Commercially Confidential
Offshore considerations on drive train
operation and development
David Reetham C.Eng, MIMechESenior Project Engineer, Wind Turbine Systems
© Copyright Romax Technology Limited.
• Offshore wind in the UK alone is planned to grow by over 33GW
with the commencement of Round 3 projects alone
• This could represent >30% of the UK electrical demand being
delivered by over 7000 additional units by 2020
• Compared to present installed capacity, this represents a +30-
fold increase – however current levels of maintenance, reliability
and availability must not follow the same pattern
• This presentation aims to provide an overview of some drivetrain
related issues affected by offshore installation, how these might
be mitigated and how future demands could affect development
Overview
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• Company Background
• System Reliability
• Drivetrain turbine planned maintenance
• Drivetrain turbine failures in context
• Potential offshore causal factors
• Mitigation strategies
• Future demands and their effects
• Summary
Contents
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Company Background – what is Romax
• ROMAX – derived from ROtatingMAchinery eXcellence
• One of the worlds leading consultancies in
the design and analysis of bearings, gears
and gearboxes, drivetrains and mechanical
transmission systems
• Covers automotive, off-highway
equipment and latterly renewable energy
– notably wind turbines
• Major growth in RE in last 4 years –
accounts for nearly over 50% of sales and
profit, and almost half the personnel
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Company Background – Romax Services
Gearbox Design Drivetrain Design Drivetrain Dynamics
Manufacturing & Certification “Innovative” Research
Test Specification & Test Design Instrumentation and
measurement
Field Support
Large Bearing Analysis
Drivetrain Concept Layout
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My Background
• Design engineer –earthmoving equipment
• Project engineer –Aerospace actuation systems
• Engineering Manager – A380 Landing Gear Integration• Senior Project Engineer –
Wind Turbine Systems
© Copyright Romax Technology Limited.
My Background
• Design engineer –earthmoving equipment
• Project engineer –Aerospace actuation systems
• Engineering Manager – A380 Landing Gear Integration• Senior Project Engineer –
Wind Turbine Systems
But what relevance to Wind?
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System reliability – Aerospace vs. WindCivil airliners: -
• Have >99% dispatch/service reliability
• Have long heavy maintenance-free periods
• Extensive CM, Fatigue and system monitoring
• Are designed for a long life
But
• They do get regular small maintenance periods
And
• Cost BILLIONS to develop
Which offshore wind
strives to achieve
Which offshore wind
cannot have easily
Which offshore wind
CANNOT afford!!
Offshore wind needs aerospace reliability
but at a fraction of the cost and support
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Drivetrain Turbine Planned Maintenance
Onshore needs…
• Van + technicians
Typically yearly intervals for: -
o Gearbox oil / filter changes
o Generator brush inspections
o LSS bearing grease refill / container removal
However: -
Offshore needs…
• Boat + crew + overheads
• Sea trained technicians
• Survival PPE
• Standby accommodation?
(weather delays)
Upwards of £2000
extra direct costs per
turbine per visit is not
unreasonable
for offshore
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Drivetrain Turbine Failures – in context (1)
…cause14% per
turbine per year
…yet account for
39% of all downtime
Including the generator in scope, Drivetrain related failures…
A ratio 4
times the
Remaining
items!!
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Drivetrain Turbine Failures – in context (2)
HSS & generator
bearing damage
Internal Gearbox
component failure
Typical failures include...
HSS coupling
degradation
To rectify: -
•2 technicians, boat, crew – good availability
•New bearing(s)
•1 day?
•Perhaps £2k?
To rectify: -
•Gearbox replacement
•Jack-up boat/crew
•Variable availability
•3 days?
•Perhaps £50k plus?
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Potential offshore specific causal factors (1)
• Higher average windspeeds
(small distance offshore
increases average m/s by
25%) leading to...
Improved average energy yield
BUT
at the expense of greater induced
fatigue damage on all systems
Equal to approx.
90% increase in
kinetic energy
hitting the rotor
0 5 10 15 20 25 30
Power Output
Windspeed Dist r ibut ion
Energy Output
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Potential offshore specific causal factors (2)
• Turbulence offshore –
windshear impacted by
varying boundary layer at
high sea-states
Prevailing wind
Varying surface relative to rotor C/L
rapidly changes BL increasing…
TURBULENCE
• This is compounded by large
grid arrays, that despite
careful analysis do cause
downstream turbulence
Wind Turbulence
per turbine
Also…
• Tower attachment grout
loosening –
o increased tower flex
o changed natural
frequency
o Rotor movement
relative to horizontal
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Potential offshore specific causal factors (3)
End result (compared to onshore)…
• Greater maximum offaxis loads
imparted onto the drivetrain
• Increase in range and number of
varying load cycles seen
Whilst simultaneously delivering…
• Higher power outputs
• Longer operating periods
Causing…Edge contact
with overloading
at gear meshes
Bearing fatigue
due to bad
contact pattern
and overload
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Mitigation strategies (1)• Duplicated/redundant and
longer between-service systems
• Better modelling of drivetrain in the context of its installation
• Real-time monitoring of imparted loads and the accumulated damage on the drivetrain
• Stiffer bedplates and improved mounting of drivetrain units BETTER
Extended
duration
auto-greaseLonger life oil,
reserve tanks
and duplicated
filters
Load data
Live damage
figures for: -
•Bearings
•Gears
•Shafts
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Mitigation strategies (2)
• Where could these be applied?
YesLater projects
mostlyMinor changes
Improved mounting &
installation
New installRetrofit and
new installRetrofit
Improved modelling & real
time load monitoring
New installRetrofit and
new installRetrofit
Extended service & system
redundancy options
050%-Plans frozen
05%>99%Built
33 GW7.2 GW1 GWSize
321
UK Offshore Round
• Round 3 projects represent the best opportunity for the application of
improved service, modelling, monitoring and mounting/installation to
be included from the start
• However, alternative generation topologies may provide simplification
opportunities….
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Future demands and their effects• From Round 3 to Round 4 and on…
R3 - 33GW R4 - >50GW ?
• Rising oil prices, nuclear concerns and increasing
demand will need larger, cheaper, more
autonomous and more reliable offshore units
• Pressure will increase all installation resources,
driving costs up
• Consider the potential solutions…
Floating,
quick deploy
structure
But more induced
turbulence from
sea & tower
pitch, so needs…
Robust, reduce
part, integrated
drivetrain?
Add in demands
of long power
cables - does
HVDC help
drivetrains?
Future Drivetrain?
•2-blade higher
input speed
•Single stage GB
•Integrated, robust
generator
•Current converts
to DC only
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Summary
• Drivetrain related failures do account for a high proportion of turbine
downtime based upon current data - Offshore conditions will serve to
exacerbate these
• Opportunities must be examined to reduce maintenance demands through
longer life oil, grease, cleaning and filtration systems
• Potential exists for real time monitoring of imparted loads and their resultant
effect of drivetrain damage accumulation, enabling problem avoidance
strategies to be employed pro-actively before they become failures
• Improved installation and mountings can reduce off axis load effects
• Round 3 offshore represents the biggest single opportunity to deploy these
improvements at the design stage
• Deep water, offshore, demanding HVDC links, might provide array level
opportunities and system cost reductions for simpler, more robust drivetrain
designs
• DO consider the drivetrain design within the Turbine context
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