offshore considerations on drive train operation and ......offshore considerations on drive train...

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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