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Procedia Computer Science 16 (2013) 814 – 823
Conference on Systems Engineering Research (CSER’13)
Eds.: C.J.J. Paredis, C. Bishop, D. Bodner, Georgia Institute of Technology, Atlanta, GA, March 19-22, 2013.
A Systems Approach towards Reliability-Centred Maintenance
(RCM) of Wind Turbines
Joel Igbaa,b,*, Kazem Alemzadeha, Ike Anyanwu-Ebob, Paul Gibbonsa, John Friisb
a
b
University of Bristol, BS8 1TR, UK
Vestas Wind Systems A/S, Denmark
Abstract
Wind turbines are a proven source of clean energy with wind power energy harvesting technologies supplying about 3% of global
electricity consumption. However there is an increasing demand on maintenance and operational improvements since turbines
have been plagued with downtime problems of major components e.g. gearboxes and generators, especially with offshore
turbines which are difficult to access. Reliability Centric Maintenance (RCM) is a way of capturing the potential causes of
downtime and poor performance by preventing failures and having a proactive approach to operations and maintenance (O&M).
However, for a large fleet of turbines, adopting the RCM approach becomes difficult due to the complexities that arise as a result
of the interactions between individual elements that make up the system in the product lifecycle. This paper discusses how a
systems thinking approach can be used to identify the relevant aspects and possible interactions between the RCM approach and
wind turbine gearboxes and also how the gaps that exist within the system can be closed so as to add value to business. The
outcome of the paper is a proposal for applying a systems approach to wind turbine gearbox operation and maintenance,
optimising the asset value adding contribution at minimal total cost to the operator.
© 2013
The Authors.
Published
by Elsevier
B.V. OpenB.V.
access
under CC and/or
BY-NC-ND
license.
© 2013
The Authors.
Published
by Elsevier
Selection
peer-review
under responsibility of Georgia
Selection
and/or
peer-review under responsibility of Georgia Institute of Technology
Institute of
Technology
Keywords: Systems Thinking; Systems Engineering; Reliability-Centred Maintenance (RCM); Wind Turbine; Failure Mode, Effects and
Criticlity Analysis (FMECA); Gearboxes;
1. Introduction
The wind industry within three decades has come a long way, with wind turbines now being a proven source of
clean energy producing about 3% of the electricity consumed globally [1]. Consequently, the requirements and
expectations of wind turbines keep increasing. Fulfilling the increasing demand, wind turbines have become larger
generating more power for consumers, but still are expected to perform their required duty without interruption for
the most part of their in-service lifecycle. However there is an increasing demand on maintenance and operational
* Corresponding author. Tel.: +447411731118.
E-mail address: ji0905@bris.ac.uk.
1877-0509 © 2013 The Authors. Published by Elsevier B.V. Open access under CC BY-NC-ND license.
Selection and/or peer-review under responsibility of Georgia Institute of Technology
doi:10.1016/j.procs.2013.01.085
Joel Igba et al. / Procedia Computer Science 16 (2013) 814 – 823
815
improvements since turbines have been plagued with downtime problems of major components e.g. gearboxes and
generators, especially with offshore turbines which are difficult to access. With the annual installed capacity growth
rate slowing down due to the global economic crisis [2], the service business is now a means at which wind turbine
manufacturers can remain profitable. A recent article on Bloomberg [3] indicates that there is now a shift from
manufacturing towards the service business, in which the service business of Vestas Wind Systems A/S, the leader
in the wind industry, grew at an annual rate of 25% during 2011. This is because about 96% of all turbines sold by
Vestas are on some form of service agreement.
In the wind turbine industry, it is not uncommon to see many of the wind park projects having some form of
operation and service agreement or warranty structure between the wind turbine manufacturer and the customer.
These agreements may run for 2-3 years or up to 10 years or more (for a full service agreement). Vestas has what
they call the Active Output Maintenance® service programme (AOM)†, which has 5 stages depending on the level
of turbine services the customer is willing to pay for during the life time of the turbine. With the risk involved in the
business, the majority of wind farm owners/operators sign full agreements with turbine manufacturers. It is then the
responsibility of wind turbine manufacturers to ensure that the turbine is monitored continuously and is always
available. Once there is a fault, they are also responsible for the maintenance and repair. This is a double-edged
sword as turbine manufacturers incur costs for downtime of a failed turbine but also the knowledge derived from
continuous monitoring and maintenance of the systems, can and should help turbine manufacturers improve the
quality and reduce costs of their products and services.
