Motor current is monitored using 3 Current Transform- ers (CTs) per motor, one on each phase. The C.T.'s are located in the Motor Protector Module.
Average motor current is monitored after 4 seconds of compressor operation. From this time the system will be shut down if average motor current is less than 10% of FLA.
Compressor Motor Protection Modules, and Me- chanical High Pressure Cutouts are integral to each system. All of these devices stop the compressor by removing power from the motor contactor coils. This causes the CTs to obviously sense a zero current draw by the compressor motor and causes a Low Motor Cur- rent Fault to be displayed. These devices operate as follows:
The Motor Protection Module protects against ex- cessive motor winding temperature by monitoring sen- sors built into the motor windings. If the temperature becomes excessive, the module will cause power to be removed from the compressor contactors shutting down the compressor. Auto restart will not occur since manual reset by power removal is required. A fault lockout will automatically occur after the micro attempts 2 more starts with the MP contacts open. Manual reset is ac- complished by removing 115VAC control power from the micro panel after the motor sensors have sufficient time to cool. Details relating to operation of the Motor Protection Module can be found on page 16.
The Mechanical High Pressure Cutout protects against excessive refrigerant discharge pressure and is set to 405 PSIG (28 bar).
Low Evaporator Temperature Cutout (R407C Only):
S | Y S | 1 | L O W | E V A P | T E M P |
S | Y S | 2 | L O W | E V A P | T E M P |
|
|
|
|
|
|
The Low Evaporator Temperature Cutout is to protect the evaporator from
FORM
407C units. If the refrigerant temperature falls below 20°F (11.1°C) in water cooling mode, the system will be shut down. If the refrigerant temp falls 15°F (8.3°C) below the leaving chilled liquid temp in glycol cooling mode, the system will shut down. If a malfunctioning or missing evaporator inlet refrigerant temp sensor reads out of range low, the system will also shut down. The low evap temp safety is ignored for the first 3 minutes of operation. After 3 minutes of run time there is a 5 minute Low Evap Temp Safety Bypass Ramp: Any time the evaporator inlet temperature drops below the cutout, the cutout will be lowered 6ºF and ramped up to original value over the next 5 minutes. If the evaporator inlet temperature rises above the original cutout during the ramp, the cutout will be reset to the original value and the ramp will be ended.
2.7PRINTOUT ON FAULT SHUTDOWN
If an optional printer is installed, the contents of His- tory Buffer 1 will be sent to the printer any time a fault shutdown occurs. This will allow record keeping of individual faults, even if they do not cause a lockout of the system. This information may be useful to identify developing problems and troubleshooting.
The No Run Permissive fault messages will not be stored in the History Buffer and will not cause an auto printout.
Due to extreme operating conditions or systems where control deficiencies are present, occasional faults may occur with the corresponding auto- matic printout. This is not a cause for concern.
8
YORK INTERNATIONAL | 143 |
