Transmission Line Capacity Research Articles

Congestion management using multi-objective hybrid DE-PSO optimization with solar-ess based distributed generation in deregulated power Market

Transmission congestion is one of the major drawbacks of deregulated power system. Due to increase in load demand, generation increases, but capacity of transmission line is limited, and transmission lines carry power more than its rated capacity, as a result congestion occurs. Congestion management in deregulated power system is a challenging and tough task which can be achieved by introducing one or more Distributed Generators (DG) at optimal location. Optimal location and sizing of DGs is very important for maximizing the social welfare function which is profit to both the producers and consumer of electricity. In this paper hourly congestion management is proposed. It manages the network congestion by optimal placement and sizing of DG in ‘24 h’ time frame. Transmission Congestion Rent (TCR) is used to find the optimal location for DG placement whereas hybrid Differential Evolution (DE) and Particle Swarm Optimization (PSO) technique is used for finding optimal size of DG. In this work, Solar PV along with Energy Storage System (ESS) is utilized as Distributed Energy Storage System (DESS). ESS along with DG is used to store surplus energy during off-load period which will be utilized at peak load thereby enhancing the overall efficiency of the system. 24 h solar irradiance and temperature data of Delhi is taken to mathematically model the power generated from Solar PV. Results obtained with hybrid optimization technique are compared with PSO based optimization. It is observed that hybrid optimization technique outperforms the PSO optimization technique in managing resources and congestion problem in the network for the ‘24 h’ time frame. Proposed work has been carried out on IEEE 30 bus test system.

Engineering Practices of Determining Transmission Capacity and Delay of Interconnecting Line Taking into Account its Configuration and Cost

This article contains information on engineering practice of determining transmission capacity of computer network line. The article presents a variant of engineering synthesis of computer network, which is a combined process of mathematical and heuristic methods combining. The engineering synthesis is offered as vector and global, because it must result in network development, optimal in terms of its practical use. All the significant network quality indicators, including economic and practical, are taken into consideration. In case of engineering synthesis, it is not possible that only one quality indicator is significant: there are always at least two significant indicators – a cost and an indicator that characterizes the main effect that is achieved in case of network use (efficacy). If at least one of the quality indicators significant for practical use is not taken into account, such network cannot be considered optimal. Computer network synthesis usually consists of structure synthesis, parameters optimization and discrete network selection. If network topology is maintained unchanged, it is possible to formulate an optimization task for line transmission capacity. The solution of transmission capacity task, which is constantly changing, may be chosen as a starting point for the selection of discrete indicator of transmission capacity.

Engineering Practices of Determining Transmission Capacity and Delay of Interconnecting Line Taking into Account its Configuration and Cost

This article contains information on engineering practice of determining transmission capacity of computer network line. The article presents a variant of engineering synthesis of computer network, which is a combined process of mathematical and heuristic methods combining. The engineering synthesis is offered as vector and global, because it must result in network development, optimal in terms of its practical use. All the significant network quality indicators, including economic and practical, are taken into consideration. In case of engineering synthesis, it is not possible that only one quality indicator is significant: there are always at least two significant indicators – a cost and an indicator that characterizes the main effect that is achieved in case of network use (efficacy). If at least one of the quality indicators significant for practical use is not taken into account, such network cannot be considered optimal. Computer network synthesis usually consists of structure synthesis, parameters optimization and discrete network selection. If network topology is maintained unchanged, it is possible to formulate an optimization task for line transmission capacity. The solution of transmission capacity task, which is constantly changing, may be chosen as a starting point for the selection of discrete indicator of transmission capacity.

Coordinated operation of reconfigurable networks with dynamic line rating for optimal utilization of renewable generation

