Unit-Mounted Vfd; Vfd Cooling Cycle; Lubrication Cycle - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

2.7 - Unit-mounted VFD

The 19XRV chiller is equipped with a variable-frequency
drive motor controller mounted on the condenser. This VFD
is used with low-voltage motors between 380 and 460 V a.c.
It reduces the starting current inrush by controlling the
voltage and frequency to the compressor motor. Once the
motor has accelerated to minimum speed, the PIC III
modulates the compressor speed and guide vane position to
control chilled water temperature.
Operational parameters and fault codes are displayed
relative to the drive. The display is is also the interface for
entering specific chiller operational parameters. These
parameters have been pre-programmed at the factory.

2.8 - VFD cooling cycle

The unit-mounted variable frequency drive (VFD) is
cooled in a manner similar to the motor and lubricating oil
cooling cycle (Fig. 1).
If equipped with a unit-mounted VFD, the refrigerant line
that feeds the motor cooling and oil cooler also feeds the
heat exchanger on the unit-mounted VFD. Refrigerant is
metered through a solenoid valve at the exit of the VFD
heat exchanger to regulate the flow of refrigerant. The
refrigerant leaving the heat exchanger returns to the cooler.

2.9 - Lubrication cycle

2.9.1 - Summary
The oil pump, oil filter, and oil cooler make up a package
located partially in the transmission casting of the compressor-
motor assembly. The oil is pumped into a filter assembly to
remove foreign particles and is then forced into an oil
cooler heat exchanger where the oil is cooled to proper
operational temperatures. After the oil cooler, part of the
flow is directed to the gears and the high speed shaft
bearings; the remaining flow is directed to the motor shaft
bearings. Oil drains into the transmission oil sump to com-
plete the cycle (Fig. ).
2.9.2 - Details
Oil is charged into the lubrication system through a hand
valve. Two sight glasses in the oil reservoir permit oil level
observation. Normal oil level is between the middle of the
upper sight glass and the top of the lower sight glass when
the compressor is shut down. The oil level should be visible
in at least one of the  sight glasses during operation.
Oil sump temperature is displayed on the ICVC default
screen. During compressor operation oil sump temperature
ranges between 52 to 66°C.
The oil pump suction is fed from the oil reservoir. An oil
pressure relief valve maintains 14 to 17 kPa differential
pressure in the system at the pump discharge. This differential
pressure can be read directly from the ICVC default screen.
The oil pump discharges oil to the oil filter assembly. This
filter can be closed to permit removal of the filter without
draining the entire oil system. The oil is then piped to the
oil cooler. This heat exchanger uses refrigerant from the
condenser as the coolant. The refrigerant cools the oil to a
temperature between 49°C and 60°C.
As the oil leaves the oil cooler, it passes the oil pressure
transducer and the thermal bulb for the refrigerant expansion
valve on the oil cooler. The oil is then divided, with a portion
flowing to the thrust bearing, forward pinion bearing, and
gear spray. The balance then lubricates the motor shaft
bearings and the rear pinion bearing. The oil temperature is
measured as the oil leaves the thrust and forward journal
bearings within the bearing housing. The oil then drains
into the oil reservoir at the base of the compressor. The
PIC III (Product Integrated Control) measures the tempe-
rature of the oil in the sump and maintains the temperature
during shut-down. This temperature is read on the ICVC
default screen.
During the chiller start-up, the PIC III will energise the oil
pump and provide 15 seconds of prelubrication to the bear-
ings after pressure is verified before starting the compressor.
During shut down, the oil pump will run for 60 seconds to
post-lubricate after the compressor shuts down. The oil
pump can also be energised for testing purposes in the
Control Test.
Ramp loading can slow the rate of guide vane opening to
minimise oil foaming at start-up. If the guide vanes open
quickly, the sudden drop in suction pressure can cause any
refrigerant in the oil to flash. The resulting oil foam cannot
be pumped efficiently; therefore, oil pressure falls off and
lubrication is poor. If oil pressure falls below 103 kPa
differential, the PIC III will shut down the compressor.
If the controls are subject to a power failure that lasts more
than 3 hours, the oil pump will be energised periodically
when the power is restored. This helps to eliminate refrige-
rant that has migrated to the oil sump during the power
failure. The controls will energise the pump for 60 seconds
every 30 minutes until the chiller is started.
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