Level II Airborne Ultrasound Certified Analyst. By UESystems. ClearWater Beach, F.L. Mayo

Transcripción

1 Detecting Rotor Bar Problems in AC Induction Motors by Airborne/Structureborne Ultrasound Mechanical Inspection. Mechanical Department. Predictive Maintenance & Reliability Speaker: Eng. Carlos Hdz. Conti, CMRP Level II Airborne Ultrasound Certified Analyst. By UESystems ClearWater Beach, F.L. Mayo

2 Content About TLA Machine. Problem. Diagnostic Chart. Failure Zone Graph. Failure Effect. Technique. Recommendations & Diagnostics Results. References. Appendix A, MCA Diagnostics & Severity Chart. 2

3 TLA ALTAMIRA WHERE IS IT? 3

4 ORGANIZATIONAL STRUCTURE & PROCESS Type Industry Founded Joint Venture ( Shell-Total- Mitsui ) Oil & Gas 2004, by Shell-Total-Mitsui Headquarters Altamira, Tams. MX Key people Products Carlos Barajas (Managing Director) Loran Karwacki (Asset manager) Jair Rojas (Finance Manager) Carlos Oropeza (Operations Manger) Juan M. Hdz (Maintenance Manager) Verónica Zavaleta ( HR Manager) Luis Núñez (Commercial & Proyects Manager) Natural Gas Employees 80 (2010) Website 4

5 LNG Importing Terminal - Assets & Technical Scope. Berthing basin, including mooring & unloading facilities for LNG Carriers (Carrier Capacity 70,000 to 200,000 m 3 ) 2 LNG Storage Tanks (net capacity 150,000 m 3 each) Process equipment for vaporization & gas pressurizing; Seawater Supply System with capacity of up to 30,000 m 3 /hr Send Out Facilities into Pemex Pipeline and Altamira V PP Buildings (Control Room, Administration Building, Warehouse 2010 replacing temporary buildings) Terminal Capacity (Phase 1): 760 mmscf/d Peak (500mmscfd base load = 3.75 mtpa) Potential for Expansion (Phase 2):1,200 mmscf/d Peak (1070mmscfd base load = 8 mtpa) 5

6 Machine: PM-1501 PM-1501 is an electric motor of approximately 450 HP's and runs at 1800 rpm, is coupled to a double suction bipartite horizontal centrifugal pump, whose function is to provide water for fire fighting, this machine operates every week about 10 minutes and the route is inspected every 3 months. 6

7 Safe Maintenance P-F Curve, Safety and Reliability Where is safer, reliable and economic doing maintenance? Source: PdM Secrets Revealed 4 th Ed AlliedcRealiaility Are You Doing Too Much PM? 7

8 Problem: PM1501, Ultrasound Spectrum Analysis shows a typical spectrum of Rotor Loose-Broken Bar Problems in the engine, note Rotor Bar Pass kcpm and up to 4 harmonics each one with 2XFl. Bars # = cpm / 1800 rpm = bars 8

9 Diagnostic Chart: 9

10 Diagnostic Chart: A normal AC motor signature ought to include a rotor bar passing frequency (RBPF) response. This response takes place when each rotor bar passes slight disruptions within the magnetic field because of the electrical current s path through the stator/rotor geometry. An elevated RBPF is created when the rotor bars pass a significant disruption in these fields produced when the current path is altered or distorted from broken or cracked rotor bars, loose or defective rotor bar joints, improperly brazed rotor bar joints, porous rotor bar castings, or electrical arcing across the rotor bar to end ring interfaces. RBPF is recognized as an integer multiple of rotor speed, and will usually have sidebands spaced at 2x electrical line frequency (7200 CPM). Rotor eccentricity problems can be indicated by additional (less dominant) sidebands sets spaced at 1x RPM. AC motor may have from rotor bars, so an FFT spectrum with sufficient frequency range will be necessary to capture this fault. 1x and 2x RBPF will be captured by a CPM with a 1600 FFT line resolution, and will provide enough resolution to define the 2x LF sidebands. Severity is usually judged by changes in RBPF amplitudes over time. Amplitude variation with load is common. 10

11 Failure Zone Graph: 11

12 Failure Effect: When analyzing the post mortem rotor failure, locate and identify points of blackened-blue overheating areas Check dye penetrant crack. 12

13 Failure Effect: 13

14 Technique: The inspection technique used was: Mechanical inspection of bearings, using magnetic module placed closest to the loading of the bearings, a 25 khz was settled, the data was saved and downloaded to the DMS for follow-up. This type of problems typically generate audible go & back sound. 14

15 Recommendation & Diagnostics: Applying the Theory of Vibration Analysis to Ultrasound Analysis: When dealing with Problems of Rotor Bar Loose / Broken in electric motors, their physics is not due to friction or impact, and if not settled a Fmax. suitable for capturing high frequencies in the FFT, they can go unnoticed, their severity is dictated by the amount of harmonics, as well as side bands around them, this is an advantage of using ultrasound in mechanical inspections. For better results try to apply and combine diagnostics with at least 2 PdM technologies. ( see appendix A) Results: It was proceeded to prepare the respective report, continuing with routine monitoring, this type of rotor problems are usually related to manufacturing quality problems, and given that the engine do not operates continuously, its development has been slow, but by predictive task, this Potential Failure as intensified so shall be changed with the spare motor, which is already in stock. 15

