021 02 Electrics & Electronics
Basics, Batteries, AC/DC current, Generators
Basics, Batteries, AC/DC current, Generators
Kartei Details
| Karten | 57 |
|---|---|
| Sprache | English |
| Kategorie | Verkehrskunde |
| Stufe | Andere |
| Erstellt / Aktualisiert | 14.08.2022 / 13.06.2025 |
| Weblink |
https://card2brain.ch/box/20220814_021_02_electrics_electronics
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Static vs. Dynamic Electricity
Static: Imbalance of electric charges within or on the surface of a material.
Dynamic: Electrons in motion.
Static dischargers (static wicks)
A plane builds up static electrical charge during the flight by friction between the air and the surfaces of the plane.
--> Static dischargers reduce the build up of static electricity by dispensing the charge into the atmosphere.
Grounding / Bonding
ACFT is statically charged due to...
- friction between the air and the ACFT surfaces - in-flight
- friction between the fuel and the fuel pumps, pipes and filters it runs through causes positive charged fuel ions to enter the fuel tank
--> ACFT parts are connected by flexible wire strips to distribute the static charge equally across the whole ACFT to keep it at similar potential.
--> On ground ACFT is grounded to dispose of the static charge
Voltage
= difference of potential
--> On one side there is a surplus of electrons (=Minuspol), on the other side there is a shortage of electrons (=Pluspol)
Current
= electrons per time
Physical current = Movement of electrons from Minuspol to Pluspol
Technical current = Movement of electrons from Pluspol to Minuspol
DC = Direct current --> For low voltage consumers, e.g. PFD
AC = Alternating current --> For high voltage consumers, e.g. generators/motors
Every conductor has a maximum allowable current. --> Depends on the material and cross section
Resistance
= obstruction of the flow of electrons
Depends on...
- Specific resistance of the material \(\rho\) (Depends on the number of free electrons)
- Lengt L of the conductor (Longer = Higher resistance)
- Cross section A of the conductor (Larger = Lower resistance)
- Temperature
- Metalls: High temperature = higher resistance (and vice-versa)
- Semi-conductors: High temperature = lower resistance (and vice-versa)
Energy / Electrical Work
W = U * I * t [kWh]
Electrical Power
P = W / t = U * I [W]
Fuse
Fuses protect the circuit from overcurrent conditions.
--> A strip of metal melts at a specified current [A] and opens the circuit
Case material: Glass / Ceramic
Element material: Tin, Lead, Silver, Copper, Tin bismuth alloy, Copper silver alloy
Current limiters
Similar to fuse but withstands a considerable overload for a short period of time.
Element material = Copper
Circuit breakers (C/Bs)
Break the circuit to stop the current when predetermined value is exceeded.
--> CBs can be reset, fuse and current limiter must be replaced
Non Trip Free CB: Can be held in when tripped --> Closed circuit despite overload current
Trip Free CB: Cannot be held in when tripped
Push Type CB: After bimetallic strip has cooled, it can be reset
Push Pull & Toggle Switch Type CB: Can be pulled manually
Battery - General
Electrical storage device serving as a back-up to provide electrical energy by a chemical process.
Are charged with DC voltage --> Charge unit must have a higher voltage than the battery.
Galvanic Cell
Consists of two conductor elements separated by an electrolyte through which electrons flow from one element (Cathode) to the other (Anode).
Primary cell: Non-rechargeable elements (Batteries)
Secondary cell: Rechargeable (Akku)
Lead-Acid Accumulator
Elements: Lead Peroxid --> Lead
Electrolyte: Water (70%) & Sulphuric Acid (30%)
Cell voltage: 2.0 - 2.1 V
--> min. 12 cells in series required to supply the standard 24V
Ni-Cd Accumulator
Elements: Nickel Oxyde --> Cadmium
Electrolyte: Potatssium Hydroxide (KOH)
Cell voltage: 1.2 V
--> min. 20 cells required for the standard 24V
Conductors: name some examples of conductors:
Lizenzierung-Metals
-Carbon
-Humid soil
-Some liquids
Remark: in liquids ions are transporting electric energy
Semi-Conductors: name some examples of semi-conductors:
-Silicon
-Germanium
Remark: The resistance of semi-conductors is higher than the resistance of consuctors
Insulators: name some insulators
-air
-rubber
-plastics
-glass
-porcelain
Remark: The resistance is almost infinite
Series Circuit: Describe the behavior of Current, Voltage and Resistance in a serial circuit
I = Constant
U = U1 + U2 + U3...
