Showing papers in "International Journal of Electrical Engineering Education in 1964"

Measurement of Synchronous Machine Rotor Angle

Abstract: Introduction The need to measure synchronous machine rotor angle* arises both in the electrical machines laboratory and in the generating stations. Various methods of measurement have been used, some of which are described in the literature. (1-3) The most popular method appears to be one based on a light source, either controlled, as in the stroboscope or with a detector, as in the pulse generating types. These are suitable for obtaining records of transient rotor angle Variations, the record being a chart or photographic one depending on the angle-measuring Principle employed.

The Capacitance and Inductance of Overhead Transmission Lines

Abstract: The inductance and capacitance parameters ofan overhead line are derived and represented as an equivalent circuit, this representation being particularly useful when considering a line connected or energized in an unusual manner. The analysis is carried out in detail for three parallel conductors assumed parallel to a perfectly conducting earth plane, and can readily be extended to the case ofn conductors. Maxwell's concept ofpotential, capacitance and inductance coefficients is used to derive expressions for the self and mutual capacitance and inductance of the system. (1,2) One advantage of this approach is that it emphasizes that the line parameters are essentially geometrical properties of the conductor system, and are independent of the method ofexcitation. Another important advantage is that the equivalent circuit provides the student with a familiar method for solving line problems with unbalanced excitation or interconnection, e.g., single-phase operation with two conductors connected in parallel. The approach is straightforward, and, from a teaching point of view, more satisfactory than those involving additional restrictions. In particular, it is considered that derivations involving symmetrical three-phase constraints between voltages, currents or charges are to be deprecated. Expressions based on such assumptions will only hold, in general, under the assumed conditions ofexcitation, and when they result in terms such as 'complex reactance' of lines, they are both misleading and confusing.

The Colleges of Advanced Technology in Britain

Abstract: In Bradford, on 18January 1956, the then Prime Minister, Sir Anthony Eden, now Lord Avon, said: 'The prizes will not go to the countries with the largest population. Those with the best systems of education will win. Science and technical skill give a dozen men the power to do as much as thousands did fifty years ago. Our scientists are doing brilliant work. But if weare to make full use of what we are learning, we shall need more scientists, engineers and technicians. I am determined that this shortage shall be made good.'

A Note on the Mode of Induction of an e.m.f. — An Experimental Investigation

Abstract: The e.m.f equation for a d.c. generator can be derived by considering the e.m.f, per conductor = BLU volts and in this explanation, it is said that as each conductor cuts the flux at the given velocity, an e.m.f. is induced in it. The e.m.f equation for the generator may be also derived by considering the e.m.f as being due to a change of flux-linkages, and some teachers prefer to use that approach as being fundamentally more sound.

A Suggested Course on h.v.d.c. Transmission at Undergraduate and Postgraduate Level (Part II)

Abstract: I, Introduction 'the first article<1l dealt with items of general interest and of an introductory nature, considered suitable for final year undergraduate students with Power Systems as one of their main subjects. 'the other aspects of teaching, apart from special and part-time courses, etc., is the postgraduate Master's Degree or equivalent courses in which at least part of the time is spent on lectures. Where Power Systems is the subject of such a course, it is most desirable to have h.v.d.c. as 0 ne of the subject matters.

An Experiment on Probability — Estimation of Errors in Measurement from Sample Data

Abstract: Introduction In 1959 the author described an experiment on probability for undergraduate students in electrical engineering.O! This experiment is now widely used in Universities and in other training institutions in several countries and it appears to be successful in providing a feel of probability for students who do not have any grounding in the subject, and who are largely unaware of the significance and of the methods ofprobability.

