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Annunciators ...............................................................................433
Master Wanting and Annunciator Panel Lights ................................ 434
Learjet 31A
Pilot's Manual
40 4100
SECY909 9V
ELECTRICAL & LIGHTING
DC POWER DISTRIBUTION
Primary electrical power for aircraft and avionics systems requiring DC
power is supplied by two engine-driven, 30-volt, 400-ampere starter/
generators. Secondary DC electrical power is supplied by two 24-volt
lead-acid (standard) or nickel-cadmium (optional) batteries. An external
power receptacle is installed for engine start and stationary ground
operations.
A generator control unit (GCU) is installed for each generator. The
GCU's contain circuits to maintain generator output at approximately
28 VDC throughout varying engine speeds and loads. The GCU's also
contain circuits to equalize generator load during parallel operation,
provide overvoltage protection, and provide current limiting during
ground operations and during generator-assisted cross starts.
During normal operation, the generators supply all aircraft DC power
requirements. Regulated 28 VDC output from the generators is applied
to the respective generatorbuses. The voltage on the generator buses is
applied to the battery charging bus through 275-amp current limiters.
Battery charge is maintained from the battery charging bus through the
battery relays and battery buses. TheDC BUS2and 3 buses in the circuit
breaker panels are powered from the respective generator buses
through 50-amp current limiters. The battery bus in the pilot's circuit
breaker panel is powered from the LH (#i) battery through a 20-amp
current limiter. The battery bus in the copilot's circuit breaker panel is
powered from theRH (#2) battery through a5-amp current limner. The
DC BUS 1 buses in the circuit breaker panels are powered from the respective
generatorbus through an overload sensor and a control relay.
On some aircraft theCABINPWRBUSis installed in the overhead panel
between the two crew members. On other aircraft the CABIN PWR
BUS is installed on the bulkhead behind the pilot. The CABIN PWR
BUS is powered from the battery charging bus through a 50-amp current
limiter and a remote control circuit breaker. The inverters are powered
through overload sensors and control relays . Additionally, aircraft
systems producing heavy loads; such as resistance heaters, large
PM-121
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Change 4
Pilot's Manual
Learjet 31A
lamps, blowers, heavy-duty motors, and heavy-duty pumps, are supplied
power through current limiters connected to either the battery
charging bus or generator buses.
Overload sensors are installed between the DC BUS1 buses and the associated
generator bus. The overload sensors are installed to protect the
DC BUS 1 feeder circuits from an overload . Basically, each overload
sensor is a 70-amp circuit breaker mechanically connected to a switch.
Should an overload condition occur, the circuit breaker will reposition
the switch to deenergize a power relay, thereby disconnecting the DC
BUS 1 bus. Additionally, the switch will apply a ground to trip the affected
Lor R DC BUS 1 circuit breaker. When the overload sensor circuit
breaker cools, the switch will reset; however, the power relay will
not reenergize due to the open Lor RDC BUS 1 circuit breaker. When
the malfunction has been corrected and the affected L or R DC BUS 1
circuit breaker reset, the power relay will reenergize and power to the
DC BUS 1 bus will be restored.
The generators willnot come on-line ifanoperating groundpower unit
is connected to the aircraft.
Across start relaybox is installed which enables an operating generator
to assist in providing power to start the opposite engine . If one generator
is on-line and a start of the opposite engine is initiated, the cross
start relay circuits will cause both left and right starter relays to close.
In effect, this will bypass both battery charging bus 275-amp current
limiters and the output of the operating generator will supplement the
aircraft batteries in providing power for the starter.
An airstart relay box is installed which prevents the EFIS and air data
displays from blanking during airstarts. During an airstart, theRH (#2)
battery is isolated from the battery charging bus and its power is utilized
to keep the EFIS and air data systems powered at full voltage.
When the aircraft is on the ground, operation of the airstart circuits is
inhibited and both batteries will be available to power the starter.
An emergency bus system is installed to simplify load shedding in the
event ofa dual generator failure or cockpit/cabin smoke and/orfumes.
　
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