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What are the advantages of using transformers
and transformer rectifiers vice
inverters and dynamotors for supplying aircraft
power?
Lightweight, more reliable, and simple to maintain
What power system requirements do modern
naval aircraft have?
120-/208-volt ac, 3 phase and 400 Hz
What determines the voltage frequency of an
ac generator?
The number of magnetic poles and the rotor rpm
What are the two types of ac generators?
Brush and brushless
What supplies the output ac power of a generator?
The stator
How many phases is an ac generator?
Three
What are the advantages of a brushless generator
over a brush-type generator?
Increased reliability and greater operating time between overhaul
What is a prime mover?
A device that provides the driving force for a generator
What is the purpose of a CSD?
Convert variable engine speed to a constant speed output
What are inverters?
An emergency source of ac power when normal ac power fails
In an inverter, what converts electrical energy
to mechanical energy?
The dc motor
On what does the rating of an aircraft inverter
depend?
The equipment that it will supply
What is the purpose of a transformer?
To convert an input ac voltage into a usable ac output voltage by either stepping
up or stepping down that voltage
What is the function of a transformer
rectifier?
To convert ac input voltage to a dc output voltage
What is the only moving part in a transformer
rectifier?
The cooling fan
What is the difference between an autotransformer
and an ordinary transformer?
An autotransformer has one winding that is common to both primary and
secondary windings.
Autotransformers offer savings in both size
and costs over conventional units. When are
these savings greatest?
When the turns ratio is less than 2:1
What are the two general types of instrument
transformers?
Current and potential
What are the ways in which emergency power
is supplied to naval aircraft?
Aircraft storage batteries, auxiliary power units, and hydraulic motor driven
generator
What components maintain the aircraft (a/c)
storage battery in a charged state?
Ac generator and transformer rectifier
What are the two most common types of a/c
storage batteries in use today and what are
the colors of each?
Lead-acid which have a red case and nickel-cadmium which have a blue case
What manual is used for information on
securing, storing, servicing, and handling a/c
storage batteries?
NAVAIR 17-15BAD-1
On a VLAB, what is the purpose of the vent
nozzles?
The upper nozzle is connected to a tube that supplies definite pressure on the
battery while in flight. The lower nozzle is connected to a negative pressure tube,
allowing battery acid to drain without damaging the aircraft
The sump jar of a VLAB system contains a felt
pad moistened with what?
Sodium bicarbonate
In a VLAB system, what is the purpose of the
sump jar and the felt pad?
To neutralize the gases and excess battery solution
What type of electrolyte is used in a SLAB?
A mixture of sulfuric acid and water
In a SLAB, how is electrolyte immobilization
accomplished?
By using a gel or special mats to absorb electrolyte
What is considered the fundamental unit of a
NICAD battery?
The cell
What are the types of cells used in NICAD
batteries?
Vented and sealed
What is the nominal value of a NICAD battery
cell?
1.26 volts dc
Why can the hydraulic driven emergency
generator only power a small number of circuits?
The kVA rating is too low
What causes the rotor in the generator to
turn?
The hydraulic motor
What helps to maintain generator output frequency?
The motor converts 3000 pounds per square inch of fluid to a constant speed
rotation
How is the generator cooled?
By the hydraulic fluid
What is the purpose of the motor-generator
control?
It provides voltage regulation and fault detection of the generator output
What is the function of the solenoid control
valve?
It is de-energized when primary electrical power is lost and allows hydraulic
fluid to be routed to the hydraulic motor to drive the generator
What is the function of an APU?
To supply pneumatic power for starting engines and operating air conditioning
systems, electrical power for in-flight emergencies, and ground maintenance
What is needed for APU starting?
Aircraft battery and fuel
On a GTCP-95, what drives the generator?
Shaft power at the main output drive pad
What are the two main sections of an APU?
Accessory assembly and compressor/turbine assembly
The electrical system of an APU consists of
what components?
Holding relays, oil pressure switch, centrifugal switch assembly, hour meter, and
wiring harness
APU ignition cuts out at what rpm?
95%
What is the purpose of the centrifugal speed
switch assembly?
It controls the sequence of operation of various electrical components
How many sub-switches make up the
centrifugal speed switch assembly?
Three
How are the centrifugal speed switches
adjusted?
By using an adjustment screw to apply spring tension to the lever arm
What are the functions of each switch?
35%—shuts the starter down; 95%—arms load control circuit, starts hour meter,
and shuts off ignition; 106%—overspeed protection (shuts down the APU during
an overspeed condition)
Changing the setting of the 35% switch also
affects what?
The settings of the 95% and 106% switches
How does the 106% switch shut down the
APU?