The Application of Boolean Algebra to Switching Circuits

Abstract: The introduction of Boolean algebra into electrical engineering education serves a double purpose. Besides its usefulness as a design tool in switching circuits it can provide an introduction to a broad and exciting field of knowledge, including symbolic logic, probability and the algebra of sets. It is the author's experience that students readily grasp the fundamentals of the subject and are keen to pursue it. The recent availability of solid state logical elements makes it feasible to include work on Boolean algebra applications in the control or general electrical engineering laboratory. It is of interest that while the manufacturers* of the logical elements used in this Department claim that a knowledge of Boolean algebra is not necessary to design circuits using their elements, nevertheless the practical applications of Boolean algebra are readily demonstrated by their use. Boolean Algebra References (I) and (2) give a full treatment of Boolean algebra. For those not familiar with the subject, the following summary may be helpful. In switching circuits only two states are considered 'on' and 'off'. These are represented by I and 0 respectively. Consider an AND box as shown in Fig. I (a). When the inputs are 'on' (i.e. I) the output is 'on'

Book Review: Electric Circuit Analogies for Elastic StructuresElectric Circuit Analogies for Elastic Structures: MacNealR. H.John Wiley, New York.1962. 262 pp. $11.50.

Abstract: It is a most excellently written text. The conjunction of a six-chapter treatment of basic aspects of the operational calculus (in the Laplace-transform form) and of signal-flow diagram theory results in a unique and well-integrated introductory treatment of transient electric (and mechanical) circuit response analysis. Further, the many illustrative examples in the text, and the some 50 exercises at the end of the chapters (together with the answers to the exercises) renders the text well-suited to self-study. The emphasis on transforms, considered not as the results of operations on time, but as the transmittances offunction-generators excited by unit impulses; and the constraint that energy be distributed in the system in the same manner just after excitation as just before excitation enables as noted in the Introduction a useful simplification of analytic treatment and structural connection with the physical system.

Current Waveshapes in Rectifier Circuits

Abstract: The usual treatment of rectifier circuit currents based on Fourier's theorem is in general quite satisfactory, however, it is basically an approximate one and is used for currents in circuits which remain unchanged for a certain time. The following method of treating rectifier\"circuits ismathematically rigid for ideal rectifiers and constant circuit elements. In addition it allows us to study the behaviour of rectifier circuits immediately after any alteration of the circuit setup.

A Simple Treatment of Heyland's Equivalent Circuits of a Poly-Phase Induction Motor:

Abstract: v R1 R2' = .X1 = ..\\'2' = voltage applied per phase stator resistance per phase equivalent rotor resistance per phase referred to stator stator reactance per phase equivalent rotor reactance per phase referred t.o stator per-unit slip magnetising shunt reactance per phase shunt resistance per phase, representing no-load iron and rotational losses stator current per phase equivalent rotor current per phase referred to stator no-load stator current consisting of the magnetizing part Iq, and the part Ii supplying the no-load losses. llig, l(b) isobtainedfromFig. l(a) by

Linearized Phase Plots

Abstract: In this communication there can be but slight claim to originality but it is considered that the subject under notice is commonly dismissed with a brevity embarrassing to students, and it is hoped that the present contribution may offer some improvement in this respect. It is, of course, possible to reach the above results by an analytical approach* but it may be thought that the elementary treatment here adopted is preferable for introductory purposes.

Use of the Nyquist Diagram for Solving Simple Problems in Linear Servomechanisms

Abstract: The gain ofa servomechanism is usually determined by conditions other than stability, so that the central problem in the design of such systems is to determine the parameters of the devices proposed to achieve the desired degree of stability where the gain has been decided at the outset. Even the simplest problems are, in current literature, treated on the basis of trial and error. It is shown in this paper, that, where the criterion of degree ofstability is phase margin or gain margin, direct solutions can be obtained in simple cases. Where the criterion is maximum magnification, a positive procedure is suggested, based on the use of geometrical constructions, to find the maximum value ofa single parameter T, giving the desired solution, and the resonant frequency. A common method of approach has been used, for the cases of velocity feedback with or without a filter, transient velocity feedback, and phase advance. Only those cases are considered in which the modifying device is characterized by a single parameter.

