Comprehensive analysis of the reasons why wind turbines stop turning

As a clean and renewable energy source, wind power generation plays an increasingly important role in the transformation of the global energy structure. However, as a complex electromechanical device, wind turbines will inevitably encounter various problems during operation, leading to shutdowns. This article will deeply analyze the various reasons why wind turbines stop turning, helping readers to fully understand the causes and countermeasures of wind turbine failures.

1. Shutdown problems caused by insufficient wind speed

The wind speed is too low to start

Wind turbines need a specific wind speed to initiate and function properly. Typically, modern large turbines have a cut-in wind speed of around 3-4 meters per second. If the ambient wind speed falls below this threshold, the turbine blades lack the necessary torque to rotate the generator, resulting in a shutdown state.

This situation often occurs in the following situations:

During seasonal lulls in wind, certain regions endure prolonged periods of low wind speeds, leading to extended turbine shutdowns.

Diurnal wind variations arise from temperature differentials, causing brief spells of inadequate wind speeds.

Topography plays a role as complex terrain can create localized weak wind zones, impacting turbine performance.

Within expansive wind farms, the wake effect causes downwind turbines to receive reduced wind energy due to interference from upwind turbines, resulting in insufficient wind speeds for some units.

Excessive wind speed triggers protection shutdown

In addition to low wind speed, excessive wind speed can also cause wind turbines to shut down. Modern wind turbines usually have a high wind speed cut-out protection mechanism. When the wind speed exceeds the safety threshold (generally around 25 meters/second), the wind turbine will automatically shut down to protect the equipment.

High wind speed shutdown primarily occurs during typhoons or severe convective weather when wind speeds exceed turbine design limits, triggering protective measures. Special terrains can also lead to accelerated wind speeds, prompting frequent shutdowns. Offshore wind farms face complex and variable conditions, increasing the likelihood of shutdowns. Additionally, certain regions experience prolonged protective shutdowns due to seasonal strong winds.

2. Shutdown problems caused by wind direction changes

Rapid changes in wind direction cause the yaw system to respond inadequately

Wind turbines must align with the prevailing wind for optimal energy utilization. When wind shifts, the yaw system reorients the nacelle. However, abrupt or frequent changes can lead to the following issues, prompting shutdown:

①Yaw system lag: Rapid wind direction changes surpass the system’s adjustment speed, leaving the turbine in a suboptimal wind-facing position, resulting in reduced efficiency or shutdown.

② Yaw motor overload: Frequent large-scale yaw adjustments will cause the yaw motor to overheat and trigger a protective shutdown.

③ Increased wear of yaw bearings: Drastic changes in wind direction will increase the stress of the yaw bearing, accelerate wear, and affect yaw accuracy.

④ Uneven force on the blades: When the wind direction changes rapidly, the three blades may be in different force states, increasing fatigue loads.

Unstable wind direction caused by turbulence

In complex terrain or near obstacles, airflow is prone to turbulence, causing frequent changes in local wind direction. In this case, the wind turbine may have the following problems:

① Frequent action of the yaw system: Continuous small yaw adjustments will increase system wear and shorten service life.

② Reduced power generation efficiency: Unstable wind direction will make it difficult for the wind turbine to maintain the optimal windward angle, reducing power generation efficiency.

③ Intensified unit vibration: Turbulence will increase the dynamic load of the wind turbine, intensify unit vibration, and may trigger protection shutdown.

④ Blade fatigue acceleration: Unstable wind direction will increase the fatigue load of the blades and accelerate material aging.

3. Shutdown caused by overload protection triggering

Electrical system overload protection

While operating, wind turbines can encounter electrical system overloads leading to emergency shutdowns. Common overload scenarios include:

①Generator overcurrent: Sudden wind speed spikes or grid voltage fluctuations can exceed the rated current, activating overcurrent protection.

②Converter overload: Power surges may push the converter into an overload state, prompting a protective shutdown to prevent damage.

③Transformer overheating: Prolonged high-load operations can elevate transformer temperatures, activating temperature protection.

④Grid issues: Grid faults like short circuits or frequency variations feedback to the turbine, triggering a protective shutdown.

Mechanical system overload protection

In addition to the electrical system, the mechanical system of the wind turbine is also equipped with multiple overload protection mechanisms to ensure equipment safety. Mainly includes:

① Spindle overspeed protection: When the wind speed suddenly changes and the speed exceeds the safety threshold, the overspeed protection shutdown will be triggered.

② Gearbox overload protection: When the gearbox is subjected to excessive torque, the protection mechanism will be triggered to prevent damage to internal parts.

③ Yaw system overload: Continuous large-angle yaw may cause the yaw motor or reducer to overload, triggering a protective shutdown.

④ Hydraulic system overpressure: When the hydraulic pressure of the pitch system or brake system increases abnormally, the overpressure protection will be triggered.

