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Innovation Challenges

Blade Lightning Protection System Inspection

Issue

Lightning strikes to offshore wind turbine blades are a common occurrence and can cause serious damage, and potentially catastrophic failures, leading to high maintenance costs and loss of revenue generation. For this reason, manufactured blades come factory fitted with a Lightning Protection System (LPS). During the operations phase, the LPS must be regularly inspected to ensure it is in good working order.

The current method is expensive, relying on the use of several personnel (technicians) and heavy equipment (blade access platforms). A crew transfer vessel will also be required to transport the personnel and equipment to the site from shore, adding further cost and logistical complexities.

Current Systems

A blade LPS typically consists of a metallic conductor cable (fitted inside the length of the blade) and lightning receptors at the blade tip and near the blade root. The receptors attract the lightning and capture the charge from the strike, transporting it in a safe way along the conductor cable to the blade root. The receptors/cable are, in turn, grounded through additional cables and structural connections routed to the foundation, and ultimately to the surrounding earth to safely conduct the charge from the lightning strike away from the wind turbine.

ORE Catapult Offshore Wind Turbine Blade Lightning Protection System

An example of a lightning protection system.

Lightning Protection System Inspection

The LPS requires periodic inspections to ensure it is in good working order. One aspect of the inspection is to test the electrical continuity from the receptors and cables to the ground, and measure and confirm that the resistance is at or below a minimum specified threshold.  A visual inspection is also performed to assess any degradation and/or damage, so that adequate repairs can be planned.

Conventionally, the periodic inspection of an LPS is conducted manually, with several personnel and heavy equipment necessary for the procedure. The turbine must be stopped for technicians to access the blades by rope and/or using a suspended access platform. Once in position, a visual inspection of the receptors can be performed. The technician on the blade can then connect one lead of an LPS testing device to the lightning receptor, while the other lead can be connected at the earth grounding grid, thereby measuring the continuity and resistance of the LPS to ensure it is within acceptable limits. The main limitations of this approach are:

  • It is expensive: several technicians are required to conduct the inspection and a suspended platform may be required, which takes a long time to mobilise and demobilise to inspect the LPS on each blade of an offshore wind turbine.
  • It causes loss of production: the rotor must be stopped for typically six hours to conduct the inspection.
  • It is a health and safety risk suspending technicians from ropes up to 120m above sea level.
  • The results of the inspection are prone to errors from human intervention.

Challenge

The challenge is to develop an innovative and cost-effective solution that addresses one or more of the limitations associated with the manual inspection of a blade LPS.

Solutions must seek to minimise or completely remove the need for human intervention to perform LPS inspections. For example, using robotics or remote monitoring systems. It would also be advantageous if the solution could act in combination with other visual inspection requirements/techniques for blades, for example drones conducting visual inspections of the complete blade surface to identify damage e.g. leading edge erosion. A rope access technician would usually combine the LPS inspection with a full visual inspection of the blade surface.

Specifications

Solutions must be able to be operated safely and reliably in offshore conditions with:

  • Average wind speeds up to 15m/s;
  • heights of 100-200m above sea level;
  • composite blade surfaces;
  • ambient air temperatures of 0-400C;
  • distances up to 25km from shore, ideally up to 40km.

Cost

To be considered, new solutions must significantly reduce the costs associated with manual LPS inspections. For a typical 6MW offshore wind turbine, current industry practice is capable of inspecting the complete LPS system (three blades) in six hours at a cost of £9,000 (including £4,000 in lost energy generation). An ideal solution should aim to achieve a 50% overall improvement on cost and time of inspection.


The European offshore wind O&M market is estimated at between £1bn and £1.42bn per year.

Opportunities

In the UK, there are 2020 operational offshore wind turbines, with a further 2470 in operation in other European markets. The global market totals 5046 turbines. Growth is expected to continue in all key markets and in Europe, the operations and maintenance market is estimated to be worth between £1bn and £1.42bn per annum.

 

Download the Repairing Lightning Strike Damage O&M Case Study

Do you have a potential solution?

The European offshore wind O&M market is estimated at between £1bn and £1.42bn per year.

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