Section 11 - Current Module (Cm-2) - Johnson Controls YORK OPTIVIEW YK Series Service Instructions Manual

FORM 160.54-M1

SECTION 11 - CURRENT MODULE (CM-2)

On applications where the Compressor Motor is con-
trolled by an Electro-Mechanical Starter, the OptiV-
iew™ Control Center is equipped with a current module.
The Current Module provides compressor motor Over-
load and Power Fault protection. The Current Module
also provides an analog voltage representing the com-
pressor motor current to the microboard for display and
current limit control. While the chiller is running, the
microboard controls the Pre-rotation Vane (PRV) posi-
tion 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 OptiV-
iew™ Control Center TB6-53 and I/O Board TB1-16
(Refer to Figure 29 on Page 78 and Figure 46 on
Page 105). They are also connected as a Digital In-
put to I/O Board J2-1. Relay K1 is normally energized,
maintaining its contacts in a closed position. When-
ever the Current Module initiates a chiller shutdown,
it de-energizes K1, opening its contacts. This inter-
rupts 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 mes-
sage as described below.
Three current transformers in the compressor motor
terminal box (Refer to Figure 47 on Page 106) pro-
vide 3 phase motor current signals to the Diode Bridge
(DB). The required turns ratio of the Current Trans-
formers 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 Vari-
able Resistors (RES). These are factory adjusted (field
adjusted on service replacements) to provide a nominal
1.0VDC (0.15 to 1.10VDC) signal to the Current Mod-
ule at J1-1 and J1-2 when the compressor motor cur-
rent is at 100% FLA. Figure 47 on Page 106 contains
a formula to calculate the resistance of RES required to
achieve 1.0VDC at 100%FLA. The 100% FLA value
is located on a label adhered to the inside of the OptiV-
iew™ Control 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 Electro-Mechanical Starter present; UP for
Y-delta or 57% Autotransformer starters, DOWN for
all other starters.
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