CASE STUDY 9604
Cable Fault Detected
Summary: Defective surge capacitor cable identified as root cause of overheating.
Motor Information:
Type: Induction
Volt: 4160
HP: 1750
RPM: 1200
Problem:
This motor was running hotter then expected and exhibited
excessive vibration. A similar motor, Chiller #2, was tested at
the same time and provided "normal" readings for
comparison. The Space Shuttle was scheduled for an immediate
launch, limiting the test window. Therefore, the initial readings
were taken with the power factor and surge capacitors still in
the circuit.
Looking for the Root Cause:
As expected, the wye-connected ground configuration of the motors
produced a low resistance to ground and a high capacitance to
ground reading (see table). However, the 16% inductive imbalance
on Chiller #1 was much higher, than the .52% imbalance found on
Chiller #2.
During the final tests the capacitors and ground connection were removed. The inductive imbalance dropped from 16% to less than 3% for the Chiller #1 yet stayed the same for Chiller #2. One of the capacitors in the Chiller #1 circuit was suspected.
Solution
While inspecting the cables inside the controller, the engineer
found a large hole in the insulation of the cable running from
power factor capacitor #3 to the surge capacitor. The hole in the
insulation was repaired.
Industry: Aerospace
Application: Diagnostic