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The influence of polarity, polarity reversal, repeated stressing, waveshape and conductor size on the impulse puncture voltage for three sizes of single-conductor mass-impregnated 33-kV cable has been investigated. Experimental results are discussed and conclusions drawn from which a test for incorporation in a cable specification and the revision of B.S. 923: 1940 for cables has been suggested.

Impregnated-paper capacitors can fail in service from a variety of causes depending upon manufacturing and operating conditions. Under normal working conditions, the usual slow deterioration which ultimately leads to failure may be of an electrochemical nature. Factors influencing this type of deterioration are dealt with in some detail. Adverse factors are impurities, such as rosin and bitumen, which dissociate in the dielectric and accelerate the electrochemical processes, or the presence in the dielectric of moisture arising from poor impregnation or imperfect sealing. The effects of contamination are greater when polar impregnants are used, e.g. chlorinated hydrocarbons. Electrochemical deterioration of chlorinated dielectrics can be greatly reduced by the addition of "stabilizers." A theory is advanced to explain the action of these stabilizers, and experimental evidence in support of the theory is presented.

Conductor screens are now in general use on high-voltage power cables. They take several forms, and are especially effective in bringing about an improvement in a.c. electric strength. Good-quality cable paper loaded with a carbon-black material is one form used for conductor-screening purposes, but it can have adverse effects when applied to oil-filled cables. These include an increase in the ionisation factor and a decrease in the impulse electric strength. The paper records the result of comprehensive investigation into many aspects of carbon-black-paper screening, and claims conclusively to establish the behaviour of carbon loading when used in paper for screening purposes.

The main properties required of paper for use in high-voltage dielectrics are concerned with its electric strength and dielectric losses. The effect of such physical properties as thickness, apparent density and air impermeability upon the impulse strength of impregnated paper are studied by both flat-sheet and model test methods, not only for types used in cables and transformers, but also for those used in capacitors. The incorporation of synthetic and other types of fibre into softwood pulp is discussed, and the electric strength is shown to be dependent upon the associated physical properties. Factors affecting dielectric losses, on the other hand, are the chemical constitution and purity of the pulp and water from which the paper is made, as well as its apparent density. The effect on the electrical properties of changes in the pulp and washing treatment is demonstrated, and the importance is shown in the case of capacitor tissues of the presence of conducting particles and other impurities. Methods of assessment of quality are described in detail.

An investigation has been carried out into the effect of ionic and other additives on the power factor of oil-impregnated paper, with the object of relating the power factor of the impregnated paper to the power factor of the impregnant. For power-factor measurements, an improved test cell was used which was designed to operate at high stresses over a wide temperature range. it was observed that there was a variable relationship between the power factor and the volume resistivity of oils depending upon the type of additive. There was no correlation between the power factor of impregnated paper and the power factor of the impregnant, but a definite relationship was found between the power factor of impregnated paper and the volume resistivity of the impregnant, this relationship being independent of the type of additive.

A description is given of a technique which has been developed for the investigation of the electrical properties of oil-impregnated paper, with special reference to the type of lapped-paper dielectric used in power cables.The equipment described is versatile, permitting a wide range of electrical tests to be made on one type of specimen and enabling the effect of variations in construction or component dielectric materials to be assessed rapidly and conveniently. The system is well suited for routine quality control as well as for research or development.

