M3: Electrical Fundamentals PDF

M3: Electrical Fundamentals NOTE: Italic Texts are Key Definitions and Underlined Texts are Main Subjects. Green Texts are Additional Information. Please also look for Figures relative to the Subject for better Familiarization. Use WPS Office for a pleasant experience.  The centre of an Atom i...

M3: Electrical Fundamentals NOTE: Italic Texts are Key Definitions and Underlined Texts are Main Subjects. Green Texts are Additional Information. Please also look for Figures relative to the Subject for better Familiarization. Use WPS Office for a pleasant experience.  The centre of an Atom is called Nucleus. Electrons orbit around the Nucleus. Each Atom is made up of the following Components: Protons Neutrons Electrons  Protons and Neutrons are in the Nucleus. Electrons move around the Nucleus in different orbits. Elements are composed of one single kind of Atoms. These Atoms then all have the same number of Protons. Examples: Hydrogen - 1 Proton Helium - 2 Protons Oxygen - 8 Protons Copper - 29 Protons Shells are the various orbits around the Nucleus. It can be compared to the different layers of an onion.  Some particles contained within an atom are Electrically Charged. Consequently, these particles can’t be neutral. An Atom as a whole, however, is Neutral (Basic state of Matter). Protons are positively charged particles inside the Nucleus. Neutrons are electrically neutral particles inside the Nucleus. It makes sure that the Protons stay within the Nucleus. Electrons are negatively charged particles orbiting around the Nucleus in so called Shells. It is always attracted to Protons that it can't be expelled by Centripetal Force.  Protons and Neutrons make up the Mass of an Atom, Electrons have nearly no Mass at all.  All Positive charges of an Atom are within the Nucleus, while all Negative charges orbit around the nucleus. The number of Protons is equal to the number of Electrons. Ions are Electrically Charged Atoms (Not Neutral). – dahil hindi sila equal number ng Negative charge (Electrons) at Positive charge (Protons) , Cation – Positive charge , Anion – Negative Charge   If the number of Protons is higher than the number of Electrons, it is a Positively Charged Ion. If the number of Electrons is higher than the number of Protons, it is a Negatively Charged Ion. Matter is composed of several Molecules. Molecule is the smallest unit of a substance.  A Molecule consists of a fixed amount of Atoms.  All atoms of a Molecule are the same in an Element and each Molecule has Atoms from at least two different Elements in a Chemical Compound.  However, not all Elements form Molecules. Compounds are pure substances made up of different Elements (at least two) which have been joined together by a Chemical Reaction. Analysis is the splitting of a Compound.  Metals are a good example to explain the structure of Conductors.  In a metallic bond, the Atoms are close packed and have a Crystal Lattice.  The reason for the good Conductivity of metal is the high mobility of its Electrons. Examples are CRYSTAL LATTICE Copper and Aluminium. Carbon is also a good Conductor. Conductors allow the Electrons on the outer layer to separate from their Atoms and to move freely within the Atomic Structure or jump from one (Fixed) Atom to the next. Insulators/Non-Conductors are tightly connected to their Atoms/Molecules which prevent them from breaking away in a Molecular Structure.  Examples are Mica and Porcelain. Semiconductors, as in many other materials share the Electrons on the outer layer in such a way that each Atom is provided with eight Electrons. This arrangement of atoms with 8 Electrons in the valence orbit is chemically very stable.  By nature, they are Non-Conductors. Conductivity is produced by adding other foreign Atoms (Doping), by Heat (Increase mobility of Electrons) or by Light. The amount of charges available for current Conduction (In this case: Electrons) is approx. 1,5 x 1010 per cm3 at room temperature. Examples are Silicon and Germanium. Static Electricity can be caused by friction. When the Voltage is very high, there may be a discharge with a spark. This happens especially when there is high humidity. Electric Charges can be compared to magnets: Like charges repel and unlike charges attract. This Force is called Attraction and Repulsion. Electric Charges exert forces on one another, even if there is no physical link between them. This Force is called Electromotive Force (EMF). The smallest existing Charge is called Elementary Charge.  