Line Thermal Limits Research Articles

State of the art approach for comprehensive power system security assessment—Real case study

Power system security assessment plays a critical role in ensuring the safety and stability of the electric grid, evaluated by the operating state’s proximity to the loadability limits. However, with the increasing integration of intermittent renewable energy sources and rising electricity demands, there is a growing need for fast and reliable algorithms to perform power system security assessments effectively. This work reviews state-of-the-art approaches for steady-state security assessment and demonstrates the advantages of the recently proposed Transversality Enforced Newton Raphson (TENR) algorithm. The algorithm provides better computational tractability, scalability, and the capability to incorporate various technological constraints like limits on voltage setpoints, transmission line thermal limits, generator power outputs, etc. This work presents a generalization of the TENR algorithm, proof of convergence, and an adaptive step-size strategy with improved computational performance. The proposed algorithm was used to study maximum loadability, maximum boundness of the nodal power injections, and total transfer capability on a realistic case study of the Russian Far-East power system model, which expects substantial development in the nearest future.

Series FACTS Devices for Increasing Resiliency in Severe Weather Conditions

Severe weather conditions are low-probability, high-impact events that affect grid operations. The majority of power outages are caused by severe weather conditions. Grid resiliency to weather events can be enhanced by decreasing the reliance on its affected sections. One way to do this is to reduce the power flow through lines vulnerable to severe weather. If a line is disconnected, its initial power flow is distributed through the neighbor lines, which may cause congestion in the grid. FACTS devices can be used to control the power flow of lines that have a higher chance of power outages. Most previous works do not consider weather events in power flow control. In this work, a linearized optimal power flow (OPF)–based algorithm is developed to minimize the real power flow of vulnerable lines considering the thermal limits of lines to prevent infeasible solutions; the simulation is fast, making it suitable for large-scale systems. The proposed optimization problem is presented as a mixed-integer linear program (MILP), making it capable of using short-term load forecasting due to its high solution speed. The proposed optimization problem considers multiple lines with different outage probabilities and the uncertainties of the weather forecast. Moreover, it estimates the power reduction in vulnerable lines due to changes in the series FACTS devices. The performance of the proposed optimization problem is tested on IEEE 14-, 30-, and 118-bus systems for several scenarios. The results are validated with the AC power flow results from MATPOWER.

Pareto-Frontier Differential Evolution based Financial Approach for Multi-objective Congestion Management using Customer Participation and On-site Generation

Day by day increasing demand has increased the loading on the transmission network and in turn has become a cause of increased environmental pollution. Thus Congestion Management (CM) with controlled emission is a crucial issue in contemporary power market. In the present paper, issue of CM has been solved with inclusion of a renewable Wind Energy Source (WES) along with Customer Participation (CP) to create elasticity in their demands. Thus the matter of mitigating emission has been resolved with double efforts i.e. by introducing renewable energy source and by modifying customers demand. CM has been dealt with as a Multi-Objective Optimization Problem (MOOP). Three most relevant objectives have been taken to be solved simultaneously for this MOOP, which are minimization of operational cost, CO2 emission and loading on transmission lines. Moreover, the amount of customer participation and the size and site of renewable WES have also been optimized in the present research work. A promising evolutionary algorithm i.e. Pareto-Frontier Differential Evolution has been proposed for addressing this multi-objective CM problem. The proposed algorithm has also been compared with a well-established multi-objective genetic algorithm on the basis of the numerical results obtained and a statistical analysis to conclude the merit of performance. The present approach has been examined on IEEE 30-bus system and IEEE 118-bus system. Results obtained have been compared with those reported in the literature for the same power systems and for same line thermal limits i.e. for same level of congestion.

A Mathematical Programming Approach for Allocation and Analysis of TCSC in Power Transmission Systems

In this paper, a mathematical programming approach based on a branch and bound (BB) algorithm is proposed in order to determine the optimal allocation of thyristor-controlled series compensators (TCSC) in electrical power transmission systems, considering line thermal limits. The TCSC modeling is added in the Y-bus matrix, facilitating the computational implementation. BB-Y is the methodology used in this paper aiming to maximize the loading of the system considering a certain quantity of TCSC. In addition, the proposed algorithm is implemented for another test, using a determined number of TCSC, in order to improve the network voltage profile and minimize the total transmission losses. The methodology uses an interior point method to solve the problem relaxed, modeled as a reactive optimal power flow problem. Simulations are performed on the IEEE 118-bus test system, allocating different quantities of TCSC to find the maximum load the system can support. Given a certain number of TCSC, previously defined for a specific load, the TCSC are reallocated considering different objectives. For two TCSC the time for relocation is shorter than 4 seconds. The results also show that from three TCSC onwards, the maximum load increasing is not relevant, being around 0.3%. Therefore, the conclusion is that the algorithm has a low processing time, and conservative solutions allied with the presented methodology can be used in the optimal allocation of TCSC, what the aim is to optimize the systems performance.

