021 02 Electrics & Electronics
Basics, Batteries, AC/DC current, Generators
Basics, Batteries, AC/DC current, Generators
Set of flashcards Details
| Flashcards | 57 |
|---|---|
| Language | English |
| Category | Traffic |
| Level | Other |
| Created / Updated | 14.08.2022 / 13.06.2025 |
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Induction: Explain induction using the example of a simple generator
When a conductor moves perpendicular to a magnetic field, a voltage is induced in the conductor. The voltage occurs because the electrons inside the conductor become displaced to one side (the reason is the Lorentz Force). This phenomenon is called induction or induced voltage.
Induction: Voltage magnitude depends on:
- The strength of the magnetic field
- The length of the conductor within the magnetic field
- The angle at which the conductor cuts the magnetic field
- The speed at which the conductor cuts the magnetic field
Generators: What makes the shaft turn the conductor loop?
The shaft receives mechanical work from either the accessory gear box of the engine/APU or via a v-ribbed belt.
Generators: In what does the conductor loop (coil) turn and what is the effect of this?
The coil turns within a stationary magnetic field. By rotating the coil, voltage is induced in the coil (Lorentz Force).
Generators: What kind of current does a simple generator produce?
By rotating the coil, alternating voltage is induced. Alternating voltage causes alternating current.
Generators: Why does a simple generator require brushes?
The brushes act as an electrical contact on the rotating slip rings (part of the coil) in order to transfer the current from the rotating coil to stationary wiring for further use.
DC Generators: What is a commutator?
A Commutator is used instead of slip rings: the commutator changes its connection to brushes when polarity changes. This process is called rectifiying (of the alternating current).
Alternators: Instead of a rotating coil and commutators as in DC generator, an alternator delivers rectified DC by incorporating which two elements in its design?
- A rotating (permanent) magnet (within a stationary coil/loop)
- A diode (semi-conductor aka "the check-valve of electrical applications")
Alternators: Explain the working principle of a Full Wave Bridge rectifier?
The Full Wave Bridge rectifier uses 4 diodes, connected together in a “bridge” configuration, to rectify both half-cycles of a sine wave.
Alternators: Why is an excitation system required in an alternator?
Without the excitation system the alternator would have no way of building its voltage as it starts to rotate, nor would not be able to regulate its voltage to the pre-set nominal level while running at its rated speed
Voltage Control: On which three elements does voltage control mainly depend?
- RPM of generator/alternator
- Number of loads which require electrical energy
- (Variable) Magnetic Field Strength of the generator/alternator
Voltage Control: If the output of generator is not high enough to fullfill all system demands, e.g. during an emergency, what (shall) occur(s)?
Controlled elec. system shedding
Voltage Control: Higher RPM in an alternator/generator results in .... voltage
higher (due to the law of induction)
Voltage Control: in a generator/alternator, more loads -> voltage .... -> the exciter field (magnetic field) has to be adapted to control ... accordingly.
- drops
- RPM (of generator/alternator)
Voltage Control: If the loads are arranged in parallel within a closed circuit, the voltage should not drop. But why is there a drop in voltage if additional loads are supplied by the generator?
Ut = Rt + It, while:
- Ut remains constant,
- Rt decreases (in parallel circuit, sum of resistors smaller than single resistors),
- It increases
As It increases and internal resistance in generator remains the same, the voltage drop over the internal resistor increases, thus the voltage drop over the generator (in series with the inernal resistance) decreases.
Voltage Control: if the actual voltage in a generator/alternator differs from the desired voltage, the value of the resistor is changed. What is the effect of this?
By adjusting the resistor (which is in parallel with the generator and in series with the field winding), more or less current will flow through the field winding, which in return controls the excitment of the generator.
Voltage Control: Apart from variable resistor controlled, what other method exists to control the voltage of generator/alternators?
Switching type (relay or transistor), which starts/stops current through field winding.
