It has two main parts : Stator – It is the stationary part. Let Φ is the useful flux for every pole within webers, z is the total number of conductors within the armature, n is the rotation speed for an armature in the revolution for each second. Electrical Formulas AC & DC Circuits (Single-φ & 3-φ) We can Find the Following Quantities by Using Below Formulas Chart Electrical Formulas in DC Full load Current in Amperes (Alternating Current AC Motors) Alternating Current AC (Single-φ & 3-φ) Finding Motor Hp ( Horse Power), kVA (kilo-Volt Ampere) kW input, When Motor HP is known kW (kilowatts) Amperes, when kVA is known. The main function of the DC generator is to convert mechanical power to DC electrical power, whereas a DC motor converts DC power to mechanical power. 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The stator contains parts such as brushes, magnets and housing for the whole motor. AC machines differ from dc machines by having their armature windings almost always located on the stator while their field windings are located on the rotor. The direction of induced current is given by Fleming’s right hand rule. These motors are available in two types like brushes & brushes motors. The DC machine can operate as either a motor or a generator; at present its use as a generator is limited because of the wide spread use of ac power. Because of this region, flux can be spread out within the air-gap as well as extra flux can be passed through the air space toward armature. The armature characteristics of dc motors are, the armature turns whereas the magnetic field remains inactive. In the motor, the emf of rotation can be called as counter or back emf, and Er=Eb. According to Fleming’s right hand rule, the direction of induced current changes whenever the direction of motion of the conductor changes. Generally, the AC is generated and after that, it is changed into DC with the help of rectifiers. Electric Machines By DP Kothari and IJ Nagrath now in its 5″ edition, is intended for third and fourth year UG students and first-year PG students of electrical engineering-updated with latest scientific advancements. The above equation is the e.m.f. A compound machine includes both the series as well as shunt fields. The direction of this produced torque can be found by the Fleming’s left hand rule (thumb is the force). The main function of the commutator in the DC machine is to collect the current from the armature conductor as well as supplies the current to the load using brushes. There are two types of generator – DC generator, AC generator or alternator. Brushes wear with time to inspect frequently. This is the principle of dynamically induced emf. Therefore, the utilization of DC machines like motors and generators DC generators are extremely limited because they are utilized mainly for providing excitation of tiny & middle range of alternators. If the shunt-field is allied in parallel by the armature only, then the machine can be named as the ‘short shunt compound machine’ & if the shunt-field is allied in parallel by both the armature as well as series field, then the machine is named as the ‘long shunt compound machine’. Transformsmechanicalenergyintoelectric energywithDC voltage and current(DC generatoror dynamo), or conversely(DC motor) ball bearing ball bearing brush brush holder stator (inductor) collector rotor (armature) 29/05/2020. The main benefits of this machine include torque regulation as well as easy speed. Field Winding. The excitation of the DC machine is classified into two types namely separate excitation, as well as self-excitation. Hence, let's call this point as construction of a DC machine instead of just 'construction of a dc generator'. It provides the low-reluctance path toward the flux generated with field winding. Basic Parts of the DC Motor Therefore DC generator is suppressed through an AC supply which is rectified to use in several applications. Open circuit and Short circuit Test on transformer. At present, the generation of electrical energy can be done in bulk in the form of AC (an alternating current). The changes are made keeping the original flavor of the book intact, that is, in-depth coverage of fundamental concepts. 2. The applications of the DC machine is limited to trains, mills, and mines. Hence, the direction of current in every armature conductor will be alternating. The output of the DC machine is DC output because they convert AC voltage to DC voltage. The input of a brushless DC motor is current/voltage and its output is torque. The type of loss may change from one apparatus to another. Though the losses are more, DC machines find its importance in modern day to day life. DC motor is one kind of rotatory motor used to change the energy from DC to mechanical. A DC machine is used to operate the devices which use unidirectional current. In Separately Excited DC Machine, a separate DC source is utilized for activating the field coils. the equation of the DC machine. And therefore, we get unidirectional current at the terminals. The current-carrying conductor is the armature and the magnetic field is generated by the excitation winding. The pole of the DC machine is an electromagnet and the field winding is winding among pole. Another name of a yoke is the frame. The working principle of a DC machine is when electric current flows through a coil within a magnetic field, and then the magnetic force generates a torque that rotates the dc motor. It not only provides... Poles and pole shoes: Poles are joined to the yoke with the help of bolts or welding. The various losses are Electrical or Copper losses (I 2 R losses), Core losses or Iron losses, Brush losses, Mechanical losses, Stray load losses. 2. The standard value of produced voltage for each conductor, The voltage produced (E) can be decided with the no.of armature conductors within series I any single lane among the brushes thus, the whole voltage produced, E = standard voltage for each conductor x no. is directly proportional to the flux ( ) in the motor and speed of the motor ( ). The materials used in brushes are graphite otherwise carbon which is in rectangular form. Brushes in the DC machine gather the current from the commutator and supply it to the exterior load. The Segments in the commutator are protected from the thin mica layer. The stator carries the field windings and rotor carries the armature windings. The materials used for this winding are conducting material like copper. These losses are explained below in detail. The DC machine e.m.f can be defined as when the armature in the dc machine rotates, the voltage can be generated within the coils. The AC motor is frequently used in industrial applications for altering electrical energy to mechanical energy. The coils around the poles are known as field (or exciting) coils and are connected in … According to Faraday’s laws of electromagnetic induction, whenever a conductor is placed in a varying magnetic field (OR a conductor is moved in a magnetic field), an emf (electromotive force) gets induced in the conductor. This edition contains plethora of solved examples, competitive examination based MCQs and MATLAB exam… Direct current is supplied to rotating armature by means of Brush arrangement.Field winding may be in series or shunt with armature and fed with dc supply to create flux.So dc supply goes to both armature and field winding. PMDC motor Permanent magnet DC motors. Note:Theoretically, a DC generator can be used as a DC motor without any constructional changes and vice versa is also possible. The field current (I. F. )in dc machines produces a field magnetomotive force (mmf) This magnetomotive force (mmf) produces a flux ( )in the motor in accordance with its magnetization curve. The function of the field system is to produce a uniform magnetic field within which … Field system. As the flux for each pole is ‘Φ’, every conductor slashes a flux ‘PΦ’ within a single revolution. D.C Motors – Principle of Operation – Back E.M.F.– Circuit Model – Torque Equation – Characteristics and Application of Shunt, Series and Compound Motors – Armature Reaction. - Structure & Tuning Methods. Some of the parts of the DC machine is discussed below. DC machine is most frequently used for a motor. In a DC generator, field coils produce an electromagnetic field and the armature conductors are rotated into the field. Working of DC Machine. The conductors located under the other pole are subject to a force of the same intensity in the opposite direction. But with a split ring commutator, connections of the armature conductors also gets reversed when the current reversal occurs. Hence the force acts on the armature conductor in the direction perpendicular to both uniform field, and current is … A DC machine is an electromechanical energy alteration device. DC machines 1. The difference between the AC motor and the DC motor includes the following. of armature conductor within series for each parallel lane. The commutator can be built with a huge number of segments in the edge form of hard drawn copper. Thus the time for a single armature revolution is a 1/n sec. Shunt Wound. The magnetic field can be generated by means of a permanent magnet for smaller motors, and with an electromagnet (excitation winding) for larger motors. A DC Machine consists of a stator and a rotor with a uniform air gap in between them. When the field coil is energized, it creates a magnetic field (excitation flux) in the air gap, in the direction of the radii of the armature. It can be built with the annealed steel laminations for reducing the power drop because of the eddy currents. The DC machines are classified into two types such as DC generator as well as DC motor. The principal kinds of DC machines are classified into four types which include the following. Faraday’s laws of electromagnetic induction, Basic construction and working of a dc generator, Construction and working of an AC generator or alternator, Working principle and types of an Induction motor, Difference between synchronous motor and induction motor, Basic construction and working of transformers. The armature conductor is located in these slots. In this motor, brushes, and commutators are not present. Here is a question for you, what is commutation in dc machine? The DC generator is mainly useful for supplying DC sources toward the DC machine in power stations. What are the applications of Autotransformers? The lamination is used to decrease the loss because of the eddy current. It has two input terminals like positive and negative. In Shunt wound DC Machines, the field coils are allied in parallel through the armature. We know that the main function of a DC machine is to convert mechanical energy to electrical energy. These basic constructional details are also valid for the construction of a DC motor. The materials used for this are cast steel, cast iron otherwise pole core. AC motors are used wherever high speed, as well as variable torque, is required. The cheapness is main consideration therefore yoke is made up of cast iron in the small DC machines but it is made up of cast still or rolled still in the large DC machines. In Shunt wound DC Machines, the field coils are allied in parallel through the armature. Today DC motors are still found in applications as small as toys and disk drives, or in large sizes to operate steel rolling mills and paper machines. A dc generator is an electrical machine which converts mechanical energy into direct current electricity. The DC machine energy losses can be classified into Electrical otherwise Copper losses, Core losses otherwise Iron losses, Mechanical losses, Brush losses, and Stray load losses. The above figure shows constructional details of a simple 4-pole DC machine. The series winding of the machine includes few twists of a huge cross-sectional region, as well as the shunt windings, include several fine wire twists. In the self-excitation type of dc machine, the flow of current throughout the field-winding is supplied with the machine. 3 point starters in DC Shunt and Compound machines serve for the following purposes. The two forces create a torque which causes th… In a separate excitation type of dc machine, the field coils are activated with a separate DC source. The efficiency of the AC motor is less because of the loss in induction current & slip of motor. … DC Generator: In DC generator armature (assembly of conductors) is the rotor and electromagnetic poles are attached on the stator. If the conductor is provided with a closed path, the induced current will circulate within the path. DC Motors and Generators DC motor Fall15 Revised: November 4, 2016 2 of 21 The materials used in this core are permeability low-reluctance materials like iron otherwise cast. As ‘n’ revolutions are completed within a single second and 1 revolution will be completed within a 1/n second. Throughout this conversion method, the whole input power cannot be changed into output power because of the power loss in different forms. Figure 1: Elementary doubly-excited magnetic system. The rotor contains the windings, the communicator and the output shaft. A is the no. DC motor has- Armature that rotates, & Field winding that stays stand still. And also provides uni-directional torque for DC-motor. Whereas DC motor drives some devices like lathes, fans, centrifugal pumps, printing presses, electric locomotives, hoists, cranes, conveyors, rolling mills, auto-rickshaw, ice machines, etc. The voltage produced for each conductor = flux slash for each revolution in WB / Time taken for a single revolution within seconds. Figure 1 shows an elementary doubly-excited magnetic system. The conversion of this mechanism is known as the commutator, thus these machines are also named as commutating machines. DC machines. Each DC machine contains two separate terminals with a magnetized center between them. Brushless DC Motors Work. These losses will decrease the apparatus efficiency as well as the temperature will be increased. The construction of the DC machine can be done using some of the essential parts like Yoke, Pole core & pole shoes, Pole coil & field coil, Armature core, Armature winding otherwise conductor, commutator, brushes & bearings. The two windings are carried-out with every machine pole. Thus, this is all about DC machines. The yoke is a stationary and outer cylindrical part of DC machines. The materials used in the yoke are designed with cast iron, cast steel otherwise rolled steel. What are Ferromagnetic Materials – Types & Their Applications, AC motor is an electric device which is driven through an AC. The DC machine can be classified into two types namely DC motors as well as DC generators. 3/23/2007 ELEC A6 DC Machine 2 DIRECT CURRENT (DC) MACHINES Fundamentals • Generator action: An emf (voltage) is induced in a conductor if it moves through a magnetic field. Whenever an armature winding is turned with the help of prime mover then the voltage, as well as magnetic flux, gets induced within it. For example, underground subway cars, as well as trolleys, may utilize DC motors. If you look at the above figure, you will know how the direction of the induced current is alternating in an armature conductor. What is the Difference between 8051, PIC, AVR and ARM? From the above information, finally, we can conclude that DC machines are dc generator & dc motor. In series-wound D.C. Machines, the field coils are allied in series through the armature. Input supply phases of ac motors are both single and three-phase, Input supply phases of dc motors are single phase. The magnitude of induced emf can be calculated from the emf equation of dc generator. In Separately Excited DC Machine, a separate DC source is utilized for activating the field coils. In this motor, carbon brushes and commutators are present. Parallel operation of shunt generators Operating 2 dc shunt generators in parallel. These are classified into two types like synchronous & induction motors. The armature characteristics of ac motors are the armature is inactive whereas the magnetic field turns. Types of DC Machines Separately Excited. Most of the DC machines are equivalent to AC machines because they include AC currents as well as AC voltages in them. Direct Current Motor Basics The first type of motor built is still in widespread use In the late 1800s, several inventors built the first working motors, which used direct current (DC) power. Electric braking of DC motors Different methods of electric braking of dc motors. DC generators. A DC machine consists of two basic parts; stator and rotor. Large DC motors with separately excited fields were generally used with winder drives for mine hoists , for high … In the past, automobiles were designed with DC dynamos for charging their batteries. This magnetic field “enters” the armature from the North pole side of the field coil and “exits” the armature from the South pole side of the field coil. and Commutation.Speed Control of D.C. Motors: Armature Voltage and Field Flux Control Methods. The material used for field windings is copper. Whenever field winding is energized then the pole gives magnetic flux. Construction of a DC machine: Yoke: The outer frame of a dc machine is called as yoke. This winding is allied to an exterior circuit. Basic construction and working of a DC Generator. The materials used