#:
This event was discussed with System Engineering and the HVAC Maintenance personnel. No
new issues were raised during the review of this event. Being mindful of plant conditions and the
effect on the running chiller is important. No other actions have been identified during this adverse
CRDR evaluation.
CRDR 2553858 Documents that several of the normal chillers have tripped due to low lube
oil pressure.
The description of the event:
There is an increasing trend for the normal chillers to trip when the chillers are started after being
in standby for a while. The chillers start normally and then trip due to a low oil differential trip after a
few minutes of operation.
Histor y:
The 800 Ton 19FA Carrier chillers were converted from R-12 to R-134a over the last few years
under D MWO # 218621. The last chiller conversion w as completed early in 2002. The mineral oil
used in the chillers was replaced with a synthetic polyol ester (POE) oil that is compatible w ith the
new refrigerant.
There is noticeably more foaming when pulling an oil sample from a machine with the new POE oil.
The oil sample is cold to the touch even though the sump temperature is above 140°F. There are
times when we have noticed that the oil differential pressure fluctuates on chiller startup and
settles out after several minutes of operation. Pressure fluctuations are attributed to refrigerant
absorption in the oil.
Normal chiller 1MWCNE01C has been converted to R-134a and later had a modification that
installed a new microprocessor control panel (D MWO # 219505). C arrier made the microproces sor
control panel for the R-134a machine with the oil controller set between 150°F and 160°F in the
program scheme. We have seen less forming of the oil in the Unit 1 C chiller because of the higher
temperature.
Normal chiller 1MWCNE01C has been in operation with the new control panel for about two years.
A review by Palo Verde’s Lube Engineer found that there has been no difference in the oil samples
from all the normal chillers during this time. There is no indication that elevated sump temperature
has a negative impact on the POE oil. Raising the normal chiller sump temperature to control
between 150°F to 160°F should help drive the R-134a refrigerant from the POE oil as it sits in the
chiller sump as well as reduce the number of nuisance trips due to oil pressure differential. This will
also ensure the chiller lubricating system delivers the needed lubrication to the chiller bearings
during initial startup and while operating.
DMWO # 2569741 changes the oil sump temperature setpoint from 145°F ± 5°F to 155°F ± 5°F. This change will be
implemented on the 800 Ton normal chillers 13MWCNE01A, B, and 23MWCNE01C.
(36 pagine)
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