Reliability-Centred Maintenance (RCM) which many industries have used historically to tackle similar
challenges in service industry [4, 5] is now finding its way towards wind applications [6, 7, 8]. Compared to the
aircraft, nuclear and many other industries, the wind industry is relatively young and has had only about 30 years to
work towards getting to the status which took industries like aircraft and automotive about a century to achieve.
Hence, the successful application of RCM in the wind sector might be flawed if there is not a full understanding of
the impacts and contributions the various elements of the system to delivering an effective RCM programme. In this
paper, the authors look at the main RCM tools and techniques and how systems thinking can be applied to
effectively use the tools optimally without affecting the performance of the overall system. A focus will be directed
more on the interactions between the major elements and not on the specific description of how to apply RCM tools.
However, a brief and taxonomic literature review on RCM and its applications in wind and other industries will be
presented to give an overview of the methodology.
2. Reliability-Centred Maintenance
According to SKF Reliability Systems [9] RCM is:
“an approach that employs reactive, preventive, and proactive maintenance practices and strategies in an
integrated manner to increase the probability that a machine or component will function in the required manner
over its design lifecycle with minimum maintenance”.
RCM which started in the aircraft industry, and later within the military, nuclear and oil & gas industries,
provides a framework that utilises operating experience in a more systemic way [4]. The goal of RCM is to preserve
the most important equipment (system) function with the required reliability and availability at the lowest cost of
maintenance [4, 9]. Most authors, including Selvik and Aven [5], agree that as well as reducing maintenance costs,
RCM also increases safety and reliability. However, Rausand [4] suggests that RCM cannot improve reliability of a
system but only ensure that the inherent reliability is realized. He went further by arguing that reliability can only be
improved through redesign or modification.
This paper looks to examine the links between the main stages of the RCM technique and other aspects of the
product lifecycle including feedback to the design phase, hence building on Rausand’s argument [4]. This paper
aims to take the RCM technique further from just the functional failure analysis and optimization of maintenance
strategies by looking more holistically through the application of systems thinking tools & techniques. The authors
do not wish make an indepth study of the specific analysis of the most relevant functional system failures and
Preventive Maintenance (PM) optimisation techniques of wind turbines, but choose instead to look into how the
† http://www.vestas.com/en/wind-power-plants/operation-and-service/service.aspx#/vestas-univers
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Joel Igba et al. / Procedia Computer Science 16 (2013) 814 – 823
interacting elements of RCM can be manipulated towards achieving the desire of maximising the asset value adding
contribution (focused on improved reliability) at a minimal total cost reduction through applying systems thinking.
The authors also argue that a good implementation of RCM should be fully integrated with other interacting
elements in the product lifecycle. This implies that there should be some explicit linkage of RCM to other processes
such as design, manufacturing, validation and quality management. The wind industry is now cost driven which
implies that RCM should optimally satisfy both cost and reliability objectves.
2.1. RCM Framework
Rausand [4] presents a structured approach to RCM using a sequence of twelve activities and steps which Selvik
and Aven [5] summarised into a two step procedure:
i.Inductive analysis of potential failures, where a failure mode, effects and criticality analysis (FMECA) is used to
determine critical components of the system.
ii.Application of logical decision diagrams to specify suitable categories of predictive maintainance (PM),
replacement, etc.
There have also been several improvements to the traditional RCM methodology for different applications, e.g.
RCM 2 [10], Reliability and Risk Centred Maintenance (RRCM) [5], Streamlined RCM [11], Reliability Centred
Asset Maintenance [12, 8] and the SRCM methodology [9]. Although the detailed procedures of the various forms
of RCM listed above are different, the main ideas of RCM presented in each source are more or less the same. Fig 1
shows how interpretations from Rausand [4], Selvik and Aven [5] and Fisher et. al. [7], can be used to summarise
the main steps of the RCM methodology.
