Trane CVGF - Manual (Page 16)

CTV-PRC001-GB 1 6
Controls
Standard
Protections
Tracer ™ Chiller Controller
The chiller controller uses proportional-
integral-derivative (PID) control for all
limits—there is no dead band. This
removes oscillation above and below
setpoints and extends the capabilities
of the chiller.
Some of the standard protection
features of the chiller controller are
described in this section. There are
additional protection features not listed
here.
High Condenser-Pressure Protection
The chiller controller’s condenser limit
keeps the condenser pressure under a
specified maximum pressure. The
chiller runs all the way up to 100
percent of the setpoint before reducing
capacity using its adaptive control
mode.
Starter-Contactor Failure Protection
The chiller will protect itself from a
starter failure that prevents the
compressor motor from disconnecting
from the line to the limits of its
capabilities.
The controller starts and stops the
chiller through the starter. If the starter
malfunctions and does not disconnect
the compressor motor from the line
when requested, the controller will
recognize the fault and attempt to
protect the chiller by operating the
evaporator-and condenser-water
pumps and attempting to unload the
compressor.
Loss of Water-Flow Protection
The chiller controller has an input that
will accept a contact closure from a
proof-of-flow device such as a flow
switch or pressure switch. Customer
wiring diagrams also suggest that the
flow switch be wired in series with the
cooling-water (condenser-water) pump
starter’s auxiliary contacts. When this
input does not prove flow within a
fixed time during the transition from
Stop to Auto modes of the chiller, or if
the flow is lost while the chiller is in the
Auto mode of operation, the chiller will
be inhibited from running by a
nonlatching diagnostic.
Evaporator Limit Protection
Evaporator Limit is a control algorithm
that prevents the chiller tripping on its
low refrigerant-temperature cutout. The
machine may run up to the limit but
not trip. Under these conditions the
intended chilled-water setpoint may
not be met, but the chiller will do as
much as it can. The chiller will deliver
as much cold water as possible even
under adverse conditions.
Low Evaporator-Water Temperature
Low evaporator-water temperature
protection, also known as Freeze Stat
protection, avoids water freezing in the
evaporator by immediately shutting
down the chiller and attempting to
operate the chilled-water pump. This
protection is somewhat redundant with
the Evaporator Limit protection, and
prevents freezing in the event of
extreme errors in the evaporator-
refrigerant temperature sensor.
The cutout setting should be based on
the percentage of antifreeze used in the
customer’s water loop. The chiller’s
operation and maintenance
documentation provides the necessary
information for percent antifreeze and
suggests leaving-water temperature-
cutout settings for a given chilled-water
temperature setpoint.
Oil-Temperature Protection
Low oil temperature when the oil
pump and/or compressor are running
may be an indication of refrigerant
diluting the oil. If the oil temperature is
at or below the low oil-temperature
setpoint, the compressor is shut down
on a latching diagnostic and cannot be
started. The diagnostic is reported at
the user interface. The oil heaters are
energized in an attempt to raise the oil
temperature above the low oil-
temperature setpoint.
High oil-temperature protection is
used to avoid overheating the oil and
the bearings.
Low Differential Oil-Pressure
Protection
Oil pressure is indicative of oil flow and
active oil-pump operation. A significant
drop in oil pressure indicates a failure
of the oil pump, oil leakage, or other
blockage in the oil-circuit.
The differential pressure during oil
pump, compressor prelube mode
should not fall below 12 psid. A failure
on this parameter generates a shutdown
diagnostic. When the compressor is
running, a diagnostic is issued when
the differential pressure is lost.
Phase-Unbalance Protection
Phase-unbalance protection is based
on an average of the three phase-
current inputs. The ultimate
phase-unbalance trip point is 30
percent. In addition, the RLA of the
motor is derated by resetting the active
current-limit setpoint based on the
current unbalance. The RLA derate
protection can be disabled in the field-
startup menu.
The following derates apply when the
phase-unbalance limit is enabled:
10% unbalance = 100% RLA derate
15% unbalance = 90% RLA derate
20% unbalance = 85% RLA derate
25% unbalance = 80% RLA derate
30% unbalance = Shutdown
Phase-Loss Protection
The controller will shut down the chiller
if any of the three phase currents
feeding the motor drop below 10
percent RLA. The shutdown will result
in a latching phase-loss diagnostic. The
time to trip is 1 second at minimum, 3
seconds maximum.
Phase Reversal/Rotation Protection
The controller detects reverse phase
rotation and provides a latching
diagnostic when it is detected. The time
to trip is 0.7 seconds. Phase-rotation
protection can be disabled in TechView.