Online ISSN
1751-8695
Print ISSN
1751-8687
IET Generation, Transmission & Distribution
Volume 5, Issue 4, April 2011
Volumes & issues:
Volume 5, Issue 4
April 2011
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- Author(s): A.A. Romero ; H.C. Zini ; G. Rattá ; R. Dib
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 393 –404
- DOI: 10.1049/iet-gtd.2010.0361
- Type: Article
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p.
393
–404
(12)
Harmonics in power systems are responsible for several technical problems that justify the development of models to study them. Well-established models exist to analyse the harmonic load-flow (HLF) from a deterministic point of view. Moreover, models based on the probability theory have been developed to deal with the inherent variability and random nature of loads, network configuration etc. In the last few years, possibility theory has arisen as an alternative tool that in many cases could be better suited to describe and quantify the real nature of the uncertainty involved in harmonic studies. In this study a methodology for HLF calculation based on the possibility theory is presented. Possibility distributions instead of probabilities are the input used to describe the uncertainty in the magnitude and composition of the loads. Tests presented shows that the results of the proposed model are consistent with those obtained with a probabilistic method, and that both models lead to the same ranking of the risk that the bus harmonic voltages exceed a given level. Independent possibility distributions are assumed at the development stage reported here; research is being carried out in order to overcome this constraint. - Author(s): A.M. Miah
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 405 –416
- DOI: 10.1049/iet-gtd.2010.0314
- Type: Article
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p.
405
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(12)
Earlier, a simple dynamic equivalent for a power system external area containing a group of coherent generators was proposed in the literature. In the proposed method, all the coherent generators are first decomposed into smaller generators. This is a new concept. The smaller generators are then aggregated in two levels. In this study, a new alternative and much more justified approach is proposed for the first-level aggregation. However, for the second-level aggregation, the same earlier approach is used. The resulting dynamic equivalent has a power system structure. In online applications, this equivalent does not require any measurement data from the external area. Very recently, the performance of the dynamic equivalent has been extensively investigated on the New England 39-bus 10-generator system, the IEEE 162-bus 17-generator system and the IEEE 145-bus 50-generator system. The results of this investigation are presented here for a complete validation of the proposed method. - Author(s): P. Aree and E. Acha
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 417 –424
- DOI: 10.1049/iet-gtd.2010.0442
- Type: Article
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p.
417
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(8)
The initialisation of most power system stability studies is carried out with the outcome of a power flow solution using a constant power representation of the load that may contain voltage dependency. However, such an approach may not be suitable when an important component of the system load is made up of induction motors because of a natural mismatch between the power flow scheduled power and the actual induction motor power, which is computed using the final converged value of the motor terminal bus voltage. To solve this problem, a method for incorporating the non-linear model of induction motors in Newton–Raphson power flow algorithm is put forward in this study. The prowess of the improved power flow algorithm is demonstrated using the Ward–Hale, the IEEE 30-bus and the New-England test systems in connection with industrial motor subsystems. The results show that the extended power flow algorithm provides the correct steady-state initialisation and still preserves the basic Newton–Raphson's quadratic convergence characteristics. - Author(s): A. Ulinuha ; M.A.S. Masoum ; S. Islam
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 425 –439
- DOI: 10.1049/iet-gtd.2010.0168
- Type: Article
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p.
425
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(15)
A hybrid genetic-fuzzy algorithm (GA-Fuzzy) is proposed for optimal volt/var/total harmonic distortion (THD) control in distorted distribution systems serving non-linear loads. Load interval division (over a 24 h period) and optimal scheduling of load tap changer and switched shunt capacitors for simultaneously minimising energy losses and improving the power quality (as recommended by the IEEE 519 and IEC 61000 standards) are performed using GAs with fuzzy reasoning. The non-linear load flow is solved using a decoupled harmonic power flow algorithm. The integration of fuzzy rules and GA enables the approach to maintain the promising chromosomes and offer further improvement of the near-global solution. The IEEE 30-bus and 123-bus distribution systems with a number of harmonic generating loads are selected for the analyses. Simulation results using GA and GA-Fuzzy optimisation approaches are presented and compared for sinusoidal and non-sinusoidal treatments of the systems to demonstrate the advantages of the proposed hybrid approach. - Author(s): I. Albizu ; E. Fernández ; A.J. Mazón ; J. Bengoechea
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 440 –447
- DOI: 10.1049/iet-gtd.2010.0470
- Type: Article
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p.
440
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(8)
Many real-time overhead line ampacity monitoring systems are based on the calculation of wind speed. The wind speed is obtained from the conductor temperature. The conductor temperature can be measured directly or it can be obtained indirectly from other magnitudes such as the tension or the sag. An error in the temperature difference gives as a result an error in the calculated wind speed and ampacity values. This study analyses and quantifies the influence of the temperature difference error in the obtained ampacity value. As a result, a method for the evaluation and the correction of the ampacity error that can be used in the monitoring systems is proposed. - Author(s): M. De and S.K. Goswami
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 448 –460
- DOI: 10.1049/iet-gtd.2010.0209
- Type: Article
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p.
