Journal articles: 'Load Flow Methods'

1

Seng, Chieng Kai, Tay Lea Tien, and Syafrudin Masri. "Load Flow Analysis Using Second-Order Load Flow Methods and its Variations." Applied Mechanics and Materials 785 (August 2015): 73–77. http://dx.doi.org/10.4028/www.scientific.net/amm.785.73.

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The load flow or power flow computer program is the basic tool for investigating the steady-state conditions of power system. This paper introduces improved algorithms based on the basic Second-order Load Flow method for a wide range of electrical bus system sizes. It is attractive for accurate or approximate off- and on-line calculations for routine and contingency purposes. Tests of 4 different variations based on the basic Second-order Load Flow method are run on 6 different standard bus systems and the results are discussed in this paper.

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Ekwue, A. O., and J. F. Macqueen. "Comparison of load flow solution methods." Electric Power Systems Research 22, no. 3 (December 1991): 213–22. http://dx.doi.org/10.1016/0378-7796(91)90008-b.

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3

Xiao-Ping Zhang. "Fast three phase load flow methods." IEEE Transactions on Power Systems 11, no. 3 (1996): 1547–54. http://dx.doi.org/10.1109/59.535696.

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Baldwin, T. L., and S. A. Lewis. "Distribution Load Flow Methods for Shipboard Power Systems." IEEE Transactions on Industry Applications 40, no. 5 (September 2004): 1183–90. http://dx.doi.org/10.1109/tia.2004.834128.

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Srivastava, L., S. C. Srivastava, and L. P. Singh. "Fast decoupled load flow methods in rectangular coordinates." International Journal of Electrical Power & Energy Systems 13, no. 3 (June 1991): 160–66. http://dx.doi.org/10.1016/0142-0615(91)90005-g.

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Shahriari, Amidaddin, Hazlie Mokhlis, and Ab Bakar. "Critical Reviews of Load Flow Methods for Well, Ill and Unsolvable Condition." Journal of Electrical Engineering 63, no. 3 (May 1, 2012): 144–52. http://dx.doi.org/10.2478/v10187-012-0022-x.

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Critical Reviews of Load Flow Methods for Well, Ill and Unsolvable ConditionThis paper presents a critical review of Load flow methods in well, ill and unsolvable conditioned systems. The comparison studies deals with multiple load flow solution (MLFS), second-order load-flow (SOLF) and continuation load flow (CLF). The ability of theses method to return from unsolvable solution to a solvable solution in load flow analysis is analyzed and discuss thoroughly. Special attention is given to the problems and techniques to provide optimal recommendations of the parameters that are used in these load flow methods. A part of the reviews, this paper also presents the comparison of numerical result using different type of aforesaid load flow methods for well and ill-conditioned systems.

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Zhu, Linbo, Yongsheng Zhu, and Yuping Yan. "Methods to test and generate the wear load spectrum of journal bearing in concrete pump." Advances in Mechanical Engineering 13, no. 4 (April 2021): 168781402110077. http://dx.doi.org/10.1177/16878140211007716.

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Load spectrum is the basis of wear analysis and life prediction in journal bearing. This paper proposed a method to generate the wear load spectrum from the measured loads that avoiding the errors introduced by the assumptions of traditional constant load. An axle pin load sensor that can recognize the load value and its orientation is developed to test the original wear loads of journal bearing in a concrete pump under working conditions. The interactive influence of perpendicular components in the measured loads is involved by introducing two effect coefficients. Subsequently, the amplitude distribution of the wear load and its lasting time are extracted from the measured complex load-time history using the rain-flow counting method and Weibull distribution. The wear load spectrum is generated by dividing the continuous load into eight load steps. The validity of the approach is supported by finite element analysis on the wear simulation of journal bearing using the generated load spectrum and the measured load. In addition, the effects of load types and load sequence on the wear are discussed based on the proposed method and the FE model. This study provides guidelines to efficiently generate the wear load spectrum for journal bearing, and enhances its reliability of wear prediction in the experimental tests and theoretical analysis.

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Kayser, K., S. Kunst, G. Fehr, and H. Voermanek. "Nitrification in reed beds - capacity and potential control methods." Water Science and Technology 46, no. 6-7 (September 1, 2002): 363–70. http://dx.doi.org/10.2166/wst.2002.0701.

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Vertical-flow reed beds (VFBs) are known to be very effective regarding nitrification. However, a generally accepted design formula for dimensioning reed beds for a controlled nitrification process has still not been found. Especially for the purpose of nitrification a vertical-flow reed bed (VFB) has been installed following an existing unaerated pond-system. The paper presents the results concerning the limits of the VFB's performance as well as the main factors influencing the nitrification process gained by balancing the conversion rates under different loads. Even under high loads the VFB provides an excellent nitrification performance, which is mainly influenced by the wastewater temperature. The ammonia oxidation rate is about 90% at temperatures over 10°C; at temperatures below 5°C the average nitrification rate is still approximately 50%. The hydraulic load and the TKN load have almost no impact on this efficiency (the maximum load has been: 180 mm/d, 7.1 g TKN/(m2*d)). The redox potenial, which is continuously measured in the effluent of the reed bed, proved to be dependent on the current nitrification performance and the oxygen supply of the VFB, and therefore appears to be a suitable control parameter for the operation of VFBs.

