The Three Keys
to Successful
Motor Maintenance
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The Three Keys
• Quality Control
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• Troubleshooting
• Quality Control
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• Troubleshooting
• Quality Control
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• Troubleshooting
Power
Power
Insulation
Air
Stator
Rotor
Quality
Gap
Circuit
Power Quality
Power Circuit
Stator
Insulation
Fault Zones
Air Gap
PdMA Corporation
Rotor
Case Study
Quality Assurance
PdMA Corporation
• Name Plate
-General Electric
-4000 Volt
-40.7 FLA
-300 HP
-5090Z Frame #
-1785 RPM
PdMA Corporation
PdMA Corporation
Case Study
Trending
PdMA Corporation
• Boiler Feed Pump
• 4160 V
• 309 FLA
• 2500 HP
• 3580 RPM
• 46 Bars
• 54 Slots
PdMA Corporation
Trended MCSA Data
2008
2009
2010
2011
PdMA Corporation
Trended Demodulation Data
2009
2008
2010
2011
PdMA Corporation
January 2012 Data
We have a problem
PdMA Corporation
Demodulation Data
This demodulation capture
represents nearly a 25 times
increase over baseline
PdMA Corporation
Rotor Problem Action List
• What speed is the motor?
• Rotor Design?
-Open bar or spun cast aluminum
• Limit the starts and stops of the motor
• Increase testing frequency
• Minimize load fluctuations
PdMA Corporation
Comparison Data
Data taken from Boiler Feed
Pump number 2 shows no
rotor bar related anomalies
PdMA Corporation
Damaged Rotor
Rotor has multiple cracks
and shows visible signs of
rubbing damage
PdMA Corporation
Damaged Stator
PdMA Corporation
Post Repair Data 2013
This problem still
requires
monitoring
PdMA Corporation
Case Study
Insulation
Persistent Drive Failure on
400 HP Baghouse Fan
PdMA Corporation
Problem Description
• Four (4) Variable Frequency Drive failures
within a short life span (all within 3 years)
• Electric Motor recently refurbished
• VFD’s always replaced with new components
at a cost of $45,000 each
• Frequent trips of the motor causing additional
process problems
PdMA Corporation
•
•
•
•
•
•
•
PdMA Corporation
AC Induction
General Electric
400 Horsepower
1780 RPM
509LL Frame
460 Volt
442 Amps
Initial Standard Test
• Data collected from
local disconnect
• Quickly noticed the
corrected Mohm value
was only 145
• All other data
appeared to be within
acceptable limits
PdMA Corporation
Test Date
Test Time
07/28/2003
09:17:08 AM
Frequency
Mohm Ph 1 to Gnd
Charge Time
Voltage
Motor Temp
Measured Mohm
Corrected Mohm
pF Ph 1 to Gnd
ohm Ph 1 to 2
ohm Ph 1 to 3
ohm Ph 2 to 3
mH Ph 1 to 2
mH Ph 1 to 3
mH Ph 2 to 3
Avg. Inductance
% Res. Imbalance
% Ind. Imbalance
$ Power Loss
Test Location
MCE #
User
Notes
1200
60
1000
30
289.3
145.0
41750
0.01951
0.01956
0.01952
2.775
2.575
2.790
2.713
0.15
5.10
10.37
T-Leads
030452HV
Yes
Polarization Index Test
Final value less than 400 Mohm
Erratic graph indicative of moisture
and/or contamination
PdMA Corporation
Standard Test - At Motor Leads
• Data collected from
motor leads to isolate
circuit from motor to
disconnect
• Quickly noticed the
corrected Mohm value
increased from 145 to 1700
• Began to suspect a
problem within the conduit
between disconnect and
motor
PdMA Corporation
Test Date
Test Time
Frequency
Mohm Ph 1 to Gnd
Charge Time
Voltage
Motor Temp
Measured Mohm
Corrected Mohm
pF Ph 1 to Gnd
ohm Ph 1 to 2
ohm Ph 1 to 3
ohm Ph 2 to 3
mH Ph 1 to 2
mH Ph 1 to 3
mH Ph 2 to 3
Avg. Inductance
% Res. Imbalance
% Ind. Imbalance
$ Power Loss
Test Location
MCE #
User
Notes
07/28/2003
10:08:57 AM
Baseline
1200
60
1000
30
3400.0
1700.0
40500
0.01925
0.01913
0.01918
2.830
2.780
2.615
2.742
0.33
4.62
24.90
Motor Leads
030452HV
Yes
Polarization Index - At Motor
Final value increased to over 12000 Mohm
Graph has more slope - less erratic
PdMA Corporation
Remedial Actions
• Due to problem with low Mohm values
apparently residing between the local
disconnect and motor junction box, we
suspected water in the conduit
• Conduit was removed
• NO water found
• Spirits were low
PdMA Corporation
Remedial Actions (Continued)
• Due to some abrasions on lead-wire jacket, it
was decided to have it replaced
• Would allow further investigation of the
conduit - still leaning on water in conduit
• Would allow further investigation of the circuit
for other possible sources of our problem
PdMA Corporation
Root Cause
Phase 1
Phase 2
PdMA Corporation
Phase 3
Before/After Lead Change
• Corrected Mohm
value now very close
to when tested at
motor
• Corrected Mohm
value increased from
145 to 1500
• Resistive
Imbalance, although
low before now at
0.00
Test Date
Test Time
Frequency
Mohm Ph 1 to Gnd
Charge Time
Voltage
Motor Temp
Measured Mohm
Corrected Mohm
pF Ph 1 to Gnd
ohm Ph 1 to 2
ohm Ph 1 to 3
ohm Ph 2 to 3
mH Ph 1 to 2
mH Ph 1 to 3
mH Ph 2 to 3
Avg. Inductance
% Res. Imbalance
% Ind. Imbalance
$ Power Loss
Test Location
MCE #
User
Notes
PdMA Corporation
07/28/2003
10:08:57 AM
Baseline
1200
07/28/2003
03:03:13 PM
60
1000
30
3400.0
1700.0
40500
0.01925
0.01913
0.01918
2.830
2.780
2.615
2.742
0.33
4.62
24.90
Motor Leads
030452HV
60
1000
38
1745.0
1500.0
42250
0.02000
0.02000
0.02000
2.780
2.860
2.620
2.753
0.00
4.84
0.00
Bot Fuses LD
030452HV
Yes
Yes
1200
Problem Follow-Up
• Unit has operated flawlessly without as much as a
nuisance trip
• Process problems have as a result been
tremendously reduced
• Maintenance budget has experienced a much
needed rest from drive replacement costs
PdMA Corporation
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