The Elementary Charge of an Electron is e = - 0,1602 x 10-18 C (Coulomb), and the Elementary Charge of a Proton is e = + 0,1602 x 10-18 C (Coulomb). The Electrical Charge of Protons, Electrons and Ions is referred to as Electrical Charge Q. The Unit of the Electrical Charge is Coulomb (C) or Ampere-Second (As).  The Formula to calculate the charge is: Q = I * t or Charge Q = Current (Ampere) x Time (Second) or Q = As or Q = C (Coulomb).  If a body is Charged, the Charges do repel thus distributing the Charge all over the body. They usually are found on the Surface of the body as this will ensure to have the maximum distance between the charges. Charles-Augustin de Coulomb was a French Physicist. Coulomb’s Law is about the Force electrical charges have on each other. F = Force Q = Charge ε = Permittivity d = Distance between the Charges π = pi (3.14)  Coulomb's Law Formula is (F = 1 / 4πε) (Q1 * Q2 / d2). Permittivity describes the ability of a medium, for example air, to conduct electric fields.  There are plenty of Free Electrons Available in metals to conduct Electricity. These Electrons Flow from the Negative to the Positive pole when a Voltage is applied.  Pure water does not Conduct Electricity. The process of decomposition when passing an Electric Current through a Liquid is called Electrolysis. The chemical effect of current is not only used in electrolysis, but also in galvanizing or when charging batteries. The Conducting Liquid is called Electrolyte (lyo = Greek: I dissolve).  Electrons move at a few millimetres per second. - VELOCITY Gases can be found in many fields of Electrical Engineering. For example, in Light Bulbs with a higher electrical output (> 60 W). In order to protect the Filament (Tungsten) from Burning, Oxidizing, or Vapourizing in a more effective way, the bulb is filled with Nitrogen, Argon or Krypton. Halogen Bulbs, which have an even higher capacity, are additionally filled with halogens like Iodine or Bromine. Electrical continuity in gases is called GAS DISCHARGE Oscillographs or Oscilloscopes provide a visualization of rapidly varying processes in Electrical Engineering, Electronics and other Sciences. Using an Oscilloscope, these processes can be visualized but not recorded. The Electron Beam Oscilloscope is mainly used today because it is easy to operate, versatile and shock- resistant. The technology originates from an invention of K. F. Braun, a German Physicist (1850 - 1918) the Electron Beam Tube, also called the "Braun" Tube. The German physicist A. R. Wehnelt (1871 - 1944) developed the technology further by bundling the electrons and creating an "Electron Gun". Today the benefits can be seen in a variety of applications based on this technique e. g. a Television Tube. A simple model of such a tube is an evacuated Glass Bulb with a Kathode/Cathode (Negatively Charged) on one side and an Anode (Positively Charged) on the opposite side. Electric Current is characterized by a Flow of Charges in a certain Direction.  I=Q/t The symbol for Current is I. Current is measured in Amperes (A). 1 Ampere equals 6.25 x 1018 Electrons per second.  In Solid Conductors (Mainly in metals): Electron Currents (Free Electrons)  In Conductive Liquids: Ion Currents  In Conductive Gases: Ion and Electron Currents  In a Vacuum: Electron Currents In order to measure Electric Current, the charge carriers have to flow through a Current Meter (Ammeter). NOTE: Observe the Correct Polarity when using a DC Ammeter (Positive to Positive Pole and Negative to Negative Pole). OHMETER – Measure resistance (R), ohms Ω VOLTMETER – Voltage (U), Volts (V) Ammeter – Current (I), Amperes (A) Current Conversion in AC Ammeter: 1 A = 1000 mA 1mA = 0.001 A 1 kA = 1000 A Current ratings found in everyday life: Electronics / Radio, TV - 1 nA... 100 uA Electronics / Telecommunications - 1 mA... 10 A Appliances / Domestic or Commercial - 100 mA... 50 A Energy Transfer - 100 A... 10 kA Lightning - Up to 200 kA Nuclear Technology - Up to 1 MA A constant Flow of Charge carriers in one Direction is called Direct Current. If the Flow of carriers changes its Direction and Magnitude repeatedly in a certain period of time, it is called Alternating Current.  As you already know, Electricity itself is Invisible and only its effects are perceptible. In order to make Electrons move, a Force needs to act upon them. This force is called Electromotive Force (EMF). Voltage is generated by the separation of Charges. This will create a Positive and a Negative Pole.  