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In this paper, we model topology control through transmission switching as a recourse action in the day-ahead operation of power systems with large-scale renewable generation resources. We prove that transmission switching could only reduce the linear objective value of direct current optimal power flow when congestion exists. However, we also show, through a simple example, that unit commitment cost could be reduced by transmission switching even in the absence of congestion. To solve the stochastic unit commitment with topology control within reasonable computational time, we proposed a heuristic that first decomposes a practical system into zones and then solves the problem for each zone in parallel. The benefit of topology control recourse is demonstrated on a network representing the Central European System. We compare the costs of the network with different loading and renewable generation conditions. The cost reduction of the test system can reach 3.34% with heavy load and large-scale renewable generation while in a single zone the cost reduction can be above 7%. [ABSTRACT FROM PUBLISHER]

This paper proposes a method for studying the reliability implications of line switching operations in power systems. Two case studies are conducted on RTS and IEEE 118-bus system to illustrate this method. This method is designed to explore previously overlooked areas in reliability evaluation of line switching operations. Line removal test is proposed to obtain simulation data of the system, and then with risk analysis and impact analysis, six reliability indices are used to evaluate reliability performance of each transmission line in the system. Instead of the traditionally used mean value, this method introduces variance into analysis. Weibull distribution is used to reconstruct distributions of reliability indices which provide worst case scenario comparisons in reliability evaluation. Eventually, with results obtained from the proposed reliability evaluation method, categorization for line switching operations is introduced to classify all transmission lines based on their reliability performance. The categories provide reliability implications of line switching operations and can be used for guidance in actual operations. [ABSTRACT FROM PUBLISHER]

The protective devices and switches play an important role in the reliability of electrical distribution systems by minimizing the impact of interruption. In this paper, a method for identifying the type and location for protection devices and switches on the prerouted distribution system using value-based optimization. is proposed. The proposed method is based on the contingency analysis of various components, e.g., the faults of line sections, switches, protective devices, and the restoration through switching actions such as upstream restoration and downstream restoration. The formulation of the optimization problem in this paper is appropriate for linear integer programming, where each nonlinear term can be translated by only two additional linear constraints. The detailed design of the protection devices and the switches are determined by minimizing the total cost of reliability that comprises apparatus investment, maintenance, and interruption cost. The efficiency and validity of the proposed method are demonstrated in case studies. [ABSTRACT FROM AUTHOR]

High congestion costs and new congestion patterns, formed by intermittent renewable generation, demand for more efficient utilization of the transmission system. Transmission switching (TS) and variable-impedance series FACTS devices are two technologies that provide such efficiency gains through controlling the power flows. As the system operators begin to utilize these tools, it is essential to understand the interdependence between them at various stages, such as planning and operation. This paper develops an optimal power flow framework that incorporates both FACTS and TS to study the link between the two power flow control technologies. The simulation results on an RTS 96-bus system suggest that: 1) substantial economic savings can be achieved through utilization of both TS and FACTS, beyond the independent capabilities of each technology; 2) performing TS actions affect the optimal location and set point of FACTS devices; and 3) operation of FACTS devices affect the location and frequency of TS actions. It is, thus, essential to acknowledge the interdependence between the two technologies both at the planning and operation stage. Failure to do so will lead to economic inefficiencies that can be avoided through co-optimization of generation dispatch, TS, and FACTS. [ABSTRACT FROM PUBLISHER]

This paper considers line switching as a remedial action to mitigate the geomagnetically induced currents (GICs) in large-scale power syste-kazerooni-2753840ms. The algorithm uses linear sensitivity analysis to find the best switching strategy which minimizes the GIC-saturated reactive power loss. Furthermore, the coupling between the ac power flow solution and the GIC flows is modeled and heuristic strategies are designed to maintain the system security measures in terms of both GICs and ac power flow. Finally, the computational complexity of the algorithm is analyzed for large-system implementations. To reduce the complexity, the critical lines are identified through the sensitivity analysis and the calculations are performed only on the reduced system. The effectiveness of the proposed algorithm is demonstrated through numerical results using a small 20-bus test case as well as large power systems. [ABSTRACT FROM PUBLISHER]