The paper gives the results of an experimental laboratory investigation of model bushings, with the object of predicting the behaviour of full-scale e.h.v. oil-impregnated paper bushings operating at a radial a.c. stress of 3kV r.m.s./mm. One of the aims was to determine whether discharges of up to 5pC in full-scale bushings might damage the insulation during prolonged periods in service, and so reduce the prospective life. Frequency-accelerated life tests were made on over 90 model bushings, some of which were constructed according to accepted manufacturing methods, whilst others contained defects of various kinds. It was found that, while the initial-discharge magnitude is a good indication of air trapped in the windings in a region of high electric stress, it is not a good guide to the prospective life of the bushings. The most critical factor is the ability of the oil to dissolve any trapped gas. If the trapped gas dissolves, bushings working at a stress of 3kV r.m.s./mm will have a low discharge level and a long life, provided they have no constructional defects. If not, the discharge magnitude may fall at first, but will then rise steadily until breakdown occurs after 12–20 years. A further aim of the investigation was to determine the extent to which either permanent damage or temporary impairment of the dielectric properties could be caused by overvoltages in the range 7–16kV r.m.s./mm, applied for periods of 1–50min. The effects of impulse stresses up to 19kV peak/mm were also studied. It was found that a sensitivity of about 0.1pC would be required to detect the discharge resulting from the gas generated during a normal overvoltage test on a well made 400kV bushing, but that much larger quantities of gas produced in this way would dissolve in the oil within a few days, and the bushing would then return to a discharge-free condition, without apparent physical damage. Where a quantity of air was trapped in the winding during manufacture, it was shown that a discharge level of 30pC at working voltage in a 400kV bushing having a moisture content not greater than 1% would not involve a risk of degradation by a single overvoltage test having a duration of 1 min at a stress of 14kV r.m.s./mm.

An independent search through the Heaviside Collection of the Institution of Electrical Engineers for the material discussed in Heaviside's ‘posthumous papers’ is reported.

The online computer control system at Wolvercote Paper Mill, Oxford, was the first of its kind in the UK. An account is given of the events leading to the installation in 1965. The papermaking process is seen as a problem of control and the application of the digital computer to the process is described. The direct, practical approach and the low cost of both hardware and software are considered to be important factors. The benefits from this installation have been considerable. The computer has proved to be a completely reliable tool which can extend the operator's skill. There have, however, been problems in taking measurements accurated and reliable enough to be used in an automatic control system.

Absorption of moisture causes paper to change its electrical resistance and permittivity. The second effect is approximately linear and little affected by changes in furnish. It is most conveniently measured by means of a fringing capacitor. Instruments for use statically and on a moving web are described. Theories of the water-cellulose bond are discussed.

Mechanical stresses in a paper-lapped insulation which arise from the bending of a cable around a drum immediately after the lapping process are considered theoretically, and an estimate is obtained for the stress arising from the contact of the insulation with the drum. A known relation between interfacial pressure and lapping tension is rewritten to give the tension explicitly in terms of a prescribed interfacial pressure distribution. Finally, a certain form of internal buckling which could be relevant to the problem is briefly discussed.

After brief discussion of special vacuum cells developed for this investigation, results are presented showing the effect of adding between 0.1 and 10% moisture content on (a) the dielectric loss tangent and permittivity at frequencies between 50c/s and 100kc/s (b) the dielectric dispersion measured at intervals of 0.1 and 3s and 3 and 300ms (c) the 1 min insulation resistance (d) the 50c/s capacitance increment. In all cases the results were recorded at 10degC intervals between 20°C and 100°C. The effect of the electrode pressure on the electrical properties of paper insulation is discussed and the practical significance of the results and mechanisms giving rise to them are considered.

The paper deals with development work on which the authors have been engaged since 1945 on machines for the transmission of pictures and facsimiles over land-lines and radio. Faithful tone reproduction of photographic material has been attained, and machines have been produced to fulfil the needs of the Press. Machines with more precise scanning, up to 500 lines per inch, have been developed. A method of controlled retoning of a picture is also described. Further developments have been made using an electrochemical action instead of photographic paper as the recording medium. Machines have been produced to receive tone pictures and to act either independently or as monitors to the photographic machines. Recent applications of the electrochemical recorder to facsimile and telegraph purposes are described.

The paper summarizes operating experience with transformer oils from the aspect of sludge formation and the increase of acidity with life, and it describes tests designed to study the correlation of increasing acidity found in service with predictions of performance based upon the Michie sludge test. The basis of selection of transformers and oils for these tests?which were initiated in 1943?is given, and themethod of preparing the transformers is described. Acidity values are discussed from the aspect of working conditions and transformer site. The results show a trend towards greater deterioration of oils yielding higher acidity values in the sludge test, and B.S. 148: 1933 has been revised to exclude such oils. It is concluded that, under normal operating conditions, oils complying with B.S. 148: 1951 may give satisfactory service, with the minimum of maintenance, for the whole of the expected life of the transformer.