The greater the separation of charges, the higher the Voltage. The symbol for Voltage is U. (In some countries, however, the symbol for Voltage is V) The unit of Voltage is V (Volt). A Voltmeter is connected in parallel with the terminals of a source or load. Make sure that the selected measuring range of the Voltmeter is sufficient. If the selected measuring range is too small, the Voltmeter may eventually be overloaded or damaged. 1V = 1000 mV 1 mV = 0.001 V 1 kV = 1000 V Common Voltages: Radio Aerial - 0.1 uV... 5 mV Telephone - 1 mV... 800 mV Single Cell Battery - 1.5 V Mains Voltage - 230 V... 400 V Power Line - 6 kV... 380 kV Lightning - Several MV Lowest Voltage Hazardous to Human beings is 50 V AC or 120 V DC. Two kinds of Voltage: Direct Voltage, causing DC Alternating Voltage, causing AC The Current that flows constantly in one Direction and is called Direct Current (DC).  The Direction of the Electrons flowing through a Conductor depends on the Polarity of the applied Voltage. The Current which periodically changes its flow of Direction is designated as Alternating Current (AC). Conventional / Technical Current Flow refers to the flow of Current from the Positive Pole to the Negative Pole. Electron Flow refers to the flow of Current from the Negative Pole to the Positive Pole. Hertz (Hz) is used to measuring the Frequency or Cycle Per Second (CPS) of the Voltage.  In an Aircraft, the standard Voltage and Frequency are 115 V and 200 V, while 400 Hz. Voltage Generation Methods: Friction (Oldest) Pressure Heat Light Chemical Action Induction  It is said that even B. C. the Greeks did rub Amber with a woolen cloth or leather clothes. They did spot out a force being exerted between the Amber and other objects. This effect is called Triboelectric Effect. If an Insulator is rubbed, Electrical Charges are separated and voltage is generated (Static Electricity). The Voltages can reach high values up to the kV range, which is normally not intended. If a so called Piezo crystal is deformed by using Pressure, a Voltage is generated. This is referred to as the Piezoelectric effect. Electron Emission is the separation of electrons from a metal bonding is referred to as electrons emission. Heating is one method to emit Electrons. This form of Emission is referred to as Thermionic Emission. Heating causes the Emission and the Emission causes the Voltage generation.  Voltage generation by Heat is used for measuring the Exhaust Gas Temperature (EGT) of an Aircraft turbine engine. The Thermoelectric Voltage depends on the Temperature Difference between the junction and the two free ends as well as on the combination of metals: Chromel - Alumel : 4.2 mV per 100° C Bismuth - Antimony : 10.0 mV per 100° C Constantan - Copper : 4.2 mV per 100° C Platinum - Platinum-Rhodium : 1.0 mV per 100° C Thermocouples are used to measure Temperatures (Temperature range from 200° C to 2300° C).  In Aviation, Thermocouples are mainly used to measure Exhaust Gas Temperatures (EGT) of engines. For modern engines, the metals Chromel and Alumel are used. The Temperature of Exhaust Gases is called Exhaust Gas Temperature (EGT). The part of the circuit with the Thermocouple is called "Hot Junction". The part in the indicator is called "Cold Junction".  To compensate the different length with the resulting different resistance, a variable resistor is installed which must be calibrated. This resistor is called "Balancing Resistor".  Some Thermocouples are connected in parallel in a Housing which is called "Junction Box". If a Photocell is exposed to Light, then Voltage is generated. Photocells are also energy converters Electrochemical Reactions (Chemical Action) can cause Electrical Voltage. If two different pieces of metal (e. g. Copper and Zinc) are immersed into an Electrically Conducting Liquid (e. g. Water with added Sulphuric Acid), a Voltage between the two Electrodes (Metals) is generated. Voltage Generators based on these Chemical Principles are referred to as Galvanic Cells (Primary and Secondary Cells): Primary Cells are Batteries Secondary Cells are Power Supplies that can be recharged and reused  Electrochemical Reactions can cause Electrical Voltage.  A Galvanic Cell consists of an Electrolyte and Electrodes made of two differently Conducting materials.  An Electrical Voltage occurs between a Metal (Electrode) and an Electrolyte (Usually an Acid).  Zinc-Carbon is the most common material combination of Batteries (Primary Cells). Primary cells cannot be charged and therefore cannot be reused.  The rated Voltage of a Lead Battery Cell is 2 V. The Capacity of a Lead Battery is the charge that it can supply until it reaches the cell voltage of 1.83 V (Final Discharge Voltage). Its unit is Ampere Hours (Ah) (e.g. 50 Ah is 5 A * 10 Hours).  