Guardian 4389 Repair Manual page 25

GENERAL INFORMATION
INTRODUCTION
When the prepackaged generator is installed in
conjunction with a prepackaged transfer switch,
either manual or automatic operation is possible.
Manual transfer and engine startup, as well as
manual shutdown and retransfer are covered in
Section 1.6. Selection of fully automatic operation is
also discussed in that section. This section will pro-
vide a step-by-step description of the sequence of
events that will occur during automatic operation of
the system.
AUTOMATIC OPERATING SEQUENCES
PHASE 1 - UTILITY VOLTAGE AVAILABLE:
With utility source voltage available to the transfer
switch, that source voltage is sensed by a circuit
board in the generator panel and the circuit board
takes no action.
Electrical loads are powered by the utility source and
the AUTO-OFF-MANUAL switch is set to AUTO.
PHASE 2 - UTILITY VOLTAGE DROPOUT:
If a dropout in utility source voltage should occur
below about 60 percent of the nominal utility source
voltage, a 15 second timer on the circuit board will
start timing. This timer is required to prevent false
generator starts that might be caused by transient util-
ity voltage dips.
PHASE 3 - ENGINE CRANKING:
When the circuit board's 15 second timer has finished
timing and if utility source voltage is still below 60 per-
cent of the nominal source voltage, circuit board
action will energize a crank relay and a run relay.
Both of these relays are mounted on the circuit board.
If the engine starts, cranking will terminate when gen-
erator AC output frequency reaches approximately
30 Hz.
PART 1
AUTOMATIC OPERATING PARAMETERS
PHASE 4 - ENGINE STARTUP AND RUNNING:
The circuit board senses that the engine is running by
receiving a voltage/frequency signal from the engine
run windings.
When generator AC frequency reaches approximate-
ly 30 Hz, an engine warm-up timer on the circuit
board turns on. That timer will run for about ten (10)
seconds.
The engine warm-up timer lets the engine warm-up
and stabilize before transfer to the "Standby" source
can occur.
NOTE: The engine can be shut down manually at
any time, by setting the AUTO-OFF-MANUAL
switch to OFF.
PHASE 5 - TRANSFER TO "STANDBY":
When the circuit board's engine warm-up timer has
timed out and AC voltage has reached 50 percent of
the nominal rated voltage, circuit board action com-
pletes a transfer relay circuit to ground. The transfer
relay is housed in the prepackaged transfer switch
enclosure.
The transfer relay energizes and transfer of loads to
the "Standby" power source occurs. Loads are now
powered by standby generator AC output.
PHASE 6 - "UTILITY" POWER RESTORED:
When utility source voltage is restored above about
80 percent of the nominal supply voltage, a 15 sec-
ond timer on the circuit board starts timing. If utility
voltage remains sufficiently high at the end of 15 sec-
onds, retransfer can occur.
PHASE 7 - RETRANSFER BACK TO "UTILITY":
At the end of the 15 second delay, circuit board action
will open a circuit to a transfer relay (housed in the
transfer switch). The transfer relay will then de-ener-
gize and retransfer back to the utility source will
occur. Loads are now powered by utility source
power. On retransfer, an engine cool-down timer
starts timing and will run for about one (1) minute.
PHASE 8 - GENERATOR SHUTDOWN:
When the engine cool-down timer has finished timing,
and if the minimum run timer has timed out, engine
shutdown will occur.
SECTION 1.7
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