107YORK INTERNATIONAL
FORM 201.18-NM1 (102)
1.9 MOTOR PROTECTION MODULES
A Motor Protection Module for each compressor is lo-
cated in the Control Panel. These modules supply mo-
tor over-temperature protection, 3-phase current pro-
tection, phase imbalance, phase rotation, and a program-
ming and troubleshooting 7-segment display.
The motor over-temperature protection is supplied by
3 temperature sensors imbedded in the motor wind-
ings 120 degrees apart. The module monitors these
sensors allowing it to sense a hot winding and shut
down the compressor if motor cooling is inadequate.
The on-board C.T.s provide 3-phase current protec-
tion which look at 3 of the 6 motor legs and send
an analog signal proportional to average motor cur-
rent to I/O Expansion board and on to the micropro-
cessor board for microprocessor low/high current pro-
tection and current display. This allows the micro to
monitor current and shut a system down if low or high
motor current is sensed. This is a non-adjustable pro-
tection circuit electronically sized to a system's motor
specifications.
Internally, the on-board 3 C.T.s and internal circuitry
allow the Motor Protection Module to protect against
high motor current as programmed on the Motor Pro-
tector dip switches. These switches are set at the fac-
tory according to motor specifications.
The module also provides phase rotation protection to
ensure the screw compressor does not rotate back-
wards.
A single phase protection circuit located in the module
also monitors for a phase imbalance. If current imbal-
ance exceeds 17% of the average motor current in one
of the phases, the Motor Protector will recognize it and
shut the system down.
Whenever the Motor Protection Module senses a fault,
internal contacts will open and shut the system down.
These contacts are wired in series with the compressor
motor contactor. When the contact opens, the micro will
attempt to start the system 2 more times. Since the motor
contactor signal path from the Relay Output Board to
the motor contactor is broken by the Motor Protection
Module contacts, it will lock the system out after 3
faults. The Motor Protection Module must then be re-
set by removing 115VAC power from the Control Panel.
After the Motor Protector is reset, the individual sys-
tem SYS switch must be switched OFF and then ON to
reset the microprocessor to allow restart of the system.
Anytime the module faults, a thorough
investigation of the problem should be
performed before attempting to return
the system to operation. Failure to per-
form this investigation could lead to
motor or compressor failure. Addi-
tional details on the Motor Protection
Module can be found on page 13.
8
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