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Purposes of an FMEA

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

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Purposes of an FMEA

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  1. 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

  2. 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 EWEC2010, Warsaw, Poland

  3. Introduction to FMEA Background Standards EWEC2010, Warsaw, Poland

  4. 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 EWEC2010, Warsaw, Poland

  5. 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. EWEC2010, Warsaw, Poland

  6. FMEA of ReliaWindR80 Turbines Structure of the R80.1 Drive Train: • Three Stage Gearbox (1st stage Planetary) • LV Doubly Fed Induction Generator • LV Partially-rated Converter • Transformer 1 EWEC2010, Warsaw, Poland

  7. FMEA of ReliaWindR80 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 B 2 EWEC2010, Warsaw, Poland

  8. FMEA of ReliaWindR80 Turbines Structure of the R80.3 Drive Train: • Two Stage Gearbox (1st stage Planetary) • WinDrive (Gearbox + Torque converter) • MV Synchronous Generator • No Transformer EWEC2010, Warsaw, Poland

  9. Taxonomy used for FMEA EWEC2010, Warsaw, Poland

  10. FMEA of ReliaWindR80.1, R80.2 & R80.3 Turbines Defining the system structures • System, Assembly, Sub-Assembly, Part EWEC2010, Warsaw, Poland

  11. FMEA of ReliaWindR80.1, R80.2 & R80.3 Turbines Defining the severity scales • A measure of the significance of the failure on the availability of the wind turbine High MTTR (1/m) Low MTTR (1/m) • Could actual values of MTTR be used to distinguish the different levels of severity? • Yes, if they are known EWEC2010, Warsaw, Poland

  12. FMEA of ReliaWindR80.1, R80.2 & R80.3 Turbines Defining the occurrence scales • A measure of the frequency or probability of the cause of failure Low MTBF (1/λ) High MTBF (1/λ) • Could actual values of MTBF be used to distinguish the different levels of severity? • Yes, if they are known. EWEC2010, Warsaw, Poland

  13. FMEA of ReliaWindR80.1, R80.2 & R80.3 Turbines 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 EWEC2010, Warsaw, Poland

  14. FMEA of ReliaWindR80.1, R80.2 & R80.3 Turbines Defining generic failure modes and root causes EWEC2010, Warsaw, Poland

  15. 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 EWEC2010, Warsaw, Poland

  16. 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 EWEC2010, Warsaw, Poland

  17. 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 EWEC2010, Warsaw, Poland

  18. 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 EWEC2010, Warsaw, Poland

  19. 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 EWEC2010, Warsaw, Poland

  20. 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 EWEC2010, Warsaw, Poland

  21. 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 5 x 2 x 3 = 30 EWEC2010, Warsaw, Poland

  22. 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 EWEC2010, Warsaw, Poland

  23. 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 EWEC2010, Warsaw, Poland

  24. Severity, occurrence and detection scales. • Any single change at any level within any of the criteria to has the same effect on RPN EWEC2010, Warsaw, Poland

  25. RESULTS:Normalised RPNs EWEC2010, Warsaw, Poland

  26. Summary of findings and recommendations • Link between Occurrence and MTBF, 1/l • Link between Severity and MTTR, 1/m • 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 EWEC2010, Warsaw, Poland

  27. 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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