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FORM 160.54-M1
ISSUE DATE: 10/25/2019
SECTION 12 - CURRENT MODULE (CM-2)
On applications where the Compressor Motor is con-
trolled by an Electromechanical Starter, the OptiView
Control Center is equipped with a current module. The
Current Module provides compressor motor Overload
and Power Fault protection. The Current Module also
provides an analog voltage representing the compressor
motor current to the microboard for display and cur-
rent limit control. While the chiller is running, the mi-
croboard controls the Pre-rotation Vane (PRV) position
to limit the motor current to the system 100% Full Load
Amp (FLA) value.
The contacts of Current Module K1 relay (identified as
CM contacts on the OptiView Control Center wiring
diagram) are interfaced into the Motor Controller initi-
ated shutdown circuit that is located between OptiView
Control Center TB6-53 and I/O Board TB1-16 (See
Figure 37 on page 104 and Figure 55 on page 131).
They are also connected as a Digital Input to I/O Board
J2-1. Relay K1 is normally energized, maintaining its
contacts in a closed position. Whenever the Current
Module initiates a chiller shutdown, it de-energizes
K1, opening its contacts. This interrupts the circuit
to I/O Expansion Board RUN relay coil 1R (K18),
de-energizing it and causing the Starter to shutdown.
Simultaneously, the microboard reads the opening of
these contacts via I/O Board J2-1, initiates a System
Coastdown and displays the appropriate message as
described below.
Three current transformers in the compressor motor
terminal box (See Figure 56 on page 132) provide 3
phase motor current signals to the Diode Bridge (DB).
The required turns ratio of the Current Transformers
is determined by the system 100% FLA. The Diode
Bridge rectifies and combines the three signals into one
DC signal that is applied to the parallel Variable Resis-
tors (RES). These are factory adjusted (field adjusted
on service replacements) to provide a nominal 1.0 VDC
(0.15 to 1.10 VDC) signal to the Current Module at
J1-1 and J1-2 when the compressor motor current is at
100% FLA. Figure 56 on page 132 contains a formula
to calculate the resistance of RES required to achieve
1.0 VDC at 100%FLA. The 100% FLA value is located
on a label adhered to the inside of the OptiView Con-
trol Center door.
The motor current signal input at J1-1 and J1-2 is ap-
plied to potentiometer R8. This is factory adjusted
(field adjusted on service replacements) to illuminate
the 105% CURR indicator (CR6) when the compressor
JOHNSON CONTROLS
motor current reaches 105% FLA. This calibrated volt-
age is applied to the Power Fault detector, Overload
detectors and Multiplexer (MUX).
The power fault circuit protects the compressor motor
and driveline from transient torque damage. It antici-
pates the transient torque condition by detecting a mo-
mentary interruption in motor current and de-energiz-
ing the starter before damage can occur. If the chiller
has been running for greater than 75 seconds and the
motor current decreases to less than or equal to 10%
FLA, a Power Fault shutdown is initiated. The Power
Fault indicator (CR5) is illuminated and remains illu-
minated until manually reset with RESET switch S2.
Relay K1 is de-energized for 1 second and then re-
turned to the energized state. Relay K1 contacts (CM)
open for 1 second and then return to the closed state.
A System Coastdown is initiated and POWER FAULT
is displayed on the Display. The chiller will automati-
cally restart upon completion of System Coastdown.
If the motor current remains continuously at greater
than or equal to 105% FLA for 50 seconds (Nominal),
an OVERLOAD shutdown is initiated. The Overload
indicator (CR4) is illuminated and remains illuminated
until manually reset with RESET switch S2. Relay K1
is de-energized, opening K1 contacts (CM). Relay K1
remains de-energized until manually reset with RE-
SET switch S2. A System Coastdown is initiated and
MOTOR CONTROLLER - CONTACTS OPEN is
displayed. The chiller cannot be started until RESET
switch S2 is manually pressed.
If the motor current remains continuously at 245% FLA
for 40 seconds, 290% FLA for 20 seconds or 360%
FLA for 10 seconds, an OVERLOAD shutdown is ini-
tiated. Relay K1 and Overload indicator CR4 operate as
described immediately above. A System Coastdown is
initiated and MOTOR CONTROLLER - CONTACTS
OPEN is displayed. The chiller cannot be restarted
until RESET switch is manually pressed. LRA/FLA
potentiometer R16 is factory adjusted (field adjusted
on service replacements) to the ratio of Locked Rotor
Amps to Full Load Amps. The correct setting is deter-
mined by dividing the LRA by the FLA. If Switch S1 is
in the "Y-Delta/57%" position, there is no 245% FLA
threshold. Switch S1 must be positioned according to
the type of Electromechanical Starter present; UP for
Y-delta or 57% Autotransformer starters, DOWN for
all other starters.
JCI COMPANY CONFIDENTIAL
12
129
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