which part of a vertical wind turbine becomes the first maintenance pr 6

[etrobal]

gentlemen:

relative to my previous posts dated 12 August 2009 and 27 August 2009, wherein we are bidding out the erection of a more than 100MWe wind farm, i would like to solicit your kind advises or insights on which part of the wind turbine will most likely become a maintenance problem within a year or so of operation.

i have surfed the net and the most likely will be the drive train, notwithstanding a lightning or a catastrophic event like an earthquake.

if, indeed, the drive train will be our area of maintenance priority, can we as the owner operator, require the turbine manufacturer to stock up on drive trains, or gears for that matter, as a precaution, sort of looking ahead and avoiding maintenance shutdowns?

in your experiences, if it is not the drive train or gears, which should we be looking at, being first time owner operator?

thank you again, indeed, for the time and patience.

 

[MikeHalloran]

Since a drivetrain failure is no small inconvenience for a wind turbine, a smart o/o would at least try to make it someone else's problem.

I.e. instead of planning to stock replacements for parts that should _never_ break, try demanding a really long warranty. Maybe it will induce the manufacturers to hire some actual mechanical engineers to get their failure rates down.



Mike Halloran
Pembroke Pines, FL, USA

 

[lumenharold]

Considering the cost of installing a wind turbine would it "pay" to incorporate a wear monitoring system such as the infrared/thermal cameras common in manufacturing? They could be linked to communicate remotely so that the system could be serviced before total failure.

Harold
SW2009 SP4.0 OPW2009 SP2 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[MikeHalloran]

I'd expect >at least<:
monitors and alarms (separate sensors and channels) for
lube oil temperature
bearing temperature (each and every bearing)
cooling air temperature (in and out)
rotor speed \____ shutdown on difference
generator speed / other than gear ratio

all with
local indication (inside the box)
regional indication (visible from nearby highway)
remote indication (dial a phone or otherwise phone home)



Mike Halloran
Pembroke Pines, FL, USA

 

[metengr]

To answer the OP

i would like to solicit your kind advises or insights on which part of the wind turbine will most likely become a maintenance problem within a year or so of operation.

gear box
blades (manufacturing defects)
generator bearings
yaw drives and bearings

 

[KENAT]

You mention Vertical wind turbine in your title, do you mean VAWT?

I understand the bearings can be problematic in some configurations, torque tubes were a failure point in some of the 90's models due to the cyclic loading of some configurations.

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[arunmrao]

my list will be gear box, bearings and the vanes/blades(depending on who the manufacturer is). A google search will tell you serious blade problems faced by one manufacturer,and gear box problem of another.


If you think education is expensive, try Ignorance.
- Andy McIntyre


_____________________________________

 

[MintJulep]

can we as the owner operator, require the turbine manufacturer to stock up on drive trains

Yes. The RFP and contract can and should contain clear provisions for the supply and availability of spare parts.

The manufacturer will not stock a supply of spares out of goodwill. You will pay for them upfront.

Alternately, you can add provisions for maintenance agreements and penalties for downtime. You will pay for this upfront. Probably more than paying for the spares.

Or, you can include reliability and availability requirements, alone or in combination with penalties for downtime.

Basically, it's a contract. It can be whatever two parties agree to.

 

[gerhardl]

A lot of possible failure of mechanical parts, and systems to control possible wear and failure is mentioned above, along with the stated fact that a binding contract between the parties should go for a long-term guarantee.

I would go a step further. Vertical windmills could have considerable longer expected lifetime than traditional windmills, but also shorter, all depending on type of vertical windmill.

To invest sizeable in any energy-producing unit today, it be water-turbines, wave or wind-driven mills or anything else without an analysis of earning over expected lifetime, including an analyzis of expected uninterrupted operation time, downtime for planned maintenance, cost of maintenance and total expected liftime will be to take a chance.

A good and experienced producer would help you with figures for this, including a risk analyzis for unexpected occurences (shutdowns or consequences by high windspeeds? Some vertical axis constructions can withstand windspeeds shutting or breaking down conventional windmills)

Next step would be to nail down the supplier and producer to the best possible guarantee or operation/maintenance contract.

Or are you perhaps the person trying to help the producer doing this or checking his figures?

All lifetime of mechanical components are depending on correct operation and sizing, and correct preventive maintenance.

 

[plasgears]

When jet engines were showing long life and reliability, condition monitoring came into the picture. Instead of overhauling on a regular basis, monitors were installed to show indications of incipient failure like higher vibes, lube contaminants, rising temps, increasing noise, etc. This could be a whole new specialty in wind turbines.

 

[tbuelna]

plasgears,

Most of the reliability and maintenance issues with utility scale HAWT's are just a function of the learning curve the turbine designers are going through. The utility scale wind turbine sector (1.5MW and larger) is a very young business that is less than 10 years old. These commercial wind turbine are typically engineered for 20 years of life, and their design criteria standards are defined by very detailed specifications produced by organizations such as AGMA and the IEC. Many turbine manufacturers also contract with independent labs to validate their designs.

I would disagree with the posters that say the most failure-prone parts of utility scale HAWT's are the transmissions and feather/yaw bearings. From what I've seen, the reliability of the inverter/rectifier PE's commonly used with DFIG's are more of a problem. Especially since they pose a serious fire hazard.

