Module 1 and 2 Introduction to DC Generator PDF

EE 2312 / ME 2613 Electrical Machines 1 / AC and DC Machinery INSTRUCTOR: KEVIN LESTER B. LOBO Module 1: Introduction to Electrical Machines Energy Conversion Process Takes place between well known Pairs of FORMS OF ENERGY. Forms of Energy Forms of Energy Forms of Energy Forms...

EE 2312 / ME 2613 Electrical Machines 1 / AC and DC Machinery INSTRUCTOR: KEVIN LESTER B. LOBO Module 1: Introduction to Electrical Machines Energy Conversion Process Takes place between well known Pairs of FORMS OF ENERGY. Forms of Energy Forms of Energy Forms of Energy Forms of Energy Forms of Energy Forms of Energy Forms of Energy  Rotating Electrical Machines Are widely used for the purpose of converting energy from one form to another. https://toppng.com/clipart-freeuse-stock-confused-people-clipart-thinking-man-clipart-PNG-free-PNG-Images_201760 https://slideplayer.com/slide/13145489/ Law that governs Energy Conversion I. First Law of Thermodynamics: “Law of Conservation of Energy” This law states that energy can neither be created nor destroyed. It can only be transformed from one form to another. II. Second Law of Thermodynamics: “Law of Increased Entropy” When energy is transformed from one form to another, some of the input energy is turned into a highly disordered form of energy, like heat, which resulted to energy loss. Machine A device, having a unique purpose, that augments or replaces human or animal effort for the accomplishment of physical tasks. (https://www.britannica.com/technology/machine) A tool containing one or more parts that uses energy to perform an intended action. A device consisting of fixed and moving parts that converts energy from one form to another. DC Machine Is a rotary electro-mechanical energy conversion device that converts mechanical energy to direct current (DC) electrical energy or DC electrical energy to mechanical energy. Read more: http://circuitglobe.com/what-is-a-dc-machine.html#ixzz4Wl04CNqS DC Machine Mechanical Electrical Electric MACHINE Energy Generator Energy Electrical Mechanical Electric Energy Motor Energy Electric Generator A machine generates electrical energy for use in an external circuit. Although the battery is an important source of electric power, it can only supply limited amount of power to any machinery or equipment. Applications that require continuous and large quantities of electrical power, such as residential and commercial electrification, large industrial machineries, HVAC system, arc welding, electroplating, etc., relies on electric generators to deliver them power. It is driven (rotated) by a mechanical machine called the Prime Mover. Electric Generator Prime mover an initial source of motive power (rotation) designed to receive and modify force and motion as supplied by some natural or chemical source and apply them to drive a machinery. (Source: Merriam-Webster Dictionary) It can be Steam Turbines, Water turbines, Internal Combustion Engines (ICE), Wind Turbines, Electric Motor or even a Hand- operated crank shaft. Electric Motor A machinery that produces rotational mechanical energy to drive external physical loads. Works on the principle that when a current carrying conductor is placed under a magnetic field, it experiences a force and has a tendency to move. Examples of electric motor driven loads are: pumps, compressors, conveyors, lifts, drive shaft etc. Construction and Principle of Operation of DC Generator The Principle of Generator Action Faraday’s Fist Law of Electromagnetic Induction: “Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced.” To generate electricity, the Principle of Generator Action requires: 1. The presence of magnetic lines of force. 2. Motion of conductors cutting the flux (at a speed that is high enough). 3. Proper relation between the direction of rotation and the field connection to the armature. Parts of DC Generator (according to function) I. Field/Poles – the one responsible for the creation of magnetic lines of force. II. Armature – holds and rotates the copper windings that cuts the magnetic lines of force. https://www.mawdsleysber.co.uk/services/field-coil-repair-and-rewinds/ https://www.indiamart.com/proddetail/75-gpd-dc-armature-10263723462.html Parts of DC Generator (according to construction) I. Stator – the stationary part of the DC generator II. Rotor – The moving/rotating part of the DC generator Under the Stator: a. Poles – magnets or electromagnets that creates magnetic lines of force to be cut by the armature conductors. – always work in pairs b. Yoke – houses the entire machine – where the magnets/poles are mounted. c. Pole Shoe – holds the poles together and spread the flux evenly. Parts of DC Generator (according to construction) Under the Rotor: a. Core – a laminated steel core that holds and contains the current carrying conductors (windings) on its conductor slots. – also called as the armature core b. Windings – copper conductors that are wounded around the core that cuts the magnetic lines of force. – also called as the armature conductors c. Shaft – coupled/connected to the prime mover that rotates the core.  