Electric Motor

6 Key excerpts on "Electric Motor"

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  eBook - ePub

  Practical Electricity for Aviation Maintenance Technicians

  • Dale Crane, Dennis Wilt(Authors)
  • 2017(Publication Date)
  • Aviation Supplies & Academics, Inc.

    (Publisher)

  8 Electric Motors and Generators

  Electric Motors have become such a standard part of our lives that they are usually taken for granted. They are made in all sizes and power outputs, from the tiny motors that move the hands in analog wrist watches to the motors that drive ocean-going ships. Regardless of their size, all Electric Motors work on the same principle. One magnetic fields reacts with another magnetic field to produce a physical force.

  Figure 8-1 shows the basic way an Electric Motor works. The conductor (represented by the circle) in view A has no current flowing in it, and the lines of flux pass straight across the space from the north pole of the magnet to the south pole. But when current flows in the conductor as in view B, it produces a magnetic field, which surrounds the conductor.

  Figure 8-1 . When the magnetic field surrounding the conductor distorts the lines of flux between the poles of the magnet, a force is produced that tries to move the conductor out of the magnetic field.

  The lines of flux between the poles of the magnet try to remain as short as possible, and when they are distorted by the field surrounding the conductor, they produce a physical force that tries to move the conductor to the left, out of their field.

  The right-hand rule for motors helps understand this action. Hold the fingers of your right hand as shown in Figure 8-2, with the forefinger pointing in the direction of the lines of flux (from the north pole of the magnet to the south pole) and the second finger pointing in the direction of electron flow in the conductor (from negative to positive); the thumb will point in the direction the conductor will move. The amount of force that acts on the conductor is determined by the strength of the two magnetic fields.

  Figure 8-2

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  Automotive Innovation

  The Science and Engineering behind Cutting-Edge Automotive Technology

  • Patrick Hossay(Author)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  power electronics (the combined electronic, electromagnetic, and electrochemical components that control and convert power) have fundamentally reshaped what is viable in Electric Motors and thus what is achievable in EVs and HEVs. As a result, ideas and concepts that have been known for many decades as conceptually possible but not feasible, have now become technically practicable options.

  The Principles of the Electric Motor

  As always, let’s start at the beginning. Motors function by exploiting electromagnetic force, one of the four fundamental forces of nature. As might be obvious from the name, electromagnetism defines a relationship between magnetism and electricity. In fact, magnetic and electric forces are really fundamentally the same sort of thing; both are defined by the exchange of photons between charged particles, called an exchange force . In our case, the particles are electrons. You can think of photons as elementary particles or waves that act as force carriers , traveling between electrons and exerting force, and defining both electric and magnetic fields.

  Of course, to understand magnetic fields we need to understand magnets. Three elements, iron, nickel, and cobalt, demonstrate the property of ferromagnetism , or the ability to be permanently magnetized when placed in a magnetic field. This magnetization happens at the atomic level. The atoms that compose these materials are themselves like tiny magnets with opposing poles, or magnetic moments , that produce a magnetic field, interact with other magnetic moments and change their orientation in response to magnetic fields. When these atoms are similarly oriented throughout the material, their fields combine together and define a uniform magnetic domain. So, by exposing a ferromagnetic material to a powerful magnetic field, the orientation of these crystals can be aligned so that all the magnetic axes point in the same direction, thus creating a magnet. Importantly, with these three materials, when the magnetic field is removed the polarization remains, defining a permanent magnet (PM). When certain rare earth elements, in particular neodymium and samarium–cobalt, are combined with these elements, they can form magnets that are several orders of magnitude more powerful than the simple ferrite magnets on your refrigerator. In addition, as we will see later, some metals, such as copper and aluminum, do not become PMs themselves, but can exhibit magnetic qualities when an electric current is passed through them. This allows us to define controllable magnets that can be switched on and off, called electromagnets

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  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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  Electrical Machines

  Fundamentals of Electromechanical Energy Conversion

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

    (Publisher)

  1 INTRODUCTION TO ELECTROMECHANICAL ENERGY CONVERSION

  1.1What is electromechanical energy conversion?

  Electromechanical energy conversion is a conversion of mechanical energy into electrical energy (generator) or vice versa (motor) with the aid of rotary motion (rotary machines) or translatory (linear) motion (linear machines and actuators).

  Electrical machines, solenoid actuators and electromagnets are generally called electromechanical energy conversion devices (Fig. 1.1 ).

