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IEE Proceedings C (Generation, Transmission and Distribution)

Volume 138, Issue 6, November 1991

Volumes & issues:

Volume 138, Issue 6

November 1991

Recursive real-time calculation of basic waveforms of signals
Reliability assessment of hydrothermal generation systems containing pumped storage plant
Stability of loadflow techniques for distribution system voltage stability analysis
Identification of generalised models of synchronous machines from time-domain tests
  • Author(s): I. Kamwa ; P. Viarouge ; E.J. Dickinson
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 6, p. 485 –498
  • DOI:  10.1049/ip-c.1991.0063
  • Type: Article
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  • p. 485 –498 (14)
    Recent developments have shown that numerical models of synchronous machines are, in many cases, improved by introducing an increased number of dampers or dynamic constants. The major issues affecting the model identification by such an extension, which in fact becomes necessary when the machine possesses a solid rotor are discussed from a time-domain point of view. The first result is that all methods which determine the equivalent circuit from test data in an indirect manner, by using the time constants or operational impedances as intermediate tools, give rise, along the d-axis, to systematic errors in the sub-transient and sub-subtransient time constants of the estimated circuits. Unfortunately, when the identification experiment is the standard short circuit, even the direct method suffers from the drawback of weak identifiability of the model, with the result that the uniqueness of the equivalent circuit, directly estimated from test data, is not at all guaranteed. In fact, from an information content point of view, the richer tests are those made at standstill, with a perfect decoupling between the two axes. It is demonstrated by simulation that if the direct approach is applied to such a test, with pulse wave modulated (PWM) voltages as the excitation signals, a numerically cheap and accurate one-step procedure for time-domain identification of circuit models is obtained.
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Probabilistic voltage stability indexes
  • Author(s): T.A.M. Sharaf  and  G.J. Berg
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 6, p. 499 –504
  • DOI:  10.1049/ip-c.1991.0064
  • Type: Article
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  • p. 499 –504 (6)
    A probabilistic voltage stability index is proposed: the expected voltage instability proximity. To account for the system elements' forced outages, elements are represented by a two-state model. The resulting statespace is truncated by using a practical technique. Voltage stability is assessed for the truncated statespace by using sensitivity parameters that are evaluated from a fast decoupled load-flow contingency analysis exploiting optimal ordering and sparsity techniques. Voltage stability worst scenario is defined, and critical system elements are identified along with the probability of worst scenario to occur. Evaluation and use is demonstrated for a 30-bus system.
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Modelling of large nonlinear loads and thyristor controlled shunt compensators
  • Author(s): C.K.K. Tang  and  D.R. Turner
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 6, p. 505 –517
  • DOI:  10.1049/ip-c.1991.0065
  • Type: Article
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  • p. 505 –517 (13)
    The experimental modelling of large nonlinear loads (such as arc furnaces), their supply systems and reactive shunt compensation is described. The laboratory model can be programmed to draw a load current which is a scaled copy of a system load or any other waveform that may be required. The modelling of the compensator is based on a thyristor controlled shunt reactor (TCR), using a fast, but very simple, integral of voltage controlling algorithm. Using a variety of amplitude modulated and synthesised load current waveforms it is shown how the frequency response of the compensator can be determined, indicating that there is a range of modulating frequencies over which the compensator is effective in reducing the voltage fluctuations, whereas for higher modulation frequencies its effect is to increase these fluctuations. The results of the laboratory model are compared with those from a mathematical model, with good agreement. The ability of the equipment to model a 56 MVA electric arc furnace is described and it is shown that to model such a load mathematically, a degree of randomness has to be introduced into the synthesised current waveform. Spectral estimation techniques are used to judge both the laboratory and mathematical models' performances and the reader's attention is drawn to some of the problems associated with the use of such techniques.
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Artificial intelligence algorithm for daily scheduling of thermal generators
  • Author(s): K.P. Wong  and  K. Doan
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 6, p. 518 –534
  • DOI:  10.1049/ip-c.1991.0066
  • Type: Article
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  • p. 518 –534 (17)
