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Online ISSN 1751-8695 Print ISSN 1751-8687

IET Generation, Transmission & Distribution

Volume 4, Issue 12, December 2010

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Volume 4, Issue 12

December 2010

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    • Optimising the balance between security and economy on a probabilistic basis
      • Author(s): J. He ; L. Cheng ; D.S. Kirschen ; Y. Sun
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 12, p. 1275 –1287
      • DOI:  10.1049/iet-gtd.2010.0039
      • Type: Article
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      • p. 1275 –1287 (13)
        Decision-making methods based on a deterministic criterion, such as optimal power flow (OPF) and security-constrained optimal power flow (SCOPF), have been widely applied to practical power system operation. With these methods, the operating conditions of the power system are classified as secure or insecure based on predefined deterministic criteria. However, such a binary secure/insecure index based on a deterministic analysis does not take into account the relative risks associated with random outages of generation and transmission facilities. Therefore using deterministic decision-making methods such as OPF and SCOPF to balance the security and economy can be unnecessarily expensive. This study proposes an optimal probabilistic security (OPS) approach, which balances security and economy on a probabilistic basis. The objective of the OPS is to minimise the expected social cost, which is the sum of the expected operating cost and the expected interruption cost. An improved particle swarm optimisation technique is used to solve this probabilistic optimisation problem. Unlike other risk-based decision-making algorithms, the OPS is a self-contained decision-making tool, which does not require the definition of an arbitrary risk threshold. The OPS determines operator actions that optimally balance security and economy for given weather and operating conditions. The OPS is compared with the OPF and SCOPF using a six-bus system and the IEEE-RTS.
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      Multi-objective reconfiguration of distribution systems using adaptive genetic algorithm in fuzzy framework
      • Author(s): N. Gupta ; A. Swarnkar ; K.R. Niazi ; R.C. Bansal
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 12, p. 1288 –1298
      • DOI:  10.1049/iet-gtd.2010.0056
      • Type: Article
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      • p. 1288 –1298 (11)
        This study presents an efficient method for the multi-objective reconfiguration of radial distribution systems in fuzzy framework using adaptive genetic algorithm. The initial population for genetic algorithm is created using a heuristic approach and the genetic operators are adapted with the help of graph theory to generate feasible individuals. This avoids tedious mesh check and hence reduces the computational burden. The effectiveness of the proposed method is demonstrated on 70-bus test system and 136-bus real distribution system. The simulation results show that the proposed method is efficient and promising for multi-objective reconfiguration of radial distribution systems.
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      Lightning attachment models and maximum shielding failure current of overhead transmission lines: implications in insulation coordination of substations
      • Author(s): P.N. Mikropoulos  and  T.E. Tsovilis
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 12, p. 1299 –1313
      • DOI:  10.1049/iet-gtd.2009.0685
      • Type: Article
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      • p. 1299 –1313 (15)
        The maximum shielding failure current of overhead transmission lines is an important parameter in evaluating the shielding performance of the lines and in insulation coordination of substations. General expressions for the estimation of the maximum shielding failure current of transmission lines, derived by employing several lightning attachment models in shielding analysis, are presented. An application to typical 110 kV up to 1150 kV overhead transmission lines shows that there is a great variability in maximum shielding failure current among lightning attachment models. The importance of maximum shielding failure current in insulation coordination of substations is demonstrated with the aid of alternative transients program-electromagnetic transients program (ATP-EMTP) simulations. The computed overvoltages impinging on 150 and 400 kV gas insulated system (GIS) substations because of shielding failure of the incoming overhead transmission lines, being dependent upon shielding failure current, vary with the lightning attachment model employed in shielding analysis of the lines. Implementation of the electrogeometric model adopted by IEEE Std 1243:1997 in shielding analysis imposes high requirements on protection of the substations against incoming shielding failure surges.
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      Application of augmented Lagrangian relaxation to coordinated scheduling of interdependent hydrothermal power and natural gas systems
      • Author(s): C. Liu ; M. Shahidehpour ; J. Wang
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 12, p. 1314 –1325
      • DOI:  10.1049/iet-gtd.2010.0151
      • Type: Article
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      • p. 1314 –1325 (12)
