Electrical Systems Flashcards
What is an ohm?
The unit used to measure resistance.
It’s how much a wire in a circuit resists voltage and how much is converted into heat.
Wires are not perfect conductors.
What are volts?
Pressure - how fast the electricity flows.
Amps (flow rate) x ohms (resistance) = volts
With water, this would be the force or pressure of the nozzle.
Volts measure the electromotive force / EMF that drives electrons around a circuit.
When you think of volts, also think of compatibility. If you have a device in a home that uses 220 volts (like overseas), that’s all you can use.
The smaller the volts, the bigger the wire / the more amps you need. Check this???
In the United States, small devices such as lights, computers, and cell phones run on 110 volts. Larger, energy-hungry appliances such as refrigerators, dish washers, and washing machines use 220 volts.
What are amps?
The amount of electricity or flow rate in a circuit is measured in amperes / amps.
To push more amps, you need a larger wire.
Current is electrons flowing in a conductor.
When a really high number of millions of electrons flows per second, we say we have one ampere / amp.
With water, this is the size of the hose. (Some may say the resistance of a wire measured in ohms is a better analogy for amps, though).
You’ll likely see amps inside your home’s service panel known as the breaker box. You’ll see different circuit breakers listed as 15 amps, 20 amps and 30 amps.
The larger the amperage, the more electricity can flow through the circuit. Large appliances like air conditioners, washers and dryers will be connected to 30-amp circuits, while most outlets in a home will be powered by 20-amp or 15-amp circuits.
If you try to run too many appliances on the same circuit, the breaker will “trip” and cut off power in order to protect the wiring from overheating.
In Europe, where they use 220 volts in buildings instead of 110, they can use smaller wires. That means they are likely to cost less. It also means you’ll have to move everything through faster / have more volts. That increases the chance of an overload when all the electricity can’t pass through easily, and the wire heats up increasing the risk of a fire.
What are watts?
Volts x amps = watts. It’s the total volume of electricity.
In the US, electrical systems in homes use 110 volts. So if you have a 900 watt tool, you can produce those watts with 8 amps - 110 x 8 = 880 (rounded off).
The Citation Sovereign DC electrical system produces 28.5 volts and 300 watts up to FL300. 28.5 x 300 = 8,550 watts.
What is an amp hour?
A measure of storage capacity.
It’s amps x hours. Take the output the battery puts out and multiply it times the number of hours it can put it out.
A battery that puts out 45 amps normally and can do that for 2 1/2 hours will have a 112.5 amp hours.
The main batteries on the Citation Sovereign are 44 amp hours.
What is a relay?
A device for switching on a circuit from a distance.
When the distance switch is closed, the current flows into the coil making it an electromagnet. This attracts the pivoted bar, and the contacts come together completing the main circuit.
When the distance switch is opened, the spring pulls the contacts apart breaking the circuit.
What is a reverse relay?
A relay where the spring holds the contacts closed instead of open when the circuit is open and electricity is flowing.
When the current flows, the contacts are pulled open.
What do fuses and circuit breakers do?
They protect the electrical system. Most planes use circuit breakers instead of fuses because you can reset them.
A circuit breaker pops when you have too much voltage. That causes high heat in the electrical wire.
When a fuse breaks, that circuit won’t be complete until you replace the fuse.
Circuit breakers on the same bus are usually located together in the cockpit.
What does a voltage regulator do?
It monitors and controls the electric system.
While the engine RPM’s will vary, the voltage regulator stabilizes the output of the alternator and makes sure it puts out the right amount of voltage.
It is usually incorporated into the alternator or generator.
Thus, it helps keep the system safe and prevent electrical fires.
What does a resister do?
Lowers the volts in a circuit.
For example, if you have a supply of 28 volts and a lamp that operates at 6 volts, you need to lose some volts somewhere in the circuit.
A resister is shown on an electrical diagram either as a or a zig zag line or a horizontal box.
What does an ammeter do?
It shows if the battery is being charged or drained.
What does a load meter do?
It shows how much demand - or load - is being used by the alternator or generator.
What kinds of circuits on an aircraft use a lot of power?
Anything that produces heat - such as pitot heat - or light.
The number on the circuit breakers will tell you how much current a circuit draws.
What does a rectifier do?
It converts AC to DC power.
They are sometimes also called transformers or TRUs - transformer-rectifier units.
Small GA planes use alternators, and they produce AC power - generators produce DC power.
The alternating current has three legs - it starts at zero, climbs to a positive value, goes to a negative value, and then returns to a negative.
The rectifier removes the negative - or unusable part - of each leg’s output to produce a DC-like output.
What does an inverter do?
Converts DC to AC power.
What do the batteries do?
They are used to power up the plane and then are there for emergency use.
