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electric engineering science Vol. common chord locate legitimate automobiles Edward Spo iodinr DIRECT CURRENT MACHINES Edward Spo wizr The University Of New South Wales, Australia. Keywords voltaic machines, dc get, electro attractive depictic induction, Faradays Law, commutator. Contents U SA NE M SC PL O E C EO H AP LS TE S R S 1. Introduction 2. Magnetism and Electro attractivenessic principles 2. 1. changeless Magnets 2. 2. charismatic plain most Conductors 2. 3. Magnetic sketch more or less a Coil 2. 4. Electro attractivenesss 2. 5. Magnetic Strength of Electro attractive features 2. 6. Electro charismatic installing 3. oc online Carrying Wires and Coils 3. . Force on a Wire in a Magnetic Field 3. 2. Force and tortuosity on a Coil in a Magnetic Field 4. Basic labour Principles 4. 1. The Commutator and Motor Action 4. 2. Simplified Version of the dc Motor 4. 3. Sizes of political machines (related to contortion) 4. 4. Construction of Motors 4. 5. The Stator of a dc Machine 4. 6. rotor 4. 7. The Commutator 4. 8. Electromotive Force (EMF) in dc Machines 5. Machine equations and rotarys 5. 1. Basic Equivalent circle of a dc Motor. 5. 2. get up circulating(prenominal) Motor Operation & torsion generation 5. 3 DC Machine Torque Equations 5. 4. DC Machine Equations and Speed Regulation . 5. Machine Power and Losses 6. Types of dc Machine 6. 1. Permanent Magnet 6. 2 Shunt Wound 6. 3 singly Excited 6. 4. Series Connected 6. 5. Compound Connected Motor 7. hoofer Motors 7. 1. General 7. 2. Permanent Magnet Stepper Motors 7. 3. Reluctance Stepper Motors 7. 4. Torque Step Rate 8. Conclusions Encyclopedia of lifetime hold out Systems (EOLSS) ELECTRICAL ENGINEERING Vol. III Direct Current Machines Edward Spooner Glossary Bibliography Biographical resume summary This chapter gives a background to the principles behind the exercise of dc motors and stepper motors.Permanent magnet, shunt, separately excited, series and compound wound dc motor connections are described. A description of the equations behind the basic behavior of these machines is given and the torque vs hasten and speed vs armature (voltage and current) characteristics are illustrated, which gives a background to the secure of these motors. U SA NE M SC PL O E C EO H AP LS TE S R S 1. Introduction Electrical machinery has been in introduction for m any(prenominal) years. The applications of electric machines have expanded rapidly since their first employ many years ago.At the surrender time, applications continue to increase at a rapid rate. The use of electrical motors has increased for home appliances and industrial and commercial-grade applications for driving machines and sophisticated equipment. Many machines and automated industrial equipment require tiny control. Direct current motors are ideal for applications where speed and torque control are required. Direct current motor design and complexity has changed from proto(prenominal ) times where dc machines were used primarily for traction applications.Direct current motors are used for various applications ranging from steel rolling mills to tiny robotic clays. Motor control methods have now commence more critical to the effectual and effective operation of machines and equipment. Such innovations as servo control systems and industrial robots have led to new developments in motor design. Our complex system of transportation has also had an impact on the use of electrical machines. Automobiles and other(a)wise means of ground transportation use electrical motors for starting and generators for their battery-charging systems.Recently there have been considerable developments in electric vehicles and also in crossbreeding electric vehicles which use a combination of a dc motor and an internal combustion engine for efficient operation. In this chapter machines driven by dc electrical supplies are considered. Since the operation of this compositors case o f machine is base upon the flow of current in film directors and their interaction with magnetised celestial orbits, common principles that be the behavior of dc machines will be examined first. 2. Magnetism and Electro magnetised PrinciplesMagnetism and electro magnetic principles are the basis of operation of rotating electrical machines and power systems. For this reason, a come off of basic magnetic and electromagnetic principles will be given. Encyclopedia of brio Support Systems (EOLSS) ELECTRICAL ENGINEERING Vol. III Direct Current Machines Edward Spooner 2. 