Joe geiman baker instruments 12 2006

Vane-axial Fan Maintenance Challenge:vibration on bearing housing for all Vane axial Fans for this Nuclear Power Plant.. average cost per meter of retrofitted wire > U$ 5,000 vibration o

On-line Motor Monitoring

Joe Geiman Baker Instrument Co.

What are we really after?

Induction motor and VFD applications

Motor Failure Areas:

Motor Failure Areas:

Bearing

44%

Rotor 8%

Other

22%

Stator 26%

Bearing 41%

Other 14% Rotor

9%

Stator 36%

Motor Failure Causes:

Safety and Connecting:

Low Voltage (Less than 600V)

Step five: STOP motor Step six: Disconnect Explorer

Explorer

Safety and Connecting:

Medium and High Voltage (More than 600V)

Motor

Load

CTs Breaker

Step one: Motor is running Step two: Connect Explorer CTs Step three: Connect Explorer PTs

Explorer

PTs

CTs Breaker

Power Quality Analysis

Motor Overheating

 I 2 R Losses Motor Currents

 100% rated Current 100% rated Temperature

 110% rated Current 121% rated Temperature

Fan 1 hp 1740 rpm

Motor Condition: Broken Rotorbar

Rotorbar Frequency:

slip Synchronous rotor bar freq.

0.1 1798.2 59.88 0.2 1796.4 59.76 0.3 1794.6 59.64 0.4 1792.8 59.52 0.5 1791 59.4 0.6 1789.2 59.28 0.7 1787.4 59.16 0.8 1785.6 59.04 0.9 1783.8 58.92 1.0 1782 58.8

.

.

.

slip

2 1

synch

operat synch

fund rotorbar

RPM

RPM

RPM s

s f

•Harder to assess with lesser load

•Harder to assess with bigger motor

•Harder to assess with more efficient motor

Increasing Lines of Resolution:

New Rotorbar y-axis Scale

l fundamenta

signal dB

res

300

42log

105

.38

log10

].[

down'dB

'

Good Rotor Bar

Bad Rotor Bar

• Turn off motor 7200 peek disappears

 Electricians do not believe it could be a rotor bar

• They have never seen a rotor problem

• Electricians have no way to confirm or deny theallegations of the mechanics

Show Data

 Broken Rotor Bar

 Good Rotor Bar

2A High Pressure Pump Broken Rotor Bar

2A High Pressure Pump Broken Rotor Bar

1C High Pressure Pump

Good Rotor Bar (comparison)

1C High Pressure Pump

Good Rotor Bar (comparison)

2A High Pressure Pump

 It appeared to be a broken

 All thought, only slightly into the caution

we questioned how saver the problem

was

2A High Pressure Pump

3 Broken Rotor Bars

2A High Pressure Pump

3 Broken Rotor Bars

Case Study 2

4a PA Fan

 Problem Slight vibration

Broken Rotor Bar

Case Study 3

 Rotor Issue

 Show need for higher acquisition

 Show other places in spectrum to represent or confirm rotor issues

Low Resolution Data

No Assessment Can Be Made

Low Resolution Data

No Assessment Can Be Made

High Resolution Data

Assessment Can Be Made

High Resolution Data

Assessment Can Be Made

 Inspection found brazing issues at the end ring causing high resistance joints.

Epoxy Melting Off Rotor Bars Representing Excessive Heat

Cracked End Ring (Case Study 4)

Motor Current Signature Analysis Values From Technical Associates.

 54 – 60 dB 54 – 60 dB Excellent Excellent

 48 – 54 dB 48 – 54 dB Good condition Good condition

 42 – 48 dB 42 – 48 dB Moderate condition Moderate condition

 36 – 42 dB 36 – 42 dB Rotor bar crack Rotor bar crack

resistance joints.

 30 – 36 dB 30 – 36 dB multiple cracked / broken multiple cracked / broken

bars or end – rings indicated

 < 30 < 30 dB dB multiple cracked / multiple cracked /

broken bars or end-rings very likely

• Requires constant torque level

• Torque ripple

• Next one breaks sooner

• Current increases

• Temperature increases

• Insulation life shortens

• Typically non-immediate death Motor Condition:

Broken Rotorbar issues

S

F

F I

Flux: Generated by stator Voltage

Rotor Current: Monitored with Stator Current

T

T(t) = f( V(t), I(t) )

According to Park’s theory, 1920.

Rotor Stator

Calculating Torque:

 Explorer showed that not all motors run at constant

operating condition The 4 motors at the center display

a larger variability to their operation These are the

locations which’ motors break with unusually high

frequency.

• The maintenance supervisor noted that some stirring

pool motors (decontamination and recycling process) break with unusually high frequency.

Case study I: Hydro-mechanical resonance Brewery.