The large-scale penetration of renewable generation, the ever-increasing load, and aging of the transmission infrastructure all pose excessive stress on secure power system operation due to increasing congestion levels of the network. This arises the need for system operators to exploit the inherent flexibility in the system by using new cost-effective transmission topologies to better utilize the existing transmission assets. Dynamic Line Rating (DLR) and Optimal Transmission Switching (OTS) technologies both provide flexible ways to boost power system performance and maximize the use of existing infrastructure. In this paper, OTS and DLR are co-optimized in a stochastic unit commitment (SUC) formulation to characterize its influence on the scheduling of power system operation in the presence of renewable energy resources. Based on the predicted meteorological parameters and loading, the optimization problem i.e. Flexible Transmission Dynamic Line Rating (FTDLR) determines when and which line should be upgraded to adopt DLR and which line should be removed from the network. The inherent flexibility in transmission system is utilized by anticipating the capacity of transmission lines using DLR in co-ordination with reconfiguring network topology to relieve system congestions and reduce system operating cost. The flexibility obtained from the current transmission system can help in postponing the need for building new transmission corridors and deepen the integration of renewable generation. Numerical results establish that the enforcement of DLR and the practice of OTS are complementary, which can help minimize the system operating cost, wind curtailment, and network congestion.

Market design for renewable energy auctions: An analysis of alternative auction formats

Abstract Auctions are widely used to determine the remuneration for renewable energies. They typically induce a high concentration of renewable energy plants at very productive sites far-off the main load centres, leading to an inefficient allocation as transmission line capacities are restricted but not considered in the allocation, resulting in an inefficient system configuration in the long run. To counteract these tendencies effectively, we propose a combinatorial auction design that allows to implement regional target capacities, provides a simple pricing rule and maintains a high level of competition between bidders by permitting package bids. By means of extensive numerical experiments we evaluate the combinatorial auction as compared to three further RES auction designs, the current German nationwide auction design, a simple nationwide auction, and regional auctions. We find that if bidders benefit from high enough economies of scale, the combinatorial auction design implements system-optimal target capacities without increasing the average remuneration per kWh as compared to the current German auction design. The prices resulting from the combinatorial auction are linear and anonymous for each region whenever possible, while minimal personalised markups on the linear prices are applied only when necessary. We show that realistic problem sizes can be solved in seconds, even though the problem is computationally hard.

Multi‐stage risk‐based dispatch considering short‐term reliability of transmission lines

The reliability of transmission lines (TLs) has great influences on the safe operation of power systems. Random failures from TLs can be caused by multiple uncertainties such as the high load current. In this study, a multi-stage risk-based dispatch model is proposed to minimise the sum of generation cost and risk cost. Impacts of natural ageing, load current, health condition and disaster weather on the short-term reliability of TLs are studied. For ensuring the operation security of power systems in the post-contingency stage, the dynamic thermal rating (DTR) technology is implemented to improve capacities of TLs for coping with the potential overload. In order to solve this non-linear optimiation problem caused by load current-dependent failure probabilities and thermal rating constraints, a double-iteration solving strategy is proposed. In exterior iterations, the sequential linear programming is applied to decouple bilinear terms of the risk cost and locally linearise failure probabilities. Meanwhile, in interior iterations, the Benders decomposition is utilised to further divide the model into the main problem and the sub-problem for coordinating the preventive and corrective control and checking the feasibility of DTR, respectively. Proposed approaches are validated on a modified IEEE 24-bus test system.

Economic load intervals for selecting 10 kV cable cross-sections for agricultural consumers

District electric networks for agricultural purposes are characterized by a constant increase in loads. In these conditions, it is important to choose the correct parameters of power lines and, first of all, the cross-sections of overhead lines (overhead lines) and cable lines. There are technical possibilities to increase the capacity of overhead power lines, which can be carried out in the following ways: voltage regulation; reactive power compensation; replacement of existing wires with wires of a larger cross-section; load unbundling; transfer of the network to an increased voltage. Increasing the capacity of cable transmission lines by all of these methods is not possible due to their design features. Thus, due to the difficulties of increasing the capacity of cable lines and dynamically developing networks, the problem of choosing the optimal cable cross-section for lines with an ever-increasing load is becoming more acute. Currently, agricultural distribution electric networks have a constant increase in load. In these conditions, the correct choice of the parameters of cable lines and the residential cable line is of great importance. Due to the complexity of increasing the throughput of cable lines and dynamic networks, problems arise with the choice of optimal paths for wires and residential cables for agricultural lines.

