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SECTION IX
APPE~DIX
9.1 DETAILED THEORY OF OPERATION
9.1.1 AC Power and Protective Circuits
Three phase AC power is brought into the top of the circuit breaker
in each cabinet.
This circuit breaker is one of the main protective
devices in the system.
It has two internal power shutdown (circuit
breaker trip) modes.
The two modes of protection are thermal trip
and magnetic trip due to high current.
From the circuit breaker the three phase power goes to four places.
It supplies power to the variable speed motor starter (MAl) and the
constant speed motor starter (MA2).
Operation of the KXA motor
thermal protection or the conversion module heat sink thermal pro-
tection will drop out starter
"MAl"
removing AC power.
Operation
of one of the constant speed motor overload heaters will drop out
starter
"MAl"
removing its power.
Operation of system protective
switches such as the zero suction pressure
~witch
will drop out
both starters.
The circuit
breake~
also supplies power to the
Synchronizing Transformer Assembly (STA) which in turn is re-
sponsible for all timing relationships in the system.
Lastly AC
power is supplied to the Control Power Transformer (CPT) which in
turn supplies the 11SVAC power for the control circuitry and its
associat~d
control relays.
The control power transformer also
supplies ll5VAC to the STA which in turn supplies 25VAC input to
the ±20V power
supply~card.
9.1.2
Command and Logic Circuits
The command and logic portion of the system will be divided into
two parts;
(1)
command, such as start/stop or transfer, and
(2)
logic, which is the command that initiates a series of actions.
The
command functions of the system are as follows:
Start, Stop, No.
1
Pump Auto, No.2 Pump, Foreign Circuit ON-OFF, and the Manual Speed
Control.
The logic is a series of actions that occur from a command of the
system; i.e., the logic behind the start command (pressing the start
button) tirggers the following series of actions:
the start button
picks up the run relay.
A normally open (N.O.) interlock on the run
relay closes around the start button, thereby sealing the circuit
closed, when the start button is released.
These contacts also supply
the voltage to the Power On indicator.
If a fault or trouble exists in the system neither starter
"MAIII
nor "MAl" will be allowed to energize.
If the KXA motor thermal
switch or the conversion module thermal switch operate the IlMAl"
9-1
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