Aircraft Batteries are commonly Nickel-Cadmium types. The rated Voltage of the NiCd Battery is 1.2 V and may fall to 1 V during discharging. They also come as Round Cells or Coin Cells. NiCd Batteries are used for notebook computer, radios, TVs etc. WARNING: The Nickel Cadmium Battery may only be refilled when it is charged, otherwise there is a Hazard of Explosion! Mercury-Oxide Coin Cells consist of pressed Zinc Powder as Negative Pole and Mercury-Oxide (chemical symbol HgO) as Positive Pole. The Electrolyte is Lime Potash. The rated Voltage is 1.35 V. The Cell is used for hearing aids, watches, meters, exposure meters, cameras, pocket calculators etc. Silver Oxide Coin Cells contain Silver Oxide, Lime Potash and Zinc; they have a high energy density and a low Voltage Depression. The rated Voltage is 1.55V and they are used for gadgets. Lithium Coin Cells come in multiple combinations and designs. They have high rated Voltages of up to 3.5V, a high energy density and a high lifespan. Lithium Silver Chromate Cells are used for pacemakers, for cameras, video cameras and many other devices. If a Coil enters the Magnetic Field of a Magnet, an Electrical Voltage is generated in the coil during the movement. This kind of Voltage Generation is referred to as Induction.  Due to the movement of the Conductor and the influence of the Magnetic Field, the Free Electrons of a Conductor are deflected in one Direction. These Electrons form a Magnetic Field. Resistance is an opposition to the Electron Flow. The symbol for Resistance is R. Resistance is measured in Ohms ( Greek capital letter Omega). High Resistance - Low Conductance Low Resistance - High Conductance The symbol of the Conductance is G. This unit is referred to as "Siemens", the symbol for it is "S".  The Formula is G = 1/R (Unit used is "S"). If Power Sources or so called Cells are connected in Series, parallel or in both, a Battery is created. Connecting unlike terminals of Power Sources will create a Series Connection. Connecting like terminals of power sources will create a parallel connection. The sinusodial alternating Voltage is an Oscillation. The graphical representation is called Graph or Line Chart. T is also called Period of Oscillation. The Period is measured in Seconds (S). The Time for one Cycle to complete is called Cycle Time T. Frequency is also defined as the reciprocal of the cycle time T.  The Formula for Frequency is f (Frequency) = 1 / T (Cycle Time).  The higher the Frequency, the shorter the Cycle Time and the lower the Frequency, the longer the Cycle Time. The Frequency states the number of cycles completed in one second. Frequency is measured in Hertz (Hz). The three most important Frequency Bands are: HF - High Frequency VHF - Very High Frequency UHF - Ultra-High Frequency The symbol for Wavelength is λ (Greek Lambda). The Wavelength is measured in Meters (m) as used for distances. The Speed of Light has a symbol for Quantity: c.  The Formula for Wavelength is λ = c * T = c / f [m] The Average Value of AC is Zero. The Positive or Negative Maximum Value which a Sine Curve can assume is called the Peak Value. The Peak Value of a Wave in an AC Voltage or an AC is called Amplitude. The unit of the Amplitude is either Volt or Ampere.  The Instantaneous Power is calculated by multiplying the instantaneous Voltage (u) with the Instantaneous Current (i). P = U x I  u = Instantaneous Voltage and Upeak = Peak Voltage; i = Instantaneous Current and Ipeak = Peak Current.  For the Calculation of Instantaneous Voltage, use u = Upeak * sin (2π * f * t) and for the Calculation of Instantaneous Current, use i = Ipeak * sin (2π * f * t).  With these formulae, it is possible to Calculate the Trigonometric Function, depending on time. The calculation is 2π * f * t = α > sin (2π * f * t) = sin α.  α is the Angle of Rotation.  The Formula for Peak-To-Peak Value is Upp = Up * 2 or Ipp = Ip * 2.  