A Structural Characterization of Market Power in Electric Power Networks

We consider a market in which capacity-constrained generators compete in scalar-parameterized supply functions to serve an inelastic demand spread throughout a transmission constrained power network. The market clears according to a locational marginal pricing mechanism, in which the independent system operator (ISO) determines the generators' production quantities to minimize the revealed cost of meeting demand, while ensuring that network transmission and generator capacity constraints are met. Under the stylizing assumption that both the ISO and generators choose their strategies simultaneously, we establish the existence of Nash equilibria for the underlying market, and derive an upper bound on the allocative efficiency loss at Nash equilibrium relative to the socially optimal level. We also characterize an upper bound on the markup of locational marginal prices at Nash equilibrium above their perfectly competitive levels. Of particular relevance to ex ante market power monitoring, these bounds reveal the role of certain market structures---specifically, the \emph{market share} and \emph{residual supply index} of a producer---in predicting the degree to which that producer is able to exercise market power to influence the market outcome to its advantage. Finally, restricting our attention to the simpler setting of a two-node power network, we provide a characterization of market structures under which a Braess-like paradox occurs due to the exercise of market power---that is to say, we provide a necessary and sufficient condition on market structure under which the strengthening of the network's transmission line capacity results in the (counterintuitive) increase in the total cost of generation at Nash equilibrium.

Optimal configurations and operations of concentrating solar power plants under new market trends

It is a challenge for investors to decide optimal configurations and operations of a concentrating solar power plant because of the new market trends, namely that the governments no longer offer secured and fixed tariff schemes regulated by Power Purchase Agreements, nor do they continue to provide subsidy over the power plant’s entire life. The concentrating solar power plant must adjust configurations and operations to address market price variation and subsidy decrease. This study presents a non-linear optimization model that captures the critical component investment costs and operational flexibility in the plant configuration. We use it to analyze economies of scale, thermal energy storage, economic curtailment, and hybrid systems with wind plant, and to evaluate their impact on plant configuration decisions under the new market trends. First, we find that the economic performance of the concentrating solar power plant, despite market price variation and subsidy decrease, can be enhanced substantially by optimal configurations and operations flexibility, which improve the overall plant utilization. Second, compared to the traditional fixed tariff scheme, the market-price-based tariff scheme can yield substantially higher net present value for the plant investment, due to the optimal configurations and flexible operations. Finally, our sensitivity analyses show that the optimal plant configurations are significantly affected by market price variations and the constraints of transmission line capacity.

Provide a simple model of the Comprehensive Electric Power Controller

The UPFC in Power Systems controls the line parameters and the power flow of the lines. On the other hand, controlling the power flow and lines parameters in transmission lines, maximizes the capacity of power transmission lines, increases network reliability, reduces line losses, increases power system efficiency, reduces energy loss and consumption management. Therefore, presenting a simple model of UPFC in power systems analysis is of interest to experts. In this paper, a simple model of upfc in steady state is presented. In the proposed model, the converter of upfc series is modeled with circuit elements. The proposed model will be included in the load distribution program without changing the dimensions of the Jacobine network matrix. To demonstrate the efficiency of the proposed model, the standard 14 bus are simulated

Bulk FDTD Simulation of Distributed Corona Effects and Overvoltage Profiles for HSIL Transmission Line Design

Power system load growth and transmission corridor constraints are driving industry activity in the area of high surge impedance loading (HSIL). Examples include compact structure design and uprating existing transmission lines. Recent research relating electric field uniformity to transmission line capacity and critical flashover voltage underscored the need for better overvoltage data to quantify insulation margins for HSIL design. To that end, this work extends the finite difference time domain (FDTD) method with distributed corona losses to transmission lines with bundled conductors. The model was adapted for practical use in high-volume statistical transient simulation and applied to an example 500 kV line. Transients included line energization and trapped charge reclosing. Overvoltage profiles and statistical distributions were generated from 9500 simulations obtained by random breaker close timing and variation in line length and altitude. Distributed corona losses reduced 98th percentile line-to-ground switching overvoltages by 4%–14% of nominal. The estimated line-to-ground switching surge flashover probability was 54%–80% lower with corona loss. Corona had less impact on line-to-line overvoltages, but the effects were still notable. Results highlight the importance of considering detailed overvoltage profiles and accounting for corona loss attenuation when seeking to carefully quantify insulation design margins.

