摘要:

A method is described of calculating the effect of large induction motors on the transient performance of a multimachine power system under fault conditions. The representation of an induction motor is similar to that used for synchronous machines, and is therefore suitable for describing composite systems. The method is based on Park's equations and, unlike earlier methods, allows for the ‘deep-bar effect’ usually present in large cage induction motors. The most accurate result is obtained by using the full set of equations, but more approximate methods using simplified equations are considered. The method is verified by tests on model machines connected by impedances representing transmission lines. Preliminary tests were made on a simple system comprising an induction motor connected to an infinite busbar through an impedance, and were followed by tests on a composite system containing a synchronous machine and an induction motor connected in parallel parts of the system. The results slow that good results are obtained with the accurate calculation which, however, requires a large amount of computer time, but that any approximation introduces considerable error.

DOI:10.1049/piee.1971.0269

出版商:IEE    

年代:1971

数据来源: IET

摘要:

To prevent undue radio interference and energy loss from overhead conductors, the permissible operating stress must be minimised. Therefore, the design of such conductors was investigated theoretically using a conformal transformation proposed by Timascheff. First, the effect of the design parameters, that is, the subconductor diameter, subconductor spacing, number of subconductors and phase spacing on the maximum surface stress, was considered. This showed that the surface stress decreases as the subconductor diameter, number of subconductors and phase spacing is increased. It also showed that there is an optimum subconductor spacing at which the surface stress is a minimum. Secondly, an equation defining the optimum subconductor spacing was determined. From this equation, it was found that the optimum spacing is affected by all the other parameters, and that subconductor spacings close to the optimum can be justified economically. Finally, the general design of conductor systems was discussed, and possible conductors for a 765kV system were computed using optimum spacings. This showed that the total conductor material is considerably reduced and that the overall diameter of the bundle remains unchanged with an increasing number of subconductors. A suggested computational method for determining possible conductor systems was also described.

DOI:10.1049/piee.1971.0271

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper describes a design study for a 750 MVA 33 kV superconducting a.c. power cable. Conductor and dielectric design, thermal insulation and refrigeration and methods of construction and installation are all considered. Niobium is the chosen conductor material, and a triple coaxial construction the chosen conductor geometry. The capital costs of the systems considered are estimated to be rather more than twice that of the equivalent 275kV conventional oil-filled cables. The running costs are about the same as that of the conventional equivalent, but represent only a small proportion of the total cost. Problems which need further study and development work, and whose solution could lead to significant design improvements and cost reductions, are: (a) protection of the conductors against current overload, (b) thermal contraction and (c) dielectric design. It is concluded that, though superconducting cables are unlikely to be economical at the power level considered in the study, they may find application in the multi-GVA region.

DOI:10.1049/piee.1971.0272

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper presents a method of designing digital controllers for randomly disturbed single-input/single-output linear systems with time delay which minimise the cost functionE{y2t+k+λu2t}. The process and noise models used are those obtained from current identification programs, and the control law developed has significant advantages over standard minimum-variance designs. (a) There is no difficulty with nonminimum-phase systems. (b) For processes with constraints on control effort, a marked improvement in the resultant output variance can be achieved. (c) There is a flexibility in the design to deal with cases where the closed-loop performance becomes unsatisfactory because of parameter drift or other causes. A typical example of the design procedure is given, and a comparison between the new control law and a minimum-variance law is made.

DOI:10.1049/piee.1971.0275

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The problem of determining the least order of transfer-function matrices without computing a minimal realisation is considered. A new method is developed for determining the least order of a proper transfer-function matrix, and an algorithm is presented which is computationally attractive.

DOI:10.1049/piee.1971.0276

出版商:IEE    

年代:1971

数据来源: IET

摘要:

By considering the solution of the differential equation governing the current delivered, via a thyristor bridge, to a seriesR-Lload, an exact nonlinear difference equation relating the current at consecutive firing instants is established. The behaviour of the system, both statically and dynamically, is thereby examined and use is made of transition-mapping concepts. Perturbational analysis is performed to linearise the equation and it is demonstrated that the system can be considered as a discrete controller with proportional and derivative control having a varying time constant. Computer simulation and experimental results are presented as evidence of the validity of the developed models.

DOI:10.1049/piee.1971.0277

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The calculation of the transient response corresponding to a given frequency response is a problem of numerical inversion of a Laplace transform. Two methods are presented: a very economical method, which is suitable only for a limited class of Laplace transforms, and a general method. FORTRAN programs for both methods are described. The general method is compared with other general methods.

DOI:10.1049/piee.1971.0278

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The effect of humidity, polarity and irradiation on the 1/50μs impulse voltage breakdown and time lag of standard rod gaps has been determined for a range of spacings from 5cm to 30cm and a range of humidities from 1g/m3to 24g/m3. An anomalous condition is reported for a 5cm unirradiated gap under positive impulses in which the slope of the humidity characteristic is opposite to that normally obtained. It is shown that, although the time lag is independent of humidity, the probability of breakdown in the sigmoid region is not independent of humidity.

DOI:10.1049/piee.1971.0279

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The prebreakdown phenomena of impulse corona, corona propagation and leader propagation in the standard rod gap in air have been studied for spacings of up to 30 cm. The variations occurring in the measured quantities of corona-current amplitude, time of occurrence, corona-propagation time, corona speed, number and length of steps in the leaders, leader-propagation time and leader speed are correlated to the variations in the conditions of gap length, applied voltage, humidity and irradiation. The results of the prebreakdown phenomena have been shown to explain the characteristics of impulse breakdown of the rod gap.

DOI:10.1049/piee.1971.0280

出版商:IEE    

年代:1971

数据来源: IET