CASE STUDY 9603
Fault Isolated to Control Circuit
Summary: Misdiagnosis caught with MCE testing. Unnecessary motor replacement avoided.
Motor Information:
Type: Induction
Volt: 4160
HP: 3500
RPM: 1765
FLA: 490
Problem
While on third shift, a jet water motor was shut down for
standard maintenance operations. After completion and on a
restart, the primary bus circuit breaker tripped. Repeated start
attempts produced similar results.
Looking for the Root Cause
Initial troubleshooting efforts concluded that the fault was in
the motor and provisions were made for pulling upon arrival of
the first shift. Once notified of the situation, a first shift
technician employed an MCE to verify the condition of the motor.
The test indicated that both the motor and power circuit were in
good condition with no apparent faults. These findings confirmed
the technician's belief that the problem was in the MCC. Further
investigation revealed a fault in the control circuit.
Savings
With the MCE, the refinery used off-line testing to verify the
sound condition of the motor and power circuit. The savings from
this action were substantial considering removal, installation
and replacement expenses were prevented. Additionally, costly
down time resulting from a misdiagnosis was avoided and
production was maximized.
Estimated Failure Costs
-Downtime $200,000
-Removal Unknown
-Motor Repair/Replacement $90,000
TOTAL LOSSES PREVENTED $290,000
Industry: Refinery
Application: Diagnostic