An efficient, open-bid procurement auction for small-scale electricity markets

Despite early calls to investigate the application of Vickrey auctions in electricity markets, academic literature still provides little insight into the matter. Similarly, despite general auction-theoretic literature discussing various advantages of employing revealed rather than sealed bidding procedures, publications on electricity market auctions rarely even mention differences between these opposing features. This paper marries these neglected features into a new auction model for electricity markets. We propose a novel open-bid, descending-clock auction capable of handling inter-bidder dependencies such as thermal line limits. A novel set of termination criteria ensures that our proposed auction facing markets with power balance and generator capacity constraints and thermal line limits, preserves truthful bidding as a dominant strategy, which, if employed by all bidders, allocates supply efficiently constituting an ex-post perfect equilibrium. Furthermore, we discuss known disadvantages of Vickrey–Clarke–Groves type auctions in the context of our proposed auction applied in electricity markets.

A MILP model for optimal renewable wind DG allocation in smart distribution systems considering voltage stability and line loss

This paper introduces a new model for optimal wind distributed generation (WDG) allocation based on mixed integer linear programming (MILP) in todays' smart grids considering on-load tap changing (OLTC) and power factor control (PFC) strategies. The objectives of the proposed optimization model are improving voltage stability and energy loss minimization subject to power flow constraints, line thermal limits, maximum number and size of WDG units, penetration limit, discrete OLTC tap position constraints, and PFC constraints. An efficient voltage phasor-information-based probabilistic voltage stability index (VSI) is extracted to measure the improvement of voltage stability with WDGs. Besides energy losses, reduction index is used to measure the energy loss reduction with the integration of renewable WDGs in the distribution system. An efficient linearized power flow (LPF) model as well as piecewise linearized model of the quadratic terms associated to the PFC constraints are represented to convert the original nonconvex problem into the form of a well-known MILP problem, which guarantees optimal solution and computationally is efficient to be solved using powerful commercial solvers. The effectiveness and validity of proposed model is investigated in compared to the state-of-the-art population-based methods and classical models.

Contingency Control Capability of an Optimized HVDC-Based VSC Transmission System

Power network operations are increasingly becoming complex due to upsurge in power transactions, following the ongoing power system deregulation and restructuring. The alteration in dynamics of power operations based on this upsurge, usually results into contingency because power facilities are made to operate in region of their limits. In this regards, high voltage direct current (HVDC) based voltage source converter (VSC) and other flexible alternating current transmission systems (FACTS) imbedded with VSC have established competence for noticeable diverse power network characteristics improvements. Therefore, this study applies optimized VSC-HVDC transmission system for mitigation of bus voltage and line thermal limit violation as a result of n-1-line outage contingency during bilateral, simultaneous and multilateral transactions. Line contingency evaluation through real power performance index (RPPI) is adopted for severe contingency identification purposes. Optimization of VSC-HVDC system is achieved through statically developed sensitivity-based analysis of VSC control parameters, while its performance for both steady state and contingency conditions are verified with IEEE 6 and 30 bus networks. An improvement in power flow, voltage deviation minimization and automatic alleviation of violated thermal and voltage limits during contingency present optimized VSC-HVDC system as a solution for network performance optimization especially during various transactions occasioned by unbundling power processes. Besides, the superiority of the proposed optimization techniques is established through performance comparison with other sensitivity methods involving reactive power (RPSM), active power (APSM) and performance index (PISM), where the proposed sensitivity method (PSM) outperformed these other methods.

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

Optimal Feeder Routing in Urban Distribution Networks Planning with Layout Constraints and Losses

We address the problem of optimally re-routing the feeders of urban distribution network in Milano, Italy, which presents some peculiarities and significant design challenges. Milano has two separate medium-voltage (MV) distribution networks, previously operated by two different utilities, which grew up independently and incoordinately. This results in a system layout which is inefficient, redundant, and difficult to manage due to different operating procedures. The current utility UNARETI, which is in charge of the overall distribution system, aims at optimally integrating the two MV distribution networks and moving to a new specific layout that offers advantages from the perspectives of reliability and flexibility. We present a mixed-integer programming (MIP) approach for the design of a new network configuration satisfying the so-called 2-step ladder layout required by the planner. The model accounts for the main electrical constraints such as power flow equations, thermal limits of high-voltage (HV)/MV substation transformers, line thermal limits, and the maximum number of customers per feeder. Real power losses are taken into account via a quadratic formulation and a piecewise linear approximation. Computational tests on a small-scale system and on a part of the Milano distribution network are reported.

