Online ISSN
1751-8695
Print ISSN
1751-8687
IET Generation, Transmission & Distribution
Volume 1, Issue 5, September 2007
Volumes & issues:
Volume 1, Issue 5
September 2007
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- Author(s): G.B. Shrestha and P.A.J. Fonseka
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 697 –706
- DOI: 10.1049/iet-gtd:20060391
- Type: Article
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p.
697
–706
(10)
The debate is still on regarding the rationale for transmission expansion in deregulated power markets. Transmission planning with social welfare as the objective would lead to a different optimal expansion plan compared to the planning deemed optimal by individual merchants acting on market forces with profits as their objective. This issue remains to be resolved amid varying rationales and conflicting interests. Fundamental formulations and analyses for long-term network expansion are presented under the paradigms of (i) system-wide social cost minimisation under central planning, and (ii) profit maximising objectives of merchant entrants covering a range of market structures. Distinct planning outcomes under centralised (regulated monopoly) and decentralised (merchant transmission) network managements, and the relation between these optimal solutions have been quantified analytically. These fundamental formulations would be useful for detailed policy studies, and in the formulation of practical regulatory frameworks in the context of transmission sector market liberalisation. Simple and clear examples are presented to illustrate the theoretical results. - Author(s): W. Wang ; E.E. Nino ; W. Xu
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 707 –713
- DOI: 10.1049/iet-gtd:20060488
- Type: Article
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p.
707
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(7)
An effective and easy-to-implement method for measuring power system harmonic impedances is presented. The method uses a thyristor to create a controlled short circuit at the measurement point. The short circuit produces a pulse current and a voltage distortion, which are then used to estimate the system impedance. The strength of the current pulse is controlled through the thyristor firing angle so that enough signal energy is available for precise measurement and yet the disturbance is small enough not to cause power quality problems. The method can be implemented into a portable impedance measurement device. Computer simulations and lab tests were used to verify the effectiveness of the method. A criterion for determining the frequency range of reliable measurements using the proposed device is also established. - Author(s): T.T. Nguyen and V.L. Nguyen
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 714 –723
- DOI: 10.1049/iet-gtd:20060372
- Type: Article
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p.
714
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(10)
Drawing on constrained optimisation based on Newton's method, a systematic and general method for determining optimal reference inputs to unified power-flow controllers (UPFCs) in steady-state operation is developed. The method is directly applicable to UPFCs operation with a high-level line optimisation control. Through the selection of weighting coefficients used in the objective function which is formed from the weighted difference between the specified reference inputs and their optimal values, the method represents the priority assigned for any UPFC control function in constraint or limit resolution. Another key advance reported is that of combining the sparse Newton's method with the continuation technique for solving the nonlinear constrained optimisation. The composite algorithm extends substantially the region of convergence achieved with the conventional Newton's method. The method uses a general and flexible UPFC model based on nodal voltages developed. Any UPFC control functions together with operating limits can be included in the model. The steady-state formulation developed together with its software implementation is tested with a practical long-distance transmission interconnection where a UPFC is required. - Author(s): P. Ju ; F. Wu ; Z.-Y. Shao ; X.-P. Zhang ; H.-J. Fu ; P.-F. Zhang ; N.-Q. He ; J.-D. Han
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 724 –730
- DOI: 10.1049/iet-gtd:20060430
- Type: Article
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p.
724
–730
(7)
The composite load model with an induction motor in parallel with a static load has been studied and applied in analysis of dynamics of power systems for a long time. However, the load parameters from field tests are still very limited. Based on the theoretical results of identifiability and estimation methodology of load parameters that have been achieved in the previous work, a project of load modelling based on field measurements is described. Eight sets of equipment for load modelling were installed in HeNan Electric Power Grid (HNEPG) Corporation, and the dynamics of the load were recorded and a dynamic index is proposed to evaluate the dynamic characteristics of the data measured. The load models derived from the field measurements are applied to stability analysis of HNEPG. The critical clearing time and power transfer capability analyses illustrate the enhancement of the stability analysis of the power grid using the load parameters derived from the field measurements and show the benefits of application of such model parameters in power system dynamic analysis. - Author(s): M.J. Rider ; A.V. Garcia ; R. Romero
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 731 –742
- DOI: 10.1049/iet-gtd:20060465
- Type: Article
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p.