Analysis of curtailment at The Geysers geothermal Field, California

Geothermal energy has traditionally been viewed as a baseload energy source, but the rapid growth of intermittent renewable energy has led to a need for more flexibility in power generation to avoid mandatory curtailment imposed by grid operators. This study of curtailment at The Geysers provides insights into the magnitude, duration, frequency, temporal and spatial distribution, and potential causes of curtailment events between 2013 and 2018. Annual levels of curtailment range during this period from 9 to 47 GW h, representing 0.15 to 0.81 % of the net generation. Most curtailments occurred at the power plants connected to a lower capacity transmission line and may result from transmission constriction. There is a clear link between negative pricing and economic curtailment, especially when solar production is higher. Economic curtailment events tend to be only a few hours and vary in magnitude up to almost 300 MW, whereas transmission-related curtailment events can be up to several weeks in duration. It is likely that curtailment of geothermal power will be an increasing concern, and could be mitigated by flexible generation strategies and increases in energy storage. It is critical to know the nature of curtailment events so that flexible generation options can be assessed properly.

Impact Analysis of Transmission Congestion on Power System Flexibility in Korea

This study proposes a method to evaluate the impact of transmission congestion on the flexibility of a power system, based on the ramping capability shortage expectation (RSE). Here, flexibility refers to the ability to retain a power balance in response to changes in the net load. The flexibility issue arises due to the extensive integration of renewable energy resources; specifically, the higher the degree of integration, and the greater the variability and uncertainty in the power system. Flexibility is further limited by the net transfer capacity (NTC) of transmission lines. Here, we propose a method capable of capturing the extent to which transmission congestion affects the power system, to identify transmission reinforcement options for improved flexibility. In Korea, transmission congestion occurs frequently in regions to the north and southeast. A case study for a Korean power system in 2030 was conducted. Simulation results showed that the impact of transmission reinforcement in flexibility tends to be proportional to the NTC and is greater when the penetration level is low.

Cost-optimal evaluation of centralized and distributed microgrid topologies considering voltage constraints

Optimal design of hybrid renewable mini-grids requires both economic and power quality considerations. Existing modeling approaches address these considerations via separate or loosely coupled models. Here, we extend REopt—a techno-economic optimization model developed at the National Renewable Energy Laboratory—to consider both within a single model. REopt formulates the design problem as a mixed-integer linear program that solves for a site's optimal technology mix, sizing, and operation to minimize life cycle cost. REopt has traditionally assumed a single node system. In the work presented here, we expand the REopt platform to consider multiple connected nodes with associated voltage constraints. In order to do this, we model power flow using a fixed-point linear approximation method. We then use the model to explore design considerations of mini-grids in Sub-Saharan Africa. Specifically, we evaluate under what combinations of transmission line distance and capacity it is technically viable and economically preferable to build multiple isolated mini-grids versus an interconnected, centralized system.

Transmission Expansion Planning Including TCSCs and SFCLs: A MINLP Approach

We propose a transmission expansion planning model that integrates thyristor-controlled series compensators (TCSCs) to enhance line transmission capacity, and superconducting fault current limiters (SFCLs) to control short-circuit levels. The harmonious interplay between TCSCs and SFCLs results in effective and economically attractive optimal expansion plans. This multi-stage planning model translates into a complex mixed-integer nonlinear programming problem, which is hard to solve. To solve it, we propose a successive linearization technique within a Benders’ decomposition scheme that proves effective in finding optimal solutions and efficient in terms of computational burden. We illustrate the methodology proposed using the IEEE 39-bus system.

Mitigation of Subsynchronous Interactions in Hybrid AC/DC Grid With Renewable Energy Using Faster-Than-Real-Time Dynamic Simulation

Transmission line capacity enhancement by series compensation is commonly used in power systems, which consequently faces potential subsynchronous interaction (SSI). In this work, faster-than-real-time (FTRT) simulation based on the field-programmable gate arrays is proposed to mitigate the disastrous SSI in a hybrid AC/DC grid integrated with wind farms. Dynamic simulation is applied to the AC system to gain a high speedup over real-time, and a detailed multi-mass model is specifically introduced to the synchronous generator to show the electrical-mechanical interaction. Meanwhile, the DC grid undergoes electromagnetic transient simulation to reflect the impact of power converters' control on the overall grid, and consequently, the EMT-dynamic co-simulation running concurrently due to FPGA's hardware parallelism is formed. As the two simulations are inherently distinct, a power-voltage interface is adopted to separate them which enables their coexistence in one program. It shows that following the detection of a contingency, the FTRT hardware platform can generate an optimum solution with precisely quantified power flow changes in advance to keep the hybrid AC/DC grid stable. The FTRT efficacy is proven by a number of cases where the accuracy is validated by offline simulation tool Matlab/Simulink.