    An artificial-intelligence-based algorithm is developed for scheduling thermal generators in a 24-hour schedule horizon. The primary requirement of meeting the daily system load demand and spinning reserve, the ramp rate characteristics and minimum up and down times of units, and the operational constraints including the crew constraints, station synchronisation intervals, station shut-down intervals and the allowable operating limits of units, are incorporated in the algorithm. The scheduling algorithm consists of an algorithm for the run-up-to-peak period, an algorithm for the period between the midday and midafternoon peaks and an algorithm for the end-of-day decommitment period. The algorithms are based on the heuristic-guided depth-first search technique. A ‘look-ahead’ and ‘constraint satisfaction’ technique is also developed in the algorithm for the scheduling period between the midday and midafternoon peaks. The combinatorial explosion in the search space of the scheduling problem is greatly reduced by the use of the heuristics derived, some of which are based on economic considerations. A method for further reducing the search space to a manageable size is also developed. In addition, a new and recursive algorithm for solving the power dispatch problem is developed. This algorithm is employed in the 24-hour scheduling algorithm in the process of evaluating the costs of the generated schedules. The application of the developed scheduling algorithm to schedule ten thermal generators, implemented in Prolog, is presented.
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Partitioning of power networks and applications to security control
  • Author(s): V.H. Quintana  and  N. Müller
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 6, p. 535 –545
  • DOI:  10.1049/ip-c.1991.0067
  • Type: Article
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  • p. 535 –545 (11)
    The performance of power-system application programs, such as online contingency analysis and security control, VAR control etc, can be significantly improved by partitioning a power network into strongly connected subnetworks, and by using only the most appropriate subnetworks. Unreferred portions of the network can be modelled by an external equivalent that reduces each unreferred subnetwork to a single PV busbar. A network partitioning algorithm based on the electrical distances among the system busbars is proposed. The proposed technique clusters interdependent busbars together and weakly connected busbars are placed in different clusters. The proposed partitioning technique is applied to small and medium size power system networks. Results are also presented on the use of the partitioning technique in a security-control algorithm for alleviating system emergencies (thermal overloads and voltage violations) by transmission branch and shunt device switching, and real and reactive power generation rescheduling.
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Identification of coherent generators for power system dynamic equivalents using unstable equilibrium point
  • Author(s): M.H. Haque
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 6, p. 546 –552
  • DOI:  10.1049/ip-c.1991.0068
  • Type: Article
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  • p. 546 –552 (7)
    A new technique for identifying coherent generators in dynamic equivalencing of large power systems is presented. Coherency of generators in the early part of the transient period is determined by directly checking the relative rotor angle deviations. This requires the prefault angles, faulted angles and the angles at the unstable equilibrium point corresponding to the expected mode of system instability. The faulted angles are estimated by the Taylor series expansion and the unstable equilibrium point is computed by the Davidon-Fletcher-Powell method in the centre of angle reference frame. The method also requires a checking on the admittance distances between the generators to maintain coherency for the later part of the transient period. The proposed method was tested on two power networks and the results obtained were perfectly matched with those found from direct examination of swing curves. The results obtained by the proposed method were also compared with some other reported methods.
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Integrating an expert system into a thermal unit-commitment algorithm
  • Author(s): Md-Sayeed Salam ; Abdul-Razak Hamdan ; Khalid Mohamed-Nor
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 6, p. 553 –559
  • DOI:  10.1049/ip-c.1991.0069
  • Type: Article
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  • p. 553 –559 (7)
    An expert system has been developed by combining the knowledge of experienced power system operators and unit commitment experts to assist operators in scheduling thermal generating units. The expert system is used as a preprocessor as well as a postprocessor to the truncated dynamic-programming based unit commitment program to obtain an operationally feasible and/or preferable solution. The operator's interaction with the expert system is minimised by transferring all the relevant data and results of the unit commitment program to the expert system as a knowledge base. Some of the complex operating constraints that are not violated frequently and/or are difficult to include in the unit commitment program are enforced by the expert system.
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Effects of underexcitation limiters on operation of remote generating station
Minimisation of uncharacteristic harmonics in HVDC convertors through firing angle modulation
Reply: Minimisation of uncharacteristic harmonics in HVDC convertors through firing angle modulation

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