Senior Engineer Says

Jul 7, 2015

The Senior Engineer has been in the wind industry since the 1980's. He has spent his entire career in power transmission and knows everything there is to know about gearboxes. In an industry as young as ours, there are false beliefs that the Senior Engineer wants to correct. Because all he really wants is the wind industry to work together to lower the cost of wind energy and make renewables the no. 1 energy source globally.

The Senior Engineer answers one question a week on this page and our social media channels so stay tuned!

Belief	Senior Engineer Says
Gearbox manufacturers only service their own products.	We service a wide range of other manufacturer’s gearboxes in our workshops and on-site and we also provide excellent upgrades for improvement of most brands in the industry. In fact, a majority of our repair work is now made on third party gearboxes.
There is no after sales service for the old Valmet, Metso and Santasalo gearboxes.	Moventas and its predecessors, Valmet Power Transmission, Metso Drives and Santasalo, have manufactured wind turbine gearboxes under several brands since the 1980’s. These days, we own the brands Santasalo and Moventas and service & offer replacements for all our legacy brands.
The more bearings, the better the concept.	Several gearbox models in the market have either three or four roller races on planet gear bearings. These concepts are extremely sensitive to failure due to uneven load distribution between bearings. There is always uncertainty around load sharing when the number of raceways is more than two. This is due to the deformation of the planet gear for several reasons, such as • Helix angle deviations • Profile deviations • Gear deformation • Planet carrier deformation • Bearing component level deviations • Gearbox installation/alignment We have eliminated the problem by using a two-row bearing concept on planet gears, with an integrated outer race of the bearing into the planet gear. This secures the even load distribution between the two bearings, which helps avoid failures. We provide a bearing upgrade that considerably prolongs your gearbox lifetimebefore it’s compromised.
Is it possible that 2 missing teeth on an IMS pinion gear could contribute to fatigue cracking of a planet gear? Specifically in a Rexroth GPV 442 gearbox. We had both of these failure modes in a single gearbox – I doubt it is a coincidence but do not know enough to be sure.	Missing teeth causes significant extra load in the gearbox by the increase of the dynamic factor. So, if the gearbox has been in use for a long time with the missing teeth, the secondary failures would have been possible. I think you have two separate issues in your gearbox.
In service, a warranty is only valid for new or repaired components by the service provider.	Moventas warranties cover the entire concept serviced. The service process also includes complete and detailed inspection and testing procedures for all components of the serviced gearbox.
Applying upgrades on the gearbox during service is an additional cost.	During service, many components are replaced due to damage. An upgrade can therefore be applied with the same effort as replacing damaged components. Actually, in some cases the cost of a Moventas upgrade can even be lower than that of a like for like repair. With our 35 years of learning from gearboxes, a Moventas upgrade prolongs gearbox life so much that the cost pays itself back manifold over the years.
Anybody can manufacture or refurbish the gearing of a gearbox.	Proper micro geometry definition is needed in both manufacturing and service, and it requires CMM measurement, calculations and 3D modeling. This is to eliminate the possibility of repeating any possible defect, design or manufacturing error from the reference component. Why would you want to repeat the same mistakes? The engineering phase that we carry out also indicates any needed upgrades. As an OEM, we are gearbox experts who know what the best and the most sustainable choice is in each situation.
Gearing failure always requires a workshop service.	Moventas is capable of a multi brand repair of the most typical failures up-tower, e.g. exchange individual components such as bearings or geared components, or even perform a full helical stage change out on-site. We always aim to carry out repairs up-tower where possible to provide not only savings, but also a reliable, Moventas quality repair that prolongs gearbox lifetime.
A test run of a gearbox is just to analyze performance after service or manufacturing.	The “wear in’’ of a gearbox that we take care of on behalf of our customers is a crucial step before the gearbox is placed in production conditions. All generated fine particles in the first load steps are monitored and filtered out with special filtration devices to eliminate any possible cased damages to bearings and gearing.
Vibration measurement is the key indicator of upcoming failures & adequate condition management.	An increased signal of vibration is already a sign of existing failure. If increased vibration is detected, the failure can be in a more advanced state and therefore vibration is less a preventative tool than an indicative tool. The CMaS monitoring of vibration is how the progression of the failure is followed and interventions such as alignment and balance checking are forms of corrective action that may be taken along with up-tower replacement of bearings and shafts etc. Early detection of upcoming failure would show the increased size and count of particles on lubrication oil. Oil particulates, especially in the planetary section, tend to show the onset of failure before vibration, so particle count is early detection and if action taken can prevent further degradation. Vibration measurement only gets you so far. If you really want to manage your gearbox condition, get recommendations on courses of action and plan service carefully, the Moventas CMaS will provide a rapid return on investment. CMaS allows you to manage the gearbox/drivetrain conditions. CMaS can monitor oil condition, oil particle content, vibration, RPM, temperatures and pressures depending on the platform installed. Management is provided by the analysis, recommendations and actions derived from the measure parameters. With CMaS, you have smart predictive maintenance, an early warning of problems and in most cases you only need an up tower visit instead of gearbox exchange.
