1

Mechanical Department.

Predictive Maintenance & Reliability

Speaker: Eng. Carlos Hdz. Conti, CMRP

Level II Airborne Ultrasound Certified Analyst. By UESystems

ClearWater Beach, F.L. Mayo 2011

Detecting Rotor Bar Problems in

AC Induction Motors

by Airborne/Structureborne Ultrasound

Mechanical Inspection.

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Content About TLA Machine. Problem. Diagnostic Chart. Failure Zone Graph. Failure Effect.

Technique. Recommendations & Diagnostics Results. References. Appendix A, MCA Diagnostics & Severity Chart.

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TLA ALTAMIRA WHERE IS IT?

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ORGANIZATIONAL STRUCTURE & PROCESS

Type Joint Venture ( Shell-Total-

Mitsui )

Industry Oil & Gas

Founded 2004, by Shell-Total-Mitsui

Headquarters Altamira, Tams. MX

Key people Carlos Barajas (Managing Director) Loran Karwacki (Asset manager) Jair Rojas (Finance Manager) Carlos Oropeza (Operations Manger) Juan M. Hdz (Maintenance Manager) Vernica Zavaleta ( HR Manager) Luis Nez (Commercial & Proyects Manager)

Products Natural Gas

Employees 80 (2010)

Website http://www.shell.com/

http://www.altamiralng.com.mx

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LNG Importing Terminal - Assets & Technical Scope.

Berthing basin, including mooring & unloading facilities for LNG Carriers (Carrier Capacity 70,000 to 200,000 m3)

2 LNG Storage Tanks (net capacity 150,000 m3 each)

Process equipment for vaporization & gas pressurizing;

Seawater Supply System with capacity of up to 30,000 m3/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)

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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.

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Safe Maintenance P-F Curve, Safety and Reliability

Where is safer, reliable and economic doing maintenance?

Source: PdM Secrets Revealed 4th Ed AlliedcRealiaility

Are You Doing Too Much PM?

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Problem: PM1501, Ultrasound Spectrum Analysis shows a typical spectrum of Rotor Loose-Broken Bar Problems

in the engine, note Rotor Bar Pass Frec. @102.7 kcpm and up to 4 harmonics each one with

SideBands @ 2XFl. Bars # = 102700 cpm / 1800 rpm = 57.05 bars

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Diagnostic Chart:

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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 currents 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 35-96 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 360000 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.

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Failure

Zone Graph:

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Failure Effect:

When analyzing the

post mortem rotor

failure, locate and

identify points of

blackened-blue

overheating areas

Check dye penetrant

crack.

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Failure Effect:

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Technique:

The inspection technique used was: Mechanical inspection of bearings, using

magnetic module placed closest to the loading of the bearings, a freq. @ 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 .

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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.

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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 4/14/2011 01:21:31 PM Test Type Electrical

Name Plate Measured

Hp 450.00 326.72

RPM 1785 1792.6

Volts 4160 4261.3

Amps 55.0 38.6

pf (pu) 1.0 0.9

Nema Derating (pu) 1.0 1.0

Torque (ft-lb) 1324.7 957.7

Efficiency 98.5 96.4

Percent Load 100.0 72.6

Test Value Status Caution Level Warning Level

% Over Voltage 2.43 GOOD 10.0 20.0

% Unbalance 0.75 GOOD 2.0 3.5

% Voltage Dist. 0.57 GOOD 7.0 9.0

% Current 71.33 GOOD 110.0 120.0

Ef. Service Factor 0.73 GOOD 1.1 1.2

Rotor Bar (db) -30.87 WARNING -45.0 -36.0

% Op. Point 0.00 GOOD 20.0 30.0

% Loss Diff. 0.00 INDET 25.0 50.0

% Loss Diff. N/A INDET 60.0 24.0

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Appendix A: MCA

Power Spectrum

Graphics showing

the Rotor Bar

Pass Problem,

which also is

affected in

response to

torque.