There is currently a national push to create a smarter grid. Currently, the full control of transmission assets is not built in network optimization models. With more sophisticated modeling of transmission assets, it is possible to better utilize the current infrastructure to improve the social welfare. Co-optimizing the generation with the network topology has been shown to reduce the total dispatch cost. In this paper, we propose the concept of just-in-time transmission. This concept is predicated on the fact that transmission that is a detriment to network efficiency can be kept offline when not needed and, with the proper smart grid/advanced technology, can be switched back into service once there is a disturbance. We determine which lines to have offline based on the optimal transmission switching model previously proposed. A secondary topic of this paper focuses on flowgate bidding. Approved by the Federal Energy Regulatory Commission and implemented within the SPP and NYISO networks, flowgate bidding is defined as allowing a line's flow to exceed its rated capacity for a short period of time for a set penalty, i.e., price. We demonstrate the effectiveness of these models by testing them on large-scale ISO network models. [ABSTRACT FROM AUTHOR]

The power oscillation damping (POD) controllers implemented in the two thyristor controlled series compensators of the Brazilian North-South (NS) interconnection, in the year 1999, were solely intended to damp the low-frequency NS oscillation mode. These controllers are still under operation and are derived from the modulus of the active power flow in the NS line that is phase-lagged at the frequency of the NS mode and may experience relatively large excursions generated by exogenous disturbances. This paper utilizes the same 1999 data to compare the performance of a proposed robust POD controller design with those of two conventional designs. A recent robust control synthesis algorithm used in this work is based on a nonsmooth optimization technique and has the capability to handle various controller structures, including reduced-order, and to deal with time-domain constraints on both controlled and measured outputs. Moreover, the nonsmooth design technique encompasses multiple operating conditions subject to various test signals, hence building a truly time-domain multi-scenarios approach. According to the results discussed hereafter, this is a key advantage in the industrial context of increasing demand for performance and robustness. The described results relate to a large-scale system model used in the feasibility studies for that interconnection. [ABSTRACT FROM AUTHOR]

Distribution restoration process is done by switching actions of sectionalizing and tie switches on the feeders. The state of these switches can be determined by applying logical reasoning. Thus, knowledge-based systems are ideal tools to accomplish the task. In this paper, an expert system is developed by utilizing its fast reasoning mechanism and object-oriented features. The feeder component and configuration data are organized in a hierarchy way using the object-oriented programming paradigm. On the other hand, facts are used for representing the information during inference process. Service restoration procedure proposed in this paper takes load variation into consideration. The simulation results indicate that more solutions can be obtained for service restoration problems when load variation is considered. Another unique property of the proposed system is that it is capable of proposing multiple restoration plans. Multiple plans are important for the system operators since the best solution proposed by the system may not be workable in reality. By proposing multiple plans, the system operator can choose a plan which is more suitable to the real situation for service restoration problems. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for distribution system reconfiguration (DSR) based on optimum power flow (OPF) in which the branch statuses (open/close) are represented by continuous functions. In the proposed approach, all branches are initially considered closed, and from the OPF results, a heuristic technique is used to determine the next loop to be broken by opening one switch. Then the list of switches that are candidates to be opened is updated, and the above process is repeated until all loops are broken, making the distribution system radial. This paper includes results and comparisons on test systems utilized in three classical papers published in the technical literature, as well as in a previous paper by the authors. Results obtained on a real large-scale distribution system are also presented. [ABSTRACT FROM AUTHOR]