        This study proposes an optimisation model for the coordinated scheduling of interdependent electric power and natural gas transmission systems from a joint operator's viewpoint. The objective is to minimise the coordinated social cost while satisfying network and temporal constraints of the two interdependent systems. The joint operator will coordinate hourly schedules to supply natural gas to loads or generate electric power. The authors consider the application of Lagrangian relaxation (LR) or augmented LR to relax the coupling constraints of the two systems. The Lagrangian dual is decomposed into the security-constrained unit commitment subproblem with the hydro coordination and the natural gas allocation subproblem. The application of LR for solving the coordinated problem could cause oscillations in the dual solution which is due to the non-convex characteristics of the coordinated problem represented by integer variables and network constraints. Moreover, with slight changes in multiplier values, the linear cost function of the natural gas well may result in a cycling behaviour of the gas well output between its max and min limits. To avoid numerical oscillations and improve the solution quality, the augmented LR with a piecewise linear approximation of quadratic penalty terms and the block descent coordination technique are proposed. The authors consider the 6-bus with 7-node and the 118-bus with 14-node systems to verify that the applicability of the proposed method to the coordinated scheduling of electric power and natural gas transmission systems.
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      Phase distance relaying algorithm for unbalanced inter-phase faults
      • Author(s): Z.Y. Xu ; S.J. Jiang ; L. Ran
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 12, p. 1326 –1333
      • DOI:  10.1049/iet-gtd.2009.0609
      • Type: Article
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      • p. 1326 –1333 (8)
        This study presents a new fault impedance estimation algorithm for inter-phase faults for the purpose of phase distance relaying of extra high voltage (EHV) and ultra high voltage (UHV) transmission lines. The principle is based on the assumption that the fault arc path is predominantly resistive, and the phase angles of the unmeasured fault point voltage and fault arc path current are equal. This is used to construct the fault impedance estimation equation, which naturally prevents the effects of fault arc path resistance, load current, power swing and load encroachment. PSCAD (simulation software) simulation shows the validity of the proposed algorithm.
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      Ensemble decision trees for phasor measurement unit-based wide-area security assessment in the operations time frame
      • Author(s): S.R. Samantaray ; I. Kamwa ; G. Joos
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 12, p. 1334 –1348
      • DOI:  10.1049/iet-gtd.2010.0201
      • Type: Article
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      • p. 1334 –1348 (15)
        This study proposes ensemble decision trees for phasor measurement units (PMUs)-based wide-area security assessment to provide early warnings of deteriorating system conditions. In the proposed technique, the wide-area response signals in real-time operation are captured after 1 and 2 s fault clearing time, from the respective monitoring buses where PMUs are placed. These wide-area post-disturbance records are processed in time and frequency domains for extracting selected decision features such as the peak spectral density of the angle, frequency and their dot product evaluated over the grid areas called as wide-area severity indices (WASI). WASI are used as input features to train the random forests (RFs) to build effective predictor for early warnings in security assessment. The RF-based learning not only provides high performance accuracy but is also effective in valuing the importance of, and the interaction among, the various WASI input features, for developing the reliable predictor. The RF has been successfully tested for classifying both system-wise and area-wise NERC-compliant contingencies, using 55 196 cases (76% stable) from system operations studied on the Hydro Québec network providing 99.9% reliability.
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      Improved geometric parameterisation techniques for continuation power flow
      • Author(s): A.B. Neto  and  D.A. Alves
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 12, p. 1349 –1359
      • DOI:  10.1049/iet-gtd.2010.0048
      • Type: Article
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      • p. 1349 –1359 (11)
        This study presents efficient geometric parameterisation techniques for the continuation power flow. The Jacobian matrix singularity is eliminated by the addition of the line equations which pass through the points in the plane determined by the variables loading factor and the sum of nodal voltage magnitudes, or angles, of all system buses. These techniques enable the complete tracing of P–V curves and the computation of the maximum loading point for any power system, including those with voltage instability problems that have the strong local characteristics, for which the global parameterisation techniques are considered inadequate. An efficient criterion to change the set of lines, based on the analysis of the total power mismatch evolution, is also defined. The obtained results show that the characteristics of Newton's conventional method are preserved and the convergence region around the Jacobian matrix singularity is enhanced. The computational time required to trace the P–V curve can also be reduced, without losing robustness, when the Jacobian matrix is updated only after the system undergoes a significant change.
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