- •Textbook Series
- •Contents
- •1 DC Electrics - Basic Principles
- •Introduction
- •Electromotive Force (EMF)
- •Current
- •Resistance
- •Factors Affecting the Resistance
- •Units of Resistance
- •Resistors
- •Power
- •Series and Parallel Circuits
- •Kirchoff’s Laws
- •Annex A
- •2 DC Electrics - Switches
- •Switches
- •Proximity Detectors
- •Time Switches
- •Centrifugal Switches
- •3 DC Electrics - Circuit Protection and Capacitors
- •Electrical Faults
- •Circuit Protection Devices
- •Fuses
- •The Cartridge Fuse
- •Spare Fuses
- •High Rupture Capacity (HRC) Fuses
- •Dummy Fuses
- •Current Limiters
- •Circuit Breakers
- •Reverse Current Circuit Breakers
- •Capacitors
- •Capacitance
- •Capacitor in a DC Circuit
- •Capacitor in an AC Circuit
- •Capacitors in Parallel
- •Capacitors in Series
- •4 DC Electrics - Batteries
- •Batteries
- •Secondary Cells
- •Lead Acid Battery
- •Alkaline Battery (Nickel Cadmium, NiCad)
- •Battery Checks
- •Battery Charging
- •Secondary Batteries Summary
- •5 DC Electrics - Magnetism
- •Magnetism
- •Temporary Magnets
- •Permanent Magnets
- •Permeability
- •Magnetism
- •The Molecular Structure of Magnets
- •The Magnetic Effect of a Current
- •The Corkscrew Rule
- •The Magnetic Field of a Solenoid
- •The Right Hand Grasp Rule
- •The Strength of the Field of a Solenoid
- •Solenoid and Relay
- •The Forces on a Conductor Which is Carrying a Current
- •Questions
- •Answers
- •6 DC Electrics - Generators and Alternators
- •Electromagnetic Induction
- •Fleming’s Right Hand Rule
- •Faraday’s Law
- •Lenz’s Law
- •Simple Generator
- •Simple DC Generator
- •Characteristics of the Series Wound DC Generator
- •Commutator Ripple
- •Characteristics of the Shunt Wound DC Generator
- •A Compound Wound DC Generator
- •Flashing the Generator Field
- •Alternators
- •Voltage Control
- •Voltage Regulator Operation
- •Layout of a Generator System
- •Load Sharing Circuits
- •Operation of Load Sharing Circuit
- •7 DC Electrics - DC Motors
- •Electric Motors
- •Fleming’s Left Hand Rule
- •Practical DC Motor
- •Back EMF
- •Slow Start Resistor
- •Commutation
- •Series Wound Motors
- •Shunt Wound Motors
- •Starter-generator Systems
- •Actuators
- •Solenoid Actuators
- •Motor Actuator Construction
- •The Split Field Series Actuator
- •The Split Field Series Actuator Operation
- •Motor Actuators
- •Rotary Actuators
- •Linear Actuators
- •Actuator Brakes
- •Actuator Clutches
- •Visual Indicators Used with Linear Actuators
- •Visual Indicators Used with Rotary Actuators
- •Indicator Lights
- •Electromagnetic Indicators
- •Questions
- •Answers
- •8 DC Electrics - Aircraft Electrical Power Systems
- •Aircraft Electrical Power Systems
- •Dipole or Two Wire System
- •Single Pole (Unipole or Earth Return) System
- •Generators and Alternators
- •Voltage Regulators
- •Overvoltage Protection Unit
- •Generator Cut-out or Reverse Current Relay
- •Rectifiers
- •Inverters
- •The Generator Differential Cut-out
- •Generator (or Alternator) Warning Light
- •Generator (or Alternator) Master Switch
- •Monitoring Instruments
- •Ammeters and Voltmeters
- •The Battery
- •Bus Bars
- •Bus Bar Systems
- •Parallel Bus Bar System
- •Load Shedding
- •Generator or Alternator Failure
- •9 DC Electrics - Bonding and Screening
- •Bonding
- •The Static Discharge System or Static Wicks
- •Discharge of Static on Touchdown
- •Screening
- •Questions
- •Answers
- •10 DC Electrics - Specimen Questions
- •Questions – General 1
- •Questions – General 2
- •Answers – General 1
- •Answers – General 2
- •11 AC Electrics - Introduction to AC
- •Introduction
- •The Nature of Alternating Current
- •Terms
- •The Relationship of Current and Voltage in an AC Circuit
- •Resistance in AC Circuits
- •Inductance in AC Circuits
- •Inductive Reactance
- •Capacitance in AC Circuits
- •Capacitive Reactance
- •Impedance
- •Resonant Circuits
- •Summary
- •Power in AC Circuits
- •Power in a Purely Resistive Circuit
- •Power in a Purely Inductive Circuit
- •Power in a Capacitive Circuit
- •Power in a Practical AC Circuit
- •Power Factor
- •Power Factor Resume
- •Questions
- •Answers
- •12 AC Electrics - Alternators
- •Introduction to Aircraft Power Supplies
- •Generators / Alternators
- •Rotating Armature Alternator
- •Rotating Field Alternator
- •Alternator Output Rating
- •A Single Phase Alternator
- •Polyphase Circuits
- •Three Phase Alternator Connections
