Load Flow Simulation Research Articles

An intelligent transformer enabled medium voltage AC network for loss minimization and node voltage improvement

Abstract The research work presented here discusses about design and integration of intelligent transformer (IT) to the 15 kV/0.4 kV overloaded distribution feeder in Wolaita Sodo Town. The feeder contains 113 distribution transformers with different capacities ranging from 50 kVA to 1250 kVA. The proposed intelligent transformer is a three-stage modular type using phase shift multicarrier modulations for MMC front end converter. Its middle stage is dual active bridge having input series output parallel (DAB-ISOP) configuration using a phase shift modulation. The smart transformer’s back end uses an MMC inverter using interleaved phase shift modulation. The distribution feeder is modeled in MATLAB/Simulink and the designed intelligent transformer is allocated to it using voltage stability index (VSI). The peak load data, feeder data and transformer data of the distribution system under study are obtained from the utility office. The existing distribution feeder’s performance was evaluated by using backward-forward sweep load flow simulation for peak loading condition. The line flows and voltage profile at all nodes were observed and candidate nodes for enhancement were identified. Placement of modular intelligent transformer by using voltage stability index (VSI) was conducted to improve the voltage profiles, minimize reactive power flows and losses. Based on the simulation results for base case scenario, total power loss of 936.5 kW is obtained. The minimum node voltage of 0.81PU and maximum reactive power flow of 10.9MVAr were observed for the base case simulation. Placement of intelligent transformer at weak node 67 and node 111 improves the node voltages to have a minimum value 0.965 PU and maximum value of 1.05PU. The total power loss is reduced to 511.5 kW (54.5% improvement) after integration of intelligent transformer

A Comparative Evaluation of Community-Used District and Individual Battery Storage Systems for Photovoltaic Energy Systems

The significant expansion of renewable energies has led to an increased importance of storage systems. Decentralized storage solutions, including Home Battery Energy Storage Systems (HBESSs) and District Battery Energy Storage Systems (DBESSs), play a crucial role in this context. This study compares individual HBESSs with a community-used DBESS regarding the grade of autarky and self-consumption, specifically focusing on a planned residential area consisting of 36 single-family houses. A simulation tool was developed to conduct load flow simulations based on household electricity consumption, wallbox profiles for electric vehicle charging, and photovoltaic generation data across various battery capacities and system boundaries. The results demonstrate that the DBESS, compared to individual HBESSs with equivalent cumulative battery capacities, can achieve a maximum increase in the grade of autarky of up to 11.6%, alongside an 8.0% increase in the grade of self-consumption for the given use case. In terms of capacity, the DBESS allows for a saving of up to 68% compared to HBESS to achieve similar results for the studied neighborhood.

An analysis of circuit breaker capacity according to IEC 60909 and IEC 60059 standards at the PT Borneo Alumina Indonesia electrical system

At PT Borneo Alumina Indonesia (PT BAI), the D01 Power Distribution System uses circuit breakers (CB) with a current rating capacity of 1250A for both incoming and outgoing 10kV busbars. Replacing outgoing CBs with the same capacity during maintenance leads to unnecessary waste. This study was conducted to examine the appropriate CB capacity as a substitute for the old CBs in the outgoing 10 kV busbars for loads of 10 kV induction motors and transformers so that recommendations can be made to improve efficiency during maintenance on the D01 Power Distribution System. The Electronic Transient Analyzer Program (ETAP) 19.0.1 software was used to perform short circuit simulations based on IEC 60909 and load flow simulations, which were then adjusted to IEC 60059 and CB products from Siemens. The results show that we can replace the current Siemens CB, which has a rated breaking current specification of 31.5kA, with 25kA during the maintenance period. We can also replace the rated peak value of 80kA with 63kA, and the rated current of 1250A with 630A. Replacement of CB specifications does not change/modify the switchgear panel because the replacement CB matches the brand, dimensions, and size of the currently installed CB. These findings would also help increase efficiency during maintenance on the D01 Power Distribution System. The discussion includes limitations and recommendations for future research.

