Published on 06-Jun-2024

Ensuring Reliability and Sustainability in Wind Turbine Inspection

Ensuring Reliability and Sustainability in Wind Turbine Inspection

Table of Content

The earliest record of harnessing Wind Energy dates back to 5000 BC Egypt where wind was used to power sailboats on the Nile. Scottish Professor, Dr James Blyth built the first wind turbine to generate electricity. From then, the wind industry has grown ten-fold, with Denmark, through their large-scale wind turbine installations, becoming an industry leader in the 1980s.

The global installed wind power capacity has grown exponentially since the 1990s. In 2000, the global installed capacity was approximately 17GW. By 2010, this number had increased to around 197GW. The global installed capacity in 2023 was approximately 1,021 GW, with continuous growth expected. (Lucía Fernández, 2024). The Compound Annual Growth Rate (CAGR) for onshore wind from 2024 to 2028 is projected to be 6.6%. Yearly additions are expected to average 130 GW, totalling 652 GW by 2028. (Joshi, 2024)

Components and Operation of Wind Turbines

Wind energy is a clean, renewable source of power that significantly reduces greenhouse gas emissions compared to fossil fuels. Offshore wind farms have become increasingly prevalent, with the World's largest offshore wind farm, Hornsea One in the UK, having a capacity of 1.2 GW and becoming fully operational in 2020.

Early wind turbines had capacities of less than 100 kW. While, modern wind turbines commonly have capacities of 2-4 MW, with some offshore turbines exceeding 10 MW.

1. Basic Principles of Wind Turbine Operation

A vertical axis wind turbine

The basic principles of wind turbine operation include:

Energy Capture:

  • Wind turbines harness kinetic energy from the wind using rotor blades.
  • The aerodynamic design of the blades allows them to capture wind energy efficiently, creating lift and causing rotation.

Conversion of Kinetic Energy to Mechanical Energy:

  • The rotating blades are connected to a hub, transferring rotational energy to a low-speed shaft.
  • This shaft transmits the mechanical energy to the gearbox.

Mechanical Energy Transfer:

  • The gearbox increases the rotational speed from approximately 30-60 RPM (low-speed shaft) to around 1,000-1,500 RPM (high-speed shaft).
  • This step-up in speed is essential for efficient power generation.

Mechanical to Electrical Energy Conversion:

  • The high-speed shaft drives the generator, converting mechanical energy into electrical energy through electromagnetic induction.
  • Magnets within the generator move past wire coils, inducing an electrical current.

Electricity Generation:

  • The generated electrical energy is alternating current (AC).
  • Power electronics within the turbine convert this AC into a stable form compatible with the grid.
  • The electricity is transmitted via cables to a substation, where it is stepped up to higher voltages for distribution.

Control Systems:

  • Advanced control systems manage turbine operations, including blade pitch and yaw control, to optimise energy capture and protect against excessive wind speeds.

2. Components of Wind Turbines

Components of Wind Turbines

The different components of wind turbines include:

Rotor Blades: 

  • These are aerodynamic surfaces designed to capture wind energy. 
  • The blade design, material, and length influence energy capture efficiency. 
  • Non-Destructive Testing is crucial for inspecting and maintaining blade integrity to prevent structural failures.

Nacelle: 

  • The nacelle houses critical components such as the gearbox, generator, and control systems. 
  • It serves as the central hub for the conversion process. 
  • Regular wind turbine inspection and repair are essential to ensure the smooth functioning of the nacelle components.

Gearbox: 

  • This component steps up the rotational speed from the rotor blades to a speed suitable for the generator. 
  • Gearbox inspection is vital as it is subject to high mechanical stress and potential flaws such as gear tooth wear and cracking.

Generator: 

  • The generator converts mechanical energy from the gearbox into electrical energy. 
  • It is a key component where electrical and mechanical systems intersect, requiring careful inspection to avoid faults that could disrupt electricity production.

Tower: 

  • The tower supports the nacelle and rotor blades, elevating them to capture stronger winds at higher altitudes. 
  • Tower integrity is vital, with NDT Techniques employed to detect weld defects, corrosion, and structural deformations.

Control System: 

  • This system ensures the turbine operates optimally and safely, adjusting the blade pitch and yaw to maximise energy capture and minimise stress on components. 
  • Effective condition monitoring is vital to pre-emptively address any control system malfunctions.

Flaws in Wind Turbines

To understand the necessity or functioning of NDT operations on Wind Turbines in operation or during manufacture, one must thoroughly understand the flaws that Wind Turbines are susceptible to exhibiting.

In-service Defects in Wind Turbines

In-service Defects in Wind Turbines

Some of the defects observed in wind turbines in operation include:

Laminations:

  • Laminations refer to the layered structure of composite materials used in wind turbine blades. 
  • Defects such as delaminations, voids, and resin-rich/lean areas can occur during manufacturing or operation. 
  • These flaws compromise the structural integrity of blades, making blade inspection crucial for maintaining performance and safety.

Transmission Bearing Flaws:

  • Transmission bearings are subject to high loads and rotational speeds, leading to wear and fatigue. 
  • Misalignment can further exacerbate these issues, causing uneven load distribution. 
  • Regular Wind Turbine Inspection Repair and condition monitoring are essential to detect and address these flaws early.

Gear Flaws:

  • Gears in the gearbox experience significant stress, leading to wear, pitting, and potential cracking. 
  • Effective gearbox inspection techniques, including visual and non-destructive testing methods, are critical to ensure continued structural integrity and prevent failures.

Rotor Bearing Flaws:

  • Rotor bearings endure cyclic loads, that lead to fatigue and spalling.
  • Inadequate lubrication can accelerate these issues, increasing friction and wear. 
  • Routine rotor maintenance and lubrication checks are vital for longevity.

Electrical Component Flaws:

  • Electrical components can suffer from insulation degradation, leading to failures, arcing, and overheating. 
  • These issues can cause significant downtime and safety hazards, making regular inspection techniques essential for maintaining electrical integrity.

Turbine Blade Flaws:

  • Turbine blades can develop delaminations, cracks, and surface erosion due to environmental exposure and mechanical stress. 
  • Thorough blade inspection using ultrasonic testing and thermography is necessary to identify and repair these defects.

Tower Flaws:

  • The tower, exposed to harsh environmental conditions, can suffer from corrosion, welding defects, and structural deformations. 
  • Ensuring tower integrity involves regular inspections and repairs to prevent catastrophic failures.

In-Service Flaws:

  • In-service turbines face vibration issues, material fatigue, and environmental damage. 
  • Continuous condition monitoring helps in early detection and mitigation of these flaws to maintain operational efficiency.

Generator Bearing Flaws:

  • Generator bearings are prone to thermal degradation, wear, and misalignment, affecting the generator’s performance. 
  • Regular wind turbine inspection and targeted maintenance practices are key to preventing these issues and ensuring reliable power generation.