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Generation, Transmission and Distribution, IEE Proceedings C

Issue 6 • Date Nov 1992

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Displaying Results 1 - 11 of 11
  • System voltage and reactive power control: a computer-assisted manual/automatic concept

    Page(s): 491 - 498
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    The authors describe a new computer-assisted software concept for hierarchic control of voltages and reactive powers in the real-time operation of power systems. The concept uses the local and centralised control levels. The local level employs existing automatic or manually operated control devices on regulating resources. The centralised level applies a superimposed computer-assisted manual control, based on reactive optimal power flow, with a dedicated criterion function dealing with system economy and security. An adaptive system zoning is incorporated in the concept, aimed at the matching, inherently local, character of voltage/reactive power control View full abstract»

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  • Modified theory of modal analysis for the modelling of multiwinding transformers

    Page(s): 505 - 512
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    With a view to optimal representation of multiwinding power transformers under test and service transient conditions, the authors present a modification to a model structure proposed previously by D.J. Wilcox (see ibid., vol.138, no.2, p.121-8, 1991). The development is applicable to all transformers, whether or not account is taken of frequency-dependent parameters and losses. The authors clarify the structural nature of the new modal model by treating the special case where losses are neglected and the parameters are taken to be independent of frequency. The importance of this special case is that it is definitive in revealing the character of the proposed modal approach View full abstract»

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  • Numerical approximation of heat run test results of transformers by means of double exponential and power functions

    Page(s): 469 - 470
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    Two methods of estimating the average oil temperature rise inside a winding are presented. The first method is based on a differential equation of the nonlinear cooling of a uniform body. The second method is a modification of a graphical method given in IEC Publication 76-2 (1976). The first method assures excellent agreement with measurements in the case of OD cooling. The accuracy of the modified graphical method is also quite good. The verification carried out is not sufficient to state whether the methods can be applied to ON cooling. Numerical calculation based on an optimisation method of Fletcher-Powell-Dawidon with golden cut is incorporated. Newton's method is used to calculate the coefficients of approximation functions of a top oil temperature rise and an average winding temperature rise after shutdown View full abstract»

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  • Algorithm for load-shedding operations in reduced generation periods

    Page(s): 478 - 490
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (944 KB)  

    The authors develop an algorithm for the selection of load circuits to shed in periods of reduced generation. After reviewing the requirements and operational constraints in load shedding and circuit restoration, the authors develop strategies for the selection of substations and circuits to be shed and restored. These strategies form the basis of the developed algorithm. Formulae for calculating the operating frequency under overload conditions are derived for systems containing motive and nonfrequency-dependent loads. Based on the operating frequency, formulae for the determination of the load shed size are developed and incorporated in the algorithm. The algorithm is declarative in nature and is implemented using Prolog. A logic approach to represent the information and decision parameters of substations and load circuits is outlined. The structure of the developed software system is described and the system is applied to an application example in which the period of reduced generation lasts for 6 h View full abstract»

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  • Adaptive, rule based fault diagnostician for power distribution networks

    Page(s): 461 - 468
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    A fast, adaptive, rule based fault diagnostician for distribution networks is described. It uses two distinct types of rules. A fixed set of core rules, expressed in terms of breaker trips and bus status, is applied for all faults and networks. For particular cases in which the core rules fail, exception rules are generated by interaction with operators. These rules make use of suitable features of the faulted system, in particular, of the islands formed in the faulted network. The data used by the rules is topological information and the real time data normally available from a modern SCADA system. Test results using a distribution system protection simulator show that the diagnostician is accurate, and that speed compares very favourably with earlier schemes described View full abstract»

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  • Load modelling for generating capacity reliability evaluation using the frequency and duration method