Decision Process for Identifying Appropriate Devices for Power Transfer between Voltage Levels in Distribution Grids

During the energy transition, new types of electrical equipment, especially power electronic devices, are proposed to increase the flexibility of electricity distribution grids. One type is the solid-state transformer (SST), which offers excellent possibilities to improve the voltage quality in electricity distribution grids and integrate hybrid AC/DC grids. This paper compares SST to conventional copper-based power transformers (CPT) with and without an on-load tap changer (OLTC) and with additional downstream converters. For this purpose, a corresponding electricity distribution grid is set up in the power system analysis tool DIgSILENT PowerFactory 2022. A DC generator like a photovoltaic system, a DC load like an electric vehicle fast charging station, and an AC load are connected. Based on load flow simulations, the four power transformers are compared concerning voltage stability during a generator-based and a load-based scenario. The results of load flow simulations show that SSTs are most valuable when additional generators and loads are to be connected to the infrastructure, which would overload the existing grid equipment. The efficiency of using SSTs also depends on the parameters of the electrical grid, especially the lengths of the low-voltage (LV) lines. In addition, a flowchart-based decision process is proposed to support the decision-making process for the appropriate power transformer from an electrical perspective. Beyond these electrical properties, an evaluation matrix lists other relevant criteria like characteristics of the installation site, noise level, expected lifetime, and economic criteria that must be considered.

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.

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.

Techno-economic Analysis of New Wind Power Plant Development in Southern Sulawesi Electrical Power System

Global warming due to carbon emissions has resulted in climate change, which negatively impacts the lives of living things. On the other hand, electricity demand is increasing every year due to the increasing human population, economic growth and equipment electrification. At the moment, most of the electricity generation in Indonesia uses fossil energy power plants which produce carbon emissions. PT. PLN (Persero) is a State-Owned Enterprise tasked with managing the electricity system in Indonesia. PT. PLN (Persero) through the General Plan for Electricity Supply (RUPTL) for 2021-2030 is targeting the construction of New and Renewable Energy Power Plants. One of possible plan is the Wind Power Plant (WPP) construction in the Southern Sulawesi electrical power system. The use of WPP is expected to reduce carbon emissions. However, the integration of WPP causes other problems in the existing system such as dropped voltage, increased equipment loading, increased short circuit current and decreased stability. So, it is necessary to conduct a study on the effects of integrating WPP into the existing system. Using DIgSILENT Power Factory software, Load Flow, Short Circuit and Transient Stability simulations were carried out. Then an economic analysis was carried out including calculating net present value (NPV), internal rate of return (IRR), profitability index (PI), payback period (PBP) and levelized cost of energy (LCOE. The use of WPP at a certain capacity will not disrupt the stability of the system's power because it is still supported by the fast response generators in the system during variable WPP output. Also voltage drop, equipment loading and short circuit current will not exceed the design value of the system. From financial aspect, with certain assumptions, WPP development can be proven to be economically feasible.

Power-Flow Simulations for Integrating Renewable Distributed Generation from Biogas, Photovoltaic, and Small Wind Sources on an Underground Distribution Feeder

The rapid expansion of distributed generation leads to the integration of an increasing number of energy generation sources. However, integrating these sources into electrical distribution networks presents specific challenges to ensure that the distribution networks can effectively accommodate the associated distributed energy and power. Thus, it is crucial to evaluate the electrical effects of power along the conductors, components, and loads. Power-flow analysis is a well-established numerical methodology for assessing parameters and quantities within power systems during steady-state operation. The University of São Paulo’s Cidade Universitária “Armando de Salles Oliveira” (CUASO) campus in São Paulo, Brazil, features an underground power distribution system. The Institute of Energy and Environment (IEE) leads the integration of several distributed generation (DG) sources, including a biogas plant, photovoltaic installations, and a small wind turbine, into one of the CUASO’s feeders, referred to as “USP-105”. Load-flow simulations were conducted using the PowerWorldTM Simulator v.23, considering the interconnection of these sources. This dataset provides comprehensive information and computational files utilized in the simulations. It serves as a valuable resource for reanalysis, didactic purposes, and the dissemination of technical insights related to DG implementation.

