MindMap Gallery Flight technology professional flight electrical
Summary of knowledge on flight electrical aspects of the aviation technology major, including circuit control and protection, power supply system, aircraft power transmission and distribution system, aircraft electrical equipment, electromagnetic interference and protection, etc.
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Electrical parts
Overview
Power system composition and functions
1 Main power supply, auxiliary power supply, emergency power supply, secondary power supply, external power supply
2 Auxiliary power supply is used when the aircraft engine is not working and part of the power supply fails.
3 The emergency power supply is used to supply power to necessary flight equipment when the main power supply fails.
4 Aircraft power transmission and distribution systems are divided into: centralized, decentralized, and hybrid based on power distribution methods.
Centralized is only suitable for small aircraft
5 Power transmission and distribution control methods: conventional, remote control, solid-state
Power supply status and battery capacity
6 The abnormal working state of the power supply system is unpredictable and uncontrollable, but restoring it to normal state is controllable.
7 Aircraft power system capacity = number of main power generation systems × rated capacity of a single power generation system
8 Flight electrical equipment is divided into: flight critical equipment, mission critical equipment, and general electrical equipment.
Circuit Control and Protection
circuit connection device
1 Wires and cables form the backbone of the power distribution system and are used to transmit electrical parameters and electrical energy between various areas of the aircraft.
2 Classified by use: internal wires, equipment wires, starting ignition wires, thermocouple wires, data lines and radio frequency system wires
3 According to working voltage: high voltage wire, low voltage wire
4 There are 5 types of signal transmission lines: coaxial cable, three-core coaxial cable, twisted pair, shielded twisted pair, parallel line
Coaxial cable has a wide signal range and is most commonly used
5 Wire connections are divided into: permanent connection and disassembly according to maintenance plan
Permanent connections are soldered or crimped
Features
①Easy to connect
②Can ensure good conductivity and low voltage drop
③High connection strength
④ Eliminates short circuits caused by solder spillage and flux contamination
⑤ Eliminates possible virtual soldering between wires and connectors
6 Bus bar (distribution bar): The power output is connected to one or several low-impedance conductors
circuit control device
7 commonly used
Manual controls: switches, buttons
① Toggle switch: switch circuit
② Push button switch: The circuit is temporarily closed or interrupted
③ Rotary switch: select multi-circuit
④ Micro switch (micro switch, sensitive switch or snap switch): used in small current circuits
⑤ Timing switch: control equipment to work in sequence within a predetermined time
⑥ Proximity switch: no fixed contacts, the sensor is sensitive to approaching objects, use this feature to control the switch
Photoelectric proximity switch: using the photoelectric effect
Infrared proximity switch: pyroelectric principle
Doppler Proximity Switch: Doppler Effect
Electromagnetic control device
Relay (<25A)
Electromagnetic relays: mostly DC relays, the load current for electric shock switching is limited to 25A
solid state relay
No contacts, high sensitivity, long service life, high reliability, strong impact and vibration resistance
Polarizing relay
Can reflect the polarity of the input signal
Has high sensitivity
Two magnetic fluxes
Polarized magnetic flux generated by permanent magnets
The working magnetic flux generated by the electromagnet coil
The size and direction determine the size and direction of the input signal.
Hybrid relay
Reaction mechanism: solid state relay, which plays the role of delay and amplification
Actuator: electromagnetic relay
Contactor (>25A)
① Single winding contactor
② Double winding contactor
2×solenoid coil
Pull-in winding
Keep winding
③ Mechanical latching contactor
Mechanical method is used to ensure that the main contacts can still work after power failure.
New Control Devices: Transistor Devices
circuit protection device
fuse
① Fusible fuse: often used in circuits with relatively small overload capacity
② Refractory fuse: Insensitive to tiny currents, used for power system protection
③ Inertia fuse: includes two parts, short circuit protection part and overload protection part
Circuit breakers (automatic protection switches, automatic safety switches) can replace fuses
Push type: consists of bimetallic thermal element, switch device, and mechanical latch device
Pull type
electronic circuit breaker
Power Systems
aviation battery
aircraft battery
Acid batteries (lead-acid batteries: low price, long life, can be float charged)
Basic working principle
capacity
The size is expressed in "amp hours (A·h)"
Effective capacity is related to working conditions and usage conditions
Precautions
① Not allowed to be used on the ground
② Voltage check should be performed before flying. When discharging at double the rated current, the voltage should not be lower than the rated value.
③ Try to avoid using it in low temperature conditions.
