Electronics

The only difference is that the generator is part of the IDG ==> lighter and more compact unit => provided a 400 Hz constant supply if an electrical system with constant frequency => cooled by its own hydraulic oil system

Variable speed constant frequency Generator: supplies the aircrafts AC system with constant AC-volatge and frequency without the help of a CSD

==> a speed increaser gear is installed between the accessory gearbox and the generator and increases the RPM of the brushless AC generator by a factor of approximately 1:3 

VSCF => the variable RPM result in a variable voltage and frequency => The output is feed to a rectifier that converts teh AC into a DC volatge 

Rectifier: Gleichrichter => AC to DC     transformer rectifier Units  TRU 

Inverter: Wechselrichter => DC to AC 

Transformer: Frequencies changes 

the disconnect switch deactivated the generator by interrupting the field current but without opening a decoupling clutch as in a hydraulic CSD or IDG

the generator is directly connected to the engine and no technical system ( e.g. CSD) is required to keep the RPM constant. The frequency typically from 360 Hz to 800 Hz

=> Variable frequency generator type can be run only in isolated power supply systems => the frequency variations are not suitable for the direct operation of all types of AC consumers 

A Variable Frequency Starter Generator ( VFSG) is used as a synchronous motor to start the engine => Advantages: Replaced the bleed air system and thereby weight saving and simplifies the APU design

Auxiliary Power Unit: produces electrical power => same type of electrical power (200V/115V; three phases, 400Hz) => supplies compressed air on the ground for engine start => some APU's are equipped with their own dedicated 24 V battery

External power source (200V/115, three phases, 400 Hz) => the receptacle consists of four thick pinks which provide the connection for the three electrical power phases A,B, and C as well as for the common neutral port

NiCd batteries with a DC voltage of 24 V is charged during normal operation of the electrical power system => Only the hot battery bus is always powered by the battery ==> Monitore the battery temp. for a thermal runway

Because of the high power desnity compared to NiCa batteroes more and more Li-Ion batteries are installed in modern aircrafts

As a chemical principle they are using graphite at the negative electrode and a water free electrolyte mostly based on organic solvents

the Ram Air Turbine provides hydraulic power to powered actuation of flight control surface and electric power for flight control computers, essential instruments, radio, cockpit lighting, windshield- and pitot tube de-icing

1. hydraulic RAT: directly a hydraulic pump

2. electrical RAT: directly an AC generator 

3. hybrid RAT: a hdraulic pump and a AC generator are driven => power by hydraulic lines and cables directly from the RAT 

The mechanism adjusts blade angle to maintain const. station speed by a spring, which moves the blades in the starting position and a counter weight on each blade

=> reduces the speed, the inertia force decreases ant the spring force rotates the counterweights and the blades backe

1. Automatic switching occurs if the respective AV buses ( 1 and 2) fail to ne provided with a power at a minimum

2. the pilot can extend the RAT

=> when a RAT extends, a proximity switch operates and sends a signal to the system => RAT out

Three phases AC systems enable aircraft systems to make use of asynchronous motors and effective three phase transformers => three phases generators provided two different AC output voltage

400 Hz

There is no change in ohmic resistance

The Capacity resistance decrease

The inductive resistance increases

Feeding back the output voltage of the main generator to the voltage regulator closes the central loop. The voltage regulator is then able to keep the voltage constant throughout a wide range of load variations. It provided a constant voltage output for the generator by varying the current flow through the field coils of the exciter generator 

The three-stator windings, which generate the output power generators, are connected in a star configuration

to keep the generator frequency at 400 Hz in all engine RPM ranges from idle to full thrust

a hydro-mechanical speed regulator is integrated in the IDG

If emergency power, the batteries have to supply AC busses directly via a static Inverter and DC busses => All AC power is provided at 115 V and at a frequency of 400 HZ

=> 30 minutes with 24 V DC diretly to the emergency bus 

1. main power: => supplied by teh main power distrubution (main bus) 

2. essential power distribution => when the main busses fails

3. emergency- or the standy- power distrubution system  => supplied by the main power sourced via the essential power distrubution 

=> sometimes (Airbus) there  isn't a seperate emergency bus => essential bus takes over teh functions of teh emrgency bus 

Isolated/split system and parallel system => Each system consist of an AC generator and contains it own AC and DC busses => If one fails = changer relay

If APU or engine generator power i supplied to a single generator bis while ground power is connected to both generator busses, the ground power continues to supply power to the other generator

1. by the corresponding generator 

2. external power 

3. APU 

4. by the other generator 

teh AC ESS BUS is restored automatically by the constant speed motor/generator as soon as RAT hydraulic port is available => without CSM/G the battery supplies the AC ESS BUSS via s static inverter

1. GEN 1 or 2 or the APU 2. EMER GEN 3. the batteries

allows for synchronized generator to run in parallel => If a generator fails, the remaining generators support the total load without switching

1. Close the bus Tie Breaker (BTB)

2. the respective Generator aligns itself parallel to the AV synchronous buss after the Generator Breaker GB closes (if the voltage of bus and generator are equal)

to ensure that all parallel generators work at the same capacity => they share the same load

==> Independent load regulation circuits are necessary to provide identical lading conditions for all parallel generators, because the total AC load, the so-called apparent load, is cimposed of a real and a reactive component