The equipment described in the paper was developed to record automatically the speed/time curve of an experimental homopolar machine undergoing retardation. These retardation tests were being made to determine tooth-ripple losses, and the highest rates of retardation required were beyond the range within which normal visual observation of a stroboscopic disc is practicable. An electronic binary counter and a punch unit provide a speed/time record on punched paper tape, which may be directly processed in a computer programmed to calculate the tooth-ripple losses. The input to the counter can be made from one or other of two independent detector systems. The first operates on the principle of the stroboscope, interpreted electronically, and is thus essentially a rotational speed-interval detector. As this system presents novel features, it is dealt with in more detail. The alternative system, based on counting revolutions in known time intervals, is utilised in existing commercial instruments. The maximum rate of retardation which this equipment can handle is about 1000 rev/min per second.

In the paper a review is given of the properties of oil-impregnated lapped-plastic-tape dielectrics for use as insulation in extra-high-voltage underground cables. The following subjects are discussed: choice of combinable materials, impregnation technique, results of breakdown measurements as a function of various different parameters, dielectric-loss measurements and thermal conductivity, it appears that a cable insulation with a breakdown strength 80% higher than that of oil-impregnated-paper insulation is technically possible. The new insulation, consisting of film tapes of polyphenylene oxide impregnated with paraffinic oil, has a dissipation factor more than five times smaller than that of conventional oil-impregnated paper. in cables with such an insulation, operating stresses of 15–37kv/mm, depending on tape thickness and pressure, may be applied.

Transformer oils usually serve well for many years, and often for the entire life of the transformer, but trouble still occurs from time to time through oxidation of the oil, which causes sludging and the formation of acids. Oxidation may be retarded by using an oxidationinhibited oil. Available types of anti-oxidant, their properties, mode of action and influence on oil properties are discussed. For the evaluation of inhibited transformer oils, new and more informative oxidation tests are required, and such tests are briefly described in the paper. A description is given of some results obtained in the laboratory, in trials with small transformers under laboratory conditions and with transformers in service. It was possible to distinguish between contamination and deterioration of oil in service, and to assess the rate of decrease of oxidation stability of the oil. Questionswhich arise from the use of inhibited oils are discussed. It is concluded that, at present, the greatest value of inhibited oils will be in distribution transformers (particularly those which have given trouble because of oil oxidation) rather than in large transformers or in switchgear. With more practical experience of the superior oxidation stability of these oils, smaller and cheaper transformers may become possible. Further development work includes attempts to improve the correlation of laboratory test methods with service performance.

This short paper describes an investigation into the behaviour of a divided-winding-rotor (d.w.r.) synchronous generator, equipped with regulators for controlling the terminal voltage, torque angle and speed, when subjected to unbalanced short circuits at its terminals. The performance of the machine has been compared with that of a conventionally wound rotor arrangement. It has been observed that the d.w.r. arrangement exhibits exceptionally superior transient-performance characteristics compared with the c.w.r. machine, even under unbalanced-fault conditions, which the machine has to encounter more often in practice than balanced faults.

Digital recording techniques are applied to the operation of a die-sinker. The system described uses magnetic recording in preference to punched paper tape where cost, transportation and simplicity are the major design considerations. Irregular shapes and contours are traced by a stylus which is electrically connected via an arc to a conductive coating on the model. The position of the stylus is related to pulses which are recorded on tape. The recorded tape may be transported to any workshop which employs similar techniques for cutting a work-piece with a permissible tolerance of ±0.005 in.

