Current Transformer and Current Input
24 RTHC-SVD01B-EN
From the calculated CT Factor, the Motor Current Overload Settings
#1 and #2 can be found in 4-2.
The current transformers provide the input for seven basic functions of
the Starter module:
1. Starter contactor interrupt failure. If currents corresponding to
greater than 5% RLA are detected on all three of the monitored
compressor phases within approximately 5 seconds after an
attempted contactor drop-out, the compressor will continue to be
commanded off, the unload solenoid will be pulsed, the EXV will
control the liquid level, and the condenser water pump and chilled
water pump will remain operating if controlled through UCP2. This
condition will exist until the diagnostic is manually reset.
2. Phase Loss: Running. If the detection of any or all of the three
motor phase currents falls below 10% RLA for 2.6 seconds while
the branch circuit should be “energized”, UCP2 will trip out the
compressor.
3. Phase Loss: Starting. Failure of a contactor to pull in will also
cause the Phase Loss diagnostic if no current is detected 0.3 sec-
onds after the start was commanded. However when reduced
voltage starting is employed, it may take an additional 3 seconds
to detect a phase loss at start-up, as phase loss protection is not
active during the 3 second transition time.
4. Phase Reversal. Screw compressors cannot be allowed to run in
reverse direction. To protect the compressors, the phase rotation
is detected by the current transformers immediately at start up. If
improper phasing is detected, within 0.3 seconds of start-up,
UCP2 will trip out the compressor, and the Phase Reversal diag-
nostics will be displayed.
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