A damaged gearbox might as well be scrapped and exchanged for a new one.	You don't want to throw money in the bin, do you? A damaged gearbox should never ever be scrapped. With our Replacement Gearbox Pool, we can have a replacement ready for you in days. We will refurbish the damaged gearbox and store it for you. We also have new gearboxes and refurbs available all the time from stock for e.g. Vestas, RePower (Senvion), Nordex, NEG Micon, GE, Gamesa, Acciona turbines. Check out this week’s list of available replacements!
Moventas does not offer gearboxes to end-users.	We do manufacture gearboxes for turbine manufacturers, yes, but we also offer Moventas quality replacements for the most common turbine brands in the industry. In many cases, our replacements are on site within three days. We also store gearboxes fully accessorized, thus minimizing turbine downtime and exchange costs. Check out this week's list of available replacements globally! Also, why not enquire about a payback programme where we take care of the damaged gearbox for you and you get a reimbursement?
Tooth fracture is a design error.	Tooth fracture may occur in different ways that exclude design fault as a root cause. • Heat treatment defect • Grinding burn • Material defect • Overload due to turbine operation • Fretting corrosion on tooth by turbine still standing By using Moventas replacement parts, material and manufacturing process related choices are secured by material purchase specifications, quality processes and supply chain control. Sub surface initiated crack growth is eliminated by raw material process and cleanliness requirements inside the Moventas specific material specification. Grinding burn is avoided by 100% inspection rate after grinding by Barkhausen method and by long experience of gear manufacturing.
Case hardening and case carburizing – tomato, tomato.	Actually no, they are different things. The term “case hardening” is used if there is just thin hardening or coating top of the base material. Also, a nitrated gear wheel is sometimes called case hardened. The best method with ring wheels is however the case carburized AND hardened gears. Here, we implement additional carbon to a very deep layer of gear material and cause of additional carbon. This way you get a hardened layer as strong as in external gears. Why? The reason is very simple – wear resistance. With our long experience of case carburizing, practice has shown that its failure rate is 0. Moventas has always used this technique for all geared components and is leader in this technology in the wind business. Because we want to see gearboxes live longer.
With a gearbox, bigger is better.	Actually, less is more these days and what the industry needs from gearboxes is torque density. The race for grid parity calls for smaller and lighter drivetrains that reduce cost throughout the turbine value chain. The Moventas Exceed series has clearly proved that a 10% smaller size and weight with 20% higher torque than in conventional gearboxes is possible. In other words, why directly and indirectly pay for more for raw material when same safety factors, measured load sharing factors and better dynamic behaviour are all available with less?
Integrated and semi-integrated drivetrains is new, suspicious technology.	Actually, at least in our case it's based on proven technology. Moventas masters all levels of integration between a gear and a generator. Generally the technology responsibility is divided between gear and generator supplier as in traditional high speed solutions. For example, our Exceed high torque density gearbox can be integrated with a generator supplier either chosen by us or the customer.
Inadequate lubrication causes bearing failure in a gearbox.	Gearbox design calculations and prototype and field tests ensure that each bearing position is adequately lubricated during each operational mode. The needed oil amount for lubrication is typically very small when comparing to the oil volume needed to the cooling of the bearing. This means to say that the first failure indication should always be the bearing temperature, which is tested from every delivered unit in serial test up to nominal power. With Moventas test run standards that also apply on serviced gearboxes, assembly, component or other quality related problems are 100 % avoided.
White etching cracks (WEC) cannot be avoided.	WEC is so called pre mature failure mode that cannot be taken into account when calculating bearing lifetimes for wind gearboxes. Normally, WEC appears after 1-3 years of operation, in some cases even after a longer operating time. Moventas has studied the phenomena together with bearing manufacturers. Based on the outcome, we can offer solutions to avoid WEC based defects. This can be done in the design phase of a new gearbox and we can also offer retrofit solutions that can be done up in the tower.
Gearbox is the most prone to failure component in a turbine.	Not true. Based on studies, the gearbox is not even the top ten when calculating statistics of component failures of wind turbines. Gearbox failure can of course cause long idling for the turbine in the case that the defect has not been predicted early on. To avoid long unplanned shutdowns, predictive maintenance is key, e.g. with the CMaS Condition Management System. This tool is specially designed for wind turbine use and it helps avoid unplanned shutdowns. It often also prevents failure from escalating due to early detection, keeping repair costs under control.

Source: http://www.moventas.com/news/articles/senior-engineer-says

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Senior Engineer Says