Parts of DC Generator (according to construction) Other Parts of DC Generator: a. Commutator or Slip Rings Commutator – serves as termination point of the armature windings and at the same time periodically reverses the direction of the current flow to an external circuit. For DC Generator: Split Rings – makes the current change direction every half-rotation. Slip Rings – merely maintains a connection between the moving rotor and the stationary stator. Does not reverses the direction of current flow. Used in small AC Generators or Alternators. b. Carbon Brushes – harvest the current from the rotating commutator. It always work in pairs. Operation of a DC Generator In order to achieve the requirements of the “Principle of Generator Action”: 1. The presence of magnetic lines of force ◦ Field poles or Magnets (Electromagnets or Permanent Magnets) to produce magnetic flux. 2. Motion of conductors cutting the flux ◦ Conductors are wounded/wrapped around the armature which are then placed and rotated in between the field poles. 3. Proper relation between the direction of rotation and the field connection to the armature. ◦ Conductors are rotated perpendicular to the direction of the magnetic field. Watch: https://www.youtube.com/watch?v=Ylgb8FFMgd4&t=91s Module 2: Generated Voltage of DC Generator Faraday’s Law Second Law of Electromagnetic Induction: “The magnitude of the generated voltage is directly proportional to the rate at which a conductor cuts magnetic lines of force.” When a conductor moves at a constant speed across a uniformly dense magnetic field, “1-volt is generated for every 100,000,000 (or 1*108) magnetic lines of force (or Maxwell) cut per second”  Did you know? A measuring device that measures magnetic flux(∅) of a magnet system or a single magnet is called a Flux meter. Unit of Magnetic Flux: Maxwell or Weber Conversion: 1 Wb = 1*108 Mx Image Source: https://www.list-magnetik.com/en/magnetic-measuring/fluxmeter-fl-4 Faraday’s Law If the flux density is not constant, the average generated voltage per conductor, 𝑬𝒈𝑐𝑜𝑛𝑑 , will be: ∅𝑡𝑜𝑡𝑎𝑙 𝑬𝒈𝒄𝒐𝒏𝒅 = (volt / conductor) 𝑡 × 108 where: (unit) 𝐸𝑔 Average generated voltage Volt ∅total Total flux produced by the field Maxwell 𝑡 Rate of cutting of flux (Note: for rotating conductor, it is the time it take to make one complete revolution) second/rev Zeff Total number of effective armature conductors conductor General Voltage Equation of DC Generator Given the total number of effective armature conductors, Zeff, the average generated voltage, Eg, of the DC Generator will be: ∅𝑡𝑜𝑡𝑎𝑙 (Volt) 𝑬𝒈 = ∗ 𝑍𝑒𝑓𝑓 𝑡 × 108 where: (unit) 𝐸𝑔 Average generated voltage Volt ∅total Total flux produced by the field Maxwell 𝑡 Rate of cutting of flux (Note: for rotating conductor, it is the time it takes to make one complete revolution) second/rev Zeff Total number of effective armature conductors conductor Effective Armature Conductors, Zeff Conductors that contributes to the resulting generated voltage of the DC generator. The number of conductors connected in series in each parallel path. The total number of conductors are equally distributed in each parallel paths, a. 𝑍 𝑍𝑒𝑓𝑓 = (conductors) 𝑎 where: (unit) Z Total number of conductors in the armature conductors 𝑎 Number parallel paths of armature (determined by the type of armature winding) unitless # of Conductors and # of Parallel Paths NOTE: The generated voltage is determined only by the strings of conductors joined in series and not by the number of parallel paths through the current may pass. The situation existing in a generator with regards to voltage and current is analogous to dry- cell battery connections. Example: If the voltage and current ratings of 1.5 volts and 5 amperes are assured per cell, determine the relative power ratings of 120 cells connected when the number of parallel paths is: a) 2, b) 4, c) 6, d) 8 The power rating is independent of the manner in which the cells or conductors are connected. Example A 4-pole DC generator has an armature winding containing a total of 648 conductors connected in 2-parallel paths. If the flux per pole is 0.321*106 Maxwell and the speed of rotation is 1,800-rpm; calculate the average generated voltage. Answer: 124.8-V General Voltage Equation of DC Generator Most of the time, in the nameplate of most machines where the specification and ratings are found; the given values are: No. of Poles ∅𝒕𝒐𝒕𝒂𝒍 = 𝑃 ∗ ∅𝑝𝑒𝑟 𝑝𝑜𝑙𝑒 Flux per pole 1 60𝑠𝑒𝑐 Speed of rotation, N (rev/min or rpm) 𝐭= ∗ 𝑁 1𝑚𝑖𝑛 No. of Parallel paths, a (or type of armature winding) 𝑍 𝒁𝒆𝒇𝒇 = Total no. of conductors 𝑎 General Voltage Equation of DC Generator 𝑃∗∅∗𝑁∗𝑍 𝐸𝑔 = ∗ 10−8 ; 𝑣𝑜𝑙𝑡𝑠 60∗𝑎 where: (unit) 𝐸𝑔 Average generated voltage Volts ∅ Flux per pole produced by each magnet/electromagnet Maxwell / pole 𝑃 Number of poles, an even number poles 𝑁 Speed of rotation of the armature rpm 𝑍 Total number of conductors in the armature conductors 𝑎 Number parallel paths of