Chapter 1 Aircraft Electrical System
Chapter 1 Aircraft Electrical system
• Electrical component
• Storage Battery
• DC & AC Generator
• Control and Protection in DC Electrical
System
• Electrical Machine and control
• Lighting
When, Why Electric Energy was
used in an aircraft?
Electrical energy is being widely used
• Clean form of energy – absence of smoke,
ashes, dust, etc.
• Easily convertible to light, heat,
mechanical, chemical energy etc.
• Easily and economically transportable by
means of running cables.
• Electrical systems have been an
onboard fixture since the Wright
Flyer. In those days the role of
electricity was limited to the magneto
which provides sufficient voltage to
spark the fuel/air mixture.
Magnetos still supplied the spark to the
engines, but 14- or 28-volt direct-current
generator supplied current to operate the
navigation and landing lights, the radios.
Generators kept the batteries charged to
operate the electric motor used to start the
engines.
• The years between the two world wars is
the golden age of aviation, improved in
importance and complexity.
• As the twentieth century ended, electrical
systems have become just about equal in
importance with the engines.
• For many years, light planes exclusively
used the 14-volt electrical system. Starting
approximately in the early 1980s, the 28-
volt system began to take over light
aircraft.
• The primary purpose of igniting the
fuel/air mixture is still the domain of the
magneto. However, the demand for
electrical energy in the airplane has
increased tremendously.
• Jet airliners have extremely complex
electrical systems and use alternating
current as the primary source of electricity.
• Batteries are used for emergency and
backup operations and for some special
applications.
DEFINITIONS OF
AIRCRAFT ELECTRICAL SYSTEM
Electrical System
An electrical system consists of an
electrical power source, its power
distribution system and the electrical load
connected to that system.
A typical aircraft electrical system
consists of a primary (main) power source,
emergency power source, secondary
power conversion equipment, system
control and protection devices,
interconnection network, and power
distribution system.
Electrical Source
The electrical equipment which produces,
converts or transforms electrical power.
Electrical Source
Some common AC sources are identified
as follows:
• AC alternators
• inverters
• transformers
• frequency changers.
Electrical Source
Some common DC sources are
• DC generators
• converters
• batteries.
Primary (Main) Power Source
Primary Power Source
A primary source is equipment that
generates electrical power from energy
other than electrical, and is independent
of any other electrical source.
Secondary Source
• A secondary source
is equipment that
transforms and/or
converts primary
source power to
supply electrical
power to either AC
or DC powered
equipment .
Secondary source.
• A secondary source is equipment that
transforms and/or converts primary
source power to supply electrical power
to either AC or DC powered equipment.
• A secondary source is entirely dependent
upon the primary source and is
considered part of the load of the primary
source.
Emergency Power Source
Emergency power
In the event of a primary power source
failure, emergency power is usually
provided from independent auxiliary
power unit (APU)-driven generator(s),
ram air or hydraulically-driven
generator(s), or batteries.
Ground power
ground power source
A ground power source can be connected
to the bus bar distribution system thus
allowing all electrical systems to be
powered independently of aircraft battery
or generating systems. The source can be
either a motorised generating unit or a
battery unit.
Nominal rating
This rating is usually a continuous duty
rating for specified operating conditions.
Condition of Power Sources
• Normal electrical power operation
• Abnormal electrical power operation
• Emergency electrical power operation
Normal electrical power operation
Normal operating conditions assumes that
all of the available electrical power system
is functioning correctly within Master
Minimum Equipment List (MMEL)
limitations (e.g. AC and/or DC Generators,
Transformer Rectifier Units, Inverters,
Main Batteries, APU etc.).
Abnormal electrical power operation
Abnormal operation occurs when a
malfunction or failure in the electric
system has taken place and the protective
devices of the system are operating to
remove the malfunction or the failure from
the remainder of the system before the
limits of abnormal operation are exceeded.
Emergency electrical power operation
Emergency operation is a condition that
occurs following a loss of all normal
electrical generating power sources or
other malfunction that results in operation
on standby power (batteries and or other
emergency generating source such as an
APU or Ram Air Turbine (RAT) only.
Classification of electrical load
• Vital (critical, emergency)
• Essential
• Non-essential
Typical Aircraft Electrical System
• Primary (main) power source
• Emergency power source
• Secondary power conversion equipment
• System control and protection devices
• Interconnection network
• Power distribution system
As a engineer, we should know the
following information
• electrical system operation, which
describes primary and secondary power
sources, bus configuration with circuit
breakers and connected loads for each
bus. A copy of the bus wiring diagram or
electrical schematic should also be
considered for inclusion in the report.
As a engineer, we should know the
following information
• alternators and other power source
description and related data (including
such items as battery discharge curves,
Transformer Rectifier Unit (TRU), Inverter,
APU, RAT, etc.)
List of Electrical Data
END OF CHAPTER 1
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