Vfd Cooling Cycle; Lubrication Cycle; Details; Oil Reclaim System - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

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. 3).
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 thermostatic expansion valve (TXV). To maintain
proper operating temperature in the VFD, the TXV bulb is
mounted to the heat exchanger to regulate the flow of refdger-
ant. The refdgerant leaving the heat exchanger returns to the
coolel:
LUBRICATION CYCLE
Summary
-- The oil pump, oil filtel; and oil cooler make
up a package located p_utially in the transmission casing 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 gems and the high speed shaft bearings; the
remaining flow is directed to the motor shaft bearings. Oil
drains into the transmission oil sump to complete the cycle
(Fig. 4).
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 2 sight glasses during operation. Oil sump
temperature is displayed on the ICVC (International Chiller
Visual Controller) default screen. During compressor opera-
tion, the oil sump temperature ranges between 125 and 150 F
(52 and 66 C).
The oil pump suction is fed from the oil reservoil: An oil
pressure relief valve maintains 18 to 30 psid (124 to 207 kPad)
differential pressure in the system at the pump discharge. The
normal oil pressme on compressors equipped with rolling
element bearings is between 18 and 40 psid (124 and
276 kPad). This diffelential pressure can be read directly from
the [CVC default scleen. The oil pump discharges oil to the oil
filter assembly. This filter can be closed to permit removal of
the filter without dnfining the entire oil system (see Mainte-
nance sections, pages 75 to 78, for details). The oil is then
piped to the oil cooler heat exchangel: The oil cooler uses
refrigerant from the condenser as the coolant. The refrigerant
cools the oil to a temperature between 120 and 140 F (49 and
60 C).
As the oil leaves the oil cooler, it passes the oil pressure
transducer and the thermal bulb for the refrigerant expansion
vNve on the oil cooler The oil is then divided. Pro1 of the oil
flows to the thrust bearing, %rward pinion bearing, and gear
spray. The rest of the oil lubricates the motor shaft bearings and
the rear pinion beming. The oil temperature is measured in the
bearing housing as it leaves the thrust and forwaN journal
bearings. The outer bearing race temperature is measured on
compressors with rolling element bemings. The oil then drains
into the oil reservoir at the base of the compmssol: The PIC III
(Product Integrated Control III) measures the temperature of
the oil in the sump and maintNns the temperature during shut-
down (see Oil Sump Temperature and Pump Control section,
page 39). This temperature is mad on the ICVC default screen.
Dudng chiller stmt-up, the PIC Ill energizes the oil pump
and provides 45 seconds of pro-lubrication to the be_uings after
pressure is verified before starting the compressor During
shutdown, the oil pump will mn for 60 seconds to post-
lubricate after the compressor shuts down. The oil pump can
also be energized for testing purposes during a Control Test.
Ramp loading can slow the rate of guide vane opening to
minimize oil foaming at st_ut-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 foaln cannot be
pumped efficiently; therefore, oil pressure falls off and lubrica-
tion is pool: If oil pressure falls below 15 psid (103 kPad)
differential, the PIC III will shut down the compressol:
If the controls me subject to a power failure that lasts more
than 3 hours, the oil pump will be energized periodically when
the power is restored. This helps to eliminate lefrigerant that
has migrated to the oil sump during the power failure. The
controls energize the pump for 30 seconds every 30 minutes
until the chiller is started.
Oil Reclaim System
--
The oil reclaim system returns
oil lost from the compressor housing back to the oil reservoir
by recovering the oil from 2 meas on the chillel: The guide
vane housing is the primary area of recovery. Oil is also recov-
ered by skimming it from the operating refrigerant level in the
cooler vessel.
PRIMARY OIL RECOVERY MODE -- Oil is normally re-
covered through the guide vane housing on the chillel: This is
possible because oil is normally entrained with refrigerant in
the chillel: As the compressor pulls the refrigerant up from the
cooler into the guide vane housing to be compressed, the oil
norm_dly drops out at this point and falls to the bottom of the
guide vane housing where it accumulates. Using discharge gas
pressure to power an eductol: the oil is diawn from the housing
and is dischmged into the oil reservoil:
SECONDARY OIL RECOVERY METHOD -- The sec-
on&try method of oil recovery is significant under light load
conditions, when the refrigerant going up to the compressor
suction does not have enough velocity to bring oil along. Under
these conditions, oil collects in a greater concentration at the
top level of the refrigerant in the coolel: This oil and refrigerant
mixture is skimmed from the side of the cooler and is then
drawn up to the guide vane housing. There is a filter in this line.
Because the guide vane housing pressure is much lower than
the cooler pressure, the refrigerant boils off. leaving the oil
behind to be collected by the primary oil recovery method.
Bearings -- The 19XRV compressor assemblies include
four radi_d bemings and four thrust bearings. The low speed
shaft assembly is suppolled by two journal bemings located
between the motor rotor and the bull gem: The bearing closer to
the rotor includes a babbitted thrust face which opposes the
normal axial forces which tend to pull the assembly towmds
the transmission. The beming closer to the bull gear includes a
smaller babbitted thrust face, designed to handle counterthmst
forces.
For most 19XRV compressors the high speed shaft assem-
bly is supported by two journal bearings located at the
transmission end and mid-span, behind the labyrinth seal. The
transmission side of the midspan bearing _dso contains a tilting
shoe type thrust beming which opposes the main axkd forces
tending to pull the impeller towards the suction end. The
impeller side face of the midspan bearing includes a babbitted
thrust face, designed to handle counterthrust forces.
For 19XRV Frmne 3 compressors built since mid-2001, the
high speed shaft assembly has been redesigned to utilize rolling
element bearings (radial and thrust). Machines employing the
rolling element bearings can be expected to have higher oil
pressure and thrust beming temperatures than those compres-
sors using the alternate bearing design.