Inside the nacelle of a wind turbine being inspected

A Guide To Wind Turbine Inspection Programmes How to Protect Your Investment

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How to Define & Approach Your Inspection Programme

An effective inspection programme needs to be tailored to suit your portfolio’s needs. It needs to consider your organisation, its specific operations and also the types of assets you own and operate. Most importantly this means understanding who you are as a business, what it is you do and also your strengths & weaknesses.

Step 1: Know Your Business and its People (the “Man”)

This is a key initial step to developing an effective wind turbine inspection strategy. It will help you determine where you must focus your attention and efforts.

What type of Organisation are you?

Are you a long-term or a short-term operator? This will influence how important equipment longevity is to your business and also how aggressively you run your assets.

Is your organisation a technical “hands on” organisation or a non-technical “investor” type? This will influence how you manage your resources and therefore how you maximise value from them. Knowing this will allow you to determine the level of monitoring that you feel is appropriate for you as an organisation.

What personnel do you have?

Are you a large or small organisation? How many technical personnel do you have? This will allow you to determine what capacity you have to perform field work.

What expertise do you have in-house?

Do you have knowledgeable engineering experience in-house? Are your people tooled and trained to perform skilled technical investigations in the field? And finally, most importantly is having this expertise one of your organisation's goals?

What is your operational budget?

Having a handle on what available operational budget you have will help you map out where you see the best “bang for buck”.

What risk exposure do you have and where?

This is very important. You must identify where you have the greatest exposure when something goes wrong. What in your portfolio is covered by contract? What is too critical to fail on your watch? Therefore where should you be focusing your time and effort?

What systems do you use to schedule or validate maintenance activity?

Simple maintenance management tools go a long way and help you flag potential risks in your portfolio. These are highly important to ensure the maintenance compliance of your service providers. They are critical to allow your organisation highlight, monitor and prioritise Technical and Safety issues just like any incident management system.

Step 2: Know Your Assets & Equipment (the “Machine”)

Now that you have taken the time to understand your organisation and its goals the next step is to clearly define what assets and equipment you have.

What is your WTG technology mix?

You must determine what your technology mix is. Not all wind turbines or their equipment will require the same maintenance or attention. The potential for component failure is heavily dependent on manufacturer, model and the technology’s design and operating principles.

For instance, a Direct Drive WTG (i.e. one which does not utilise a gearbox) does not have high RPM rotating equipment or gear oil systems. Therefore oil monitoring and conventional vibration monitoring systems are not required. The design variation also means that the typical failure modes associated with high speed equipment are not seen in these machines.

Having complete awareness of your technology mix will allow you to tailor your inspection programme to take account of these attributes and center your attention where it matters most.

Foundation Design Mix - Sample Portfolio chart - *B Buoyant *NB Non-Buoyant
Foundation Design Mix - Sample Portfolio - *B Buoyant *NB Non-Buoyant

What is the split between age groups?

It is important to understand the age split between your projects and determine where each of them sit on the Bathtub Curve. This will allow you to determine the type of failures you can expect to see during the life of your components.

Tracking replacements of major components is also important as this will shift their position on the curve and therefore alter their inspection and maintenance requirements vs. their peers.

Figure: Bathtub Curve (for a wind farm project)
Bathtub Curve (for a wind farm project)

Due to the fact that many wind energy projects are now maturing they are starting to enter the “wear out” phase. This is an unpredictable period where maintenance quality and condition monitoring of equipment and structural elements is far more important than it has been in previous years.

Do you keep up to date a full equipment register of major components?

Knowing the full list of your primary components is crucial to understanding your exposure to financial risk. Having an up to date or “Live” equipment register will allow you to determine exactly what assets and equipment you have installed, their serial numbers, make, model, age/running hours and whether or not there are any known serial defects associated with those components.

Your monitoring and inspection strategy can be directed as appropriate given this knowledge.

What equipment is under warranty or protection?

Your equipment register will help you conclude where your risk exposure is. For instance, wind turbine foundations may or may not be included in the Turbine Supply Agreement (TSA) or the O&M Services Agreement. Similarly many service agreements may exclude wind turbine blade inspections and repairs.

Knowing what areas you are responsible for will help you focus your operational budget in the right direction to minimise financial risk with your projects.

Warranty Coverage - Sample Portfolio chart
Warranty Coverage - Sample Portfolio
*MSA Maintenance Services Agreement
*ISP Independent Service Provider
*TSA Turbine Supply Agreement

Step 3: Know Your O&M Service Providers (The “Method”)

A pragmatic owner knows that the goals and motivations of their third-party maintenance providers are not always aligned with their own objectives. Monitoring and verification of your contractors work is important to ensure your organisation is receiving the quality expected from your annual service fees.

Is maintenance being carried out according to specification and schedule?

There are three components which can be verified to get a good picture of the service quality of your maintenance provider;

  1. Monitoring of the maintenance schedule - Is maintenance being completed on time and outside of high wind periods? Are any of these activities being missed?
  2. The scope of the maintenance - Has the contractor reduced the scope of their maintenance in any way? For example have they extended service intervals or omitted certain routine component replacements?
  3. Maintenance Validation (Field Inspection) - A sample inspection of your WTG’s will give a much better picture of the actual condition and whether or not maintenance is being carried out to an acceptable quality.

How forthcoming are your maintenance contractors with information?

If you are experienced working in the wind industry then you most likely have encountered this sort of thing in the past. Depending on who maintains your assets you may or may not have a good exchange of technical information between both you and your contractor.

Where communication is poor your organisation will often need to seek out that information through technical investigations, field inspection and advice from the relevant wind turbine industry experts.

How are your assets being run?

This ties back to what kind of organisation you are. If you are in for the long haul you will most likely put greater emphasis on equipment longevity. You will be keen to avoid overworking your assets and will also pay greater attention to indicators of equipment condition.

The question is, does your maintenance contractor have the same motivation? If they are the ones who are operating the WTG’s (as many do because they are the Original Equipment Manufacturer - OEM) then they will decide how hard they work your assets. The maintenance strategy adopted by the OEM will also have an impact on the Safety and Integrity of your asset.

By appreciation of the difference between these motivations you will be able to determine what areas you should be more concerned about and what the impacts of certain practices will be.

Typical Life of a Wind Farm Project And Inspection Programme
Typical Life of a Wind Farm Project And Inspection Programme

Know What You Are Looking For

At this point you will have identified where your risk areas are and you will have defined a suitable inspection programme for these areas. Now you will need to determine what it is exactly you are looking for.

A cleverly designed inspection programme will aim to obtain in an intelligent way the information you need but at the lowest possible cost to your OPEX budget. Below are some examples of the types of things an owner should be looking for;

Performance Issues

Equipment Reliability Issues

Alarm & Warning Logs (SCADA)

Equipment Sensors (SCADA)

Oil Quality Monitoring

Condition Monitoring Systems (CMS)


Service/Maintenance Issues

Maintenance Logs

Operation Related

Safety Related

Structural Issues



Hub Casting

Blades & Blade Bearings

Last Updated: 01 February 2022

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