Integrated transmission expansion and PMU planning considering dynamic thermal rating in uncertain environment

Dynamic line rating (DLR) technologies are fast becoming a key instrument in power systems with high penetration of wind farms, because power companies can reduce the value of wind power spillage and also can postpone the investments of transmission lines by using DLR equipment. However, what the authors know about DLR is largely based on empirical studies that investigate how to change the capacity of transmission lines with changing the weather data. Therefore, lack of a mathematical model for estimating the capacity of lines by considering the weather conditions across the line and wind farm generations can be accounted as a research gap of DLR problems. This study proposes a solution for transmission expansion planning considering DLR technologies. Also, this study seeks to develop a model, which will help to address the research gap of DLR problems. The geostatistical analysis is used to develop a mathematical model, which can provide the relationship between wind farms as well as the capacity of lines calculated based on the weather conditions across the line. The efficiency of the proposed model is examined on a modified IEEE 118-bus test system.

Calculating the locational marginal price and solving optimal power flow problem based on congestion management using GA-GSF algorithm

An important factor in reviewing the performance of generation units and calculating their profit is the calculation of their locational marginal price (LMP), and this depends on our knowledge on the capacity of transmission lines and optimal power flow (OPF) based on reality by which we aim to minimize the total cost of the generators, solve the congestion of transmission lines, and hence, reduce the price of electricity in the market. Since power flow equations are nonlinear, they should be solved using numerical and repetition-based methods. In this paper, genetic algorithm (GA) has been employed to solve these equations, and in order to improve the performance of GA in its structure, generating scaling factor (GSF) has also been used for simultaneous calculations of power passing through in transmission lines so that by gaining some knowledge on the capacity of transmission lines, in addition to optimal power flow becoming real, we could determine the electricity price by uniform market pricing or LMP methods depending on using the full capacity of lines and generating power of the units, and thus, we can calculate the profit of generators. Finally, the output of the proposed GA-GSF algorithm would include values of buses voltages, lines losses, injected power to buses, power passing through lines, total generation cost, and generators’ profits. Also, the proposed algorithm in this paper has been tested on IEEE 14-BUS, IEEE 30-BUS, IEEE 57-BUS network, and the results show improvements on the OPF problem.

Effective Utilization of Transmission Line Capacity in a Meshed Network with Series Capacitor Upto its Thermal Limit

Power system networks are becoming interconnected for the purpose of power delivery to decrease the overall power generation cost. With insufficient control, the power systems become more complicated to function and less secure. The economics of AC power transmission have always forced the planning engineers to transmit as much power as possible through a given transmission line. The smaller and thermally limited lines are crowded in many networks while other higher capacity lines run well below their thermal maximum. When series capacitors are introduced in the higher voltage cables, power may be transferred from the overloaded lines, maximizing the use of the existing line as well as complementing the performance of the power system. In this paper, a three-line meshed power system network with different thermal line limits is considered for the purpose of showing effective utilization of line network for maximum power flow through the intended line with series capacitor compensation. The simulations are performed by using PowerWorld simulator confirms the addition of series capacitor increases the power transfer through the line up to its thermal limit

Simultaneous Multi-area Economic-Environmental Load Dispatch Modeling in Presence of Wind Turbines by MOPSO

Multi-objective particle swarm optimization (MOPSO) algorithm was proposed in this paper to solve the load dispatch problem among thermal and wind turbines considering the environmental factors in multi-area power systems. The unpredictable nature of wind generations has resulted in the higher complexity of the economic load dispatch (ELD) problem. As the wind farm’s generation is very difficult to predict, the extra cost during the evaluation of the ELD are taken into account as well. In the developed method, the storage and additional cost are defined in the objective function of the ELD problem, using the mean value of wind energy density. The operational constraints among multi-areas, including the transmission lines capacity limit and generation-demand balance constraints as well as the constraints of generation limit of generators are considered in the economic-environmental load dispatch (EELD) problem. The efficiency of the proposed method was evaluated based on the simulation results on IEEE 118 bus test system, considering twelve thermal power plants, two wind farms and three areas.