Motor ID PM 1501 TLA Database WORK 2005 Tested by Building Bba contraincendio Tested for Location BASEMENT Explorer SN# 333

Date/Time 4/14/2011 01:21:31 PM Test Type Electrical

Voltage and Current Waveforms Phasor Diagram

Rotor Bar Torque Ripple

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Appendix A:

MCA

Diagnosis and

Severity Table for

MCA, used to

assess Electric AC

Motors problems.

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References:

A New Version of MachineLibrary Multimedia Training Package is Now Available, pp. 66-67, or visit the MachineLibrary www.bently.com. 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 Mxico & 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 : carloshconti@yahoo.com C.Hernande@shell.com

1Depto.Mecnico

Mantto. Predictivo y Confiabilidad.

Presenta: Ing. Carlos Hdz. Conti, CMRP

Level II Airborne Ultrasound Certified Analyst. By UESystems

ClearWater Beach, F.L. Mayo 2011

Detectando Problemas de Rotor

por medio de

Inspeccin Mecnica de Ultrasonido Estructural

2Contenido Maquina. Problema. Carta de Diagnstico. Esquema de Zonas de Falla. Efectos de Falla.Tcnica.Recomendacin DiagnsticoResultado.ReferenciasAnexo A, MCA & Carta de Diagnstico y Severidad.

3TLA ALTAMIRA EN DONDE SE UBICA?

4ESTRUCTURA ORGANIZACIONAL & PROCESO

Type Joint Venture ( Shell-Total-

Mitsui )

Industry Oil & Gas

Founded 2004, by Shell-Total-Mitsui

Headquarters Altamira, Tams. MX

Key people Carlos Barajas (ManagingDirector)Loran Karwacki (Asset manager)Jair Rojas (Finance Manager)Carlos Oropeza (OperationsManger)Juan M. Hdz (Maintenance Manager)Vernica Zavaleta ( HR Manager)Luis Nez (Commercial & Proyects Manager)

Products Natural Gas

Employees 80 (2010)

Website http://sww.shell.com/

5Terminal de Importacin de LNG- Activos & Alcance Tcnico.

Berthing basin, including mooring & unloading facilities for LNGCarriers (Carrier Capacity 70,000 to 200,000 m3)

2 LNG Storage Tanks (net capacity 150,000 m3 each)

Process equipment for vaporization & gas pressurizing;

Seawater Supply System with capacity of up to 30,000 m3/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 (500mmscfdbase load = 3.75 mtpa)

Potential for Expansion (Phase 2):1,200 mmscf/d Peak(1070mmscfd base load = 8 mtpa)

6Mquina: PM-1501

PM-1501 es un motor elctrico de aprox 450 HPs y gira a 1800 rpm, est acoplado a una bombacentrfuga bipartida de doble succin, cuya funcin es proveer agua de contra incendio, ste equipo

opera cada semana alrededor de 10 minutos y la ruta se inspecciona cada 3 meses.

7Problema:

PM1501, El Anlisis de Espectros de Ultrasonido muestra espectro tpico de Problemas de Barras de

Rotor Flojas/Rotas en el Motor, ntese Frec. Paso de Barras de Rotor @ 102.7 Kcpm y hasta 4

armnicos c/u con Bandas Laterales @ 2XFl. # Barras= 102700 cpm / 1800 rpm = 57.05 barras

8Carta de Diagnstico:

9Carta de Diagnstico: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 campomagntico debido a la trayectoria de la corriente elctrica a travs de la geometra del estator / rotor. UnaRBPF elevada se crea cuando las barras del rotor pasan una interrupcin significativa en estos camposproducida cuando la trayectoria actual se ve alterada o distorsionada de las barras de rotor rotas oagrietadas, juntas de barra del rotor sueltas o defectuosas, mal soldadas, piezas de fundicin porosas debarra del rotor, o arcos elctricos a travs de la barra del rotor a travs de las interfaces de anillo.

