York SSS 7L-B, Руководство по эксплуатации

Страница: 11 / 40

JOHNSON CONTROLS
11
SECTION 1 – THEORY OF OPERATION
FORM 160.00-O2
ISSUE DATE: 04/30/2019
1
GENERAL
The Style B LCSSS provides a soft continuous-current
start for the compressor motor. During the starting se-
quence, the inrush motor current is limited to the pro-
grammed value of the starting current, by reducing the
voltage applied to the motor. This reduction in voltage
is accomplished when the silicon controlled rectifiers
(SCRs) are turning on in a “phase-back” technique
during motor acceleration. The trigger portion of the
Logic/Trigger Board provides the firing (Turn-ON)
pulses to the SCRs based upon a control voltage
(VCON or Delay angle) provided by the Logic portion
of the Logic/Trigger Board located in the Solid State
Starter cabinet. After the motor has accelerated to syn-
chronous speed, the SCRs are turned full on to conduct
the full AC line voltage to the motor.
The Logic/Trigger Board provides safety functions
to protect the compressor motor and the starter from
many different conditions, such as high and low AC
line voltage problems, high motor current, and pos-
sible SCR failure.
In order to reduce size of the starter, the cooling
to the SCR assemblies is provided by a water-to-
water heat exchanger between the chiller condenser
water loop and the coolant in the closed loop. The
heat exchanger length has been reduced and is now
mounted on the starter itself. To reduce the length
of the heat exchanger, the diameter of the tube has
been increased.
SYSTEM MICROPROCESSORS
The system microprocessors have back-up protection
in case they fail to function. A watch dog circuit is
used, in which, the system microprocessor will strobe
an output at a regular time interval. If the output strobe
is missing, the Logic/Trigger Board will safely shut
down the chiller. Another back-up circuit requires that
the LCSSS receive a hardware and software signal
from the OptiView Control Center, for the chiller to
be started. If the two signals are not received within a
certain period of time, a shutdown will occur.
TT
SCR
ASSY.
TT
SCR
ASSY.
TT
SCR
ASSY.
OA
OB
OC
CURRENT
TRANSFORMERS
CONTROL
POWER
XFMR
LOGIC/TRIGGER BOARD
MOTOR
CURRENT
115VAC
CONTROL POWER TO
OPTIVIEW CONTROL CENTER
COOLANT
PUMP
POWER
SUPPLY
I/O
BOARD
MICRO
BOARD
STARTER INITIATED SHUTDOWN
SERIAL COMMUNICATIONS LINK
OPTIVIEW
CONTROL
CENTER
HEATSINK
TEMP.
COMPRESSOR
MOTOR
FIGURE 2 - LCSSS – BASIC BLOCK DIAGRAM
LD05246