A Practical Aid to the Teaching of Digital Computing Techniques

Abstract: Introduction The student coming for the first time to study the techniques involved in digital computer design enters a field entirely divorced from other more conventional branches ofelectronics. The unfamiliar usage of the familiar words 'and', 'or', and 'not', the extensive use of the binary number system, and the strange connectives of Boolean algebra, all tend to confuse ifnot bewilder the uninitiated. Lack offacilities and the necessary equipment often leads to a purely theoretical study of the subject. The implementation oflogical circuits into actual 'hardware' can seldom be accomplished and realizations are limited to 'paper studies'. Thus appreciation ofthe principles of operation of such circuits can only be achieved by 'working through' for a givenset of input conditions. This can be a very tedious process and only those people with some degree of enthusiasm for the subject can have the necessary patience to carry out this procedure.

Equivalent Circuits of Interconnected a.c.-d.c.-a.c. Power Transmission Systems

Abstract: List of Symbols R, = rectifier In = inverter a = grid control angle of rectifier :\" = grid control angle of inverter PI = number of rectifier phases P2 = number of inverter phases Xl = commutation reactance of rectifier X 2 = commutation reactance of inverter 1.:1, K2 = constants dependent on the valve connections of the rectifier and inverter respectively K3, K4 = constants which are functions of the firing and commutating angles of the rectifier and inverter respectively VI = a.c, terminal voltage of rectifier V2 = a.c. terminal voltage of inverter <1>1 = phase angle of VI <1>2 = phase angle of V2 c/>o = 4>14>2 h = a.c. terminal current of rectifier lz = a.c, terminal current of inverter Vd , = sending end d.c, voltage Vd , = receiving end d.c. voltage 1<1 = current in d.c.Iine R, = resistance ofd.c, line 4>s = displacement angle of h 4>, =, displacement angle of 12

The SCR Converter as a Laboratory Experiment

Abstract: I. Field of Semiconductor Converters In Relation to Mercury Arc Converters Every electrical engineer is aware ofthe major revolution that has taken place in the field of a.c./d.c. conversion. No one can deny that through the development of semiconductor devices particularly germanium and silicon diodes and now SCRs, mercury arc converters have largely been, and are still being replaced by semiconductor converting equipment. The pace of development in semiconductor devices has been very swift and although there will always remain a few important applications, such as 'high voltage direct current transmission' in which mercury arc converters will be used for many years to come, the great majority of converter applications will involve the use ofsemiconductor devices.

A Computer Project at Marlborough, and its Implications in Science Teaching

Abstract: Boys enter Marlborough having passed the Common Entrance Examination to Public Schools at 13 years of age. Science is not yet a compulsory subject in this examination, and many boys at present have done little or none. Thus, all boys embark as beginners on a two-year course in the 'Lower School'. Most of these take Physics and Chemistry at the Ordinary level of the General Certificate of Education ('O' level) at about 15 years. Most boys do a little Biology. After '0' level, all boys choose a more specialized set of subjects to pursue to the Advanced level of the General Certificate of Education ('A' level) or beyond, together with a number of compulsory non-specialist subjects. The latter include for example, History and English for scientists, Science or Mathematics for classicists, as well as English, Scripture and a small amount of Art or Music for all. On the science side, the Specialist 'options' include three main trios of subjects:

A Conductive-sheet Analogue for ‘Open Type’ Fields:

Abstract: A useful and adequately accurate method of simulating these infinite fields is based on an adaptation of the double-layer electrolytic tank, Boothroyd.(3) Two identical circular sheets of Teledeltos paper are superimposed on either side of an insulating circular-sheet of cartridge Paper and are made electrically contiguous by.either of the two methods described below. The upper sheet, on the matt-grey surface of which the sources and sinks simulating the model are disposed, represents the region of interest. The lower sheet contains a central electrode whkh represents any nett source or sink at infinity. In this form the upper sheet behaves as ifit was Part of an infinite domain and the lower sheet as the transform of the external infinite field.

