Load Flow Research Articles

Simulation-based probabilistic-harmonic load flow for the study of DERs integration in a low-voltage distribution network

<abstract><p>The integration of distributed energy resources (DERs) and, therefore, power electronic devices into distribution networks leads to harmonic distortion injection. However, studying harmonic distortion solely through deterministic approaches presents challenges due to the inherent random behavior of DERs. This study introduced a strategy that leverages PowerFactory's harmonic load flow tool. By combining it with Python co-simulation, probabilistic load flows can be developed. These load flows utilize current sources to represent harmonic distortion emitters with predefined harmonic spectra. The proposed strategy was implemented on a real network, where two different capacities of DERs were integrated at various locations within the network. The distributions for the total harmonic distortion of voltage ($ THD_{v} $) and the total harmonic distortion of current ($ THD_{i} $) were obtained 24 hours a day in nodes and lines of the network. The procedure allowed considering the uncertainty associated to the DERs integration in distribution networks in the study of harmonic distortion, which, speaking from a simulation approach, is scarce in the literature.</p></abstract>

Stochastic Transmission Planning: Latent Factor Approximation of AC Costs With DC Subproblems

Transmission planning requires solving an optimal power flow problem for each considered investment plan for multiple operating conditions. AC power flow formulations are more accurate, but for transmission planning on large systems may be computationally intractable and can converge to local optima. Regional transmission studies usually rely on linearized DC power flow formulations, which reduce computation time but sometimes produce solutions that are inferior when the AC flows are resolved. We propose an approach to regional-scale transmission planning that approximates the AC power flow results using the faster DC formulation. An initial sample of investment plans is simulated with both AC and DC power flows, and then the singular value decomposition is applied to characterize the error between the two formulations and form a projection that estimates the AC costs from the DC costs. The estimation is used in a DC formulation of the transmission investment problem. We show that the proposed approach accurately estimates the AC operation costs and returns expansion plans that are consistently reliable with AC power flows. We also demonstrate that traditional DC formulations can produce low-cost, AC-feasible investment plans if enough representative hours are selected and weighted effectively.

Application of Covariance Matrix Adaptation‐Evolutionary Strategy for Modified Constrained Optimal Power Flow Problem Incorporating Valve Point and Emission Effect

A prevailing problem in power and energy subsystems is the smooth operation of electric energy systems. This work presents recent, efficient, and reliable evolutionary algorithm for solving the optimal power flow (OPF) analysis. All various practical complex equality and inequality constraints, namely, bus voltages, real powers of the generator buses, tap settings of the transformers and the reactive power generations, shunt compensation, and emission, are considered for the real‐world scenario. Primary feature in a gas power plant that raises a lot of computational shortcomings with nonlinear structure in fuel cost is valve point effect. The existing research works have not factored the valve point effect and lack the accuracy in the fuel cost minimization and do not reflect the various practical complexities such as valve point and emission effects in the OPF problem formulation. This paper, for the first time, introduces modified OPF problem formulation incorporating valve point effect and applies covariance matrix adaptation‐evolution strategy (CMA‐ES) for solving the modified OPF problem. The algorithm is scrutinised and tested on a modified IEEE‐30‐bus platform for various OPF objectives such as cost minimization, transmission loss, and total voltage deviation, subjected to practical constraints. Load flow analysis has been carried out using the Newton–Raphson method. This work aims to lay the foundation in such a way that it can be applicable in a real‐world scenario for any number of buses.

Constant Voltage Model of SCIG-Based Variable Speed Wind Power Plant for Load Flow Analysis

In recent years, the application of variable-speed wind power plants (WPPs) has become more and more popular and surpassed fixed-speed WPPs. This popularity is mainly because variable-speed WPPs are much more efficient in capturing or extracting wind energy than fixed-speed WPPs. Due to its relatively cheaper cost, the use of SCIG (Squirrel Cage Induction Generator)-based variable-speed WPP is currently increasing. This type of WPP is usually equipped with a power electronics converter to obtain a broader range of variable-speed operations. Modeling the power system components is undoubtedly necessary for performing the system analysis (including load flow analysis). This paper discusses the steady-state model of SCIG-based variable-speed WPP for load flow analysis of electric power distribution systems. The proposed model can be used for SCIG-based variable-speed WPP with voltage control operating mode. The model was developed based on formulas that calculate the turbine mechanical power input and the WPP electrical power output. This paper also presents a case study in which the proposed model is applied to a representative electric power distribution system.

