offshore considerations on drive train operation and ......offshore considerations on drive train...
TRANSCRIPT
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
© Copyright Romax Technology Limited.
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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