Peak to peak value means twice the peak value  If Unknown AC and AC Voltages are measured with a measuring Oscilloscope, the following Formula applies: Upeak = Upp / 2. The short abbreviation for Root Mean Square is RMS. Triangular Waves are given if the Voltage increases linearly and, if a certain level is achieved, decreases linearly. The same happens with the corresponding Negative Voltage. Square Waves are given if the Voltage periodically changes between two Values. The Voltage change is abruptly. In Generators, usually a permanent Magnet (Or a Current-carrying Coil) rotates whilst the Output Windings are fixed. Frequency of sinusoidal AC depends on the rotational speed of the generator. (frequency increase - generator speed increases) A quadripolar device with two pole pairs at the same rotational speed is used. The frequency will be twice as high. The Rotor acts as a permanent Magnet and therefore must be supplied with DC via Sliprings. The three Coils form the so called Phase Windings of the Generator. In each of these Phase Windings, a Voltage is generated, the Line to Neutral Voltage. A Transformer consists of two Coils and an Iron Core. The Input Coil is also called Primary Winding or the High−Voltage Winding. The Output Coil, also called Secondary Coil or Low−Voltage winding. The Core is composed of isolated thin Iron layers (Laminated Core) in order to suppress Eddy Currents (Unintended Heating of the Iron Core). Transformers can Step Up or Step Down Voltages, Currents and Resistances.  The size of the transformer mainly depends on the power to be transferred. In Core-form Transformers, the Coils are wound around opposite sides of a rectangular Iron Core. This kind of transformer is mainly used for technical devices. In Shell-form Transformers, both Coils are located around the same part of an Iron Core. The Iron Core offers two rectangular leads for the Magnetic Flux. They are used mainly for High Voltage devices. Toroidal Transformers overcome some of the disadvantages of other Transformers. As the Shell-form Core is made from an E shape and an I shape Iron piece gaps between the Iron parts are inevitable. The Toroidal is one single piece of iron with no air gaps. Also Magnetic Flux has problems following the 90 Degrees Angle at the corners of other Transformers causing loss of Magnetic Flux. The constant Curve of the Toroidal avoids such losses.  The efficiency of Toroidal Transformers are higher than on other Transformers but production is more costly. The No-load Voltage is the Voltage of the secondary Coil if no load is connected. Then the secondary side has an open Circuit. This is the No-load Condition. If a Load is connected to the secondary Coil of the Transformer, the Circuit is closed and there is a Current. This is the Load Condition.  Voltage Transformation: U1 / U2 = N1 / N2  Current Transformation: I2 / I1 = N1 / N2  Transformation of Resistances: R2 / R1 = N1 / N2 The efficiency is the ratio of power output to power input Rectifiers convert AC to DC. Inverters convert DC to AC. In an Aircraft Rectifiers are TRUs (Transformer Rectifier Units) and Inverters are Static Inverters. The only way to avoid such losses is to form the Iron Core from Sheet Metal instead of one Piece of Metal. These Sheet Metals are called Laminations. They are made from material that is very easy to Magnetize and Demagnetize to reduce losses from Hysteresis.  The Laminations must be insulated from each other to prevent the Eddy Currents. This is usually done by a Non-Conductive paint that is applied to every Lamination.  Iron losses are measured with an Open−Circuit Test.  Copper losses are measured with a Short−Circuit Test. Power Factor (Input Vs Output) is: Active Power / Apparent Power (PF). Copper losses and iron losses The nominal power output of a transformer is the apparent power When the inductive load increases the output voltage will decrease when the capacitive load increases the output voltage will increase Different types of load are: - Ohmic Resistor - Inductive Resistor - Capacitive Resistor The Short-Circuit Voltage of a Transformer is a reference for the internal Resistance of the Transformer. Its also a reference for the change of the Output Voltage when the Load increases. - low circuit voltage means that the internal resistance is low A Conventional Transformer has two Windings. With a Transformer with two Windings, the Total Power must be transmitted from the one Winding through the Magnetic Flux to the other Winding. An Auto-Transformer has only one Coil for both Input and Output side. Primary and secondary sides share a part of the Windings. - With an auto transformer voltage can be stepped up and stepped down. A Current Transformer are special transformer which allow the measurement of AC currents without breaking the current-carrying leads. A Three-Phase Transformer consists of three Transformers where usually a common Iron Core is used. Can be found in a star or delta arrangement. Lenz's Law (Lenz's Rule) states that an Induced Current always flows in a Direction such that it opposes the change which produced