Optimal PV Penetration for Power Losses Subject to Transient Stability and Harmonics

Abstract Meeting the load growth and limiting the pollution level of fossil fuel based power generation are global challenges. One solution is to integrate clean and renewable energy sources to the power system. However high penetration of renewable energy sources can affect transmission line thermal limits and harmonics injection in the system. This paper illustrates the optimal location of Photovoltaic (PV) plant penetration in power system. The objective is to minimize real power system losses. This analysis is subjected to transient stability as well as individual and total harmonic distortion level constraints. IEEE 30 bus system is considered for such investigation by using Electrical Transient and Analysis Program (ETAP 19.5). Multi case capability of ETAP was the base of the analysis. The contribution of this paper is the consideration of the accumulated impact of transmission losses, transient stability, transmission line thermal limits, harmonic level and steady state voltage limits. The results of the investigation for this system within the applied constraints have brought the penetration level (PL) to 50%. This result is satisfactory and encouraging.

Application of Voltage and Lines Stability Index for Optimal Placement of Wind Energy with a System Load Increase Scenario

Background: Modern power system operations often faced with very unsafe conditions caused by voltage stability problems. If the problem cannot be controlled with the right method, then a cascade system can occur. This condition can cause a voltage reduction drastically and leads to a power outage. Objective: The Fast Voltage Stability Index (FVSI) and Line Stability Factor (LQP) implemented in this study. Both indices can determine the optimal location and capacity of Wind Energy (WE) into the grid to anticipate a sustained increase in load. Method: One type of optimization method, a new variant of Genetic Algorithms, is used to solve the multi-objective optimization problem known as Genetic Algorithm Sorting Non-Domination Sorting II (NSGA-II). This algorithm can determine the optimal location and WE's capacity into the grid by minimizing line power loss (Ploss) of power system with a system load increase scenario. Bus voltage security, thermal line limits, and stability system are used as obstacles to maintain the system in a safe condition due to the increasing the maximum load. Results: The method suggested in this paper has been adequately tested on modification of the IEEE 14-bus standard test system connected to the WE. The WE integrated into the grid modeled using the Power System Analysis Toolbox (PSAT). Based on the multi-objective manner, the method developed can determine the best location and capacity of the WE simultaneously by minimizing Ploss with SLI and satisfied all the system's security and stability constraints. Conclusion: The technique provides well-distributed non-dominated solutions and well exploration of the research space.

Coordinating the operations of smart buildings in smart grids

With big thermal storage capacity and controllable loads such as the heating ventilation and air conditioning systems, buildings have great potential in providing demand response services to the smart grid. However, uncoordinated energy management of a large number of buildings in a distribution feeder can push power distribution systems into the emergency states where operating constraints are not completely satisfied. In this paper, we propose a bi-level building load aggregation methodology to coordinate the operations of heterogeneous smart buildings of a distribution feeder. The proposed methodology not only reduces the electricity costs of buildings but also guarantees that all the distribution operating constraints such as the distribution line thermal limit, phase imbalance, and transformer capacity limit are satisfied.

Deferral of Power Distribution Reinforcement by Using Battery Energy Storage System

This paper focuses on the applications of the battery energy storage system (BESS) to be installed in distribution systems for deferment of the distribution reinforcement investment in the short-term power distribution planning. The distribution system in this paper refers to the cost and standard criteria of Provincial Electricity Authority (PEA). The existing system is 22-kV voltage level includes 115/22 kV substation, the 45-km. distribution feeder, 1 photovoltaic plant and 8 load points with mixed customer types. The technical problem often occurred in 22-kV distribution feeders is the power demand exceeds the line thermal limit in short time (1-4 hour per day) every day. Following PEA’s standard and criteria, distribution network owners (DNO) has 2 choices to solve this problem; taking the risk of fault or reinforce feeders. Nowadays, energy storage technologies play the interested role in smart grid era. It illustrates from the analysis that BESS can solve this problem and postpone the time of system reinforcement such as construction of the new distribution line with worthy investment. Power flow of the study system is calculated by DIgSILENT PowerFactory software. The best alternative is chosen based on the maximum net present value (NPV).

ATC using FACTS Devices in Deregulated Power Systems

A Repeated Power Flow with FACTS devices including ATC is used to evaluate the feasible ATC value within real and reactive power generation limits, line thermal limits, voltage limits and FACTS operation limits. An IEEE-30 bus system is used to demonstrate the effectiveness of the algorithm as an optimization tool to enhance ATC. A Genetic Algorithm technique is used for validation purposes. Introduction of FACTS devices in a right combination of location and parameters could enhance ATC and Ant Colony optimization can be efficiently used for this kind of nonlinear integer optimization.