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Wang, An, and Qinghua Zeng. "Load Characteristics and Modeling Methods for the Flow Regulator of a Solid Ducted Rocket." International Journal of Aerospace Engineering 2019 (November 18, 2019): 1–10. http://dx.doi.org/10.1155/2019/8031290.

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The load characteristics for the flow regulator of a solid ducted rocket are discussed in this paper. The mechanism and the influence factor of the load in the flow regulator were studied both theoretically and experimentally, and the system load and the working load were divided according to the mechanism. Additionally, the load influence on the working quality of the flow regulator and the ducted rocket were analyzed. System modeling of the flow regulator was carried out based on the working mechanism of the gas generator and the Stribeck friction model, and models of the actuator, gas generator, and load were built. Furthermore, considering the identification of the model parameters and the inapplicability of the conventional Stribeck identification method to the flow regulator, a new Stribeck model parameter identification method was proposed. A sine wave was used as the signal source, and specially designed devices were used to accomplish the switch of the working condition. Through the use of the genetic algorithm, the rotational inertia and parameters of the system load and working load were identified by stages. Finally, the validation of the identification method was carried out with a simulation.

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Quintana, V. H., and N. Müller. "Studies of load flow methods in polar and rectangular coordinates." Electric Power Systems Research 20, no. 3 (March 1991): 225–35. http://dx.doi.org/10.1016/0378-7796(91)90067-w.

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Bhaya, A., D. M. Falcāo, E. Kaszkurewicz, and N. Roqueiro. "Parallel Block-iterative Methods: Application to the Load Flow Problem." IFAC Proceedings Volumes 22, no. 10 (August 1989): 339–44. http://dx.doi.org/10.1016/s1474-6670(17)53196-1.

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Khaitan, Siddhartha Kumar, James D. McCalley, and Mandhapati Raju. "Numerical methods for on-line power system load flow analysis." Energy Systems 1, no. 3 (May 6, 2010): 273–89. http://dx.doi.org/10.1007/s12667-010-0013-6.

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Rao, Bharath, Friederich Kupzog, and Martin Kozek. "Three-Phase Unbalanced Optimal Power Flow Using Holomorphic Embedding Load Flow Method." Sustainability 11, no. 6 (March 24, 2019): 1774. http://dx.doi.org/10.3390/su11061774.

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Distribution networks are typically unbalanced due to loads being unevenly distributed over the three phases and untransposed lines. Additionally, unbalance is further increased with high penetration of single-phased distributed generators. Load and optimal power flows, when applied to distribution networks, use models developed for transmission grids with limited modification. The performance of optimal power flow depends on external factors such as ambient temperature and irradiation, since they have strong influence on loads and distributed energy resources such as photo voltaic systems. To help mitigate the issues mentioned above, the authors present a novel class of optimal power flow algorithm which is applied to low-voltage distribution networks. It involves the use of a novel three-phase unbalanced holomorphic embedding load flow method in conjunction with a non-convex optimization method to obtain the optimal set-points based on a suitable objective function. This novel three-phase load flow method is benchmarked against the well-known power factory Newton-Raphson algorithm for various test networks. Mann-Whitney U test is performed for the voltage magnitude data generated by both methods and null hypothesis is accepted. A use case involving a real network in Austria and a method to generate optimal schedules for various controllable buses is provided.

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Tien Tay, Lea, William Ong Chew Fen, and Lilik Jamilatul Awalin. "Improved newton-raphson with schur complement methods for load flow analysis." Indonesian Journal of Electrical Engineering and Computer Science 16, no. 2 (November 1, 2019): 699. http://dx.doi.org/10.11591/ijeecs.v16.i2.pp699-605.

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<p>The determination of power and voltage in the power load flow for the purpose of design and operation of the power system is very crucial in the assessment of actual or predicted generation and load conditions. The load flow studies are of the utmost importance and the analysis has been carried out by computer programming to obtain accurate results within a very short period through a simple and convenient way. In this paper, Newton-Raphson method which is the most common, widely-used and reliable algorithm of load flow analysis is further revised and modified to improve the speed and the simplicity of the algorithm. There are 4 Newton-Raphson algorithms carried out, namely Newton-Raphson, Newton-Raphson constant Jacobian, Newton-Raphson Schur Complement and Newton-Raphson Schur Complement constant Jacobian. All the methods are implemented on IEEE 14-, 30-, 57- and 118-bus system for comparative analysis using MATLAB programming. The simulation results are then compared for assessment using measurement parameter of computation time and convergence rate. Newton-Raphson Schur Complement constant Jacobian requires the shortest computational time.</p>

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Mohamed, Norainon, and Dahaman Ishak. "Improved load flow formulation for radial distribution networks." Indonesian Journal of Electrical Engineering and Computer Science 15, no. 3 (September 1, 2019): 1144. http://dx.doi.org/10.11591/ijeecs.v15.i3.pp1144-1153.

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This paper aims to provide an improved load flow formulation for solving load flow problem in radial distribution networks. The improved algorithm is formulated from the basic Kirchoff’s voltage law. The proposed method does not need any matrix multiplication, and the voltage equation is derived to compute the voltage at each node. The proposed method is then tested on 28-bus, IEEE-33 and IEEE-69 systems of radial distribution networks with different resistance to reactance ratio and different condition of loads. The simulation results from the suggested algorithm show that the proposed method has fast convergence capability compared with other existing methods. A very good agreement is achieved.

