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Using an FMEA Method to Compare Prospective Wind Turbine Design Reliabilities Prof. Peter Tavner, Andrew Higgins, Dr Hooman Arabian, Dr Hui Long, Dr. Yanhui Feng, New & Renewable Energy Subgroup of Energy Group. Purposes of an FMEA. To improve system reliability - PowerPoint PPT Presentation
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Using an FMEA Method to Compare Prospective Wind Turbine Design Reliabilities
Prof. Peter Tavner, Andrew Higgins, Dr Hooman Arabian, Dr Hui Long, Dr. Yanhui Feng, New & Renewable Energy Subgroup of Energy Group
EWEC2010, Warsaw, Poland 1 of 27
Purposes of an FMEA
• To improve system reliability• To identify the failures which have unwanted effects
on system operation• To allow improvement of the system’s maintainability • To determine the criticality or priority for addressing
each failure
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Introduction to FMEA
Background
Standards
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Introduction to FMEA
• Background– Introduced by military, aerospace, railway, automotive
and nuclear power industries concerned to improve reliability
– Systematically identifies all failure modes of a system– Quantifies the Severity, Occurrence and Detectability
of each failure– Allows the calculation of a Risk Priority Number
(RPN):RPN = Severity*Occurrence*Detection
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Performing an FMEA
• Procedural steps needed to perform an FMEA are as follows:– Define the system structure.– Define severity, occurrence and detection criteria.– Define generic failure modes and root causes– Understand the system requirements and function.– Determine each item’s failure modes and effects.– Establish the severity of each of the items failure modes– Establish the occurrence and detectability of each cause of
failure.– Calculate Risk Priority Numbers– Report findings at all levels of analysis.
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FMEA of ReliaWind R80 Turbines
Structure of the R80.1 Drive Train:
•Three Stage Gearbox (1st stage Planetary)• LV Doubly Fed Induction Generator• LV Partially-rated Converter•Transformer
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1
EWEC2010, Warsaw, Poland
B
FMEA of ReliaWind R80 Turbines
Structure of the R80.2 Drive Train:
• Two Stage Gearbox (1st stage Planetary)• LV Brushless Doubly Fed Induction Generator• LV Partially-rated Converter•Transformer
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2
EWEC2010, Warsaw, Poland
FMEA of ReliaWind R80 Turbines
Structure of the R80.3 Drive Train:
•Two Stage Gearbox (1st stage Planetary)•WinDrive (Gearbox + Torque converter)• MV Synchronous Generator• No Transformer
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Taxonomy used for FMEA
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FMEA of ReliaWind R80.1, R80.2 & R80.3 Turbines
Defining the system structures
– System, Assembly, Sub-Assembly, Part
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Defining the severity scales– A measure of the significance of the failure on the availability of the
wind turbine
– Could actual values of MTTR be used to distinguish the different levels of severity?
– Yes, if they are known
High MTTR (1/)
Low MTTR (1/)
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FMEA of ReliaWind R80.1, R80.2 & R80.3 Turbines
EWEC2010, Warsaw, Poland
Defining the occurrence scales– A measure of the frequency or probability of the cause of failure
– Could actual values of MTBF be used to distinguish the different levels of severity?
– Yes, if they are known.
Low MTBF (1/λ)
High MTBF (1/λ)
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FMEA of ReliaWind R80.1, R80.2 & R80.3 Turbines
EWEC2010, Warsaw, Poland
Defining the detection scales– A measure of the extent to which the root cause of the failure can be
detected
– How do we distinguish between the levels? VERY SUBJECTIVE.
– Is there an argument to simplify the scales and suggest that it is either detectable or it is not detectable?
– Could detectability be related to Logistic Delay Time
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FMEA of ReliaWind R80.1, R80.2 & R80.3 Turbines
EWEC2010, Warsaw, Poland
Defining generic failure modes and root causesRoot Cause
Calibration Error
Connection failure
Corrosion
Design Fault
Electrical Overload
……
Mechanical Overload
Presence of Conducting Debris
Presence of Debris
Software Design Fault
High Cycle Fatigue
Overheating
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FMEA of ReliaWind R80.1, R80.2 & R80.3 Turbines
EWEC2010, Warsaw, Poland
FMEA of ReliaWind TurbineExample R80.1 Gearbox Casing
• Performing the FMEA:– Understand the system requirements and function.
– Determine each item’s failure modes and effects.
– Establish the severity of each of the items failure modes
– Establish the occurrence and detectability of each cause of failure.
– Calculate Risk Priority Numbers
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• Performing the FMEA:– Understand the system requirements and function.
– Determine each item’s failure modes and effects.
– Establish the severity of each of the items failure modes
– Establish the occurrence and detectability of each cause of failure.
– Calculate Risk Priority Numbers
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FMEA of ReliaWind TurbineExample R80.1 Gearbox Casing
EWEC2010, Warsaw, Poland
• Performing the FMEA:– Understand the system requirements and function.