Time-series quasi-dynamic load flow analysis with seasonal load variation to resolve energy nexus for a practical distribution network in Puducherry smart grid system incorporating harmonic analysis and mitigation

Time-series quasi-dynamic load flow analysis is an important methodology to estimate the voltage profiles across various nodes in modern distribution networks. This paper describes the necessity of time-series load flow analysis (LFA) for a real-time power distribution network in Puducherry smart grid system by considering seasonal load variations in the union territory of Puducherry, India to obtain optimal performance. In this study, this load flow analysis has been applied to test systems such as IEEE 69, IEEE 37, IEEE 34 and the Indian utility 29 node distribution network (IU29NDN) in Puducherry smart grid system with unbalanced load patterns and energy sources in close proximity. Modified Decision Making (MDM) algorithm is proposed in this paper to improve voltage profiles with in distribution networks by choosing the size and location of solar photovoltaic (SPV) systems. The variations in the node voltages, real power, and reactive power flows are estimated for distribution networks subjected to seasonal load variations by quasi-dynamic load flow simulations conducted over a period of 24 h with 15-minute step size. Furthermore, a harmonic power flow is illustrated and extended to mitigate the harmonics by optimal placement of shunt capacitors (SCs) in all the test systems by incorporating MDM algorithm.

An efficient method for estimating energy losses in distribution's feeder

This paper explains a simple and efficient methodology for calculating monthly energy losses (EL) using the load loss factor technique and a representative composite load profile. One of the important benefits of the proposed work is a simpler, more efficient and less rigorous method to estimate the system-wide energy loss of an extensive distribution network with reasonable accuracy. The sum of all EL provided by each feeder section is used to calculate the total feeder EL. A base case feeder with a typical cable type and power factor is used to generate regression equations, a peak power loss function to estimate the EL. A case study is then used to show the models and techniques that have been established. The result indicates a high level of agreement with the time-series load flow simulations (smaller than 10% deviations). With this model, an approach to estimate the EL of all radial feeders of various configurations and characteristics could be extended and implemented. The spreadsheet approach is ideal for completing a quick energy audit of existing distribution feeder EL and determining the sensitivity of distribution network efficiency to changes in feeder sections and load characteristics.

An efficient method for estimating energy losses in distribution's feeder

This paper explains a simple and efficient methodology for calculating monthly energy losses (EL) using the load loss factor technique and a representative composite load profile. One of the important benefits of the proposed work is a simpler, more efficient and less rigorous method to estimate the system-wide energy loss of an extensive distribution network with reasonable accuracy. The sum of all EL provided by each feeder section is used to calculate the total feeder EL. A base case feeder with a typical cable type and power factor is used to generate regression equations, a peak power loss function to estimate the EL. A case study is then used to show the models and techniques that have been established. The result indicates a high level of agreement with the time-series load flow simulations (smaller than 10% deviations). With this model, an approach to estimate the EL of all radial feeders of various configurations and characteristics could be extended and implemented. The spreadsheet approach is ideal for completing a quick energy audit of existing distribution feeder EL and determining the sensitivity of distribution network efficiency to changes in feeder sections and load characteristics.

Fundamentals of State-Space Based Load Flow Calculation of Modern Energy Systems

Our current energy landscape is ever-changing, resulting from the ongoing energy transition and introducing a massive expansion of volatile generation feed-in and energy consumption (due to electrification). In turn, the energy supply’s requirements are also being affected. In this context, the energy system’s optimisation across all sectors will only grow in significance, especially in terms of future developments. Facilitating and researching methods for carrying out the aforementioned optimisation creates new demands pertaining to load flow simulation programmes. The volatility of specific participants and their interactions within existing power grids must be evaluated, wherefore the consideration of a large number of time steps but also dynamic simulations becomes inevitable. Carrying out such simulations is possible but very time-consuming. This article compared a variety of conventional load flow simulations such as the current iteration and Newton–Raphson methods and also introduced a novel, state-space based calculation approach, which boasts the potential of structurally increasing simulation speeds. Each of the method’s underlying principles, requirements, and mathematical correlations will be discussed and explained. In the second part of this article, the most important state-space equivalent circuit models of critical operating equipment are introduced. These models are essential for carrying out load flow simulation tests for an exemplary test network but could also be used for dynamic purposes. The previously showcased load flow methods were applied to a test network, with which the simulation methods should be validated. The results show that the state-space simulation has high accuracy while also being very flexible. All in all, the load flow calculation in state-space offers many advantages that could be an interesting alternative to conventional load flow simulations, especially for the analysis of complex, time series-based, and intelligently controlled smart grid power systems. In this context, the direct application of system theoretical methods for stability calculations, controllability, and dynamic system studies is to be mentioned. Optimisation options regarding the processes within the state-space calculation software still promise further significant increases in performance.

