DOI:10.1049/ji-2.1947.0060

出版商:IEE    

年代:1947

数据来源: IET

摘要:

Equivalent circuits representing simultaneous dissymmetries on 3-phase systems have been treated previously,1, 2, 3but the analysis has been purely mathematical and the ultimate evaluations have been formal. In this paper the more direct method of superposition is employed, as this retains the physical aspect and in general reduces the labour of computation; it also has the indirect advantage that the faults are developed in proper sequence.All possible combinations of two dissymmetries are analysed, with the exception of simultaneous open-circuits. The results are tabulated suitably for direct computation.The primary operation is to reduce the symmetrical-component sequence networks of a given system to the simplest arrangement of impedances between the source and the dissymmetry locations. The networks are then interconnected so that the pertinent constraints between the sequence currents and voltages are complied with at both locations. In general the interconnections at one location can be made direct, whereas at the other magnetic coupling will be required. The constraints and the direct- and magnetically-coupled interconnections for all types of faults and open-circuits are tabulated.The interconnections for any particular dissymmetry can be introduced for faults by the closure, and for open-circuits by the opening, of a switch. The procedure employed is, with the switch (S1) controlling the magnetic interconnections open, to close or open the switch (S2) controlling the direct interconnections, and to determine the current and voltage distributions throughout the network, in particular the voltage across S1. The current or voltage distribution which would be due to the closure of S1is then determined by an operation equivalent to closing it, i.e. by applying across its terminals a voltage equal and opposite to that determined from the operation of S2. The actual current or voltage distribution for the simultaneous dissymmetries is then the vector sum of the distributions due to the closure (or opening) of S2and the equivalent closure of S1.

DOI:10.1049/ji-2.1947.0061

出版商:IEE    

年代:1947

数据来源: IET

摘要:

The Wheatstone bridge method of resistance measurement is noted for its simplicity, accuracy and reliability. It is claimed that these attributes can be retained in remote-indication systems which employ the principle of the balanced bridge. This method ensures freedom from any undesirable effects of self-inductance, capacitance, induced voltage or supply-voltage variation within normal limits. A detailed description is given of an automatic signalling system of this type which has been in continuous operation since 1929 in Georgetown, British Guiana, under extremely onerous conditions.The paper also indicates how the balanced-bridge principle may be developed to superimpose telemetering facilities on a single-pair telephone circuit.Two appendices set out general formulae and examples of their application in the design of the Georgetown installation.

DOI:10.1049/ji-2.1947.0064

出版商:IEE    

年代:1947

数据来源: IET

摘要:

A number of accidents occur with dangerous machinery and processes, which though not of an electrical character, such as electric shock or burns, are due to the failure of electrical control equipment, or could have been prevented by the use of suitable electrical control or protective gear.This paper discusses such matters in as systematic a manner as their varied character allows. Typical instances are interlocking of danger areas, design and adjustment of limit switches, safety equipment on cranes and lifts, pushbutton circuits and the prevention of inadvertent starting of dangerous machines. The dangers from fire risks have been dealt with in an earlier paper in association with Mr. F.H. Mann, and the author has given some account of furnace control elsewhere.The author would point out that the conclusions and suggestions set out below are his own. They are relevant to the present stage of development of electrical control, and are subject to modification in the light of further experience. They do not necessarily represent the views or considered policy of his Department.

DOI:10.1049/ji-2.1947.0075

出版商:IEE    

年代:1947

数据来源: IET

摘要:

The development of the gas-cushion cable over the last ten years for the highest voltages is traced from the point of view of performance under tests which have been formulated to give data for design purposes.Comparison is made with the normal solid cable-dielectrics under 50-c/s and impulse conditions. The special requirements pertaining to impulse testing when dealing with cables are enunciated, and the present dearth of data in this respect is revealed. Reference is made to possible future developments.

DOI:10.1049/ji-2.1947.0078

出版商:IEE    

年代:1947

数据来源: IET

摘要:

A circuit is described which permits a highly-selective transmission-measuring equipment to be designed to meet a specified accuracy of measurement; it is suggested that ±0.25 db is quite readily obtainable. The basic principles of the method are (a) the direct demodulation of the test signal by means of an identical frequency obtained from an oscillator synchronized to the test tone, (b) discrimination against unwanted line signals obtained by means of low-pass filters, (c) the elimination of the effect of the phase difference between the test and demodulating tones by Barber's two-path method, and (d) the use of an envelope-modulated test signal.

DOI:10.1049/ji-2.1947.0081

出版商:IEE    

年代:1947

数据来源: IET