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16

Hubbi, W. "Effects of neglecting resistances in XB and BX load-flow methods." IEE Proceedings C Generation, Transmission and Distribution 138, no. 5 (1991): 452. http://dx.doi.org/10.1049/ip-c.1991.0057.

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Nikmehr, N., and S. Najafi Ravadanegh. "Solving probabilistic load flow in smart distribution grids using heuristic methods." Journal of Renewable and Sustainable Energy 7, no. 4 (July 2015): 043138. http://dx.doi.org/10.1063/1.4929804.

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Braz, L. M. C., C. A. Castro, and C. A. F. Murati. "A critical evaluation of step size optimization based load flow methods." IEEE Transactions on Power Systems 15, no. 1 (2000): 202–7. http://dx.doi.org/10.1109/59.852122.

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19

Padiyar, K. R., and R. S. Shanbhag. "Comparison of methods for transmission system expansion using network flow and DC load flow models." International Journal of Electrical Power & Energy Systems 10, no. 1 (January 1988): 17–24. http://dx.doi.org/10.1016/0142-0615(88)90004-x.

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20

LYAPIN, S. A., Y. N. RIZAEVA, D. A. KADASEV, and N. V. VORONIN. "INVESTIGATION OF THE INFLUENCE OF TRAFFIC FLOW CONTROL ON THE LOADS OF THE MAIN LOAD-BEARING ELEMENTS AND THE CAPACITY OF BRIDGES." World of transport and technological machines 77, no. 2 (2022): 27–35. http://dx.doi.org/10.33979/2073-7432-2022-77-2-27-35.

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The article shows the influence of such methods of traffic flow management as limiting the speed of vehicles on the loads of the main load-bearing elements and the capacity of bridge structures on the example of the Oktyabrsky Bridge in Lipetsk. To determine the density of traffic flow and the load on the bridge structure, to collect information about the parameters of traffic flows, road traf-fic simulation is used. The vertical moving load on the bridge is calculated.

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PODDUBKO, Sergey N., Nikolay N. ISHIN, Arkadiy M. GOMAN, Andrey S. SKOROKHODOV, and Vladimir V. SHPORTKO. "METHODS FOR CALCULATING THE LOAD OF ELECTRIC VEHICLE GEARBOXES USING THEIR DYNAMIC MODELS." Mechanics of Machines, Mechanisms and Materials 2, no. 59 (June 2022): 16–23. http://dx.doi.org/10.46864/1995-0470-2022-2-59-16-23.

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A two-mass dynamic model of an electric vehicle is considered to obtain analytical dependences describing the gearshift process in a shaft-planetary gearbox. The calculations are based on the optimal diagram of shifting gears from low to high without interruption of the power flow from the electric motor. At the stage of gear shifting, at which the kinematic gear ratio of the gearbox changes from u1 to u2, Lagrange equations of the second kind are used to determine the time dependences of angular velocities of the input and output shafts of gearbox. An example is given for calculating the gearshift time from low gear to high one for the MAZ-4381EE delivery electric truck, as well as a refined calculation for a multi-mass dynamic scheme is carried out.

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22

Yasuda, Tomohiro. "Selected Methods of Resistance Training for Prevention and Treatment of Sarcopenia." Cells 11, no. 9 (April 20, 2022): 1389. http://dx.doi.org/10.3390/cells11091389.

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Resistance training is an extremely beneficial intervention to prevent and treat sarcopenia. In general, traditional high-load resistance training improves skeletal muscle morphology and strength, but this method is impractical and may even reduce arterial compliance by about 20% in aged adults. Thus, the progression of resistance training methods for improving the strength and morphology of muscles without applying a high load is essential. Over the past two decades, various resistance training methods that can improve skeletal muscle mass and muscle function without using high loads have attracted attention, and their training effects, molecular mechanisms, and safety have been reported. The present study focuses on the relationship between exercise load/intensity, training effects, and physiological mechanisms as well as the safety of various types of resistance training that have attracted attention as a measure against sarcopenia. At present, there is much research evidence that blood-flow-restricted low-load resistance training (20–30% of one repetition maximum (1RM)) has been reported as a sarcopenia countermeasure in older adults. Therefore, this training method may be particularly effective in preventing sarcopenia.

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Lingaswamy, K., T. Anil Kumar, G. Hari Krishna, and N. Shiva Prasad. "UPFC based transmission line power load flow control under different operating methods." International Journal of Engineering & Technology 7, no. 1.1 (December 21, 2017): 346. http://dx.doi.org/10.14419/ijet.v7i1.1.9850.

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In this paper the methods to control operation of shunt and series inverters using power flow controller (UPFC) is analyzed with real power flow in power system transmission line. These operation mode using UPFC are executed to reduce Swaying in the control framework transport. The execution about every system may be resolved toward the predefined administrative control. Those arrangement What's more shunt converter working under four separate blending from claiming working modes may be used to ponder An example force framework organize. The line flow in MW oscillation damping is predicated with various modes of operations and verified same with MATLAB/ SIMULINK.

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Ketabi, Shiva, Matthew Buckley, Parsa Pazhooheshy, Faraz Farahvash, and Yashar Ganjali. "Correlation-Aware Flow Consolidation for Load Balancing and Beyond." ACM SIGMETRICS Performance Evaluation Review 49, no. 4 (June 2, 2022): 105–10. http://dx.doi.org/10.1145/3543146.3543170.

