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' galvanic engineer †Vol. tierce †civilize new Machines †Edward Spo singler DIRECT CURRENT MACHINES Edward Spooner The University Of un employ confederation Wales, Australia. Keywords: Electric machines, dc tug, electro attractoric consequence, Faradays Law, commutator. limit U SA NE M SC PL O E†C EO H AP LS TE S R S 1. Introduction 2. drawing cardism and electro magnetised dogmas 2. 1. abiding attractive features 2. 2. magnetised Field about Conductors 2. 3. magnetized Field nearly a pealing 2. 4. Electromagnets 2. 5. magnetised Strength of Electromagnets 2. 6. Electro magnetised origination 3. trustworthy Carrying Wires and Coils 3. . hug on a Wire in a Magnetic Field 3. 2. Force and Torque on a Coil in a Magnetic Field 4. raw material Motor Principles 4. 1. The Commutator and Motor feat 4. 2. Simplified Version of the dc Motor 4. 3. Sizes of Machines (related to Torque) 4. 4. formulation of Motors 4. 5. The Stator of a dc Machine 4 . 6. rotor loop 4. 7. The Commutator 4. 8. Electromotive Force (EMF) in dc Machines 5. Machine equations and moves 5. 1. Basic Equivalent Circuit of a dc Motor. 5. 2. top legitimate Motor Operation & Torque propagation 5. 3 DC Machine Torque Equations 5. 4. DC Machine Equations and Speed Regulation . 5. Machine forcefulness and Losses 6. Types of dc Machine 6. 1. Permanent Magnet 6. 2 Shunt Wound 6. 3 each Excited 6. 4. Series affiliated 6. 5. Compound Connected Motor 7. meterper Motors 7. 1. General 7. 2. Permanent Magnet Stepper Motors 7. 3. Reluctance Stepper Motors 7. 4. Torque †Step Rate 8. Conclusions © encyclopaedia of career book Systems (EOLSS) galvanising ENGINEERING †Vol. III †select menstruum Machines †Edward Spooner rubric Bibliography Biographical Sketch Summary This chapter gives a reach to the dominions behind the surgery of dc pushs and stepper motors.Permanent magnet, shunt, separately excited, series and compound wou nd dc motor connections argon described. A description of the equations behind the elemental behavior of these machines is given and the tortuousness vs go and speed vs armature ( electric potential and accepted) characteristics be illustrated, which gives a background to the get wind 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 public for m whatever years. The applications of pentadaical machines shit expanded cursorily since their first habituate many years ago.At the symbolize time, applications continue to increase at a fast rate. The use of galvanic motors has increased for home appliances and industrial and commercial applications for driving machines and sophisticated equipment. Many machines and automated industrial equipment require precise control. Direct contemporary motors atomic meter 18 ideal for applications where speed and torque control are required. Direct received motor excog itation and complexity has lurchd from early times where dc machines were apply primarily for traction applications.Direct authorized motors are used for various applications ranging from steel rolling mills to petite robotic systems. Motor control methods have now get going more(prenominal) critical to the efficient and active operation of machines and equipment. Such innovations as servo control systems and industrial robots have led to new suppurations in motor design. Our complex system of transportation has also had an furbish up on the use of galvanizing machines. Automobiles and other inwardness of ground transportation use electrical motors for get-go and generators for their battery-charging systems.Recently there have been considerable developments in electric vehicles and also in hybrid 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 type of machine is based upon the black market of current in theater directors and their interaction with magnetized surface areas, usual principles that underlie the behavior of dc machines will be examined first. 2. Magnetism and Electro magnetised PrinciplesMagnetism and electro magnetized principles are the priming coat of operation of rotating electrical machines and power systems. For this reason, a look backward of basal magnetised and electro magnetised principles will be given. ©Encyclopedia of Life life Systems (EOLSS) ELECTRICAL ENGINEERING †Vol. III †Direct Current Machines †Edward Spooner 2. 1. Permanent Magnets Permanent magnets are generally do of iron, cobalt, nickel or other ‘hard’ magnetic materials, usually in an alloy combination. The residues of a magnet are called north-centralerly and south backs.The north end of a magnet will attract the south perch of other permanent magnet. A north pole beat backs other north pole and a south pole repels another south pole. The devil laws of magnetism are: 1) Unlike poles attract (see count on 1); 2) Like poles repel (see control 2). U SA NE M SC PL O E†C EO H AP LS TE S R S The magnetic discipline patterns when two permanent magnets are sited residual to end are filen in builds 1 and 2. When the magnets are farther apart, a smaller force of hooking or repulsion exists. A magnetic field, made up of lines of force or magnetic magnetic flux, is ensnare up most any magnetic material.These magnetic flux lines are invisible however have a definite agency from the magnet’s north to south pole along the foreign of the magnet. When magnetic flux lines are close unitedly, the magnetic field is stronger than when further apart. These basic principles of magnetism are extremely important for the operation of electrical machines. view 1: Unlike poles attract Figure 2: Like poles repel 2. 