it. If the Voltage increases, Current decreases as such that if the Voltage decreases, Current increases. Generators and motors are summarized in the term “rotating electrical machines” Electrical machines make use of magnetism. Induction of motion is the principle of all generators The Stator consists of a Steel Ring (Yoke), the main Poles made of Sheet Metal with Pole Core and Pole Shoe and the Excitation Winding. The Armature, also called Rotor, has 3 parts: The Shaft that is fixed on the Laminated Core of the Rotor, the Armature Winding embedded in grooves and the Commutator that is fixed on the Shaft; this Commutator is also referred to as the Collector. The Power Supply for the Armature is provided by the Commutator. The Armature is connected via Sliding Contacts. For this purpose, Carbon Brushes are used.  Transformers are "Reposing Electrical Machines". They convert High Voltages or Currents into Lower Voltages or Currents and vice versa. The Main Field is generated by Electromagnets. The Winding of the Main field is the Winding in the Stator. As the Field of the Armature Crosses to the Main Field, it is called Armature Cross Field. The higher the Current Clow in the Armature, the stronger the Cross Field. The Main Field and the Armature Field overlay and result in a Total Field. The impact of the Armature Cross Field on the Main Field is referred to as Armature Reaction. This reaction displaces the Neutral Zone and distorts the Main field. If the Neutral Zone which is free of Induction displaces, it causes "Heavy Brush Sparking" to the Carbon Brushes. Commutating poles are small poles that are located between the main poles.  As the Commutating Pole Field cannot cover the total Armature Cross Field, an additional Compensating Winding can be placed in the Main Poles. Voltage control – speed control via the armature is applied where a speed range from a standstill to rated speed is required. Thyristor – controlled rectifier provides different, considerably more efficient method for speed variation Field control – reducing the stator field and the rotor field, will decrease the output power of such a motor Shunt-Wound DC Machines are used as DC Motors and as DC Generators. Machine generates a voltage and works as a generator. Separately Excited Shunt Wound Generators – the field winding is replaced by an external power supply. Self-Excited Shunt Wound Generators – the field winding is connected in parallel to the armature. Alternator : To transfer the exciter current into the rotating part of the generator it uses sliprings and brushes. The Output Voltage of modern DC Generators are rectified within the Alternator. Brushless Motors usually are small DC Motors with a construction quite similar to Synchronous Motors. Two types of Brushless Motors are available: Inrunners and Outrunners. Inrunners – High rpm but low rpm Outrunners – Low rpm but high rpm A very special kind of DC machine is the so-called Starter Generator. It is a combination of DC Generator and DC Motor. - It is used to start up a Turbine as well as to provide Electrical Power as soon as the Turbine is running. In order to start up a Turbine, a high Torque is required. The Series−Wound Machine – are used as motors. It is possible, but very unusual to use them in generators Very high starting torque. They must never be operated without torque load. - basically consists of the Stator with the Excitation Winding, the Rotor with the Armature Winding and the Carbon Brushes. - Series−wound motors are applied as car starters, in hoists, municipal railroads, tramways and electric vehicles, but also for windscreen wiper motors or shut-off valves. The Compound DC Machine – shunt-series DC machine can be either used as a shunt-wound DC machine or as a series-wound DC machine. Shunt-series machines can be used as motors or as generators - can be connected as a Shunt-Wound Machine and used as a DC Generator. The Universal Motor is a small Series-Wound Motor, which can be either operated by a DC or by a Single- Phase current at normal Power Frequency. For this reason, the Universal Motor is also called All-Mains motor.  