• The maintenance supervisor noted that some stirring

pool motors (decontamination and recycling process) break with unusually high frequency.

• The Explorer showed that not all motors run at

constant operating condition The 4 motors at the

center display a larger variability to their operation These are the locations which’ motors break with

unusually high frequency.

• The Torque Ripple graphs clarified the source of the

operation’s variability.

Case study I: Hydro-mechanical resonance Brewery.

Corrective action:

4160V submersible pump

Torque Signature:

Torque Ripple vs Time

Hz s

s period

0

2 _







Torque Ripple vs Time

Hz s

s period

0

2 _







Torque vs Frequency:

Mechanical Imbalance

• Investigating vibration and torque for inaccessible loads:

Comparison of Duct-Mounted Vibration and InstantaneousAirgap Torque Signals for Predictive Maintenance of Vane Axial

Problem Application:

Problem Application:

unplanned outages, health and safety costs, and extensive damage to surrounding equipment.

unplanned outages, health and safety costs, and extensive damage to surrounding equipment.

• Vane Axial Fans are common

in nuclear environments

• It is almost impossible to

predict bearing faults for

Vane Axial Fans.

• Vane Axial Fans are common

in nuclear environments

• It is almost impossible to

predict bearing faults for

Vane Axial Fans.

Nuclear Comanche Peak Station

TXU Electric

Horizontal Application Vertical

Application

Vane-axial Fan Maintenance Challenge:

(vibration on bearing housing)

for all Vane axial Fans for this Nuclear Power

Plant (Nuclear Industry in U.S average cost per meter of retrofitted wire > U$ 5,000)

(vibration on bearing housing)

for all Vane axial Fans for this Nuclear Power

Plant (Nuclear Industry in U.S average cost per meter of retrofitted wire > U$ 5,000)

Laboratory Investigation:

 Set up a Vane Axial Fan in a Laboratory, and create:

• Healthy operation (baseline data)

• Advanced Bearing fault (Stage III)

 Gathering Data:

• Vibration data obtained from the bearing housing – preferred diagnostic method – (used as benchmark of planted faults).

• Accelerometers connected to the outside of the duct.

• Calculated Instantaneous Airgap Torque using Park’s theory.

 Statistical Data Analysis:

• Statistical evaluation using “single sided experiment design”.

• 9 samples needed for certainties exceeding 95% and 90% for errors type I, and type II, respectively.

 Set up a Vane Axial Fan in a Laboratory, and create:

• Healthy operation (baseline data)

• Advanced Bearing fault (Stage III)

 Gathering Data:

• Vibration data obtained from the bearing housing – preferred diagnostic method – (used as benchmark of planted faults).

• Accelerometers connected to the outside of the duct.

• Calculated Instantaneous Airgap Torque using Park’s theory.

 Statistical Data Analysis:

• Statistical evaluation using “single sided experiment design”.

• 9 samples needed for certainties exceeding 95% and 90% for errors type I, and type II, respectively.

Chosen Fan / Motor:

 Motor: Baldor 3.7kW (5hp), 4-pole, 480V.

 Fan: Aerovent 304 mm (24 in).

 System used in the Exhaust of the Electrical Control Room.

 Motor: Baldor 3.7kW (5hp), 4-pole, 480V.

 Fan: Aerovent 304 mm (24 in).

 System used in the Exhaust of the Electrical Control Room.

Note: The support system of this motor/fan has a long transmission path – which may dampen

mechanical signals on their way to the duct.

Note: The support system of this motor/fan has a long transmission path – which may dampen

mechanical signals on their way to the duct.

The “known good” Signals:

Redundant verification:

 Accelerometers: 100mV/g ICP

 Cognitive Systems CV395B Analyzer

 Bentley Nevada ADRE 208P

 SWANTECH stress wave analysis

Redundant verification:

 Accelerometers: 100mV/g ICP

 Cognitive Systems CV395B Analyzer

 Bentley Nevada ADRE 208P

 SWANTECH stress wave analysis

Additional Instrumentation

ensuring constant operating condition:

Airfolow Meters Humidity Meter Thermocouples Current Meters Laser tachometers

Additional Instrumentation

ensuring constant operating condition:

Airfolow Meters Humidity Meter Thermocouples Current Meters Laser tachometers

Field-friendly alternative #1:

Duct-mounted Accelerometers

Field-friendly alternative #1:

Duct-mounted Accelerometers

 Vibration Transducers 100mV/g ICP.

 Cognitive Systems Spectrum Analyzer

 Accelerometers mounted directly at Mounting Rod on the Duct.

 Vibration Transducers 100mV/g ICP.

 Cognitive Systems Spectrum Analyzer

 Accelerometers mounted directly at Mounting Rod on the Duct.

