Electronics
T2a
T2a
Set of flashcards Details
| Flashcards | 474 |
|---|---|
| Language | Deutsch |
| Category | Electronics |
| Level | Primary School |
| Created / Updated | 12.01.2015 / 21.01.2020 |
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how you can change the direction of rotation by the Asynchronus AC Motor
only two of three phases have to be changed
Two Phase Induction Motor / Servomotor
a rotating stator magnetic field => The difference is that only a single-phase AC voltage supply is needed to produce a rotating stator magnetic field via two coils at 90
What is the trick by the Servomotor ?
=> The trick of obtaining a two phases current from a single phase current is to connect a capacitor in series => To change the direction, the capacitor must be connected in series with the other coil
What is the supply voltage of synchronous motors?
Only AC voltage
What does RPM of an AC motor (synchronous motor) depend on?
It depends on number of pole pairs and the voltage supply frequency
nominal batter voltage is
24 V
teh nominal generator/alternator voltage is
28 V
When the generator voltage drops to a level below the battery voltage, what happens?
the current flows from that battery to the germinator = reverse current => the generator works like a load = discharged the battery
2 Arten den reverse current zu verhindern?
1. Reverse Current Diode
2. Reverse Current Relays
Reverse Current Diode : how you can avoid the reverse current
to prevent the flowing from the battery to the generator is to use a diode => The current can flow only in one direction = diode works like a check valve
What can't happen wehn you use a alternator instead a generator
the reverse current problem cannot occur, because of the integrated diodes
2. Reverse Current Relays Prizip
normally open relay closed by two coils => normal closed = current flows through the low resistance current coil
=> If the voltage drops below that of the battery, current flows from the battery via the bus and the current coil to the generator = causing a magnetic field o current coil to change direction => teh two magnetic fields is too weak to hold close the relay => the relay opens and prevents teh current flow to the gnerator
Overvoltage Protection => What happens by a overvoltage?
some receive a too high current and that the battery starts to produce goxygen = gassing
What you must do by a overvoltage?
Shut down the generator, switch the generator off and on => If the generator shuts down again, it must be switched off and remain switched off ==> max. 30 min with the battery
Electrical System of Small Aircraft with one Generator: function
the battery supplies the hot bus directly to ensure that power is available all times to certain systems
Electrical System of Small Aircraft with one Generator: external power
the external power plus has three contacts; two large main contacts and one small auxiliary contact => the auxiliary contact must be connected to the pole to switch the corresponding relay, which then closes the main circuit
Electrical System of Small Aircraft with one Generator: engine starter => why there are no circuit breakers betwee the starter and the battery
very high current flows between the battery and the starter, the ires and switches in that part of the system, must be designed accordingly. => This is the reason why there is no circuit breaker between the starter and the battery
Electrical System of Small Aircraft with Starter Generator: Prinzip
Only DC power system = a Starter generator has dual function: motor and generator. the generator function operates afters engine start(produces voltage for the electrical system, the motor function operates during engine start (supplied with battery powe
Bus Design of Aircrraft with two or more generators: 4 Arten
1. Parallel Bus System
2 .Parallel Electrical System with Commutator Generators
3. Parallel Electrical System with Alternators
4. Selective Bus System
Bus Design of Aircrraft with two or more generators: Parallel Bus System
all alternators supply their voltage to a single common bus => high expense of voltage control to ensure the loading of each alternator is the same => otherwise, the alternator with the higher output voltage would drive the other one
Bus Design of Aircrraft with two or more generators: Parallel Bus System => Bei 2 Arten muss mann andere Dinge synchronisieren
1. AC system: the voltage, teh frequency and the phase of teh different alternatrs must be synchronised
2. DC system: Only teh voltage must be synchronised
Bus Design of Aircrraft with two or more generators: Parallel Electrical System with Communator Generators
The voltage outputs , the generator circuits are directly linked via so called equalizing bus => current will there flow when the two generators are producing different voltage
=> when the current flows through the current coil of the first voltage regalator (VR1), the resistance of the variable reistors is increased resulting in a weaker exciter magnetic field
=> The field currents change heir intensity until both generators produce teh same output voltage
Bus Design of Aircrraft with two or more generators: Parallel Electrical System with Aternators
to connect both field windings to only one voltage regulator => Both alternators are controlled at the same time and they may produce slightly different voltages => bis zu 10% => A second voltage only backup
Bus Design of Aircrraft with two or more generators: Selective Bus System
Each generator supplies its own bus during normal operation. If on generator fails, the bus supply is re-routed to the other generator
Electrical System Monitoring
a) battery charge light: when teh geni(alternator ouput is too low
b) discharge/charge meter: to check whetever the battery is supplying the loads or discharge
c) load meter: to see how much current teh geni is supplying to the bus
d) Ammeter /Ampère) and Voltmeter: switch between
Two static electricity
1. static charge during fligh
2. static charge during refuelling: fuel flows through teh fuel pumps, pipes and filters of teh refuelling track = this friction between the fuel and teh components loads the fuel
Electrical fire in flight; Gründe?
a) friction between two wires
b) Overloading of a wire
c) A Stuck electrical motor
=> Best reaction to shut off all electrical loads
Which electrical protection systems are connectes between teh main buses and teh electrocal loads
circuit brakers (Sicherungen, die man wieder hineindrücken kann) and fuses ( diese Sicherung schmilzt bei zur grossen current)
For which elecrical system, starter generators are installed
The starter generator is only installed on aircraft with a DC power system
Potential difference (PD) is:
The value of the difference in the number of electrons between two points of a circuit measured in volts
What is the letter symbol used to represent electrical pressure?
U
The true statement among the following in relation to the application of Ohm's law is:
Current in a circuit is directly proportional to the applied electromotive force.
Which basic principle is fundamental for all electric motor operation?
Physical force is produced when two magnetic fields react with each other
What is magnetic flux
lines of force
If the diameter of a wire is increased its resistance will:
Decrease
The Root Mean Square value of a voltage is equal to:
70.7% of the peak voltage
What is the result when increasing the thickness of the dielectric of a capacitor, with all else being the same ?
the capacity decreases
The electrolyte of a NiCad battery consists of ...
30 % by weight solution of potassium hydroxide (KOH)
How can the charge level of a lead acid battery best be checked?
By checking the specific gravity of the electrolyte.
The method of ascertaining (feststellen) the voltage of a standard aircraft lead-acid battery is by...
The voltage with rated load (Nennleistung) switched ON
