Investigation of the NRG #40 Anemometer Slowdown Steven Clark, - - PowerPoint PPT Presentation

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Investigation of the NRG #40 Anemometer Slowdown Steven Clark, - - PowerPoint PPT Presentation

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Investigation of the NRG #40 Anemometer Slowdown Steven Clark, Mechanical Engineer NRG Systems, Inc. AWEA WINDPOWER Conference and Exhibition 2009 Chicago, IL May 4-7, 2009 Global Leader in Wind Measurement Technology www.nrgsystems.com

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www.nrgsystems.com

Global Leader in Wind Measurement Technology

Investigation of the NRG #40 Anemometer Slowdown

Steven Clark, Mechanical Engineer

NRG Systems, Inc.

AWEA WINDPOWER Conference and Exhibition 2009 Chicago, IL May 4-7, 2009

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Page 2 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Outline

History Problem Definition Investigation Highlights Outcome of Investigation Design Validation Conclusions

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Page 3 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

History

February 2007 – customer informed NRG Systems some #40s were exhibiting “drag” November 2007 – Received 12 sensors from field for engineering evaluation Intensive investigation into the #40 sensor – Feb „08 Laboratory and data analyses now reveal that a portion of the population of the NRG #40 sensors dating back to the middle of 2006 exhibit slowdown

– Affected sensors all passed initial calibration – Affected sensors exhibit slowdown within 2-26 weeks Global Leader in Wind Measurement Technology

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Page 4 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Problem Definition

Sensor slow-down is defined by:

  • 1. Excess scatter:
  • Qualitative by sensor pair scatter plots
  • Quantitative by sensor pair statistics
  • 2. Performance change in time
  • Calibration values

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Page 5 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Problem Definition

Excess scatter - Qualitative by scatter plots

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Page 6 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Problem Definition

Sensor slow-down is defined by:

  • 1. Excess scatter:
  • Quantitative by sensor pair statistics

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Statistic Expected normal performance Mean bias ≤ ±0.2 m/s Ratio Within 0.98-1.02 Correlation coefficient ≥ 0.995 Standard deviation of the wind speed ratio ≤ 0.02

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Page 7 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Problem Definition

Problem of sensor slow-down is defined by:

  • 2. Performance change in time
  • Change in wind tunnel calibration results

– Abnormal residual pattern AND – Standard Error is greater than 0.12 AND – Offset increase > 0.15 m/s from initial calibration Global Leader in Wind Measurement Technology

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Page 8 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Problem Definition

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Initial calibration with normal residual pattern

Residual: Reference WS – Transfer Function WS 4 m/s – (0.757*5 Hz + 0.36) = -0.14

Post calibration with abnormal residual pattern

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Page 9 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

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Naming Convention Manufacturing Date

Pre-2006 Before middle of 2006 Post-2006 After middle of 2006 and before January 1, 2009 Post-1/1/2009 After January 1, 2009 (manufactured with design improvement)

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Page 10 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

Dimensional analysis between normal and affected sensors showed no obvious dimensional differences Intensive review of affected sensors revealed visual signature termed “spirograph” motion

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Page 11 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

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Investigation Highlights

Vibration mode – “spirograph”

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Page 12 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

Quantified spirograph motion using video and accelerometers

  • GE Bently-Nevada validated NRG-developed

vibration measurement system

Associated visual spirograph with vibration

– Vibration signature correlated to slowdown and termed “vibratory mode” – Verified “vibratory mode” in lab and field

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Page 13 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

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Investigation Highlights

Vibration signature and correlation to slowdown

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Page 14 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

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Investigation Highlights

Vibration signature and correlation to slowdown

Peak power difference (previous plots at 12 m/s)

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Page 15 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

Boom/sensor interaction

Studied boom/sensor interaction (ie., external excitation)

– Booms not root cause of vibratory mode

  • Contribute to the „dynamic system‟ that initiates the

sensor vibratory mode

– Source of vibration sensor-borne

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Stem mount 2.4 m boom

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Page 16 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

Spinning bearing hypothesis

Observed lower and upper bearings rotate during vibratory mode

– Determined spinning bearing is a symptom, not a cause,

  • f the vibration

– Securing the lower bearing in an affected sensor exacerbated the problem

Measured upper and lower radius-to-clearance ratio in normal and affected sensors

– Determined to be poor predictor of performance (R2 ~ 0)

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Page 17 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

Vibration characteristics

Characteristics of the slowdown due to vibratory mode (based on wind tunnel results):

  • 0.2 m/s – 0.6 m/s slow-down when in mode
  • Preferentially occurs at 5-10 m/s wind speeds
  • Can sustain in mode for long periods of time
  • Can enter and exit mode
  • Onset of mode occurs more often in decelerating speeds

than in constant or accelerating speeds

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Page 18 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

Investigated self-excited vibratory phenomena Retained rotor dynamic experts to help identify specific vibratory mode

