摘要:

A careful examination is made of many factors affecting the cost of overhead equipment, taking the 0.75 in2Liverpool Street-Shenfield type as a standard.Figures are quoted to show that considerable economies can be achieved by making reasonable track alterations in junctions and yards, wherever possible, to permit the use of light short-span structures.Present practice in Britain is examined; while still ensuring safety and reliability, modifications to achieve economies are recommended, including reduced wind loading, increased stress in steel, reduced minimum thickness of steel, smaller and less costly foundations, longer spans between structures on open lines, spliced catenaries between stations, crossed contact wires, cap and pin insulation, simpler droppers and rail bonds of smaller copper section.Other possible economies mentioned include reduction of copper section to 0.6 in2, use of bare feeders, reduced switching and sectioning, span-wire registration, and the use in certain circumstances of tubular steel and pre-stressed concrete structures. Economies not recommended include less effective cleaning of steel before painting, simplecatenary construction, copper instead of cadmium-copper contact wire on main lines, and ferrous fittings on live equipment.Finally it is shown that careful advance planning, completion of all survey and civil engineering work well ahead of overhead-line construction, and a steady programme of work will produce additional economies amounting to a high proportion of the total of all other recommended economies.

DOI:10.1049/pi-1.1953.0041

出版商:IEE    

年代:1953

数据来源: IET

摘要:

After an introduction to vibrator-contact problems it is shown that platinum contacts exhibit reverse and zero migration in two sets of circumstances, namely at 1–2 volts and at 10–20 amp, a small arcquench inductance having a critical influence. A long, though not unlimited, vibrator-contact life was obtainable either from platinum contacts with appropriate circuit conditions or from contacts of dissimilar metals, but an adequate life on heavy duty was obtained only with tungsten contacts in an atmosphere free of oxygen to a high degree. The trend of methods for producing exceptionally long contact life is reviewed.

DOI:10.1049/pi-1.1953.0045

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The paper commences with a brief review of the previous work on fine transfer between contacts. The investigation described was undertaken to find out whether there is a connection between fine transfer and the inductive energy stored in a circuit at break. The work was carried out with platinum contacts in a 6-volt circuit breaking currents of the order of 1 amp. The circuit inductance was controlled from 0.05 to 10 μH. The results show that there is a residual transfer independent of inductance, but that the transfer is dependent on inductance when this is greater than about 0.3 μH. In both cases the transfer results in cathode gain. It is deduced that this second transfer is due to a “short arc.” Possible explanations of the two types of transfer are given.

DOI:10.1049/pi-1.1953.0046

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The conditions in which electrical discharges can occur at low-power contacts are surveyed, special attention being paid to the cases of make and break at medium voltage. The mechanism of production of the electrons which can initiate such discharges has been investigated experimentally by measuring the electron emission from the cathode under a succession of voltage pulses. Results showed that the emission was a cold-field process determined by the nature of the surface tarnish layers on the metal, the mechanism for thin (≃10−7cm) layers being different from that for thicker surface layers, which are usually oxide. The influence of the nature of the electrode surface and of the gas atmosphere was examined, and it was concluded that an insulating surface-tarnish layer was essential for the comparatively high rate of production of the initiatory electrons under the low electric fields (104≃ volts/cm) usually set up at small contact gaps. A theory of the mechanism is outlined.

DOI:10.1049/pi-1.1953.0047

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The surfaces of electrical contacts are usually contaminated by foreign layers. Such layers may consist of dust or grease, or of films produced by adsorption, tarnishing or corrosion. The applied voltage is regarded as “low” when it is too small to initiate conduction by any process analogous to breakdown. The problem in such circumstances is to obtain a metal-to-metal contact mechanically. An attempt is made, for the first time, to describe the behaviour of a closed contact subjected to corrosion, and the closure processes for a corroded contact, both with and without “wipe.” The principles outlined provide some theoretical basis for design and testing techniques. Attention is also given to sliding contacts and, in particular, to the exposed intermittently-operating type: some new approaches to the problems involved are suggested, perhaps the most important being the development of a new technique for the continuous dry lubrication of sliding contacts in mechanical and electrical systems.

DOI:10.1049/pi-1.1953.0048

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The carbon brush depends for its frictional properties on atmospheric water. At high altitudes, where the atmosphere is very dry, friction is high and wear rate is catastrophic. Laboratory apparatus for the study of the phenomenon must simulate the conditions in the upper atmosphere. Conventional lubricants are unsuitable on account of their effect on the electrical contact and their failure to withstand the conditions at the rubbing face. Effective inorganic lubricants give immunity by building up a stable film on the commutator surface, but they adversely affect machine performance.

DOI:10.1049/pi-1.1953.0049

出版商:IEE    

年代:1953

数据来源: IET