- •The Four Wire Star Connection
- •Delta Connected Alternator
- •Practical AC Generators
- •Brushed Alternators
- •Brushless Alternators
- •Frequency Wild Alternators
- •Obtaining a Constant Frequency Supply from a Frequency Wild System
- •Constant Frequency Alternators
- •Constant Speed Generator Drive Systems
- •CSDU Fault Indications in the Cockpit
- •The Drive Disconnect Unit (Dog Clutch Disconnect)
- •Variable Speed Constant Frequency Power Systems (VSCF)
- •Self-excited Generators
- •Load Sharing or Paralleling of Constant Frequency Alternators
- •Real Load
- •Reactive Load
- •Parallel Connection
- •Before Connecting in Parallel
- •Layout of a Paralleled System
- •Real Load Sharing
- •Reactive Load Sharing
- •Load Sharing General
- •Alternator Cooling
- •Generator Fault Protection
- •Bus Tie Breakers (BTBs)
- •Discriminatory Circuits
- •Differential Fault Protection
- •Synchronizing Units
- •Generator Failure Warning Light
- •Load Meters
- •Voltage and Frequency Meters
- •Generator Control Unit (GCU)
- •Emergency Supplies
- •The Ram Air Turbine (RAT)
- •The Auxiliary Power Unit (APU)
- •The Static Inverter
- •Ground Power Constant Frequency Supply System
- •Typical Controls and Indications
- •Questions
- •Answers
- •13 AC Electrics - Practical Aircraft Systems
- •Power Distribution
- •The Split Bus System
- •Parallel Bus Bar System
- •Questions
- •Answers
- •14 AC Electrics - Transformers
- •Transformers
- •Transformation Ratio
- •Power in a Transformer
- •Three Phase Transformers
- •Autotransformers
- •Rectification of Alternating Current
- •Half Wave Rectification
- •Full Wave Rectification
- •Three Phase Rectifiers
- •Transformer Rectifier Units (TRUs)
- •Inverters
- •Questions
- •Answers
- •15 AC Electrics - AC Motors
- •Alternating Current Motors
- •The Principle of Operation of AC Motors
- •The Synchronous Motor
- •The Induction Motor
- •The Squirrel Cage Rotor
- •The Induction Motor Stator
- •Slip Speed
- •Starting Single Phase Induction Motors
- •Fault Operation
- •Questions
- •Answers
- •16 AC Electrics - Semiconductors
- •An Introduction to Semiconductors
- •Conductors and Insulators
- •Semiconductors
- •N-Type Material
- •P-Type Material
- •Current Flow
- •The P-N Junction
- •Reverse Bias
- •Forward Bias
- •The Junction Diode
- •The Bipolar or Junction Transistor
- •Summary
- •17 AC Electrics - Logic Gates
- •An Introduction to Logic Gates
- •Binary Logic
- •Truth Tables
- •Gate Symbols
- •Positive and Negative Logic
- •The ‘AND’ Gate
- •The ‘OR’ Gate
- •The ‘INVERT’ or ‘NOT’ Gate
- •The ‘NAND’ Gate
- •The ‘NOR’ Gate
- •The ‘EXCLUSIVE OR’ Gate
- •Questions
- •Answers
- •18 Index
Chapter
8
DC Electrics - Aircraft Electrical Power Systems
Aircraft Electrical Power Systems |
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Dipole or Two Wire System |
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Single Pole (Unipole or Earth Return) System |
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Generators and Alternators . . . . . . . |
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Voltage Regulators . . . . . . . . . . |
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Overvoltage Protection Unit . . . . . . . |
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Generator Cut-out or Reverse Current Relay . |
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Rectifiers |
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Inverters . . . . . . . . . . . . . . |
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The Generator Differential Cut-out . . . . |
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Generator (or Alternator) Warning Light . . |
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Generator (or Alternator) Master Switch . . |
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Monitoring Instruments . . . . . . . . |
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Ammeters and Voltmeters . . . . . . . . |
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The Battery . . . . . . . . . . . . . |
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Bus Bars . . . . . . . . . . . . . . |
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Bus Bar Systems . . . . . . . . . . . . |
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Parallel Bus Bar System . . . . . . . . . |
