Overloading Of Transmission Lines Research Articles

Static Security Assessment: A Case Study of the Saudi National Grid

The static security assessment of the Saudi National Network helps to identify the weaknesses and potential threats and provides a comprehensive understanding of the network’s ability to address such incidents due to probable outages. This paper presents the static security assessment of the Saudi national grid with reference to the transmission line overloads and the bus voltage deviations in the system following the initiation of the specified contingencies. Critical contingencies are identified, and these are ranked on the basis of the limit violations of the line overloads and the bus voltage deviations obtained through the Newton-Raphson load flow analysis. The system loading conditions considered correspond to that of a typical day of the Hajj Pilgrimage period, during which millions of pilgrims from various parts of the country and also the world visit the Holy Mosque at Makkah. The preliminary investigations reveal that there are some transmission lines and certain substations requiring special attention to enhance the system security.

Two-Area Automatic Generation Control for Power Systems with Highly Penetrating Renewable Energy Sources

Currently, renewable energy sources (RESs) are gradually replacing traditional power sources that use fossil fuels. In some countries, such as Vietnam, RESs are developed on a massive scale and are concentrated in some key areas. This causes negative impacts on a power system when its transmission system is not deployed synchronously to release their capacity from these new renewable energy plants. An important challenge today is to ensure frequency stability in power systems with high uncertainty in RES output power. Additionally, the system requires solutions to prevent transmission line overloads during periods when RESs make a substantial contribution to the electricity generation capacity. Therefore, this paper builds an automatic generation control (AGC) system for a two-area power system with high penetration of RESs. This AGC system model aims to maintain system frequency stability amid unpredictable changes in RESs while also ensuring that tie-lines transmit the predetermined power levels to mitigate frequent congestion. By continuously monitoring and adjusting the system’s frequency, the challenges posed by the inherent variability of RESs can be effectively mitigated. The AGC model is simulated on DIgSILENT PowerFactory software and tested with a 106-bus system. The simulation results of this study show that the AGC system operates effectively, ensuring that the frequency returns to the rated value and maintaining the exchange capacity on the tie-lines after occurrences of RES power decrease events.

Optimization of position and rating of shunt and series connected FACTS devices for transmission congestion management in deregulated power networks

<abstract><p>Transmission congestions are caused by electricity trading between generators and distribution companies in a deregulated environment. Power system operation and security in liberalized scenarios are maintained by removing branch overloads. A flexible alternating current transmission system (FACTS) controller is installed in a suitable location to redistribute the power flow among the transmission lines so that the power flows are brought within the capacity of the lines. In this work, series-connected thyristor-controlled switched compensators (TCSCs) and shunt-connected Volt-Ampere reactive (VAR) static compensators (SVCs) are installed in appropriate locations to alter the power flow patterns and to remove overloads. It is proposed to reduce the overload of transmission lines by locating series and shunt connected FACTS devices at proper locations. The size and location of TCSC and SVC devices greatly affect their ability to meet a congestion management goal. An optimization process optimizes the location and size of these devices to maximize the congestion mitigation benefits of the TCSC and SVC controllers. In this work, the whale optimization algorithm (WOA) is used to optimize the value of the objective function by appropriately choosing the location and size of the FACTS controllers. This algorithm has a few parameters that are tuned to give the best overall results. A WOA-based method is proposed to optimize the size and location of the FACTS devices and is implemented on the IEEE-30 bus test case. The results were compared and found to be improved with those of other algorithms such as the particle swarm optimization algorithm (PSO) and the firefly algorithm (FFA).</p></abstract>

Uncertainty parameters of battery energy storage integrated grid and their modeling approaches: A review and future research directions

