摘要:

The principal application of distance relays is for the protection of essential sub-transmission networks and transmission lines operating at EHV and UHV, whose performance depends on various factors. The task of selecting a universal operating characteristic for distance relays is difficult. Although, over the years, different characteristics have been in use, there is a general agreement that the quadrilateral characteristic is superior to other characteristics. This agreement is largely based on application successes. In the first part of the paper, the objective is to introduce the concept of obtaining the operating characteristics by applying the method of pattern recognition.

DOI:10.1049/ip-c.1992.0045

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In the first part of the paper, the limitations of the existing operating characteristic of distance relays were mentioned. With increasing interconnection between power systems, it has become necessary to avoid relay maloperation and obtain operating characteristics adaptive to the operation of the overhead line being protected by it. In this part of the paper, the resulting of applying pattern recognition in designing distance relays with adaptive operating characteristics is reported. In proposing this approach, the stochastic nature of the power system is acknowledged. The purpose is to obtain a near-optimal operating characteristic matching the performance characteristics of the overhead line the distance relay is to protect. A further advantage obtained by this approach is that the distance relay can be organised to generate an online database or learning set which can be further used to tune the operating characteristic and prevent maloperation under stringent duty conditions.

DOI:10.1049/ip-c.1992.0046

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Dynamic tariffs such as RTP (real-time pricing) and day-ahead pricing function as load management tools because they interact with consumer behaviour. Hence analytical models for an electricity supply system with RTP would need to incorporate behavioural models for consumers. These models have to be logically and mathematically consistent and empirically meaningful. The model developed here relies on the concepts of demand elasticity across time, degree of consumer economic rationality and, on the supply side, on the price formation model. The paper explores a range of assumptions in respect of these matters.

DOI:10.1049/ip-c.1992.0047

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The abstract of the paper is to outline the technical and economical factors which characterise the uniform, all solid-state power-flow controller approach for real-time controlled, flex ible AC transmission systems.The unified power-flow controller in its general form can provide simultaneous, real-time control of all basic power system parameters (transmission voltage, impedance, and phase angle), or any combinations thereof, determining the transmitted power. The parameters selected for control can be changed without hardware alterations, e.g. the function of the controller can be changed from that of a phase-shifter to that of a series line compensator, orvice versa, with or without additional terminal voltage regulation and shunt VAr compensation, to adapt to particular short term contingencies or future system modifications.

DOI:10.1049/ip-c.1992.0048

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The effects of frequency dependence, line asymmetry, and varying ground conductivity on ultrahigh speed, travelling wave based, single ended, protection schemes are investigated in this paper. Typical schemes assume the transmission lines to be balanced and frequency independent which simplifies the analysis of the fault transients. Investigation of a single circuit vertically configured transmission line reveals that better results can be obtained by using modal parameters based on the configuration of the transmission line. The problem of modal mixing at discontinuities on the transmission line is demonstrated in the case of an unbalanced line to ground fault. The results described in this paper have applications in both protection and fault location schemes.

DOI:10.1049/ip-c.1992.0049

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A new parallel algorithm for estimation of parameters of sinewave, distorted by DC exponential signal and contaminated by noise, is proposed. The method may be seen as an extension and generalisation of the standard least-squares (L2-norm) optimisation approach. The advantage of the developed algorithm is that it is more robust with respect to the modelling error and impulsive (wild) noise than when a standard least-squares criterion is employed. The implementation of the algorithm by a suitable adaptive analogue network is also given. Computer simulation results are presented to confirm the validity and performance of the proposed network. The proposed method seems to be particularly useful for real-time high-speed and low-cost estimation of parameters of sinusoidal signals.

DOI:10.1049/ip-c.1992.0050

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A flux linkage model for a three-phase five-legged transformer is derived for the first time. The effects of mutual and leakage inductances, saturation, eddy current loss, hysteresis and residual fluxes of the nonlinear iron core are included. A straightforward and novel method for determining both the apparent and incremental inductance matrices for a loaded two-winding five-legged transformer is derived. Simulations presented in this study are based on apparent inductance (λ/i) rather than incremental inductance (dλ/di) because this approach was found to be preferable for predicting the behaviour of the laboratory transformer used. Eddy current and hysteresis losses are combined into one core loss term which is accounted for by a voltage-dependent resistance load on the secondary. The flux in each segment of the iron core and in the air gaps and tank are computed at each step. The model thus yields a completely detailed description of the transformer's behaviour. A predictor-corrector algorithm written in FORTRAN is used to solve the set of nonlinear differential equations that describe the transformer. A 386-based computer has been used to generate voltage and current waveforms faithful to laboratory data. Transformer inrush current and ferroresonance are selected as test cases because of the extreme computational demands that these transients place on the computer model. The model can be implemented using only nameplate and conventional test data along with theB-Hcurve of the core material. The method is thus well suited to the practical needs of engineers in industry.

DOI:10.1049/ip-c.1992.0051

出版商:IEE    

年代:1992

数据来源: IET

摘要:

System designers need to know the maximum current which may flow in any system component to ensure that otherwise healthy plant is not put at risk due to a fault in other equipment. This is particularly the case for switch-gear which is required to interrupt fault current safely and to close and latch safely for the maximum peak current, including any DC offset, when closing onto a fault. Historically, within switchgear specifications contributions from synchronous machines have formed the basis for this duty. In these specifications, the relationship between make and break duty is given by a factor of 2.55 or, more recently, 2.5, and in the calculation of the break duty an allowance may be made for any current decrement in the time interval between the initiation of a fault and the instant of contact parting. It has been realised that large three-phase induction motors make a contribution to both break and make duty and that, due to the rapid decrement of their contribution, the 2.55 factor is inadequate. It is shown by means of calculation and test results that even small single-phase induction motors make a contribution to switchgear make duty. For the present, it is necessary to calculate both the make and break duty, but it is suggested that, for the longer term, the relationship between break and make should be raised, possibly to a factor of 3. Failure to allow for the higher make duty may lead to dangerous conditions on a system.

DOI:10.1049/ip-c.1992.0052

出版商:IEE    

年代:1992

数据来源: IET