Fig 1 RCM Stages [4, 5, 7]
A typical wind turbine consists of a Rotor (which carriers the blades), Nacelle and a Tower. The major
components (Drive Train and Generator) are contained in the Nacelle. Literature has shown that gearbox failure and
downtime are one of the major causes of poor wind turbine reliability [13, 6]. Also Fischer et. al. [6] suggested the
gearbox to be the most critical sub-system of the wind turbine after analysing the failure frequencies and downtime
of all major sub-systems of the wind turbine. The authors agree with Fischer et. al. [6] and add that not only because
the effect of failure frequencies and subsequent downtime are gearboxes very critical but also because of the
relatively high costs attributed to downtime mobilisation, logistics and replacement of gearboxes. This is also
emphasised by Musial et. al. [13]. Therefore the direction of this study will focus on the wind turbine gearbox when
examining the various relationships between RCM and the overall lifecycle of a wind turbine. Furthermore, from the
product lifecycle management (PLM) perspective, a product‡ is described by the stages it passes through in its
lifetime from its ‘conception’ as an idea up to its ‘end of life’ or decommissioning. Fig 2 below elaborates on the
different stages of a product’s life from its design, through its production, use and disposal. The iterative feedback
loops represent the continuous knowledge accumulation feedback process for improving each stage of the lifecycle.
RCM is usually implemented during the operational stage of the lifecycle when the product is being used. However,
RCM can also be planned for during the design and other early stages of the lifecycle.
‡
In the context of this study product refers to the wind turbine gearbox
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Joel Igba et al. / Procedia Computer Science 16 (2013) 814 – 823
Fig 2 Product lifecycle diagram as described in [14]
The importance of integrating RCM with design through continuous iterative knowledge feedback will be
explored further in the following section.
3. Systems perspective towards RCM
In systems thinking, the effects or outputs of any system are dependent on the interaction of its parts and studying
the parts in isolation will not provide an accurate picture of the system [15]. A systems thinking approach helps to
interpret real world problems and situations by looking at the bigger picture and clearly identifying the boundaries
and levels of interaction between constituent parts of a system and also between several systems. Literature shows
that all systems can be defined by common characteristics [16]. Such characteristics include: 1) system-environment
boundary, 2) input, 3) output, 4) process, 5) state, 6) hierarchy, 7) goal-directedness, and 8) information [17]. Fig 3
for example, shows a summary of the inputs, outputs, controls and enablers (IOCE) context diagram for the wind
turbine gearbox RCM framework. This diagram begins formulating the problem in a way that will help to find a
better understanding of the interacting elements of the RCM framework and other systems.
Controls
Inputs
1. Data
Design information &
Requirements
Field failure data & statistics
Wind site & SCADA data
2. Others
Environmental & Logistics
Factors
Technical competencies
Guidelines for RCM
Component inspection
manuals, procedures &
guidelines
Internal and external
gearbox standards
Outputs
RCM Framework for
Wind Turbine
Gearboxes
1. Data
FMECA Report & Data
In-Service Data
2. Others
Optimized Maintenance
Strategy
Field operations experience
Cross-functional team
Computerised maintenance
management system (CMMS)
Tools and Equipment for O&M
Enablers
Fig 3 RCM framework context diagram
3.1. RCM and the product lifecycle
From Fig 3 it can be seen that the constituents of the IOCE for the RCM framework make up the other stages in
the product lifecycle. Using the context diagram and the product lifecycle (Fig 3 & Fig 2) as a guide, a SIPOC
(suppliers, inputs, process, outputs and customers) diagram [18] (see Fig 4) can be made for the RCM framework to
clearly understand the specific links of RCM framework for a wind turbine gearbox to other stages of the gearbox
lifecycle. Suppliers and customers define the cross-functional teams and individuals who are stakeholders in
providing the inputs and making use of the outputs respectively, from the RCM framework. For the purpose of this
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Joel Igba et al. / Procedia Computer Science 16 (2013) 814 – 823
example, the majority of suppliers and customers are internal to the organisation, with the only external stakeholder
being the gearbox manufacturer. The inputs to the process considered here are mainly the data which are required
for RCM. This data varies from design to field data and requires individuals with respective technical competencies
to make use of them for RCM. Also, the suppliers and customers of the RCM process are mostly the same groups of
individuals, however, they make use of different inputs and outputs of the process. For example, the design
engineering team are responsible for providing design information which are needed for RCM, however, they also
have to make use of other data like failure and repair information for design reviews. Hence for an ideal RCM
framework to be implemented, these stakeholders will have to participate in shaping the requirements for the
process directly or indirectly. For example, design & manufacturing data are needed to be correlated with field
operations data in order to identify the functional failures and select critical components. Therefore, the RCM group
working on these aspects should be made up of representatives with the knowhow of the design and manufacturing
details of the gearbox as well as those with field O&M experience.