731
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(12)
An optimisation technique to solve transmission network expansion planning problem, using the AC model, is presented. This is a very complex mixed integer nonlinear programming problem. A constructive heuristic algorithm aimed at obtaining an excellent quality solution for this problem is presented. An interior point method is employed to solve nonlinear programming problems during the solution steps of the algorithm. Results of the tests, carried out with three electrical energy systems, show the capabilities of the method and also the viability of using the AC model to solve the problem. - Author(s): I. Tamrakar ; L.B. Shilpakar ; B.G. Fernandes ; R. Nilsen
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 743 –750
- DOI: 10.1049/iet-gtd:20060385
- Type: Article
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p.
743
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(8)
Parallel operation of synchronous and induction generators in micro hydro scheme is presented. The synchronous generator has an exciter, which provides a fixed excitation to produce normal rated terminal voltage at full resistive load. On the other hand, the induction generator has neither exciter nor speed controller. Static compensator (STATCOM) is connected to the common bus for terminal voltage and frequency control. A resistive dump load is connected across the DC link capacitor of STATCOM through a chopper to control active power. Simulink model is developed to perform transient analysis of the proposed scheme. Experimental results are presented to compare with the simulation results. It is found that connection of an induction generator in parallel with the synchronous is much simpler than connecting two synchronous generators in parallel. - Author(s): F. Wu ; X.-P. Zhang ; K. Godfrey ; P. Ju
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 751 –760
- DOI: 10.1049/iet-gtd:20060395
- Type: Article
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p.
751
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(10)
A novel method using particle swarm optimisation (PSO) is proposed for optimising parameters of controllers of a wind turbine (WT) with doubly fed induction generator (DFIG). The PSO algorithm is employed in the proposed parameter tuning method to search for the optimal parameters of controllers and achieve the optimal coordinated control of multiple controllers of WT system. The implementation of the algorithm for optimising the controllers' parameters is described in detail. In the analysis, the generic dynamic model of WT with DFIG and its associated controllers is presented, and the small signal stability model is derived; based on this, an eigenvalue-based objective function is utilised in the PSO-based optimisation algorithm to optimise the controllers' parameters. With the optimised controller parameters, the system stability is improved under both small and large disturbances. Furthermore, the fault ride-through capability of the WT with DFIG can be improved using the optimised controller. Simulations are performed to illustrate the control performance. - Author(s): G.Y. Wu ; C.Y. Chung ; K.P. Wong ; C.W. Yu
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 761 –768
- DOI: 10.1049/iet-gtd:20070075
- Type: Article
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p.
761
–768
(8)
Voltage stability is a challenging problem for independent system operators because of less regulation in power flow patterns and more intensive use of available transmission facilities in deregulated power systems. An equitable and effective scheme for rescheduling pool generation and adjusting contract transactions is proposed in order to ensure adequate voltage stability margin (VSM). A linear optimisation methodology with the objective of minimising the social benefit loss because of generation rescheduling and transaction curtailment is formulated with consideration of the static functional operating constraints and VSM requirements with respect to normal condition and contingencies, and then solved by a linear programming technique. Since the pattern of load increase is difficult to be predicted in new market environment, the system loadability of the locally closest bifurcation is computed and used as the VSM in the proposed method. The effectiveness of the proposed method has been verified using a modified 39-bus New England test system. A study on the effects of post-contingency corrective capability of the system on social benefit loss and voltage stability performance is also presented. - Author(s): J. Pedra ; F. Córcoles ; L. Sainz
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 769 –775
- DOI: 10.1049/iet-gtd:20060555
- Type: Article
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p.
769
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(7)
The consequences of unsymmetrical voltage sags on the three-phase squirrel-cage induction motor behaviour are analysed; namely torque and current peaks, and speed loss. These effects depend on several variables such as sag duration, depth and sag type. The study takes into account that the voltage recovery instant can take only discrete values since fault clearing occurs in the natural current zeroes. The torque and current peaks have a periodical dependence on the sag duration, and a linear dependence on depth. The study of the influence of sag type on speed loss shows that sag types C and D have the same behaviour, and the same is true for sag types E, F and G. - Author(s): E. Bompard ; G. Ciwei ; R. Napoli ; F. Torelli
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 776 –783
- DOI: 10.1049/iet-gtd:20060250
- Type: Article
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p.