Voltage Quality Analysis on Power Transmission Networks: A Case Study of 330kV Power Transmission Networks in Nigeria

The 330kV power transmission system in Nigeria is associated with numerous problems ranging from voltage instability, ageing network, long and weak transmission lines and insulators, absence of protection schemes on the distribution network, lack of spinning reserve to compensate for power shortages, obsolete substation equipment, and higher power losses which substantially affect the reliability of power supply in Nigeria. This study aimed at analysing this scenario and to propose stability improvement measures in the power Network. Voltage instability is a major factor responsible for several system collapse and blackout experienced in the country. This work used necessary data obtained from the National Control Centre (NCC) of Transmission Company of Nigeria (TCN) for load flow simulation with the help of MATLAB R2021a software. Newton-Raphson iterative technique was used to carry out the load flow analysis due to its ability to converge faster with less iteration than Gauss-seidel and fast decoupled iterative techniques. The simulation results revealed that buses 4 (Akangba), 5 (Jos), 7 (Ikeja-west), 10 (Alagbon), 19 (Damaturu), 23 (Sakette), 28 (Ajah), 33 (Oke-Aro), 34 (Ayede) and 42 (Lekki) violate the acceptable limits as its voltage magnitude falls below the standard limit of 0.95-1.05pu. It was also observed that buses 6 (Kaduna), 13 (Yola), 16 (Gombe), 22 (Kano) and 34 (Ayede) are close to the point of instability as their voltage magnitudes are between 0.95 and 0.96 pu. These buses need urgent compensation if stability improvement in the entire Nigerian transmission system is to be achieved.

Electrical load flow analysis of Auchi distribution network without load shedding

The occurrence of loadshedding under normal operating condition in Distribution Network caused a lot of inconveniences to the consumer. However, there is need to examine the state of the distribution network to know the performance without load shedding under normal condition. This research examines the state of Auchi distribution network without load shedding. In order to achieve the aim of the research data was obtained from the distribution company, the modelling of the distribution network obtained was done using ETAP and the load flow simulation was done using Newton Raphson Algorithm to determine the power flow in the network, Bus voltage, losses along the line and transformer losses. The results of the study show that at 80% loading of the transformers in the network, the voltage supply to the consumer is bad under normal condition, since the two out of three 33 kV bus voltages is below the acceptable range of plus or minus 5% of the nominal voltage. Likewise, almost all 11 kV and 0.415kV voltages in the network is below the acceptable limit of plus or minus 10% of the nominal voltage. Furthermore, the result indicates that active power loss in the network is 0.2MW which is very high. This research therefore recommends that the voltage profile of AUCHI distribution network needs improvement in order to improve the quality of supply. Also, since the supply from the grid is be allocated based on the generating capacity this research also recommends that DISCO in charge of Auchi distribution network should also considering the usage of DG in the network which can perform a dual purpose of voltage improvement and addition of power supplied.

A Comparison of Active Power Generated Under Normal Circumstances with the Optimization State Electric Power System

To see the power at normal conditions and at optimal conditions, the researchers used the Electrical Transient Analyzer Program (ETAP). Simulation using Load Flow (LF) and Optimal Power Flow (OPF) is a tool to produce power flow during normal conditions and when the power flow is optimal as a comparison for calculating the cost of generation from the power produced by each generator. After carrying out the Load Flow simulation process, when normal conditions were obtained, the simulation results showed that the active power released by the plant was 807.3 MW. Whereas after carrying out the Optimal Power Flow (OPF) simulation process, at optimal conditions. The simulation results show that the active power released by the generator is 806.2 MW. Keywords: Electrical Transient Analyzer Program (ETAP), Optimal Power Flow (OPF), Losses

Optimal sizing of battery energy storage to enable offshore wind farm black start operation