– Determine each item’s failure modes and effects.
– Establish the severity of each of the items failure modes
– Establish the occurrence and detectability of each cause of failure.
– Calculate Risk Priority Numbers
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FMEA of ReliaWind TurbineExample R80.1 Gearbox Casing
EWEC2010, Warsaw, Poland
• Performing the FMEA:– Understand the system requirements and function.
– Determine each item’s failure modes and effects.
– Establish the severity of each of the items failure modes
– Establish the occurrence and detectability of each cause of failure.
– Calculate Risk Priority Numbers
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FMEA of ReliaWind TurbineExample R80.1 Gearbox Casing
EWEC2010, Warsaw, Poland
• Performing the FMEA:– Understand the system requirements and function.
– Determine each item’s failure modes and effects.
– Establish the severity of each of the items failure modes
– Establish the occurrence and detectability of each cause of failure.
– Calculate Risk Priority Numbers
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FMEA of ReliaWind TurbineExample R80.1 Gearbox Casing
EWEC2010, Warsaw, Poland
• Performing the FMEA:– Understand the system requirements and function.
– Determine each item’s failure modes and effects.
– Establish the severity of each of the items failure modes
– Establish the occurrence and detectability of each cause of failure.
– Calculate Risk Priority Numbers
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FMEA of ReliaWind TurbineExample R80.1 Gearbox Casing
EWEC2010, Warsaw, Poland
• Performing the FMEA:– Understand the system requirements and function.
– Determine each item’s failure modes and effects.
– Establish the severity of each of the items failure modes
– Establish the occurrence and detectability of each cause of failure.
– Calculate Risk Priority Numbers5 x 2 x 3 = 30
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FMEA of ReliaWind TurbineExample R80.1 Gearbox Casing
EWEC2010, Warsaw, Poland
Severity, Occurrence & Detection scales• Modifications to Severity and Occurrence scales
– Note that RPN = BSev * BOcc * BDet – B is base which could be 2 or 10– This allows one level change within any criterion, Severity,
Occurrence or Detectability to have the same effect on RPN– But we require RPN = Sev*Occ*Det– Don’t modify base but power– Use exponential scales for – Severity and Occurrence:– Severity = 1,2,4,8,16– Occurrence = 1,2,4,8,16
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Severity, occurrence and detection scales.
Modification to detection scales
– For Detection it can be subjective to differentiate between levels.
– Simplify
– A failure is either detectable or undetectable
Detection= 1 or 2
– Still meets the requirement that any single change at any level within any of the criteria to have the same effect on RPN
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Severity, occurrence and detection scales.
• Any single change at any level within any of the criteria to has the same effect on RPN
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RESULTS:Normalised RPNs
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Subassembly Description RPN
Drive Train
R80.1, Conventional LV Doubly Fed Induction Generator with 3 stage gearbox, partially-rated Converter and Transformer 100.0R80.2, Innovative LV Brushless Doubly Fed Induction Generator with 2 stage gearbox, partially-rated Converter and Transformer 90.1
R80.3, Innovative Hydraulic Converter with 2 stage gearbox and MV Synchronous Generator. 96.2
Generator
R80.1- DFIG 17.5
R80.2- BDFIG 15.6
R80.3- Synchronous Generator 16.1
Gearbox
R80.1- Three Stage (1st stage Planetary) 30.4
R80.2- Two Stage (1st stage Planetary) 22.4
R80.3- Two Stage (1st stage Planetary) 26.0
Converter
R80.1- Electrical Converter+Control 21.7
R80.2- Electrical Converter+Control 21.7
R80.3- WinDrive+Control 27.0
Two stage Planetary Gearbox 17.9
Torque Converter 9.1
Transformer
R80.1- Transformer 3.3
R80.2- Transformer 3.3
R80.3- No Transformer 0.0
Balance of Plant 27.1
Summary of findings and recommendations
• Link between Occurrence and MTBF, 1/• Link between Severity and MTTR, 1/• Use of generic Failure Modes & Root Causes allows more strategic analysis
• Normalising RPNs allows easier comparison
• Choice of scales impacts overall system RPN
• Recommend exponential scales for Severity and Occurrence and a logic scale for Detectability
• Provides a thorough comparison of different systems for conceptual design/redesign.
• Requires a team of experienced individuals with thorough knowledge of the systems
• Can be subjective
• Knowing assembly MTTF & MTTR can reduce subjectivity
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Thank you
• United States Department of Defense, MIL‐STD‐1629A‐Military standards for performing a Failure Modes, Effects and Criticality Analysis. 24th November 1980.
• International Electrotechnical Commission. Analysis techniques for system reliability‐ Procedure for failure mode and effects analysis (FMEA). 2006, IEC 60812:2006
• A Birolini, Reliability Engineering, Theory & Practice, Springer, New York, 2007, ISBN 978-3-527-49388-4
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