CMS for Wind Turbines

After working over a decade in wind CMS, I’ve tried to condense my wind turbine knowledge into one introductory article, exploring what is available out there and what is worth instrumenting. Enjoy.

Condition monitoring is the practice of using sensory data to determine machine state. It is useful to predict faults in remote machines that are in constant use, and where downtime is expensive.

Operators can use the data to make informed decisions such as planning inspections, maintenance or replacement, ordering spare parts and budgeting. It is particularly useful for wind turbines, as they have a blend of mechanical and electrical equipment subject to dynamic loads, effects and forces such as:

• Shear forces – parallel forces to a surface or plane, such as the difference in wind speed and direction with height. Also seen in gear teeth and blade bolts
• Torsion – twisting of the blades and blade bearings
• Tension – bending of the blades and tightening of cables
• Torque – such as the high-speed coupling between the generator and the gearbox or flange bolt tightening
• Eddy/stray currents – such as electrostatic pitting on generator bearings
• Impact – such as a metallic particle being run over by a bearing roller
• Lightning – such as blade damages, main bearing electrostatic pitting
• Arcing – the flashing of electricity over two channels or phases, such as generator slip rings, delta modules or electrical contactors
• Corrosion – from salt spray or water ingress
• Freeze thaw expansion – such as cracks appearing in foundations
• Oil ingress – such as oil getting into the slip ring through the hollow shaft
• Electrical noise – interference produced by electrical components affecting other electrical functions
• Icing – ice build up on the blades and anemometry

Main shaft strain gauging to measure stress and strain

This is not an exhaustive list, but you can see how many different sensor types and locations would be needed to include all the wind turbine components. This is expensive, both from an equipment and specialised labour perspective, in a cost-sensitive industry. So how do we optimise condition monitoring for coverage and cost?

What is available out of the box when you buy a wind turbine?

Vestas

You can buy the vibration condition monitoring system (CMS) system historically provided by B&K Vibro and high-resolution SCADA as part of the Vestas toolbox setup. This system involves paid access to data, manuals and engineering support from Vestas and is tiered. It is generally seen as providing limited and expensive access, and it is frustrating for operators who want to self-perform on their assets.

Thankfully, controller retrofit can unlock both high resolution data (millisecond rather than 10-minute data), vibration data and the ability to set parameters.

The lightning detection system on the later versions is both reliable and provides the time of strikes remotely. Optional extras include blade vibration sensors for imbalance and metal particle counters for detecting gearbox damage.

Typical data acquisition system (DAQ)

Siemens

Siemens TCM (Turbine Condition Monitoring) system is better than most in providing access to  high-resolution SCADA and vibration data, via site servers, at low or no cost to most operators.

Lightning detection using the lightning cards system is still manual on the SWT2.3 and SWT3.6, however, labour intensive and erases historical data. There are aftermarket offerings which can give you both continuous lightning detection data (time, turbine and magnitude) as well as lightning protection system (LPS) status for support in substantiating force majeure claims.

Gamesa

The Gamesa SMP system is usually encrypted and only available via Gamesa service contracts. Following the merger with Siemens, those supporting the system are difficult to find and even harder to get to respond. There are options available for people to access this data and we can help those suffering: contact us. sales@windyproductions.com

Enercon

Being direct drive, conventional drivetrain monitoring is limited to a vibration sensor that monitors imbalance. Grease sampling may be on offer to give some indications of bearing wear, but this is a manual process. If you can get access to the SCADA data, then you may get some temperature alarms to give an indication of machine health. The data is limited but thankfully the WTGs are generally reliable. However if you do want more data access, including to the converters and pitch system, there is a full WTG controller retrofit available.

Control linked vs non-control linked

Condition Monitoring Systems (CMS) linked to the wind turbine controller (WTC) are set to stop the turbine to prevent further damage or catastrophic failure. Typically, these are temperature or vibration sensors linked into the SCADA system. Whilst useful in prevention, they can often give false alarms, requiring inspection confirmation or senior authorisation clearance to reset. Out of hours, this can lead to expensive callout costs and wind turbine downtime. However, as part of the wind turbine safety chain, it is an essential part of the WTC. These are usually provided by the OEM, however in some instances where controller access is provided, CMS can be integrated into the WTC to enable remote resets and stops such as ice detection systems. When a blade is thawed, then the turbine can restart without inspection.

Non-control-linked CMS is usually provided by a third-party specialist or consultancy company to address lack of asset integrity visibility. Targeted towards expensive or troubled components, this information can be integrated into SCADA software platforms alongside other reliability metrics, and collated with other sources of information. This information is typically advisory, and alarms result in a recommendation for inspection for damage confirmation. The operator can then decide  whether to stop the turbine, but the standalone CMS system alone cannot stop it.

Wind turbine controllers are at the heart of your wind turbines data

What type of sensors are typical?

