York SSS 7L-B, Operation Manual

Page: 12 / 40

JOHNSON CONTROLS
12
FORM 160.00-O2
ISSUE DATE: 04/30/2019
SECTION 1 – THEORY OF OPERATION
The main system microprocessor performs many func-
tions. It provides the serial communications link be-
tween the Logic/Trigger Board, and the Micro Board
in the OptiView Control Center. It determines the
proper current scaling for the size of starter, and in-
terrogates the RUN/STOP signal from the OptiView
Control Center. This processor also interrogates feed-
back signals to determine Open and Shorted SCR,
Phase Loss, Phase Rotation, Motor Overload, High In-
stantaneous Current, High Line Voltage, and Low Line
Voltage shutdowns.
The VCON signal is generated by the main system
microprocessor. It is a digital signal placed on the
data bus. This processor compares the starting current
value, programmed at the OptiView Control Center,
with the current feedback from the three output cur-
rent transformers. A new value of VCON is generated
every line cycle. This signal is then sent to the pro-
grammable logic device (PLD). The PLD determines
the proper firing order for the SCRs to maintain the
programmed starting current value. As the speed of
the motor approaches synchronous speed output cur-
rent drops off, the VCON value increases, and the PLD
turns the SCRs full on. The output of the PLD is sent
to a digital driver chip and then to six optical couplers,
one for each SCR.
The optical couplers are the first stage of the trigger
portion of the Logic/Trigger Board. They isolate the
high power circuit from the low power circuit. The
power for the high power circuit is supplied from the
J5 connector. The trigger section is made up of six out-
put drivers, one for each SCR. Each output driver has
a dedicated transformer, that steps down the incoming
voltage, and provides isolation between each output
driver.
A digital signal processor (DSP) is used for many
timing and calculation functions. Root Mean Square
(RMS) calculations require that input line voltage and
output current values be calculated on a cycle-by-cycle
basis. These calculations are used to display the RMS
voltage and current for each phase, kW, and kWh on
the OptiView Control Center. The DSP is also used
to interpret the feedback signals from the thermistors
mounted on the SCR’s assemblies. All of these values
are placed on the data bus for the main system micro-
processor to generate faults, if required, and to send
data on to the OptiView Control Center via the serial
communication link.
FIGURE 3 - LCSSS – REAR VIEW, EXTERIOR
PIPE
PLUG
WATER
RESERVOIR
WATER
PUMP
DRAIN CAP
HEAT EXCHANGER
00284VIP