Elec-Machines-1_EngRBucayu.pdf

The class is about to start… Opening Prayer “Our Lord God in heaven. Thank you for the new day you've bestowed upon us. Until this moment, we still have our borrowed life and strength from you. We worship and praise Your Holy Name. This moment, we will continue to study and acquire new knowledge...

The class is about to start… Opening Prayer “Our Lord God in heaven. Thank you for the new day you've bestowed upon us. Until this moment, we still have our borrowed life and strength from you. We worship and praise Your Holy Name. This moment, we will continue to study and acquire new knowledge. May you bless your students with witty brain to think fast and an inquiring mind to be curious on whatever knowledge they will learn today. Most importantly bless them with Your wisdom and a heart that will follow your commandments in order for them to become worthy in their studies. You know that in this recent times, most are suffering from hardships and economic crises. We humbly ask You to bless the parents of your students. May you shower Your abundant blessings and prosperity to each of their homes. So that we can use these not only for our daily lives but especially for the performance of our duties to your Holy name. We hope that you heard our prayer. We ask all of these. In the name of Jesus Christ, our Saviour. Amen. ELECTICAL MACHINES 1 ENGR. ROMEL BUCAYU, REE TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES CAVITE In this lesson we will talk about… Lesson 1 Lesson 2 Classifications: Lesson 3 Introductions to Generators, DC Machines Electric Motors, -Separately Excited Machines Tranformers -Self- Excited Lesson 4 Lesson 5 AC Machines -Composition of Single-Phase Trasnformers AC Structure And Three-Phase Trasnformers  Introduction to AC/DC Machine Application of electric machines in the world of engineering Direct Current vs Alternating Current Alternating Current (AC) is a type of electrical current, in which the direction of the flow of electrons switches back and forth at regular intervals or cycles. Current flowing in power lines and normal household electricity that comes from a wall outlet is alternating current. Direct Current vs Alternating Current Direct Current vs Alternating Current Almost every household in the world is powered by AC. AC is also the more popular current when it comes to powering electric motors, a device that converts electric energy into mechanical energy. AC is less expensive and easy to generate than DC. AC can be transmitted across long distances without much energy loss, unlike DC.* The power loss during transmission in AC is less when compared to DC. Direct Current vs Alternating Current Direct Current vs Alternating Current What is Electric Machine? “In electrical engineering.. electric machine is a general term for machines using electromagnetic forces, such as electric motors, electric generators, and others. ”- wiki https://www.youtube.com/watch?v=-MlkASchodc Examples such as: Transformer Electric Generator Electric Motor What is Electric Machine? “In electrical engineering.. electric machine is a general term for machines using electromagnetic forces, such as electric motors, electric generators, and others. ”- wiki https://www.youtube.com/watch?v=-MlkASchodc Examples such as: Electric Generator Transformer Electric Motor They are electromechanical energy converters “an electric motor converts electricity to mechanical power while an… electric generator converts mechanical power to electricity.” Classifications of Electric Machine Classifications of Electric Machine Electrical Machines DC AC Machines Machines DC Synchronous Asynchronous DC Motor Machine Machine Generator Synchronous Synchronous Induction Motor Generator Machines Single Phase Three Phase Single Phase Three Pase Classifications of Electric Machine DC Machine DC DC Motor Generator Permanent Separately Self Excited Magnet DC Excited Series Shunt Compound Short Shunt Long Shunt Classifications of Electric Machine DC Machine DC Generator DC Motor Self Excited Separately Excited Series Shunt Compound Short Shunt Long Shunt Permanent Magnet DC Classifications of Electric Machine Working Principle of Electromagnetics Working Principle of Electromagnetics Faraday’s law of induction explains the working principle of transformers, motors, generators, and inductors. The law is named after Michael Faraday, who performed an experiment with a magnet and a coil. The most widespread version of Faraday's law states: The electromotive force around a closed path is equal to the negative of the time rate of change of the magnetic flux enclosed by the path. Working Principle of Electromagnetics Electromagnetic induction is an incredibly useful phenomenon with a wide variety of applications. Induction is used in power generation and power transmission, and it's worth taking a look at how that's