When the switch is actuated it cuts off fuel flow, causing the APU to shut down
At what rpm is the starter disengaged?
35%
What could happen to the starter if the
dropout relay fails?
The starter may fail internally due to an overheat or overspeed condition
Why do we use external electrical power on
aircraft?
It provides ground crews with electrical power for servicing, fueling, and
performing maintenance actions
What is the most common method of voltage
regulation for ac generators?
Varying the current to the field windings
Why would we use a permanent magnet on the
generator rotor in place of exciter windings?
It helps to maintain a constant load on the generator and simplifies generator
construction
What happens when magnetic fields of
alternating polarity pass across the armature
windings?
Ac voltage induction occurs
What controls the voltage induced into the
armature windings?
1. The number of turns of conductor per winding
2. Generator rpm
3. Magnetic field strength
What must ac generator control systems
protect against?
1. Over- or undervoltage
2. Over- or underfrequency
3. Improper phase sequence
What is the purpose of the rotating
three-phase rectifier in a brushless generator?
Change the rotating ac output voltages of the exciter to dc voltages
What is the chief advantage of having dc
exciter units integrated into ac generators?
Each generator has its own independent source of excitation so no external
source of electrical power is necessary
What is the only moving mechanical part in a
solid state voltage regulator?
Exciter control relay
What happens if the output of the control
amplifier section of a voltage regulator is too
low?
Regulator circuitry increases the field strength of the ac exciter
In a solid-state voltage regulator, what component
supplies the power to the bridge
circuit?
CR1
What prevents the generator from receiving
excitation voltages when the frequency is too
low?
Underspeed switch
Why is controlling the rotor rpm the only
means of fine-tuning the output frequency of a
generator?
The generator has a fixed number of poles
What two components are joined by the CSD?
Engine and generator
List the components of the CSD.
Hydraulic pump, hydraulic motor, governing system, gear pump, charge pump,
replenishing pump, and scavenge pump
When the input engine rpm is too low, what
happens to the CSD hydraulic pump?
The pump supplies more oil to the hydraulic motor causing it to increase rpm
How is the CSD/generator system protected
during underspeed conditions?
An underspeed pressure switch is used to break the electrical circuit
What component provides circuit protection
for an ac generator?
Supervisory panel
A supervisory panel will disconnect the generator
from the load under what conditions?
Over-/underfrequency
Over-/undervoltage
Feeder fault
What is the required output frequency of the
PMG?
600 Hz
How many amperes are required through the
exciter coil to generate a 120-/208-volt,
60-kilovolt ampere (kVA) load?
1.7 amps
During an undervoltage condition, at what
voltage will the generator be dropped off
line?
When one or more phases drops to 90 volts or less
At what voltage will the generator be dropped
off line during an overvoltage condition?
When one or more phases is 129 volts or greater
What is feeder fault?
A condition where the current leaving the generator does not pass through the
load
In an electrical system, what is a “bus?”
A primary power distribution point that is connected to the main power source
Usually holds systems of like priority
How are buses identified?
By the priority of the equipment it powers
What are the types of output protection devices
used by buses?
Circuit breakers, fuses, or current limiters
What are the two basic types of power contactors?
Single coil and double coil
What are the four power sources available to
the F-14 aircraft?
Left main generator, right main generator, emergency power, and external power
List the three-phase buses of the F-14 aircraft.
Left and right main ac buses, number one and two ac essential buses, and the ac
monitor bus
What dc bus willNOT be powered in the event
of one TR failure in the F-14 aircraft?
Dc monitor bus
In an F-14 aircraft, what is the purpose of the
GPM?
It prevents external power from being applied if it is not within specified
tolerances
How will the pilot of an F-14 know if external
power is applied to or disconnected from his
aircraft?
Hand signals from the plane captain
What is the purpose for jumping pins E and F
on the external power receptacle?
It energizes the external power contactor
In an F-14 aircraft, with both main generators
on line, which buses does the left main
generator power?
All 115-Vac essential and instrument buses, and 26-Vac instrument and navigation
buses
With both generators on line, 115-Vac essential
bus number two fails to be powered.
Which components could be faulty?
Power contactor K3
External power is applied to the aircraft, the
right generator comes on line, and only the
main ac bus loses power. What component
could be faulty?
Power contactor K2
If the right TR fails, what bus, if any, will be
lost?
None
What will cause the monitor bus to lose
power?
If both TRs fail
What ac bus does the emergency generator
supply power to?
Essential bus
What is the main advantage of a grounded
system?
It alleviates an extra conductor
What are the disadvantages of ungrounded
systems?
Added weight, cost, and space