York MILLENNIUM YCAS Installation Operation & Maintenance page 18

Product Description
unit alarm contacts, chilled liquid pump control, auto-
matic reset after power failure, automatic system opti-
mization to match operating conditions.
The software is stored in non-volatile memory (EPROM)
to eliminate chiller failure due to AC power failure. The
Programmed Setpoint is stored in lithium battery backed
memory.
Motor Current Protection
The microprocessor motor protection provides high cur-
rent protection to assure that the motor is not damaged
due to voltage, excess refrigerant, or other problems
that could cause excessive motor current. This is ac-
complished by sending 3 phase current signals propor-
tional to motor current from the Motor Protector mod-
ule to the Power Supply Board where the signals are
conditioned and routed to the I/O Expansion board to be
multiplexed and sent to the Microprocessor Board. If
the motor current exceeds the 115% FLA trip point af-
ter 3 seconds of operation on either Wye-Delta or ACL
starters, the micro will shut the system down and lock it
out after one fault. A manual reset of the respective
system switch is required to clear the fault and restart
the system. A thorough check of the motor, wiring, and
refrigerant system should be done before restarting a
system that has faulted on high motor current.
The micro also provides low motor current protection
when it senses a motor current less than 10% FLA.
The micro will shut the system down whenever low
motor current is sensed and will lock out a system if
three faults occur in 90 minutes. Low motor current
protection is activated 4 seconds after start on both
Wye-Delta and ACL starters to assure the motor starts,
the system doesn't run without refrigerant, the motor
protector is not tripped, and the mechanical high pres-
sure cut-out is not tripped. Once the system is locked
out on Low Motor Current, it must be manually reset
with the system switch. See also Motor Protector Mod-
ule section below.
The micro senses low motor current whenever a HPCO
or Motor Protector contact opens. This occurs because
the MP and HPCO contacts are in series with the mo-
tor contactor. Whenever either of these devices are open,
the contactor de-energizes and the motor shuts down.
Since the micro is sending a run signal to the contactor,
it senses the low motor current below 10% FLA and
shuts the system down.
18
Motor Protector Module
The mechanical motor protector is a Texas Instruments
2ACE Three Phase Protection Module (Fig. 39, page
101) thermal and current motor overload protection. This
module protects against phase-to-phase current imbal-
ance, over-current, under-current, and phase rotation.
The module, mounted in the power panel, utilizes a 7-
segment display which provides operating status and
fault diagnostic information. The 7-segment display will
display either a stationary or a flashing alphanumeric
value which can be decoded by the operator. A list of
the codes is shown below:
Normal motor off display. Sequentially
HAXXX sweeps through the motor protector dip
switch setting.
0 Normal - no fault detected (Running)
Flashing "0" Motor off or unloaded < 5A AC current level.
(Running)
1 High current fault.
Loaded phase to phase current
2
imbalance > 17%.
Unloaded phase to phase current
3
imbalance > 25%.
4 Improper incoming phase rotation.
High motor temperature.
5
Trip point = 13kW , reset = 3.25kW .
6 Communication error.
7 Unload Balance ( > 50%)
8 Phase Loss ( >60%)
E Out of range of RLA calibration.
Other symbols Defective module or supply voltage.
Working voltage 18-30 VAC, 224 VAC nominal.
Low voltage trip = 15 VAC.
Whenever a motor protector trips, the motor protector
contacts wired in series with the motor contacts opens
and the motor contactor de-energizes allowing the motor
to stop. The micro senses the low motor current and shuts
the system down. The micro will try two more starts
before locking the system out. The system locks out be-
cause the motor protector is a manual reset device. Af-
ter the first start the modules' contacts will be open pre-
venting the motor contactors from energizing. Power must
be removed and reapplied to reset the module.
Current Overload
The 2ACE module design uses one integral current trans-
former per phase to provide protection against rapid
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