Parallel Operation for 11 kV Ring System with Normally Open Point at Distribution Networks in AADC

Currently, Al Ain Distribution Company (AADC) 11 kV distribution circuits are electrically split by Normal Open Points (NOP)s. NOPs can be closed for load restoration in case of planned or unplanned outages. Also, changing the NOP locations helps in load shifting to achieve network optimization between adjacently located 33/11 kV primary substations. This paper discusses a new operation mode in medium voltage distribution power network of AADC at Al Ain area in the United Arab Emirates by introducing closed loops of parallel 11 kV feeders from different busbars or substations. This operation mode is intended to end the continuous debate of optimal NOP locations in addition to expected reduction in the required time for load restoration in case of failures at distribution (11/0.4 kV) substations. A detailed case study is performed to explore the achieved benefits and enhancements on load balancing, voltage profile, and power factor in medium voltage networks. On the other hand, the impact on load flow, protection scheme, and loading violation are evaluated. Furthermore, the proposed model is in line with the regulations of the Department of Energy (DoE), regulatory body in Abu Dhabi Emirate, and should fully comply with Electricity Distribution Code (EDC) of Security of Supply Standards. Accordingly, while the current used operation mode is still valid, it is found that closed loops arrangement can be only allowed for rings from same 33/11 kV substations feeding from same source with considerable protection limitations. Moreover, it was concluded that closed loops from different 33/11 kV Substations will result in load flow problems.

Load flow, short circuit and motor starting studies in electrical power substations

Load flow, short circuit and motor starting studies in electrical power substations

ASSESSMENT OF MECHANICAL RESPONSES BETWEEN TRABECULAR BONES AND POROUS SCAFFOLDS UNDER STATIC LOADING AND FLUID FLOW CONDITIONS: A MULTISCALE APPROACH

A three-dimensional porous scaffold is one of the standard and evocative approaches to create a favorable biomechanical environment in tissue engineering for tissue regeneration and repair. The architectural design parameters (e.g., pore-shape, size, distribution and interconnectivity; permeability; specific surface area; etc.) of the porous model have significant influence on their mechano-biological behavior. Along with this, interstitial fluid flow dynamics within the porous scaffold also regulate cell behavior. Therefore, von Mises stress, deformation, wall shear stress, and permeability across the model have been investigated. In this work, a multiscale approach has been applied to explore the various mechanical stimuli that control the cell mechanobiology within a scaffold and compare it to the natural bone with different porosity to identify which architectural design of the scaffold is close to the bone.

Analysis and Dynamic Stabilization of a HighVoltage VSC-MTDC Grid with DC Power Flow Controller Connected to Extremely Weak AC Systems

Analysis and Dynamic Stabilization of a HighVoltage VSC-MTDC Grid with DC Power Flow Controller Connected to Extremely Weak AC Systems

A Steady State Model of Solid-State Transformer for a Sequential AC–DC Power Flow in AC–DC Power Grids

A Steady State Model of Solid-State Transformer for a Sequential AC–DC Power Flow in AC–DC Power Grids

Smart Grid Solutions for Loss Minimization and Voltage Profile Enhancement using Genetic Algorithm-Optimized Capacitor and Solar PV Integration in Radial Feeder

This research addresses the critical challenge of power loss in distribution systems caused by increasing electricity demand. It focuses on reducing power losses and enhancing voltage profiles in a radial distribution system through the optimal placement of capacitors and solar PV. The project employs comprehensive analysis and optimization techniques, including forward and backward sweep algorithms for load flow analysis and Genetic Algorithm (GA) in MATLAB. The performance of the distribution system is evaluated by considering parameters such as power loss and voltage characteristics. Simulation results on an IEEE 33-bus radial distribution network validate significant improvements after various configurations, including the base case, capacitor case, DG case, and combined DG and capacitor case. In each scenario, active power losses are reduced, reactive power loss diminishes, and voltage profile enhancements are observed. The study further validates these results using ETAP software, ensuring consistency and reliability. Notable improvements are also observed in the Thimi Sallaghari 11KV feeder, showcasing potential practical implementations in real feeders in the future. Different case scenarios are explored for the number of capacitors and DGs, providing insights into the optimal combination for enhanced distribution system performance.