  Fig. 1.1.Electromechanical energy conversion.

  Transformers and solid-state converters do not belong to the group of electromechanical energy conversion devices because they only convert one kind of electrical energy into another kind of electrical energy with different parameters (change in voltage, current, frequency, number of phases, conversion of DC into AC current, etc.) without any motion.

  1.1.1Block diagrams of electromechanical energy conversion devices

  Fig. 1.2a shows a block diagram of a motor, while Fig. 1.2a shows a block diagram of a generator. An example of application of an Electric Motor is

  shown in Fig. 1.3 . An example of application of an electric generator is shown in Fig. 1.4 .

  Fig. 1.2.Block diagrams of electromechanical energy conversion devices: (a) motor; (b) generator.

  Fig. 1.3.Power tool: an example of conversion of electrical energy into mechanical energy.

  Fig. 1.4.Wind turbine generator: an example of conversion of mechanical energy into electrical energy.

  1.1.2Left-hand and right-hand rule

  The left-hand rule (Fig. 1.5a ) indicates the direction of the phasor of the electrodynamic force (EDF), i.e.,

  d F = I d l × B

      ( 1.1 )

  Fig. 1.5.Left-hand and right-hand rules: (a) left-hand rule shows the direction of electrodynamic force (EDF); (b) right-hand rule shows the direction of electromotive force (EMF).

  or, in scalar form

  F = B I l

      ( 1.2 )

  The right-hand rule (Fig. 1.5b

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  Electrical Engineering for Non-Electrical Engineers

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

    (Publisher)

  Chapter 7 Electric Motors and Generators

  Introduction

  Generators and motors are, primarily, rotating machines. The rotating machines are called motors when they consume electrical energy, and are referred to as generators when they produce electrical energy. In practical applications, while DC machines are almost always single phase, 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. Roles that slip and frequency play in the determination of the motor shaft speed are illustrated through example problems. Significance of certain common classifications of motors is explained. Interpretation of a common motor nameplate is discussed.

  DC GENERATOR

  A direct current 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 consists of DC current 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 a “commutator.” A common commutator consists of two rings as shown in Figure 7.1 . As depicted in Figure 7.1, the current, I

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  Electrical Motor Diagnostics 2nd Edition

  • Howard W. Penrose(Author)
  • 2014(Publication Date)
  • Success By Design

    (Publisher)

  An industrial synchronous motor consists of a three-phase stator winding, a squirrel-cage rotor windings, and a series of rotor fields (field-poles) designed to carry DC power. The stator fields generate a synchronous magnetic field which interacts with the rotor windings in the same way as an induction motor. As the rotor begins to turn, a direct current is introduced into the rotor fields either through a generator attached to the rotor shaft or through a static control. The DC magnetic fields lock with the stator fields causing the rotor to turn at synchronous speed. The rotor windings then act to counter any sudden load changes so that the motor continues to operate at synchronous speed. Industrial synchronous motors are often found in reciprocating compressors. They can also be used to correct power factor by over-exciting the rotor fields.

  Another type of synchronous motor involves the use of permanent magnets. The stator fields interact with the rotor magnets. These motors tend to be smaller in size and used in machining applications as stepper or servo motors.

  Direct Current Electric Motors

  Direct Current Electric Motors operate under a basic principle of electricity: interaction between two magnetic fields positioned at an angle from each other will attract/repel resulting in movement. In the case of a DC Electric Motor, power is provided to a stator field and an armature creating magnetic fields that are, electrically, about 90 degrees from each other. The resulting attraction/repulsion of the armature from the field generates a torque and the armature turns.

  The basic components of a DC Electric Motor include: Frame – Makes up the outer structure of the machine. It is used to mount most of the other components of the motor. Fields – Are coils mounted on field pole pieces that generate a stationary magnetic field. Interpoles – Are coils that are placed between the field coils that generate a field that is used to prevent excessive sparking of the brushes. Endshields – Also called bearing housings, are used to house the brushes, brush rigging, and to house the shaft bearings, holding the armature centered in the frame. Brush rigging – Holds and positions the brushes above the armature commutator. Usually, a tension device is used to maintain a constant pressure on the brushes. Brushes – Are used to provide DC to the armature. The brushes ride on the commutator. Commutator – Consists of many copper bars that are separated by mica. Each bar is connected to coils in the armature.

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