摘要:

The paper describes the originalraison d'etreof consulting engineers, their activities and the part played by them in the early years of the electricity supply industry in the UK. It then traces the work of consultants in the large projects, mainly overseas, during the 1960s and 1970s. More recently the prolonged worldwide recession, the desire for more involvement of the client's engineering personnel and the need for their training have brought about widespread changes in thinking, collaboration and areas of activity of the consultant. These changes are reflected in project funding by the major world lending agencies. Increasing levels of bilateral lending and disbursement of grants by Western Governments as a vehicle for overseas aid and the simultaneous support of indigenous industry is now also apparent. With increasing competition for fewer large projects overseas, the development of ‘UK Limited’ with shareholders in the financial and industrial sectors, and UK central Government, is a desirable objective. The recent replacement of the engineering ‘mega projects’ by smaller ones, often involving widespread plant refurbishment, now characterise the current activities of consulting engineers. An increase in the amount of UK based work is also apparent as UK Government policy dictates the increased use of private sector consultants. Much of this is now in the electrical and mechanical building services area in which the consulting profession in the UK (and the IEE) have a considerable stake. The need to involve consulting engineers in research and development in their home country is justified and the paper ends with some comments on the present trends in selecting consultants mainly on the basis of fee competition.

DOI:10.1049/ip-c.1987.0015

出版商:IEE    

年代:1987

数据来源: IET

摘要:

A micromachine is described for use in studies of standstill (particularly frequency-response) test methods for obtaining the transient impedance parameters of a tubogenerator. The severe design compromises associated with dynamic micromachines are completely avoided, rotor induced-current field and magnetic nonlinearity being correctly scaled. Advantages for the micromachine are listed and a detailed specification provided. First tests, in open-circuit field configuration, have shown the effect of surface contact resistance of aluminium wedges to be very pronounced, as is coming to be recognised in turbogenerator studies. Tests with wedges removed are compared with field computations, and with new data (obtained from installed probes) on the measured effectiveness of inducedcurrent paths in wedges and teeth. Standstill frequency-response measurements are possible in the micromachine up to 20% current, contrasting with 0.5% in a turbogenerator. Measurements of operational inductance and transfer function, over a full frequency range, thus show for the first time the changes that occur as excitation increases above the low-Brange of magnetic nonlinearity. It becomes clear that the standard procedure for adjusting only the mutual branches of thed- andq-axis equivalent circuits, to allow for this nonlinearity, is inadequate.

DOI:10.1049/ip-c.1987.0016

出版商:IEE    

年代:1987

数据来源: IET

摘要:

A discrete version of a variable structure controller (VSC) for load frequency control of a two-area thermal and multiarea interconnected power system is presented in this paper. System nonlinearities, such as generation-rate constraint and governor dead band, have been included in the simulation studies. Comparative studies between conventional integral control and variable structure control, conducted on a multiarea power system show the effectiveness of VSC.

DOI:10.1049/ip-c.1987.0017

出版商:IEE    

年代:1987

数据来源: IET

摘要:

Compensation methods are computationally simple methods of quickly finding changes to an existing nodal-voltage solution of a linear network when changes are made to the network topology or parameters [1]. This paper investigates the efficient detection of ‘singular’ networks and computational instabilities, which can occur during a compensation process, in order to prevent physical maloperations and the propagation of computation errors. These singular networks include those which have no solution, multiple solutions or an island (totally disconnected subnetwork). Efficient methods are given for the detection and identification of an island, for continuing the compensation process both in the main network and in the island, and for reconnecting the main network to the island so that compensation methods can continue as usual for the reconnected network. Extensions of the method efficiently deal with the removal of a short circuit of a branch (opening a switch), for which case the standard method always fails because of the singularity of the nodal impedance matrix when there is a short circuit.