Transformer Outage Contingency in the Southern Interconnected Grid of Cameroon Based on Dynamic Power Flow Simulation

The power system is a network of components having specific operational limits such that any violation of these limits during their operation could lead to more damage in the grid. The grid in Cameroon has been facing several undesired loading events at some sections of the network and the utility company has over the years, employed measures to mitigate these issues. This study has used the ETAP software to conduct a contingency analysis on the largest independent grid in Cameroon, supplying 6 regions in Cameroon. Seventeen transformer outage events in the network were used to conduct the N‐1 scenario‐based contingency, so that the vulnerability of the network can be evaluated. The fast decoupled power flow method was continuously applied on the network, and the different contingency scenarios were ranked using a combination of 4 performance indices. These four performance indices gave information on the impact of the various transformer outage scenarios on the grid. The four indices were added to give a combined value, and the outages were ranked in order of severity based on this combined index. A major contribution of this paper is the use of four scalar indices to classify the critical elements in the grid of a developing country. The initial load flow simulation of the network showed that 12 nodes had under voltages, while 3 transformers and one transmission line were overloaded. The Ngousso corridor suffered one of the worst under voltage situation during the initial power flow study. This is an indication that the utility company needs to undertake intensive network upgrade and implore measures to increase power generation to support the growing loads. It was observed that all the contingency scenarios experienced convergence. The Oyomabang transformer 1 had the highest combined index of 71.20, showing a huge negative impact on the network as a result of the outage of the transformer. This was followed by the Oyomabang transformer 2 with a combined index of 48.63. The results will be very useful to utility operators in prioritizing transformers in the network with high risk of causing huge impact on the network in case of an outage.

Monitoring of medium voltage distribution networks by balance smart meters

This study addresses the issue of monitoring the unbalanced load flow of power distribution networks. To that end, instead of relying on medium voltage meters, we make use of balance smart meters installed on the low-voltage side of distribution transformers. We use a mathematical model of such transformers for real-time calculation of the powers and voltages on the medium voltage side.

Achieving Accurate and Efficient Load Flow Model in Distribution Networks using Hybrid Linearization approach

Achieving Accurate and Efficient Load Flow Model in Distribution Networks using Hybrid Linearization approach

Adsorption and desorption characteristics of flavonoids from white tea using macroporous adsorption resin

White tea contains the highest flavonoids compared to other teas. While there have been numerous studies on the components of different tea varieties, research explicitly focusing on the flavonoid content of white tea remains scarce, making the need for a good flavonoid purification process for white tea even more important. This study compared the adsorption and desorption performance of five types of macroporous resins: D101, HP20, HPD500, DM301, and AB-8. Among the tested resins, AB-8 was selected based on its best adsorption and desorption performance to investigate the static adsorption kinetics and dynamic adsorption-desorption purification of white tea flavonoids. The optimal purification process was determined: adsorption temperature 25 °C, crude tea flavonoid extract pH 3, ethanol concentration 80%, sample loading flow rate and eluent flow rate 1.5 BV/min, and eluent dosage 40 BV. The results indicated that the adsorption process followed pseudo-second-order kinetics. Under the above purification conditions, the purity of the total flavonoids in the purified white tea flavonoid increased from approximately 17.69 to 46.23%, achieving a 2.61-fold improvement, indicating good purification results. The purified white tea flavonoid can be further used for nutraceutical and pharmaceutical applications.

Simulation of 4-Leg Inverter based APF for PV based System with Effective Controller

Today’s rising electricity consumption need more robust power plants. As a result, we’re running out of fossil fuels, which increases pollution. As a result, we are shifting to renewable energy sources, which are better for the environment and save us money in the long run. Power electronic converters are being used more often in distribution networks to link RES. Solar radiation is one of the most widely distributed renewable energy sources worldwide. PV Cell is used to convert solar energy into usable electricity. Consequently, the PV Cell is applied to the converter and disseminated to the matrix later being thus constructed. Numerous controlling issues arise from the non-linear features of the load, despite the fact that numerous methods have been provided for modelling and engineering the PV cell and its point of interaction to the matrix. This exploration presents another control strategy for advancing the exhibition of these framework connecting inverters in 3-stage 4-wire appropriation organizations. The inverter is customized to fill a few needs by including a functioning power channel. To adapt to flow unevenness, load flow music, receptive power interest, and burden impartial flow, the inverter might act as a power converter while infusing power created from RES into the lattice, and as a shunt dynamic power channel while adjusting the framework’s current. It is feasible to do every one of these activities independently or at the same time. An inverter that connection points with the lattice and a 3-stage, 4-wire straight/non-direct lopsided burden at the purpose in like manner coupling might be made to appear to the network as a fair direct burden by using this kind of control. Extensive MATLAB/Simulink simulation experiments prove the efficacy of this novel control strategy.

