AIRCRAFT MAINTENANCE MANUAL
5.
R
AC Power Supply
A.
Three not-related ac generator busses supply power to the
aircraft ac busses and transformer rectifier units (TR). Each
IDG takes the loads on its cz generator bus through Its own
supply network (see Figure 1%
B.
The ac tie bus and bus tie relays permit the ac generator
busses operate in parallel. This lets the ISGs balance the
necessary aircraft electrical loads.
c.
The APU generator can power each of the ac busses through its
own independant supply network (see Figure 11).
D.
Emergency ac power is aVail 'e from a static inverter and an
air-driven generator (ADG). T:* .- Latic inverter is energized
by the battery and gives emergency ai? power to the left
emergency ac bus. The ADG is deployed into the airstream and
operates in one of two modes (see Figure 16).
(1)
For the hydraulic mode the EKE: PWR switch on the electrical
system control panel (ESCP) in ON and the ADG ELEC switch is
OFF. In mode 1:
- The batteries supply power to the left emergency dc bus
- The ADG supplies power to the left emergency ac bus and
the No. 1 auxiliary hydraulic pump
- The static inverter is off.
(2)
For the electrical mode the EMER PWR switch is ON and the
In mode 2:
ADG ELEC switch is ON.
- The ADG supplies power to the left and the right emergency
ac busses
- The riqht emergency ac bus supplies power to the No. 3
transformer rectifiex (TR)
- TR 3 supplies power to the battery bus, the left emergency
dc bus, and thf.r: right emergency bus
- The right emergency dc bus supplies power to-the battery
charger. With the BAT switch on, the batteries are
charged by the ADG.
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LEFT EMERGENCY
BUSSES-BATTERY
POWER ONLY
AIRCRAFT
BATTERY
LEFT EMERGENCY
BUSSES-BAT-MY
POWER AN0 ADG IN
THE HYDRAULIC MODE
LEFT AND RIGHT
EMERGENCY BUSSES
AOG IN THE
ELECTRICAL MODE
AlACRAFT
BAnERY
BATTERY
CHARGER
ri ’ 1 ‘I-
I
BATTERYI
1
F
Id
r”L EMER AC BUS
ADG - AIR-DRIVEN GENERATOR
TR - T R A N S F O R M E R RECTIFIF’I
DB2-24-0069A
CAG(IGDS)
ADG Power Supply System
Figure 16/TASK 24-08-00-990-819.
*+* FOR ALL AIRCRAFT
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E.
The generator busses and the ac ground service bus supply the
power for:
- Most of the loads that are close together
- Most of the high current loads (the hydraulic pumps, most of
the fuel pumps, the ac busses and galley power).
F.
Power for:
- Lower current loads
- Loads that are not close together
- Flight necessary loads.
Is supplied through:
- The three main ac busses
- The cabin ac busses
- Remote ground service busses
- The two ac emergency busses.
The instrument busses suppiy their Tomponent loads.
G.
The ac ground service bus supplies power to those components
necessary to ground service operations. The APU generator or
main external power can supply power to the ac ground service
bus without power to the other ac generator busses. This
permits ground maintenance of the aircraft without a supply of
The ac
power to all of the electrical power supply system.
ground service bus is usually energized in flight.
No Break Power Transfer a.nd Parallel Operation
6.
A.
A no break power transfer (NBPT) system is installed on the
Usual power transfers between the external power
aircraft.
the
APU generator, and the XDG electrical pcwer- occur
sourcer
without d pobur3r -.,iteruptior,.
B.
The alternative electrical sources are made parallel for a
the power transfer occurs. This parallel
operation supplies non -interupted electrical power to the
aircraft busses. The power source with the higher priority
momentarily is parallel with the lower priority power source
before the lower priority power source is disconnected from the
bus.
brief time before
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AIRCRAFT MAINTENANCE MANUAL
c.
