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Online ISSN 1752-1424 Print ISSN 1752-1416

IET Renewable Power Generation

Volume 1, Issue 2, June 2007

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Volume 1, Issue 2

June 2007

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    • Wind turbine dynamic response–difference between connection to large utility network and isolated diesel micro-grid
      • Author(s): J.A.M. Bleijs
      • Source: IET Renewable Power Generation, Volume 1, Issue 2, p. 95 –106
      • DOI:  10.1049/iet-rpg:20060024
      • Type: Article
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      • p. 95 –106 (12)
        The difference in dynamic behaviour of wind turbines connected to different size networks is analysed for synchronous and induction generators. Modal analysis has been applied to equivalent mechanical models of the wind turbine generator and the grid connection to show the difference in dynamics for a wind turbine generator connected to a large (interconnected) utility network or an (isolated) diesel micro-grid. Frequency domain analysis of these models has been used to quantify the effect of system parameters, such as enhanced drive train damping, diesel governor action and generator slip, on dynamic interaction. It has been shown that for wind turbines connected to a large grid an induction generator can reduce dynamic interaction. In contrast, for an isolated diesel micro-grid the diesel governor response and the compliance of the diesel generator dominate the system's dynamics, and the choice of either generator option for the wind turbine is dictated by other factors.
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      Electrical collector system options for large offshore wind farms
      • Author(s): G. Quinonez-Varela ; G.W. Ault ; O. Anaya-Lara ; J.R. McDonald
      • Source: IET Renewable Power Generation, Volume 1, Issue 2, p. 107 –114
      • DOI:  10.1049/iet-rpg:20060017
      • Type: Article
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      • p. 107 –114 (8)
        The work presented is part of the EC FP6 DOWNVIND project activities, which focus on the requirements and implications of very large offshore wind farms. A comparative analysis of various design options for the electrical collector system of large offshore wind farms is presented, and the advantages and disadvantages in terms of their steady-state performance and economics are discussed. The case under consideration is that of a proposed 1-GW wind farm located off the northeast coast of Scotland. The impact on power losses and voltage level changes on the collector system busbars are investigated under various operating conditions. Contingency conditions of losing one of the cables to the hub end are also explored for collector system designs with redundant cables. Finally, the authors introduce an alternative design, based on conceptual ringed arrangements, and its advantages are illustrated and discussed.
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      Probabilistic three-phase load flow for unbalanced electrical distribution systems with wind farms
      • Author(s): P. Caramia ; G. Carpinelli ; M. Pagano ; P. Varilone
      • Source: IET Renewable Power Generation, Volume 1, Issue 2, p. 115 –122
      • DOI:  10.1049/iet-rpg:20060013
      • Type: Article
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      • p. 115 –122 (8)
        A probabilistic method is proposed to take into account the uncertainties of loads and wind production in electrical unbalanced distribution systems. The proposed method is based on Monte-Carlo simulation applied to the nonlinear three-phase load flow equations including wind farms, thereby taking into account all load and line unbalances that can characterise the distribution systems. The method allows the evaluation of phase-voltage and unbalance factor probability functions and in particular the maximum values and 95th percentiles, being the statistical measures of greatest interest in many international standards for power quality. Numerical applications are presented and discussed with reference to the three-phase unbalanced IEEE 34-bus test distribution system in presence of wind farms connected at different busbars.
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      AC and DC aggregation effects of small-scale wind generators
      • Author(s): N. Stannard ; J.R. Bumby ; P. Taylor ; L.M. Cipcigan
      • Source: IET Renewable Power Generation, Volume 1, Issue 2, p. 123 –130
      • DOI:  10.1049/iet-rpg:20070001
      • Type: Article
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      • p. 123 –130 (8)
        Small-scale embedded generation (SSEG) has the potential to play an important part in the future UK generation mix. If a single SSEG is considered, its environmental, commercial and network operational value is low, but if a cluster of SSEGs are considered and their outputs aggregated they have the potential to be significantly more valuable. The aggregation of small-scale wind generators is considered. Each turbine is driven by a wind that is turbulent in nature and varies from location to location. The output from an individual turbine can be very variable, but when aggregated together with the power output from a number of turbines in the same locality, can produce a power output that is much less variable. The authors examine, by simulation, how the output from a number of small turbines can aggregate together to form a more consistent power output. Aggregation of the turbine outputs both after the power inverter, at alternating current (AC), and before the inverter, at direct current (DC), are examined. In both cases power variations are shown to reduce as the number of turbines connected increases. Aggregation at DC can lead to non-optimum performance of the turbine itself, if passive rectifiers are used, but can also lead to savings in the cost of the power conversion equipment required.
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      Comparative study on transient stability analysis of wind turbine generator system using different drive train models
      • Author(s): S.M. Muyeen ; Md. Hasan Ali ; R. Takahashi ; T. Murata ; J. Tamura ; Y. Tomaki ; A. Sakahara ; E. Sasano
      • Source: IET Renewable Power Generation, Volume 1, Issue 2, p. 131 –141
      • DOI:  10.1049/iet-rpg:20060030
      • Type: Article
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      • p. 131 –141 (11)
        A huge number of wind generators are going to be connected with the existing network in the near future. Therefore it is necessary to analyse the transient stability of power systems, including wind turbine generator systems (WTGS). It has already been reported that one-mass or lumped model of wind turbine system is insufficient to analyse the transient behaviour of WTGS. It has also been reported that for the precise transient analysis of WTGS, a six-mass drive train model is needed. The reduced order models (three-mass and two-mass) have also been adopted so far for transient behaviour analysis. But the transient stability analysis of using six-mass, three-mass and two-mass drive train models has not been reported sufficiently so far in the literature. The authors have conducted an analysis using these methods. First, a detailed transformation procedure is presented from six-mass drive train model to two-mass model, which can be used in the analysis of transient stability simulation with sufficient accuracy. It is then determined which drive train model is appropriate for transient stability analysis of grid-connected WTGS. The effects of drive train parameters (such as inertia constant, spring constant and damping constant) on stability are examined using the above mentioned types of drive train models. Moreover, different types of symmetrical and asymmetrical faults at different wind generator power levels are considered in the simulation analyses with and without considering damping constants in six-mass, three-mass and two-mass shaft models. Considering the simulation results, it can be concluded that two-mass shaft model is sufficient for the transient stability analysis of WTGS.
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      Influence of wind turbine behaviour on the primary frequency control of the British transmission grid
      • Author(s): R. Pearmine ; Y.H. Song ; A. Chebbo
      • Source: IET Renewable Power Generation, Volume 1, Issue 2, p. 142 –150
      • DOI:  10.1049/iet-rpg:20060003
      • Type: Article
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      • p. 142 –150 (9)
        System frequency of a synchronous power system varies with the imbalance of energy supplied and the electrical energy consumed. When large generating blocks are lost, the system undergoes a frequency swing relative to the size of the loss. Any deviation in the system frequency is limited using frequency responsive plant. Changes have occurred to the generation mix of the British transmission system in the past 10 years. This has influenced the type of machines contracted for frequency response services. Future increased levels of wind turbines will also influence the operational characteristics of the system and warrant investigation. A process to optimise the response requirements while maintaining statutory limits on frequency deviation has been developed. This method requires suitable load and generator models to replicate transmission system performance. Validation of the complete system against historic loss events has established confidence in the method. A review of the current system with the dynamic model showed that utilising CCGT plant for responsive services requires additional primary response in some cases. Simulations including extra wind generation have shown that under appropriate circumstances, there is a potential to reduce the primary response requirement in the future. The secondary response requirements are maintained in all cases.
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