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Existing load balancing solutions rely on direct or indirect measurement of rates (or congestion) averaged over short periods of time. Sudden fluctuations in flow rates can lead to significant undershooting/ overshooting of target link loads. In this paper, we make the case for taking variations and correlations of flows into account in load balancing. We propose correlation-aware flow consolidation, i.e. aggregating inversely correlated (or uncorrelated) flows into superflows and using them as building blocks for load balancing. Superflows are smoother than individual flows, and thus are easier to estimate with a higher confidence, and can reduce overshooting/ undershooting of link capacities. We present heuristic methods combined with predictive models to consolidate flows and show they can lead to significant reductions in rate standard deviations compared to correlation-agnostic solutions (up to 33% and 12% improvements at the 50th and 99th percentiles respectively for 20 superflows based on real traffic traces).

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Goldstein, A., S. Kislyakov, and M. Fenomenov. "Chaos Theory Methods for Contact-Center Dinamic Control." Proceedings of Telecommunication Universities 7, no. 2 (June 30, 2021): 18–23. http://dx.doi.org/10.31854/1813-324x-2021-7-2-18-23.

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The work is devoted to searching for optimal control methods for contact center, in particular, methods for predicting the load for further calculation of required number of operators. If the number of operators is always more than required, then the owners of the contact center will incur financial losses. If there are too few employees, the quality of service will decline. Predicting the load of the contact center is required in order to bring the optimal number of operators to work in advance. It is proposed to apply chaos theory to predict the incoming load of a contact center. Positive value of the Lyapunov index indicates the chaotic behavior of the input flow of the load. To predict the load, the methods of linear and nonlinear forecasting and the method of global approximation are used. The paper presents the results of comparing these methods for the problem of predicting the incoming load of contact center.

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Ferreira, L. A. F. M. "Tellegen's theorem and power systems-new load flow equations, new solution methods." IEEE Transactions on Circuits and Systems 37, no. 4 (April 1990): 519–26. http://dx.doi.org/10.1109/31.52753.

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27

Leonidopoulos, Georgios. "Fast linear method and convergence improvement of load flow numerical solution methods." Electric Power Systems Research 16, no. 1 (January 1989): 23–31. http://dx.doi.org/10.1016/0378-7796(89)90034-5.

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Mao, Chunliu, Juan-Carlos Baltazar, and Jeff S. Haberl. "Comparison of ASHRAE peak cooling load calculation methods." Science and Technology for the Built Environment 25, no. 2 (October 4, 2018): 189–208. http://dx.doi.org/10.1080/23744731.2018.1510240.

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Acarnley, Paul. "Power System Load Flow Analysis Using an Excel Workbook." International Journal of Electrical Engineering & Education 42, no. 2 (April 2005): 185–202. http://dx.doi.org/10.7227/ijeee.42.2.6.

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The paper describes the development and features of an MS-Excel Workbook (available at www.reseeds.com ), which illustrates four methods of power system load flow analysis. Iterative techniques are represented by the Newton-Raphson and Gauss-Seidel methods. The Workbook also includes two search algorithms: genetic algorithms and simulated annealing.

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Aien, M., R. Ramezani, and S. Mohsen Ghavami. "Probabilistic Load Flow Considering Wind Generation Uncertainty." Engineering, Technology & Applied Science Research 1, no. 5 (October 17, 2011): 126–32. http://dx.doi.org/10.48084/etasr.64.

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Renewable energy sources, such as wind, solar and hydro, are increasingly incorporated into power grids, as a direct consequence of energy and environmental issues. These types of energies are variable and intermittent by nature and their exploitation introduces uncertainties into the power grid. Therefore, probabilistic analysis of the system performance is of significant interest. This paper describes a new approach to Probabilistic Load Flow (PLF) by modifying the Two Point Estimation Method (2PEM) to cover some drawbacks of other currently used methods. The proposed method is examined using two case studies, the IEEE 9-bus and the IEEE 57-bus test systems. In order to justify the effectiveness of the method, numerical comparison with Monte Carlo Simulation (MCS) method is presented. Simulation results indicate that the proposed method significantly reduces the computational burden while maintaining a high level of accuracy. Moreover, that the unsymmetrical 2PEM has a higher level of accuracy than the symmetrical 2PEM with equal computing burden, when the Probability Density Function (PDF) of uncertain variables is asymmetric.

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31

Chowdhury, Amit Kumar, Surajit Mondal, Mainak Mukherjee, and Pabitra Kumar Biswas. "Mega Watt Security Assessment of Power Systems." International Letters of Chemistry, Physics and Astronomy 58 (September 2015): 9–15. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.58.9.

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This paper deals with the security aspects of power system by evaluating the severity of transmission line outage. MW security assessment is made by determining the power flow in the line using load flow for each contingency. The severity of contingency is measured using a scalar index called performance index (PI). DC load flow and Fast Decoupled load flow are used as approximate and exact load flow methods for MW security assessment respectively. Contingency analysis is carried out and ranked lists in the decreasing order of severity based on PI values are prepared for standard test systems. The severity of line is evaluated and compared using these load flow methods. A new method is proposed to avoid Masking problems in MW security assessment. Security analysis is made on standard test systems such as 5, 6, IEEE 14 and IEEE 30 bus systems under present study.

