Surge Protection - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

the control's model of the surge prevention line up. Guide
vanes are not permitted to open further when surge prevention
is on. Once speed has been increased to maximum, if still oper-
ating in the surge prevention region, and if the Hot Gas Bypass
option is installed, the hot gas bypass valve will open. When in
Surge Prevention mode, with a command to decrease capacity
the guide vanes will close but speed will not decrease.
NOTE: If upon ramp-up, a chiller with VFD tends to go to full
speed before guide vanes open fully, it is an indication that the
lift at low load is excessive, and the operating point moved
directly into the surge prevention region. In this case, investi-
gate the ability of the condenser cooling means (e.g., cooling
tower) to provide cooling water in accordance with the design
load/entering condenser water temperature schedule.
A surge condition occurs when the lift becomes so high the
gas flow across the impeller reverses. This condition can
eventually cause chiller damage. When enabled, the Surge
Prevention Algorithm will adjust either the ACTUAL GUIDE
VANE POSITION or ACTUAL VFD SPEED to maintain the
compressor at a safe distance from surge while maintaining
machine efficiency. If the surge condition degrades then the
algorithm will move aggressively away from surge. This
condition can be identified when the SURGE/HGBP ACTIVE?
on the HEAT_EX display screen displays a YES.
The surge prevention algorithm first determines if correc-
tive action is necessary. The algorithm checks two sets of
operator-configured data points, the lower surge point (MIN.
LOAD POINT [T1,P1]) and the upper surge point (FULL
LOAD POINT [T2,P2]). The surge characteristics vary
between different chiller configurations and operating
conditions.
The surge prevention algorithm function and settings are
graphically displayed on Fig. 22 and 23. The two sets of load
points on the graph (default settings are shown) describe a
line the algorithm uses to determine the maximum lift of
the compressor for the design maximum operating speed.
When the actual differential pressure between the cooler and
condenser (delta P) and the temperature difference between the
entering and leaving chilled water (delta T) are above the line
on the graph (as defined by the MIN LOAD POINTS and FULL
LOAD POINTS), the algorithm operates in Surge Prevention
mode. This is determined when the ACTIVE DELTA T is less
than SURGE/HGBP DELTA T minus the SURGE/HGBP
DEADBAND.
When in Surge Prevention mode, with a command to
increase capacity, the VFD speed will increase until VFD
MAXIMUM SPEED is reached. At VFD MAXIMUM SPEED,
when Capacity still needs to increase, the inlet guide vanes
(IGV) open. When in Surge Prevention mode, with a command
to decrease capacity, the IGVs will close. The optional hot gas
bypass will open in surge prevention mode only if the TARGET
VFD SPEED is at the VFD MAXIMUM SPEED.
The PIC III monitors surge, which
Surge Protection —
is detected as a fluctuation in compressor motor amperage.
Each time the fluctuation exceeds an operator-specified limit,
the PIC III registers a surge protection count. The current
fluctuation threshold that triggers a surge protection count is
equal to the sum of SURGE DELTA % AMPS plus the
CHILLED WATER DELTA T. If more than 5 surges occur
within an operator-specified time (SURGE TIME PERIOD),
the PIC III initiates a surge protection shutdown of the chiller.
The SURGE PROTECTION COUNTS remain displayed in the
COMPRESS screen until the alarm is reset, at which time they
are re-zeroed.
If a surge count is registered and if ACTUAL VFD SPEED
is less than VFD MAXIMUM SPEED then motor speed will be
increased by the configured VFD INCREASE STEP. While
the SURGE PROTECTION COUNTS are > 0, a speed decrease
will not be honored.
The portion of the surge count threshold attributable to cur-
rent can be adjusted from the OPTIONS screen (see Table 4).
Scroll down to the SURGE DELTA % AMPS parameter, and
use the
INCREASE
percent current fluctuation. The default setting is 10% amps.
The SURGE TIME PERIOD can also be adjusted from the
OPTIONS screen. Scroll to the SURGE TIME PERIOD
parameter, and use the
to adjust the amount of time. The default setting is 8 minutes.
Access the display screen (COMPRESS) to monitor the
surge count (SURGE PROTECTION COUNTS).
LEGEND
ECW — Entering Chilled Water
HGBP — Hot Gas Bypass
LCW — Leaving Chilled Water
ΔP = (Condenser psi) – (Cooler psi)
ΔT = (ECW) – (LCW)
Fig. 22 — 19XRV Hot Gas Bypass/Surge
Prevention with Default English Settings
LEGEND
ECW — Entering Chilled Water
HGBP — Hot Gas Bypass
LCW — Leaving Chilled Water
ΔP = (Condenser kPa) – (Cooler kPa)
ΔT = (ECW) – (LCW)
Fig. 23 — 19XRV Hot Gas Bypass/Surge
Prevention with Default Metric Settings
46
or softkey to adjust the
DECREASE
or
INCREASE DECREASE
softkey
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