How to extend wind turbine lifespans?

Wind turbines must endure ongoing mechanical and environmental stresses throughout their lifespan, starting the day they are commissioned. Over time, these stresses accumulate as varying levels of fatigue on the unit. This often results in component and structural failures earlier than anticipated in a wind turbine’s lifecycle.

However, by utilizing advanced control software, some of these stresses can be mitigated, thereby prolonging a wind turbine’s lifespan while at the same time often increasing energy production. Implementing these control strategies is a time and cost-effective alternative to untimely mechanical repairs or component upgrades.

Load Mitigation – Thrust Limiting and Turbulence-based Derate

Turbine loads are mainly driven by aerodynamic forces that can vary due to changing wind speeds, direction and controller response. These loads can result in accelerated fatigue but can be addressed through the control system.

One common method for load mitigation is through thrust limiting and turbulence-based derate algorithms that can help counteract extreme and fatigue loads.

A thrust limiter will estimate the thrust force based upon the wind speed. When the thrust estimate is high (thereby increasing turbine load and stress) the pitch is increased. This reduces fore-aft tower loads by up to 5% but can reduce annual energy production (AEP) slightly.

A turbulence scaled thrust limiter can be used in addition to a thrust limiter. In this scenario, the thrust limit decreases with increasing wind turbulence. This results in a lower impact on AEP compared to static thrust limit control.

Lastly, a turbulence-based derate system will decrease power output during periods of high turbulence to reduce the stresses of extreme loads. This is done by making a turbulence estimation based on nacelle acceleration and estimated wind.

Load Mitigation - Reducing Drivetrain Oscillations

Wind speed variations, turbulence, and improper alignment are some of the factors that can create wind turbine drivetrain oscillations. In turn, these oscillations cause increased drivetrain fatigue loads.

To correct this, a drivetrain damper will extract the drivetrain oscillation at its eigenfrequency. This produces a counter-phase oscillation (or drivetrain dampening power) that is added to the control system’s power setpoint. The result is a generator torque setpoint that dampens the drivetrain eigenfrequency. Adding a drivetrain dampening solution can reduce drivetrain fatigue loads up to 10%.

Load Mitigation - Reducing Tower Oscillations

Whether caused by turbulence, resonance, or blade imbalance, tower oscillations increase tower fatigue loads and can shorten wind turbine life spans. However, a tower damper solution can counteract tower oscillations. This is done by using tower top accelerometer measurements for both the transversal and axial directions.

For the transversal direction, the system produces a counter-phase power oscillation that is added to the power setpoint. For the axial direction, it produces a counter-phase pitch oscillation that is added to the pitch setpoint. The result is a generator torque setpoint and pitch setpoint that dampens the tower eigenfrequency, which can reduce fatigue loads by up to 8%.

Turbine Optimization – Yaw and Pitch Alignment

The improper positioning that occurs in yaw misalignment or pitch misalignment can significantly increase wind turbine fatigue loads. Yaw misalignment can be corrected by a self-calibrating yaw control algorithm that provides continuous yaw alignment. For pitch misalignment, a rotor imbalance detection algorithm applies an automatic correction to the pitch setpoints. Correcting either of these misalignments through advanced control software will reduce system wear and tear, thereby increasing the lifespan of the wind turbine with the parallel benefit of increasing energy output.

Balancing Power Output vs. Turbine Wear and Tear

There are no significant power output tradeoffs when addressing stress-inducing challenges like yaw or pitch misalignment, and drivetrain or tower oscillations. Utilizing advanced control techniques is a proven method for lengthening a wind turbine’s lifespan without degrading power output.

While there can be tradeoffs when implementing thrust limiting solutions, advanced control system processes can determine the proper balance between turbine power output versus extreme and fatigue load mitigation.

Emerson offers a full suite of wind turbine retrofit solutions and expertise that tackles these challenges in a manner suited to your operational demands.