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Chowdhury, Amit Kumar, Surajit Mondal, Mainak Mukherjee, and Pabitra Kumar Biswas. "Mega Watt Security Assessment of Power Systems." International Letters of Chemistry, Physics and Astronomy 58 (September 2, 2015): 9–15. http://dx.doi.org/10.56431/p-ycsnwz.

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This paper deals with the security aspects of power system by evaluating the severity of transmission line outage. MW security assessment is made by determining the power flow in the line using load flow for each contingency. The severity of contingency is measured using a scalar index called performance index (PI). DC load flow and Fast Decoupled load flow are used as approximate and exact load flow methods for MW security assessment respectively. Contingency analysis is carried out and ranked lists in the decreasing order of severity based on PI values are prepared for standard test systems. The severity of line is evaluated and compared using these load flow methods. A new method is proposed to avoid Masking problems in MW security assessment. Security analysis is made on standard test systems such as 5, 6, IEEE 14 and IEEE 30 bus systems under present study.

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Chen, Qing Lin, and Shao Fen Lin. "Weight Reduction Design Methods of Wring Based on Load Spectrum." Advanced Materials Research 655-657 (January 2013): 340–48. http://dx.doi.org/10.4028/www.scientific.net/amr.655-657.340.

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The hydraulic systemic load spectrum of wring has been constructed by time with press and flow rate under deferent working condition on ship. The root mean square value of reel axial torque was calculated by weighted processing and was taken for the basis of the calculation on structure critical load. Based on the block of load spectrum, the virtual fatigue calculation showed the relation about the static strength and critical load block of load spectrum. Keeping the ratio of the static strength and critical load, the force analysis of wring reel aimed to the structure weight reduction by finite element analysis (FEA). The established wholly parametric and weight reduction model of wring structural part had been computed and meets the strength and stiffness requirement. The weight of this reel is reduced by 15.5 kg and lightweight effect is 8%. This method of weight reduction can be used to the reference on the design of hydraulic deck machinery of ship and hydraulic actuation construction machinery.

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Breitenstein, C., and R. Radespiel. "Flow simulation of the flight manoeuvres of a large transport aircraft with load alleviation." Aeronautical Journal 126, no. 1298 (October 28, 2021): 681–709. http://dx.doi.org/10.1017/aer.2021.93.

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AbstractA new method for predicting manoeuvre loads on a large transport aircraft with a swept-back wing and a load alleviation system based on control surface deflections is developed. For this purpose, three-dimensional Reynolds-averaged Navier–Stokes (RANS) simulations of the rigid wing–fuselage configuration are performed while the aerodynamics of the tailplane are estimated by means of handbook methods. For a closer analysis, different quasi-steady pitching manoeuvres are chosen based on the CS-25 regulations. One of these manoeuvres is also simulated with active load alleviation, leading to a reduction in the wing-root bending moment by more than 40%. Besides demonstrating the potential of the considered load alleviation system, it is shown which manoeuvres are especially critical in this context and which secondary effects come along with load alleviation.

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Herrera-Briñez, María Camila, Oscar Danilo Montoya, Lazaro Alvarado-Barrios, and Harold R. Chamorro. "The Equivalence between Successive Approximations and Matricial Load Flow Formulations." Applied Sciences 11, no. 7 (March 24, 2021): 2905. http://dx.doi.org/10.3390/app11072905.

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This paper shows the equivalence of the matricial form of the classical backward/forward load flow formulation for distribution networks with the recently developed successive approximations (SA) load flow approach. Both formulations allow solving the load flow problem in meshed and radial distribution grids even if these are operated with alternating current (AC) or direct current (DC) technologies. Both load flow methods are completely described in this research to make a fair comparison between them and demonstrate their equivalence. Numerical comparisons in the 33- and 69-bus test feeder with radial topology show that both methods have the same number of iterations to find the solution with a convergence error defined as 1×10−10.

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Clement, A. "Improving uncertain nutrient load estimates for Lake Balaton." Water Science and Technology 43, no. 7 (April 1, 2001): 279–86. http://dx.doi.org/10.2166/wst.2001.0436.

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Annual nutrient loads have been estimated for Lake Balaton over three decades. Tributaries may transport about half of the loads into the lake. The contribution of diffuse sources may reach two thirds of the total load. Biweekly/monthly water quality monitoring on small inflows (0.01 m3/s-0.3 m3/s range) results in a high uncertainty of load estimates. This paper evaluates the degree of uncertainties by using analytical expressions of sampling theory. Load-flow relationships were derived for five streams and annual total phosphorus load was predicted by four load estimation methods. A seasonal regression model, based upon the evaluation of historical set of observed phosphorus loads, appeared best to refine load estimates on small inflows. Correction frequently led to load estimates that exceeded uncorrected loads by a factor of two to three. Since the dynamics of the watercourses determined the errors of load estimates, stratified sampling is needed to decrease the uncertainties.

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Bernards, Raoul, Werner van Westering, Johan Morren, and Han Slootweg. "Analysis of Energy Transition Impact on the Low-Voltage Network Using Stochastic Load and Generation Models." Energies 13, no. 22 (November 21, 2020): 6097. http://dx.doi.org/10.3390/en13226097.