The oxidation stability of inhibited insulating oils is usually assessed in the laboratory under one set of highly accelerated test conditions. The service life of these oils under normal operating conditions is now being shown to be very much less than that predicted by these tests, and in some cases it is no better than that of the base oil. As inhibited oils have always been considered capable of giving a satisfactory performance under much more severe conditions, it is necessary to know why their service performance under normal conditions is poor. This will enable them to be assessed correctly in future, and may suggest how they can be improved if more severe operating conditions arise. Commercially available, laboratory-blended and experimental oils were examined by the assessment procedure described by Wilson.1 Results are compared with service performance and with performance in experimental inductors. Tests were also carried out at higher temperatures and with nitrogen sealing to show the comparable effectiveness of inhibited oils and nitrogen sealing. It is shown that the susceptibility of oils to the effects of copper and oxygen is radically changed by the addition of oxidation inhibitors. The temperature susceptibility is, in general, less affected. Inhibitors are shown to be most effective under high-oxygen conditions and when the copper/oil ratio is high (as found in highly accelerated laboratory tests). The combination of an oxidation inhibitor and a metal passivator, or deactivator, is more successful than an oxidation inhibitor alone, but, even so, these combinations of additives have only limited economic advantage, as they will enable the oil to withstand only marginally more severe conditions. Lack of correlation between oil acidity and resistivity is shown to exist after aging in the case of inhibited oils, passivated oils and oils operating under a blanket of nitrogen.

A method of designing transistor 2-state circuits which accepts transistors having a relatively large spread in characteristics has already been described. Although subsequent improvement in the uniformity of transistors has removed the primary object of the system, it has been retained in the circuits described in the paper because of the many other advantages it confers where accuracy and speed of operation are important. The transistor is considered as a regenerative amplifier, and the first part of the paper describes various methods of connection and endeavours to evaluate the merits of each circuit. The second part illustrates the application of some of the basic circuits to more complex circuits of the type used in digital computers. These circuits operate at a basic frequency of 125 kc/s and use rectangular pulses to allow adequate time for comparing two or more waveforms and performing operations on them. It is concluded that, owing to its adequate stage gain, low output impedance and standard output pulse, the transistor regenerative amplifier constitutes an economical and versatile computer element.

It is normal to regard the loss in a ferromagnetic material undergoing magnetization as the sum of a hysteresis loss, which might be measured by a ballistic method, and an eddy-current loss, calculable from a knowledge of the shape and resistivity of the material and the flux changes involved. For some sheet steels the measured loss is considerably in excess of this sum, and it is with this discrepancy that the paper is concerned. A pulse method of excitation is used, a constant voltage being applied suddenly to the specimen for times ranging from 0.2 to 2.5 microsec. It has been found that, in most instances, B/H curves are either linear or can be closely approximated by functions of the form B = B(1−e−αH) or B = B(e−αH−1), where B and α are constants. By adopting these exponential expressions, accurate calculation of eddy-current losses in the non-linear regions has been made possible. In the paper, several theories of the cause of the discrepancy are suggested and examined in the light of experimental evidence in which the rate of change of mean flux density, the polarizing field, the grain orientation and the lamination thickness are varied. It is concluded that the discrepancy is at least partly caused by a variation of permeability and resistivity across the lamination thickness; but it is also shown that a reduction of the effective permeability, due to the inability of the elementary irreversible changes of magnetization (Barkhausen jumps) to be completed in the time available, could also contribute to a “discrepancy loss” which would vary with the factors above in a manner consistent with the experimental results.

The first part of the paper outlines the significance of impedance irregularities in a coaxial cable and develops the relations between the actual irregularities, the curve of input impedance against fre quency, and the echo response of the cable to a voltage impulse. The steady-state and transient methods of measurement are then compared theoretically, on the basis of resolving power, and are found to lead to the same result. These theoretical conclusions are proved experimentally by measure ments on an artificially faulty cable. Suggestions are made for the application of these results to factory production of cables; in particular the statistical aspect is considered and parameters giving the maximum correlation are discussed. A simple pulse-testing method, using two spaced pulses, is then described with particular reference to the testing of factory lengths of cable intended for television transmission. Although the results described in this paper are taken from work carried out between 1945 and 1948 the matter is still one of practical interest to manufacturers and users of cables and to all who are concerned with long-distance coaxial-cable transmission problems.