④ Prolonged high current discharge or excessive discharge is prohibited
Alkaline batteries (cadmium-nickel batteries) are widely used on large and medium-sized transport aircraft
It has high reliability, can work normally under severe impact, large acceleration and pressure conditions, and has a long life.
working principle
Electrical characteristics
Memory effect (disadvantages)
Neutral battery (lithium battery)
Advantages: high specific energy; light weight; low maintenance workload; no memory effect; high single cell voltage; wide operating temperature range
Disadvantages: poor safety; electrolyte is flammable; high cost
Rated energy (W·h) = battery capacity (A·h) × rated voltage (V)
Organic solution battery
DC generator
commutator type
Composition: stator (generates magnetic field), rotor, brush device
Working principle: When the coil rotates in the magnetic field, the coil will generate alternating electromotive force
E=Ke·Φ·n
Transistor rectifier type (widely used in small aircraft)
Overcome brush and commutator performance issues limited by altitude
alternator
Brushless rotating rectifier type
Two-stage type (self-excited generator)
Composition: AC exciter, main generator
three-stage
Composition: auxiliary exciter, main exciter, main generator
Similarity
① Output electric energy on the stator (armature)
② The main generator adopts a rotating magnetic pole structure and is equipped with a rotating rectifier.
③ The frequency of the generator is adjusted by changes in its speed
④ Adjust the generator voltage by changing the intensity of the generator excitation magnetic field
Main parameters of AC power supply
Quality indicators: voltage, frequency
Increasing the voltage and frequency of the generator will help reduce the weight of the generator and the power grid
Speed ↑ frequency ↑, limited by equipment strength
Constant frequency AC power supply
Constant speed and constant frequency AC power supply
Hydro-mechanical constant speed transmission
Transfer engine energy to generator
Main components: transmission system, lubricating oil system, speed control system, protection system
working principle
① Zero differential working state
② Positive differential working state
③ Negative differential working state
Failure and protection
Failure: Oil system is clogged or leaking, oil temperature is too high, moving parts are worn or stuck, output underspeed or overspeed
There is a manual release mechanism at the input end
Combined transmission generator
Composition: constant speed transmission device and alternator
Variable speed constant frequency AC power supply
Convert variable frequency AC power into three-phase AC power through an electronic converter
Advantages compared to constant speed and constant frequency AC power supply
① High power quality and no frequency transient phenomenon
② High energy conversion efficiency
③ Few rotating parts and high reliability
④ Flexible power system structure
⑤ Able to achieve brushless starting and power generation
⑥ Easy to produce, use and maintain, and low cost
Variable frequency AC power supply (mostly used in turboprop engines)
Used as main power supply on B787 (narrow frequency conversion) and A380 (wide frequency conversion)
secondary power supply
Converter
rotary converter
Single phase converter
Three-way converter
Can convert low-voltage DC power into 36V/400Hz (500Hz) three-phase AC power
static converter
Can convert DC power into single-phase or three-phase AC power at 400Hz or other frequencies
Composition: DC converter, DC inverter
Core component: inverter (adjustable output voltage)
transformer rectifier
Used to convert 115/200V, 400Hz or variable frequency AC power into 28V DC power
Used on large and medium-sized aircraft that mainly use AC power
Electronic transformer rectifier: high-voltage alternating current → high-voltage direct current → high-frequency alternating current → low-voltage direct current
Emergency Power Supply
Type: battery, ram air turbine (RAT) generator, hydraulic motor generator (HMG)
HMG is not limited by flight time and flight speed
Ram air turbine generator
Ground power
Ground DC power supply: The three-pin plug consists of 2 positive pins and 1 negative pin. The positive pin is short and has a smaller diameter.
Ground AC power
Three-phase alternating current is often used
The four longer and larger diameter pins correspond to the three phases A, B, C and the neutral line N respectively. E and F are shorter and thinner and are auxiliary pins.
Aircraft power transmission and distribution system
Grid type and distribution method
Grid type
DC grid
Usually single-wire or double-wire system is used
AC power grid
Three-phase four-wire system with the aircraft body as the neutral line (the power supply form commonly used in modern aircraft)
Three-phase three-wire system without neutral wire
Mainly single-phase but also three-phase power supply system
Aircraft power distribution method
Transmission and distribution form
Power supply network
From the aircraft power supply, the part between the power bus bar and the bus bar of the electrical equipment
2 types of power supply networks
Open type (radiant type)
High reliability and strong vitality
Closed type (ring type)
Simple structure, light power grid
distribution network
From the bus bar of electrical equipment to the part between electrical equipment
3 power distribution methods
Centralized power distribution
The equipment voltage is relatively stable, the power grid is simple, and it is easy to check and troubleshoot.