1. Permanent Magnets Permanent magnets are generally made of iron, cobalt, nickel or other hard magnetic materials, usually in an alloy combination. The oddments of a magnet are called north and siemens depots.The north pole of a magnet will attract the in the south pole of another unchangeable magnet. A north pole repels another north pole and a south pole repels another south pole. The 2 laws of magnetis m are 1) impertinent poles attract (see enter 1) 2) Like poles repel (see sign 2). U SA NE M SC PL O E C EO H AP LS TE S R S The magnetic scene of action patterns when two permanent magnets are placed end to end are order of battlen in human bodys 1 and 2. When the magnets are farther apart, a smaller lunge of attraction or repulsion exists. A magnetic field, made up of lines of force or magnetic conflate, is set up most any magnetic material.These magnetic flux lines are invisible but have a decisive forethought from the magnets north to south pole along the outside of the magnet. When magnetic flux lines are close together, the magnetic field is stronger than when further apart. These basic principles of magnetism are extremely important for the operation of electrical machines. attribute 1 Unlike poles attract Figure 2 Like poles repel 2. 2. Magnetic Field around Conductors Current-carrying conductors, such as those in electrical machines, spring up a magnetic field. It is possible to show the presence of a magnetic field around a current-carrying conductor.A arena may be used to show that magnetic flux lines around a conductor are circular in shape. Encyclopedia of Life Support Systems (EOLSS) ELECTRICAL ENGINEERING Vol. III Direct Current Machines Edward Spooner A method of remembering the explosive charge of magnetic flux around a conductor is the function- perish cork-screw rule. If a conductor is held in the right hand as shown in Figure 3, with the buck bakshishing in the direction of current flow from positive to negative, the fingers then encircle the conductor, pointing in the direction of the magnetic flux lines. U SA NE M SC PL O E C EO H AP LSTE S R S Figure 3 Right-hand rule The circular magnetic field is stronger near the conductor and becomes weaker at a greater distance. A cross-sectional end meet of a conductor with current flowing toward the observer is shown in Figure 4. Current flow towards the observer is shown by a circle with a dot in the centre. Notice that the direction of the magnetic flux lines is counter-clockwise, as verified by exploitation the right(a) rule. Figure 4 Current out of the rapscallion When the direction of current flow by dint of a conductor is reversed, the direction of the magnetic lines of force is also reversed.The cross-sectional end view of a conductor in Figure 5 shows current flow in a direction away from the observer. Notice that the direction of the magnetic lines of force is now clockwise. Figure 5 Current into the page Encyclopedia of Life Support Systems (EOLSS) ELECTRICAL ENGINEERING Vol. III Direct Current Machines Edward Spooner When two conductors are placed parallel to each other, and the direction of current done both of them is the same, the magnetic field lines amalgamate to become one and the two conductors attracted together. See Figure 6. Figure 6 cardinal parallel conductors U SA NE M SC PL O E C EOH AP LS TE S R S The presence of magne tic lines of force around a current-carrying conductor can be observed by using a circumnavigate. When a master is go around the outside of a conductor, its harry will align itself tangentially to the lines of force as shown in Figure 7. Figure 7 Fields effect on a compass When current flow is in the opposite direction, the compass polarity reverses but remains tangential to the conductor. 2. 3. Magnetic Field around a Coil The magnetic field around one loop of telegraph is shown in Figure 8. Figure 8 Loop of telegraph Encyclopedia of Life Support Systems (EOLSS) ELECTRICAL ENGINEERING Vol.III Direct Current Machines Edward Spooner U SA NE M SC PL O E C EO H AP LS TE S R S Magnetic flux lines extend around the conductor as shown when current passes through the loop. at heart the loop, the magnetic flux is in one direction. When many loops are fall in together to form a gyre as shown in the Figure 9, the magnetic flux lines surround the coil as shown in Figure 10. The f ield produced by a coil is much stronger than the field of one loop of wire. The field produced by a coil is similar in shape to the field around a bar magnet. A coil carrying current, often with an iron or steel core inside it is called an electromagnet.The dissolve of a core is to provide a low reluctance rail for magnetic flux, thus change magnitude the flux that will be present in the coil for a given number of turns and current through the coil. Figure 9 Coil formed by loops Figure 10 Cross-sectional view of the above coil 2. 