The continuously growing population and urban growth rates are responsible for the sharp rise in energy consumption, which leads to increased CO2 emissions and demand-supply imbalances. The power sector is switching to alternative energy sources, including renewable energy resources (RES) such as Photovoltaic (PV) and wind power (WP) and battery energy storage systems (BESS), among others, due to an increase in the use of fossil fuels and their shortage. Since the power generation of these resources is uncertain due to climatic fluctuations and the direct integration of these resources into the power grid is very complex due to the issues such as; voltage and frequency regulation, overloading of active transmission lines, and supply-demand disparity, the research on system uncertainties is receiving increasing attention. This study provides a comprehensive analysis of the several parameters of uncertainty, approaches for dealing with the uncertainty in battery energy storage (BES)-based RES integrated grid, and the advantages and disadvantages of each method. Moreover, various analytical and numerical approaches were developed for integrating RES and BESS into the power grid, including probabilistic methods, possibilistic methods, robust optimization-based techniques, and machine learning algorithms. The comparative analysis of these approaches highlights their relative strengths and weaknesses, providing a valuable resource for researchers and utility planners. Additionally, this review paper identifies several issues and challenges associated with the integration of RES and BESS into the power grid, such as power quality, economical effect, battery aging effect, and environmental effect. Furthermore, the paper suggests a few future research directions, including the development of novel models for analyzing uncertainty in power systems, coordination of uncertainty parameters, integration of BESS into RES and grid, power electronics integration, and environmental factor. Overall, this article's novel contributions include a comprehensive analysis of uncertainty parameters, a comparative analysis of uncertainty modeling approaches, an identification of critical issues and challenges, and the suggestion of future research directions to promote a sustainable and reliable power system. This article will aid in defining the requirements and specifications for novel models for analyzing uncertainty in power systems. The discussion and analysis will assist researchers and utility planners in selecting a suitable uncertainty modeling approach with significant penetrations of distributed RESs, which can lead to achieving a reliable and sustainable power system.

Generation Rescheduling Based Contingency Constrained Optimal Power Flow Considering Uncertainties Through Stochastic Modeling

The generation rescheduling is described as the power generation shifting from one or more generators to one or more other generators as a preventive action to improve and maintain the security of the power system. Since, there is a direct link between security improvement and the lines overload under contingencies, by rescheduling generation, the transmission lines become more flexible and thus, the overload can be relieved. In this paper, contingency constrained optimal power flow (CCOPF) problem based on generation rescheduling by considering the uncertainty of photovoltaic (PV), wind turbine (WT), and plug-in hybrid electric vehicle (PHEV) have been addressed. Water cycle algorithm (WCA) using its potential in finding optimal solution has been used in order to reschedule the generators and optimize the total fuel cost, power losses under contingency scenario, and system security. Moreover, stochastic approach has been proposed for taking into account the uncertainty of PV, WT, and PHEV. Overall performance index including the power and the voltage severity indices have been provided for determining overloaded transmission lines due to the lines’ outage and consequently elimination of overloaded lines. The efficiency of the proposed algorithm has been evaluated on two IEEE-30 and IEEE 118-bus systems. The results are compared with the results of other classical and metaheuristic optimization algorithms. The simulations reveal that the WCA outperforms the other reported optimizers, and is more efficient and effective in improving security for power systems. In addition, the obtained numerical results show that renewable energy sources can significantly reduce fuel costs.

The Operation Strategy of the MIDC Systems for Optimizing Renewable Energy Integration of Jeju Power System

The power system on Jeju Island currently faces challenges due to an imbalance between power supply and demand owing to increasing renewable energy (RE) generation. Consequently, the multi-infeed high-voltage direct-current (MIDC) systems are expected to play an important role in reducing RE curtailment and increasing RE penetration. However, despite the balance between power supply and demand, transmission line (TL) overloads on Jeju Island, which has a low permissible rating, may lead to RE curtailment. We propose an operational strategy for the MIDC systems to mitigate TL overloading and RE curtailment. This strategy was aimed at managing the possible congestion of TLs, maintaining a power supply–demand balance, and increasing the penetration level of RE. In this paper, we present a scheme for calculating the operating points of the MIDC systems and allocating RE curtailment using optimization with security constraints to mitigate TL overloading. The proposed optimization model simplifies solving the mathematical equations involved by employing a sensitivity factor called the power transfer distribution factor (PTDF), using which linear programming (LP) optimization can be performed. To verify the feasibility of the operational strategy, case studies are conducted using an actual Jeju Island power system with a power system analysis tool—Power System Simulator for Engineering (PSS/E). The optimization problem was solved using MATLAB.