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The energy transition poses a challenge for the electricity distribution network design as new energy technologies cause increasing and uncertain network loads. Traditional static load models cannot cope with the stochastic nature of this new technology adoption. Furthermore, traditional nonlinear power methods have difficulty evaluating very large networks with millions of cables, because they are computationally expensive. This paper proposes a method which uses copulas for modeling the uncertainty of technology adoption and load profiles, and combines it with a fast linear load flow model. The copulas are able to accurately model the stochastic behavior of solar irradiance, load measurements, and mobility data, converting them into electricity load profiles. The linear load flow model has better scalability and stability compared to traditional load flow models. The models are applied to a case study which uses a real-world dataset consisting of a realistic technology adoption scenario and a low-voltage network with millions of cables, which considers both voltage and current problems. Results show that risk profiles can be generated for all cables in the network, resulting in a valuable map for the district network operator as to where to focus their efforts.

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Tien Tay, Lea, and Kai Seng Chieng. "Performance Study of Load Flow Algorithms in Well and Ill-Conditioned Systems." Indonesian Journal of Electrical Engineering and Computer Science 8, no. 2 (November 1, 2017): 414. http://dx.doi.org/10.11591/ijeecs.v8.i2.pp414-419.

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Existing transmission systems are classified as either ill systems or healthy systems. Most of the load flow algorithms works proficiently under well-conditioned systems. However, some of those algorithms fail to produce the accurate results for ill-conditioned systems. This paper investigates the performance of eight load flow algorithms based on the conventional Newton-Raphson, Fast-decoupled and Second-order Load Flow methods for a wide range of electrical bus system sizes. Tests are carried out for each load flow algorithm on six different standard bus systems, each with five different ill-conditioning levels. The results show that improved load flow model with constant Jacobian has advantages over the conventional load flow approach in both well and ill-conditioned system, especially for large-scale system.

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Aleshkin, A. P., A. R. Pavlov, O. M. Stepanyuk, and N. S. Toporkov. "Methods of prediction intensity of user loads subscribers Earth stations in a satellite communication network." Issues of radio electronics, no. 11 (November 20, 2019): 11–17. http://dx.doi.org/10.21778/2218-5453-2019-11-11-17.

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There are considered the features of a satellite communication system organization on the basis of DVB-RCS standard. In order to use effectively the satellite channel capacity it is necessary to form an optimal frequency-and-time structure of a reverse channel that depends, as well, on efficiency of earth stations user load intensity forecast. The methodology of forecast of earth stations subscribers user loads by means of estimation of static and dynamic characteristics of a packet data traffic is proposed. For estimation of input flow intensity and forecast of required capacity approximation methods are used. The method uses linear and polynomial approximation models. First, the parameters of approximating equation are defined, than adequacy of approximation equations to the input information flow intensity is performed. After extrapolation of information flow intensity estimation the maximum value of input information flow intensity forecasted at the moment tk is defined.

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Tostado‐Véliz, Marcos, Salah Kamel, and Francisco Jurado. "Development of different load flow methods for solving large‐scale ill‐conditioned systems." International Transactions on Electrical Energy Systems 29, no. 4 (December 9, 2018): e2784. http://dx.doi.org/10.1002/etep.2784.

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Khalil, Umair, Muhammad Yousaf Ali Khan, Umer Amir Khan, and Shahid Atiq. "Power Flow Control by Unified Power Flow Controller." April 2020 39, no. 2 (April 1, 2020): 257–66. http://dx.doi.org/10.22581/muet1982.2002.04.

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The demand of energy usage is increasing rapidly and to meet the energy requirements, best possible transmission systems should be adopted to avoid energy losses in our transmission systems. In Pakistan’s WAPDA (Water & Power Development Authority) system, the rapid increase in load and less generation capacity has increased load shedding thought the country. The government has planned to increase the generation capacity but the supply companies are facing line load-ability, environmental constraints, power limitations problems etc. Most of the supply companies prefer to extend the existing electrical networks instead of building new network to reduce financial burdens. In this paper the implementation of the FACTS (Flexible AC Transmission Systems) Devices in an electrical network is described. The FACTS devices enhance power transfer capacity of the line without adding new transmission line. These devices also protect the system from overloading in case of any contingency in the electrical network. The control of power flow, reactive power compensation and voltage control are the main capabilities of FACTS devices. This paper describes the impacts of FACTS devices on improving the voltage stability and power handling capability of a transmission line. The proposed methods for the controllable flow of active and reactive power in a transmission line are also elaborated. A simple electrical system is examined to explain the improvement in the constraints of power system using FACTS devices.

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Liu, Jianbin, Haibo Xie, Liang Hu, Huayong Yang, and Xin Fu. "Flow force regulation of the main poppet in a large flow load control valve." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 231, no. 8 (June 9, 2017): 706–20. http://dx.doi.org/10.1177/0957650917714370.

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This paper presents the regulation methods of flow forces acting on the main poppet in a large flow load control valve. The negative flow forces working on the originally designed main poppet, which is as high as 10% of the control force, act as a big disturbance to the main poppet position control, resulting in poor lowering speed control performance of the load control valve or even instability of the main poppet. Firstly, by introducing a damping tail structure to the main poppet, the direction of the flow forces can be regulated to positive and best stability of the main poppet can be achieved with the calculated best parameter combination. Secondly, by introducing a damping tail with holes to the main poppet, the positive flow forces of all main poppet positions can be reduced to minimum, which results in minimum disturbance for the control of main poppet. Computational fluid dynamics calculations were conducted to analyze how the damping tail parameters affect the flow forces and obtain the best parameter combinations. A test rig was set up to validate the effect of above methods. Good agreement of the computational fluid dynamics calculations and experiment results indicates that the proposed methods can provide guidance for the flow force regulation of other valve poppets.