The use of aluminium as an alternative to lead for power-cable sheaths became a focus of attention to cable makers and users as a result of drastic curtailment of supplies and increase in price of lead which took place after the 1939-45 War. During the past six years significant progress has been made in its employment, and to-day several thousands of miles of aluminium-sheathed cables are in service. The paper reviews the development and assesses the value of aluminium as a sheathing material against a background of test performance and operational experience. Beginning with a brief summary of aluminium production and consumption figures, the paper proceeds to discuss qualities of the metal in relation to cable-sheath requirements. The historical background of aluminium sheathing is outlined and a brief description is given of the tube-sinking process originated in 1947. Standard sheath thicknesses of aluminium-sheathed cables manufactured by the tube-sinking process are recorded, their mechanical and electrical characteristics and performance are surveyed, and the advantages deriving from light weight and mechanical strength are presented. An account is then given of installation procedure and operating experience, including analysis of failures encountered in service and methods of dealing with jointing, corrosion protection and sheathexpansion problems. The authors claim that aluminium has been established as a technically suitable and economic sheathing material to replace lead, and that its availability at an economic level constitutes an important asset to the cable industry.

The paper is complementary to a paper by G.A. Montgomerie and it suggests that the method of algebraic manipulation proposed by Montgomerie may be considerably improved. In Montgomerie's paper, a closed contact is allotted the symbol unity, and an open ontact the symbol zero. Contacts in series are then treated as if additive, while contacts in parallel are treated as if multiplicative.The present paper shows that, if contacts in series are treated as multiplicative and contacts in parallel as additive, a considerable simplification of algebra results, with a concomitant gain in elegance. This usage avoids the necessity for rules such as 1+0 = 0, 1×0 = 1, which are in direct conflict with those of ordinary algebra. Also, many results which according to the original proposal would be obtained only after considerable manipulation are obtainable at sightusing the methods now proposed.

Transmission by long-distance cable and repeaters using a vestigial-sideband carrier is becoming standard practice in television. The paper describes some factors affecting the performance of coaxial cables in such an application. A brief description of the inherent properties of a typical coaxial cable and their effect on system design is given. The main part of the paper describes an experimental programme for evaluating the irregularities of coaxial cable, and an estimate is given of their effect on television transmission. It is found that the most probable magnitude of the distortion from this cause is lower than the distortion from other causes.

This survey paper has been written with the object of presenting information about the development in Great Britain of the engineering technique associated with the origination of the B.B.C. television programmes. In any developing art a decision made at a certain time depends upon previous experience. In order to present an understandable account of television engineering methods as at present practised, it is desirable to trace their origins back to the beginning.The paper starts by considering very briefly the development of the pre-war B.B.C. television service and refers, for further information, to other papers published during that period. The paper then records the results of post-war planning for expansion and discusses the origin of the White City scheme, the Lime Grove studio building and lastly the marked development in television outside broadcasts which has been such a feature of the period from 1946 to 1951.Up to this point the paper is concerned with the broader basis of planning and not with technical detail. Section 4 discusses the several types of camera equipment which have been used in this country for studio or outside-broadcast purposes. The technique of television engineering operations is closely concerned with the properties of camera tubes and their associated circuits, so that this subject has been treated in some detail. Brief mention is also made of the associated sound equipment.Certain points of interest in the design of control and apparatus rooms are treated next. This is followed by a discussion of the purposes and technique of presentation as opposed to production, presentation being an aspect of television activity which has assumed considerable importance in recent years. It is acknowledged that the televising of film has been brought to a high standard of perfection in this country. Some account is given of the development of telecine and telefilm recording. In addition to such matters as camera channels, telecine apparatus, studios and control rooms, a television system requires a number of other mechanical and electrical aids to production. Some of these are of special interest and are surveyed in Section 10.Section 11 discusses the standards of circuit performance which it has been found both desirable and practicable to ask the manufacturer to meet in designing his apparatus.The paper is written largely from the standpoint of the user, but not, it is hoped, without some sympathy for the problems of the designer. However, several supporting papers have been contributed by designers, so that the complete series should present a comprehensive picture.