armature (determined by the type of armature winding) unitless Note: if the flux is given in Webber (Wb); the *10-8 is omitted Armature Windings THE NUMBER OF PARALLEL PATHS Winding Terminology CONDUCTOR An individual piece of wire placed in the slots of the DC machine. TURN Formed by looping wires or conductors around the armature. COIL Made when one or more turns of wire (single-turn Note: coil or multi-turn coil) are placed in an almost 1-turn makes, 2-conductors similar magnetic position inside the DC machine. COIL SIDE A COIL always has TWO COIL-SIDES, A part of the coil in each conductor slot. regardless of the number of turns. Types of Armature Windings I. Lap winding Forms a loop as it expands around the armature core. II. Wave winding Forms a wave as it expands around the armature core. III. Frog-Leg winding Combination of lap and wave coil windings. Lap Winding In this winding, the coil ends of each armature coil (start and finish) is connected to adjacent commutator segments. The finishing end of one coil is situated under the same pair of poles of the starting end of the next coil. The number parallel paths and brushes is equal to the number of poles. This type of winding is used for high-current and low-voltage rating generators. https://circuitglobe.com/lap-and-wave-winding.html Wave Winding In this winding, the coil ends of each armature coil (start and finish) is separated by the distance between two pairs of poles. The finishing end of the one coil is connected to the starting end of the next coil situated under different pairs of poles. The number parallel paths and brushes is always 2. This type of winding is used for low-current and high-voltage rating generators. https://circuitglobe.com/lap-and-wave-winding.html Number of Parallel Paths, a Machine’s “Plex” Value: Multiplicity Factor, m: ▪ The number of sets of armature winding m = 1, for simplex winding m = 3, for triplex winding connected in parallel before terminating m = 2, for duplex winding m = 4, for quadruplex winding in a commutator segment. Lap Winding: ▪ Increases the number of parallel paths by a multiplicity factor in lap and wave Number of parallel paths, a = Multiplicity x Poles armature windings that is equal to the 𝒂 = 𝒎𝑷 additional sets of armature coils made. Number of Brushes = Number of Poles 𝑵𝒃𝒓𝒖𝒔𝒉 = 𝑷 Wave Winding: Number of parallel paths, a = Multiplicity x 2 𝒂 = 𝟐𝒎 Number of Brushes = always two (2) 𝑵𝒃𝒓𝒖𝒔𝒉 = 𝟐 https://www.engineeringslab.com/all_engineerings_dictionary_terms/parallel-paths.htm Problems 1. A four-pole generator, having wave-wound armature winding has 51 slots, each slot containing 20 conductors. What will be the voltage generated in the machine when driven at 1,500 rpm assuming the flux per pole to be 7.0-mWb ? Answer: Eg = 357V 2. An 8-pole d.c. generator has 500 armature conductors, and a useful flux of 0.05-Wb per pole. What will be the e.m.f. generated if it is lap-connected and runs at 1,200 rpm ? What must be the speed at which it is to be driven to produce the same e.m.f. if it is wave-wound? Answer: 𝐄𝐠 = 𝟓𝟎𝟎𝐕, 𝐍𝐰𝐚𝐯𝐞 = 𝟑𝟎𝟎𝐫𝐩𝐦 3. The armature of a four-pole shunt generator is lap wound and generates 216 volts. If this armature is rewound as wave connected, find the emf generated at the same armature speed and flux per pole. Assume that the total number of armature conductors remains the same after re-wounding. Answer: 𝐄𝐠 = 𝟒𝟑𝟐𝐕 Online References http://harmonscience6.wikispaces.com/file/view/Forms_of_Energy.jpg/276538606/Forms_of_E nergy.jpg http://hornedoreesescience.weebly.com/uploads/8/5/1/3/8513063/5367849_orig.gif http://static.trunity.net/files/186001_186100/186073/energyconversionmatrix.png https://www.youtube.com/watch?v=gW45N2WpD64 https://www.youtube.com/watch?v=-xebh8wU8gY http://www.ustudy.in/sites/default/files/lap%20and%20wave.GIF http://www.electrical4u.com/lap-winding-simplex-and-duplex-lap-winding/ https://www.electricaleasy.com/2012/12/basic-construction-and-working-of-dc.html https://www.indiastudychannel.com/resources/151550-How-Does-a-DC-Generator-Work-.aspx Online References https://www.theengineeringknowledge.com/construction-of-dc-machines/ https://serc.carleton.edu/details/images/46570.html https://www.powermag.com/press-releases/doosan-skoda-power-is-sending-a-turbine-to-the- land-of-the-rising-sun-for-the-first-time/ https://electrical-engineering-portal.com/whats-important-for-water-power-designer-to-make- the-right-choice-of-a-turbine https://www.offshorewind.biz/2020/04/21/mingyang-turbines-for-400-mw-wind-farm-offshore- china/ https://www.udemy.com/course/internal-combustion-engine-basics/ https://www.canstockphoto.com/machine-ac-and-dc-currents-excitatrice-31336418.html https://www.crompton.co.in/product/consumer-pumps/agricultural-pumps/centrifugal- monoset-agricultural-pumps/centrifugal-monoset-pumps/ Online References http://bescousa.com/index.php?main_page=index&cPath=169_205_235 https://circuitglobe.com/lap-and-wave-winding.html https://www.engineeringslab.com/all_engineerings_dictionary_terms/parallel-paths.htm