4. Electromagnets Electromagnets are produced when current flows through a coil of wire as shown below. Almost all electrical machines have electromagnetic coils. The north pole of a coil of wire is the end where the lines of force exit, while the south polarity is the end where the lines of force enter the coil.To find the north pole of a coil, use the right-hand rule for polarity, as shown in Figure 11. Grasp the coil with the right hand. Point the fi ngers in the direction of current flow through the coil, and the thumb will point to the north polarity of the coil. When the polarity of the voltage address is reversed, the magnetic poles of the coil reverse. Figure 11 Finding the north pole of an electromagnet Encyclopedia of Life Support Systems (EOLSS) ELECTRICAL ENGINEERING Vol. III Direct Current Machines Edward Spooner The poles of an electromagnet can be checked by placing a compass near a pole of the electromagnet.The north-seeking pole of the compass will point toward the north pole of the coil. 2. 5. Magnetic Strength of Electromagnets The magnetic strength of an electromagnet depends on three factors (1) the bill of current passing through the coil, (2) the number of turns of wire, and (3) the type of core material. The number of magnetic lines of force is increased by increasing the current, by increasing the number of turns of wire, by decreasing any air power gap in the path of the magnetic flux, or by using a more desirable type of core material. . 6. electromagnetic Induction U SA NE M SC PL O E C EO H AP LS TE S R S The principle of electromagnetic induction is one of the most important discoveries in the development of forward-looking electrical technology. Electromagnetic induction is the induction of electric voltage in an electrical circuit caused by a change in the magnetic field coupled to the circuit. When electrical conductors, such as alternator windings, are moved within a magnetic field, an electrical voltage is developed in the conductors.The electrical voltage produced in this way is called an bring forth voltage. A alter illustration showing how induced voltage is developed is shown in Figure 12. Michael Faraday developed this principle in the early nineteenth century. Figure 12 Faradays Law If a conductor is placed within the magnetic field of a horseshoe magnet so that the left side of the magnet has a north pole (N) and the right side has a south pole (S), magnetic lines of force travel from the north pole of the magnet to the south pole.The ends of the conductor in Figure12 are connected to a volt meter to measure the induced voltage. The meter can move each to the left or to the right to indicate the direction and magnitude of induced voltage. When the conductor is moved, the amount of magnetic flux contained within the electrical circuit (which includes the wire and the connections to the meter and the meter itself) changes. This change induces voltage through the conductor. Electromagnetic induction takes place whenever there is a change in the amount of flux coupled by a circuit.In this case the motion of the conductor in the up direction causes more magnetic flux to be contained within the circuit and the meter Encyclopedia of Life Support Systems (EOLSS) ELECTRICAL ENGINEERING Vol. III Direct Current Machines Edward Spooner needle moves in one direction. Motion of the conductor in the down direction causes less magnetic flux to be c oupled by the circuit and the meter needle moves in the opposite direction. The principle demonstrated here is the basis for big electrical power generation.In order for an induced current to be developed, the conductor must be in a complete path or closed circuit, the induced voltage will then cause a current to flow in the circuit. 3. Current Carrying Wires and Coils The basic requirement of any electrical machine, whether ac or dc, is a method of producing torque. This section explores how two magnetic fields in a machine interact to produce a force which produces a torque in a rotating machine. U SA NE M SC PL O E C EO H AP LS TE S R S TO ACCESS ALL THE 34 PAGES OF THIS CHAPTER, Visit http//www. eolss. net/Eolss-sampleAllChapter. spx Bibliography Clayton, Albert E. , Hancock N. N. 1959 The performance and design of direct current machines. Pitman Edwards J. D. (1991) Electrical machines and drives an introduction to principles and characteristics. Basingstoke Macmillan Fit zgerald A. E. , Kinglsey C. Jr. , (1961) Electric Machinery 2nd Edition, McGraw Hill. Comprehensive textual matter on electric machines. Guru B. S. , Hiziroglu H. R. , (2001) Electric Machinery and Transformers 3rd Edition, New York, Oxford University Press. Good general text on electrical engineering including machines. Say M. G. (1983). Alternating Current Machines, fifth Edition, London Pitman. This covers the more advanced theory of electrical machines Biographical Sketch E. D. Spooner graduated from the University New South Wales, Australia, and obtained his ME in 1965. He is presently a project leader for Australias Renewable Energy Systems testing laboratory and Lecturer in Electrical Engineering. His research has covered power electronics and drives and is currently focused in renewable energy systems. Encyclopedia of Life Support Systems (EOLSS)