It is well known that certain factors, notably flicker noise and zero drift, determine the smallest signal voltage that can be satisfactorily amplified by a thermionic d.c. amplifier. Better results can often be obtained by using a suitable modulator to convert the direct current to alternating current and following this by an a.c. amplifier and rectifier. The paper discusses the advantages of the second-harmonic type of magnetic modulator for this purpose, and presents a theoretical analysis of an idealized modulator of this type, with particular reference to the influence of various controllable parameters on the signal/noise ratio and zero error. The paper also describes experimental work, which, with allowance for the idealizations in the theoretical analysis, is considered to provide a satisfactory qualitative verification of the latter. Particular emphasis is placed on the need for great care in the design of the various circuits, toeliminate additional sources of noise and zero error, and it is believed that the noise output of the apparatus described is due mainly to Barkhausen effect in the modulator cores, and is equivalent to a signal input of about 10?19 watt for a bandwidth of 1 c/s; the zero drift is, however, considerably greater than this, and is equivalent to a signal input of about 3 × 10?18 watt over a two-hour period.

Attention is being given in Britain and other countries to the possibilities of automatic telephone exchanges constructed with electronic switches, in order to determine whether exchanges cheaper and more reliable than the present types using electro-mechanical switches may thereby be produced. The paper discusses some practical forms which electronic exchanges might take, the possibilities and characteristics of such exchanges and-cursorily-the questions of cost and reliability. Multipled, frequency-division and time-division multiplex types of connector switches for speech and line-signal transmission are described, together with typical subscriber's line equipment. General principles of selection systems, with examples of group and free-circuit marking and of a post-setting-up control circuit, are given. Transmission gain and loss, variation of loss, and distortion are features of electronic connector switches not found in existing types using metal-to-metal contacts, but, on the whole, better speech transmission could be given by electronic systems using the connector switches described in the paper, because of the 4-wire switching which would be inherent in most and desirable in all such systems. Estimates of cost show favourable signs, but are as yet indeterminate. Total system costs must take into account line plant, the design of which may be profoundly influenced by electronic exchanges. Reliability has yet to be proved, but here the signs are also favourable.

In earlier papers a theory of space charges and their fluctuations was developed, in which it was tacitly assumed that the characteristic of a diode could be accurately expressed in terms of thirty differential coefficients of the characteristic. One of these, the slope conductance, was subsequently shown not to be measurable during a fluctuation event and to have a mean square value considerably greater than its squared mean value.In the present paper the effect of fluctuations in another of the differential coefficients is studied. As a result a serious error in all prior work on the subject has been located. Consequently, it is now possible to utilize the assumption that the total emission of the valve fluctuates according to the law derived by Schottky in 1918, and to obtain from this, not, as hitherto, a very severe underestimate of the fluctuations, but one that is much closer to the fluctuation observed experimentally.

The paper outlines the merits of a number of high-permeability magnetic alloys under a variety of conditions likely to be met in instrument practice. The properties found with d.c., a.c. and combined a.c./d.c. operation are indicated, and recommendations are made for the best alloy to be employed in particular circumstances. Information is given on the spread of the magnetic characteristics of Mumetal spiral cores produced on a commercial scale. A Section of the paper is devoted to a.c. permeability and losses of spiral cores, rings and particular assemblies of laminations, and the adverse effect of joints in the magnetic circuits is clearly demonstrated. A method of predicting harmonic distortion in small transformers and chokes is described briefly, and curves of distortion-coefficient variation with induction for a number of nickel-iron and silicon-iron alloys are given. Non-uniform flux distribution has a marked effect on harmonic generation, and this is studied in detail; a number of anomalies are examined and practical recommendations are made. Magneto-striction and the variation of magnetic properties with temperature are treated, together with a brief comparison of permeability and relative costs of a number of magnetic materials. The paper includes curves which will be of reference value to designers.

The paper discusses the regulations relating to the design and practice of overhead-line construction, with particular reference to the Electricity Commissioners' Overhead Line Regulations. It gives a short history of the Commissioners' Regulations and the author's views on what would constitute a good code of regulations. The author traces the background of the existing regulations and examines the proposed revised code prepared by The Institution's Code of Practice Committee on Overhead Power Lines.The paper has been prepared primarily to elicit criticism of the Committee's proposals, in the hope that such criticism will be helpful when preparing the final draft.Attached to the paper are the present code El.C. 53 (1947 Revise) (Appendix 8.1) and the draft proposals of the Code of Practice Committee (Appendix 8.2).

