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SECTION 4.2
OPERATIONAL ANALYSIS
PART 4
DC CONTROL
UTILITY VOLTAGE RESTORED / RE-
TRANSFER TO UTILITY
The "Load" is powered by the "Standby" power
supply. The circuit board continues to seek an
acceptable "Utility" source voltage. On restoration of
"Utility" source voltage, the following events will
occur:
• On restoration of utility source voltage above 80
percent of the nominal rated voltage, a "retransfer
time delay" on the circuit board starts timing. The
timer will run for about fifteen (15) seconds.
• At the end of fifteen (15) seconds, the "retransfer
time delay" will stop timing and circuit board action
will open the Wire 23 circuit to ground. The transfer
relay (TR) will then de-energize.
• When the transfer relay (TR) de-energizes, its
normally-closed contacts close. "Utility" source
voltage is then delivered to the utility closing coil
(C1), via Wires N1A/N2A, the closed TR contacts,
Wire 126, limit switch XA1, and a bridge rectifier.
• The utility closing coil (C1) energizes and moves
the main current carrying contacts to their "Neutral"
position. The main contacts move to an over center
DUAL SEC.
ALT. EXCITATIO
E 7.
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