航空电理论航空英文培训课件.ppt

1、1,Electricity - 101,Airline Transition Course,2,Lesson Objectives,Develop a basic understanding of physics related to Electrical systems Look at specific electrical components Learn the basic operation of electrical systems,3,Electrical Theory,4,Electrical Physics,Electricity: the flow of electrons

2、Whats an electron? A very small particle that orbits the nucleus of an atom When one electron is passed from one atom to another electricity is produced,5,Why do Electrons Flow?,A balanced atom has three parts: Neutrons: No charge Protons: Positively charged Electrons: Negatively charged Ions pull e

3、lectrons off of the atoms and leaves them with more protons than electrons. The atom now holds a positive charge because of the unbalance of electrons and protons. More protons (positively charged particles) results in a positive charge.,6,More Electrical Knowledge,Conductors: Hold their electrons l

4、oosely to allow the exchange of electrons more easily Insulators: Hold their electrons more tightly so electrons cant flow as easily,7,More Electrical Knowledge,Electromotive force: The force that causes electrons to flow A group of positively charged particles would flow electrons toward a group of

5、 negatively charged particles Usually measured in Volts Electron Flow: From positive to negative,Area of Excess Electrons (Negative Charge),Area of Electron Deficiency (Positively Charged),8,Electrical Measurement,Quantity: the coulomb (culom) is the basic unit of electron flow, 1 coulomb 6.28 x 10

6、18 Thats 6,280,000,000,000,000,000 electrons Flow: 1 coulomb per second = one Ampere Pressure: pressure required to force one amp of flow through one ohm of resistance, the potential electromotive force= 1 Volt,9,Electrical Measurement,Resistance: opposition to current flow, the amount of force to a

7、llow a pressure of 1 volt to force a flow of 1 amp = Ohms Power: 1 amp of flow under of pressure of one volt = 1 Watt,10,Magnetism,Magnet: is a body that has the property of attracting iron and producing magnetic fields external to itself. Lines of magnetic force, or FLUX, leave the magnets north po

8、le, at right angles to its surface, and reenter the magnets south pole in the same manor. Ex: the Earth,11,Electromagnets,Conductive material holding electrical current will produce an invisible magnetic field around the material. When electricity is sent through a coil that is rapped around a condu

9、ctor, the conductor/core becomes magnetized,12,Relays & Solenoids,13,Relays Fixed core Electricity is applied and magnetism draws a circuit open or closed. Used for voltage regulators,Solenoids: Movable core Electricity is applied to the coil which draws the core inward, closing or opening a circuit

10、,Relays and Solenoids are used when it is necessary to control switches which carry large amounts of power from a small switch. Ex: Starter motor, Battery. or Avionics master A small amount of electricity is run to the actual switch, when turned on this electricity energizes an electromagnet,14,Sole

11、noids: Movable core Electricity is applied to the coil which draws the core inward, closing or opening a circuit,15,Solenoids: Movable core Electricity is applied to the coil which draws the core inward, closing or opening a circuit,16,Solenoids: Movable core Electricity is applied to the coil which

12、 draws the core inward, closing or opening a circuit,17,Solenoids: Movable core Electricity is applied to the coil which draws the core inward, closing or opening a circuit,18,AC vs. DC,Alternating Current: continually changes its values of voltage and current while periodically reverses its directi

13、on of flow Easier to develop large quantities of power Current (Amps) and voltage can be converted easily Ex: The current flowing through a conductor creates heat, and therefore determines the size of the conductor. We can trade some current for voltage and still achieve the same work remember: W =

14、V x A Thats why we have high tension power lines with 15,000 Volts, then the electricity is brought down to 115 Volts right before it enters our house.,19,Why do we use DC then?,A few reasons: We dont require large sums of electricity to power our aircraft Our instruments operate on DC Power is stor

15、ed (the battery) as DC,20,Circuits,Series and Parallel,21,Circuits,Series: All electricity must flow through all active components, If one component fails then the entire series fails.,22,Parallel: A portion of the current flows through each circuit If a bulb burns out in a parallel then the remaini

16、ng bulbs share the power,Circuits,23,Types of Power Sources,24,Generators,Simple AC Generators: Remember: any time a conductor is moved in a magnetic field, it cuts across the lines of flux and voltage is produced, causing a current flow A generator spins a loop inside a magnet,25,Controlling Genera

17、tor Output,Voltage in a generator is regulated by the rate of at which the lines of flux are cut More lines of flux (stronger magnet) means more output (in a generator this cannot be changed) Faster rpm means more output A voltage regulator is used to prevent generator runaway, uses electromagnetism

18、 to regulate output More electromagnetism means a larger magnetic field which means more votage,26,3 Phase Generator,A variable phase generator runs multiple loops giving a more constant peak of power Ex: A three phase generator has three loops and the power peaks three times more often than a singl