Batteries store energy but do not produce it. Corresponds to water system reservoir.
However, a battery also acts as a shock absorber in a circuit because (again like a spring or a reservoir) it can absorb a surge or “spike” of electrical energy that might otherwise damage components of the circuit.
So they will be used to start the APU. Once the APU is available, if the batteries are fully charged, they will be disconnected from the aircraft’s electrical system.
They are the last resort for power in the event of a full electrical failure in flight.
What are the two types of generators?
DC generators and AC generators (which are also known as alternators).
What is a hot battery bus?
A hot battery bus is a bus that is hot wired to the batteries and works even when the aircraft is completely shut down.
Items like emergency lights and built-in fire extinguishers are usually powered off the hot battery bus.
What is the difference between an alternator and generator?
Alternators…
- Produce AC current
- Lighter
- Produce more current - especially at low RPMs.
The landing lights in a DC powered system can dim when you cut power when landing. In fact, DC powered systems require a higher minimum RPM to even generate electricity.
- Have higher amp ratings than generators.
- Produce more stable current. An alternator’s current is at a fairly constant rate regardless of RPM’s, but a generator’s current varies based on RPM’s.
- Are more reliable.
- Its voltage and current / amperage can be stepped up or down easily, which is not the case with DC current.
Generators
- Produce DC current.
- Can produce electrical power even when the batteries are completely dead while alternators cannot.
Alternating current is useless in GA aircraft electrical systems, so it must use rectifiers that convert it to DC.
What do diodes do?
Allow electrical flow only in the direction of the arrow, like check valves in water, hydraulic, and pneumatic systems.
What is a GCU / generator control unit?
Turbine aircraft generators are normally controlled by generator control units (GCUs).
They connect and disconnect the generator from the system when electrical abnormalities occur. They also serve as a voltage regulator, directing electricity to the battery when recharging is required. The GCU corresponds to a “smart” valve in the reference water system.
What is a starter generator?
On many smaller turbine aircraft, single unit starter/generators serve double duty as both electric generators and engine starter motors. When electricity is applied from an outside source, the unit acts as a motor. When turned mechanically, the same unit “pumps” out electricity.
Why is it important to check battery voltage before starting the engine on a turbine engine?
Weak batteries can cause a hot start because they won’t spin up the engine compressors enough.
Many turbine operators use GPUs for starting whenever they’re available, in order to reduce wear and tear on their expensive engines and batteries.
What is the difference in lead-acid and ni-cad batteries?
Lead Acid
- What you’ll see in cars and piston airplanes.
- Less expensive
Ni-cad / nickel cadmium
- Much more expensive
- Put out lots of current - since a weak battery can lead to a hot start, many operators are willing to pay more for ni-cad batteries
- Put out sustained voltage over a longer period of time whereas lead acid batteries drop out quickly
- Memories - If a ni-cad battery is kept nearly fully charged all the time, it tends to lose some of its ability to meet more demanding situations. For example, if GPUs are used for every start over a period of months, the battery gets used to providing only limited power and then recovering over a short time span. It may not then be able to fully power a battery start. When this happens, the battery must be removed by maintenance and deep-cycled. This refers to the process of fully discharging the battery and then slowly recharging it on a trickle charger.
- Ni-cads are sometimes subject to thermal runaway - sometimes called runaway battery. Thermal runaway occurs when excessive current is drawn from and then replaced to the battery. The battery overheats and begins to self-destruct. Unless attended to early, overheating sometimes cannot be stopped until the battery is completely physically destroyed. Some aircraft have battery temperature indicators in the cockpit for identifying this condition; others may only be tested electrically by the pilots. In any case, thermal runaway can be a very serious problem. The procedure is to immediately isolate the battery from all other circuits and to make a prompt landing. Runaway batteries can potentially damage other electrical components, cause fires, and damage airframes due to release of internal battery chemicals.
What are relays and solenoids, and why are they important?
Relays and solenoids are remotely or automatically controlled switching devices built around electromagnets. In each device, a small amount of current is sent through a coil to move a switch or shaft.
Relays, solenoids, and associated devices are very important in modern aircraft because of the trend toward computerized systems. They allow remote electronic control of all types of aircraft systems, whether hydraulically, pneumatically, or electrically powered.
What do relays do?
A relay is an electrically powered remote control device that controls circuits carrying large amounts of current. However, newer technology solid-state devices are replacing relays for many applications.
What do solenoids do?
A solenoid is an electrically powered remote control device that is designed to move a shaft over a short distance when powered. Solenoids are used to remotely operate hydraulic and pneumatic valves and small mechanical devices, as well as other switches.
Remember this by thinking two S’s. Solenoids move shafts.
What are the three kinds of electrical faults?
An open, short, and logic failure.
