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Current Limit Protection
Current Limit Protections exist to avoid motor current overload and damage to the
compressor motor during starting and running.
The Current Limit Setpoint (CLS) can be changed from: Front Panel, External Ana-
log input (with GBAS option), or Tracer (Tracer option). Tracer current setpoint has
the highest priority, unless disabled in the Large display ™ Setpoint source override
menu. The External CLS has second priority, and will be used if Tracer is disabled or
not installed. The Front Panel Setpoint has the lowest priority, and will be used if Tracer
and the External CLS are both disabled.
Compressor motor current is continuously monitored and current is controlled using
a limit function to prevent running into overload diagnostic trips. The current limit
control logic attempts to prevent the motor from shutting down on a diagnostic trip
by limiting compressor current draw relative to an adjustable current limit Large dis-
play™ CLS.
This setpoint can also be lowered to provide electrical demand limiting on the unit as
required. This could also be set to allow the chiller to continue to run at a lower load to
avoid tripping off using a diagnostic.
The Current Limit function uses a PID algorithm (similar to the Leaving Water Tempera-
ture control) that allows the chiller to run at the CLS. At machine startup, or with any
setpoint change the new current limit setpoint reached after the filtered setpoint time
elapses. The minimum current limit setpoint is default set to 40 percent RLA (20-100
percent). The filtering time default is set to 10 minutes (0-120 minutes); however these
can be altered using the UT ™. This filtered setpoint allows for stable control if the
Current Limit setpoint is adjusted during a run.
Phase Loss Protection
Loss of phase detection protects the chiller motor from damage due to a single-phas-
ing condition. The controls will shut down the chiller if any of the three phase currents
feeding the motor are lost. The shutdown will result in a latching diagnostic indicating
the failure.
Reverse Rotation Protection
This function protects the compressor from damage caused by being driven in the re-
verse direction. Incorrect phase rotation detection results in a manually resettable di-
agnostic. Phase Reversal protection default is set to enable, however can be disabled
using UT ™.
Differential to Start or Stop
The Differential to Start setpoint is adjustable from 1 to 10°F (0.55 to 5.5°C) and the Dif-
ferential to Stop setpoint adjustable from 1 to 10°F (0.55 to 5.5°C). Both setpoints are
with respect to the Active Chilled Water Setpoint. When the chiller is running and the
Leaving Water Temperature (LWT) reaches the Differential to Stop setpoint the chiller
will go through its shutdown sequence to Auto. Reference Figure 11.
CVGF-SVX03B-EN
Machine Protection and Adaptive Control
105
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