Investigation of wide band Fiber Bragg grating accelerometer use for rotating AC machinery condition monitoring

Transcription

1 Investigation of wide band Fiber Bragg grating accelerometer use for rotating AC machinery condition monitoring Sinisa Djurovic a, Peter Kung b et al. a School of Electrical and Electronic Engineering, The University of Manchester, UK; b QPS Photronics, Pointe Claire, Canada.

2 Outline 1. Introduction 2. Motivation---Wind generator failure statistics 3. FBG wide band vibration monitoring system 4. Generator test rig 5. Bearing fault specific vibration frequencies 6. Measured Vibration spectra under bearing fault conditions 7. Generator electrical fault specific vibration frequencies 8. Measured Vibration spectrum for stator short-circuit and open circuit fault 9. Conclusions

3 Motivation Vibration analysis frequently used to detect mechanical and electrical faults in rotating machines Wind generators larger than 2MW show combined bearing and stator winding failures of more than 73% Cost effective and robust wide bandwidth vibrations required to replace currently used costly piezoelectric (PE) accelerometers

4 Fibre optics Vibration sensing Immune to EMI and high voltages Longer life Proven for monitoring low frequency end winding vibration in large generators Direct electrical output Distributed vibration sensing using Long Gauge technology Single sensor measures both temperature and vibration

5 Large wind turbines failure statistics UpWind: Design limits and solutions for very large wind turbines, EWEA 2011

6 Wind generator failure modes 1-2 MW >2 MW

7 Wide Band Vibrofibre Bandwidth of 1000 Hz to cover bearing, stator/rotor electrical faults frequencies achieved by changing the diving board material to Polycarbonate Cross Section Fiber Cavity

8 Measured Vibration Acceleration (m/s 2 ) Measured Vibration Amplitude (um) Performance and Characteristics Interrogator unit and software interface Applied Vibration Amplitude (um) Response at 100 Hz vibration frequency Accelerometer Reflection Spectrum Frequency (Hz) FBG accelerometer frequency response

9 Wind turbine generator test rig Laboratory test bed (viewed from above) Stator terminal box Drive end bearing

10 Sensor performance testing Benchmarked against Bruel&Kjaer Pulse vibration platform utilising piezo-electric(pe) accelerometers Both sensor types mounted on generator frame Typical winding and bearing faults artificially introduced Sensor mounting

11 Rolling bearing race frequencies 1 cos 2 b b o r c N D f f D 1 cos 2 b b i r c N D f f D Outer race Inner race f r =rotational frequency, N b =number of rolling elements D b =ball diameter, D c =cage diameter, β=contact angle

12 Bearing Fault Emulation Various severity of bearing outer race fault introduced in experiments Drive-end SKF 6313 N b = 8 f o =3.07f r f i =4.93f r Machined bearing fault (localised outer race fault) Laboratory generator bearing design data

13 Acceleration [m/s 2 ] Acceleration [m/s 2 ] Spectrum showing bearing fault effects mm fault healthy B&K, bearing fault vibration spectrum, 1590 rpm Frequency [Hz] 10 0 QPS, bearing fault vibration spectrum, 1590 rpm mm fault healthy Frequency [Hz] Piezoelectric (top) and FBG (bottom) vibration frequency spectra 3mm outer race bearing fault at 1590 rpm

14 Acceleration [m/s 2 ] Acceleration [m/s 2 ] Zoom-in View 0.12 B&K, bearing fault vibration spectrum, 1590 rpm 0.1 healthy 3mm fault PE sensor Frequency [Hz] 0.08 QPS, bearing fault vibration spectrum, 1590 rpm healthy 3mm fault FBG sensor Frequency [Hz]

15 Typical Stator Winding Faults U1 U1 U1 U2 U2 U2 U2 U2 U2 U1 U1 U1 U2 U2 U2 V2 V2 V2 W1 W1 W1 V2 V2 V2 W1 W1 W1 V2 V2 V2 W1 W1 W1 V1 V1 V1 W2 W2 W2 Winding configurations: a) a) a) V1 V1 V1 W2 W2 W2 b) b) b) V1 V1 V1 W2 W2 W2 c) c) c) Healthy Open-circuit fault Short-circuit fault Winding Balanced Unbalanced Torque frequencies 6k 1 s fs 2 6k 1s fs k 1 s fs p k 2 1s fs p Achieved experimentally using stator terminal box k=0,1,2,3 s=slip p=pole pairs f s =supply frequency

16 Acceleration [m/s 2 ] Acceleration [m/s 2 ] Spectrum showing short circuit fault effects [(3),k=6] [(2),k=6] [(3),k=6] B&K, stator winding short-circuit fault, 1590 rpm [(3),k=18] [(2),k=18] [(3),k=18] [(3),k=30] [(2),k=30] [(3),k=30] short-circuit healthy Frequency [Hz] [(3),k=6] [(2),k=6] [(3),k=6] [(3),k=18] QPS, stator winding stator short-circuit fault, 1590 rpm [(2),k=18] [(3),k=18] [(3),k=30] [(2),k=30] [(3),k=30] short-circuit healthy Frequency [Hz] Piezoelectric (top) and FBG (bottom) vibration frequency spectra stator short-circuit fault at 1590 rpm

17 Acceleration [m/s 2 ] Acceleration [m/s 2 ] Spectrum showing open circuit fault effects [(3),k=6] [(2),k=6] [(3),k=6] [(3),k=18] B&K, stator winding open-circuit fault, 1590 rpm [(2),k=18] [(3),k=18] [(3),k=30] [(2),k=30] [(3),k=30] open-circuit healthy Frequency [Hz] 10 1 QPS, stator winding stator open-circuit fault, 1590 rpm [(3),k=6] [(2),k=6] [(3),k=6] [(3),k=18] [(2),k=18] [(3),k=18] [(3),k=30] [(2),k=30] [(3),k=30] open-circuit healthy Frequency [Hz] Piezoelectric (top) and FBG (bottom) vibration frequency spectra stator open-circuit fault at 1590 rpm

18 Speed [RPM] Variable Speed Operation Emulating realistic wind turbine variable speed operating conditions Open-circuit winding fault introduced and PE and FBG platforms compared Time [s] Typical measured generator speed profile

19 Frequency [Hz] Frequency [Hz] Transient vibration signal spectrum HEALTHY FAULTY F A U L T Time [sec] HEALTHY FAULTY Time [sec] Piezoelectric (top) and FBG (bottom) vibration short-time FFT spectra for variable speed operation with and without open-circuit fault F R E Q U E N C I E S

20 Single fault frequency zoom-in FAULT FREQUENCY M A G N I T U D E 3d spectrogram, PE sensor FAULT FREQUENCY FREQUENCY TIME 3d spectrogram, FBG sensor M A G N I T U D E FREQUENCY TIME

21 Summary Wideband VibroFibre was shown to provide comparable performance to high cost PE sensor under electrical and mechanical fault conditions Improvements ongoing in sensor characteristics and signal processing to further enhance performance and bring it closer to PE benchmark Future work will show distributed vibration sensing and investigate sensor design with simultaneous temperature and vibration sensing ability VibroFibre can become a competitive alternative to current high cost sensing solutions

22 Thank You Questions?