• Piezoelectric sensors (temperature and pressure) – useful in mechanical and electrical systems to highlight increased resistances
• Accelerometers (vibration) – measuring gear and bearing damage and tower oscillation. A useful indicator of mechanical damage as well as imbalances. Dam sensors that measure baseplate movement in the Z direction can give an indication of pitch misalignment
• Strain Gauges (strain) – measure stress and strain due to changes in forces on main shafts, for example using strain gauges. Tiny changes in electrical resistivity are used to calculate stress and strain.
• Microphones (acoustic) – measuring blade damage such as leading-edge erosion, using microphones to listen for increases in noise changes between blades and neighbouring turbines
• Fibre (continuity) – measuring cracks such as those which arise on blade bearings. When a crack occurs, the fibre expands and the crack is highlighted in FFT.
• Particle counters (metal) – measures the metal particulates in gearbox oil to determine whether the gearbox is failing.

How do I get access to my data?

Build data access into your turbine supply contract when selecting a WTG OEM. This ensures they are contractually obligated to provide it, and you have all the reliability data you need to make informed decision making on changeouts, end of warranty claims and remaining useful life assessments.

Getting access to that data from the OEM is the next challenge as it is very much a case of the fox guarding the hen house. This relationship is vital and the importance of this cannot be overstated. Good engineering contacts, a strong development pipeline (and WTG order book) and asking the right questions of the right people. Paying for access to your own turbines seems perverse but sometimes it’s the only way to get some progress.

I think it is criminal that wind turbine owners do not have access to their own turbine’s data, and I have built a career around empowering owners. I have installed accelerometers next to perfectly good pre-existing systems for no other reason than the data is encrypted. Most of the time this is done at the wind turbine controller rather than the data aquisiton system (DAQ) and there are retrofit options to enable access to pre-existing systems whilst preserving the safety chain.

Failing that you could hire a private investigator to build a blackmail case against stubborn OEM engineers.

Obtaining data access can be frustrating

What can be improved?

When embarking upon any asset management strategy, start with your contractual exposure. What will you have to pay for if stuff goes wrong? Technicians’ tools dropped into gearboxes?  Acts of God such as lightning strikes? From here, establish a baseline of what data is currently available from existing systems on the wind turbine. Don’t pay for what you already have and can access. Data is useless unless it is actionable and then it becomes information. Information helps make good decisions.

Once you’ve established what you have got, determine what you need, and which CMS providers have the best products aligned to your vulnerability, both contractually and from a technology perspective. What ammo do you need to get the OEM, insurer or service provider to act and take responsibility? Does it need to be certified and up to IEC standards? If your turbine has known serial defects such as blade bearing cracks and you want to stem the bleed, what CMS coverage do you need to ensure that you don’t end up on the local news stood in front of your collapsed wind turbine?

What components can be monitored and what is the benefit?

There are over 8000 components in a wind turbine. Some are expensive, some are cheap, some have redundancy, some are a single point of failure, some require a crane to replace. Whether it’s a contactor or a gearbox causing downtime, if your wind turbine is off it is not generating and producing money.

Main bearings and gearboxes

Main bearing and gearbox condition monitoring is well established, tracing its routes through conventional rotational machinery, and any mechanical engineer unfortunate enough to have done some Matlab at University can give you FFT and RMS analysis. Most WTGs have drivetrain CMS fitted as standard but some companies offer CMS hardware with a view to selling their monitoring service or software. The vibration and temperature data will give you coverage of all bearings and gears and a 3-6 month lead time to failure notification for gearboxes and sometimes more than a year’s warning for main bearings. This can be a big help when planning major component replacement campaigns, particularly offshore, as well as handy in budgeting and arranging spare parts.

Main bearing spalling on the outer raceway. Main bearing CMS can give a long lead time to failure (>12 months) due to the slow rotational speed.

In support of this, particle counters reveal gearbox failures arising from metal particles freed from gears or bearings in service. This can be used to prioritise inspections, reduce oil sampling frequency and optimise servicing and gearbox replacement. For offshore WTGs particle counters can be particularly (get it!) useful in better optimising jack-up vessel costs.

Blades

Blades have long been a condition monitoring oversight despite being among a short list of major components requiring a crane to replace. Historically blade strain, vibration and other retrofits have been prohibitively expensive and sensitive, liable to false positives. As technology has improved in mobile and wireless communications, batteries and processing blade CMS now has several providers who enable data to be fed back from one of the darkest places in a wind turbine. Tower base mounted acoustic sensors can detect leading edge erosion (LEE) and lightning damage. Similar technology can be mounted in the root zone to detect cracks in the first 12m of the blade. Root zone inspections are difficult terms of access (greasy and confined), health and safety and cost. Crack detection and propagation monitoring can be vital.

