Kevin Alewine: 2013 Sandia National Laboratoies Wind Plant Reliability Workshop

Understanding Wind Turbine Generator

FailuresModes and Occurrences – 2013 Update

Kevin AlewineDirector of Renewable Energy Services

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


Introduction and CreditsThanks 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


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.


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.


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.


Operations Issues Improper Installation Voltage irregularities Traditional sources Convertor failure or miss-match Improper grounding Over-speed conditions Transit damage Excessive production cycling


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


Environmental Conditions Thermal cycling Moisture Contamination Electrical Storms


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:


Failure Occurrences in Machines <1MWEarlier 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.

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Rotor Stator Bearings Other RotorLeads

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Generators <1MW (450 total in study)

Occurrence

% of failures

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Failure Occurrences in Machines 1-2MWThe 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.

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Generators 1-2MW (939 total in study)

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Failure Occurrences in Machines >2MWAgain, 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.

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Generators >2MW (679 total in study)

Occurrence

% of Failures

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Comparison to General IndustryBased 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.

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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


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)


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?

Questions?Kevin Alewine

Business

Kevin Alewine: 2013 Sandia National Laboratoies Wind Plant Reliability Workshop