The electrical system in the Bristol Type 167, or Brabazon I Mark I, aircraft is one of the most ambitious installations so far fitted in any aircraft in Britain. The special requirements of this large aeroplane necessitated a power-supply system which, at its inception, was for many reasons unique, although its principles have since been applied in a number of other large aircraft. The object of the paper is to deal mainly with the development of the power-supply system, but some attention has been given to the problems associated with the design of aircraft electrical equipment in general, since the standard of development reached by this equipment merits consideration. The paper therefore deals briefly with the development of typical important items of aircraft electrical equipment, and shows how its specific weight has progressively decreased with its development. After a short review of the generating-speed problem and the ways in which it has been tackled, the performance characteristics of the present power-supply system are stated and its operating characteristics are finally discussed in the light of the results obtained by extensive instrumentation of a ground test-rig. The scope of the subject is large, and it is not possible to cover in the paper the design of the individual items of equipment or describe any of the specialized electrical controls which are now in common use in aircraft.

The first of the two previous papers discussed the general principles of electrical control of dangerous machines and the second their particular application to interlocked guards. In this paper are examined various methods of remote supervisory control developed for large power systems but also used for other industrial processes, such as the distribution of gas and railway signalling. The paper is not concerned with details of construction, and is not intended to advocate any particular system or arrangement, but it analyses the underlying principles and assumptions of a number of different methods and attempts to deduce general requirements which all systems should fulfil. In introducing this subject, the author would point out that where opinions are expressed they are his own and do not necessarily represent the considered policy of his department. They are subject to modification in the light of further information or experience. Some suggestions and comments which are deliberately controversial or go beyond current practice have been included with the object of promoting discussion. In his choice of graphical symbols the author has not followed B.S. 530: 1948 exactly, but has used symbols which he hopes will be easily recognized by power engineers, to whom the paper is primarily addressed.

The first part of the paper discusses the occurrence of unwanted Actuations of frequency in sound recording and reproducing systems and considers methods of measuring these fluctuations in disc-recording systems. A particular procedure is discussed in detail and new apparatus that has been developed for these measurements is described. It has been found that frequency fluctuations vary in magnitude in a random manner, and the second part of the paper indicates how useful information may be extracted from the highly complex data that result from continuous measurement. The statistical properties of the variations of magnitude have been found to be in accordance with theory developed for analogous electrical systems, and examples are given of a number of practical cases in which statistical analysis has enabled the causes of frequency fluctuations to be identified and appropriate action to be taken.

The paper describes an experimental study of the properties of externally corrugated cylindrical metal surfaces when used for the support of electromagnetic waves. In particular brass rods of 3/16 in outside diameter and grooved transversely at regular intervals along the length were employed to guide cylindrical surface-waves of the kind familiar in single-wire transmission. Measurements were made at a number of frequencies in the range 2 500–10 000 Mc/s using a surface-wave resonator. In no case did the depth of corrugation exceed 0.050in.It is shown that a uniformly corrugated cylindrical surface acts as a satisfactory guide for a surface wave if there are at least two corrugations within the guide wavelength. The results of measurements on the surface reactance of corrugated guides are recorded in a number of graphs. An approximate expression for the surface reactance of a corrugated surface is derived in the paper and found to be in reasonable agreement with the experimental results, provided that the slot width is less than the slot depth, and each wavelength includes several corrugations.

Part 1 of the paper is concerned with the theory of a.c. bridges in which the ratio arms consist of tightly-coupled inductors, and refers particularly to bridges in which two sets of such ratio arms are used together in order to obtain very large ratios between the unknown and standard impedances. Reference is made to the important property of inductively-coupled ratio arms which enables the direct impedance between two points to be measured independently, within limits, of any impedances connected between a third point and the two terminals of the impedance being measured. The logical development of bridges with two such ratio arms follows. The material in Part 1 of the paper is the original work of the late A.D. Blumlein, B.Sc.(Eng.), Associate Member, and the present authors have used verbatim a considerable portion of a hitherto unpublished memorandum written by him in January, 1941. Part 2 of the paper describes Blumlein's application of the principles described to a general-purpose mutual-admittance bridge for the measurement of capacitance and resistance. This has a wide range of impedance measurement, and the facility of being able, in many circumstances, to measure components in situ when it is difficult or impossible to isolate them from other components of a circuit.