摘要:

The wet flashover voltage of an insulator depends partly on the angle at which the water-drops fall but mainly on the quantity of water striking the insulator. A visual estimate of the angle and a measurement of the vertical rate of fall does not give a satisfactory indication of the quantity striking the insulator if spiral nozzles are used. A suggestion is made to improve the consistency of wet-test results by using plain nozzles and by making two simple measurements of spray intensity.

DOI:10.1049/piee.1963.0149

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The effects of humidity, for alternating voltages up to about 700 kV r.m.s. and impulse voltages up to about 1500kV, on gaps between 1m spheres, on rod-gaps, on suspension insulators and on pedestal-post insulators are described. Data are given on cylindrical-post insulators with alternating current and on point-plane gaps with impulse voltages.The data are limited but appear to be sufficient to justify conclusions which could affect practice, in particular, it appears that the a.c. flashover voltage of some gaps and insulators falls at high humidities, so that the negative correction in use at present should be replaced by a positive correction.The data for positive impulses, except for the sphere-gap, show that flashover voltages increase continuously with humidity. The effect with negative impulses is in some cases negligible.

DOI:10.1049/piee.1963.0150

出版商:IEE    

年代:1963

数据来源: IET

摘要:

Impulse flashover voltages are given for air-gaps, string insulators and post insulators which might be used in transmission systems at voltages from 132 to 400 kV. For a given length of air-gap, the flashover voltage with 1/50 μs impulses is least between a positive point and an earthed plane, and for this arrangement the 50% flashover voltage for gaps above lm is about 525 kV/m. For a negative point the voltage is considerably higher, the proportionate difference decreasing as the gap length increases. For point-point gaps and for suspension-insulator strings, on which flashover takes place clear of the intermediate metal fittings between insulator units, there is less polarity effect, and the voltage/length characteristics are intermediate between the positive and negative characteristics for point-plane gaps. For air-gaps and such insulator strings the voltage range over which the flashover probability is fractional is small. For long post insulators, over which flashover takes place via the intermediate metal fittings, the fractional-flashover-probability voltage range may be larger and the increase of flashover voltage with length may be smaller than for suspension strings. The polarity effect decreases with length of gap or insulator.

DOI:10.1049/piee.1963.0151

出版商:IEE    

年代:1963

数据来源: IET

摘要:

An idealized induction furnace, in which the motion is due to thermal buoyancy, is analysed by the simultaneous solutions of the Maxwell, Navier–Stokes and energy equations commonly used in magnetohydro-dynamics. Temperature and velocity profiles are obtained, and an understanding of the coupling between electromagnetic, thermal and mechanical phenomena is gained. It is shown that, for a given applied magnetic field produced by the exciting coil and a given furnace width, there is an optimum frequency of exciting current which produces maximum motion of the molten charge.

DOI:10.1049/piee.1963.0152

出版商:IEE    

年代:1963

数据来源: IET

摘要:

Control systems are considered which have two saturation non-linearities separated by a linear phase-advance network. Because of the high-pass-filter characteristic of the linear element, distortion produced by the first saturation element is amplified and changes the gain given, to the fundamental component, by the second saturating element. It is shown that the change so caused produces a phase shift through the saturating elements. A joint describing function for the two elements is derived and used to predict sustained oscillations. These oscillations are found to be unstable, and once disturbed, diverge to infinite amplitude. Methods of excitation are examined, and the amplitudes of step functions and sine waves which just excite divergent oscillations are determined. However, the power level of a noise signal which also excites a divergent transient, when applied to the input of the system, is not determined. Analysis of the system when noise is injected into the second saturating element indicates that, in this case, noise has a stabilizing influence.

DOI:10.1049/piee.1963.0153

出版商:IEE    

年代:1963

数据来源: IET

摘要:

Either the Goss (110) [011] texture or the cube (100) [001] texture may be developed in 0-004 in 3% silicon-iron strip. The texture that develops on secondary recrystallization is dependent on the purity of the furnace atmosphere and the temperature at which the final heat treatment is carried out.A simple theoretical treatment of the energy-balance equation of a growing grain in a primary recrystallization matrix shows how the experimental results can be explained on the basis of surface-energy differences between grains of different orientations, and the dependence of these differences on the heat-treatment conditions. It is predicted that a grain with six or more sides can undergo unlimited growth, provided that the difference in surface energy (σm− σg) between the growing grain (σg) and the matrix grains (σm) is greater than about 70 ergs/cm2.Power-loss measurements on both cube-texture and Goss-textured materials are presented, and a comparison is made with commercial grain-oriented material. Experimental results from measurements on single-crystal picture frames are used to predict how far it should be possible to lower this loss. Magnetostrictive measurements on Goss- and cube-textured strip show no appreciable difference in the magnetostrictive behaviour of the two materials, and a general discussion on magnetostriction in terms of domain-wall movements is given.It is concluded that an increase in the degree of grain orientation will bring about a reduction in power loss and magnetostriction.

DOI:10.1049/piee.1963.0154

出版商:IEE    

年代:1963

数据来源: IET