What is a wind turbine trip, and how to reduce wind turbine trips?

What is a wind turbine trip?

A wind turbine trip is an event where the turbine is shut down to protect against damage or unsafe conditions. During a trip, the turbine typically goes into a safe state by feathering the blades to reduce aerodynamic forces while aero-braking to slow the rotation, and disconnecting from the grid.

High speed winds that exceed design thresholds are a common cause for wind turbine trips. Other possible causes include insufficient wind speeds to generate electricity, issues within the power grid, and mechanical or electrical faults. 

Once the underlying trip condition has been safely resolved, the turbine can be reset and brought back online automatically or manually.

How to reduce wind turbine trips caused by wind gusts and storms?

It’s not uncommon for wind gusts to exceed the operating limit of a wind turbine. In these situations, the OEM solution for some wind turbines is to simply trip the unit. This will result in the loss of generation until those turbines are reset, and adds wear and tear to the machine. However, sophisticated wind turbine control algorithms can mitigate the effects of sudden wind gusts and turbulence, and reduce trips.

A basic wind turbine generator (WTG) controller with simple control logic will attempt to respond to a sudden gust by immediately changing the blade pitch to reduce torque on the gearbox/ generator based primarily on a table. To avoid overacting and causing a trip, the reaction must be proportional to the environmental variables. This is especially challenging given the inertia of the rotating blades and large lag in response time to a sudden gust, plus other variables that result in an inaccurate control response.

A better approach is to utilize advanced, adaptive wind gust control logic that handles wind gusts and turbulence with specific logic algorithms to compensate for a wide range of environmental factors. There are three tiers of responses to excessive wind gusts/speeds. 

• The top tier is Overspeed Protection. While it is the least desirable, it may be the best choice for protecting wind turbines subjected to high wind speeds. One approach to Overspeed Protection is to predict the rotor speed by several seconds ahead in time and allow earlier reaction in pitch movement to reduce fatigue on the rotation components. 
• The next tier is more active by including advanced control methods and calculations to improve the controller’s response to gusts. Instead of responding to wind speed alone, this approach inputs the adjusted wind speed into a turbulence estimator along with a nacelle accelerometer to calculate, with other inputs, a thrust limit to drive the pitch setpoint. This is especially useful for turbines experiencing turbulent air flows. 
  As a last measure, if gusty conditions are excessive, a Turbulence-Based Derate calculation drives the pitch system. This allows safer operation to prevent reaching overspeed trip settings but still maintain power production at a reduced setpoint.
• The final tier is an automated response to trips. Within the SCADA system, conditional logic can be introduced so that when a trip occurs, the logic reacts as a human operator would—by checking the fault conditions, timing, and overall unit status—to reset the trip and restart the unit. This mimics what an operator would do—but in split seconds—for faster recovery of lost generation, especially on large wind farms. Systems utilizing open logic enable the parameters can be changed to accommodate new ideas or changing conditions.

Emerson has 30+ years of experience in wind control design and offers wind turbine retrofit solutions that meet the needs of varying environmental conditions, reduce tripping, and improve the annual energy production (AEP) of wind farms.