Turning toward a smart region by implementing a hybrid power system

Distributed generation (DG) especially energy acquired from renewable energy sources (RES) plays a significant role in modern power sector due to high carbon emissions around the globe. Its emerging potential is feasible by implementing microgrids as they are beneficial for networks in terms of increasing flexibility and stability, providing frequency and voltage support, power factor compensation etc. This makes the investment into microgrid incorporating RESs attractive, while at the same time reducing overall investment in the grid. Higher cost and stochastic nature of intermittent RES are complications for the implementation and operation of such solutions. This paper will analyse economic feasibility of hybrid power system (HPS) implementation consisting of a wind generator (WG), a photovoltaic system (PVS), gas combined heat and power plant (CHP) and storage batteries. Each of the elements is optimized according to power demand and RES’s potential. Technical analysis of the grid integration, parallel operation of the system and the grid is analysed with an example of a real medium-voltage distribution network operating in Bosnia and Herzegovina by using quasi-dynamic load flow simulation of one-week time-period. Finally, different operating mechanisms and strategies will be proposed, following the minimal power form the grid premise to satisfy maximum usability of RES’s potential. It is shown that implementing such HPS would be beneficial in terms of both economy and, ecology, as well as in reducing energy losses. Besides, it will reduce power supplying costs and energy losses, as well as and secure better exploitation and utilization of natural renewable energy sources. These technologies positively affect power network by decreasing the risk of network-components overloading, better exploiting the power-generation facilities based on renewable resources and positively impacting voltage profiles. Similar places, situated on remote locations, may use this analysis as an example to follow, to reduce their costs of electricity, acquire more reliable and sustainable power supply, and embrace green future.

Heat Price Field Calculation Based on the Extreme Problem of Searching the Optimal Load Flow in Heat-Supply Systems

Heat Price Field Calculation Based on the Extreme Problem of Searching the Optimal Load Flow in Heat-Supply Systems

Field method for preservation of total mercury in waters, including those associated with artisanal scale gold mining.

Analysis of mercury (Hg) in natural water samples has routinely been impractical in many environments, for example, artisanal and small-scale gold mines (ASGM), where difficult conditions make monitoring of harmful elements and chemicals used in the processes highly challenging. Current sampling methods require the use of hazardous or expensive materials, and so difficulties in sample collection and transport are elevated. To solve this problem, a solid-phase extraction-based method was developed for the sampling and preservation of dissolved Hg in natural water samples, particularly those found around ASGM sites. Recoveries of 85% ± 10% total Hg were obtained during 4 weeks of storage in refrigerated (4 °C, dark) and unrefrigerated (16 °C, dark) conditions, and from a representative river water spiked to 1 μg L-1 Hg2+, 94% ± 1% Hg recovery was obtained. Solid-phase extraction loading flow rates were tested at 2, 5, and 10 mL min-1 with no breakthrough of Hg, and sorbent stability showed no breakthrough of Hg up to 2 weeks after functionalisation. The method was deployed across five artisanal gold mines in Kakamega gold belt, Kenya, to assess Hg concentrations in mine shaft water, ore washing ponds, and river and stream water, including drinking water sources. In all waters, Hg concentrations were below the WHO guideline limit value of 6 μg L-1, but drinking water sources contained trace concentrations of up to 0.35 μg L-1 total Hg, which may result in negative health effects from long-term exposure. The SPE method developed and deployed here is a robust sampling method that can therefore be applied in future Hg monitoring, toxicology, and environmental work to provide improved data that is representative of total dissolved Hg in water samples.

An Approach Inspired by Quantum Mechanics for the Modeling of Large Power Systems

The ever increasing complexity of power systems mandates a further improvement of the numerical methods used for their simulation. We propose a new approach that is inspired by an exact analogy with quantum mechanics, but requires no specific knowledge of quantum physics. This approach allows in particular to use local methods commonly applied in quantum mechanics, such as Lanczos' algorithm. It is applied to computing the load flow and extended to simple dynamic studies where the nodes are described by swing equations. The first set of results are for an ideal 2D-lattice grid to illustrate the method and its main features. Then a contingency analysis by the proposed approach is performed for various realistic power systems, including a model of the European network. This demonstrates the interest of the new approach and its efficiency when compared with state-of-the-art methods, especially for large power system.

Modeling and analyzing multi-megawatt directdrive wind-turbine power system in offshore application: Power flow and short circuit

Renewable energy is experiencing a dramatic growth, in which wind energy plays a key role. The design technique of wind turbines must change to meet high requirements for accuracy and auto-ability. A designed wind turbine must be evaluated with various operational scenarios, while the traditional calculation method could be less effective and time-consuming. Recently, the technical calculation and simulation for electrical power system of a wind turbine are rapidly developed and show the high effectivity in analysis and optimal design. This study performs crucial simulations and analyses, including load flow and short circuit, to evaluate the design of a five-megawatt offshore wind turbine according to International Electrotechnical Commission (IEC) standards using Electrical Transient Analyzer Program (ETAP) software. The technique and methodology presented in this paper help engineers make the right decisions regarding equipment selection and design of a wind turbine’s power system. Therefore, the reliability of designed wind turbine power system is improved in comparison with that of the conventionally designed one.