DOI:10.1049/pi-1.1951.0023

出版商:IEE    

年代:1951

数据来源: IET

DOI:10.1049/pi-1.1951.0024

出版商:IEE    

年代:1951

数据来源: IET

DOI:10.1049/pi-1.1951.0025

出版商:IEE    

年代:1951

数据来源: IET

DOI:10.1049/pi-1.1951.0026

出版商:IEE    

年代:1951

数据来源: IET

DOI:10.1049/pi-1.1951.0027

出版商:IEE    

年代:1951

数据来源: IET

DOI:10.1049/pi-1.1951.0028

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The intrinsic electric strength of polyvinyl alcohol has been measured at temperatures ranging from −195° C to + 90° C. At the lowest temperature, the electric strength is slightly higher than that of any other material yet measured, but it falls rapidly with increasing temperature throughout the range. Comparison of this behaviour with that of other high polymers suggests that the temperature variation of the intrinsic electric strength of these materials is determined by the dipoles present, and not by the physical structure. Lack of information on the value of the dielectric constant at low temperatures precludes exact comparison between the actual electric strength in this region and values calculated from Frohlich's formulae, but satisfactory agreement was obtained between the experimental and calculated values for polyvinyl alcohol, using the high-frequency value of the dielectric constant.

DOI:10.1049/pi-1.1951.0029

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The work described in the paper is concerned with predicting the r.m.s. current which a simple harmonic voltage will drive through a non-ohmic resistor in series with an impedance, having either positive or negative phase angle. The non-ohmic resistor is supposed to be of the general character of those constructed from silicon carbide; i.e. its resistance is independent of the direction of the current, and the magnitude of the current varies approximately as the fifth power of the voltage. The paper is mainly experimental but there is an analytical Appendix in which it is shown that the observed experimental results can be predicted by simple algebraic methods.Experiments were made to discover the voltage which is needed in order to maintain a given r.m.s. current through a silicon-carbide resistor which is placed in series with (a) a variable ohmic resistor, (b) a variable condenser, and (c) a variable inductor. In all three cases it is found that the silicon-carbide resistor behaves substantially as though it were a constant ohmic resistance, at any assigned current. The magnitude of this constant resistance is a function of the given current and it can readily be deduced from the static characteristic of the given non-ohmic resistor. It is nearly accurate to say that the equivalent constant resistance, at any given current, is equal to the r.m.s. voltage divided by that current, in the circumstances when there is no impedance in series with the non-ohmic element.In the main, the experimental portion of the paper is concerned with r.m.s. values and not with waveforms, which are discussed in the Appendix. Taken as a whole, the paper should suffice to predict r. m. s. current, waveform and phase angle when a given non-ohmic resistor is connected in series with any general impedance.

DOI:10.1049/pi-1.1951.0030

出版商:IEE    

年代:1951

数据来源: IET

摘要:

It is well known that the actual measurements of coefficients characterizing the electrostatic induction from power lines to parallel or transverse telephone lines do not always agree with the values obtained using the generally accepted theory. The paper analyses the possible causes of the observed discrepancies. By taking into account the effect of harmonics existing in the power system, the conclusion is reached that these discrepancies arise mainly through ignoring the effects of pylons or other earthed structures and the unevenness of the ground.The second part of the paper examines the relations between the values given by the simplified formulae contained in the Directives of the C.C.I.F. and those given by the more rigorous formulae. It is found that the C.C.I.F. formulae are generally adequate.

DOI:10.1049/pi-1.1951.0047

出版商:IEE    

年代:1951

数据来源: IET