Examination of Three Different ACOPF Formulations With Generator Capability Curves

This paper examines three different formulations of AC optimal power flow problem and compares performance of well-established general-purpose optimization algorithms for each, over different initial conditions. Polar power–voltage, rectangular power–voltage, and rectangular current–voltage are formulated to evaluate ACOPF solution characteristic. The formulation here maintains line flows as explicit variables and employs summations of these quantities to impose conservation conditions at each node. Two representations of line thermal limits are considered, one using real power (to allow comparisons to dc power flow approximations), and a more physically based ampacity limit using current magnitude. Nonlinear generator capability curves are represented (“D-curves”), including options to allow active and reactive limits dependent on generator voltage. A uniform objective function is used throughout, that of minimizing quadratic generator operating cost curves. Numerical performance case studies are performed for these formulations over six different classes of initial conditions, evaluating computational time and also robustness of convergence.

Optimal power flow in distribution network considering spatial electro‐thermal coupling effect

The conductor resistance changes in accordance with the conductor temperature, in turn the line thermal capacity limit and power flow are influenced by its spatial characteristics of line routes and surrounding weather conditions. In light of the significant difference of spatial characteristics of line routes and weather conditions in different regions covered by distribution network, a novel optimal power flow (OPF) model in distribution network considering spatial electro-thermal coupling effect is proposed to integrate heat transfer constraints and electro-thermal coupling constraints into normal distribution network operation constraints. To address the computational complexity of the proposed model, the line thermal capacity limit is calculated firstly using the spatial steady-state heat balance equation. Then, a genetic algorithm combined with an extended back/forward sweep method is presented to solve the distribution system OPF problem, in which the heat balance equation is embedded in the forward sweep stage of the power flow calculation. Consequently, line temperatures, resistances, and power flows are dynamically updated during the iterative procedure. A 14-bus system with nine regions shows that the spatial electro-thermal coupling effect has a significant impact on the result of power flow and the optimal dispatch of the distributed generation in the distribution network.

Reconstruction of security region with high information content using effective attributes extraction

Summary Security region-based power system operation guides operators in a fast and relevant decision-making process as to what conditions require operators' actions. The key to this approach is the manner in which effective attributes are extracted among the network's operating variables. This paper reconstructs the security region of power system with high information content. The security region of power system is constructed by means of the static security boundaries such as static voltage stability limit, generator output power limit, and transformer and transmission line thermal limits by increasing loading factor along various directions until these limits are violated. Then, the security region is described by means of effective features set that contain maximum information content. In this paper, nonlinear feature extraction techniques have been proposed to dimensionality reduction and relevant extraction of power system operating variables. Convex and nonconvex techniques of feature extraction are analyzed based on a mutual information index and generalization error. The simulation results on the IEEE 9-bus and the IEEE 118-bus test systems demonstrate the effectiveness of the proposed method for describing the security region by considering high information content.

Impact of Dynamic Thermal Limits of Transmission Lines on Power System Operation

This paper discusses a methodology to determine the ampacity of transmission lines based on their dynamic thermal limits. In this sense, temperature, wind speed, season conditions, and system loading are taken into account, rendering a methodology that determines, for each operating point and weather condition, the actual thermal limit of a transmission line. The proposed technique is tested in a real scenario and compared with the technique currently employed for this purpose.

Optimal Placement of Distributed Generation Using Bacterial Foraging Optimization Algorithm

This paper presents the determination of the optimal distributed generation (DG) placement using bacterial foraging optimization algorithm (BFOA). The BFO mimics the seeking-nutrient behavior of the E. coli bacteria. It is utilized here to find the location and size of the DG installation in radial distribution system in order to obtain minimum system losses. The operation constraints include bus voltage limits, distribution line thermal limits, system power balance and generation power limits. The algorithm is tested on the IEEE 33 bus system. The result shows that the algorithm could be used as an alternative to the other techniques and improvement of the algorithm is required for acceleration and better accuracy of the calculation.

An Optimal and Distributed Method for Voltage Regulation in Power Distribution Systems

This paper addresses the problem of voltage regulation in power distribution networks with deep-penetration of distributed energy resources, e.g., renewable-based generation, and storage-capable loads such as plug-in hybrid electric vehicles. We cast the problem as an optimization program, where the objective is to minimize the losses in the network subject to constraints on bus voltage magnitudes, limits on active and reactive power injections, transmission line thermal limits and losses. We provide sufficient conditions under which the optimization problem can be solved via its convex relaxation. Using data from existing networks, we show that these sufficient conditions are expected to be satisfied by most networks. We also provide an efficient distributed algorithm to solve the problem. The algorithm adheres to a communication topology described by a graph that is the same as the graph that describes the electrical network topology. We illustrate the operation of the algorithm, including its robustness against communication link failures, through several case studies involving 5-, 34-, and 123-bus power distribution systems.