done. The discovery of electromagnetic induction in 1831 was heralded a decade earlier by a related discovery by Danish physicist Hans Christian Oersted (1777–1851). While Oersted’s surprising discovery of electromagnetism paved the way for more practical applications of electricity, it was Michael Faraday who gave us the key to the practical generation of electricity: electromagnetic induction. Working Principle of Electromagnetics As the magnet moves back and forth a current is said to be induced in the wire. Working Principle of Electromagnetics  Working Principle of Electromagnetics Fleming’s Left-Hand Rule and Fleming’s Right-Hand Rule are essential rules applicable in magnetism and electromagnetism. John Ambrose Fleming developed them in the late 19th century as a simple way of working out the direction of electric current in an electric generator or the direction of motion in an electric motor. It is important to note that these rules do not determine the magnitude; instead show only the direction of the three parameters (magnetic field, current, force) when the direction of the other two parameters is known. Working Principle of Electromagnetics Electromagnetic Induction:Useful Application AC Motors use Faraday’s law to produce rotation and thus convert electrical and magnetic energy into rotational kinetic energy. This idea can be used to run all kinds of motors. Since the current in the coil is AC, it is turning on and off thus creating a CHANGING magnetic field of its own. Its own magnetic field interferes with the shown magnetic field to produce rotation. Electromagnetic Induction:Useful Application TRANSFORMER Probably one of the greatest inventions of all time is the transformer. AC Current from the primary coil moves quickly BACK and FORTH (thus the idea of changing!) across the secondary coil. The moving magnetic field caused by the changing field (flux) induces a current in the secondary coil. If the secondary coil has MORE turns than the primary you can step up the voltage and runs devices that would normally need MORE voltage than what you have coming in. We call this a STEP UP transformer. We can use this idea in reverse as well to create a STEP DOWN transformer Electromagnetic Induction:Useful Application Electromagnetic Induction: Sample Problems Ex.: A circular antenna of area 3 m2 is installed at a TUP grounds. The plane of the area of antenna is inclined at 47º with the direction of Earth’s magnetic field. If the magnitude of Earth’s field at that place is 40773.9 nT find the magnetic flux linked with the antenna.. Electromagnetic Induction: Sample Problems Ex.: A coil with 200 turns of wire is wrapped on an 18.0 cm square frame. Each turn has the same area, equal to that of the frame, and the total resistance of the coil is 2.0ohms. A uniform magnetic field is applied perpendicularly to the plane of the coil. If the field changes uniformly from 0 to 0.500 T in 0.80 s, find the magnitude of the induced emf in the coil while the field has changed as well as the magnitude of the induced current.  B BA  N N t t (0.500  0)(0.18 x0.18)   200 0.80     IR  I (2) I  Electromagnetic Induction: Sample Problems : Ex. A closed coil of 40 turns and of area 200 cm2, is rotated in a magnetic field of flux density 2 Wb m-2. It rotates from a position where its plane makes an angle of 30º with the field to a position perpendicular to the field in a time 0.2 sec. Find the magnitude of the emf induced in the coil due to its rotation. Electromagnetic Induction: 900 kph Video Presentation(from Youtube) Fundamentals of Electrical Machines https://www.youtube.com/watch?v=PGihCyWoVGE&t=15s How DC Motors Work https://www.youtube.com/watch?v=CWulQ1ZSE3c&list=PLEWLv0FhTf6WOjKCaNE81t5xO8CjwuP1d&index=6 DC Machines DC Machines A DC machine is an electromechanical device that is used to convert electrical energy into mechanical energy or vice versa. The working principle and operation of a DC machine is based on an effect when a current carrying conductor coils laying in a magnetic field, the magnetic field produces a mechanical force on it known as torque which rotates the conductor coils in magnetic field. The direction of this produced torque can be found by the Fleming’s hand rule (thumb is the force). The generated force can be calculated as follow DC Machines Why D.C motors are used? While some may claim that direct-current (DC) motors are no longer relevant, that is definitely not the case. DC motors and DC converters/drives are alive and well in the industry. D.C motors have some advantages like Low construction cost Speed control over a wide range High starting torque Quick Starting and Stopping, Reversing and Acceleration Speed control of dc motor is just simple: only adjust the terminal voltage, often using a local potentiometer. Until the late of the 1980s, when the variable frequency drive was not invented, dc