16 Appendix A MCA: MCA results performed on this same engine to confirm the problem, note the warning notice indicating possible failure of rotor bars. Motor ID PM 1501 TLA Database WORK 2005 Tested by Building Bba contraincendio Tested for Location BASEMENT Explorer SN# 333 Date/Time 4/14/ :21:31 PM Test Type Electrical Name Plate Measured Hp RPM Volts Amps pf (pu) Nema Derating (pu) Torque (ft-lb) Efficiency Percent Load Test Value Status Caution Level Warning Level % Over Voltage 2.43 GOOD % Unbalance 0.75 GOOD % Voltage Dist GOOD % Current GOOD Ef. Service Factor 0.73 GOOD Rotor Bar (db) WARNING % Op. Point 0.00 GOOD % Loss Diff INDET % Loss Diff. N/A INDET

17 Appendix A: MCA Motor ID PM 1501 TLA Database WORK 2005 Tested by Building Bba contraincendio Tested for Location BASEMENT Explorer SN# 333 Date/Time 4/14/ :21:31 PM Test Type Electrical Power Spectrum Graphics showing the Rotor Bar Pass Problem, which also is affected in response to torque. Voltage and Current Waveforms Rotor Bar Phasor Diagram Torque Ripple 17

18 Appendix A: MCA Diagnosis and Severity Table for MCA, used to assess Electric AC Motors problems. 18

19 References: A New Version of MachineLibrary Multimedia Training Package is Now Available, pp , or visit the MachineLibrary Technical Associates Of Charlotte, Vibration Analysis Level II & III Aknowledgements: Special thanks to Ing. Alvaro Castillo, BASF of Altamira, for support with the MCA analysis by Baker, all under the Interplant support of the AISTAC Reliability Committee. Special thanks to Ing. Carlos Garza, UESystems Regional Manager for México & LA for the chance to take part in this Conference. Special thanks to all those M&R Practitioners for sharing knowledge and experience at WU VII Mr. Carlos Hdz. Conti can be reached at : 19

20 Detectando Problemas de Rotor por medio de Inspección Mecánica de Ultrasonido Estructural Depto.Mecánico Mantto. Predictivo y Confiabilidad. Presenta: Ing. Carlos Hdz. Conti, CMRP Level II Airborne Ultrasound Certified Analyst. By UESystems ClearWater Beach, F.L. Mayo

21 Contenido Maquina. Problema. Carta de Diagnóstico. Esquema de Zonas de Falla. Efectos de Falla. Técnica. Recomendación Diagnóstico Resultado. Referencias Anexo A, MCA & Carta de Diagnóstico y Severidad. 2

22 TLA ALTAMIRA EN DONDE SE UBICA? 3

23 ESTRUCTURA ORGANIZACIONAL & PROCESO Type Industry Founded Joint Venture ( Shell-Total- Mitsui ) Oil & Gas 2004, by Shell-Total-Mitsui Headquarters Key people Products Altamira, Tams. MX Carlos Barajas (Managing Director) Loran Karwacki (Asset manager) Jair Rojas (Finance Manager) Carlos Oropeza (Operations Manger) Juan M. Hdz (Maintenance Manager) Verónica Zavaleta ( HR Manager) Luis Núñez (Commercial & Proyects Manager) Natural Gas Employees 80 (2010) Website 4

24 Terminal de Importación de LNG- Activos & Alcance Técnico. Berthing basin, including mooring & unloading facilities for LNG Carriers (Carrier Capacity 70,000 to 200,000 m 3 ) 2 LNG Storage Tanks (net capacity 150,000 m 3 each) Process equipment for vaporization & gas pressurizing; Seawater Supply System with capacity of up to 30,000 m 3 /hr Send Out Facilities into Pemex Pipeline and Altamira V PP Buildings (Control Room, Administration Building, Warehouse 2010 replacing temporary buildings) Terminal Capacity (Phase 1): 760 mmscf/d Peak (500mmscfd base load = 3.75 mtpa) Potential for Expansion (Phase 2):1,200 mmscf/d Peak (1070mmscfd base load = 8 mtpa) 5

25 Máquina: PM-1501 PM-1501 es un motor eléctrico de aprox 450 HP s y gira a 1800 rpm, está acoplado a una bomba centrífuga bipartida de doble succión, cuya función es proveer agua de contra incendio, éste equipo opera cada semana alrededor de 10 minutos y la ruta se inspecciona cada 3 meses. 6

26 Problema: PM1501, El Análisis de Espectros de Ultrasonido muestra espectro típico de Problemas de Barras de Rotor Flojas/Rotas en el Motor, nótese Frec. Paso de Barras de Kcpm y hasta 4 armónicos c/u con Bandas 2XFl. # Barras= cpm / 1800 rpm = barras 7