Estimation Method for Transmission Line Overloads Due to Renewable Energy Source (RES) Output Forecast Errors in Daily Supply and Demand Planning

AbstractWe propose a method to estimate transmission‐line overloads due to forecast errors of power output of renewable energy sources. The proposed method involves particle swarm optimization and optimal power flow calculations. The effectiveness of the method is confirmed via numerical simulations using a modified IEEE RTS 24‐bus system model. The results indicate that the proposed method can determine the forecast errors of the renewable power output that causes thermal overload, and further predict the occurrences of transmission‐line overload under generator activation in supply and demand planning. Furthermore, we explain the occurrence mechanism of transmission‐line overload due to forecast errors, which may contribute to improve the daily supply and demand planning. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Design and Sizing of Electric Bus Flash Charger Based on a Flywheel Energy Storage System: A Case Study

At present, the trend of all sectors and industries, especially the oil and gas industry, is towards reducing carbon dioxide emissions. Along with the modernization of technological processes, special attention has been paid to the reduction in greenhouse gas emissions from vehicles that run on gasoline and diesel. An effective solution in this field is the transition from vehicles with combustion engines to electric vehicles, similar to the use of the electric bus in public transportation. How to charge these electric buses is a challenge for researchers. By proposing a flash charging method for electric buses, the feasibility of using these buses is obtained. Due to the pulsating nature of the power demand in this charging method, the prevention of negative effects on the network by this type of load should be considered. These negative effects can include power quality problems, voltage drop, frequency instability, and overload of transmission lines and transformers. This paper presents a flywheel energy storage system (FESS)-based flash charging station for electric buses. The specifications of the components of this charging station are designed and sized for a case study for line 1 of Tehran Bus Rapid Transit (BRT). A charging strategy based on the proposed charging cycle is presented to minimize the high-power short-duration demand from the grid. The energy consumption of the electric bus based on the electricity consumption model is calculated. Based on theoretical calculations, for the case study, there is a need for installing 12 flash charging stations based on FESS in line 1 Tehran BRT. In this line, an electric bus with a battery capacity of 80 kWh is proposed. The power and energy capacity of these charging stations are sized to 600 kW and 3.334 kWh, respectively. Additionally, an economic comparison regarding the proposed charging station is conducted. The theoretical results of the design and sizing of the proposed charging station are validated based on simulation and experimental results for a small-scale laboratory setup.

STUDY OF NON-SYMMETRICAL MODES OF THREE-PHASE FOUR-WIRE NETWORKS WITH DISTRIBUTED GENERATION

The use of distributed generation electric energy sources allows efficient use of energy resources, including available renewable energy sources, contributes to the reduction of harmful emissions during traditional electric energy generation, improves the quality of electric energy for consumers and reduces overloading of transmission lines. Meanwhile, if the load supplied by the source of distributed generation is asymmetrical, then the voltage at the zero point of the inverter interface feeding the neutral conductor can deviate quite noticeably from the set level. The easiest way to provide a neutral point for connecting the neutral conductor is to use two capacitors with balancing resistors connected in parallel to them, that is, to create a zero voltage by dividing the total voltage of the direct current link in half. Circuits with voltage separation in the direct current circuit are widely used in electric drives with three-level energy converters, since in this case there is no need to connect the zero point of the direction to the load, and the main purpose of this electrical circuit is to obtain equal halves of the total voltage in the direct current circuit. This will lead to asymmetry of the output voltage, that is, to a decrease in its quality, the presence of significant constant components in alternating voltages, as well as to the flow of a significant current in the neutral conductor. In this regard, a three-dimensional space-vector pulse-width modulation method was proposed for controlling a four-arm inverter, which differs from the existing ones by the possibility of minimizing the components of negative and zero-sequence voltages in networks with distributed generation with parallel connection of three- and four-arm inverters . To develop approaches to control the inverters of such systems, it is necessary to obtain analytical dependencies that describe the flow of active and reactive power between inverters depending on the parameters of their generated output voltages.