448
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(13)
In deregulated power systems ancillary services including reactive power supply are unbundled for transparency and accurate cost identification. Sufficient reactive power supply is essential for secure operation of power systems. Reactive power is supplied by generation-based and static reactive power sources and is used for two purposes: direct consumption at loads and system-wide voltage management. The task of the system operator is to identify which part of reactive power is supplied by any source and who consumes this. Accordingly, revenue is collected from consumers and distributed among reactive power providers. Therefore an appropriate and transparent reactive power pricing scheme will encourage more generators to participate in reactive power market, increasing stability of the system because of increased reactive power availability. However, existing reactive power allocation methods do not always provide unquestionable results. The proposed circuit theory-based method identifies different reactive power sources and allocates the amount of reactive power provided to different sources by using an improved Y-bus technique along with proportional or equal sharing principle. Line charging reactance present in transmission line supplies reactive power to the system, which is identified as a separate reactive power source for the first time in this study and the proposed method, offers a part of revenue to system operator for supplying reactive power to the system by means of this line charging reactance. By doing so, the proposed method eliminates some important drawbacks of existing allocation methods. The method is tested on different IEEE systems and also a 400 KV practical system. - Author(s): Y.-Y. Hong and Y.Y. Chen
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 461 –466
- DOI: 10.1049/iet-gtd.2010.0397
- Type: Article
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p.
461
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Power quality (PQ) problems include harmonics, voltage flicker, three-phase imbalance, voltage swell/sag, interruption, switching transient and so on. Identification of accurate location and occurrence time of PQ problem is important for understanding the underlying cause and to prevent future occurrence. This study presents a new method for placement of power quality measurement facilities to identify PQ problems. The power harmonics and capacitor switching transients are used as disturbance sources for illustration. The proposed method first utilises harmonic voltages and wavelet coefficients as PQ features. An enhanced genetic algorithm is proposed for solving the modified K-means clustering to place PQ measurement monitors. Simulation results for an 18-bus system show that the proposed approach is effective in comparison with the existing approaches. - Author(s): R.H. Salim ; K.C.O. Salim ; A.S. Bretas
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 467 –478
- DOI: 10.1049/iet-gtd.2010.0446
- Type: Article
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p.
467
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(12)
In this study, further improvements regarding the fault location problem for power distribution systems are presented. The proposed improvements relate to the capacitive effect consideration on impedance-based fault location methods, by considering an exact line segment model for the distribution line. The proposed developments, which consist of a new formulation for the fault location problem and a new algorithm that considers the line shunt admittance matrix, are presented. The proposed equations are developed for any fault type and result in one single equation for all ground fault types, and another equation for line-to-line faults. Results obtained with the proposed improvements are presented. Also, in order to compare the improvements performance and demonstrate how the line shunt admittance affects the state-of-the-art impedance-based fault location methodologies for distribution systems, the results obtained with two other existing methods are presented. Comparative results show that, in overhead distribution systems with laterals and intermediate loads, the line shunt admittance can significantly affect the state-of-the-art methodologies response, whereas in this case the proposed developments present great improvements by considering this effect. - Author(s): K.-H. Tseng and P.-Y. Cheng
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 479 –488
- DOI: 10.1049/iet-gtd.2010.0453
- Type: Article
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p.
479
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(10)
This study presents a successful mitigation experience of ferroresonance (FR) with damping reactors (DR) involving electromagnetic potential transformers (PT) of a 161 kV gas-insulated switchgear (GIS) in Taiwan. PTs have a typically low thermal capacity and high accuracy because of their measuring functions. Low core losses are necessary to obtain high accuracy, but they also reduce its damping ability and therefore increase the possibility of FR. FR happened twice and destroyed PTs for half a year in the study case. Complete FR waveforms of 161 kV PT were obtained via field tests never conducted before in Taiwan. The first field test had a reappearing FR which sustained up to 22.9 s in 11 random operations and the second one confirmed the validity of DR which shortened FR <3.9 s in 12 random operations. A reliable prediction by EMTP/ATPDraw simulation and a useful mitigation method with a proper DR were proved by both field tests and the following 23 months satisfactory operations for 82 times since November 2008. It would prove valuable for further research in higher grade voltage GIS. - Author(s): T.R. Limbu ; T.K. Saha ; J.D.F. McDonald
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 489 –495
- DOI: 10.1049/iet-gtd.2010.0467
- Type: Article
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p.
