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38612 results in Cambridge Textbooks

Page 1279 of 1931

  • 12 - Special Purpose Machines

  • S. K. Sahdev
  • Book:
    Electrical Machines
    Published online:
    03 August 2019
    Print publication:
    04 October 2017, pp 893-932

  • Summary

    Introduction

    So for, we have discussed about synchronous machines, induction machines, fractional kW machines etc. These machines are the basic machines which are employed at various places as per requirement. However, in industries, at commercial places and in houses there are variety of jobs for which these general purpose basic machines are not suitable. But these machines with suitable amendments in their design can be employed to perform these jobs. Such specially designed machines are called special purpose machines.

    The machines which are designed specially to perform a particular job are called special purpose machines.

    Feedback Control System

    A control system which tends to maintain a prescribed relationship between a controlled variable and a reference input by comparing relationship between a controlled variable and a reference and difference as a means of control is call a feedback control system.

    Electrical feedback control systems rely upon mainly electrical energy for operation. The essential of this type of control are (i) an error detecting device, (ii) an amplifier and (iii) an error-correcting device as shown in Fig. 12.1. Each one of them serves a functional purpose in matching the controlled variable to the reference input.

    The error-detecting device determines when the controlled variable is different from the reference input. It then sends out on error signal to the amplifier, which is turn supplies power the error correcting device changes the controlled variable so that it matches the reference input. The closed loop at feedback control system is shown in Fig. 12.1.

    Thus, a system in which output is compared with the input and error is used to control the operating system is called feedback control system.

    Servomechanism

    The mechanism in which the control variable is adjusted by the error served by comparing output and input is called servomechanism.

    Any quantity e.g., voltage, speed, temperature, position, direction or torque be controlled by providing appropriate feedback. Any quantity can be used as a reference input. Moreover, the reference input need not have the same units as the controlled variable provided that the proper error detecting device is employed.

  • 2 - MATLAB Simulation of Power Semiconductor Devices

  • L. Ashok Kumar, A. Kalaiarasi, Y. Uma Maheswari
  • Book:
    Power Electronics with MATLAB
    Published online:
    19 August 2025
    Print publication:
    04 October 2017, pp 60-145

  • Summary

    A semiconductor is a robust device whose electrical conductivity is controlled over a wide range for superior or dynamic control. Semiconductor devices are electronic components that, like insulators, exploit the electronic properties of semiconductor resources, principally silicon, germanium, and gallium arsenide, as well as natural semiconductors. Semiconductors are financially and commercially attractive; these solid state devices have replaced vacuum tubes in most applications.

    Semiconductors are remarkable in their innovation and financial viability and financially. Semiconductors are the crucial materials for many electrical devices, from machines to cell phones to advanced sound players. When the circuit is not connected, pure semiconductors and insulators have generally comparable electrical properties.

  • 4 - Broad transcription of Australian English

  • Felicity Cox, Macquarie University, Sydney, Janet Fletcher, University of Melbourne
  • Book:
    Australian English Pronunciation and Transcription
    Published online:
    21 June 2018
    Print publication:
    04 October 2017, pp 103-140

  • Summary

    Introduction

    In this chapter you will be introduced to the technique for conducting a broad transcription of AusE. This type of transcription provides a general representation of the phonemes in spoken language. By convention, the broad transcription also includes the characteristic features of connected speech such as elision, assimilation, use of intrusive/linking /ɹ/, and reduced vowels, among other features to be described below.

    Broad transcription does not attempt to record allophonic variation that occurs in speech, nor does it attempt to describe the complexity of a speaker's idiolect, which instead requires detailed narrow transcription (to be discussed in Chapter 5). In contrast, broad transcription represents the broad classes of speech sounds – in other words, the phonemes used to differentiate words. Some contextual variation is transcribed but only if the context promotes the substitution of one phoneme for another. For instance, a word like uncool may be perceived to contain an /n/ or an /ŋ/ depending on how much the tongue dorsum gesture for /k/ in cool overlaps with the tongue tip gesture for the preceding nasal consonant in un. If the modification to a sound does not involve a substitution of this kind, the shades of variation are ignored in broad transcription as only symbols for phonemes can be used. For instance, in the word triumph the nasal /m/ is typically produced as a labiodental [ɱ] in anticipation of the following labiodental fricative /f/. It is not necessary to capture this detail in the broad transcription but it is required in the narrow transcription (see Section 5.2.6).

    It is very important to be aware that coarticulation (the influence of speech sounds on each other) is fundamental to the speech-production process. The extent and degree of coarticulation is determined by many factors, including rate of articulation, prosodic context, requirements of the specific communicative context, the tolerance of the dialect to particular processes, and individual speaker preference. Stylistic factors, such as the speaker's judgement about the formality of the interaction or perception of the listener's ability to comprehend, also fundamentally affect the nature of the connected speech processes. In natural unguarded speech, the speaker embraces connected speech processes to produce an efficient and effective spoken output. Such speech-production strategies are essential for natural speech and should never be considered as laziness.

