Electrical Principles

Question 1

Definition of electricity

Answer 1

Electricity is the flow of electrons along a conductor.

Question 2

Electrons

Answer 2

•The electron is a very small electronically charged particle that exists as a part of every atom.
•The three particles that construct an atom are protons (positive), neutrons (neutral) and electrons (negative).

•The flow of electrons is called electrical current
•Current is measured in Amperes
•One Ampere is the flow of 6.241 × 1018 electrons per second

Question 3

Electronic principles

Answer 3

•Resistance
•The Ohm is the standard unit of resistance, or opposition to current flow.

•Electromotive Force - Pressure
•The force that causes electrons to flow
•The Volt is the unit of electrical pressure and is the amount of pressure required to force on amp of flow through one ohm of resistance.

Question 4

Ohm’s law

Answer 4

•The current that flows in a circuit is directly proportional to the voltage that causes it, and inversely proportional to the resistance in the circuit.
•One volt will cause one ampere of current to flow in a circuit with a resistance of one ohm.

Question 5

Electrical theory

Answer 5

Electrical Power
•The end result for practical electricity is power, expressed in Watts.
•Power (watts)= volts x amps
▪1 Watt is the amount of power required for one amp to flow under a pressure of one volt.
▪1hp = 746 watts
•Alternating Current (AC)
•A cycle is one complete sequence of voltage from zero, to positive, back to zero, through negative and back to zero.
▪The time required for one cycle is the period, and the number of periods in a second is the frequency in Hz.

Question 6

Conductors vs insulators

Answer 6

•Conductor
•Materials composed of atoms with loosely held electrons are considered conductors
•The flow of electrons has less resistance than materials which have atoms with tightly held electrons that will resists flow.
•Examples of conductors: Metals (silver is best), Water, Gas Plasma
•Insulator
•Materials which are composed of atoms that have tightly held electrons which resist or cannot flow in response to an electromotive force.
•Examples of insulators: Glass, rubber, air

Question 7

Electron flow

Answer 7

•Electron Flow
•Occurs when a conductor is connected to a source of electrons.
•An atoms which looses an electron becomes a positive ion and pulls an electron away from the next atom.
•This exchange continues until the electron that left the conductor is replaced by one from the negative terminal and is repeated as long as a voltage pressure exists.

•Effects of Electron Flow
•As electrons flow, magnetic fields will be produced.
•If electrons are forced to flow in a direction of resistance, heat will also be produced.

Question 8

Electromagnetism

Answer 8

A fundamental force of nature
•An electric current in a wire creates a circular magnetic field around the wire
▪its direction (clockwise or counter-clockwise) depending on that of the current.
•A current is induced in a loop of wire when it is moved towards or away from a magnetic field, or when a magnet is moved towards or away from it
▪the direction of current depending on that of the movement

Question 9

Electromagnetic induction

Answer 9

Lines of magnetic flux pass between the poles of a magnet, and if a conductor is moved through these lines of flux, they will transfer to the conductor and force electrons to flow through it.

Question 10

Chemical

Answer 10

Matter (solid/liquid/gas) can have an imbalance of protons and electrons
•If a material having an excess of electrons is connected by a conductor to a material having a deficiency, electrons will be forced through the conductor
•Example: Lead-Acid battery

Question 11

Heat

Answer 11

•When certain combinations of metal are joined together with junctions, a thermocouple is formed. (Chromel + & Alumel -)
•An electrical current will flow through the wires when there is a difference in temperature of the two junctions.

Question 12

Pressure

Answer 12

Certain materials such as quartz will build an excess of electrons if caused to bend on one side and a deficiency on the other side.
•This type of material was used in early microphones to record sound vibrations as electrical pulses.

Question 13

Light

Answer 13

•Light is a form of energy, and when it strikes certain materials that are photo-emissive.
•Switches may be controlled by light sensitive devices to turn airport lights on at dark and off at dawn.

Question 14

Electrical energy source

Answer 14

Typically the battery is the source until the alternator or generator is operating.
•Once the alternator or generator is operating, it is the primary source of power because it has a higher voltage.

Question 15

Circuit

Answer 15

This is the transportation and distribution system for the electrical energy.
•A path way from the electrical source to the load and back must exist in order for electrons to flow.

Question 16

Active component

Answer 16

The site where the work is done, heat is generated, or a voltage drop occurs.