19、e phase,27,Alternators,No magnets, generate AC power initially Stator: Stationary winding of wires (coil) Since this stator is stationary we dont need to transfer the load through brushes The wires within the coil are connected as three windings joined together to form a Y. This produces three phase

20、s of alternating current,28,Alternators,The rotor is attached to two slip rings and uses DC power to energize its coil, producing magnetic charge as it is spun inside the Stator Once the rotor is energized it contains its own N & S poles,Slip Rings,29,Generators vs. Alternators,Generators Typically

21、used for DC power with one slip ring (commutator) Can produce AC by adding a second slip ring, or produce AC by adding an inverter Self excited: there is a mild magnetic field (from the magnet) which produces a small charge (when rotating that is added to the field to produce a larger charge Voltage

22、 is regulated by field charge,Alternators More efficient Produces 3 phase, AC current The power is produced by the stator, which is stationary The rotor is also a coil that, when charged, holds its own N & S poles, needs DC Not self excited, therefore an initial charge must come from somewhere (batt

23、ery) For DC we must use RECTIFIERS,30,ELECTRICAL FORMULAS,31,Electromotive Force / VoltageIntensity of Flow / Amperage / CurrentResistance in Ohms,The voltage is equal to the amperage multiplied by the resistanceThe current is equal to the voltage divided by the resistanceThe resistance is equal to

24、the voltage divided by the current,32,Electromotive Force / VoltageIntensity of Flow / Amperage / CurrentResistance in Ohms,The voltage is equal to the amperage multiplied by the resistanceThe current is equal to the voltage divided by the resistanceThe resistance is equal to the voltage divided by

25、the current,33,Electromotive Force / VoltageIntensity of Flow / Amperage / CurrentResistance in Ohms,The voltage is equal to the amperage multiplied by the resistanceThe current is equal to the voltage divided by the resistanceThe resistance is equal to the voltage divided by the current,34,Confused

26、 Yet?,Just remember: Amps = Flow Ohms = Resistance Volts = Pressure Watts = Power And: Watts = Volts x Amps,35,Types of Storage Devices,36,Batteries,A device composed of one or more cells in which chemical energy is converted into electrical energy The chemicals with in a battery provides an excess

27、of electrons at one end and a deficiency at the other,37,Modern Battery Chemicals Modern batteries use a variety of chemicals to power their reactions. Typical battery chemistries include: Zinc-carbon battery - Also known as a standard carbon battery, zinc-carbon chemistry is used in all inexpensive

28、 AA, C and D dry-cell batteries. The electrodes are zinc and carbon, with an acidic paste between them that serves as the electrolyte. Alkaline battery - Used in common Duracell and Energizer batteries, the electrodes are zinc and manganese-oxide, with an alkaline electrolyte. Lithium photo battery

29、- Lithium, lithium-iodide and lead-iodide are used in cameras because of their ability to supply power surges. Lead-acid battery - Used in automobiles, the electrodes are made of lead and lead-oxide with a strong acidic electrolyte (rechargeable). Nickel-cadmium battery - The electrodes are nickel-h

30、ydroxide and cadmium, with potassium-hydroxide as the electrolyte (rechargeable).,38,Nickel-metal hydride battery - This battery is rapidly replacing nickel-cadmium because it does not suffer from the memory effect that nickel-cadmiums do (rechargeable). Lithium-ion battery - With a very good power-

31、to-weight ratio, this is often found in high-end laptop computers and cell phones (rechargeable). Zinc-air battery - This battery is lightweight and rechargeable. Zinc-mercury oxide battery - This is often used in hearing-aids. Silver-zinc battery - This is used in aeronautical applications because

32、the power-to-weight ratio is good. Metal-chloride battery - This is used in electric vehicles.,Modern Battery Chemicals Contd,39,Batteries (cont.),Lead-acid Batteries: Most commonly used on GA applications Filled with lead plates under each electrode An electrolyte of sulfuric acid and water covers

33、the plates (acidic, use baking soda to neutralize) The Capacity of the battery is measured by its ability to produce a given amount of current for a specific time: ampere-hours 1 ampere-hour means the battery can supply 1 ampere for 1 hour We have 35 amp-hour batteries if we use only 10 amps how man

34、y hours will our battery last?,40,Batteries (cont.),Rated capacity: indicates the batteries ability to perform when it is new and is typically effected by: Battery Temp: colder temps decrease performance Battery Charge: A battery that is not fully charged will not perform as well Battery Condition:

35、Affected by age, service history, any excess g-forces or hard landings,41,Batteries (cont.),Components Lead Acid,42,Batteries,Nickel-cadmium Batteries: can accept high charge rates and discharge at equally high rates without voltage drop (unlike lead acid batteries) Each cell is an individual unit 1

36、2 volt batteries use 9 or 10 cells linked in series, while 24 volt use 18 or 20 cells Quick review on series vs. parallel connections An electrolyte of potassium hydroxide and water covers the plates (a strong base, use vinegar to neutralize,43,Batteries (cont.),Nickel-Cadmium batteries problems Hea