    Page(s): 529 - 535
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    This method makes it possible to determine all major reliability indices: probability and frequency of system deficiency states and the expected energy not supplied to the consumers. Simple two-level daily load models have been suggested. The higher load level is taken to match with the estimated daily load peak and the lower level is usually assumed to be equal to mean value for different days. To investigate the applicability of two-level load models for assessing generation system reliability for planning purposes, a series of comparative analyses of the IEEE Reliability Test System has been performed, applying the exact and various two-level load models. The applicability of two-level models in estimating the absolute and relative system reliability indices is analysed for various generation system structures and load diagram shapes. It has been shown that the two-level load approximation offers a very good estimation of the relative values of all main reliability indices View full abstract»

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  • Design model for electrical distribution systems considering renewable, conventional and energy storage units

    Page(s): 499 - 504
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    A new model to solve the design problem of integrated electrical distribution systems is presented, considering special modelling for the load, different sources-conventional, renewable and energy storage-as well as connection lines. The resulting formulation is a linear programming problem, which is solved by a standard optimisation package. The advantages of this `distributional approach' to the design problem of integrated distribution systems can be clearly seen from the results of the case study. The model determines the optimal size and site of all types of power supply units and connection lines. The same model can also be easily extended for the solution of the distribution expansion planning problem, when the planning period is divided into multiple subsequent stages View full abstract»

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  • Fuzzy expert systems: an application to short-term load forecasting

    Page(s): 471 - 477
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    An expert system using fuzzy set theory is presented for short-term load forecasting. Since most statistical methods for short-term load forecasting rely heavily on weather variables and statistical models, errors may appear in the forecasted hourly loads due to uncertainties in weather variables and statistical models. thus, to have better accuracy, the operators in many utilities try to update the forecasted loads in real time using the records of the past few hours and their heuristic rules. An expert system to perform this updating function is developed. Experienced operators' heuristic rules are imbedded in the knowledge base. The uncertainties in weather variables and statistical models are dealt with using the fuzzy-set theory. To demonstrate the effectiveness of the proposed fuzzy expert system, short-term load forecasting is performed on the Taiwan power system. Test results indicate that the fuzzy expert system is very effective in improving the accuracy of the forecast hourly loads View full abstract»

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  • Short-term scheduling of a pumped storage plant

    Page(s): 521 - 528
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The problem is formulated as a mixed-integer nonlinear program where the prices of energy and spinning capacity are assumed known and where two kinds of constraints are considered: first dynamic plant constraints, concerning the operation of several units and including startup costs and minimum up time requirements, and secondly dynamic reservoir constraints, concerning the operation of the upper and lower reservoirs within specified levels. The consideration of dynamic plant constraints together with dynamic reservoir constraints has never been attempted. It is an extended problem and its solution is difficult to approach. Approaches based on dynamic programming, Lagrangian duality and network flow programming are analysed in view of the extended problem and their advantages and disadvantages are indicated. To bridge the gap between the application range of the programming techniques to this problem of pumped storage scheduling, approximate assumptions and a new approach are proposed View full abstract»

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  • Application of modified modal theory in the modelling of practical transformers

    Page(s): 513 - 520
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The authors discuss validating a new form of transformer model aimed at efficient and accurate representation of power transformers in the calculation of electromagnetic transients arising under service and test conditions, where the duration of interest may be as short as tens of microseconds or as long as 5 ms or more. The principal concern is to confirm that modal models, based on a modified theory of modal analysis, retain their efficient structure when proper account is taken of the effects of transient-flux penetration into a practical core, and consequent frequency dependence of inductive and resistive parameters. this is done by modelling representative test windings on a commercial laminated core and comparing computed results with test results View full abstract»

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  • Production costing using mixed-radix and Winograd Fourier transforms

    Page(s): 536 - 540
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    The application of the mixed-radix fast Fourier transform algorithm and the Winograd Fourier transform algorithm for solving a power system probabilistic production costing problem is proposed. The two algorithms are used to estimate the energy generated by each unit of a generation system directly in the Fourier domain which saves a considerable amount of computational time. A comparison between the two algorithms is provided; both have been applied to the IEEE reliability test system. The results obtained are found to be in close agreement with the results obtained by the basic recursive approach. Sensitivity analysis has been carried out to study the relative efficiency of the two algorithms View full abstract»

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