Showing papers in "Journal of the Institution of Electrical Engineers in 1955"

The International Electrotechnical Commission

Abstract: Meetings of the Advisory Technical Committees of the International Electrotechnical Commission were held in Brussels March 27th to April 1st. The meetings were attended by delegates from eight national committees — Belgium, France, Great Britain, Holland, Italy, Spain, Switzerland, and the United States. There were about 40 delegates in all.

Transistor power amplifiers

Abstract: The factors governing the power-handling capabilities of p-n-p junction transistors in sinusoidal amplifiers are discussed. It is shown that, although the maximum allowed collector dissipation, Pc max, is an important transistor design criterion, it does not necessarily indicate the limit to the maximum output power possible; limitations set by other factors, notably the variation of current gain with emitter current, become particularly significant in Class B amplifiers because of their very high efficiencies.The relative importance of Class A and Class B amplifiers is considered, and the three possible Class B push-pull arrangements are analysed in detail. It is shown that load-line techniques, such as are used in designing thermionic-valve power amplifiers, are not really suitable for transistors, and a different approach is made.It is concluded that the common-collector Class B push-pull amplifier has a number of attractive features which favour its use. The design of a driver stage for this amplifier is described.Complementary arrangements of n-p-n and p-n-p transistors are examined, but it is found that their advantages are not very great.Finally, some non-sinusoidal power-amplifier applications are mentioned, and it is seen that transistors can be very important in this context.

Noise in cut-off magnetrons

Abstract: Experiments have been made on the characteristics of magnetron oscillators at anode voltages from zero to the value at which the oscillations start. In particular, the noise in the anode current was investigated. Discrete peaks of noise were found in the spectrum, and the frequency at which they occurred varied in a regular manner with anode voltage and magnetic field strength. A qualitative explanation of these peaks is given, and the implication of these results on the mechanism of build-up of oscillations and the selection of modes of oscillation is discussed.

The capability of alternators

Abstract: The method of constructing complete capability diagrams for alternators is presented. The various limits of operation, namely rotor and stator heating, stator-end heating and steady-state stability are considered both for a salient pole and for the special case of a round-rotor machine. Methods are given to enable the diagrams to be drawn for various terminal voltages and also for the case of a generator plus unit transformer.

Automatic circuit reclosers

Abstract: Of recent years there has been a large increase in the use and application of electricity in rural areas. The loads are usually small but are distributed over very large areas, and a high standard of service is an essential requirement as prolonged interruption of supply may cause serious inconvenience to users. Supplies in such areas are generally provided by high-voltage overhead lines, from which distribution transformers provide links with the general medium-voltage distribution networks. The transformers and spur h.v. lines are usually protected by fuses, with the number of h.v. circuit-breakers kept to a minimum. Under these conditions, therefore, h.v. faults of both a transient and a permanent nature might cause prolonged interruption of supply, owing to the distances to be covered before fuses can be replaced or circuit-breakers reclosed. Where only a limited breaking capacity is required an automatic circuit recloser can be made to overcome the operational difficulties detailed above. The paper reviews some of the factors influencing the design, selection and application of circuit reclosers. The principles determining whether the main contacts of a recloser are to "lock open" or "hold closed" upon the completion of an operating sequence are discussed, and the co-ordination of reclosers with other reclosers and with fuses is described. The development of the use of automatic-reclosing features is also discussed in relation to operation in conjunction with automatic sectionalizers.

The adhesion of electric locomotives

Abstract: After the results of previous investigations have been considered, the paper describes measurements of adhesion made on electric locomotives on the recently electrified lines between Manchester, Sheffield and Wath. Measurements were made under controlled conditions with the aid of the mobile testing plant on one driving axle of a locomotive, the tractive effort of this axle being separately regulated, and on all driving axles of a locomotive in normal condition, while the adhesion of locomotives working trains in service was observed by the use of dynamometer cars. It is shown that there exists a relationship between adhesion and speed, and between adhesion and water on the head of the rail, while variations in adhesion were found to occur between different parts of the track. A subsidiary investigation revealed that considerable variation occurred in the values of the locomotive axle loads during running. Various methods of temporarily improving adhesion were investigated, such as the use of sand or of certain esters. The conclusions are particularly considered in relation to the working of trains up the Wentworth incline; recommendations are made as to the methods of driving to be employed under difficult conditions; and a modification to the locomotive control to increase adhesive performance is described.

The performance of star-star transformers

Abstract: To obtain a satisfactory performance with a star-star transformer it is sometimes, but not always, necessary to provide the transformer with a delta-connected tertiary winding. Much misapprehension exists among electrical engineers about the reasons for such a winding, and most users of these transformers in Britain demand a delta winding in all instances, although, in fact, its additional cost is often not justified and its provision is technically undesirable. The subject is rarely mentioned in textbooks and then, as a rule, only briefly. The authors of this article explain in plain words when a star-star transformer should be fitted with the extra winding. This will be familiar to transformer specialists, but it is believed that the article will be useful to many other electrical engineers who use star-star transformers and enable them to decide whether a tertiary winding is necessary in a particular transformer. The authors show that in most instances a decision can be reached easily and without an exact numerical assessment.

Miniature circuit-breakers

Abstract: 2065031 9102370 PCTABS00003 A miniature circuit breaker for domestic and like electricity supply circuits has a double break design featuring a contact carrier (28) mounted on a plastic sliding carriage (60) directly connected to a coiled tension spring (108) and controlled by a latch mechanism which releases it for completely independent breaking movement on overload. Major parts of the latch mechanism are moulded in a plastics material. An anti-bounce stop (120) is provided for the carriage. Simple adjustement of the trip point is provided by a threaded adjuster which moves a thermal trip lever (88). Leaf springs(114, 134) position the movable contacts and the plunger (126) of the overload-detecting solenoid (24).

Current summations with current transformers

Abstract: The behaviour of current transformers in parallel, and of similar circuits employing summation transformers, is studied for different conditions of load distribution.After the existing theory concerning idle currents has been rejected it is demonstrated that the overall error is very nearly constant for a given total load, no matter how the current may be shared among the line transformers. A complete equipment may thus be regarded as a single current transformer and the circuit parameters are considerably simplified, enabling practical formulae to be established for determining the overall errors.In the latter part of the paper it is shown how the effective burdens on the individual transformers may be estimated and how test results at these burdens may be used to compute the overall errors. Worked examples are given, together with confirming test results.

The transatlantic telephone cable

Abstract: Last year the American Telephone and Telegraph Company announced that the Bell Telephone Laboratories had perfected a deep sea telephone cable suitable for transatlantic operation. Work is now going forward actively on the development of a cable system of this type for connection between London and New York City and it is possible that this circuit will go in service as early as 1932. While the new cable will yield only a single telephone circuit, this will be one of maximum reliability, free from the variations characteristic of radio circuits. It is not the idea that the cable will replace radio circuits but it will add considerably to the reliability of New York-London service as well as adding to the total message capacity.