When an electrical power source is on, the power source
priority for the ac generator busses are is as follows (see
Figure 11).
- The related IDG
- The APU generator
- The ac tie bus (external power or IDG).
D.
when an electrical power source is on, the power source
priority for the ac tie bus is as follows (see Figure 11):
-.The
- The
- The
- The
external power source
engine No. 2 IDG
engine No. 1 IDG
engine No. 3 IDG.
E.
After the flight crew sets the rtzlated power source on or off:
a momentarily parallel operation occurs. The parallel
operation occurs between one of the 1DGs and the APU generator
or the external power source. The parallel operation is
automated through the generator control units (GCU) and the
electrical power control unit (EPCU).
F.
The IDGs usually operate in the parallel mode. For the dual
land operation, the IDGs operate in the isolated mode.
Parallel operation of the IDGs is also automated through the
For the dual land logic, see Figure 17.
GCUs and the EPCU.
Generator Control Unit
7.
A.
There are four generator control units (GCU) installed in the
electrical power system (see Figures 6 and 18): one for each
IDG and one for the APU generator. Control of the GCU's is as
follows:
- Generator relys (GR) 1, 2, and 3
- BUS tie relays (BTR) 1, 2, and 3
- The IDGs disconnect function (on flight crew command)
- The DC ties 1 and 3
- NBPT between the APU generator and the external power source
- NBPT between the APU generator and the IDGs
- NBPT between the IDGs and the external power source (across
BTR 1, 2, and 3).
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AIRCRAFT MAINTENANCE MANUAL
B.
The related GCUs give control as follows:
-
c.
IDGs voltage control
APU generator voltage control
IDGs frequency control
IDGs reactive load division
IDGs real load division
IDGs current limit.
The GCUs give protection to their generators as follows:
-
D.
The
The
The
The
The
The
Generator above or below voltage
Generator above or below frequency
Generator phase sequence
Generator feeder fault;
The ac generator bus 1, L, fi-.l 3 faults.
The GCUs give automatic operation as follows:
- IDG reset for above or below voltage
- IDG reset for above or below frequency
- IDG reset for feeder faults
- AC generator bus 1, 2, and 3 fault reset.
- IDG oil temperature and pressure fault indicatons.
8.
Electrical Power Control Unit
A.
The EPCU controls the electrical system as follows (see Figures
6, 7, and 19):
-- The bus tie relay-external power (BTR-EP)
- The ground service relay (GSR) external power position
- The three auxilary power relays (APR) 1, 2, and 3
- The galley transfer relays (GTR) 1, 2, and 3
- Load shedding
- The APC X2 peed for .WU NBPT operation
- NBPT between the external power source and the APU generator
- NBPT between the IDGs and the external power source
- NBPT between the IDGs and the APU generator
- The dua. land electrical power configuration system
- The electrical power system mode
- Frequency reference for the three IDG GCUs.
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B.
The EPCU gives protection as follows:
- The main external power phase sequence
. - The main external power above or below voltage
- The main external power above or below frequency
- The main external power feeder faults
- The galley external power above or below voltage
- The galley external power above or below frequency
- The galley external power phase sequence
- The ac tie bus faults
- The APU generator overcurrent (when the APU generator is more
than 110 Kva continuously during ground operation).
c.
The EPCU gives automatic operation of the electrical system as
follows:
-
D.
The APU generator reset fo above or below voltage
The APU generator reset for above frequency
The APU generator reset for feeder faults
The emergency power transfer
The smoke procedure.
The EPCU gives system status as follows:
- Electrical power system (EPS) data to the electronic
instrument system (EIS)
- EPS line replaceable unit (LRU) fault data to the central
fault display system (CFDS) for maintenance.
E.
Protection for the ac bus, t1.e galley bus, and the utilization
equipment feeder faults (line to line and line to neutral
shorts) is given by each remote con'rrol circuit breaker (RCCB),
circuit breakers (CB) or fuses.