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Haraldsen, Trond Knapp, and Per Stålnacke. "Methods for water quality sampling and load estimation in monitoring of Norwegian agricultural catchments." Hydrology Research 37, no. 1 (February 1, 2006): 81–92. http://dx.doi.org/10.2166/nh.2006.0007.

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Different sampling procedures are applied to monitor water quality in agricultural catchments in the Nordic countries. The need for comparing monitoring results from the Nordic countries was the incentive for establishing a project aimed at comparing estimates of nutrient losses determined using different sampling strategies. Three different sampling methods were compared in three Norwegian catchments: weekly flow-proportional composite sampling (FPCS), weekly composite sampling with temporally equidistant subsampling every second hour (TECS) and temporally equidistant weekly point sampling (PS). Differences in load estimated between the three tested sampling strategies were smaller for nitrogen than for phosphorus or suspended solids. Point sampling tended to miss some of the peaks in concentrations of phosphorus and suspended solids, particularly during flow events, causing significantly lower load estimates for phosphorus and suspended solids by point sampling compared with composite sampling strategies. Flow-proportional composite sampling gave the most reliable data for event-responsible compounds or when the predictability of peaks was low. Based on this investigation, and similar studies in the other Nordic countries, a flow-proportional sampling strategy is recommended for studies of water quality in agricultural streams.

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Seng, Chieng Kai, Tay Lea Tien, Janardan Nanda, and Syafrudin Masri. "Load Flow Analysis Using Improved Newton-Raphson Method." Applied Mechanics and Materials 793 (September 2015): 494–99. http://dx.doi.org/10.4028/www.scientific.net/amm.793.494.

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This paper describes a simple, reliable and swift load-flow solution method with a wide range of practical application. It is attractive for accurate or approximate off-and on-line calculations for routine and contingency purposes. It is applicable for networks of any size and can be executed effectively on computers. The method is a development on conventional load flow principle and its precise algorithm form has been determined to bring improvement to the conventional techniques. This paper presents a comparative study of the new constant Jacobian matrix load flow method built based on several conventional NR load flow methods. Assumptions are made so as to make the matrix constant, thus eliminating the need of calculating the matrix in every iteration. The proposed method exhibits better computation speed.

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Hiwarkar, Dr Chandrashekhar S., Abhay M. Halmare, Anurag A. Belsare, Nitin B. Mohriya, and Roshan Milmile. "Load Flow Analysis on IEEE 14 Bus System." International Journal for Research in Applied Science and Engineering Technology 10, no. 4 (April 30, 2022): 1572–74. http://dx.doi.org/10.22214/ijraset.2022.41590.

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Abstract: This article presents a load flow analysis of an IEEE14 BUS system using the Newton-Raphson method, which simplifies the analysis of load balancing problems. The software used for the programming platform is MATLAB. This paper gives an overview of the electrical performance and power flows (real and reactive) under a steady state. There are various methods for load flow computations. The gauss-seidel method is more popular in smaller systems because of less computational time. In the case of larger systems computation time increases in this condition, the Newton-Raphson method is preferred. This project aims to develop a MATLAB program to calculate voltages and active and reactive power at each bus for IEEE 14 bus systems. The MATLAB program is executed with the input data and results are compared. Keywords: load flow studies, Newton-Raphson method, IEEE 14 bus system.

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Kirthiga, M. Venkata, and S. Arul Daniel. "Computational Techniques for Autonomous Microgrid Load Flow Analysis." ISRN Power Engineering 2014 (May 11, 2014): 1–12. http://dx.doi.org/10.1155/2014/742171.

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This paper attempts at developing simple, efficient, and fast converging load flow analysis techniques tailored to autonomous microgrids. Two modified backward forward sweep techniques have been developed in this work where the largest generator is chosen as slack generator, in the first method and all generator buses are modeled as slack buses in the second method. The second method incorporates the concept of distributed slack bus to update the real and reactive power generations in the microgrid. This paper has details on the development of these two methodologies and the efficacy of these methods is compared with the conventional Newton Raphson load flow method. The standard 33-bus distribution system has been transformed into an autonomous microgrid and used for evaluation of the proposed load flow methodologies. Matlab coding has been developed for validating the results.

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Yan, Qi, Chao Yang, and Zhiqiang Wan. "A Comparative Regression Analysis between Principal Component and Partial Least Squares Methods for Flight Load Calculation." Applied Sciences 13, no. 14 (July 21, 2023): 8428. http://dx.doi.org/10.3390/app13148428.

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This study investigates and compares various multivariate regression methods, including principal component regression (PCR) and partial least squares regression (PLSR), for flight load analysis and demonstrates their high learning efficiency and strong generalization capabilities, making them highly suitable for this purpose. The flight load data of a civil aircraft use altitude, Mach number and load factors as input parameters, which are used as sample data to establish regression models for predicting wing loads under different flight conditions. The accuracy of all regressions are confirmed through evaluation, with PLSR being the most efficient. In the comparison of computational times, it was found that the computational efficiency of regression methods was significantly superior to traditional panel methods. The flight load calculation shows that PCR and PLSR can significantly improve analysis efficiency and provide new insights into efficient flight load analysis.