489
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This study proposes a new ‘value-based probabilistic optimal allocation’ methodology for energy and spinning reserve through cost–benefits analysis approach. The model implements an AC optimal power flow (AC OPF)-based co-optimisation algorithm for dispatching energy and operating reserve. A state sampling Monte Carlo simulation (MCS) approach is implemented to model random failure of system elements during the AC-OPF solution. The proposed MCS-based technique is simple and efficient, and yet models the system uncertainties and network constraints. Three types of generators for active and reactive energy, fictitious spinning reserves and fictitious negative energy generation are modelled in the AC-OPF algorithm. A comparison of reserve dispatch from the deterministic approach and the proposed value-based approach are presented. The finding suggests that for an optimal dispatch of spinning reserve, an independent system operator (ISO) will have to seek a balance between benefits and cost of providing the services. Sensitivity studies of optimal operating reserve dispatch based on the cost of generation, value of lost load (VOLL) and network size were investigated. This study also proposes a new solution methodology based on the MCS for allocation and settlement of reserves. The 24 bus IEEE-reliability test system (RTS) has been used to demonstrate the performance of the proposed methodologies. - Author(s): K. De Kerf ; K. Srivastava ; M. Reza ; D. Bekaert ; S. Cole ; D. Van Hertem ; R. Belmans
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 496 –503
- DOI: 10.1049/iet-gtd.2010.0587
- Type: Article
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496
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A new protection algorithm for DC line faults in multi-terminal high voltage DC (MTDC) systems is proposed in this study. A four-terminal MTDC model is used to investigate fault behaviour and detection using the simulation program PSCAD/EMTDC. The simulation results are post-processed using Matlab. The fault clearing must be done very rapidly, to limit the effect of the fault on neighbouring DC lines because of the rapid increase in DC current. However, before clearing the line, the fault location must be detected as soon as possible. A rapid fault location detection algorithm is therefore needed, preferably without communication. The protection algorithm proposed in this study uses wavelet analysis to detect the fault location based on local measurements. The protection algorithm consists of three independent fault criteria, of which two use wavelet analysis. The third criterion is based on a detection method in the time domain. The latter is an additional detection method independent of wavelet analysis. Using a two out of three selection criteria results in an increased reliability of the whole protection algorithm. The final objective is to implement a protection algorithm which allows to detect a DC fault within 1 ms without using communication between the participating converter stations. - Author(s): C. Vyjayanthi and D. Thukaram
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 504 –518
- DOI: 10.1049/iet-gtd.2010.0553
- Type: Article
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p.
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The amount of reactive power margin available in a system determines its proximity to voltage instability under normal and emergency conditions. More the reactive power margin, better is the systems security and vice-versa. A hypothetical way of improving the reactive margin of a synchronous generator is to reduce the real power generation within its mega volt-ampere (MVA) ratings. This real power generation reduction will affect its power contract agreements entered in the electricity market. Owing to this, the benefit that the generator foregoes will have to be compensated by paying them some lost opportunity cost. The objective of this study is three fold. Firstly, the reactive power margins of the generators are evaluated. Secondly, they are improved using a reactive power optimization technique and optimally placed unified power flow controllers. Thirdly, the reactive power capacity exchanges along the tie-lines are evaluated under base case and improved conditions. A detailed analysis of all the reactive power sources and sinks scattered throughout the network is carried out in the study. Studies are carried out on a real life, three zone, 72-bus equivalent Indian southern grid considering normal and contingency conditions with base case operating point and optimised results presented. - Author(s): D. Granados-Lieberman ; R.J. Romero-Troncoso ; R.A. Osornio-Rios ; A. Garcia-Perez ; E. Cabal-Yepez
- Source: IET Generation, Transmission & Distribution, Volume 5, Issue 4, p. 519 –529
- DOI: 10.1049/iet-gtd.2010.0466
- Type: Article
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p.
519
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(11)
The relevance of power quality (PQ) issues has recently augmented because of the increased use of power electronic equipment, which results in a voltage deviation and current waveforms. The PQ monitoring is covered by two main subjects: the development of PQ indices to quantify the power supply quality and the electrical disturbances detection such as harmonics, sags, swells etc., which allows knowing the conditions of the electric power systems. In this study a review of techniques and methodologies developed for PQ analysis and power disturbance classification is presented in order to show their major characteristics.
Harmonic load-flow approach based on the possibility theory
Study of a coherency-based simple dynamic equivalent for transient stability assessment
Power flow initialisation of dynamic studies with induction motor loads
Hybrid genetic-fuzzy algorithm for volt/var/total harmonic distortion control of distribution systems with high penetration of non-linear loads
Influence of the conductor temperature error on the overhead line ampacity monitoring systems
Reactive support allocation using improved Y-bus matrix method
Placement of power quality monitors using enhanced genetic algorithm and wavelet transform
Further improvements on impedance-based fault location for power distribution systems
Mitigating 161 kV electromagnetic potential transformers' ferroresonance with damping reactors in a gas-insulated switchgear
Value-based allocation and settlement of reserves in electricity markets
Wavelet-based protection strategy for DC faults in multi-terminal VSC HVDC systems
Evaluation and improvement of generators reactive power margins in interconnected power systems
Techniques and methodologies for power quality analysis and disturbances classification in power systems: a review
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