The goal of transitioning toward 100% renewable energy sources (RES) poses serious challenges to the black start service in electrical power systems. In the instance of a blackout, black start units must restore the power. Conventional black start sources are often taken out of operation to accommodate a larger share of RES and this jeopardises the resiliency of the grid. To replace conventional black start units, offshore wind farms (OWFs) can become future black start providers. However, a black start unit must meet stringent technical requirements, and due to the variable power output of OWFs, it may be challenging to meet these requirements without external support. Therefore, battery energy storage systems (BESSs) are a promising solution to support OWFs to satisfy black start requirements. In this paper, a probabilistic method is applied to determine the optimal BESS power output to support the OWF during black start operation. The considered black start technical requirements are taken from the British Transmission System Operator (TSO). The wind generation behavior is approximated with a Weibull distribution, and BESS power output is estimated considering a worst-case scenario logic. Finally, results are validated with a series of load-flow simulations to verify the time series generation of an OWF. The analysis conducted shows that the required power output from a BESS is dependent mainly on the size of the OWF and the availability requirement dictated by the TSO.

Evaluation and Analysis of Harmonic Distortion on 330kV Network Case Study Selected Sub-Region Nigerian Power System for Improve Power Quality

This paper presented fundamental characteristics of harmonic studies and its related work. The total harmonic distortion (THD) of the transmission line were computed using harmonics contents parameters of the waveform (harmonic voltage and impedance magnitude values). Results of THD for the 330kV transmission line are presented using harmonic load flow analysis in ETAP—domain on the view to measure the level of distortion in the network. Figure 2 shows the section of the harmonic load flow simulation in order to check for degree of harmonic distortion in the system under investigation. The provision of the harmonic frequency with greater magnitude exceeding THD and IHD limits are violated in accordance to IEC 61000-3-6:2008 (European Standards) are used as benchmark for measurement. That is the distortion for current and voltage (THDi% and THD%) are 0.5 and 1.5 respectively particularly harmonic order (h) ≤ 13. Consequently, the harmonic frequency violations with greater magnitude of 5th, 7th, 11th, and 13th order in the network are mitigated with 3-unit of single tuned filter to the affected buses for improved power quality.

Towards locally appropriate electric vehicle hosting capacity regulations

The rapid uptake of electric vehicles (EVs) has introduced significant impacts on various fields, including power distribution grids. To ensure power quality standards are adhered to, network planners and policymakers need to develop EV hosting capacities that guide EV-grid integration. This paper focuses on the practical implementation of EV hosting capacity regulations in various political and social contexts. There is a growing body of literature on EV hosting capacities informed by load flow simulations; these studies typically define the EV hosting capacity as the percentage of households that can install an EV charger before the grid becomes constrained. However, little attention has been given to the practical implementation of these hosting capacities. The way in which EV hosting capacities are defined and enforced has a major impact on both the uptake of EVs as well as the potential to overwhelm grid infrastructure. There are a range of legal mechanisms to implement EV hosting capacities, and these can range from “hard laws” that limit EV charger capacities through legally binding instruments to “soft laws” that utilize tariff-based incentives to shift EV loads to times when the grid has available capacity. Our hypothesis is that a range of factors should influence the design of locally appropriate EV regulation. These criteria may include the history of regulatory compliance in that customer segment, the technical capacity of the grid operator, and the urgency of implementation. The contribution of this paper is to initiate the development of a decision framework to guide the policymakers design locally appropriate EV hosting capacity regulations. The eventual decision framework will be of relevance to network planners and policymakers that are developing regulations to manage the uptake of EVs on their networks.

Electrifying one of the world's largest mass transit systems, Bogotá city

Development and implementation of an electrical distribution network planning methodology using scenarios based on the integration of: Data Analytics, Geospatial Analytics and load flow simulation. At the end of the process, it is possible to determine the network needs and the projects to be included in the Industrial Budget Plan and to update the projects in the medium term to allow the connection of the different E-mobility projects.

Simulation of the effects of high shares of electric vehicles on voltage unbalance in the distribution grid level

Due to increasing shares of electric vehicles and thus of charging facilities, a multitude of issues and challenges arise for the operation and planning of distribution grids. In this context, voltage quality and in particular the impact on voltage unbalance is gaining more and more attention. For this reason, this paper addresses the impact of high penetration rates of electromobility on voltage unbalance in the low-voltage grid and the related question of whether current limits for the maximum customer-side unbalanced load need to be adjusted. For this purpose, different technological scenarios and exemplary grids are analyzed by a phase-accurate Monte-Carlo-based load flow simulation method. The results show a noticeable influence of unbalanced EV charging power on the voltage unbalance in the considered grids.