Bryant ASPAS1BBA007, Руководство по диагностике и ремонту

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Page 19
SECTION 1.5
ENGINE-GENERATOR PROTECTIVE DEVICES
GENERAL INFORMATION
GENERAL
Standby electric power generators will often run
unattended for long periods of time. Such operating
parameters as (a) engine oil pressure, (b) engine
temperature, (c) engine operating speed, and (d)
engine cranking and startup are not monitored by an
operator during automatic operation. Because engine
operation will not be monitored, the use of engine
protective safety devices is required to prevent engine
damage in the event of a problem.
Prepackaged generator engines mount several
engine protective devices. These devices work in
conjunction with a circuit board, to protect the engine
against such operating faults as (a) low engine oil
pressure, (b) high temperature, (c) overspeed, and (d)
overcrank. On occurrence of any one or more of
those operating faults, circuit board action will effect
an engine shutdown.
LOW OIL PRESSURE SHUTDOWN:
See Figure 1. An oil pressure switch is mounted on
the engine oil filter adapter. This switch has normally
closed contacts that are held open by engine oil
pressure during cranking and startup. Should oil
pressure drop below approximately 10 psi, the switch
contacts will close. On closure of the switch contacts,
a Wire 86 circuit from the circuit board will be
connected to ground. Circuit board action will then de-
energize a "run relay" (on the circuit board). The run
relay's normally open contacts will then open and a
12 volts DC power supply to a Wire 14 circuit will then
be terminated. This will result in closure of a fuel
shutoff solenoid and loss of engine ignition.
HIGH OIL TEMPERATURE SHUTDOWN:
An oil temperature switch (Figure 1) is mounted on
the engine block. The thermal switch has normally
open contacts that will close if oil temperature should
exceed approximately 284° F (140° C). This will result
in the same action as a low oil pressure shutdown.
OVERSPEED SHUTDOWN:
During engine cranking and operation, the circuit
board receives AC voltage and frequency signals
from the generator engine run windings, via Wire 66A.
Should the AC frequency exceed approximately 72Hz
(4320 rpm), circuit board action will de-energize a
"run relay" (mounted on the circuit board). The relay's
contacts will open, to terminate engine ignition and
close a fuel shutoff solenoid. The engine will then
shut down. This feature protects the engine-generator
against damaging overspeeds.
NOTE: The circuit board also uses engine run
winding output to terminate engine cranking at
approximately 30 Hz (1800 rpm). In addition, the
engine run winding output is used by the circuit
board as an "engine running" signal The circuit
board will not initiate transfer of electrical loads
to the "Standby" source unless the engine is
running at 30 Hz or above.
Figure 1. Engine Protective Switches on an
Air-Cooled Engine
OVERCRANK SHUTDOWN:
Automatic engine cranking and startup normally
occurs when the circuit board senses that utility
source voltage has dropped below approximately 60
percent of its nominal rated voltage and remains at
that low level longer than fifteen (15) seconds. At the
end of fifteen (15) seconds, circuit board action will
energize a crank relay and a run relay (both relays
are on the circuit board). On closure of the crank relay
contacts, circuit board action will deliver 12 volts DC
to a starter contactor relay (SCR, for v-twin models)
or a starter contactor (SC, for single cylinder models).
The control contactor will energize and battery power
will be delivered to the starter motor (SM). The engine
will then crank.
During a manual startup (Auto-Off-Manual switch at
MANUAL), action is the same as during an automatic
start, except that cranking will begin immediately
when the switch is set to MANUAL.
Circuit board action (during both a manual and an
automatic start) will hold the crank relay energized for
15 seconds on. The relay will then de-energize for 15
seconds off. It will then energize for seven (7)
seconds on and de-energize for seven (7) seconds
off. It will repeat this same cycle for another 45
seconds.
If the engine has not started after approximately 90
seconds of these crank-rest cycles, cranking will
automatically terminate and shutdown will occur. The
circuit board uses AC signals from the stator engine
run winding as an indication that the engine has
started.
PART 1