  • Dr. Dara Childs (Texas A&M)
  • Dr. Fred Ehrich (MIT)

Identified vibratory mode as Dry Friction Whip (DFW) via its properties:

– Self-excited – Super-synchronous – Asynchronous – Counter-rotating whip direction

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Page 19 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Investigation Highlights

Focused investigation on published causes of DFW:

1. Friction above a minimum threshold 2. Friction above lower threshold and:

a) Excessive bearing clearances and/or b) Similarity of rotor/stator natural frequency Global Leader in Wind Measurement Technology

Confirmed friction is a necessary but not sufficient condition to cause DFW Bearing clearances not a factor (R2~0)

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Page 20 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Outcome of Investigation

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Guided by theory that similarity in rotor/stator natural frequency can cause DFW Searched for design changes that could impact rotor or stator natural frequency

– In-spec dimensional change in mid-2006 to Well ID

Small dimensional and material property changes to stator govern sensor response to DFW

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Page 21 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Lab verifications of new Post-1/1/2009 sensor Global Leader in Wind Measurement Technology

Design-of- Experiment (DOE) of design space

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Page 22 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Outcome of Investigation

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Root cause of sensor slowdown is dry friction whip (DFW) Causes of DFW in NRG #40 anemometer:

  • Friction is a necessary but not sufficient condition
  • Heuristically DFW is well understood – can instigate or

eliminate DFW on command

  • Theoretical mechanism of sufficient condition under

investigation:

– 8 degree-of-freedom (DOF), 2 contact point mathematical model derived – Numerical analysis underway

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Page 23 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

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Validation of Design Fix:

–Lab verification –Field validation

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Page 24 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Lab Verifications of new Post-1/1/2009 sensor Global Leader in Wind Measurement Technology

One Factor at a Time (OFAT) and Design-of- Experiments (DOE) of design space (extreme dimensional limits, exploratory tests) Run-in of old Post 2006 and new Post-1/1/2009 sensors Extensive wind tunnel testing (at NRG Systems and OTECH Engineering, Inc.)

  • Confirmed dry friction whip cause of abnormal residual

pattern

  • Confirmed that modifying an affected sensor corrects

calibration results

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Page 25 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

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Design Validation

Lab Verification – NRG Wind Tunnel Testing

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Page 26 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Lab Verification – OTECH Wind Tunnel Testing Global Leader in Wind Measurement Technology

Stock Sensor - vibe mode present at speeds 12,14,10,6 m/s Vibratory mode present

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Page 27 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Lab Verification - OTECH Wind Tunnel Testing Global Leader in Wind Measurement Technology

Same sensor with well ID and o-ring fix - vibe mode absent

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Page 28 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Lab Verification - OTECH Wind Tunnel Testing Global Leader in Wind Measurement Technology

Stock Sensor - vibe mode present at Speeds 12,14,10,6 m/s Abnormal residual pattern present

12 14 10 6 14 10 6 12

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Page 29 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Lab Verification - OTECH Wind Tunnel Testing Global Leader in Wind Measurement Technology

Same sensor with well ID and o-ring fix- vibe mode and abnormal residual pattern absent

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Page 30 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Field Validation

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Page 31 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Field Validation

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Participants in field test campaign include AWS Truewind, Garrad Hassan, DNV-GEC, Genivar, GPCo, KB Energy, NRG Systems Field time: 10-20 weeks as of April 17, 2009 122 new Post-1/1/2009 sensors deployed

– 52 pairs – 18 single sensors paired with other sensors

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Page 32 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Field Validation Global Leader in Wind Measurement Technology

Field Performance

  • No. of Sensors

Scatter Statistics 96 Normal Normal 1 Inconsistent Normal 1 Inconsistent Bias (-0.2 m/s) Total = 98

  • No. of Sensors

Status 98 Sufficient data 24 Insufficient data due to icing Total = 122

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Page 33 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Field Validation – Performance Summary

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6 Post-2006 sensors field tested concurrently

  • Field time: 17-20 weeks as of April 17, 2009
  • 5 sensors exhibit excess scatter
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Page 34 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Design Validation

Field Validation – Initial Post Calibration Results

Global Leader in Wind Measurement Technology Sensor Scatter Statistics Post-Cal Vibratory mode Post-2006 Excess Ratio SD high Poor Present Post-2006 Excess Ratio SD high Poor Present Post-1/1/2009 Normal Normal Normal Absent Post-1/1/2009 Normal Normal Normal Absent

Pair Pair

4 sensors post calibrated

  • Pair of Post-2006 sensors; Pair of Post-1/1/2009 sensors
  • Field time: 8 weeks
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Page 35 AWEA WINDPOWER 2009 CHICAGO, IL MAY 4-7, 2009

Conclusions

Root cause of sensor slowdown is dry friction whip Design improvement has eliminated dry friction whip and the associated slowdown Manufacturing and shipping new sensor as

  • f :

– January 1, 2009 – SN 95000 transition

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