DOI:10.1049/ip-c.1987.0018

出版商:IEE    

年代:1987

数据来源: IET

摘要:

The adoption of voltage-controlled oscillator based firing systems has almost completely eliminated the harmonic instabilities experienced in early HVDC systems. However, the basic feature of such systems (equidistant firing) is adversely affected by the feedback action of the current control loop, since the direct current may contain uncharacteristic harmonics which are not filtered out by the controller. Under certain circumstances (such as an imbalance and/or a distortion in the alternating voltage, DC-or AC-side resonances near DC or AC harmonic frequencies, respectively) instabilities may occur which are characterised by oscillations synchronised with the alternating voltage, i.e. harmonic instabilities. Nonlinear control-system theory, namely the describing-function method, was used to show that these oscillations are limit cycles whose conditions of occurrence can be predicted. A detailed computer model for an hvdc link was developed which allows the calculation of both the DC and the AC harmonics in the steady state and the describing function for subharmonics of the firing frequency of the convertor. Limit cycles can be predicted by the Nichols chart technique.

DOI:10.1049/ip-c.1987.0020

出版商:IEE    

年代:1987

数据来源: IET

摘要:

A method for the computation of transmission-line transients is proposed which takes into account the frequency dependence of the conductor and earth series impedances, and the travelling-wave reflection and refraction phenomena caused by discontinuity points present in the system. The use of the discrete Fourier transform (DFT) and variable-step sampling in the frequency domain greatly reduce the amount of computer time and memory needed for this method. As an example, a practical case is examined.

DOI:10.1049/ip-c.1987.0021

出版商:IEE    

年代:1987

数据来源: IET

摘要:

Certain key principles of insulation coordination quoted from IEC publications are examined and shown to be sufficient to cover all voltage stress situations, only if all factors involved are considered. The complexity of insulation co-ordination is illustrated by examining cases covering different types and configurations of insulators, different load stress amplitudes and shapes, and considering the effects of system layouts.

DOI:10.1049/ip-c.1987.0022

出版商:IEE    

年代:1987

数据来源: IET

摘要:

Substation automation has, as its prime objective, the need to satisfy the increasingly demanding requirements of the power systems concerned. The most important requirement is to ensure that the power system, as a whole, is operated and controlled in the most effective, secure and economic manner possible. In HV and EHV substations, decisions must be taken quickly and safely to achieve rapid restoration of supply and speedy return to normal operating conditions following a substation equipment fault or other substation abnormality. The paper presents interactive techniques for substation automation by describing the models and computational techniques that have been developed to model the substation configuration and detect the available restoration operations following a fault in substation equipment. These techniques recognise the existing, at the time of fault, operational configuration of the substation by inputting the operating states of the breakers and isolators. The increased and more meaningful information of substation operation that can be gained from these techniques is illustrated by the analysis of a typical Hellenic high-voltage substation.

DOI:10.1049/ip-c.1987.0024

出版商:IEE    

年代:1987

数据来源: IET

摘要:

In the analysis of harmonic power flows, the transformer is generally represented as a passive component. However, due to the magnetisation nonlinearity, the transformer constitutes a source of harmonic currents which can aggregate and cause substantial waveform distortion. This paper describes the development of a Norton equivalent circuit which accurately represents the transformer magnetising branch in harmonic power-flow studies. It is shown that even in the absence of other nonlinearities in the system, the transformer magnetising current can give rise to considerable harmonic voltage levels.

DOI:10.1049/ip-c.1987.0025

出版商:IEE    

年代:1987

数据来源: IET

摘要:

An investigation has been carried out into possible methods of oil-leak location in pressure-assisted cables. A hydraulic method of leak location, making use of the cable resistance to oil flow and involving measurements of pressure and flow at both ends of the cable is suggested as the most viable alternative to the present freezing technique on 3-core cables. The same principle can also be applied to single-core cables. The method was first tested in the laboratory using a long length of small-bore pipe to simulate a cable and the accuracy of location was repeatedly better than 1% of the total length. A small number of initial field trials on various types of cables provided useful information on the factors affecting the accuracy of locating actual leaks. Subsequent location tests on a wide variety of cables which developed leaks whilst in service, have proved highly successful. In most cases it was possible to correctly identify the leak position, without the need for freezing. The reasons for the variations in accuracy of test results together with practical problems are discussed.

DOI:10.1049/ip-c.1987.0026

出版商:IEE    

年代:1987

数据来源: IET