摘要:

The problem of scattering of electromagnetic waves by a thin conducting flat plate loaded with doubly periodic small circular apertures has been theoretically investigated. An expression for the monostatic scattering cross-section has been obtained by treating the planar array of circular apertures as an array of (a) induced electric and magnetic dipoles and (b) diffracting apertures for parallel and perpendicular polarisations. The effect of punched apertures on the monostatic scattering cross-section has been presented.

DOI:10.1049/piee.1979.0194

出版商:IEE    

年代:1979

数据来源: IET

摘要:

When a body is several wavelengths long, the full matrix required in the method-of-moments solution of Maxwell's equations of electromagnetic theory is too large to be handled economically by present-day computers. A method by which this full matrix is reduced to a sparse matrix is outlined. This approach works best for open structures composed of long wires. It does not work so well for a solid surface. This is illustrated by means of radar-cross-section calculations for some simple shapes.

DOI:10.1049/piee.1979.0195

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The energy and power requirements of sodium/sulphur batteries to meet three different rail-traction applications are considered. Cell design options to meet these requirements are discussed briefly, and it can be shown that the central-sulphur tube-cell design can meet the requirements of the three rail-traction applications. The design features of a central-sulphur cell design are discussed and data are presented to indicate the state of cell development in terms of cell performance, reliability reproducibility and safety. The electrical properties of cells connected in series/parallel arrays for battery operation are discussed, together with battery thermal management and safety. A practical 10kWh battery comprising 176 cells connected as two 11 × 8 series-parallel arrays has been tested, and problems which can arise from overdischarge, thermal management and electrical short circuits are discussed.

DOI:10.1049/piee.1979.0196

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The paper describes experiments on a small double-sided single-phase linear travelling-wave induction motor with overlapping coils. Theoretical and experimental values of thrust and efficiency are compared. Improved by reduced slot harmonics, the travelling-wave machine now rivals the conventional 3-phase linear induction motor.

DOI:10.1049/piee.1979.0197

出版商:IEE    

年代:1979

数据来源: IET

摘要:

This paper presents a theoretical and experimental study of the dynamic performance of a doubly-fed single-frame cascade induction machine which can operate synchronously from rest over a wide speed range. The dynamic electromechanical-system equations are developed and theoretical performance boundaries for stable operation are found and compared with experimental results. The nature of its instability and an easily implemented feedback control which stabilises its operation are both described. It is shown that the machine can be operated as a stable variable-speed brushless machine with controllable dynamic response. Its mechanical construction is potentially only a little more complicated than that of a squirrel-cage induction machine.

DOI:10.1049/piee.1979.0199

出版商:IEE    

年代:1979

数据来源: IET

摘要:

With the use of digital-simulation and hybrid-simulation techniques, investigations have been carried out on the distribution of front time of switching overvoltages caused by line energisation. The effect of front time on flashover probability of a line has been clarified. Further consideration is given to the variation of the front-time distribution due to various parameters such as line length, source inductance and so on.

DOI:10.1049/piee.1979.0200

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The ability to determine quickly and accurately where faults have occured on a transmission line has long been an operating man's dream. This paper describes a completely digitalised online fault locator which takes input signals from existing c.t.s and p.t.s and works on a reactance-ratio-measurement principle. It operates in less than two cycles from the instant that the relay delivers a trip output, and is therefore capable of locating transient as well as permanent short-circuit faults. Furthermore, a suitable compensation in fault-locator inputs is proposed which results in increased resistive coverage for the suggested fault locator when applied to double-end feed lines.

DOI:10.1049/piee.1979.0201

出版商:IEE    

年代:1979

数据来源: IET

摘要:

For some time, it has been recognised that conventional capacitor voltage transformers (c.v.t.s) have transient response limitations which affect the performance of modern high-speed protection. To take advantage of existing and new types of distance protective systems, capable of performing accurately withing the first 20 ms of fault inception, a high-fidelity voltage measurement system which overcomes the limitation of conventional c.v.t.s has been developed. The novel high-fidelity voltage sensor comprises a conventional capacitor divider and solid-state amplifier system, the latter being suitable for application with existing designs of capacitor voltage transformer, purpose-designed capacitor voltage dividers, or with capacitor-probe facilities in SF6metal-clad switchgear installations. A summary of the results of the various tests which have led to the development and design of a fully engineered system are described. Reasonable correlation is shown to exist between actual performance of the novel c.d.v.s on the 400 kV system and laboratory tests. Technical performance requirements for high-speed protection covered by the IEC Recommendations, Publications 186, 1969, and 186 A, 1970, and other special requirements are evaluated in a manner which could be used as a basis for design specifications. The paper concludes by considering economic aspects and future possibilities.

DOI:10.1049/piee.1979.0202

出版商:IEE    

年代:1979

数据来源: IET

摘要:

In a rectifier network, or group of such networks, fed by a 3-phase power supply, if the pulse numberpof the rectified voltage is equal to 3 (or a multiple of 3), the primary currents havekp±1-rank harmonics only,kbeing an integer. In this paper, a general demonstration of this property is given, regardless of whether the load is infinitely inductive or not, and without ever specifying the diagram used. This demonstration gives an expression of the peak value of harmonics that makes them much easier to calculate when the rectified current undulation is not neglected.

DOI:10.1049/piee.1979.0204

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A 3-level optimal controller for load-frequency control of a power system which is composed of several subsystems interconnected by asynchronous tie lines is presented. In addition to the conventional control (speed-changer position) of the governor, the d.c. power is considered as a new control variable. The proposed controller minimises the deviations in frequency resulting from sudden disturbance. By means of the multilevel systems concept, the controller of the interconnected power system is decomposed into three levels: d.c. power control (first level), local control (second level) and coordination (third level). Each of the local controllers in the control hierarchy controls a subsystem according to the interaction variables provided by the coordinator. The coordinator is used to improve the interaction variables to achieve global optimality, and then assigns optimal settings for the d.c. power which controls the tie-line flow via the grid control of the convertors. The proposed controller appears to be simple and fast. The work reported in this paper provides some insight into the multilevel control concept for systems with interaction via a control variable.

DOI:10.1049/piee.1979.0205

出版商:IEE    

年代:1979

数据来源: IET