摘要:

Hydroelectric generating sets controlled by conventional, mechanical, temporary-droop governors respond rather slowly to changes in system frequency and do not, therefore, realise their full potential as spinning reserves. Because of this, the electrohydraulic governor system described in this paper was developed for on-site evaluation of control strategies on a 32.5 MW set at Sloy power station, and to complement earlier work on a hybrid simulation of the plant. It is arranged so that it can be used as an alternative to the mechanical governor, and changeover from one to the other can be effected in a few minutes. Frequency-response test data are presented. Also shown are the results of a series of system-splitting tests in each of which a substantial area of West Scotland was supplied by the Sloy set when isolated from the Grid system. An electronic double-derivative governor is shown to improve greatly the response of the generator to frequency changes while at the same time preserving operational stability

DOI:10.1049/piee.1977.0026

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The paper describes how the previously published formulations for an a.c. probabilistic load-flow analysis can be extended to ensure precise computation of expected values, and how these may be used to obtain more precise values of standard deviations and probability-density curves than was possible thereto. Both of the present formulations linearise the problem around the precise expected value, and one of them accounts for the coupling effect between active and reactive powers. It is shown that this coupling effect may have a significant impact on some of the voltages and reactive powers, but little effect on angles and active powers. A typical system is analysed and discussed to illustrate the increased depth of information that can be gained from these improved techniques.

DOI:10.1049/piee.1977.0027

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The commercial incentives to obtain improved control of the steelmaking process in the electric-arc furnace are presented, and the progress made in applying computer control is reviewed. The development of a mathematical model of the refining process is shown to be restricted by the complex metallurgical nature of the process and the deficiency of existing plant instrumentation. The ability of a mathematical model, evolved from theoretical considerations, to simulate, accurately, a limited class of operating practice is demonstrated. A compromise between complexity and implied certainty of the model is obtained by a reduction in the dimension of the model state vector, and by the introduction of a white-Gaussian-noise process to account for the effect of the ignored states and the hypotheses on which the model is developed. Techniques developed recently for obtaining noisecorrupted measurements of the carbon content and temperature of the process are investigated, and the statistics of the uncertainty of these measurements is determined. The implementation of the extended Kalman filter for online state estimation is considered, and the operation of the filter under varied conditions of uncertainty is discussed. A technique for controlling divergence of the filter algorithm is presented, and the results of simulations indicate that estimates of the states can be obtained to the accuracy required for the design of a refining control strategy.

DOI:10.1049/piee.1977.0028

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The infinite timeLQRoptimal control problem is considered, and a relationship is obtained between the optimal return difference matrix and the system matrix. The derivation is based on equivalence of optimal systems and leads to physical interpretation of the result not previously available.

DOI:10.1049/piee.1977.0029

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The maximum instantaneous starting and stopping rates of stepping motors often restrict applications. Three simple methods of increasing these rates by as much as 300% are described. They apply to any type of motor and merely involve the addition of a cheap and simple circuit between the motor and its normal drive. The start/stop rates for the new techniques are predicted by simple methods which can also be usefully applied to the prediction of starting rates under normal operation.

DOI:10.1049/piee.1977.0030

出版商:IEE    

年代:1977

数据来源: IET

摘要:

Ion densities in a closed laboratory due to d.c. corona from an impulse-voltage generator and its charging set have been measured by means of a Gerdien-type aspirator. By comparison with natural ionisation, the densities of ions of the same polarity as the generator charging voltage were increased by two orders of magnitude, but ions of opposite sign were greatly reduced in density. Use of a filtering aspirator yielded information on the densities of ‘large’ ions which were shown to be an important part of the total ionisation occurring under natural and corona conditions. The significance of the results for impulse-voltage testing is briefly discussed.

DOI:10.1049/piee.1977.0032

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The numerical method for computing the growth of ionisation currents in the presence of space charge has now been extended to cylindrically symmetrical discharges. A full description of the method of calculation is given, together with some preliminary results for the experimental conditions of Doran. The growth of the discharge is computed up to the end of the cathode-directed streamer, and predicts the same variation of total current and effective discharge radius that is observed experimentally.

DOI:10.1049/piee.1977.0033

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A combination of time-resolved Schlieren and scattered-light optical techniques has been used to examine the prebreakdown events in dielectric liquids. When a negative high-voltage pulse is applied to the point of a nonuniform gap, a disturbance, associated with discrete shock waves, propagates outwards from the point. For the opposite polarity, the disturbance moves at supersonic velocity, and is characteristically different in appearance and self luminosity. In both cases, the disturbance is identified as a region of closely packed microbubbles which ultimately fragments into isolated bubbles if breakdown does not intervene. The events recorded are explained in terms of cavitation nucleated by transient cavity collapse, and the polarity differences are attributed to field emission. The mechanism is further supported by experimental findings using prestressing techniques.

DOI:10.1049/piee.1977.0034

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The ideal a.c. bridge would include a variable conductance standard, but no such component can be made for high frequencies. The need for it can be avoided by working with a slightly unbalanced bridge, in which the unbalanced signal is a measure of the conductance of the specimen. The method is particularly suitable for measurements of dielectric loss, using micrometer-controlled electrodes. There is no restriction on the frequencies which can be used; examples are given of measurements at 0.1 and 30 MHz.

DOI:10.1049/piee.1977.0035

出版商:IEE    

年代:1977

数据来源: IET