Line Overload Alleviations in Wind Energy Integrated Power Systems Using Automatic Generation Control

Modern power systems are largely based on renewable energy sources, especially wind power. However, wind power, due to its intermittent nature and associated forecasting errors, requires an additional amount of balancing power provided through the automatic generation control (AGC) system. In normal operation, AGC dispatch is based on the fixed participation factor taking into account only the economic operation of generating units. However, large-scale injection of additional reserves results in large fluctuations of line power flows, which may overload the line and subsequently reduce the system security if AGC follows the fixed participation factor’s criteria. Therefore, to prevent the transmission line overloading, a dynamic dispatch strategy is required for the AGC system considering the capacities of the transmission lines along with the economic operation of generating units. This paper proposes a real-time dynamic AGC dispatch strategy, which protects the transmission line from overloading during the power dispatch process in an active power balancing operation. The proposed method optimizes the control of the AGC dispatch order to prevent power overflows in the transmission lines, which is achieved by considering how the output change of each generating unit affects the power flow in the associated bus system. Simulations are performed in Dig SILENT software by developing a 5 machine 8 bus Pakistan’s power system model integrating thermal power plant units, gas turbines, and wind power plant systems. Results show that the proposed AGC design efficiently avoids the transmission line congestions in highly wind-integrated power along with the economic operation of generating units.

Robustness Analysis of CPPS considering Power Flow Constraints

Comprehensively considering the power flow constraints of the power network, the cyber-physical power system (CPPS) network integration model is established by combining with the topological structure information of the power network and information network. The Newton–Raphson method is used to solve the AC power flow distribution in the power network. Based on the interdependent network theory, a CPPS cascading fault analysis procedure considering the power flow constraints is given. Finally, the importance of CPPS network nodes is evaluated and analyzed. Simulation experiments are carried out with the IEEE39 node system as an example. The results show that some electrical components failures in the power network may lead to large-scale transfer of power flow, resulting in overloading of other electrical components or transmission lines. It promotes further cascade propagation of failures in the CPPS network, which eventually leads to a sharp decrease in the robustness of CPPS.

Distributed Scheme for Line Overload Mitigation With Linearized AC Power Flow

The transmission overload after a disturbance poses significant security risk to the power system. Once it happens, an efficient remedial action must be taken to relieve the line overloads as quickly as possible. The line overload mitigation problem becomes more urgent and challenging in the future power grid that integrates distributed and fluctuating renewable energies. In this brief, we propose a distributed corrective control scheme for alleviating the overloads in transmission lines. A linearized AC power flow model is introduced, and the error of linearizion is compensated through a close loop of power flow control. The proposed distributed control framework not only satisfies the need of accommodating distributed resources in future grids, but also guarantees the system security during the line overload mitigation process. The performance of our corrective control scheme is demonstrated in the simulations using the IEEE 14-bus test system.

Transmission Line Overload Risk Assessment Considering Dynamic Line Rating Mechanism in a High-Wind-Penetrated Power System: A Data-Driven Approach

The dynamic line rating (DLR) can be an effective mechanism that reduces wind curtailment induced by line congestion considering its unique correlation to wind speed. However, the calculation of the DLR depends on accurate environmental parameters, which can be challenging in look-ahead decision-making applications. Consequently, transmission line overload risk (TLOR) can exist. In this paper, we propose a two-stage TLOR assessment model for high-wind-penetrated power systems considering the DLR. An overload risk index along with the risk-averse line capacity bound (RAB) for each line can be obtained from the proposed model. Meanwhile, a computationally efficient data-driven approach that combines convex-hull and box-like modeling methods is established to characterize the uncertainty during the decision-making process. The proposed model is solved by a modified column-and-constraint generation (C&CG) algorithm, and its effectiveness and scalability are illustrated by multiple simulation experiments.