As for the designers of utility scale wind turbines employing the highly successful Condition Based Maintenance (CBM) and Health Usage and Monitoring Systems (HUMS) techniques developed for aircraft mechanical and propulsion systems, they are slowly catching on. CBM and HUMS are useful for maximizing operating life of a properly designed and manufactured system, but they are not much help in preventing issues due to poor quality. And most of the more publicized wind turbine failures (such as Clipper's blade issues) are due to poor production quality control.

To answer etrobal's original inquiry, there is no particular wind turbine component that will likely fail in the first year or two of normal operation. Drivetrain, blade, or PE failures are more likely to occur after 5 or more years.

Gears or bearings normally have very benign, easily monitored, and very predictable failure modes.

Composite blades tend to fail in a more catastrophic manner and their causes are more difficult to monitor in service.

PE failures tend to be very catastrophic in nature, since they usually result in nacelle fires. This has been such a serious problem that many wind turbine insurance underwriters now require the use of fire-resistant metal nacelle structures instead of fiberglass.

Best regards,
Terry

 

[KENAT]

Did the OP ever clarify if he actually meant VAWT as hinted in the title.

I realize there's been a big upswing in the last decade or so in wind turbines, but there have been quite a few out Mojave An Tehachapi for quite some time, long enough for some to have life expired on their 20 or so year life expectancy.

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[metengr]

tbuelna;
From my perspective, the wind turbine industry over the last 24 months suffered from scaling up production and Mw output too quickly. This is a common theme in any industry that wants to design, build and commission equipment based on customer demand with limited supply.

Gear boxes - main reliability issue has been infant mortality failures of intermediate (IM) and high speed (HS) pinions caused by lower quality gear steel. What is going to limit long term reliability of IMS and HS pinion/gear sets is infant mortality from subsurface fatigue crack propagation caused by inclusions in the steel. After infant mortality, smaller inclusions may result in failure after 5-10 years of service on existing gear sets.

Gear box bearings - here we have a serial defect problem with some wind turbine gear box designs. Spherical roller bearings that should have never been used in some gear box designs.

Solution to gear box reliability - gear steel should have been specified as vacuum degassed and forged versus continuous cast steel rounds that were air melted. As remediation efforts are underway, cleaner quality gear steels will prevail and reduce future failure rates.

Gear box bearings - remediation efforts are underway by some wind turbine OEM's to switch to a different bearing design.

Blades - once again we have a period where increased demand outpaced supply. End result was increased blade production and not enough experienced bladers to handle increased production. Quality control was compromised which resulted in wrinkles and dry spots on blade skins that located in high stress locations results in fatigue crack propagation.

Also, scaling factors for increased Mw output has resulted in blade remediation efforts to repair or strengthen original version blade designs because there was not enough time to subject bigger blades to full scale static and dynamic fatigue testing using dual axis test machines. Also, same quality control issues for larger blades have erupted.

Fortunately, the infant mortality failures for blades can be remedied by a blade repair/replacement remediation program based on static and dynamic testing of orignal blade designs that have been strengthened using double patch plates.

 

[jmw]

hen it comes to offshore, the problems multiply. You can't afford routine maintenance and need CBM programs with remote telemetry of key data.

Lube oils are a key area for on line monitoring.



JMW

http://www.ViscoAnalyser.com

 

[etrobal]

my apologies, gentlemen, for the seemingly unintentional insertion of the word "vertical" in my post. we are bidding out horizontal-axis wind turbines and most bidders will definitely offer hawt. our specs calls for a hawt.

we are now in our final stages of ranking the bidders' offers, from the wtg, electrical,scada to maintenance and project management, to financial offers.

i hope the previous advises and discussions will not be affected by this correction.

 

[tbuelna]

metengr,

You are correct when you state that the most likely failure mode for case hardened gears and rolling element bearings is case spalling due to subsurface initiated shear failures.

However, the subsurface shear failures can be caused by other factors besides raw material flaws. For example:
-Improper heat treatment can produce uneven transitions between the case and core, which promotes shear failures.
-Poor design can also lead to a condition where the point of max subsurface shear stress is outside the case, and is too high for the core material.
-Excessive case stock removal during finish grinding can result in inadequate case depth to support the design contact stress levels. The distortions are produced during the heat treat quench process.
-Surface corrosion pits are commonly the cause of case spalls. These corrosion pits can originate during manufacturing or storage due to lack of corrosion protection. And they can also result from moisture entrained in the lubricant, that is produced by condensation within the gearcase during the heating/cooling cycles at startup/shutdown. Grease lubricated bearings are also especially susceptible to surface corrosion pits, since any pockets in the grease pack readily trap moisture droplets against the bearing elements.
-Case spalls can also result from excessive contact stresses. The contact stress in bearings and gear meshes can easily exceed the design loads due to edge load effects caused by inadequate case or bearing stiffness, torsional wind-up along wide gear faces or within flexible planet carriers, high dynamic tooth loads created by geometry errors and/or low contact ratios.

As for using spherical roller bearings in gearboxes, they are commonly used to support the planet gears of simple planetary gearsets. The reason they are used is to counter the effects of torsional wind-up deflections in the planet carrier structure. They are also (sometimes) used as rotor shaft bearings to compensate for the shaft bending caused by the rotor's huge asymmetrical flapping moments.

I am enjoying the discussion. It is very enlightening.
Terry