27 Carta de Diagnóstico: 8

28 Carta de Diagnóstico: Una firma de motor de CA normal debe incluir una respuesta de frecuencia de paso de barra del rotor (RBPF). Esta respuesta se produce cuando cada barra del rotor pasa perturbaciones leves en el campo magnético debido a la trayectoria de la corriente eléctrica a través de la geometría del estator / rotor. Una RBPF elevada se crea cuando las barras del rotor pasan una interrupción significativa en estos campos producida cuando la trayectoria actual se ve alterada o distorsionada de las barras de rotor rotas o agrietadas, juntas de barra del rotor sueltas o defectuosas, mal soldadas, piezas de fundición porosas de barra del rotor, o arcos eléctricos a través de la barra del rotor a través de las interfaces de anillo. RBPF se identifica como un múltiplo entero de la velocidad del rotor, y por lo general tienen bandas laterales espaciadas a 2 veces la frecuencia de línea eléctrica (7200 RPM). Los Problemas de excentricidad del rotor puede ser indicado por otros (menos dominante) conjuntos de bandas laterales espaciados a 1 x RPM. Un Motor de CA puede tener de 35 a 96 barras del rotor, por lo que un espectro de FFT con un rango de frecuencia suficiente, será necesario para capturar esta falla. 1x y 2x RBPF será capturado con una Fmax de kcpm con una resolución de 1600 líneas, y proporcionará suficiente resolución para definir las bandas laterales a 2xFL. La severidad se evalúa considerado los cambios en las amplitudes de RBPF a lo largo del tiempo. La variación de la amplitud con la carga es común. 9

29 Esquema de Zonas DE de Fallas: 10

30 Efectos de Fallas: Cuando analize la falla de rotor, busque e identifique zonas con puntos de recalentamiento ennegrecidasazuladas. Compruebe fisuras con líquidos penetrantes. 11

31 Técnica: La técnica de inspección usada fue: Inspección mecánica de rodamientos, aplicando el módulo magnético posicionándolo lo más cerca de la zona de carga de los rodamientos, 25 khz, se salvan los datos y se descargan al DMS para su posterior seguimiento. Éste tipo de problemas generan un sonido típico audible y oscilante de vaivén. Recomendación Diagnóstico: Aplicando la Teoría de Análisis de Vibraciones al Análisis de Ultrasonido: En los Problemas de Barras de Rotor Flojas/Rotas en motores eléctricos, su física no obedece a fricción ó impactos, y si no se ajusta una Fmáx. adecuada para captar altas frecuencias en el FFT, pueden pasar desapercibidos, su severidad está dictada por la cantidad de armónicos, así como de bandas laterales alrededor de éstos, lo anterior es una ventaja del uso del Ultrasonido en Inspecciones Mecánicas. Resultado: Se procedió a elaborar el reporte respectivo, continuándose con monitoreo rutinario, éste tipo de Problemas de Rotor normalmente están relacionados con problemas de calidad de manufactura, y dado que no opera continuamente el motor, su evolución ha sido lenta, pero como actividad predictiva, ésta Falla Potencial en tanto se intensifique se procederá a cambiar el motor el cual ya está en almacén. 12

32 Anexo A MCA: Resultados de MCA practicado a éste mismo motor para corroborar el Problema, nótese el aviso de advertencia indicando fallas por posibles Barras de Rotor. Motor ID PM 1501 TLA Database WORK 2005 Tested by Building Bba contraincendio Tested for Location BASEMENT Explorer SN# 333 Date/Time 4/14/ :21:31 PM Test Type Electrical Name Plate Measured Hp RPM Volts Amps pf (pu) Nema Derating (pu) Torque (ft-lb) Efficiency Percent Load Test Value Status Caution Level Warning Level % Over Voltage 2.43 GOOD % Unbalance 0.75 GOOD % Voltage Dist GOOD % Current GOOD Ef. Service Factor 0.73 GOOD Rotor Bar (db) WARNING % Op. Point 0.00 GOOD % Loss Diff INDET % Loss Diff. N/A INDET

33 Anexo A MCA: Gráficos de Espectro de Corriente mostrando el Problema de Paso de Barras de Rotor, el cual también se ve afectado en respuesta al torque. Motor ID PM 1501 TLA Database WORK 2005 Tested by Building Bba contraincendio Tested for Location BASEMENT Explorer SN# 333 Date/Time 4/14/ :21:31 PM Test Type Electrical Voltage and Current Waveforms Phasor Diagram Rotor Bar Torque Ripple 14

34 Anexo A MCA: Tabla de Diagnóstico y Severidad para MCA, usada para evaluar Problemas Eléctricos de Motores de CA 15

35 Referencias: A New Version of MachineLibrary Multimedia Training Package is Now Available, pp , or visit the MachineLibrary Technical Associates Of Charlotte, Vibration Analysis Level II & III Mr. Carlos Hdz. Conti can be reached at : 16