Left: Standalone blade CMS to detect surface damage and lightning strikes. Centre: upward trend in noise following lightning strike: Right: confirmation of blade damage via inspection

Blade bearings

After endemic blade bearing failures on 2MW platforms, there are some good companies offering blade bearing condition monitoring to enable early detection of cracks, bolt failure and elliptical bearings; used either in serial defect applications across the wind farm or as part of a targeted campaign. Fibre optic cables are used for continuity and, when broken, indicate cracks forming. Typically cracks are seen near top dead centre (TDC) of a bearing and therefore easier to instrument for when identifying sensor locations on raceways and blade bearing bolts. 3-6 months warning can be given and targeted campaigns can be used to monitor failing bearings to allow generation through winter months until a crane can be arranged for replacement. Bearings that are under a lot of strain, partial rotation, seal and manufacturing shortcomings can often be serial issues, with particularly WTGs in the 2MW class heavily affected. If you’ve ever wondered what a failed bearing looks like, it falls a lot like buttered toast, the heavy butter side down sticking out of the soil.

Blade bearing failure resulting in blade “liberation”

Blade bearing oscillation trend showing an increasing trend. This data can be used to see whether a failure is progressing to prevent catastrohic failure

Yaw Drives

It is also possible to monitor yaw drives. Whilst relatively low value compared to major components, they are liable to serial defect and anyone who has done a yaw gear replacement knows it is a pain and calibrating load-sharing between four, five or six yaw drives circumference by a yaw ring is an art as much as a science. An adjustable setup to optimise backlash between gear surfaces will massively improve reliability but there are state of the art yaw systems able to further optimise load-sharing via controller integration and load measurement. Very clever stuff.

yaw drive replacement

Generators and Converters

Generator bearings can be vulnerable to eddy currents causing electrostatic pitting and can benefit from vibration and temperature condition monitoring.

Converters can be unreliable, sometimes due to humidity, uneven load-sharing between delta pairs or improper installation. This is still a developing area, with some companies investigating what can be measured and how this data can be used to predict and prevent failure. Converters are certainly expensive when they go wrong and are also vulnerable to legacy issues, while cores and deltas are becoming increasingly hard to find.  Keep what you have and look after it.

A simple induction loop around phase cables can be used to measure current and determine when the generator is running at rated power without requiring SCADA access. This helps capture CMS data at full power when components are working their hardest giving the cleanest data.

How to build a business case for condition monitoring?

In the kingdom of the blind, the one-eyed man is king. Developing a business case for condition monitoring can feel like this as one of the main drivers of condition monitoring is to reveal the extent of the problem. Historical failure data is key both in logistics costs, downtime costs, likelihood of occurrence and component replacement. This serves as your baseline for worst case, then it’s time to do some maths. What can you save by combining replacements, reducing inspections, having fewer call outs, running the turbine either at derated or full power? Hardware as a service (HaaS) models may fit more nicely into your operational expenditure (OPEX) and can also cover you for any equipment failures and monitoring costs. If you are less likely to get resistance in your CAPEX budget, then would the supplier consider a hardware price and a smaller monitoring and support contract which are typically priced on a per WTG/year basis?

CMS trials are a good way to deliver value to your worst turbines, while getting a feel for a few suppliers before fully committing. This can also help you build the business case for either farm wide or fleet rollout. Don’t forget the cost of downtime for installation, both in terms of Authorised Technician (AT) support and lost generation.

Anchorman 2 bloopers cure depression but not lack of CMS data.

Conclusion

The battle for CMS is often fought between engineers who want to quantify and understand everything from a reliability perspective, and accountants who want a certain return, understanding cost but not value. Neither like risk. CMS is about mitigating risk. By detecting failures earlier, you can prevent, plan and procure in good time both engineering and financial benefits. If you catch the cancer early, you’ve got a better chance of treating it.

From over a decade in working in O&M, I’ve learned the majority of an operator’s job is getting other parties to carry out works. Inevitably these conversations descend into slinging matches and the OEM, being data-rich  in both engineering understanding of the assets and condition monitoring data, inevitably wins, while assuring the operator there is nothing to worry about or that they are not responsible because “it’s force majeure” or some other bullshit. Having the ability to prove them wrong and getting them to do the work based on your own CMS findings is priceless. Typically these CMS providers are also monitoring similar turbines which, when accessed either through introductory meetings or anonymised benchmarking, can further the data-sharing and empowerment.

For those pursuing O&M independence or even just trying to keep their OEMs honest, good data access and CMS is key. One of my old mentors in CMS used to tease me for quoting Rumsfeld on this very topic and whilst you may have some disagreements with his politics you cant argue with his ability to convey the non-committal and ambiguous nature of political response:

“Reports that say that something hasn’t happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don’t know we don’t know. And if one looks throughout the history of our country and other free countries, it is the latter category that tends to be the difficult ones.”

 Maintaining your own turbines is a battle of David and Goliath when it comes to data access and knowledge. CMS is a part of that armoury and often third party providers are the best way to go to provide power to your elbow. Visit the CMS page to learn how Windy Productions can help: