DC Motors

8 Key excerpts on "DC Motors"

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  eBook - ePub

  Electrical Machines

  A Practical Approach

  • Satish Kumar Peddapelli, Sridhar Gaddam(Authors)
  • 2020(Publication Date)
  • De Gruyter

    (Publisher)

  2 DC Motors 2.1 Introduction A machine that transforms electric energy into mechanical energy is known as motor. The major applications of DC motor are buses, airplanes and cars, injection pump and cooling fan. Whenever a conductor carries current and is kept in a magnetic field, it experiences a force according to Lorenz’s law. The direction of the force experienced by the conductor is determined by the Fleming’s left-hand rule. 2.2 Principle operation of DC motor A conductor that is free to rotate in a magnetic field is shown in Fig. 2.1. A DC current flows through the rectangular conductor that is supplied by the brushes situated on a commutator. Fig. 2.1: DC motor principle. If a current-carrying conductor is placed in magnetic field, the magnetic field setup in the conductor and the field setup by the permanent magnets interact and a force F is exerted on the conductor. This force causes torque and the coil rotates. Thus, electrical energy is converted into mechanical energy. 2.3 Types of DC Motors Based on the excitation of field windings, DC Motors are categorized as separately and self-excited. Further, the self-excited motors are categorized as (a) shunt, (b) series and (c) compound. 2.4 EMF equation of a motor The supply voltage connected across terminals of the motor as shown in Fig. 2.2. will be utilized to conquer the back emf (E b) and voltage drop due to I a R a. Fig. 2.2: Equivalent circuit of DC motor. Therefore, (2.1) V = E b + I a R a The mechanical power output P m = input power – losses (2.2) P m = V ∗ I a − I a 2 ∗ R a The condition for maximum power is d d I a (P m) = 0. We. get, I a R a = V / 2 (s u b s t i t u t i n g i n (2.1)) V = E b + V 2 (2.3) E b = V 2 Thus, the power developed by the motor is maximum when the back emf (E b) is equal to half the supply voltage (V/2). a) Shunt motor The DC shunt motor is shown in Fig. 2.3, it has shunt field winding and armature winding and are connected in parallel

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  eBook - ePub

  Basic Electrical and Instrumentation Engineering

  • Sivaraman Palanisamy, Sharmeela Chenniappan, A. Thaiyal Nayagi, R. Mahendran(Authors)
  • 2020(Publication Date)
  • Wiley-Scrivener

    (Publisher)

  3 DC Machines

  3.1 Introduction

  Electrical machines are used to transfer the energy from one form to another form, i.e., transferring the energy from mechanical form to electrical form or electrical form to mechanical form. These energy conversions are called electromechanical energy conversion. The machines which deal with Direct Current (DC) are called DC machines [1, 2, 11]. Generally, DC electrical machines are classified into DC generators and DC Motors.

  3.1.1 DC Generators

  A DC generator is a machine that converts given rotating mechanical input power into equivalent DC electrical power. A DC generator produces the power according to Faraday’s laws of electromagnetic induction. As per this law, whenever the conductor rotates in a magnetic field it cuts the magnetic field due to this EMF induced on the conductor.

  3.1.2 DC Motors

  A DC motor is a machine that is used to convert the given DC electrical power into rotating mechanical power. It works on the principle of Lorentz Law, which states that “the current carrying conductor placed in a magnetic and electric field experience a force”; that force is called the Lorentz force.

  3.1.3 Construction of DC Machines

  The construction of the DC machine is shown in Figure 3.1 .

  Figure 3.1 Construction of the DC machine.

  A. Yoke

  Yoke is the outermost cover of the DC machine. It protects the equipments from dust, moisture and various gases likes acidic foams, SO2 , etc.

  • • Yoke provides the mechanical support to the pole
  • • Yoke provides the low reluctance path which provides low current and avoids wastage of power

  In order to provide low reluctance path, rolled steel, cast steel, silicon steel is used.

  B. Poles

  Poles are part of the stator and are joined to the yoke with the help of bolts or welding. The pole carries the core and pole shoes are affixed on it. The pole shoes provide the two purposes

  1. (i) Supporting field winding on it
  2. (ii) Transfers the flux uniformly in air gap

  C. Field Winding

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  eBook - ePub

  Electrical Engineering Fundamentals

  • S. Bobby Rauf(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  7 Electrical Machines – Motors and Generators

  Introduction

  Electromechanical rotating machines can be generators or motors. Rotating machines are called motors when they consume electrical energy or convert electrical energy into mechanical energy, work, or torque. Rotating machines are referred to as generators when they produce electrical energy from mechanical energy, work, or torque. In practical applications, while direct current (DC) machines are almost always single-phase, alternating current (AC) machines can be single-phase or three-phase. In this chapter, we will explore fundamental operating principles and concepts associated with DC and AC motors and generators. The electromagnetic principles behind the operation of generators and motors will be illustrated through simplified electrical diagrams. Basic principles and equations governing important and practical functions and operational parameters of motors and generators will be introduced. Common calculations involving electric motors will be illustrated. Concept of induction motor slip is explained and associated calculations are covered.

  DC Generator

  A DC generator, also referred to as a dynamo , is an electromagnetic device designed to convert mechanical energy or mechanical power – namely, brake horsepower – to electrical energy or electrical power. The electrical energy and power developed in DC dynamos consist of DC and DC voltage. A DC generator is, fundamentally, an AC generator. The feature that differentiates a DC generator’s function and output from an AC generator is called a “commutator.” Common commutator consists of two rings as shown in Figure 7.1 . As shown in Figure 7.1 , the current, I

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  eBook - ePub

  Electrical Engineering for Non-Electrical Engineers

  • S. Bobby Rauf(Author)
  • 2021(Publication Date)
  • River Publishers

    (Publisher)

  rad/sec

  DC Motor

  A DC motor can be perceived as a DC generator or dynamo operating in reverse. As in the case of a dynamo, a magnet ̶ serving as a stator ̶ provides the magnetic field (B and H) that interacts with the DC current flowing through the rotor. The DC current flowing through the rotor windings is supplied from an external DC voltage or current source, via the commutator rings that are stationary. Basic construction of a DC motor is illustrated in Figure 7.3 .

  In other words, a DC motor is a mechanically commutated electric motor powered from direct current (DC). The current in the rotor is switched by the commutator. The relative angle between the stator and rotor magnetic flux is maintained near 90 degrees, which generates the maximum torque.

  In DC Motors, different connections of the field and armature winding provide different inherent speed/torque regulation characteristics. Insofar as the control of the speed of a DC motor is concerned, it can be controlled by changing either the voltage applied to the armature or by changing the field.

  Figure 7.3 : DC motor.

  current. Since voltage is related to current by Ohm's law, V = I.R, speed control can be accomplished through introduction of variable resistance in the armature circuit or field circuit. However, modern DC Motors are often controlled by power electronics systems called DC drives.

  Historically, the introduction of DC Motors to run machinery eliminated the need for steam or internal combustion engines. Case in point, the application of DC Motors as the motive power in locomotives. An advantage of DC Motors is that they can be operated directly

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  eBook - ePub

  An Introduction to Electrical Science

  • Adrian Waygood(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  , Quad Electroacoustics , and is a high-end type that works on the principle of attraction/repulsion forces applied to large, flat, conductive-coated plastic diaphragms due to high-voltage electrostatic charges. Electrostatic loudspeakers, which require a power-supply to create the required high voltages, tend to be significantly larger than electrodynamic types, are far more expensive and are, it is argued, capable of far more accurate sound reproduction than electrodynamic loudspeakers.

  D.C. electric motor

  Now let’s turn our attention to the production of rotational motion which, of course, is what we usually think of whenever we hear the term ‘motor ’ or ‘motor action ’.

  Figure 20.10

  In this section, we’ll learn how a d.c. motor works. A.C. motors are beyond the scope of this book, but are covered in detail in the companion book Electrical Science for Technicians .

  Before we consider its principle of operation, let’s take a look at an exploded view of a typical d.c. motor (Figure 20.10 ).

  In common with all types of motor and generator, the various components of a d.c. motor can be collected together under two main headings: the stator and the rotor , as illustrated in Figure 20.11 .

  Figure 20.11

  The stator , as the name suggests, comprises all the stationary components of the motor, including: the yoke (the cylindrical housing), the pole pieces and their field windings , bearings and the brushes . In the example illustrated, there are four pole pieces, but they can vary in number from two, four, six, etc.

  The rotor comprises all the rotating parts of the motor, including: the drive shaft , armature , armature windings , commutator and impeller fan . We won’t be discussing the impeller fan in this chapter, but its purpose is to draw air through the motor in order to prevent it from overheating.

  The yoke , pole pieces , field windings and armature (a laminated-iron cylinder which supports the armature windings) form the motor’s magnetic circuit , as illustrated in Figure 20.12 . D.C. motors can have two, four or more (even numbers) of poles. The function of the low-reluctance magnetic circuit is to guide the magnetic flux, established by the field windings, to where it is needed: across the radial airgap

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  eBook - ePub

  Electrical Machines

  Fundamentals of Electromechanical Energy Conversion

  • Jacek F. Gieras(Author)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  4 DC MACHINES

  In spite of intensive development of solid-state converter-fed electromechanical drives with induction and synchronous motors, the DC brush motors are still in use. This is due to the simple and cost-effective speed control and very good performance characteristics of DC Motors.