Question 17

Batteries

Answer 17

Capacity
•The capacity of a battery is measured in its ability to produce a given amount of current is a specific period of time, generally expressed in ampere-hours. ½ amps for 2 hours is the same electrical draw as 1 ampere for 1 hour and 2 amps for ½ hour.
•Rated Capacity: The batteries ability to perform when it is brand new.
•Actual Capacity: Performance of battery with the variables of temperature (cold=less power), battery state of charge, and battery condition (age, service history, g-loads).

•Battery Load
•To determine an approximate load on a circuit breaker, use the rule that 80% of a circuit breaker capacity is generally what flows through the circuit.
•This is useful in determining how long a battery will last given an alternator failure.

Question 18

Magnetism

Answer 18

Defined
•A magnet is a body that has the property of attracting iron and producing magnetic fields external to itself.

•Magnet operation
•Lines of magnetic force, or flux, are always complete loops that leave the magnet at right angles to its surface at the north pole.
•There is no insulation against lines of flux, as they will pass through any material
▪Iron has a very high permeability and provides a path of least resistance for the lines of flux to pass through.
▪if it is important that a device be protected from magnetic fields, it can be entirely surrounded by a soft iron shield.

Question 19

Electromagnets

Answer 19

While there is a magnetic field around the conductor, it has very little strength.
•To make use of this magnetic field, the conductor is wound into the form of a coil.
•In this form, the lines of flux are concentrated and the coil attains the characteristics of a magnet

Question 20

Types of electromagnets

Answer 20

Fixed core electromagnets
•When enough current flows, the magnet will become strong enough to pull the contacts open.

•Movable core (solenoids)
•Have a soft iron core that is held out of center by a spring
•As current flows in the coil, the magnetic field will pass through the core and close the switch.

Question 21

Generators

Answer 21

Amount of current produced is dependent on:
•Magnetic flux strength
•Rate of conductors cutting flux
•Number of conductors cutting flux
▪To improve output, multiple wire loops are rotated within the magnetic field

•In a generator, the resultant high current is passed through the split rings via brushes

Question 22

Simple DC generator

Answer 22

A simple DC generator uses one split ring instead of two slip rings.
•The split ring allows current to flow only in one direction at the site of the load even though alternating current is generated in the armature coil.
•These types of devices will produce pulsing direct current.
•To reduce the intensity and period of the pulses, additional coils are added to the armature.

Question 23

Alternator theory

Answer 23

In modern alternators, the wire windings are fixed, and the magnets (and associated magnetic fields) are rotated.
•Like the generator, the magnets are not permanent, but are electromagnetics
•A small electric current is supplied to the electromagnets to provide a magnetic field when desired
•In our aircraft and many automobiles, this current comes from the battery
•A magneto uses permanent magnets, and thus is independent from an external electrical source.

Question 24

Alternator parts

Answer 24

Stator
•Fixed outer iron ring with three current loops (each with hundreds of windings)
•Rotor
•Electromagnetics which are rotated
•Slip rings & brushes
•On rotor shaft, which connect a positive & negative voltage to the electromagnets
•Diodes
•Solid-state devices
•Convert AC to DC

Question 25

Direct current alternator

Answer 25

Alternators actually produce alternating current (AC) in their stator windings.
•Before leaving the housing, AC is converted to direct current via a rectifier circuit

Question 26

Transformer rectified unit

Answer 26

TRU Purpose
•Convert 115volt to 28volt
•Convert Alternating Current to Direct Current
•TRU allows a DC bus to be powered by an AC generator
•Redundancy and Reliability
•Used in larger aircraft

Question 27

Control devices

Answer 27

Switches
•Switches used to control the flow of electrons in most aircraft circuits.

•Protective Devices-Fuses
•A fuse is a fusible link made of low-melting point alloy enclosed in a glass tube.

•Protective Devices-Circuit Breakers
•Thermal breakers open the circuit when excess current heats an element in the switch and it snaps the contacts open.

Question 28

Archer electrical system

Answer 28

Primary electrical power
▪Plane Power 70-amp, 28 volt (DC) alternator
•Secondary electrical power
▪24 volt concorde sealed lead-acid battery / 13.6 amp hour
•Emergency backup –
▪Concorde battery – 24 volt / 6.0 amp hour
•External Power
▪Piper External Power (PEP)
▪Can be connected to provide power to the aircraft without having to access the aircraft’s battery.

Question 29

Ammeter, loadmeter, and control devices

Answer 29

Ammeter
•Show the rate of charge or discharge on the electrical system

•Loadmeter
•Shows the total electrical demand on the system
•Does NOT show status of battery (rate or charge or discharge)

•Control Devices
•Solenoids are used to control high current drain function remotely from the cabin