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OPERATING MANUAL
2A-24-00 PRODUCTION AIRCRAFT SYSTEMS
Page 6
May 30/02
Revision 7
2A-24-20: AC Electrical Power System
1. General Description:
The AC electrical power system supplies power to the AC electrical buses for
distribution to AC systems and equipment. It is the primary source of electrical
power for the GIV electrical power system. The AC electrical power system also
supplies power to be converted to DC electrical power by the Transformer-
Rectifier Unit (TRU).
Figure 1 shows the entire GIV electrical power system in simplified form; Figure 7
shows only the AC electrical power system in simplified form. Units and
components for the AC electrical power system are shown in Figure 2. They are
as follows:
• Engine-Driven Alternators
• APU Alternator
• Converters
• AC Bus Power Control Unit
• Emergency Inverter
• Power Distribution Box
• AC External Power System
• APU AC Power System
• Standby Electrical Power System
• Electrical Load Warning System
• Distribution and Control System
2. Description of Subsystems, Units and Components:
A. Engine-Driven Alternators:
The AC alternators used in GIV aircraft are air-cooled, brushless,
permanent magnet type units that provide an alternating current power
output. There are three identical AC alternators: one mounted on each
engine-driven high speed gearbox and one mounted on the Auxiliary
Power Unit (APU) in the tail compartment.
The engine-driven alternators are rated at 30 kVA and provide three-phase
output. Cooling is accomplished by means of air entering an air inlet and
circulating through the unit. Being air-cooled in this manner, the units are
rated up to 50,000 feet.
Auxiliary bearings are mounted adjacent to the main bearings within the
alternator. The auxiliary bearings take over support of the rotor in the event
of main bearing malfunction. They act to prevent contact between the rotor
and the stator, which could result in major damage.
Being engine-driven alternators, output frequency will vary with engine
High Pressure (HP) RPM. Thus, in order to provide AC power at a constant
400 Hz frequency to the AC distribution buses, alternator output is first
supplied to a Variable-Speed, Constant-Frequency (VSCF) converter. The
converter then supplies 115/200V AC, 400 Hz power to the AC distribution
buses.
Failure of an engine-driven alternator will be indicated by an amber L-R AC
POWER FAIL or L-R DC POWER FAIL message displayed on CAS. This
message is displayed whenever power is available from the Essential 28
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-24-00
Page 7
May 30/02
Revision 7
VDC bus engine-driven alternator output or converter output has failed, or
the ELECTRIC MASTER LEFT PWR or RIGHT PWR switch (Figure 6
Sheet 8) is OFF.
An amber L-R ALT HOT message will be displayed on CAS when an
engine-driven alternator temperature exceeds 250° F (121° C).
An amber L-R ALT BRG FAIL message displayed on CAS indicates that an
engine-driven alternator main bearing has failed, and the auxiliary bearing
is operating. This condition is also indicated by an amber L-R ALT FAILED
BRG light on the overhead annunciator panel illuminating, as shown in
Figure 10. These messages indicate the alternator is operating ″on
condition″ and further actions shall be with reference to the latest approved
revision of the GIV Airplane Flight Manual.
B. APU Alternator:
The APU alternator is identical to the two engine-driven alternators. It is
rated at 30 kVA, provides three-phase output and is also air-cooled.
Internal bearing redundancy is identical to that of the engine-driven
alternators.
Because the APU runs at a constant 100% RPM, the APU alternator turns
at a constant speed of approximately 8,000 RPM. At this operating speed,
the alternator provides 115 VAC power at a constant 400 Hz. Thus, the
APU alternator output can be directly supplied to the AC distribution buses
without first being output to a converter.
An amber APU ALT BRG FAIL message displayed on CAS indicates that
the APU alternator main bearing has failed, and the auxiliary bearing is
operating. This condition is also indicated by an amber APU ALT FAILED
BRG light on the overhead annunciator panel illuminating, as shown in
Figure 10. These messages indicate the alternator is operating ″on
condition″ and further actions shall be with reference to the latest approved
revision of the GIV Airplane Flight Manual.
Failure of the APU alternator will be indicated by an amber AUX AC
　
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