motor was the best option for variable speed application. DC Machines What Is a DC Generator? A DC generator is an electrical machine operating in DC whose main function is to convert mechanical energy into electricity. When the conductor slashes magnetic flux, an emf will be generated based on the electromagnetic induction principle of Faraday’s Laws. This electromotive force can cause a flow of current when the conductor circuit is closed. Parts of a DC Generator A DC generator can also be used as a DC motor without changing its construction. Therefore, a DC motor, otherwise a DC generator, can be generally called a DC machine. Below we have mentioned the essential parts of a DC Generator. DC Machines Stator The main function of the stator is to provide magnetic fields where the coil spins. A stator includes two magnets with opposite polarities facing each other. These magnets are located to fit in the region of the rotor. Rotor A rotor in a DC machine includes slotted iron laminations with slots that are stacked to shape a cylindrical armature core. The function of the lamination is to decrease the loss caused due to eddy current. Armature Windings Armature windings are in a closed circuit form and are connected in series to parallel to enhance the produced current sum. DC Machines Yoke The external structure of the DC generator is known as Yoke. It is made of either cast iron or steel. It provides the necessary mechanical power for carrying the magnetic flux given through the poles. Poles The function of a pole is to hold the field windings. These windings are wound on poles and are either connected in series or parallel by the armature windings. Pole Shoe Pole shoe is mainly utilized for spreading the magnetic flux to prevent the field coil from falling. DC Machines Commutator A commutator works like a rectifier that changes AC voltage to DC voltage within the armature winding. It is designed with a copper segment, and each copper segment is protected from the other with the help of mica sheets. It is located on the shaft of the machine. Brushes The electrical connections can be ensured between the commutator as well as the exterior load circuit with the help of brushes. Introduction to DC Machines The basic structural features of a D.C. machine are: Stator - The stator carries the field winding. The stator together with the rotor constitutes the magnetic circuit or core of the machine. It is a hollow cylinder. Rotor - It carries the armature winding. The armature is the load carrying member. The rotor is cylindrical in shape. Armature Winding - This winding rotates in the magnetic field set up at the stationary winding. It is the load carrying member mounted on the rotor. An armature winding is a continuous winding; that is, it has no beginning or end. Introduction to DC Machines Each DC machine can act as a generator or a motor. Hence, this classification is valid for both: DC generators and DC motors. DC machines are usually classified on the basis of their field excitation method. This makes two broad categories of dc machines; (i) Separately excited and (ii) Self-excited. Separately excited DC machines What are Separately excited DC machines? Separately excited DC machines: Separately excited DC generators are not commonly used because they are relatively expensive due to the requirement of an additional power source or circuitry They are used in laboratories for research work, for accurate speed control of DC motors with Ward-Leonard system and in few other applications where self-excited DC generators are unsatisfactory. In this type, the stator field flux may also be provided with the help of permanent magnets (such as in permanent magnet DC motors). PMDC (permanent magnet DC) motors are popularly used in small toys, e.g. a toy car. Separately excited DC machines: In separately excited dc machines, the field winding is supplied from a separate power source. That means the field winding is electrically separated from the armature circuit. Self-excited DC machines What are Self-excited DC machines? Self-excited DC machines In this type, field winding and armature winding are interconnected in various ways to achieve a wide range of performance characteristics (for example, field winding in series or parallel with the armature winding). Self-excited DC machines In a self-excited type of DC generator, the field winding is energized by the current produced by themselves. A small amount of flux is always present in the poles due to the residual magnetism. So, initially, current induces in the armature conductors of a dc generator only due to the residual magnetism. The field flux gradually increases as the induced current starts flowing through the field winding. Self-excited machines can be further classified as” Series wound dc machines Shunt wound dc machines Compound wound dc machines Series wound