摘要:

The paper commences by reviewing the methods adopted for the protection of overhead lines and transformers from the incidence of lightning. Itis then pointed out that in manycases it is not economic, and in others technically difficult, to provide sufficient line protection, so that transformers connected to such lines are likely to be subjected to transients having high voltage-amplitudes and high time-rates of voltage change. The question of transformer winding breakdown due to transients is then reviewed and evidence is brought forward to show that the important stresses are those between coils and turns and not those in the major insulation. The conclusion drawn is that transformers can advantageously be protected in most cases by those wave-flatteners which, under all conditions, permit only safe rates of voltage-change to exist at the terminals. Three representative wave-flatteners—condensers, inductance coils, and surge absorbers—are then discussed and equations are given which indicate the manner in which their performances are calculated, consideration being given to all degrees of lightningconditions, including those which cause flashover near the protected transformer. Then follows an experimental analysis of the axial stresses, and their reduction by the use of wave-flatteners, in various transformer windingsunder travelling-wave, travelling-wave flashover, and direct lightning-stroke conditions. Several transformers, differing in rating, mode of winding, natural frequency, and value of a. are employed. The results are presented in the form of gradient-distribution curves so that the relative performances, under various conditions, of the three kinds of flattener may be readily examined and the effects of changes in transformer constants compared. Inthe Appendix are derived the equations of the surge absorber.

DOI:10.1049/jiee-1.1939.0037

出版商:IEE    

年代:1939

数据来源: IET

DOI:10.1049/jiee-1.1939.0041

出版商:IEE    

年代:1939

数据来源: IET

DOI:10.1049/jiee-1.1939.0042

出版商:IEE    

年代:1939

数据来源: IET

摘要:

The X-ray tube described has been specially built for crystal-structure analysis. A short theoretical discussion of the limits set to the power of an X-ray generator is followed by a detailed description of the machine and of the rectifier system which feeds it with high-tension current.

DOI:10.1049/jiee-1.1939.0043

出版商:IEE    

年代:1939

数据来源: IET

摘要:

For a circuitfbreaker operating at the end of a long feeder the feature determining the rate of rise of restriking voltage is the effective surge impedance of the feeder. A previous paperf dealt with the effective surge impedances and calculation of fronts of transients of restriking voltagefor substations fed through 3-core belted-type cables. The present paper deals with the surge impedance in various phase combinations of feeders consisting of three single-core paper-insulated double lead-sheathed cables laidin trefoil, and gives methods by Avhich effective surge impedances may be calculated for systems of known constants. Effective surge impedances deduced from measurements taken with the restriking-voltage indicator are compared with values deduced from calculations taking account of transient currents in the cable sheaths, and it is concluded that the agreement obtained is sufficiently good to show that all important relevant features are properlyaccounted for. As a rough guide it may be said that the effective surge impedance per phase of a system such as is described, is about 0.75√(L/C), whereLis the effective power-frequency star inductance per unitlengthandCthe core-to-sheath capacitance per unit length of the cable. ThisLandCare of course the values normally supplied by manufacturers. The inherent rate of rise of voltage for a fault current of I r.m.s. amperesin a breaker fed by such a cable is 2√(2)∫πI × (effective surge impedanceobtained as described), i.e. for a 50-cycle system it is (0.44×10−3I× surge impedance) volts per microsecond. The constant 0.75 in the above is an average obtained from empirical values for different cable arrangements, but if a more accurate determination is required for anypractical cable arrangement it is shown how this can be determined from firstprinciples.

DOI:10.1049/jiee-1.1939.0044

出版商:IEE    

年代:1939

数据来源: IET

DOI:10.1049/jiee-1.1939.0045

出版商:IEE    

年代:1939

数据来源: IET

摘要:

The paper describes a series of experiments on the electrical breakdown strength of air under sinusoidal voltage conditions over a frequency range from 50 to 900 kc./sec. It is shown that with frequencies of the orderof 200–1 000 kc./sec. there is noticeable reduction in the breakdown voltage between spherical electrodes one of which is insulated and the other earthed, the reduction becoming more marked as the frequency is increased. A modification of Townsend's theory, based on a consideration of theionization conditions prior to breakdown, is suggested, which explains the reduction in the electric strength of a sphere-gap at the higher frequencies.

DOI:10.1049/jiee-1.1939.0046

出版商:IEE    

年代:1939

数据来源: IET