Open Scr; Output Current Imbalance; Phase Rotation - York SSS 7L-B Operation Manual

SECTION 4 – SAFETY SHUTDOWNS
Possible Problems
• Check for a shorted SCR.
• Disconnect the motor and test for shorts phase to
ground, and phase to phase.
• If the shutdown occurs during the ramp up of the
motor, an open SCR maybe the problem.
• Verify that the gate of the SCR is not open.
• Verify that the programmed starting current is
correct on the OptiView Control Center.
• Verify that the output CT's are reading current
correctly.
• Check for an open input fuse.

OPEN SCR

This shutdown becomes active after the first 40 sec-
onds of starter operation. The main system micropro-
cessor looks at the voltage across each SCR via an op-
to-coupler. When the SCR is turned on, the output of
the opto-coupler is high, and when the SCR is turned
off, the output of the opto-coupler is low. If this signal
is low for 5 consecutive seconds, a Safety shutdown
will occur.
To help eliminate nuisance trips, this shutdown can be
disabled from the OptiView Control Center. Refer to
the OptiView Control Center Service form for your
style of chiller (refer to ASSOCIATED LITERATURE
in this form, page 3, for the proper form number).
The shutdown message displayed will be "LCSSS -
OPEN SCR".
Possible Problems
• Verify operation of the gate drivers.
• Verify that the starting current value is correct.
• Ensure that the motor is not overloaded on start.
This has been a problem on screw compressors.
• Verify that the motor is connected.
• Verify that the gate of the SCR is not open.
• Check for an open input fuse.
22

OUTPUT CURRENT IMBALANCE

This shutdown will become active after the starter has
been running for 45 seconds, and when the highest
of the three motor currents exceeds 80% of the pro-
grammed FLA. After these conditions are met, if any
one phase of motor current exceeds 30% of the aver-
age current for 45 seconds, a Safety shutdown will oc-
cur. Review the following example.
If
current in the A phase = 200A
current in the B phase = 200A
current in the C phase = 118A
Then
I = 200 + 200 + 118
AVE
I =
AVE
I = 173 x + 30% = 121A, 225A
ACCEPTABLE
Therefore,
Since phase "C" current = 118A which is less than the
acceptable 121A, the chiller would shut down if this
imbalance exists for 45 seconds.
The shutdown message displayed will be "LCSSS
– MOTOR OR STARTER-CURRENT IMBAL-
ANCE".
Possible Problems
• Verify the input voltage to the starter.
• Verify that the output CT's are reading current
correctly.
• Verify the gate drive on the Logic/Trigger Board.

PHASE ROTATION

The Logic/Trigger Board contains circuitry that gener-
ates a waveform for each of the input phase voltages.
These waveforms are compared to each other by the
main system microprocessor. When the "A" phase volt-
age transitions positive, the "C" phase voltage must be
positive. Also, when the "A" phase voltage transitions
negative, the "B" phase voltage must be positive. This
shutdown is only active during the first 30 line cycles
after power is applied to the starter. After the first 30
line cycles, the shutdown is no longer active.
FORM 160.00-O2
ISSUE DATE: 04/30/2019
3
173A
JOHNSON CONTROLS