Understanding Wind Turbine Generator Failures Modes and Occurrences- 2013 Update

1. Understanding Wind
Turbine Generator
Failures
Modes and Occurrences – 2013 Update
Kevin Alewine
Director of Renewable Energy Services

2. 2 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Introduction and Credits
 Review of generator failure types and root causes
 Statistical review of failure occurrences
 Some suggestions
 Conclusions

3. 3 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Introduction and Credits
Thanks to:
William Chen, TECO-Westinghouse Motor Company
VonRoll Applications Engineering Group
Chuck Wilson, Insulation Integrity Inc.
Dr. Peter Tavner, University of Durham, ret.
References:
Root Cause Failure Analysis, Electrical Apparatus Service Association, 2002-2004
Design Challenges of Wind Turbine Generators , George Gao and William Chen, IEEE EIC - 2009
A Survey of Faults on Induction Motors… , O.V. Thorsen and M. Dalva - IEEE Trans. on Industrial
Applications – 1995
Wind Turbine Failure Modes Analysis and Occurrence, Kevin Alewine and William Chen, AWEA
Windpower - 2010
Establishing an In-House Wind Maintenance Program, American Public Power Association, 2008
A Review of Electrical Winding Failures in Wind Turbine Generators, Kevin Alewine and William Chen, IEEE DEIS
Electrical Insulation Conference - 2011
Magnetic Wedge Failures in Wind Turbine Generators, Kevin Alewine and Chuck Wilson, IEEE DEIS
Electrical Insulation Conference - 2013

4. 4 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Wind turbine generator failure basics
 >60GW of wind generators in USA as of 2012
 ~45GW of that total has been installed since 2007 utilizing
mostly > 1.5MW turbines
 In vulnerable designs, generator failures are often occurring
in first 3 years of life – obviously well short of expectations
 Poor bearing life is the most common cause of generator
failure across all sizes and manufacturers. In generators
above 1.5MW, the most common electrical failure modes
are caused directly by the loss of magnetic wedges
 This review covers >2000 failed generators representing
over 3.3GW repaired or scrapped from 2005 through June
2013, updated from ~1200 machines surveyed in 2010.

5. 5 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Generator Failure Root Causes
 Design issues – materials and processing, rarely basic
mechanical design
 Operations issues - alignment, vibration, voltage irregularities,
improper grounding, over-speed, transit damage, etc.
 Maintenance practices – collector systems, lubrication
procedures, etc.
 Environmental conditions – weather extremes, lightning
strikes, etc.

6. 6 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Design and Manufacturing Issues
 Electrical insulation inadequate for
application – normally mechanical rather
than electrical weakness
 Loose components – wedges, banding
 Poorly designed/crimped lead connections
 Inadequate collector ring/brush
performance
 Transient shaft voltages
 Rotor lead failures
 Sometimes turbine OEMs add components
that might complicate service – electronics,
lubrication devices, etc.

7. 7 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Operations Issues
 Improper Installation
 Voltage irregularities
 Traditional sources
 Convertor failure or miss-match
 Improper grounding
 Over-speed conditions
 Transit damage
 Excessive production cycling

8. 8 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Maintenance Practices
 Cooling system failures leading to heat
related failures
 Collector ring contamination
 Bearing mechanical failure
 Bearing electrical failure
 Rotor lead failures
 Poor alignment
 Excessive vibration
 Often initiated by heat from failing bearing

9. 9 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Environmental Conditions
 Thermal cycling
 Moisture
 Contamination
 Electrical Storms

10. 10 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Failure Modes and Occurrences
 Rotor insulation damage (strand/turn/ground)
 Stator insulation damage (strand/turn/ground)
 Bearing failures
 Rotor lead failures
 Shorts in collector rings
 Magnetic wedge failures
 Cooling system failures
 Other mechanical damage
Indicated in the following charts are the occurrences actually recorded, as well
as the significance of the mode expressed as a percentage of the total failures
studied. The modes collected were:

11. 11 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Failure Occurrences in Machines <1MW
Earlier designed, smaller machines show a high number of failures in rotor insulation.
These are due to both electrical and mechanical failure of the conductors and the failure
of the banding as designed. Many stator winding failures were actually due to
contamination and issues with under-designed bracing.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0
25
50
75
100
125
150
175
200
225
250
275
300
Rotor Stator Bearings Other Rotor
Leads
Collector
Rings
Cooling
System
Stator
Wedge
Percentage
Occurrence
Generators <1MW (450 total in study)
Occurrence
% of failures
Cumulative %

12. 12 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Failure Occurrences in Machines 1-2MW
The increase in bearing failures among generators between 1 and 2 MW is dramatic.
These generators are generally more robust than their antecedents, but proper
installation and good maintenance practices are critical to good reliability.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0
50
100
150
200
250
300
350
400
450
500
550
Percentage
Occurrence
Generators 1-2MW (939 total in study)
Occurrence
% of Failures
Cumulative %

13. 13 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Failure Occurrences in Machines >2MW
Again, in the current class of generators greater than 2MW, many of the failures are
from bearings, but there is a dramatic rise in stator failures resulting primarily from the
loss of magnetic wedges utilized to improve the size/output functionality of the
generator design.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0
25
50
75
100
125
150
175
200
225
250
275
300
325
Stator
Wedge
Bearings Stator Rotor
Leads
Rotor Collector
Rings
Other Cooling
System
Percentage
Occurrence
Generators >2MW (679 total in study)
Occurrence
% of Failures
Cumulative %

14. 14 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Comparison to General Industry
Based on new, unpublished data compiled by Dr. Peter Tavner and his team at Durham
University, there is actually little variation in types of major failures, only in specific
machine design areas of vulnerability.
0
5
10
15
20
25
30
35
40
45
50
Bearings Windings Other
Industrial
Wind

15. 15 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Suggestions
 Understanding the failure modes helps us set the priorities for testing
protocols
 Thermal condition monitoring can be improved
 Inspection and cleanliness of the rotor leads and collector systems are also
important in DFIG designs
 Assure proper materials and processes are utilized to minimize the loss of
magnetic wedges after remanufacturing
 Bearings and lubrication are critical elements

16. 16 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Suggestions
 Condition Based Maintenance
 Should the wind industry move towards CBM?
 Many suppliers are focused on this solution
 A financial decision – pay now or pay more later
 Most other industries have embraced this solution
 Requires solid planning, professional implementation and
management support
 Many resources are available
 Excellent study from Sandia National Laboratories on advanced maintenance
strategies for wind energy installations “CMMS in the Wind Industry” available
on their website
 Society of Maintenance and Reliability Professionals (SMRP)

17. 17 of 1714 August 20132013 Wind Plant Reliability Workshop Alewine Wind Turbine Generator Failures – 2013 Update
Conclusions
 Bigger is not always more reliable
 Maintenance is THE critical factor
 Choose your suppliers carefully
 OEMs, replacement components and repair – all have key influences on
reliability and longevity
 An estimated 15% of the entire 60 GW installed fleet has already failed,
some of them within 2 years of being placed in service
 A very high percentage of these are due to bearing failures, lubrication
and other normally preventable issues
 Proper maintenance has been shown in other industries to
drastically reduce unplanned outages and improve
profitability – why not wind?

18. Questions?
Kevin Alewine