What is an open?
An open is an uncommanded interruption of electrical supply to or in some electrical component or system.
When an open occurs, the affected device or system stops operating and has little or no effect on other components outside the affected one.
What is a short?
A short is when electricity takes a “shortcut” through or around a component or system.
You’ll have a failed component or system and a drain of electricity out of the system.
Power is traveling like spilled water to the aircraft’s metal structure and then back to the generator and battery. The gizmo is unpowered, and if unchecked, a short is likely to damage or ruin virtually every component on its circuit.
It may also draw more electricity than the system power source (or sources) can produce, which would disable the power source.
If the power source is not isolated immediately from the short, it will quickly fail due to its inability to produce an infinite amount of electricity.
What is a logic failure?
This occurs when some component - often computer controlled - gets the wrong idea about what it’s supposed to do.
What are bus ties?
Bus ties are switches or relays used to connect or disconnect buses from one another.
They serve to isolate failed buses from working ones and may be manually or automatically actuated, depending on the aircraft. They are also used to reroute electrical power to buses that have lost their normal power sources.
How do generators and alternators make electricity?
By running a magnet past a coil of wire. That creates a current in the coil.
When you have a magnet inside a coil of wire, you have an electromagnet.
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current.
A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off.
The wire turns are often wound around a magnetic core made from a highly magnetic - known as ferromagnetic - material such as iron.
The magnetic core concentrates the strength of the magnetic field, known as magnetic flux, and makes a more powerful magnet.
How do DC generators work?
The electric field is on the outside, and the coil of wire on the inside rotates.
That rotating coil of wire is called an armature, and the electromagnet is called the field.
If you increase the volts in the field / the strength of the electricity, the field gets stronger, and the generator will put out more current.
What are slip rings and commutators?
The devices that collect the voltage in generators and alternators.
They are in the center of the generator.
Slip Ring - Used with alternators.
Has different channels that essentially makes it a switch that goes from positive to negative and back and forth. That’s alternating current.
On a turbine aircraft, though, It’s still called a generator even though it provides alternating current. It’s known as an AC generator instead of a DC generator.
Commutator - Used for DC power. It still has a slip ring, but little notches in the slip ring make it a commutator. A commutator gives you little blips of positive all the time instead of going from positive to negative.
To switch current from AC to DC, you would use a commutator.
As you increase the load on a generator, what happens to the amperage?
It goes up.
The voltage, however, will stay the same.
What does a generator master switch do?
Turns the magnetic field on and off.
What does a voltage regulator do?
It regulates the intensity of the electromagnetic field.
How does the alternator work in a big jet such as a Boeing?
The electrical field in the middle usually rotates and the coil of wire around it called the armature is stationary.
That’s because the field has less electricity than the armature. On a big plane, the armature pulls of a tremendous amount of current. Since the field doesn’t carry as much current as the coil of wire around it, there will be less arching.
Arching is when electricity jumps from one connection to another. At times you hear electric switches producing a sizzling/ cracking sound.
Typically, this happens when you turn them either on or off and could be cause by two things.
- A damaged cable / wire. If the cause is a damaged wire, the wiring cannot endure the current flowing, which is why the arcing takes place.
In small alternators, usually the armature rotates and the field is stationary.
If you ever hear about exciting a rotor, that relates to exciting a rotating field in a large jet.
What are rotors and stators?
Rotors rotate and stators stay in place. They are used in electrical systems in alternators and generators as well as in turbine engines.
So the rotor is the field.
In small alternators, the armature rotates and the field is stationary.
With big alternators, the field rotates and the armature is stationary.
The armature is the winding - or set of windings - of an electric machine which carries alternating current.
The armature can be on either the rotor / rotating part or the stator / stationary part.
What is amplitude?
The peak value of the current in the sine wave.
What is a conductor?
A substance that allows the flow of current and has electrons that are dislodged easily is called a conductor.
Silver, copper, and aluminum are good conductors.
What are the three items you have in any circuit?
- EMF / electromotive pressure measured in volts.
- Current measured in amps.
- Resistance measured in ohms.
To save writing ohms every time, the Greek letter omega is used instead.
How do the starter motor and ignition systems get turned on during the start sequence?
After you press the start button and watch the rpm’s come up to about 10 percent, you bring the throttles out of idle cutoff. That turns on the ignition and introduces fuel.
The starter motor and ignition will automatically turn themselves off themselves during the sequence.
When the engine starts to run on its own, the starter-motor will pull less current. It won’t have enough current to keep the starter solenoid closed. The solenoid is spring loaded, so it will pop open. That will shut off your starter motor.
What are magnetos?
Magnetos create their own sparks for the spark plugs and allow the engine to keep running if the electrical system of the aircraft fails.
