranty they provide on the product after installation. It's also essential to ask about the support and maintenance services they provide. All of this information will help make a more informed decision when choosing the required yaw shaft.

Yaw shaft Q&A

Q1. What is a yaw drive? How does it work?

A1. The yaw mechanism that rotates the turbine to face the wind is called the yaw system. The yaw motor, gearing, and yaw shaft all make up the yaw drive. Large windmills utilize chain and rack systems, while smaller ones may use slewing bearings like those found on yaw bearing wind turbines.

Q2. What is a yaw bearing?

A2. The yaw bearing supports the nacelle and its components, including the yaw system, and allows the yaw shaft to rotate freely. This bearing usually takes a form of a cross cylindrical or ball bearing with a gear.

Q3. How does the wind turbine height affect yaw?

A3. Taller turbines are generally more efficient because they can capture wind from greater heights, which typically has higher speeds and less turbulence. The yaw system also operates better in smoother winds. However, the turbine also needs to be designed for such heights, with a proper yaw system in place.

Q4. Why is yawing important in a wind turbine?

A4. The function of the yaw system is to rotate the entire turbine to face the oncoming wind direction for optimal energy capture. It helps to position the turbine in a way that the wind will exert the most force on it to generate the highest possible energy.

Q5. What are some methods used for yaw control in wind turbines?

A5. The most common method used for yawing in a wind turbine is to employ an electric motor and gear assembly called a yaw drive. In addition to this, brakes and slip rings are also used to ensure that the turbine rotates smoothly and to control its rotating speed.