A smart distribution system should restore service to interrupted customers as quickly as possible after an outage. Upgrading manual switches to remote-controlled switches (RCSs) enhances restoration capability. The placement of RCSs should consider both functional and economic requirements. This paper presents a systematic method to determine the set of switches to be upgraded for an existing distribution system. The maximum restoration capability is achieved by upgrading a near-minimum number of manual switches to RCSs. The RCS placement problem is formulated as a weighed set cover (WSC) problem. A greedy algorithm with a polynomial-time computational efficiency is designed to generate a near-optimal solution for the WSC problem. A 3-feeder 9-node test system and a 4-feeder 1069-node unbalanced test system with microgrids are used to validate the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Reliability analysis of power systems has been attracting increasing attention. Regulatory agencies establish reliability standards that, if infringed, result in costly fines for the utility suppliers. A special concern pertains to the distribution networks on which most failures occur. The allocation of switches is a possible strategy to improve reliability, by allowing network reconfiguration to isolate contingencies and restore power to dark areas. This paper proposes an optimization methodology to allocate switches on radially operated distribution networks. The solution framework considers sectionalizing and tie switches of different capacities, with manual or automatic operation schemes. The approach minimizes the costs of allocation and energy not supplied, under reliability and flow capacity constraints. The solution framework is based on memetic algorithm concepts with a structured population. Case studies with a large network and real-world scenarios were used to evaluate the methodology. The results indicate that significant cost reductions can be achieved using the proposed solutions. [ABSTRACT FROM PUBLISHER]

Transmission grid topology control makes power systems more flexible and efficient. However, a line switching action itself may cause transient instability since a large flow disturbance may be involved. In this paper, a critical switching flow (CSF) concept is developed and an associated preventive stabilizing redispatch scheme is proposed to provide control guidelines for line switching actions to prevent instability and enhance transient stability for the system. The CSF is calculated in the day-ahead stage using a two-stage Monte Carlo algorithm, in which the uncertainties of generations and loads are considered and the worst case in the system is identified statistically. The obtained information is then used in the proposed scheme in the operation stage. Selected generators are dispatched before a switching action to ensure system stability. The IEEE reliability test system, the modified IEEE-118 bus system, and the Texas 2000 system are used to demonstrate the effectiveness and scalability of the proposed algorithm and scheme. [ABSTRACT FROM PUBLISHER]

Transmission switching can improve the economic benefits of a power system through changing its topology during operations. However, the switching operation itself represents a step change in power systems, which is, to some extent, similar to a contingency that can bring disturbances into systems. This paper proposes a new model for multi-period, static-security-constrained transmission switching. Because the power flow on the network will be redistributed instantaneously after the switching operations, the new model involves using disjunctive programming, which considers two sets of power flow equations under possibly different topologies before/after switching. Each switchable transmission element is modeled into four actions or disjunctions. An action transition diagram coupling of four actions in different hours is used to represent feasible paths of instantaneous changes in the element status. Disjunctive formulations are transformed into mixed-integer programming problems. We compare the difference of the previous transmission switching model and the proposed one by using several numerical tests and verify the effectiveness of our solution methodology in the six-bus and RTS-96 systems. [ABSTRACT FROM PUBLISHER]

In power system reconfiguration, the status (ON/OFF) of switches are optimized such that maximum power is delivered to loads after the occurrence of a fault. The optimized reconfiguration is achieved by prioritizing power delivered to vital loads over semi-vital and nonvital loads. The formulation presented in this paper considers a new balanced hybrid (AC and DC) shipboard power system (SPS). Analysis of the nonconvex reconfiguration formulation is done by an appropriate nonconvex solver and by convex approximation. Unlike the nonconvex solution that is based on branch-and-bound methods, convex approximation significantly reduces complexity. It is shown that for the hybrid SPS reconfiguration problem, low complexity convex approximations are effective in finding optimal solutions. Cumulative distribution function (CDF) of the power delivered to loads is presented to showcase the system robustness against random fault scenarios. A combined objective of maximizing power delivery and minimizing the number of switching actions is included in the analysis. Tradeoff between power delivered and number of switching operations after reconfiguration has been discussed at steady state. A separate analysis is also included to observe the intermediate dynamic switch states while the reconfiguration is in progress to capture the trade-off more prominently. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the N-i reliable dc optimal dispatch with transmission switching. The model is a mixed integer program (MIP) with binary variables representing the state of the transmission element (line or transformer) and the model can be used for planning and/or operations. We then attempt to find solutions to this problem using the IEEE 118-bus and the RTS 96 system test cases. The IEEE 118-bus test case is analyzed at varying load levels. Using simple heuristics, we demonstrate that these networks can be operated to satisfy N-1 standards while cutting costs by incorporating transmission switching into the dispatch. In some cases, the percent savings from transmission switching was higher with an N-1 DCOPF formulation than with a DCOPF formulation. [ABSTRACT FROM AUTHOR]

