203
JOHNSON CONTROLS
FORM 201.21-NM4 (1020)
203
JOHNSON CONTROLS
8
VSD SAFETIES (FAULTS) (CON'T)
Motor Current Overload (Software) Fault
The Motor Current Overload will compare the highest
of the 3 phases of motor current per compressor to the
compressor’s 105 % FLA ADJUST (overload) potenti-
ometer setting on the VSD Logic Board. If the current
exceeds the setting continuously for 20 seconds, the
compressor will trip.
This safety will lock out a system on the 1st fault and
shut down with a controlled ramped shutdown. The
fault will be an individual system/compressor fault for
all systems. A sample Status display fault is shown
below:
X indicates the system and YYYYYYY indicates the
system is in a “LOCKOUT” condition and will not
restart until the operator clears the fault using the key-
pad.
Motor Current Overload (Hardware) Fault
The Motor Current Overload will compare the highest
of the 3 phases of motor current per compressor to the
compressor’s overload ADJUST potentiometer setting.
If the current exceeds the setting continuously for 30
seconds, all compressors will fault and shut down im-
mediately.
The fault will be a unit fault and will lock out all sys-
tems on the first fault. A sample Status display fault is
shown below:
SYS X YYYYYYYY MOTOR CURRENT OVERLOAD
YYYYYYYY indicates the unit is in a "Lockout" con-
dition and will not restart until the operator clears the
fault using the keypad.
UNIT YYYYYYYY
MOTOR CURRENT OVERLOAD
IGBT GATE DRIVER (HARDWARE) FAULT
The unit’s phase bank assembly(s) contains one IGBT
gate driver control board per compressor. These boards
monitor the saturation voltage drop across each of the
six IGBT’s while gated on. If the IGBT’s saturation
voltage exceeds the prescribed limit, the gate driver will
make the determination that a short circuit is present.
This in turn will cause the system to trip. During normal
operation, the voltage drop across a saturated IGBT is
low. When a short or shoot occurs, the extremely high
current causes the voltage across the device to increase.
When the electronic hardware on the IGBT Gate Driver
Board senses the current rise, it immediately turns off
all IGBT’s in the module and the system will shut down
immediately.
Additionally, if the IGBT’s Gate Driver board’s power
supply voltage falls below the permissible limit, this
same fault will be generated.
This is an auto-restart safety that will lock out on the 3rd
fault in 90 minutes. The fault will be a system fault for
all units. Following is the Status display fault messages
for all systems.
X indicates the system and YYYYYYY indicates the
system is in a “FAULT” condition and will restart or
“LOCKOUT” and will not restart until the operator
clears the fault using the keypad.
High Baseplate Temperature (Software) Fault
Each phase bank assembly contains one liquid cooled
heatsink to cool both the inverter power modules and
the converter SCR/Diode modules. Each compressor’s
inverter power module (6 IGBT’s & Gate Driver Board)
contains an internal temperature sensor (5K ohm at 25
Deg. °C) to monitor the baseplate temperature.
SYS X YYYYYYYY GATE DRIVER