The Difference in construction of the universal motor to the normal DC Motor is the compact Laminated Stator, which forms one part with the Pole Shoes to avoid Eddy Currents. Synchronous Machines have a constant Ratio of Rotation Speed and Frequency. AC Generators are mainly Synchronous Machines. Synchronous Machines are used as Generators and as Motors. This type of Excitation is present, if part of the Energy generated by the Generator is used for Excitation. This is called Self-Excitation. The Excitation Power is generated by an additional small generator mounted on the Shaft inside the Main Generator. This is Excitation by Permanent Magnet Generator. The required Excitation Energy is delivered by an External Power Supply. This is called Separate Excitation. If the Rotating Coil generates one Magnetic North Pole and one Magnetic South Pole, this is called one Pole Pair. It is possible to construct a Machine with two Pole Pairs. Then the coil is split into four parts. A Three-Phase Generators will have three of these Coils.  The Current in the Rotating Electromagnet is called Exciter Current.  The Three-Phase Generator usually is operated in a Star Connection.  If a Generator is connected in a Delta Arrangement (Delta Connection) only, the Phase-to-Phase Voltage is available and no Neutral Line is required/available. Modern High−Output Brushless Alternators are called Permanent Magnet Generators (PMG). They were developed for the purpose of eliminating some of the problems of Alternators that employ Slip Rings and Brushes to carry Exciter Current to the Rotating Field.  In Aircraft, the Brushless PMG has been used since many years. As an Aid, a Light Bulb (Indicator Light) is connected between the Phases A of both the Generators. If the Bulb is dark, the Generators are in Phase, if it is lit, there is a Phase Shift between the Generators. True Power can be calculated by Measurement of Output Voltage and current if the Phase Shift is detected and taken into the Calculation. A Two-Phase Generator consists of two Single-Phase Generators in one Housing with a common Excitation field. Auxiliary Power Unit (APU) is a Turbine Engine which provides Pneumatic Power. Additionally, it drives an AC Generator.  The APU is started with a Motor which is supplied by the On-Board Battery. Asynchronous Motors are the most important Three-Phase Motors. They are reliable, require a minimum level of Maintenance and the manufacturing costs are low. A difference in charge between two points can occur. This is called Potential Difference. The Motor consists of two major parts: The Stator (Stationary Part) and the Rotor (Rotating Part).  The Rotor of an Asynchronous Motor doesn’t require a Power Supply. The Current inside the Rotor Windings is supplied from the Rotating Magnetic Field of the Stator.  If the Rotor would have the same Rotational Speed as the Rotating Field, there would be no Difference in the Rotational speed. The lagging of the Rotor is called Slip. A Shaded-Pole Motor (Split Pole Motor) is so named because it uses a small shorted Shading Coil Wound in a small notch in the Stator Pole Piece. The Capacitor Motor is designed according to the same principle as the Three−Phase Asynchronous Motor with squirrel−cage rotor. The Capacitor Motor is used where there is no three−phase mains and electrical drives outputs of 1.5 kW are required. If the Motor must have a High Starting Torque, a Second Capacitor (Starting Capacitor) is connected in parallel to the running Capacitor during the Start−Up.  An other option to create a Rotating Magnetic Field is an Inductor. In this case, it would replace the Capacitor as Inductors create Phase Shifts between Voltage and Current.  Generators convert Mechanical Energy to Electrical Energy  Motors convert Electrical Energy to Mechanical Energy. Power sources in series as follows: I = constant - Total voltage is the sum of the voltage of all individual voltage - Total resistance is the sum of all the individual internal resistance - Total current is constant Power sources in parallel are as follows: U = constant - Total current is the sum of all individual current - Total resistance is lower than the lowest individual resistance - Total voltage is constant Shunt-Wound DC machine Series-Wound DC machine Compound-Wound DC machine - Are use as DC motors - Used as motors and very - Type of winding either and as DC generators unusual to use them as shunt-wound DC or generators series-wound DC - Have stator with the excitation winding, the - Have stator with the - Can be connected as a rotor with the armature excitation winding, the shunt-wound machine winding and the carbon rotor with the armature and use DC generator brushes winding and the carbon brushes - Use to starting a torque - the most commonly used DC motors - Very high starting - Consist of a stator with torque, they must never the two excitation - Connected in parallel be operated without windings torque load. - Applied as car starters - Connected in series