This paper discusses the application of trajectory sensitivity analysis (TSA) of power systems containing FACTS compensators. Thyristor controlled series compensator (TCSC) and static synchronous compensator (STATCOM) are the devices considered. The TCSC is modeled by a variable capacitor, the value of which changes with the firing angle. The STATCOM is modeled by a voltage source connected to the system through a transformer. The effect of their individual and simultaneous use on the system transient stability is studied by applying TSA. Two different test systems are considered. It is shown that TSA can be used to determine the best possible locations of the two devices for transient stability improvement as well as to predict the critical clearing time. [ABSTRACT FROM AUTHOR]

This paper demonstrates an adaptive control strategy for damping interarea oscillations in a large power system model, employing a probabilistic approach to model-based control. The scheme accounts for the uncertain nature of the post-disturbance dynamics of the system for computing the control moves. A number of linearized plant models are considered to represent the system dynamics following the probable contingencies. Conventional observer-based state feedback controllers are designed to achieve the desired performance for each of these models. This strategy has been used to design and test a damping controller for a thyristor controlled series compensator (TCSC) device installed in a 16-ma- chine, 68-bus system model. The control scheme worked satisfactorily following possible disturbances without any prior knowledge about the specific post-disturbance dynamics. [ABSTRACT FROM AUTHOR]

This paper suggests that the appropriate combination of a stability-oriented and a performance-oriented control technique is a promising way to implement advanced control schemes in power systems. The particular approach considered combines control Lyapunov functions (CLF) and reinforcement learning. The capabilities of the resulting controller are illustrated on a control problem involving a thyristor-controlled series capacitor (TCSC) device for damping oscillations in a four-machine power system. [ABSTRACT FROM AUTHOR]

Proposes the ant colony system (ACS), a cooperative agent algorithm for optimum switch relocation. Functions of switch relocation in distribution automation; Characteristics of an ACS; Basic concepts of ACS algorithm.

Presents a study which described a method of including subcycle transfer switches in predictive distribution system reliability assessment methods. How to quantify levels of reliability; Results; Conclusions.

Remote-controlled switches (RCSs) play an important role in prompt service restoration of distribution systems (DSs). However, the cost of RCSs and the vast footprint of DSs limit widespread utilization of RCSs. In this paper, we present a new approach to RCS allocation for improving the performance of restoration and optimizing reliability benefits with reasonable RCS cost. Specifically, the optimal number and locations of to-be-upgraded switches can be determined with different objectives: maximizing the reduction of customer interruption cost; maximizing the reduction of system average interruption duration index; or maximizing the amount of loads that can be restored using the upgraded RCSs. We show that these models can actually be formulated as mixed-integer convex programming problems. We further introduce a novel method to equivalently transform and efficiently solve each of them. The global optimum can thus be computed within a reasonable amount of time. The IEEE 33-node and 123-node test systems are used to demonstrate the proposed models and algorithms. [ABSTRACT FROM PUBLISHER]

Discusses the study "A Thyristor-Controlled Series Compensator Model for the Power Flow Solution of Practical Power Networks."

A novel technique based on a stability-constrained Optimum Power Flow (OPF) algorithm that properly captures important rotor angle and voltage stability conditions is proposed and described. The application of this technique to the optimal tuning of both Power System Stabilizers (PSS) and Thyristor Controlled Series Compensators (TCSC) to damp power system oscillations within the context of competitive electricity markets is proposed and discussed as well. The proposed technique is tested on the IEEE 14-bus benchmark system and compared with a "standard" OPF algorithm. The results obtained demonstrate the advantages of the proposed technique over existent dispatching techniques from the point of view of power dispatch and system stability conditions, and especially locational marginal prices. [ABSTRACT FROM AUTHOR]

