CASE STUDY 9605
Vibration Caused by Electrical Fault
Summary: Unbalanced rotor fields detected with RIC and inductive measurements.
Motor Information:
Type: Synchronous
Volt: 13.200
HP: 17,500
RPM: 1200
Problem
After finding unacceptable vibration levels of 4 Mils on a large
compressor motor, attempts were made to balance the rotor with a
2-lb. weight. Initially, the weight reduced the vibration to an
acceptable 1.5 Mils. However, levels climbed again until they
reached 10 Mils at no-load. Several technologies were employed to
locate the source but provided no conclusive results.
Looking for the Root Cause
A service company was contracted to perform MCE testing. Initial
test confirmed that the insulation system, power circuit and
stator windings were in good health. However, a Rotor Influence
Check (RIC) revealed a inductive imbalances which deviated by as
much as 9%. Such a variance focused the troubleshooting efforts
to the rotor. Inductance readings taken on the individual rotor
coils identified marked differences among field poles. This
imbalance, undetected by other methods, created a field
distortion substantial enough to induce the measured vibrations.
The decision to replace the rotor was made and the vibration
readings taken following the repair were normal.
Savings
Without the use of the MCE, troubleshooting efforts would have
continued for at least another 24 hours. Enormous downtime costs
had persuaded the company to replace the entire motor if no
solution had been found by this time. Utilizing the MCE
drastically reduced financial losses and prevented the
unnecessary costs of total motor replacement.
Estimated Failure Costs
-Downtime $1,440,000
-Removal/Installation $10,000
-Motor Repair/ Replacement $750,000
Total Losses Prevented $2,200,000
Industry: Refinery
Application: Diagnostic