A magneto is a combination of a generator and a transformer / coil that increases the voltage.
A generator is a magnet run near a coil of heavy copper wire to create a current in the wire.
When the points open, the field collapses and abruptly shuts off the current in the primary, which induces the current in the secondary. Any time you have a change in current in the primary coil, that creates a current in the secondary coil.
The amount of voltage generated in the secondary coil is determined by the number of windings and by the rate of the magnetic field of the primary. So the more windings and the faster the rate of collapse, the higher the voltage in the secondary coil.
The condenser is two metal plates with an insulator in between them.
It keeps the spark from jumping / arching the gap whenever the points open. If that happened, the field would not collapse. So the condenser prevents that and quickens the collapse of the field by stopping the arching so the current no longer flows.
If you have duel magnetos, they share the rotating magnet.
What are poles in electricity?
Poles are the number of legs a circuit uses.
For example, a regular 120 volt outlet is single phase, so it uses a 1-pole breaker. That means that it connects to just a single leg of the power supply.
In the US, typically any 240 volt appliance is supplied by a 2-pole breaker, which gives you 240 volts, single phase (electric ovens, electric dryers, etc.).
Four poles means the generator has four magnetic poles. Magnetic poles always come is sets of two, so two will be north and two will be south.
How many circuits do magnetos have?
Three.
The magnetic circuit is when the poles line up with the shoes.
The primary and secondary circuits both go through the coil.
What is a three-phase generator?
The windings around three-phase generators are arranged in such a manner that each phase is 120 degrees out of phase with the other.
The outputs of an AC generator are connected in what is called a star method. The three phases are joined to form a neutral point that is grounded.
What is the main difference between a DC generator and an AC generator?
The main difference between a DC generator and an AC generator in an aircraft is that in a DC generator, the armature of the generator turns.
In an AC generator, the field or the magnet turns around a stationary armature.
What does impulse coupling on a magneto do?
It automatically retards the spark and spins the magneto fast.
In order to generate a lot of electrical current, the magneto must be turning fast. However, during start, it won’t be.
Also, when an engine is starting, you need to retard the spark.
The impulse coupler does both things.
There are flyweights in the impulse coupling. When the magneto is turning slowly, they stay retracted and do not sling out.
The flyweights also delay turning the magneto even though the engine is turning.
The magneto has a spring tension that builds up. Once the tension gets to a certain amount, the flyweights are released, and the magneto all of a sudden spins rapidly.
That makes the magneto spin faster and retards the spark.
The impulse coupler only affects the magneto during the start.
What does a fuse look like on an electrical diagram?
A rectangle with a line through it.
What are the two main types of fuses?
Cartridge fuses and
Cartridge fuses use tin copper wire that is enclosed in a casing with the ends sealed with brass caps.
They are used with currents of less than 100 amps. Their advantages are that they are cheap to make and easy to change. Their disadvantages are that the climate may affect their ratings and the voltage could be enough to cause arching across the gap after the fuse has blown.
The high rupturing / HRC fuse doesn’t have those disadvantages and can be used up to several hundred amps.
These are made of several strands of silver passing through ducts in an earthenware / hardened clay casing. Quarts power is packed around the strands.
When too much current flows, the wire and quarts powder around it melt. It’s a good insulator, so no arching across the gap can occur.
What is a capacitor?
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
What three things affect the magnetic field produced by a coil?
- The more turns, the stronger the field.
- The greater the current flowing, the stronger the field produced.
- Adding an iron core to the coil concentrates the lines of force.
What is the force that drives electrons around a circuit?
Electromotive force / EMF. It is measured in volts.
Whenever you find two bodies in a different state of charge and connect them, there will be an EMF driving a current between them.
It isn’t necessary for one to be negative and the other positive. If one is negative and the other is still more negative, meaning it has accumulated more free electrons, and you connect them, there will be a driving force from the more negative body to the less negative body.
What makes a good conductor?
A substance with easily detached electrons, which allow current to pass easily. They have low resistance.
Good conductors are silver, aluminum, and copper along with carbon and water.
What three things - apart from the material - determine a material’s resistance?
- Length - The longer the conductor, the higher the resistance. So a greater EMF would be required to drive the current through it.
- The cross sectional area - The larger cross section, the lower the resistance.
- Temperature - The hotter the material of the conductor, the higher the resistance.
What does insulation surrounding a wire do?
It prevents the current from leaking away.
The longer the wire, the easier it will be for the current to leak away from the insulation.
The thicker the insulation, the harder it will be for the current to leak away.
What is dart notation?
If a dart is moving away from you, you’ll see an X. If a dart is moving towards you, you’ll see a point.
So that’s how current is written. Current that’s moving away from you is shown with an X, and current that’s moving towards you is written with a dot.