The rational buyer procedure provides the competitive the procurement of capacity-based ancillary services (AS) hi unbundled markets by the independent grid operator (IGO). The capacity-based AS are prioritized in order of ascending response times. Prioritization allows substitutability of the AS by automatically making the unused capacity of a higher priority AS usable for any lower priority AS without the need of submitting additional offers. We develop an efficient scheme for the rational buyer procedure for the acquisition of the prioritizable capacity-based AS. The scheme allows the simultaneous determination of the successful offers in the multiauction procedure through the effective deployment of discrete programming notions and the exploitation of the structural characteristics of the formulation. A key feature is the incorporation of physical constraints such as capacity ramp-rate, and interzonal constraints. The use of bounding techniques combined with procedures for the quick detection of infeasible combinations of the offer prices and the identification of avoidable calculations leads to reducing the computational burden. The effectiveness and computational efficiency of the scheme are Illustrated with representative numerical results including case studies based on the IEEE 118-bus network. [ABSTRACT FROM AUTHOR]

We propose a stochastic mathematical program for finding the optimal location and compensation level of thyristor-controlled series compensators (TCSCs) and the optimal location of line switches in a transmission network. The combined uncertainty of the load and generation is captured by scenarios. The proposed problem has polynomial constraints, and we use the general linearization technique to linearize those constraints. The model becomes decomposable into a primal master and subprograms solvable by a branch-and-price procedure with the aid of column generation. The numerical results of implementing the model for the IEEE 118-bus test system show that combined investment in TCSCs and switches decreased the cost of energy and increased the penetration of wind energy more than individual investment of TCSCs or switches. [ABSTRACT FROM AUTHOR]

Comments on a study conducted by Richard E. Brown and J. Rafael Ochoa on the impact of subcycle transfer switches (STS) on distribution system reliability. Explanations on voltage sags; Example of including an estimate of the voltage sag impact in the reliability model; Explanations on the application of the STS; Response of Brown and Ochoa to the commentary given to their study.

Load curtailment programs including direct load control and demand response allow system operators to directly and/or indirectly reduce a portion of total customer demand. One system application which can be improved by implementation of load curtailment is service restoration. As such, this work presents a problem formulation, solution algorithm, and simulation results for service restoration of power distribution systems incorporating load curtailment of in-service customers via direct load control. It is shown that the addition of load curtailment allows for one or more of the following: a reduction of the total number of switch operations required, an increase to the number of customers served, and/or an increase to the total amount of load restored. These improvements are demonstrated through simulation results from a 416-bus multiphase distribution system. [ABSTRACT FROM PUBLISHER]

Central mitigation does not necessarily provide the most economical solution to voltage-sag problems. Distributed mitigation with strategically placed compensation devices should provide a better alternative. Placement studies of this nature usually involve extensive evaluations of candidate compensation schemes, which can become unmanageable for large systems with stochastic voltage-sag data. A probability-based technique known as the weighted sampling method is proposed to simplify the problem. The technique is applied to a distribution system to optimize the cost of placing series compensation. The cost has two components: device cost and cost reduction to consumers due to implementation of the device(s). Series compensation devices being optimized are the two distinctly different dynamic voltage restorer and thyristor voltage regulator. These devices are placed and optimized to best complement each other. To achieve reliable and fast convergence, a genetic algorithm with innovative coding is proposed. A 34-node distribution system is studied with a wide range of voltage-sag data and consumer tolerance characteristics. [ABSTRACT FROM AUTHOR]

Considers advances in mixed integer linear programming (MILP) to conduct preliminary design study on the combinatorial optimal placement of thyristor controlled phase shifter transformers (TCPST) in large-scale power systems. Discussion on the loadability of a network or its ability to transmit power; Description of the TCPST model; System loadability problem; Numerical results; Conclusions.

Describes a shunt reactor automatic switching system for the Hydro-Quebec transmission system. Description of the power system; Shunt reactor tripping; Summary of MAIS functions; Closing or tripping with voltage thresholds; Execution of shunt reactor switching.