摘要:

This paper gives an account of automatic methods for handling long-distance telephone connections. It is now possible for an operator to dial any subscriber in a national network without the help of any other operator.One of the most important factors in attaining this is the design of the signalling equipment which is provided on the long-distance lines. The paper describes the signalling methods which are now available, indicates the problems which arise, and analyses the various solutions. The need for uniformity of practice with regard to the frequencies used and the signals transmitted is emphasized, and the conclusion is reached that a 2-frequency system, preferably using frequencies of 600 and 750 cycles per sec., is probably most suitable for general adoption. It is claimed that future developments will be hampered to the minimum degree by such a system.Recent developments in long-distance switchboards are described.Automatic long-distance tandem exchanges are described. These exchanges replace the through positions on long-distance switchboards and enable a distant operator to build up indirect connections over a number of long-distance lines by dialling or key-sending. These exchanges also permit a local-area operator to control long-distance connections and thus enable outgoing long-distance operators to be dispensed with.A brief summary of existing operating methods is given and the effect of the new developments upon these is considered. An improvement of the order of 12 per cent in the earning power of long-distance lines is obtained. Substantial savings in operating costs are also realized owing to the elimination of incoming positions and an increase in the traffic-carrying capacity of outward positions. The line time required to obtain ringing tone or busy tone is around 14 seconds on direct connections as compared with 40 seconds by manual methods. On indirect connections the time saved is even greater. As a result, the originating operator can, if necessary, make several attempts to obtain a subscriber in less time than she previously took for one attempt.The problems which arise in introducing automatic switching methods into existing long-distance networks are considered and resultant changes in routing methods, cable lay-outs, and transmission lay-outs, for long-distance lines are described.Subscriber-to-subscriber dialling over long-distance lines with time and zone metering is already in operation, in several countries. Methods for realizing this and the precautions to be taken with a view to its ultimate introduction in less fully developed areas, are described.

DOI:10.1049/jiee-1.1934.0166

出版商:IEE    

年代:1934

数据来源: IET

摘要:

This paper is an account of recent Continental developments associated with the gas-cooled arc and its applications to current-conversion problems. A brief survey is given of some of the physical phenomena of the arc under the special circumstances of the gas-cooled arc convertor.* The development and the construction of the main convertor equipment and its auxiliaries are described, and some test results are quoted. The adaptation of this convertor to suit polyphase and inverted working is discussed.

DOI:10.1049/jiee-1.1934.0168

出版商:IEE    

年代:1934

数据来源: IET

摘要:

Measurements of permittivity, power factor, and power loss, in alternating fields, and also of direct-current conductance, have been made with voltage gradients covering the range between 2 kV per mm and the region in which instability sets in (10 to 15 kV per mm).The law previously given, namely, that for low voltage-gradients, including the usual working range, the permittivity and power factor of the material are independent of the voltage, and the power loss is strictly proportional to the square of the voltage, was found no longer to hold when the voltage gradient exceeded a certain critical value. This value was about 2 or 3 kV per mm in all the tests made, including measurements on black and yellow material, at temperatures of 20° to 50° C. with varying moisture contents, and at frequencies of 50, 100, and 800, cycles per sec. As the voltage gradient was increased beyond the critical value, both the permittivity and the power factor of the material began to increase, slowly at first and afterwards more rapidly. The increase was smaller the drier the material, but the percentage increase was of the same order in all cases. The maximum increase of power factor observed was of the order of 10 per cent, and of permittivity 1 per cent.It was found that in all cases the power lossPin the material could be expressed as a function of the applied voltageV, by means of the formulaP=G0V2+G1V2+γP=G0V2(1 +pVγ)This formula holds for all voltage gradients, low and high, but the second term is negligible for low voltage-gradients.Gois therefore the low-voltage a.c. conductance. The values obtained for γ varied between 2.5 and 6.The increase in permittivity and power factor with increasing voltage is taken as an indication that the absorption currents in the material increase more rapidly than the voltage, and it is considered that this rules out the possibility of such currents being of the nature of the rotation of electrical doublets. An increase in the conductivity of one or more of the components of the material with voltage would seem to be the most probable explanation, and the evidence suggests that this conductance is ionic.The d.c. conductance (constant final value) of the material was also found to increase with increasing voltage gradient, but in a manner quite different from that of the a.c. conductance. Over the whole range covered by the measurements (2 to 15 kV per mm) the d.c. conductance was found to be a linear function of the voltage. This current is also probably carried by ions, and we conclude that we are concerned with at least two laws governing an increase of ionic conductance with voltage.The process of ionization by collision will account for the outstanding features of the a.c. results, namely the critical voltage-gradient corresponding to the critical ionic velocity at which a collision with a neutral molecule results in its ionization, and the more and more rapid increase of conductance as the voltage is further increased. It is, however, difficult to account for the d.c. results by this process, since these features are not apparent in them. The ions carrying the direct current are probably different from those carrying the absorption current of the a.c. measurements, and subject to a different law of motion.

DOI:10.1049/jiee-1.1934.0172

出版商:IEE    

年代:1934

数据来源: IET

摘要:

Experimental work was performed to determine the relative amount of interference caused by discharges on line insulators due to their configuration, to the atmospheric conditions, and to pollution of the insulator surfaces. Control of conditions such as humidity was obtained by investigations within a glass-sided chamber. The cap-and-pin type insulator was most free from discharges, but methods of reducing the discharges considerably were found for the pin-type insulator by means of metal insets to the binder or by the use of metal caps; and for the interlink-type insulator by using large links and compound lining. Field tests were made ot verify the conclusions reached from the laboratory work. Several points of agreement were noted.

DOI:10.1049/jiee-1.1934.0173

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper describes the electrical equipment which was applied to the construction of a large bridge across a tidal river.The difficulties which arose are discussed, and suggestions are made with a view to overcoming these difficulties in future constructional work of this nature.The method of supplying energy to the sinking sets is given, and it is suggested that this might affect the design of submarine cables for tropical waters where the teredo worm is known to exist.The paper concludes with particulars of the amount and cost of the electrical energy consumed, together with a curve showing the consumption of electrical energy during the constructional period.

DOI:10.1049/jiee-1.1934.0176

出版商:IEE    

年代:1934

数据来源: IET

摘要:

With the aid of a high-speed cathode-ray oscillograph the surge characteristics of a variety of electrode arrangements have been studied, using surges of three different waveforms. Impulse testing technique for voltages up to 1 million volts has been revised, and results are given of the impulse spark-over of the point-plane gap and the sphere-plane gap in air and in oil, and of the spark-over of porcelain suspension insulators.

DOI:10.1049/jiee-1.1934.0177

出版商:IEE    

年代:1934

数据来源: IET