776
–783
(8)
Price forecast is a key issue in competitive electricity markets. It provides useful information for the market players and the regulators, in both short and long run. Different approaches have been proposed and implemented. A new dynamic approach for forecasting the market price of electricity in the short term is proposed. The price dates are first clustered according to different types of daily profiles and then, given a proper function representing the trend in price, the set of unknown parameters are identified based on the zeroing of a Lyapunov function. The forecast can be dynamically updated with the latest data available. Higher weight can be attributed to this data in determining the future prices. The proposed approach is validated with reference to real systems in the form of the Italian, New England and New York electricity markets. In addition, an extensive price forecast is provided for the Italian market, an example of a young market that is rather difficult to predict patterns for. - Author(s): S.R. Samantaray and P.K. Dash
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 784 –792
- DOI: 10.1049/iet-gtd:20070052
- Type: Article
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p.
784
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A new approach for the protection of thyristor-controlled series-compensated (TCSC) line using wavelet packets transform (WPT) is presented. The proposed method uses one cycle post-fault-current samples just after fault inception, which is processed through WPT and decomposed into various decomposition levels. The decomposed components are grouped together to provide different frequency sub-bands. Then the phase selection signal (PSS) and section identification signal (SIS) are computed to identify the faulty phase and faulty section, respectively, involved in the fault process in transmission line including TCSC. A threshold value (THD) is selected for PSS, and PSS above THD describes the faulty phase involved, otherwise not. Similarly, another THD is selected for SIS, and SIS below THD describes fault that includes TCSC, otherwise fault that does not include TCSC. As PSS takes half cycle after fault inception to identify the faulty phase and then triggers SIS, the faulty phases and faulty sections are identified within one cycle of fault inception. The proposed WPT algorithm is also tested on physical transmission line model with TCSC, under wide variations in operating conditions and provides accurate results. Thus, the proposed method provides accurate and fast protection measures for TCSC-based line. - Author(s): S.-K. Wang ; J.-P. Chiou ; C.-W. Liu
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 793 –803
- DOI: 10.1049/iet-gtd:20070183
- Type: Article
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p.
793
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This paper presents a novel stochastic optimisation approach to determining the feasible optimal solution of the economic dispatch (ED) problem considering various generator constraints. Many practical constraints of generators, such as ramp rate limits, prohibited operating zones and the valve point effect, are considered. These constraints make the ED problem a non-smooth/non-convex minimisation problem with constraints. The proposed optimisation algorithm is called self-tuning hybrid differential evolution (self-tuning HDE). The self-tuning HDE utilises the concept of the 1/5 success rule of evolution strategies (ESs) in the original HDE to accelerate the search for the global optimum. Three test power systems, including 3-, 13- and 40-unit power systems, are applied to compare the performance of the proposed algorithm with genetic algorithms, the differential evolution algorithm and the HDE algorithm. Numerical results indicate that the entire performance of the proposed self-tuning HDE algorithm outperforms the other three algorithms. - Author(s): J.-I. Tsai
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 804 –810
- DOI: 10.1049/iet-gtd:20060534
- Type: Article
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p.
804
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(7)
The author presents a new single-pole switching technique for reducing torsional torques in turbine blades and shafts and enhancing power system stability and transmission continuity. During the dead time between single-pole tripping and line reclosing, the significant negative-sequence current flowing into the nearby turbine-generator may cause supersynchronous resonance effect on low pressure turbine blades and even results in fatigue damage. Thus, during this time, the proposed grounding capacitor set up at the neutral of the wye transformer is inserted not only to eliminate this negative current but also to recover the prefault power transmission in advance. The induced adverse effect on turbine blades can be precluded. Adaptive reclosing is then applied to reclose the tripped phase and the grounding capacitor is switched off. This effectively improves the power system stability again and prevents further torque amplifications. This scheme is suitable for a single-circuit transmission line and can improve system reliability. - Author(s): T.K. Manna and P. Chowdhuri
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 811 –817
- DOI: 10.1049/iet-gtd:20060559
- Type: Article
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p.
811
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The effective radius of the grounding electrode under high-impulse current becomes higher than the outer radius of the electrode because of soil ionisation. Because of this reason, the ground-impulse impedance is different from the 60-Hz grounding resistance, which is normally measured at low current. The impulse impedance for any given impulse current can be estimated if the critical electric field of the soil is known. It is therefore necessary to have a generalised soil critical electric field equation for grounding systems design as well as lightning performance study. A generalised equation for soil critical electric field Ec is proposed here as a function of soil dielectric constant kg and conductivity σg. Extensive impulse tests and electrical measurements were performed with different soils under different moisture contents. Dielectric constant kg was measured by the wave propagation technique using a soil-filled coaxial transmission line. Effect of waveshape on critical electric field Ec was statistically analysed for different soils. - Author(s): A. Ishchenko ; J.M.A. Myrzik ; W.L. Kling
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 818 –825
- DOI: 10.1049/iet-gtd:20070028
- Type: Article
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p.