Fig 4 SIPOC for the RCM framework for wind turbine gearbox
3.2. The Lifecycle System of Systems (SoS)
So far, there has been a gradual build-up in describing and linking RCM to the overall product lifecycle. In the
context of a wind turbine project, the systems representation of the lifecycle is shown in Fig 5 below. The two
clouds represent the production (in blue) and services/operations (in green) stages of the lifecycle showing the
important interactions between major constituents of both systems. In a quick run through, a gearbox after being
designed will go through a series of tests and then once manufactured will have to be integrated with other subsystems of the wind turbine (product integration). After integration with other components, the turbine is then
installed in the field (construction) after which the service and operations lifetime begin in the field. The field
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Joel Igba et al. / Procedia Computer Science 16 (2013) 814 – 823
operation is characterized by plant operations and platform management. Plant operations are responsible for
running individual wind farms while the platform management consists of those responsible for managing specific
wind turbine type across different regions. Both the plant operations and platform management are responsible for
overseeing service and maintenance of the turbines. The diagram also shows the connecting links from design to the
field O&M stages and also the links between the quality team and other upstream stages of the lifecycle. Finally, the
top management oversees all the different stages emphasizing the importance of aligning all stages of the lifecycle
to the overall business strategy.
Top Management, Finance,
Business Strategy etc.
Design & Product
Development
Validation & Testing
Manufacturing
Product Integration
Quality
Construction
Plant operations
Platform
management
Service & maintenance
Spare parts & Repair
Fig 5 Systems diagram representing the key stages of the lifecycle of a wind turbine gearbox
4. Discussion
The previous two sections have presented the RCM framework for wind turbine gearbox maintenance and
applied systems thinking to understand how the various stages of such a framework interact with other stages of the
product lifecycle. This section will discuss further these interactions by looking at three key stages where the RCM
framework can be anchored to the overall lifecycle.
4.1. Data collection and analysis as a vital input for RCM
During operation the gearbox is subjected to varying loads depending on the site conditions the wind turbine is
exposed to. Typically, data is needed for the functional failure analysis, some of which have been identified in the
previous section (see Fig 3). However, Fig 6 below shows the component lifecycle of a gearbox and its sub
components, indicating the various types of data within the entire lifecycle. Data required for RCM analysis spans
across the lifecycle but the data collected during RCM is limited in scope. Hence there is a need to clearly map out
and identify the potential sources of data and align them to RCM so that the right analysis can be carried out. On the
other hand FMECA should identify possible gaps in some upstream processes (e.g. problem with manufacturing
process due to error in a batch production). This can be realised through a good correlation of field failures with
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Joel Igba et al. / Procedia Computer Science 16 (2013) 814 – 823
Re-use of components
Component Lifecycle for wind turbine gearboxes
operation data to make accurate judgements about the functional failures through a root cause analysis (RCA) that
reveals this.
BOM, Drawings
& Assembly
Details
Design Lifecycle
Design
Specifications
New Component
Manufactured
Measurement
report
Material
certificate
Testing
Vibration,
Temp & Noise
Data
Gear teeth
contact
patterns
Test, Validation
and integration to
Wind Turbine
Running
gearbox on
nominal loads
Field tests
Field inspections
& online
monitoring during
operation
Inspection
Reports &
maintenance
Data
Repair &
Disassembly
Inspections
Failure
Categories
New-life or end of
component life
Peak loads, temps, oil
pressure etc. from
online S …
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