摘要:

Considerations of the short-time electric strength and of the conductivity/temperature/stress relationships show that both impregnated paper and polythene are likely to be satisfactory dielectrics for use in h.v. d.c. cables. From a.c. experience, however, it is known that polythene in particular is very vulnerable to damage caused by discharges in gas-filled cavities, and an assessment of the importance of this mode of deterioration under d.c. conditions is therefore necessary.Calculations have been made of the repetition rate of discharges in a gas-filled cavity in a dielectric subjected to a d.c. stress, since this is clearly a decisive factor determining the rate of deterioration. The repetition rate is shown to be a maximum when the surface conductivity of the dielectric is zero. Direct measurements of the repetition rate of discharges are described, and the measured rates are shown to be consistent with the calculated maximum rates. The effects of ripple voltages and polarity reversals are considered.From the predicted discharge repetition rates and from the results of accelerated life tests on samples containing cavities, a rough estimate of the effect of discharges on the probable life of an h.v. d.c. cable dielectric can be made. Polythene was selected as the example for study, on account of its known vulnerability to discharges, and it is shown that, with this material, discharge damage is unlikely to be a serious problem under d.c. conditions, provided that ripple voltages are not excessive and that very frequent reversals of polarity can be avoided.

DOI:10.1049/pi-a.1960.0052

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The paper first describes the probable sphere of application of monocrystalline semiconductor rectifiers and states the problems which must be solved to ensure reliable operation under both normal and abnormal conditions. The basic characteristics of these rectifiers are then discussed. A brief description is given of the special test methods required to establish the characteristics, and it is shown that important properties can be entirely overlooked if test methods are inadequate.Operating conditions are examined under both normal conditions and during faults and overloads, and the protection requirements are deduced.The properties of h.r.c. fuses are briefly discussed, and by consideration of the rectifier properties and operating conditions the requirements are stated for the special fuses necessary. It is shown that these special fuses provide a basis for a protective system which enables full use to be made of the new semiconductor rectifiers.The paper concludes with a description of the practical application of these special fuses, and shows how different forms of protection can be co-ordinated to ensure satisfactory operation of semiconductor rectifiers under different conditions for a wide variety of duties.

DOI:10.1049/pi-a.1960.0055

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The operation of fluorescent tubes on high-frequency (up to 20kc/s) supplies is considered. The characteristics of sine-wave and square-wave transistor inverters are discussed, and a preference is expressed for sine-wave supplies for lamp operation. Design details and component characteristics for sine-wave lamp inverters are considered and various types of circuit are mentioned.

DOI:10.1049/pi-a.1960.0058

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The principal advantage in using linear induction motors to drive conveyor belts is that force can be applied uniformly to the belt over a wide area without mechanical contact. The drive is therefore independent of the coefficient of friction between belt and rollers and belt stretch is less likely to occur. The main problem in designing a linear motor for such a drive arises from the fact that the speeds required are low, and it is shown that efficient systems are possible only if the motor is supplied with low-frequency power.Two systems are investigated, the first using a woven copper belt and the second a series of solid plates connected to chains along each side. The effect of end-ring resistance and of contact resistance between weft and warp is investigated in the case of the woven belt. The action of the plate conveyor involves the behaviour of discontinuous rotors, and a theoretical investigation of this problem included. The findings are substantiated by experimental results obtained from a fairly large model. Other applications which could utilize the short rotor effect are suggested.

DOI:10.1049/pi-a.1960.0061

出版商:IEE    

年代:1960

数据来源: IET

摘要:

An automatic method for designing housing-estate distribution systems is described which offers a practical and economical alternative to present design techniques. Substation positions and feeding arrangements are calculated instead of being determined intuitively, resulting in better layouts and closer approaches to given engineering limits. The method was applied to four housing estates and achieved savings ranging from 6 to 15% of the m.v. mains expenditure required by the previous manual designs. Apart from capital savings, uniform standards of design are obtained and designers are relieved of much tedious work.The automatic method can facilitate management decisions by supplying cost figures for variations in design. For example, alternative substation sites may be tested when optimum sites are difficult to secure, the cost of increase in assumed a.d.m.d. can be determined and variations in the number of standard cable sizes can be investigated.Special features of the automatic method are the division of irregular estate areas and a road-selection procedure which determines the shortest route between two points.

DOI:10.1049/pi-a.1960.0062

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The results of an investigation into the mathematical design, as distinct from analysis, of electrical power-system networks are described.Starting with geographical positions of the substations which it is required to interconnect, it is shown that a set of equations can be obtained which are solvable by linear-programming techniques to obtain a minimum-cost network design. Any security of supply conditions considered necessary can be incorporated into the design equations.Solution of the resulting linear programmes requires the use of a digital computer; the necessary computer size, and amount of computation, increases rapidly with increase in the number of substations to be interconnected. With this in mind, suggestions for increasing the size of problem solvable on a given computer are made.Three designs have been completed using the method proposed. These and the results of network-analyser studies on two of them are summarized.The equations for two other possible network-design criteria, minimum circuit length and minimum apparent-power by distance product, are also given and briefly commented upon.

DOI:10.1049/pi-a.1960.0063

出版商:IEE    

年代:1960

数据来源: IET