The Non-Recurrent Ladder Network

Abstract: Introduction The determination of the voltage or current at any point in a non-recurrent ladder network in terms of the voltage applied at the front end and the impedances (or admittances) of the series and shunt branches becomes very tedious for networks consisting of more than about three sections. A simple iterative method can be found, however, if the following procedures are adopted: (I) All series branches are denoted as impedances and all shunt branches as admittances. (2) The sections and branches arc numbered from the termination rather than from the source. (3) Instead ofderiving the sequence V2n( Vo, V2n+ 2(Vo, V2n+4( Vo, etc., the sequence V2n(Vo, hn+l(VO, V2n+2(VO, 12n, 3(V(h etc., is obtained (refer to Fig. I for the meaning of these symbols). Procedures (1) and (2) recognize the analogy between a ladder network and a transmission line, the analysis of which rests upon a similar approach. Procedure (3) enables a simple recurrence relation to be formulated giving every term of the required sequence. Recurrence relations can of course be written down for onlyvoltages or onlycurrents, but these are much less easy to apply.

The Electromagnetic Principles of Commutation in d.c. Machines

Abstract: Introduction When explaining the electromagnetic principles of commutation in d.c, machines it is important to distinguish the basic principles from the practical complexities of the application of those principles to the design of machines. Some textbooks(1-4) which treat commutation as a practical design problem, consider in some detail the derivation ofapproximate formulae for the calculation of the average commutation voltages due to leakage fluxes and explain the purpose of interpoles (compoles) for compensating such voltages; but they do not explain how it comes about that the commutation voltages due to the totalfluxes are compensated. Some other textbooks,(5-B)however, do treat the basic principles more or less comprehensively.

Measurements on Gas Breakdown

Abstract: After a brief survey of the two main theories of spark breakdown in gases, an account is given of certain empirical laws relating to breakdown voltages, gap lengths and pressure of the gas. Other factors which affect measured breakdown voltages are discussed namely; humidity, Proximity of neighbouring objects, irradiation, electrode geometry and polarity of unidirectional voltages. The discussion has been confined to phenomena in air but qualitatively the conclusions reached would apply to other gases.

A Slide Rule Aid for Nyquist Plots

Abstract: (b) Slide rules The main advantage of the slide rule is its speed and convenience. It is, however, comparatively expensive. The first slide rule designed specifically for frequency response computations was produced by lzawa<2l. This slide rule suffers from lack of speed and the use of strange scales. For example, it is necessary to use a different slide position for each value of frequency for the same time constant when investigating a simple lag or lead term. This is an unnecessarily long operation.

Denormalization Applied to Filter Networks

Abstract: When a suitable network function, which has a magnitude or delay characteristic acceptable for the problem in hand has been found, it is frequently expressed in a normalized form. When the function is chosen to have a desirable magnitude characteristic it will usually be arranged to have a frequency response which is 3 dB below its maximum value at an angular frequency w equal to unity. When an approximation to the ideal delay function is used it will usually be normalized to have a delay of one second. Some functions which are normalized in this manner have been described by the author (3) and the purpose of the present account is to provide a more detailed explanation of the manner in which they are denormalized.

An Experiment on the Compensation for Losses in Filters

Abstract: When filters are designed to give a required transfer function N(P), the calculations are greatly simplified ifit is assumed that the coils and capacitors are ideal loss-free components. In practice the coils will always have some resistance and there will always be some loss, usually very small, associated with the capacitors. If these losses are ignored in the design the frequency response of the completed filter will not correspond exactly to the required transfer function. The deviation from the ideal will be increased if the Qfactors for the coils are decreased.

Sensing Devices: Current transformers and linear couplers

Abstract: Steady-state operation of iron-cored transformers Equivalent circuit A current transformer has the same equivalent circuit as any other iron cored coil, but some components are modified. There is, for instance, no point in representing primary winding resistance and leakage reactance, since these have no effect on transformer characteristics in a current driven circuit. Furthermore, the secondary leakage reactance of toroidally wound coils is so low that it may be neglected.

The Silicon Controlled Rectifier

Abstract: Introduction Allcontrolled rectifiers, while differing in detail, exhibit the same general operating characteristics. The silicon controlled rectifier (SCR) is a new addition to the family of controlled rectifiers that have been used extensively in the past for the control of power. The SCRisa recently developed solid-state device which duplicates the functions performed by such disparate devices as thyratrons, amplidynes, and magnetic amplifiers. It offers many advantages over these devices in terms of size, weight, reliability, and power gain.