RBPF se identifica como un mltiplo entero de la velocidad del rotor, y por lo general tienenbandas laterales espaciadas a 2 veces la frecuencia de lnea elctrica (7200 RPM). Los Problemas deexcentricidad del rotor puede ser indicado por otros (menos dominante) conjuntos de bandas lateralesespaciados 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 unrango de frecuencia suficiente, ser necesario para capturar esta falla. 1x y 2x RBPF ser capturado conuna Fmax de 360000 kcpm con una resolucin de 1600 lneas , y proporcionar suficiente resolucin paradefinir las bandas laterales a 2xFL.La severidad se evala considerado los cambios en las amplitudes de RBPF a lo largo del tiempo. Lavariacin de la amplitud con la carga es comn.

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Esquema

de Zonas DE

de Fallas:

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Efectos

de Fallas:Cuando analize la falla

de rotor, busque e

identifique zonas con

puntos de

recalentamiento

ennegrecidas-

azuladas. Compruebe

fisuras con lquidos

penetrantes.

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Tcnica:

La tcnica de inspeccin usada fue: Inspeccin mecnica de rodamientos, aplicando el mdulo

magntico posicionndolo lo ms cerca de la zona de carga de los rodamientos, frec.@ 25 khz, se

salvan los datos y se descargan al DMS para su posterior seguimiento. ste tipo de problemas

generan un sonido tpico audible y oscilante de vaivn.

Recomendacin Diagnstico:

Aplicando la Teora de Anlisis de Vibraciones al Anlisis de Ultrasonido: En los Problemas de Barras

de Rotor Flojas/Rotas en motores elctricos, su fsica no obedece a friccin impactos, y si no

se ajusta una Fmx. adecuada para captar altas frecuencias en el FFT, pueden pasar

desapercibidos, su severidad est dictada por la cantidad de armnicos, as como de bandas

laterales alrededor de stos, lo anterior es una ventaja del uso del Ultrasonido en Inspecciones

Mecnicas.

Resultado:

Se procedi a elaborar el reporte respectivo, continundose con monitoreo rutinario, ste tipo de

Problemas de Rotor normalmente estn relacionados con problemas de calidad de manufactura, y

dado que no opera continuamente el motor, su evolucin ha sido lenta, pero como actividad predictiva,

sta Falla Potencial en tanto se intensifique se proceder a cambiar el motor el cual ya est en

almacn.

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Anexo A MCA:

Resultados de MCA practicado a ste mismo motor para corroborar el Problema, ntese 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 4/14/2011 01:21:31 PM Test Type Electrical

Name Plate Measured

Hp 450.00 326.72

RPM 1785 1792.6

Volts 4160 4261.3

Amps 55.0 38.6

pf (pu) 1.0 0.9

Nema Derating (pu) 1.0 1.0

Torque (ft-lb) 1324.7 957.7

Efficiency 98.5 96.4

Percent Load 100.0 72.6

Test Value Status Caution Level Warning Level

% Over Voltage 2.43 GOOD 10.0 20.0

% Unbalance 0.75 GOOD 2.0 3.5

% Voltage Dist. 0.57 GOOD 7.0 9.0

% Current 71.33 GOOD 110.0 120.0

Ef. Service Factor 0.73 GOOD 1.1 1.2

Rotor Bar (db) -30.87 WARNING -45.0 -36.0

% Op. Point 0.00 GOOD 20.0 30.0

% Loss Diff. 0.00 INDET 25.0 50.0

% Loss Diff. N/A INDET 60.0 24.0

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Anexo A MCA:

Grficos de Espectro de

Corriente mostrando el

Problema de Paso de

Barras de Rotor, el cual

tambin 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 4/14/2011 01:21:31 PM Test Type Electrical

Voltage and Current Waveforms Phasor Diagram

Rotor Bar Torque Ripple

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Anexo A MCA:

Tabla de Diagnstico y

Severidad para MCA,

usada para evaluar

Problemas Elctricos

de Motores de CA

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Referencias:

A New Version of MachineLibrary Multimedia Training Package is Now Available, pp. 66-67, or visit theMachineLibrary www.bently.com. Technical Associates Of Charlotte, Vibration Analysis Level II & III

Mr. Carlos Hdz. Conti can be reached at :carloshconti@yahoo.comC.Hernande@shell.com