Field-friendly alternative #2:

Torque Signature Analyzer

Field-friendly alternative #2:

Torque Signature Analyzer

 Explorer II (Baker Instrument Company)

 Measures 3 currents and 3 voltages at MCC

 Calculates airgap torque (Park 1929)

 Obtains operating speed from current and torque

signatures

 Monitoring Imbalances: 1x mechanical frequencies inairgap torque spectrum

 Explorer II (Baker Instrument Company)

 Measures 3 currents and 3 voltages at MCC

 Calculates airgap torque (Park 1929).

 Obtains operating speed from current and torque

signatures

 Monitoring Imbalances: 1x mechanical frequencies inairgap torque spectrum

• 7.6 grams create 0.39 gm (0.54 oz in) imbalance.

• Comparing amplitudes of 1 x mechanical frequencies for “unfaulted” vs “faulted” data.

• 7.6 grams create 0.39 gm (0.54 oz in) imbalance.

• Comparing amplitudes of 1 x mechanical frequencies for “unfaulted” vs “faulted” data.

• Start: Precision balancedfan (baseline)

• Planted Fault: 7.6 gramsimbalance

• Start: Precision balancedfan (baseline)

• Planted Fault: 7.6 gramsimbalance

Fault 1: Mechanical Imbalance

Comparison of the amplitudes of 29.9Hz (1x mechanical)

frequencies for 1 set of balanced data, with one set of

imbalanced operation:

Comparison of the amplitudes of 29.9Hz (1x mechanical)

frequencies for 1 set of balanced data, with one set of

imbalanced operation:

Fault 1: Mechanical Imbalance

gain renders it unfeasible for maintenance.

Airgap Torque Method:

 99% certain that imbalanced data has higher amplitude

 Amplitude is 150 times higher ( >40dB )

Conclusion:

used for maintenance.

The large amplitude gain makes it very robust and easy to interpret.

Fault 1: Mechanical Imbalance

Results:

Bearing Signature Analysis

BPFO i

s Frequencie Fault     

fund.

n 2 k

BPFO i

s Frequencie

Motor Failure Areas:

Bearings

Motor Failure Areas:

Bearings

harm * BPFO  2 * RPM

Known Good Bearing Known Outer Race Defect

“It can be found”

“It is in your face”

4 pole 5hp

Eccentricity in Spectrum:

• Location:

• “1x” types:

• Current signals: f fund. ± f mech.

• Torque signals: f mech.

• - “Bar-pass” types:

• Current signals: n · f mech. ± 1 · f fund. (hopefully there)

• Torque signals: n · f mech. (many times not

there)

• 4-pole motor.

• 1x = just below 30Hz.

rpm

Hz 60 s 1768 8 48

.

29  min 

Eccentricity, Torque Signature:

“1 x” location

Eccentricity, Current Signature:

“1 x” location

 60  30 58  Hz  60 mins  1765 2 rpm

• 4-pole motor.

• 1x = just above 30Hz.

Eccentricity, Torque Signature:

“Rotorbar Pass Frequency” location

• 1920Hz / 60Hz = 32bars (1920Hz is synchronous rotorbar pass frequency)

rpm Hz

f

Hz bars

Hz

s

mech

5 3593 60

89 59

89

59 32

56 1916

Eccentricity, Current Signature:

“Rotorbar Pass Frequency” location

• 2-pole motor

•1860Hz / 60Hz + 1 = 32bars

rpm Hz

f

Hz bars

Hz Hz

s

mech

5.359360

89.59

89

5932

6051

.1856

1x f fund fmech

Comparing Ieccent. with Teccent.

• Teccent. at “expected” frequency

• Ieccent. at “expected” frequency – 60Hz.

• Teccent. -28.43 dB relative amplitude.

• Ieccent. -34.9 dB relative amplitude.

Teccent. is at the understandable location.

Teccent. has a 4.5 times larger signal.

• Demodulated Current method does not agree with vibration’s methods.

• Demodulated Torque reacts like vibration’s methods.

• This method is independent of Motor design.

• This method does not disagree with IEEE motor scientist’s research.

Case study II: Cooling tower fan and gear signatures Coal-fired power plant.

Case study II: Cooling tower fan and gear signatures Coal-fired power plant.

Input Shaft Freq.

Intermediate Shaft Freq.

Output Shaft Freq.

Blade Pass Freq.

Case study II: Cooling tower fan and gear signatures.

Coal-fired power plant.

Case study II: Cooling tower fan and gear signatures.

Coal-fired power plant.

1 st Mesh Frequency

Case study II: Cooling tower fan and gear signatures.

Coal-fired power plant.

Case study II: Cooling tower fan and gear signatures.

Coal-fired power plant.

+ - 2 x Electrical

Case study II: Cooling tower fan and gear signatures.

Coal-fired power plant.

Case study II: Cooling tower fan and gear signatures.

Coal-fired power plant.

SKF 22310c