to build pole shoe is cast iron otherwise cast steed, and also used annealed steel lamination to reduce the loss of power because of eddy currents. As series field winding gets the armature current, as well as the armature current is huge, due to this the series field winding includes few twists of wire of big cross-sectional region. The AC motor speed control can be done by changing the frequency. The application of DC machine as a motor is used by dividing into three types like Series, Shunt &Compound whereas the application of dc machine as a generator is classified into separately excited, series, and shunt-wound generators. Thus, a DC generator or a DC motor can be broadly termed as a DC machine. The DC motor’s efficiency is high because there is no induction current as well as slip. The applications of autotransformer are as follows: … Pole shoe in the DC machine is an extensive part as well as to enlarge the region of the pole. Let’s consider an armature rotating clockwise and a conductor at the left is moving upward. After the invention of the induction motor, alternating current (AC) machines largely replaced DC machines … The armature winding can be formed by interconnecting the armature conductor. From the 1 st diagram we can see that the construction of a DC motor is such that the direction of current through the armature conductor at all instance is perpendicular to the field. Basic Components of a DC Machine. In a generator, the e.m.f of rotation can be called the generated emf, and Er=Eg. Understanding the operation of the DC motor is very simple from a basic diagram is shown below. Starting methods of a DC motor 3 point starter, 4 point starter and series motor starter. The main function of the yoke is to provide protection for whole machine. Armature core includes a huge number of slots within its edge. Thus, an electromagnetically induced emf is generated in the armature conductors. When the armature completes a half rotation, the direction of motion of that particular conductor will be reversed to downward. It limits the high starting current into the armature by having the resistance high at the time of starting and reducing it during the running conditions. DC motors are frequently used like variable speed drives & where changes in the severe torque occur. DC motors are used wherever variable speed, as well as high torque, is required. The main function of the yoke in the machine is to offer mechanical support intended for poles and protects the entire machine from moisture, dust, etc. of conductors within series for each lane. This energy conversion is based on the principle of production of dynamically induced emf. As the shunt field gets the complete o/p voltage of a generator otherwise a motor supply voltage, it is normally made of a huge number of twists of fine wire with a small field current carrying. When we evaluate with DC machines, Alternating Current machines have more advantages because of the losses that appear in DC. The advantages of this machine include the following. DC MACHINE A transformer works on alternating current, while a DC machine works on Direct Current. The input supply of ac motor is alternating current, The input supply of dc motor is direct current. However, a DC motor is applicable where good speed regulation & an ample range of speeds are necessary like in electric-transaction systems. Z/A is the no. Speed control of a DC motor Various methods for controlling speed of a DC motor. I introduce you to the construction of the field system in DC machines Direct-Current Machines • Direct-current (DC) machines are driven from a DC power supply. DC machines are the most versatile of all rotating electrical machines. In this, the windings are wounded in the region of pole core & named as field coil. DC MACHINES. A DC machine can be a DC motor or a DC generator. In industries, DC machines are used for different processes like welding, electrolytic, etc. BLDC motor The DC motor speed control can be done by changing the current of the armature winding. In practical, these are used in large industries, In practical, these are used in appliances, DC machines like dc motors have various advantages like starting torque is high, reversing, fast-starting & stopping, changeable speeds through voltage input, These are very easily controlled as well as cheaper when compared with AC. of parallel lane throughout the armature among the opposite polarity brushes. There are two main parts, the stator and the rotor. Whenever current is supplied through field winding than it electromagnetics the poles which generate required flux. Depending on that principle, all electrical generators work. DC machines are one of the three basic multiply-excited rotational electromechanical energy converters. It is made up of cast iron or steel. A set of three-phase ac voltages is induced into the stator armature windings of an ac machine by the rotating magnetic field from the rotor field windings (generator action). 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. Basic constructional parts of a DC machine are described below. Practical DC Motor consists of field windings to provide the magnetic flux and armature which acts as the conductor. Losses in DC Machine The losses that occur in a DC Machine is divided into five basic categories. In rotating machines, voltages are generated in windings or groups of coils • by rotating these windings mechanically through a magnetic field, • by mechanically rotating a magnetic field past the winding, • by designing the magnetic circuit so that the reluctance varies with rotation of the rotor. This article outlines basic construction and working of a DC generator. The connection of the compound machine can be done in two ways. As the shunt field... Series Wound.