摘要:

The main constructional features of the 66-kV and 33-kV sections of the British grid system are briefly described under headings dealing with overhead lines, cables, switching and transforming stations, and protective equipment.Illustrative examples are given of both normal construction and special constructions of particular interest, together with the most important basic data relating to the general design of the equipment.Methods of earthing are described, with particular reference to their relation to the functioning of discriminative protective equipment.The types of protective equipment used on different classes of lines and apparatus are indicated.

DOI:10.1049/jiee-1.1934.0017

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0025

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0026

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0027

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0028

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper discusses the conditions governing the design of suitable electrodes for the measurement of the permittivity and power factor of solid dielectrics at radio frequencies. Two-terminal mercury electrodes intended for the testing of sheet and tubular materials by resonance methods are first described. Typical conditions in bridge circuits used for dielectric measurements are then investigated, and the effects of the resistance and inductance of the condenser leads and those of defective insulation between the electrodes and earth are deduced from the more general solution. Two types of 3-terminal mercury clamps are subsequently described which have been designed to render the preceding effects as small as possible.

DOI:10.1049/jiee-1.1934.0029

出版商:IEE    

年代:1934

数据来源: IET

摘要:

Radio-frequency voltage-amplification by means of tuned circuits and screen-grid valves is limited by (a) stability, and (b) curvature of the amplification characteristic. As regards (a), the tuned-circuit, screen-grid valve stage is not inherently stable. A lower limit of permissible circuit-resistance is set by the residual grid-anode capacitance. As to (b), secondary emission from the screen-grid gives rise to curvature in the amplification characteristic. This curvatute may lead to a reduction in apparent selectivity due to cross-modulation, and an increase in background noise. Measured amplification characteristics of typical screen-grid valves are included in the paper, to illustrate the nature and degree of the curvature.An analysis of a triode-valve amplifying stage shows the possibility of securing inherently-stable tuned-circuit amplification by using a buffer-valve stage to minimize the effects of the input impedance of the amplifying valve. The most suitable type of valve for the purpose is a low voltage-factor low-resistance valve. The simplest load for the anode circuit of the buffer valve is a fairly low pure resistance—1 000 or 2 000 ohms only. With such a load an overall amplification of over 100 should be obtainable, but the input shunt-resistance of the buffer valve is likely to be low. Measurement of such a stage at 106cycles per sec. gives results in agreement with theory and shows that with 120 volts applied to the anode circuit an output of 100 volts or so can be obtained without appreciable curvature of the amplification characteristic.The input resistance of the buffer valve can be increased by (a) using retro-action on the input circuit; (b) an inductive-resistance load in the buffer valve; (c) minimization of the grid-anode capacitance by simple modification of the design of the triode. Measured values show that the input resistance can be raised to 100 000 ohms or more by these means.In the 200-kilocycle range the triode system gives high amplification (up to 300 or more), and the input shunt-resistance of the buffer valve is also very high.If a choke and condenser coupling is used in the amplifying stage, in place of the transformer coupling, a somewhat higher amplification is obtained (up to 150 at 106cycles per sec. and about 400 at 200 kilocycles per sec.), but the input resistance of the buffer valve is lower than for the transformer coupling.Special emphasis is laid on the desirability of simple modification of the design of the standard receiving triode, with a view to minimizing the grid-anode capacitance. The triode-valve amplifying circuit described may not be preferable to the screen-grid stage in all cases, but it should facilitate reception at large power output by radio-frequency amplification and rectification alone.

DOI:10.1049/jiee-1.1934.0030

出版商:IEE    

年代:1934

数据来源: IET