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Load Shedding . . . . . . . . . . . . |
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.131 |
Generator or Alternator Failure . . . . . . |
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Questions - Generator Cut-out |
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Questions - Generator Circuit 1 . . . . . . |
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.135 |
Questions - Generator Circuit 2 . . . . . . |
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Questions - Distribution . . . . . . . . |
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Answers - Generator Cut-out |
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Answers - Generator Circuit 1 . . . . . . |
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Answers - Generator Circuit 2 . . . . . . |
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Answers - Distribution . . . . . . . . . |
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DC Electrics - Aircraft Electrical Power Systems |
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Systems Power Electrical Aircraft - Electrics DC 8
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DC Electrics - Aircraft Electrical Power Systems |
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Aircraft Electrical Power Systems
The power system for a single-engine aircraft consists of a generator or alternator with the control and indication equipment necessary to supply all the electrical power once the system is on line.
The term on line means that the generator or alternator has been switched into the electrical system and is actually supplying power to the system.
With multi-engine aircraft two or more generators or alternators are installed in parallel. The ampere capacity of an aircraft electrical system is determined by the number of powerconsuming devices fitted.
Dipole or Two Wire System
DC Electrics - Aircraft Electrical Power Systems 8
Figure 8.1 Dipole system
A dipole or two wire system is required where an aircraft is made of a non-conductive material. The current needs a complete circuit to flow and therefore needs a negative wire to connect the load to the negative side of the generator as well as a positive or ‘live wire’ to connect from the bus bar (distribution point) to the load.
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Single Pole (Unipole or Earth Return) System |
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Systems Power Electrical Aircraft - Electrics DC 8
Figure 8.2 Unipole system
This is the most common type of system on an aircraft with metal construction. The metal airframe is used as the negative conductor completing the circuit for the current flow. The negative side of the generator is connected to an ‘airframe earth’ as is the negative side of each load.
Generators and Alternators
Generators or Alternators are used to convert mechanical energy to electrical energy.
A generator produces direct current, DC, by using a rotating armature, stationary field and a commutator as described in the previous chapter whereas an alternator produces alternating current, AC, by using a rotating field and a stationary armature. If it is required to convert the AC output of an alternator to DC, a diode rectifier is used, fitted in the end frame of the alternator.
Most modern light aircraft have a direct current system which is powered by an alternator. The full power output of a generator is closely related to the RPM of the engine and is usually attained with the engine running at half speed whereas the full power output of an alternator can be attained at slow running, one obvious advantage that an alternator has over a generator. The generator is driven at a speed which is approximately three times that of the engine.
Voltage Regulators
The Voltage Regulator maintains the output voltage of the generator or alternator at a constant value, irrespective of the engine RPM or electrical loads. This is achieved by controlling either the current flow in the field coils of a generator, or the current flow in the exciter field of an alternator.
The basic voltage regulator setting controls the generator output to maintain 14 volts for a 14 volt system with a 12 volt battery and 28 volts for a 28 volt system with a 24 volt battery.
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