4. Shutdown caused by unit failure or damage

Failure of key components

Wind turbines are composed of many precision components. Failure of any key component may cause the whole machine to stop. Common types of failures include:

①Blade issues: Crucial for wind turbines, damage like cracks or severe wear impacts safety and efficiency, necessitating shutdown for repairs.

②Gearbox malfunction: Essential for transmission, wear, bearing issues, or lubrication failures lead to turbine shutdown.

③Generator problems: Stator shorts, rotor issues, or bearing damage result in generator shutdown.

④Pitch system breakdown: Controls blade angle for power and safety; motor, reducer, or controller failures cause shutdown.

⑤Yaw system malfunction: Jammed bearings, motor damage, or control failures disrupt turbine operation.

⑥Converter troubles: Key for grid connection, IGBT module damage, capacitor failures trigger turbine shutdown.

Sensor and control system failure

Modern wind turbines rely on a large number of sensors and complex control systems to ensure safe and efficient operation. Failures in these systems can also cause wind turbine shutdowns:

①Wind sensor malfunction: Inaccurate data affects turbine control, potentially leading to unnecessary shutdowns or inefficiencies.

②Vibration sensor issues: Vital for early fault detection, sensor malfunctions can result in false or missed alarms, impacting turbine operation.

③Temperature sensor breakdown: Essential for monitoring key components, failures can delay detection of overheating issues.

④Controller software errors: Bugs or incorrect settings in the main controller can cause logic errors and unwarranted shutdowns.

⑤Communication system failure: Disrupted internal and external communication hinders control, diagnosis, and can trigger protective shutdowns.

5. Planned shutdown caused by regular maintenance and overhaul

Preventive maintenance shutdown

In order to ensure the long-term and reliable operation of wind turbines, regular preventive maintenance is required. These maintenance work usually leads to short-term planned shutdowns, mainly including:

① Lubrication system maintenance: Regularly replace gearbox oil, main shaft bearing grease, etc. to ensure that all components are well lubricated.

② Fastener inspection: Check and tighten all kinds of bolt connections to prevent looseness and cause failures.

③ Electrical system detection: Check cable connections, insulation performance, etc. to ensure that the electrical system is safe and reliable.

④ Sensor calibration: Regularly calibrate various sensors to ensure the accuracy of measurement data.

⑤ Filter element replacement: Replace various filter elements, such as gearbox oil filters, hydraulic system filters, etc.

⑥ Brake system inspection: Check and adjust mechanical brakes and pneumatic brakes to ensure quick and safe shutdown in emergency situations.

⑦ Blade inspection: Regularly check the surface condition of the blades, clean the blades, and repair them when necessary.

Overhaul and technical transformation shutdown

In addition to daily maintenance, wind turbines usually need to be overhauled or technically transformed after a certain number of years of operation, which will lead to a long period of shutdown:

① Gearbox overhaul: Dismantle the gearbox and replace worn parts, which may take several weeks.

② Generator rewinding: When the insulation performance of the generator winding decreases, rewinding is required, which usually takes 1-2 months.

③ Pitch system upgrade: Replace aging pitch motors or upgrade control systems to improve reliability and efficiency.

④ Converter update: Use a new generation of converters to replace old equipment to improve power generation efficiency and grid adaptability.

⑤ Blade replacement or extension: Depending on the blade condition and technological development, overall replacement or lengthening may be carried out.

6. Shutdown problems caused by power grid failures

Protective shutdown caused by power grid fluctuations

Wind turbines need to maintain a stable connection with the power grid to operate normally. When the grid is abnormal, the wind turbine will trigger a protective shutdown:

① Voltage fluctuation: When the grid voltage drops or rises beyond the allowable range, the wind turbine will be disconnected and shut down immediately.

② Frequency deviation: When the grid frequency fluctuates too much, the wind turbine cannot maintain synchronous operation and needs to be shut down urgently.

③ Three-phase imbalance: Severe three-phase imbalance will cause the generator and converter to overload, triggering a protective shutdown.

④ Harmonic interference: Excessive harmonic content in the grid will affect the normal operation of the wind turbine and may cause the control system to malfunction.

Grid maintenance or fault power outage

In addition to power quality issues, the maintenance or failure of the grid itself will also directly affect the operation of the wind turbine:

① Planned maintenance: When the grid company performs line or substation maintenance, it may be necessary to cut off the wind farm grid connection point, causing the entire farm to shut down.

② Line failure: Transmission line failure caused by lightning strikes, pole collapse, etc. will cause the wind farm to lose grid connection conditions and shut down.

③ Substation failure: Failure of grid-connected substation equipment may cause large-scale power outages and affect the operation of the wind farm.

④ Grid dispatching: In special circumstances, grid dispatching may require wind farms to operate at limited power or shut down to maintain grid balance.

7. Summary:

There are many reasons why wind turbines stop turning, involving natural conditions, equipment itself, maintenance management, and external grids. Understanding these potential reasons for downtime is of great significance for wind farm operation management, fault diagnosis, and preventive maintenance.

Analyzing the Aftermath: Common Wind Turbine Failures