818
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Nowadays the number of dispersed generators (DGs) is growing rapidly. This change will greatly influence power system dynamics. A distribution network, where DGs are connected to the grid, cannot be considered as passive anymore. Therefore, in the future it will not be possible to use simple equivalents of distribution networks for power system dynamic modelling, as it was done before. At the same time, the whole power system cannot generally be represented in a detailed manner for dynamic studies because of huge system dimension. Therefore special techniques have to be applied for aggregation and order-reduction of distribution networks with DG. A brief review of existing techniques is provided here, and the dynamic reduction using Hankel norm approximation is performed for a 10 kV distribution network, which includes DG of different types. - Author(s): H. Seifi ; M.S. Sepasian ; H. Haghighat ; A. Akbari Foroud ; G.R. Yousefi ; S. Rae
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 826 –835
- DOI: 10.1049/iet-gtd:20070092
- Type: Article
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p.
826
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Network expansion planning (NEP), as a major module of power system planning modules, is addressed here. For long-term transmission NEP, a new approach based on forward–backward strategy is proposed in which by defining appropriate steps and observing various technical and reliability considerations, new network reinforcements are determined. Besides assessing the capabilities of the proposed approach on a small typical system, the algorithm is successfully tested for Iranian Power Grid in 2011, as a large-scale system. - Author(s): B. Venkatesh ; T. Jamtsho ; H.B. Gooi
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 836 –846
- DOI: 10.1049/iet-gtd:20060529
- Type: Article
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p.
836
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Unit commitment (UC) of a large system is a complex puzzle with integer/continuous variables and numerous inter-temporal constraints. After deregulation, price offers submitted by GenCos are predominantly in the form of linear price quantity (PQ) pairs. A fuzzy UC formulation that uses price offers modeled as PQ pairs. This fuzzy linear optimisation formulation of UC is solved using a mixed integer linear programming (MILP) routine. In this formulation, start up cost is modelled using linear variables. The fuzzy formulation provides modeling flexibility, relaxation in constraint enforcement and allows the method to seek a practical solution. The use of MILP technique makes the proposed solution method rigorous and fast. The method is tested on a 24 h, 104-generator system demonstrating its speed and robustness gained by using the LP technique. A five-generator system is additionally used to create a see-through example demonstrating advantages of using the fuzzy optimisation model. - Author(s): G.J. Li ; X.P. Zhang ; S.S. Choi ; T.T. Lie ; Y.Z. Sun
- Source: IET Generation, Transmission & Distribution, Volume 1, Issue 5, p. 847 –853
- DOI: 10.1049/iet-gtd:20060494
- Type: Article
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p.
847
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A power injection control strategy is proposed for dynamic voltage restorers (DVR) under voltage sag or swell conditions. Under such a strategy, the error between the voltage of the energy storage capacitor in the DVR and a given reference voltage is extracted to control the injected power such that during an upstream voltage disturbance, zero or minimum power injection can be achieved automatically, while sudden phase jump of the load-side voltage can also be avoided. The proposed control strategy is analysed in detail and numerical examples are provided to demonstrate the effectiveness of the scheme.
Optimal transmission expansion under different market structures
Harmonic impedance measurement using a thyristor-controlled short circuit
Representation of line optimisation control in unified power-flow controller model for power-flow analysis
Composite load models based on field measurements and their applications in dynamic analysis
Power system transmission network expansion planning using AC model
Voltage and frequency control of parallel operated synchronous generator and induction generator with STATCOM in micro hydro scheme
Small signal stability analysis and optimal control of a wind turbine with doubly fed induction generator
Voltage stability constrained optimal dispatch in deregulated power systems
Effects of unsymmetrical voltage sags on squirrel-cage induction motors
Dynamic price forecast in a competitive electricity market
Wavelet packet-based digital relaying for advanced series compensated line
Non-smooth/non-convex economic dispatch by a novel hybrid differential evolution algorithm
A new single-pole switching technique for suppressing turbine-generator torsional vibrations and enhancing power stability and continuity
Generalised equation of soil critical electric field EC based on impulse tests and measured soil electrical parameters
Dynamic equivalencing of distribution networks with dispersed generation using Hankel norm approximation
Multi-voltage approach to long-term network expansion planning
Unit commitment – a fuzzy mixed integer Linear Programming solution
Control strategy for dynamic voltage restorers to achieve minimum power injection without introducing sudden phase shift
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