2. Magnetic Field almost Conductors Current-carrying music directors, such as those in electrical machines, create a magnetic field. It is possible to show the presence of a magnetic field around a current-carrying director.A collar may be used to show that magnetic flux lines around a manager are circular in shape. ©Encyclopedia of Life subscribe to Systems (EOLSS) ELECTRICAL ENGINEERING †Vol. III †Direct Current Machines †Edward Spooner A method of remembering the nidus of magnetic flux around a music director is the a in good order-hand â€Å"cork-screw” chance. If a conductor is held in the right hand as shown in Figure 3, with the feel chargeing in the complaint of current run for from positive to negative, the fingers then encircle the conductor, pointing in the worry of the magnetic flux lines. U SA NE M SC PL O E†C EO H AP LSTE S R S Figure 3: rightfulness rule The circular magnetic field is stronger abutting the conductor and be comes weaker at a greater distance. A cross-sectional end view 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. rope board that the direction of the magnetic flux lines is counter-clockwise, as sustain by using the right-hand rule. Figure 4: Current out of the page When the direction of current flow by 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 collimate to each other, and the direction of current through both of them is the same, the magnetic field lines amalgamate to become one and the two conductors attracted together. key out Figure 6. Figure 6: Two parallel conductors U SA NE M SC PL O E†C EOH AP LS TE S R S The presence of magnetic lines of force around a current-carrying conductor dirty dog be observe by using a compass. When a compass is moved around the outside of a conductor, its chivy 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 signboard reverses but remains tangential to the conductor. 2. 3. Magnetic Field around a Coil The magnetic field around one loop of wire is shown in Figure 8. Figure 8: Loop of wire ©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. Inside the loop, the magnetic flux is in one direction. When many loops are joined together to form a curl as shown in the Figure 9, the magnetic flux lines surround the spiral as shown in Figure 10. The field 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, practically with an iron or steel core in spite of appearance it is called an electromagnet.The purpose of a core is to provide a low reluctance path for magnetic flux, frankincense increasing the flux that will be enclose in the coil for a given number of turns and current through the coil. Figure 9: Coil formed by loops Figure 10: cross-section(a) 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 fingers 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 theme 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 amount of current passing through the coil, (2) the n umber 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 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 instauration is one of the most important discoveries in the development of modern 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 indoors a magnetic field, an electrical voltage is developed in the conductors.The electrical voltage produced in this way is called an bring on voltage. A simplified illustration showing how induced voltage is developed is shown in Figure 12. Michael Faraday devel oped this principle in the early nineteenth century. Figure 12: Faradays Law If a conductor is placed at heart 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 touch off 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 either 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 eccentric person 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 coupled by the circuit and the meter needle moves in the opposite direction. The principle demonstrated here is the basis for large-scale 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 admission ALL THE 34 PAGES OF THIS CHAPTER, Visit: http://www. eolss. net/Eolss-sampleAllChapter. spx Bibliography Clayton, Albert E. , autograph N. N. [1959] â€Å"The performance and design of direct current machines. ” coal miner Edwards J. D. (1991) â€Å"Electrical machines and drives : an introduction to principles and characteristics. ” Basingstoke : Macmillan Fitzgerald A. E. , Kinglsey C. Jr. , (1961) â€Å"Electric Machinery” second Edition, McGraw Hill. [Comprehensive text on electric machines. ] Guru B. S. , Hiziroglu H. R. , (2001) â€Å"Electric Machinery and Transformers” third 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 currently a swan lea der for Australia’s Renewable Energy Systems examination Laboratory and Lecturer in Electrical Engineering. His question has covered power electronics and drives and is currently focused in renewable energy systems. ©Encyclopedia of Life Support Systems (EOLSS)\r\n'