수요자원 인센티브를 통한 태양광발전 출력제한 대응 ESS 최적운영스케줄링에 관한 연구

The installation of energy storage system (ESS) is increased to solve the instability of the transmission system due to variable renewable energies such as Photovoltaic power generation (PV) and wind power generation. Meanwhile, recently, PV output is frequently curtailed since PV output produced after the ESS charging is finished causes transmission line congestion. For this congestion, it is common to increase line capacity or allocate the output curtailment for each power plant. However, since the unsettled loss occurs due to the output curtailment, the power plant operator should be given an incentive to induce the output curtailment for a specific time. Therefore, in this paper, the ESS optimal operation scheduling using the demand response transaction mechanism as an incentive is presented. From the perspective of PV operator with ESS, the charge/discharge capacity is determined in units of 15 minutes reflecting the PV curtailment and the demand response trading mechanism through mixed-integer linear programming. Uncertainty in the D-Day actual PV power output is considered as three scenarios such as Day-ahead forecasting PV power output and Day-ahead forecasting PV power output scenario with mean absolute percentage errors. Through optimal operation scheduling of ESS, transmission line overload and system congestion are suppressed by ESS charging and PV operators can secure additional benefits through the demand response trading mechanism without PV curtailment. Namely, total expected benefits can be maximized by the proposed method. As a result, an additional expansion of transmission lines or the introduction of a new incentive system can be avoided by the flexibility of PV operators.

Optimization of loop-network reconfiguration strategies to eliminate transmission line overloads in power system restoration process with wind power integration

With large-scale wind power integration, the uncertainty of the wind power outputs will aggravate the transmission line overloads during the black-start restoration process. By constructing regional loop-networks, this paper proposes an optimization method of network reconfiguration strategies to eliminate the line overloads. Firstly, a multi-scenario set of the wind power outputs is constructed based on the extreme scenario method. Secondly, a loop-network reconfiguration optimization model is established to meet the requirements of the multi-scenario set simultaneously, where the line overloads are not permitted. Then, a two-layer solving framework is proposed to solve the optimization model. The upper-level layer is a multi-scenario mixed integer linear programming (MILP) model with the DC power flow constraints, whose objective is to minimize the operation complexity index. The lower-level layer serves to check the standing phase angle (SPA) constraint and the AC power flow constraints of the optimal schemes obtained from the upper-level layer. Therefore, the loop-network reconfiguration optimization model is alternatively solved by iterative computation. The effectiveness of the proposed method is verified by the modified IEEE 39-bus system and the modified IEEE 118-bus system, and applicability of this method to practical systems is verified by the southwestern Yunnan power system in China.

Reinforcement-learning-based dynamic defense strategy of multistage game against dynamic load altering attack

As the current power grid is highly interconnected and more information and communication technologies (ICTs) are being deployed recently, it could be the target of malicious cyber-physical attacks. Dynamic load altering attacks (D-LAAs), as a special case of load altering attacks, could be performed to interfere the demand response and ultimately force certain generators off-line. Cascading failures due to transmission line overloads may also be triggered. In this paper, we propose a new dynamic defense strategy against D-LAAs through a multistage game between the attacker and the defender which is solved by minimax-q learning. Different from the static game, the multistage game considers the attacker and defender’s action sequences and the optimal strategies at each state are learned. After each time step, the cascading failure is measured, and the load shedding is used as the feedback for the attacker to generate the next action strategy. The performance of the proposed model is evaluated on the IEEE 39-bus system. Comparisons between the dynamic defense strategy and the passive defense strategy are conducted, and the results verify the advantage of the proposed dynamic defense strategy. To improve the power system resilience, this defense strategy can be deployed in advance when such cyber-physical attacks are anticipated.

A novel communication‐free charge controller for electric vehicles using machine learning