R = R1 + R2 + R3...
Series Circuit: After which resistor is the highest voltage drop observed?
After the highest resistor
Parallel Circuit: Describe the behavior of Current, Voltage and Resistance in a parallel circuit
I = I1 + I2 + I3...
U = Constant
1/R = 1/R1 + 1/R2 + 1/R3...
Parallel Circuit: The total resistance is ... than the lowest single resistance.
smaller
Parallel Circuit: The highest current flows through the ... resistor
lowest
Resistors: Influence of Temp. increase on a PTC
Resistance: ...
Current: ...
Resistance: increases
Current: decreases
Resistors: Influence of Temp. decrease on a PTC
Resistance: ...
Current: ...
Resistors: Influence of Temp. decrease on a PTC
Resistance: Decreases
Current: Increases
Resistors: Influence of Temp. increase on a NTC
Resistance: ...
Current: ....
Resistors: Influence of Temp. increase on a NTC
Resistance: decreases
Current: increases
Resistors: Influence of Temp. decrease on a NTC
Resistance: ...
Current: ...
Resistors: Influence of Temp. decrease on a NTC
Resistance: increases
Current: decreases
Capacitor: What is the difference compared to batteries?
The difference compared to batteries is the missing transfer from chemical energy to electrical energy. Another fact is that elec. voltage differs in scale and characteristics much more during charging and discharging compared to batteries.
Capacitor: Which unit is used to measure the capacitance C?
the Unit of Capacitance (C) is Farad (F). It indicates the ability of a substance to hold an electric charge.
Capacitor: What is the layer of electric insulation material between the two plates called?
Dielectric
Capacitor: Describe the current flow during charging of a capacitor (in DC)
When a voltage is initially supplied to the capacitor, a high current flows to charge the capacitor plates. This current is not constant because the more the plates become charged, the lower the electron flow from and to the capacitor, i.e. the smaller the current.
Capacitor: In DC, the resistance of the capacitor is very ... after being switched on and ... to an .... value when the plates are charged.
low
increases
unlimited
Capacitor: Where does the electric field in a capacitor exist?
When the capacitor is charged, an electric field exists between the plates.
Capacitor: What is capacitance related to a capacitor?
The amount of stored energy (electrons) between two metal plated is called capacitance
Capacitors: Which system in large aircraft makes usage of capacitance?
The fuel quantity probes are capacitors. The capacitance of the probes changes as the dielectric constant of the insulating medium between the capacitor electrodes changes. The dielectric in the probes is either:
- Liquid fuel
- Mixture of air and fuel vapor
- Combination of the above two
When the fuel tanks are full, the capacitance of the probes is greater than the probe capacitance when the fuel tanks are empty.
Capacitors: Express the mathematical relationsship of capacitors connected in series (based on their capacitance)
1/Ct = 1/C1 + 1/C2 + 1/C3...
Capacitors: Express the mathematical relationsship of capacitors connected in parallel (based on their capacitance)
Ct = C1 + C2 + C3
A voltmeter reaches full scale deflection at 0.3 V and 0.6 mA.
How can the same scale be used to measure higher voltages?
What size would the add. element require to measure 1.5 V with the same scale?
Add a resistor in front and in series.
R = U / I = (1.5 V - 0.3 V) / 0.0006 A = 2000 Ohm
The center pedestal light of your aircraft is dimmable. How does this work?
Old school dimmers had a pretty straightforward solution to adjusting light levels -- a variable resistor
Instead of diverting energy from the light bulb into a resistor, modern dimmers rapidly shut the light circuit off and on to reduce the total amount of energy flowing through the circuit. The light bulb circuit is switched off many times every second, undetectable to the human eye.
How can you technically adapt the scale of an Amperemeter (Ammeter) to read out larger currents which are not covered with full scale deflection?
We will use the shunt resistance to draw all the current through it so that the measuring galvanometer will only receive a very small current. This way the galvanometer can measure much higher current.