  • 1 - Electro Magnetic Circuits

  • S. K. Sahdev
  • Book:
    Electrical Machines
    Published online:
    03 August 2019
    Print publication:
    04 October 2017, pp 1-78

  • Summary

    Introduction

    It is always advantageous to utilise electrical energy since it is cheaper, can be easily transmitted, easy to control and more efficient. The electrical energy is generally generated from natural resources such as water, coal, diesel, wind, atomic energy, etc. From these sources, first mechanical energy is produced by one way or the other and then that mechanical energy is converted into electrical energy by suitable machines. For the utilisation of electrical energy, it is again converted into other forms of energy such as mechanical, heat, light etc. It is a well-known fact that the electric drives have been universally adopted by the industry due to their inherent advantages. The energy conversion devices are always required at both ends of a typical electrical system. The devices or machines which convert mechanical energy into electrical energy and vice-versa are called electro–mechanical energy conversion devices.

    The operation of all the electrical machines such as DC machines, transformers, synchronous machines, induction motors, etc., rely upon their magnetic circuits. The closed path followed by the magnetic lines of force is called a magnetic circuit. The operation of all the electrical devices (e.g., transformers, generators, motors, etc.) depends upon the magnetism produced by their magnetic circuits. Therefore, to obtain the required characteristics of these devices, their magnetic circuits have to be designed carefully.

    In this chapter, we shall focus our attention on the basic fundamentals of magnetic circuits and their applications as electromechanical energy conversion devices.

    Magnetic Field and its Significance

    The region around a magnet where its poles exhibit a force of attraction or repulsion is called magnetic field.

    The existence of the magnetic field at a point around the magnet can also be determined by placing a magnetic needle at that point as shown in Fig. 1.1. Although magnetic lines of force have no real existence and are purely imaginary, yet their concept is very useful to understand various magnetic effects. It is assumed (because of their effects) that the magnetic lines of force possess the following important properties:

  • (i) The direction of magnetic lines of force is from N-pole to the S-pole outside the magnet. But inside the magnet their direction is from S-pole to N-pole.

  • (ii) They form a closed loop.

  • (iii) Their tendency is to follow the least reluctance path.

  • (iv) They act like stretched cords, always trying to shorten themselves.

  • 6 - Controllers Using MATLAB (AC–AC Converters)

  • L. Ashok Kumar, A. Kalaiarasi, Y. Uma Maheswari
  • Book:
    Power Electronics with MATLAB
    Published online:
    19 August 2025
    Print publication:
    04 October 2017, pp 290-338

  • Summary

    The voltage controller, also called an AC voltage controller or AC regulator, is an electronic module with either thyristors, triode alternating currents (TRIACs), silicon controlled rectifiers (SCRs), or insulated gate bipolar transistors (IGBTs). The module changes a constant voltage, to get a variable output voltage conveyed to the load. AC controllers are basically employed to change the root mean square (rms) value of the changing voltage, which is connected to the load terminal of the circuit, by making thyristors lead in between the AC supply source and the load terminal. Fluctuating voltage is used for diminishing road lights, fluctuations, warming temperatures in homes or industry, regulation and control of fans and winding machines, and numerous other applications, in a similar manner to an autotransformer. Voltage controller modules are power devices. Since they need less maintenance and are extremely productive, voltage controllers have, to a great extent, supplanted such modules as enhancers and saturable reactors.

  • 7 - Simulation and Digit al Control Using MATLAB

  • L. Ashok Kumar, A. Kalaiarasi, Y. Uma Maheswari
  • Book:
    Power Electronics with MATLAB
    Published online:
    19 August 2025
    Print publication:
    04 October 2017, pp 339-371

  • Summary

    The traditional methods of analysis may not be useful in the practical analysis of sensors. Traditional calculations may also not be satisfactory to simulate real life situation. Fuzzylogic-based systems may be used to overcome traditional calculation issues. Fuzzy logic liberates us from the rigid thinking of ideal arrangements of components that are utilized as part of typical systems. Fuzzy logic models guarantee a limited subjective analysis of a quantitative element system while being pertinent to any system that can be portrayed in technical terms. Fuzzy models give a compact and dynamic representation of systems that do not have a complete quantitative model or of indeterminate systems. Static thinking is not encouraged in fuzzy semantic representation of a quantitative system.

  • 8 - Power Electronics Applications

  • L. Ashok Kumar, A. Kalaiarasi, Y. Uma Maheswari
  • Book:
    Power Electronics with MATLAB
    Published online:
    19 August 2025
    Print publication:
    04 October 2017, pp 372-387

  • Summary

    Power devices transform and control electrical energy at high productivity using exchanging mode power semiconductor devices. Some regular uses of power devices include DC- and AC-directed power supplies, uninterruptible power supply (UPS) systems, electrochemical procedures, heating and lighting control, power line static VAR, and resonant compensation, high-voltage, direct current (HVDC) systems, photo voltaic and energy unit converter systems, solid state circuit breakers, high-frequency heating, variable speed engine drives and so forth. Engine drive zones might include applications in PCs and peripherals, solid state starters, home apparatuses, paper and material factories, wind generation systems, aerating, cooling and heating pumps, rolling and concrete plants, machine devices and mechanical autonomy, pumps and compressors, ship impetus and so forth. It is no big surprise that the use of power devices is presently spreading quickly from the developed countries to the developing nations of the world.

Page 1279 of 1931