dc machines In this type, field winding is connected in series with the armature winding. Therefore, the field winding carries whole of the load current (armature current). That is why series winding is designed with few turns of thick wire and the resistance is kept very low (about 0.5 Ohm). Series wound dc machines Application of DC series motor ⇒ DC series motors are used where high starting torque required. These motors are only used where the variation of speed is possible. series motors are not suitable for constant speed applications. ⇒ DC series motor is used in a vacuum cleaner, traction systems, sewing machines, cranes, air compressors etc. Shunt wound dc machines Here, field winding is connected in parallel with the armature winding. Hence, the full voltage is applied across the field winding. Shunt winding is made with a large number of turns and the resistance is kept very high (about 100 Ohm). It takes only small current which is less than 5% of the rated armature current. Shunt wound dc machines Characteristics of DC Shunt Motor The characteristics of shunt DC motor include the following. This DC motor works at a fixed speed once the voltage supply is set. This DC motor is upturned by the turn around the motor connections like a series motor. In this type of DC motor, by a rising motor current, torque can be improved without reducing in speed. DC Shunt Motor Applications The applications of shunt DC motor include the following. These motors are used wherever stable speed is required. This kind of DC motor can be used in Centrifugal Pumps, Lifts, Weaving Machine, Lathe Machines, Blowers, Fans, Conveyors, Spinning machines, etc. Compound wound dc machines In this type, there are two sets of field winding. One is connected in series and the other is connected in parallel with the armature winding. Compound wound machines are further divided as - Short shunt – field Long shunt – field winding is connected winding is connected in parallel with only in parallel with the the armature combination of series winding field winding and armature winding Compound wound dc machines Application of DC Compound motor ⇒ By compound motor, we get high starting torque and nearly constant speed. Because of that Compound motors are used where we require high starting torque and constant speed. ⇒ A compound motor is used in Presses, Shears, Conveyors, Elevators, Rolling Mills, Heavy Planers, etc.  DC Machines Speed of a DC Motor The emf equation of DC motor is given by Here, N = speed of rotation in rpm. P = number of poles. A = number of parallel paths. Z = total no. conductors in armature. Hence, speed of a DC motor is directly proportional to emf of rotation (E) and inversely proportional to flux per pole (φ). DC Machines Example 1. : In a motor the armature resistance is 0.1 ohm. When connected across 110-volt mains the armature takes 20 amp, and its speed is 1,200 rpm. Determine its speed when the armature takes 50 amp from the same mains, with the field increased 10 percent. Ans. 1061 rpm Seatwork 1: In a motor the armature resistance is 0.2 ohm. When connected across 220-volt mains the armature takes 10 amp with an unknown speed. Moreover, the speed is 1500 rpm when the armature takes 20 amp from the same mains, with the field decreased 10 percent. Find the initial speed Efficiency of a DC Motor The efficiency of a DC machine is defined as the ratio of output power to the input power. DC Machines Problems 1. A certain 110-volt shunt motor has an armature brush resistance of 0.06 ohm at full load of 85 amperes. The resistance of the shunt field is 45 ohms, and the stray power losses are found to be 897 watts. Calculate the full-load efficiency of the motor. 2. A 250-kw 230-volt compound generator is delivering 800 amp at 230 volts. The shunt-field current is 12 amp. The armature resistance is 0.007 ohm, and the series-field resistance is 0.002 ohm. The stray power at this load is 5,500 watts. The generator is connected long-shunt. Determine generator efficiency at this load. DC Machines Problems : A certain 110-volt shunt motor has an armature brush resistance of 0.06 ohm at full load of 85 amperes. The resistance of the shunt field is 45 ohms, and the stray power losses are found to be 897 watts. Calculate the full-load efficiency of the motor.  DC Machines Problems : A 115-volt shunt motor has an armature whose resistance is 0.22 ohm. Assuming a voltage across the brush contacts of 2 volts, what armature current will flow (a) when the counter emf is 108 volts ? (b) if the motor load is increased so that the counter emf drops to 106 volts ? DC Machines Problems : 5-hp, 120-volt shunt motor has an armature resistance of 0.10 ohm, and a full-load armature current of 40 amp. Determine the value of the series resistance to add to the armature to limit the initial starting current to 150% of normal. DC Machines DC Machines