Despite many advantages, wide-spread integration of electric vehicles (EVs) in the power systems is challenging. Large-scale uncontrolled EV charging load may lead to under-voltage violations, higher power losses, overloading of transformers and transmission lines. In this research work, a machine learning-based communication-free EV charge control strategy is developed to mitigate the issues caused by the uncontrolled EV charging. Another notable feature of the proposed controller is to ensure the fairness among the EVs available at different locations in the distribution system. Moreover, two indices are proposed, that is system utilisation index (SUI) and system average voltage violation duration index (SAVVDI), to assess the performance of any EV charge controller. In the proposed control structure, a nodal voltage and the voltage-to-load sensitivity are measured at each load node which are fed to the EV charge controller. In fact, an upstream node is generally less sensitive to the changes in load, since it is closer to the feeding point, as compared to a downstream node. The output of the charge controller is the charging rate of an EV. In order to validate the robustness of the proposed controller, light and heavy loading conditions are considered which mimic the daily, monthly, yearly and seasonal load variations. Simulation results prove that the proposed controller effectively improves the voltage profiles and ensures fairness among the EVs connected at various charging points in the distribution system. Moreover, it effectively utilises the power system resources.

Optimal Location of High Voltage Direct Current (HVDC) Transmission Line using Genetic Algorithm

The aim of this research is to study the effect of HVDC transmission systems on reducing power losses and improving voltage profile. This paper presents a solution to the problems of an overloaded transmission line through selecting the optimal location for the HVDC system. For this purpose, a Genetic Algorithm (GA) uses to optimize the voltage profile, reduce power losses and handle power flow in overloaded transmission lines. MATLAB utilizes to engage both the GA and Newton Raphson method to solve the load flow problem. The proposed approach examined and tested on the IEEE Large Scale 57-bus test system. Power System Simulator for Engineering (PSS/E) package Version 32.0 is used as practical part to solve the functions of power system performance. The results demonstrated the ability of the proposed method to determine the optimum location of the HVDC line which reduces power loss and improves the “voltage profile” of the bus.

Congestion management with improved real power transfer using TCSC in 30 bus system

Secure operation and reliable utilisation of transmission lines is a challenging issue in deregulated power system. The scheduled power transactions are difficult due to the overloading of transmission lines in restructured power system as the electricity market has become more competitive. Due to congestion of transmission lines, the transfer of real power and the power system voltage profile are greatly affected in the power system. The aim of this research work is to increase the real power and the reactive power flowing in the lines of multibus system using thyristor controlled series compensator (TCSC). Real power transfer with reduced losses and improved voltage stability is an important factor in the present global scenario. This paper deals with the improvement of power flow in power transmission lines by series compensation device in 30 bus system with reduced congestion. The 30 bus system without and with thyristor controlled series compensation device (TCSC) is modelled and simulated and the results are presented. The simulation studies indicate a significant improvement in the real and the reactive power flow with the introduction of TCSC. The advantages of the proposed system include the smooth variations of the real and the reactive powers.

Dynamic Tuning of the Controller Parameters in a Two-Area Multi-Source Power System for Optimal Load Frequency Control Performance

Frequency control is becoming increasingly critical today due to the growing size and changing structure of complex interconnected power networks. Scaling up economic pressures for efficiency and reliability of the power system has necessitated a requirement for maintaining system frequency, and tie-line power flows as close as possible to scheduled values. High-frequency deviations may degrade load performance, damage equipment, resulting in overloading of transmission lines, which may interfere with system protection schemes, and, finally, may also result in an unstable condition of the power system. More so, Load Frequency Control ( LFC) plays a vital role in the modern power system as an auxiliary service to support power exchanges and, at the same time, to provide better conditions for the trading of electricity. Therefore, the tuning of the dynamic controller (i.e., net frequency and net power interchange errors) is a significant factor in achieving optimum LFC performance. Appropriate tuning of the controller parameters is required in order to achieve excellent control action. In view of this, this paper introduces the dynamic tuning of controller parameters in a two-area multi-source power system with an AC-DC parallel tie line for optimum load-frequency control performance. Matlab/Simulink software is used to realize the system simulation. System dynamic performance is observed for conventional PID tuning by the Ziegler Nichols method and the Kitamori method, fuzzy logic controllers, fuzzy-logic PID controllers, fuzzy PID controllers, and polar-Fuzzy controllers. Furthermore, the frequency and tie-line power response of the interconnected areas were compared based on the setting-time, peak-overshoot, and peak-undershoot. The simulation results show that the responses of the fuzzy-based controllers are faster than those of the classical controllers, resulting in minimized frequency and tie-line power deviations.