摘要:

The stage now seems set for developing h.f. coaxial cables whose attenuation is significantly reduced by employing a hybrid wave instead of the usual TEM mode. Owing to the complexity of design calculations made from the basic equations, it seemed desirable to attempt a simplified analysis, sufficient to give a first approach to the problems of determining the parameters required in any given case. The paper gives details of the approximate expressions so derived and illustrates their application to particular examples.

DOI:10.1049/piee.1968.0040

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The noise figure of the 4-frequency parametric amplifier investigated can be lowered substantially by deviating from power matching, as is shown by experiments performed on a low-frequency-amplifier version. This adjustment has the additional advantages of providing a larger gain-bandwidth product, an improved gain stability and a higher gain saturation. The theoretical optimums in minimum noise figure, maximum bandwidth and the associated gain stability are calculated for the case when power mismatching is permissible, and the results are compared with the experimental values and with the theoretical performance of the reflection-type amplifier employing a circulator.

DOI:10.1049/piee.1968.0041

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The relation in phased arrays between the element spacing, the array-excitation autocorrelation function and the space angular frequency of the field is examined. A method of choosing element spacings in thinned arrays based on a choice of the optimum autocorrelation function is described.

DOI:10.1049/piee.1968.0042

出版商:IEE    

年代:1968

数据来源: IET

DOI:10.1049/piee.1968.0043

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Work on an experimental turntable rig built to simulate a commutator has demonstrated that, as a direct voltage between the two brush arms is increased, (a) the tendency to form short arcs from a brush to the segment leaving the brush increases and (b) the persistence of the associated bar-to-bar arcs increase suddenly. Invariably, the intersegmental arcs are initiated at the positive brush. Once a continuous series of intersegmental (bar-to-bar) arcs exists between the brush arms, a flashover takes place. High-speed ciné photography has shown also that the intersegmental arcs increase rapidly in intensity and that the discharges are propelled into the air above the surface of the commutator to a distance of about 1 in by a process known as ‘jetting’. Under these conditions, the arc current is increasing extremely rapidly, producing a mass of ionised gas above the commutator. This behaviour, and the damage produced, is consistent with features noted on large machines after flashover, and it is likely that this mechanism of flashover applies to such machines also.Having established that the major flashover mechanism in the experimental rig involves a continuous string of intersegmental arcs, the basic properties of such arcs and means of extinguishing them rapidly were investigated. Clearly flashover can be prevented either by restricting the formation of short arcs or by extinguishing them quickly. Two simple mechanisms of extinguishing the arcs have been studied: an electromagnetic method which propels the arc rapidly along the gap to the edge of the commutator where it is extended and extinguished and a method using an airblast.

DOI:10.1049/piee.1968.0045

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Improved dynamic performance of a turboalternator may be achieved by the use of a 3-term prime-mover governor. Integral-of-speed and derivative-of-speed signals can be generated and combined with the conventional velocity signal, which then controls the input power. Transfer functions for the synchronous machine, turbine and governor mechanism are obtained from linear theory, and the frequency responses of the system operating with different prime-mover controller configurations are given on Bode diagrams. Interaction between the prime-mover steam-flow controller and the terminal-voltage exciter-field regulator is ascertained for a range of system operating conditions.

DOI:10.1049/piee.1968.0046

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The ease with which transistor comparators for distance relays can be designed for high-speed operation must be tempered with consideration of overall performance and integrity of operation. Operating speed must be defined over the whole of the working range of the relay, and neither the speed nor the measuring accuracy should be unduly affected by the severe transients generated by modern e.h.v. networks. The comparator, as well as being proof against damaging voltage surges, must operate accurately in the presence of long-duration offset transients accentuated by low-loss modern-plant parameters and the random point-on-wave inception of faults due to natural hazards and closure or reclosure of modern pressure-head circuit breakers. The attainment of high-speed operation under these practical conditions precludes the adoption of many, apparently practical transistor-comparator circuits and favours the adoption of circuits with well defined dynamic performances.Extensive laboratory investigation has shown that the block-average comparison principle is amenable to precise design in all respects, and practical fast-operating relays can be designed with good transient-free characteristics. The results obtained on such a practical relay are presented in the paper for a phase comparator with a polarised-mho characteristic. It is shown that a minimum inherent operating time of one halfcycle of the power frequency can be defined for this comparator arrangement and that both the static and dynamic operating characteristics are predictable over the whole working range. Equivalent performance for the amplitude-comparator counterpart is justified in an appendix, and underlines earlier work.Relays using the block-average comparison principle have been used successfully in field trials since 1957, and this principle now forms the basis for various production designs. Sufficient field experience is now available to justify the theoretical analysis and laboratory test results given in the paper.

DOI:10.1049/piee.1968.0047

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The paper reviews the use and purpose of automatic-reclosing circuit breakers and pole-mounted reclosers in controlling 11–66kV overhead power lines in Great Britain. The operational performance of 11 kV overhead lines is analysed and the improvement that can be obtained using high-speed tripping and reclosing techniques is described. The principles involved in obtaining the optimum system performance are stated. The extension of automatic reclosing to the higher distribution voltages is discussed and possible future developments are suggested.

DOI:10.1049/piee.1968.0048

出版商:IEE    

年代:1968

数据来源: IET

DOI:10.1049/piee.1968.0050

出版商:IEE    

年代:1968

数据来源: IET

DOI:10.1049/piee.1968.0051

出版商:IEE    

年代:1968

数据来源: IET