Hybrid distribution
Simple structure, decentralized functions, easy to inspect and repair, the power grid is light in weight
Independent (decentralized) power distribution
High working reliability, when a fault occurs, it only affects the faulty part
Electrical Load Management Center
Distribution center
Provide power to the load and maximize uninterrupted power supply by monitoring the working status of the power supply.
Solid State Power Controller
① Connect or disconnect load equipment according to instructions
② With remote control capability
③ Capable of overload protection
④ Current limiting control when overloaded
Intelligent Terminal
Monitor the operating status of each bus bar in the power system and take control measures
Generator voltage regulation
Regulator
Carbon sheet type
Composition: carbon column, electromagnet, hexagonal spring
transistor type
Parallel power supply
DC power supply in parallel
Load balancing conditions
The voltages maintained by the two voltage regulators are equal (U1=U2)
The positive line resistance of the two generators is equal (R1=R2)
Measures to improve load distribution balance
Carbon chip voltage regulator adopts balanced coil
Parallel operation of generator and battery
Parallel operation of alternators
condition
The generator voltage waveform should be consistent with the grid voltage waveform and be a sine wave.
The phase sequence should be consistent
The frequencies should be similar. The larger the frequency difference, the longer the synchronization time.
Voltage should be similar
The phase difference should be small to reduce the impact when putting in
AC load automatic balancing
Set up automatic load balancing device
Reactive load balancing
Increase the field current of an engine At the same time, the excitation current of the other unit is weakened.
Active load balancing
Aircraft AC power control
Main control objects (executive components)
Generator Excitation Control Relay (GCR)
Generator circuit breaker (GB
Bus Bar Tie Breaker (BTB)
External power contactor (EPC)
Failure and protection
Fault type
Generator phase failure
Generator voltage failure
Generator frequency failure
Generator phase failure
Rotating rectifier short circuit fault
Aircraft electrical equipment
Electric machinery
Consists of actuator module (AM) and electronic control unit (ECU)
DC motor
Series motor
Large starting torque and great acceleration performance
Shunt motor
Suitable for infrequent starts and requiring a constant speed
Compound motor
starter motor
Branch series motor
Easily achieve changes in rotational speed
Electric starting equipment
Piston engine starting method
direct start
The required starting current is large and is only suitable for small aircraft.
Coasting start
ignition start
compound start
The combination of the two, the flywheel and the electric motor drive the engine crankshaft at the same time
turboprop engine
Growth method
① Increase the starting power supply voltage and implement voltage speed regulation
② Reduce motor magnetic flux
③ Connect an additional resistor in series to the armature circuit and then short-circuit it
work process
① Starting with an additional resistor in series with the armature circuit
② Start by cutting off the additional resistor
③ Reduce motor flux to start
④ Start by increasing the power supply voltage
⑤ Reduce motor flux to start
turbojet engine
Air source starting
The APU can ensure the full power output of the generator during the entire flight, thereby adding a power source to the aircraft and improving reliability.
electric start
Variable frequency starter generator (VFSG) operating mode
stop
start
electric motor
dynamo
lighting equipment
lighting source
Incandescent Fluorescent Halogen LED electroluminescent lamp
External lighting
landing light
Function: Facilitates pilots to observe the runway and visually measure altitude under poor visual conditions
Movably mounted on the wing, front of the fuselage or opening on the engine surface Fixed installation on the leading edge of the wing, the front end of the fuselage or the landing gear
Taxi light
Function: To illuminate the taxiway when the aircraft is taxiing on the ground
Installed on the leading edge of the wing, fuselage nose or landing gear member
Navigation lights
Function: Indicate the position and direction of the aircraft in the air or on the ground during night flight
The left wing has a red light, the right wing has a green light, and the tail has a white light.
Anti-collision lights
Function: Mark the position of the aircraft to prevent aircraft collisions
Installed on the upper and lower sides of the fuselage or at the wingtips
Interior lighting
cockpit lighting
Sufficient brightness, good dark adaptability, small reflected light
cabin lighting
Service equipment bay and cargo bay
emergency lighting equipment
Electromagnetic interference and protection
Electromagnetic interference and its hazards
electromagnetic interference
Three elements: interference source, interference propagation path, and sensitive equipment
Path: Conductive transmission method radiation transfer mode
harm
① Destroy or reduce the performance of electronic equipment
② Cause flammable and explosive fires and explosions
③ Cause damage to human tissues and organs, endangering personal health
Electromagnetic compatibility control
shield
Electric field shielding
Magnetic field shielding
Low frequency magnetic field shielding
High frequency magnetic field shielding
Electromagnetic shielding