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1441 results in Energy Technology

Page 39 of 73

Chemical Looping Partial Oxidation
  • Gasification, Reforming, and Chemical Syntheses
  • Liang-Shih Fan
  • Published online:
    07 November 2017
    Print publication:
    12 October 2017
  • This is the first comprehensive guide to the principles and techniques of chemical looping partial oxidation. With authoritative explanations from a pioneer of the chemical looping process, you will:Gain a holistic overview of metal oxide reaction engineering, with coverage of ionic diffusion, nanostructure formation, morphological evolution, phase equilibrium, and recyclability properties of metal oxides during redox reactionsLearn about the gasification of solid fuels, the reforming of natural gas, and the catalytic conversion of methane to olefinsUnderstand the importance of reactor design and process integration in enabling metal oxide oxygen carriers to produce desired productsDiscover other applications of catalytic metal oxides, including the production of maleic anhydride and solar energy conversionsAspen Plus® simulation software and results accompany the book online. This is an invaluable reference for researchers and industry professionals in the fields of chemical, energy and environmental engineering, and students studying process design and optimization.

  • 3 - Three-Phase Transformers

  • S. K. Sahdev
  • Book:
    Electrical Machines
    Published online:
    03 August 2019
    Print publication:
    04 October 2017, pp 224-300

  • Summary

    Introduction

    Three phase system is invariably adopted for generation, transmission and distribution of electrical power due to economical reasons. Usually, power is generated at the generating stations at 11 kV (or 33 kV), whereas, it is transmitted at 750 kV, 400 kV, 220 kV, 132 kV or 66 kV due to economical reasons. At the receiving stations, the voltage level is decreased and power is transmitted through shorter distances. While delivering power to the consumers, the voltage level is decreased to as low as 400V (line value) for safety reasons.

    Thus to increase the voltage level at the generating stations step-up transformers and to decrease the voltage level at the receiving stations, step down transformers are employed.

    Merits of Three-phase Transformer over Bank of Three Singlephase Transformers

    The voltage level in three-phase system at the generating stations and at the receiving stations can be changed either by employing a bank of three single-phase transformers (inter connecting them in star or delta) or by employing one three phase transformer. Generally, one three phase transformer is preferred over a bank of three single phase transformers because of the following reasons.

  • (i) It requires smaller quantity of iron and copper. Hence, its cost is nearly 15% lesser than a bank of three single phase transformers of equal rating.

  • (ii) It has smaller size and can be accommodated in smaller tank and hence needs smaller quantity of oil for cooling.

  • (iii) Because of smaller size, it occupies less space; moreover it has less weight.

  • (iv) It needs less number of bushings.

  • (v) It operates at slightly better efficiency and regulation.

    • These transformers suffer from the following disadvantage.

  • (i) It is more difficult and costly to repair three-phase transformers.

  • (ii) It is difficult to transport single large unit of three-phase transformer than to transport three single phase transformers individually.

    • The advantages of three-phase transformer (such as lower cost, lower weight, lower space requirement etc.) over weighs its disadvantages and hence are invariably employed in the power system to step-up or step-down the voltage level.

  • 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 calledspecial 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 calledfeedback control system.

    Servomechanism

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

    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.

  • 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 calledmagnetic 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.

Electrical Machines
  • S. K. Sahdev
  • Published online:
    03 August 2019
    Print publication:
    04 October 2017
  • An extensive and easy-to-read guide covering the fundamental concepts of electrical machines, highlighting transformers, motors, generators and magnetic circuits. It provides in-depth discussion on construction, working principles and applications of various electrical machines. The design of transformers, functioning of generators and performance of induction motors are explained through descriptive illustrations, step-by-step solved examples and mathematical derivations. A separate chapter on special purpose machines offers important topics such as servomotors, brushless motors and stepper motors, which is useful from industrial perspective to build a customized machine. Supported by 400 solved examples, 600 figures, and more than 1000 self-assessment exercises, this is an ideal text for one or two-semester undergraduate courses on electrical machines under electrical and electronics engineering.

Page 39 of 73