F.
Feeder fault and high load protection for the gallq busses is
also qi*:-n t.:--1 galley Joad control units (GLCU).
Transformer Rectifier Unit
9.
A.
The primery source of dc electrical power is a system of four
75 amp transformer rectifiers (TR). The TRs change 3 phase,
115 Vat, 400 Hz power into 28 Vdc mower. The battery and/or
the air driven generator (ADG) (through TR 3) are also
available as emergency dc power sources (see Figure 13).
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B.The TRs are compact, low voltage, high-current power supplies.
They have an input power transformer to change high voltage,
3-phase ac power to low voltage ac power. The TRs have
rectifiers to convert the ac power to dc power. The TRs also
have output filters to prevent radio frequency interference
(see Figure 20).
10. DC Power Supply
A.
The four TRs are usually operated in parallel. The four TRs
receive ac power from the ac busses that follow:
-
TR
TR
TR
TR
1 receives power from ac gen bus 1
2A receives power from ac gen bus 2
28 receives power frcz “32 ac ground service bus
3 receives power from UC f:;'bt emergency ac bus.
B. An RCCB is used to connect each of the TRs to the dc tie bus.
Each TR has a capacity of:
- 75 amperes for continuous operation
- 125.5 amperes for 5 minutes operation
- 150 amperes for 2 seconds operation
- The four dc tie RCCBs are usually closed for parallel dc
This makes sure all dc loads are supplied power
operation.
during start up, usual operation, stop, and unusual
conditions.
11. Emergency Power
A.
The emergency power system has:
- One main battery (see Figure 5)
- 3ne air driven generatrr (IIDG) (see Figure 4)
- One stat;, ir.y ?rter (set Figure 21).
(1) The main battery is a 50 ampere hour, 28 Vdc, nicad battery
The battery has two 14-volt dc batteries connected in
series.
(2) The ADG is a 25 Xva, 3-phase, 115 Vat, 400 Hz air cooled
turbine generator assembly. The assembly has a turbine
unit, a brushJ.ess generator, and a voltage regulator.
.
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(3) A static inverter changes battery dc power into one phase,
115 Vat, 400 Hz, emergency power for the left emergency ac
bus.
B.
With the EMER PWR switch in the ARM position and the BAT switch
in the ON position (emergency power armed): the left emergency
ac and dc busses automatically transfer to main battery power
if the left emergency ac bus or the left emergency dcebus is
not energized.
c.
With emergency power on and the ADG deployed, the ADG supplies
electrical power in one of two modes:
(1) For the hydraulic mode the EMER PWR switch on the electrical
system control panel (E.X? in ON and the ADG ELEC switch is
OFF. In mode 1:
- The batteries supply power to tne left emergency dc bus
- The ADG supplies power to the ler't emergency ac bus and
the No. 1 auxiliary hydraulic pt~mp
- The static inverter is off.
(2) For the electrical mode the EMER PWR switch is ON and the
ADG ELEC switch is ON. In mode 2:
- The ADG supplies power to the left and the right emergency
ac busses
- The right emergency ac bus supplies power to the No. 3
transformer rectifier (TR)
- TR 3 supplies power to the battery bus, the left emergency
dc bus, and the right emergency bus
- The right emergency ac bus supplies power to the battery
charger. With the BAT switch on, the batteries are
charged.
D.
The klydrau:I .- rc ie configuration permits the battery and the
ADG to suppiy emergency electrical power to the captains flight
necessary equipment during a condition when all the engines do
not operate.
E.
The electrical mode configuration permits the ADG to supply
emergency power to the captains and first officers flight
nec?essary equipment during a condition when all the generators
do not operate. The supply of emergency power does not have a
time limit.
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F.
During a condition when all the engines or all the generators
the battery (without the ADG) supplies
do not operate:
approximately 15 minutes of emergency electrical power to the
captains flight necessary equipment.
.
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