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maximum speed of 12,000 RPM. When on-speed, the motor-generator
provides 5 kVA of 115 VAC, 400 Hz power to the TRU for the Essential DC
bus. It also supplies 50 amperes of filtered 28 VDC power to the E-inverter
for Phase A of the Essential AC bus.
The GCU serves to regulate motor-generator voltage and provide
generator field excitation. Deviations of output voltage and frequency from
reference values causes the GCU to apply corrective signals or, if
necessary, disconnect generator output altogether.
The STANDBY ELECTRICAL POWER control panel, shown in Figure 4, is
located above the EPMP on the cockpit overhead panel. It contains digital
displays showing AC voltage and frequency, DC voltage, and AC and DC
percent loading. Below the displays are three switchlights: STBY ELEC,
TRU and E INVERT. Manual selection of the STBY ELEC switchlight to ON
removes the Essential DC bus power from the shutoff valve, allowing the
motor-generator to operate. (The UTILITY PUMP, if previously selected to
ARM, will also operate and should be selected OFF if not needed.)
With the motor-generator operating, selection of the E INVERT switchlight
to ON supplies 28 VDC power to the E-inverter. The E-inverter in turn
supplies AC power for Phase A of the Essential AC bus.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-24-00
Page 11
May 30/02
Revision 7
Selection of the TRU switchlight to ON supplies AC power from the motorgenerator
to the TRU. The TRU in turn supplies DC power to the Essential
DC bus.
With the STANDBY ELECTRICAL POWER system operating, loads are
normally shed by the flight crew to reduce demand on the system. AC
loads are reduced by shedding DC-powered equipment and DC loads are
reduced by shedding AC-powered equipment.
J. Electrical Load Warning System:
(Aircraft SN 1156 Through 1429 and SN 1000 Through 1155 with APU
LOAD Meter Not Having ASC 420)
On Aircraft SN 1156 through 1429 and SN 1000 through 1155 with APU
LOAD Meter but not having ASC 420, an Electrical Load Warning System
(ELWS) is installed. The ELWS is designed to provide electrical load
management for the APU electrical system when the APU alternator is
used to replace a failed alternator/converter during operations above
30,000 feet Pressure Altitude (PA). It is not intended for daily operational
use.
The ELWS consists of three Line Replaceable Units (LRUs) that interface
with the aircraft’s electrical system, air data computers (ADCs), and
annunciation systems. The three LRUs are a three-phase current
transformer, an electrical load warning computer (also referred to as an
electrical load processing unit) and an electrical load warning indicator
(more commonly referred to as the APU LOAD meter). The APU LOAD
meter is located on the lower left side of the pilot’s flight panel and is shown
in Figure 5.
The current transformer receives three-phase AC inputs from the APU
alternator and provides it to the electrical load warning computer. The
electrical load warning computer rectifies the AC input, sums the resulting
DC voltage and determines the total APU load in kVA. The electrical load
warning computer then outputs the APU load to the APU LOAD meter for
display.
The APU LOAD meter consists of an analog meter, an amber TEST light
and an amber ADC light. Amber and green bands on the meter’s face
denote the normal and caution ranges of APU alternator loading in kVA.
High and low values of the amber and green bands are altitude-dependent
as follows:
ALTITUDE WARNING LOW RANGE CAUTION LOW RANGE NORMAL RANGE
(FT PA) (RED BAND) (AMBER BAND) (GREEN BAND)
≤ 32,000 < 2.1 kVA 2.1 - 3 kVA 3 - 16 kVA
≥ 34,000 < 2.1 kVA 2.1 - 3 kVA 3 - 14 kVA
ALTITUDE CAUTION HIGH RANGE WARNING HIGH RANGE
(FT PA) (AMBER BAND) (RED BAND)
≤ 32,000 16 - 17 kVA > 17 kVA
≥ 34,000 14 - 15 kVA > 15 kVA
In addition to monitoring APU load, the electrical load warning computer is
capable of automatically shedding excess APU loads to protect generating
OPERATING MANUAL
2A-24-00 PRODUCTION AIRCRAFT SYSTEMS
Page 12
May 30/02
Revision 7
capabilities by monitoring Pressure Altitude (PA) through the ADCs. At or
above 34,000 feet PA, the electrical load warning computer will
automatically shed windshield heat based on the bus powered by the APU
alternator, i.e., left windshield heat controller if APU alternator is powering
the Left Main AC bus, right windshield heat controller if APU alternator is
powering the Right Main AC bus. If the operating alternator/converter
should fail, the electrical load warning computer will automatically shed
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湾流4操作手册 Gulfstream IV Operating Manual 1(67)