  4.1Function and objective

  The basic function of DC brush machines is conversion of the DC current energy into mechanical energy with controlled parameters, i.e., variable speed or variable torque (motors), or vice versa, mechanical energy into DC energy (generator).

  The disadvantage of DC brush machines is higher cost of manufacturing and problems with the maintenance of brushes and commutator.

  4.2Prinicple of operation

  Fig. 4.1 explains the principle of operation of a DC brush electrical motor. Electric current in the rectangular coil shown in Fig. 4.1a generates a magnetic field the N polarity of which is behind the rectangular coil and the S polarity is in front of the rectangular coil. The poles of magnets and rectangular coil of the same polarity repel each other and the poles of different polarity attract each other so that the coil will turn clockwise. There is no current in the rectangular coil in the position shown in Fig. 4.1b because semi-rings connected to the coil terminals do not touch brushes. The rectangular coil can pass this position due to its moment of inertia. When the semi-rings turn more than 90°, the current in the coil flows in the opposite direction and the polarity of the magnetic field generated by the rectangular coil is also in the opposite direction (Fig. 4.1c ). Because the polarity of the magnetic field generated by the rectangular coil has been changed, the coil can turn further in the same direction. The semiring plays the role of an electromechanical inverter and creates the so-called “commutator”. It is necessary to obtain continuous rotation of the rectangular coil. In practice, there is more than one coil, which creates the rotor winding and more than two segments of commutator to provide smooth movement of the rotor. A DC brush machine with multicoil rotor winding (armature winding) and two-pole stator field excitation winding (instead of PMs) is shown in Fig. 4.2

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  Fundamentals of Electric Machines: A Primer with MATLAB

  A Primer with MATLAB

  • Warsame Hassan Ali, Matthew N. O. Sadiku, Samir Abood(Authors)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  9 Concept of DC Drive In imagination, there’s no limitation.

  Mark Victor Hansen

  A DC motor is used to drive a mechanical load. Variable DC drives have been used to control DC Motors longer than variable frequency drives have been used to control AC motors. The first motor-speed control used DC Motors because of the simplicity of controlling the voltage to the armature and field of a DC motor.

  9.1      DC Motors Drive The brushed DC motor is one of the earliest motor designs. Today, it is the motor of choice in most of the variable speed and torque control applications. 9.1.1      Advantages •  Easy to understand the design •  Easy to control the speed •  Easy to control torque •  Simple, cheap drive design. 9.1.1.1      Easy to Understand the Design The design of the brushed DC motor is quite simple. A permanent magnetic field is created in the stator by either of two means: •  Permanent magnets •  Electromagnetic windings.

  If the field is created by permanent magnets, the motor is said to be a “permanent-magnet DC motor.” (PMDC). If created by electromagnetic windings, the motor is often said to be a “shunt wound DC motor.” (SWDC). Today, because of cost-effectiveness and reliability, the PMDC is the motor of choice for applications involving fractional horsepower DC Motors, as well as most applications up to about 3 horsepower.

  At 5 horsepower and greater, various forms of the shunt wound DC motor are most commonly used. This is because the electromagnetic windings are more cost effective than permanent magnets in this power range.

  The section of the rotor where the electricity enters the rotor windings is called the commutator

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  Hands On Water and Wastewater Equipment Maintenance, Volume I

  • Barbara Renner(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  CHAPTER 5 D-C and Single-Phase Motors

  5.01 The next several chapters deal with a variety of electrical components. The intent of each chapter is to present information that relates to specific types of equipment only. The technical details of electricity will not be covered in this text because many other books have already been written about the subject. If more technical information is desired, contact a local electrical supplier. They should not only be able to answer any questions but also should be able to provide reference data.

  ELECTRICAL POWER

  5.02 Magnetism is the basis for all generated and consumed electrical power. Magnetism also provides the basis for the operating principles of most electrical machinery and electrical components.

  5.03 Magnetism is the property of a material or substance (magnet) that has the power to attract other materials to itself. All magnets have a north and a south pole and are surrounded by magnetic lines of force (magnetic field). The lines of force travel from the north pole to the south pole outside of the magnetic material and from the south pole to the north pole within the magnetic material (Figure 5.1 ). The complete cycle is called a magnetic circuit.

  5.04 Many motors and other electrical devices use permanent magnets (iron, steel, or alloy bars that have been magnetized) for their electrical field. Most motors, however, use electromagnets (soft iron cores that are wound with coils of insulated wire) (Figure 5.2 ) for their electrical field. Electromagnets become energized when an electric current is passed through the coils. The greater the number of turns of wire, the stronger the lines of magnetic force that are developed. When the electric current is stopped, the electromagnet loses its magnetism.

  5.05 Electricity is created when a conductor is placed within a magnetic field. The movement of the conductor through the magnetic field excites the electrons in the conductor to move, thereby creating an electromotive force (EMF) or voltage (Figure 5.3

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