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Thiebaud, Robert S., Takashi Abe, Jeremy P. Loenneke, Tyler Garcia, Yohan Shirazi, and Ross McArthur. "Acute Muscular Responses to Practical Low-Load Blood Flow Restriction Exercise Versus Traditional Low-Load Blood Flow Restriction and High-/Low-Load Exercise." Journal of Sport Rehabilitation 29, no. 7 (September 1, 2020): 984–92. http://dx.doi.org/10.1123/jsr.2019-0217.

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Context: Blood flow restriction (BFR) increases muscle size and strength when combined with low loads, but various methods are used to produce this stimulus. It is unclear how using elastic knee wraps can impact acute muscular responses compared with using nylon cuffs, where the pressure can be standardized. Objective: Investigate how elastic knee wraps compare with nylon cuffs and high-load (HL)/low-load (LL) resistance exercise. Design: A randomized cross-over experimental design using 6 conditions combined with unilateral knee extension. Setting: Human Performance Laboratory. Participants: A total of 9 healthy participants (males = 7 and females = 2) and had an average age of 22 (4) years. Intervention: LL (30% of 1-repetition maximum [1-RM]), HL (70% 1-RM), BFR at 40% of arterial occlusion pressure (BFR-LOW), BFR at 80% of arterial occlusion pressure (BFR-HIGH), elastic knee wraps stretched by 2 in (PRACTICAL-LOW), and elastic knee wraps stretched to a new length equivalent to 85% of thigh circumference (PRACTICAL-HIGH). BFR and practical conditions used 30% 1-RM. Main Outcome Measures: Muscle thickness, maximum voluntary isometric contraction, and electromyography amplitude. Bayesian statistics evaluated differences in changes between conditions using the Bayes factor (BF10), and median and 95% credible intervals were reported from the posterior distribution. Results: Total repetitions completed were greater for BFR-LOW versus PRACTICAL-HIGH (BF10 = 3.2, 48.6 vs 44 repetitions) and greater for PRACTICAL-LOW versus BFR-HIGH (BF10 = 717, 51.8 vs 36.3 repetitions). Greater decreases in changes in maximum voluntary isometric contraction were found in PRACTICAL-HIGH versus HL (BF10 = 1035, ∼103 N) and LL (BF10 = 45, ∼66 N). No differences in changes in muscle thickness were found between LL versus PRACTICAL-LOW/PRACTICAL-HIGH conditions (BF10 = 0.32). Greater changes in electromyography amplitude were also found for BFR-LOW versus PRACTICAL-HIGH condition (BF10 = 6.13, ∼12%), but no differences were noted between the other BFR conditions. Conclusions: Overall, elastic knee wraps produce a more fatiguing stimulus than LL or HL conditions and might be used as an alternative to pneumatic cuffs that are traditionally used for BFR exercise.

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Hu, Jiawei, Yangang Wang, Hanru Liu, Weixiong Chen, and Yong Xu. "Comparative Study on Modal Decomposition Methods of Unsteady Separated Flow in Compressor Cascade." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 38, no. 1 (February 2020): 121–29. http://dx.doi.org/10.1051/jnwpu/20203810121.

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The present work investigated the vortex structure and fluctuation frequency characteristics generated by boundary layer separation of a high-load compressor cascade using modal decomposition methods. The dominant modes and dynamic behaviors of unsteady flow in the cascade were obtained, and the differences of three modal decomposition methods (Proper Orthogonal Decomposition, Dynamic Mode Decomposition and Spectral Proper Orthogonal Decomposition) in feature recognition of cascade flow were discussed. The results show that:(1) The POD method can accurately extract the dominant spatial structure of the flow field, but the modal coefficients are multi-frequency coupled, which makes the dominant modal characteristics of cascade flow unclear. (2) The standard DMD method can obtain the spatial-temporal single frequency mode of cascade flow, as well as their growth rates and frequencies. However, this method is likely to capture the suboptimal mode of large amplitude with large attenuation rate, and fails to obtain the high-frequency coherent structure, which makes it impossible to obtain the dominant feature with limited mode number. (3) The SPOD method, based on spectral characteristics, can obtain spatial and temporal single frequency modes, and there is no modal screening problem. The use of spectral estimation method (SPOD) reduces the sensitivity to numerical noise. This method can obtain the low-rank behavior of cascade flow, which is helpful to understand cascade flow mechanisms. Therefore, SPOD method is more advantageous for the modal analysis of unsteady separated flow in high-load compressor cascade.

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Zhang, Chen Chen, Xu Zhang, Yan Hui Wang, and Ling Xi Zhu. "Research on Calculation Methods of Urban Rail Transit Station Ticket Gates Load Degree." Applied Mechanics and Materials 330 (June 2013): 569–73. http://dx.doi.org/10.4028/www.scientific.net/amm.330.569.

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There are many ticket gates at the subway station. The managers are quite careful about the load degree of the ticket gates. This paper studies two different methods to calculate the load degree of the ticket gates. One is based on the station ticket gates group as the research object, and the other one is based on the volume of passenger flow passing in and out of the station as the research object. Then we use the data investigated at Chaoyangmen station in Beijing to test and verify both of the methods. At last, we can get the conclusion that we can get the same result by the two methods, but the method of based on the volume of passenger flow passing in and out of the station is more reasonable.

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Journal articles on the topic 'Load Flow Methods'

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