37、t: This type of battery requires one of three types of warning systems to warn the flight crew of impending problems Temp: Monitoring device of the central intercell (usually 140 - 160 degrees F. and something must be done) Current: Based on the idea that a thermal problem cannot exist unless there

38、is charging current. The pilot is warned when this current becomes excessive Voltage: If all the cells are balanced voltage wise then no problems may exist,44,Batteries (cont.),Nickel-Cadmium batteries problems Heat: Thermal Runaways looks like this ,45,Batteries (cont.),NiCad Battery Construction,N

39、iCad Cell,NiCad Battery,46,Aircraft Electrical Systems,47,Aircraft Electrical Systems,The source: Usually a 12 or 24 Volt DC system (in our airplanes) Most systems will be negative ground The negative terminal will be grounded to the frame of the airplane This allows us to run one wire to the compon

40、ent that we desire to operate and use the frame as the second,48,Aircraft Electrical Systems,Most systems will be negative ground The negative terminal will be grounded to the frame of the airplane,49,Buses,A bus-bar is a physically convenient place to bring all our wires together, neatly and safely

41、 May be more than one bus in an aircraft Ex: CRJ has around 15 buses,50,Protective Devices,51,Protective Devices,Fuses: Made of a low melting point alloy, incased in a glass tube When to much current flows through, the metal heats up and melts opening the circuit,OPEN,CLOSED,52,Protective Devices,Ci

42、rcuit breakers: These automatically open the circuit if current becomes excessive The breaker pops and is able to be reset If reset and it pops again, a fault exists and it should be left open Two types: Thermal: excess current heats an element in the switch that snaps it open Magnetic: the flow of

43、electricity increases a magnetic field that will pop the circuit breaker open when the flow becomes to much.,53,Magnetic Circuit breakers:,The hot wire in the circuit connects to the two ends of the switch. When the switch is flipped to the on position, electricity can flow from the bottom terminal,

44、 through the electromagnet, up to the moving contact, across to the stationary contact and out to the upper terminal. The electricity magnetizes the electromagnet. Increasing current boosts the electromagnets magnetic force, and decreasing current lowers the magnetism. When the current jumps to unsa

45、fe levels, the electromagnet is strong enough to pull down a metal lever connected to the switch linkage. The entire linkage shifts, tilting the moving contact away from the stationary contact to break the circuit. The electricity shuts off.,54,Thermal Circuit breakers:,In the closed position, the c

46、onductive snap acting disc with its contacts, bridges the terminal contacts to maintain the current. At predetermined overloads, the resistance heat, caused by current passing through the disc, snaps the disc into reverse position to open the contacts and break the circuit. the contacts have opened,

47、 it remains so until manually reset by the pushbutton. In resetting these units, the pushbutton moves inward only while pushed and always returns to the same position when released.,55,One to the Other,Inverters: Converts Direct Current to Alternating Current Rectifiers Converts Alternating Current

48、to Direct Current,56,SAFETY CONSIDERATIONS,57,SAFETY CONSIDERATIONS,58,Plan every job and think about what could go wrong. Use the right tools for the job. Use procedures, drawings, and other documents to do the job. Isolate equipment from energy sources. Identify the electric shock and arc flash, a

49、s well as other hazards that may be present. Minimize hazards by guarding or establishing approach limitations. Test every circuit and every conductor every time before you touch it. Use personal protective equipment (PPE) as a last line of defense in case something goes wrong.,Workplace Electrical

50、Safety Tips,59,Be sure you are properly trained and qualified for the job. Work on electrical equipment and conductors only when deenergized, unless procedures and safeguards have been established to ensure zero exposure for the worker and other people in the area. Lockout/tag out and ground (where

51、appropriate) before working on equipment. Treat deenergized electrical equipment and conductors as energized until lockout/tag out, test, and ground procedures (where appropriate) are implemented. Wear protective clothing and equipment and use insulated tools in areas where there are possible electr

52、ical hazards.,Workplace Electrical Safety Tips,60,De-energize and visibly guard (where possible) whenever contact with uninsulated overhead power lines is possible. Check and double check safety regulations when a ladder or parts of any vehicle or mechanical equipment structure will be elevated near

53、 energized overhead power lines. Call your local electric utility for assistance. People standing on the ground may be particularly vulnerable to possible injury.,Workplace Electrical Safety Tips,61,Cords, Equipment, and Tool Grounding,Make sure all equipment and extension cords bear the mark of an

54、independent testing laboratory such as UL, CSA, ETL or MET Labs. Protect flexible cords and cables from physical damage. Check cords for cut, broken, or cracked insulation. Keep slack in flexible cords to prevent tension on electrical terminals. Make sure the insulating qualities of a splice are equal to or greater than the original cord. Extension cords are for