Transmission Topology Research Articles

Fast and Reliable Screening of N-2 Contingencies

System Operators in many countries are required to maintain contingency plans for critical N-2 contingencies. Huge number of possible N-2 contingencies makes their direct assessment computationally prohibitive forcing the operators to rely on engineering judgement or uncontrollable heuristics. We present a novel algorithm for identification of critical N-2 contingencies that result in line overloads in post-contingency equilibrium. High computational efficiency of the algorithm is achieved via effective certification of safety for the majority of contingencies. Unlike many common heuristics, the algorithm is guaranteed to have zero missing rate in DC approximation models. Performance of the algorithm is validated by simulation of several IEEE case scenarios which demonstrate 30 – 1000 fold acceleration of contingency selection process in comparison with naive brute-force approach. Various possible applications of the approach in the problems of security assessment, transmission topology control and planning are discussed in the end of the manuscript.

Robust optimal transmission switching with the consideration of corrective actions for N − k contingencies

In order to achieve a better economic dispatch decision of the electricity generation while guaranteeing system security, the optimal transmission switching (OTS) has been proposed with the well-known N-k contingency security criterion. However, the challenge for treating the OTS problem considering N-k contingencies lie in that it may lead to a conservative result, since the optimal solution should simultaneously satisfy all the sets of N-k constraints. To address this problem, the corrective control with respect to different contingencies is utilised during the period when the transmission topology remains unchanged, which can be formulated as a two-stage problem. Consequently, a two-stage robust optimisation is employed to optimise the objective value under the worst contingency, so as to hedge against the contingency uncertainties. Comparison of the traditional N-1 OTS and the proposed robust N-1 OTS models on IEEE 30-bus test system shows that the robust OTS model has less conservatism than the traditional OTS model with the help of corrective actions. Moreover, it illustrates that the proposed method can be fairly applicable to cases with even N-k contingencies, which can facilitate the complexity of contingency analysis.

The Line and Node Voltage Stability Index Presented Through the Porosity of High-voltage Transmission Lines

The porosity of power system high-voltage transmission lines is presented through the lens of the problem of voltage stability. The ability of transmission lines to receive and transport electric energy to load centers is determined based on the well-known relationships between the characteristic variables in the field of voltage stability. Using a simple procedure, it is possible to trace the effect of electrical power flows on power system transmission line porosity and detect unstable voltage states. Through the proposed approach, the planners and operators of transmission lines can continually calculate the effect of current power flows and transmission topology on the ability of transmission lines to receive more electric power without endangering the voltage stability and desired voltage profiles throughout a given system. Therefore, the results of the presented algorithm can operate in a manner to utilize the inherent available margins of the existing and planned transmission lines.

On the Optimal Linear Network Coding Design for Information Theoretically Secure Unicast Streaming

The continuous growth of media-rich content calls for more efficient and secure methods for content delivery. In this paper, we will address the optimal linear network coding (LNC) design for secure unicast streaming against passive attacks, under the requirement of information theoretical security . The objectives include 1) satisfying the information theoretical security requirement, 2) maximizing the transmission rate of a unicast stream, 3) minimizing the number of additional random symbols, and 4) minimizing the total bandwidth cost of content delivery. To fulfill the first three objectives, we formulate an information theoretically secure unicast streaming (ITSUS) problem, and then solve it by transforming it to a maximum network flow problem with node-capacity constraints. Based on the solution of the ITSUS problem, we develop an efficient algorithm that can find the optimal transmission topology with minimum bandwidth cost in a polynomial amount of time. With the optimal transmission topology, we investigate the design of both deterministic LNC and random LNC. For the deterministic LNC design, we not only prove that it achieves the four objectives but also analyze the size of required finite field. Moreover, for the random LNC design, we analyze the probability that a random LNC scheme satisfies the information theoretical security requirement. Finally, extensive simulation experiments have been conducted, and the results demonstrate the effectiveness of the proposed algorithms.

On the optimal design of secure network coding against wiretapping attack

In this paper, we study the optimal design of weakly secure linear network coding (WSLNC) against wiretapping attack. Specifically, given a set of wiretapped links, we investigate how to maximize the weakly secure transmission rate of multiple unicast streams between a pair of source and destination nodes, and how to minimize the size of the required finite field, over which the WSLNC can be implemented. In our study, we apply a novel approach that integrates the WSLNC design and the transmission topology construction. We first provide theoretical analysis and prove that the problem of finding the optimal transmission topology is NP-hard. We then develop efficient algorithms to find optimal and sub-optimal topologies in different scenarios. With the transmission topology, we design WSLNC schemes and theoretically analyze the relationships between the transmission topology and two important system factors: (1) the size of the finite field, and (2) the probability that a random linear network coding is weakly secure. Based on the relationships, we further improve our algorithms to address the two system factors, while keeping the same maximal STR. Extensive simulation results show that the proposed heuristic algorithms can achieve good performance in various scenarios.

The Development of the Routing Pattern of the Backbone Data Transmission Network for the Automation of the Krasnoyarsk Railway

The paper deals with the data transmission network of the Krasnoyarsk Railway, its structure, the topology of data transmission and the routing protocol, which supports its operation, as well as the specifics of data transmission networking. The combination of the railway automation applications and the data transmission network make up the automation systems, making it possible to improve performance, increase the freight traffic volume, and improve the quality of passenger service. The objective of this paper is to study the existing data transmission network of the Krasnoyarsk Railway and to develop ways of its modernization, in order to improve the reliability of the network and the automated systems that use this network. It was found that the IS-IS and OSPF routing protocols have many differences, primarily due to the fact that the IS-IS protocol does not use IP addresses as paths. On the one hand, it makes it possible to use the IS-IS protocol for the operation in IPv6 networks, whereas OSPF version 2 doesn’t provide this opportunity; therefore, OSPF version 3 was developed to solve this problem. However, on the other hand, in case of using IPv4, the routing configuration by means of the IS-IS protocol will imply the need to study a significant volume of information and use unusual methods of routing configuration

The Impacts of Transmission Topology Control on the European Electricity Network

The European Union is targeting a 20% share of energy from renewable resources by 2020, and this increase is in turn expected to lead to operational challenges that will require various congestion management actions by system operators. In this paper, we deal with topology control of the transmission network as a congestion management resource and evaluate the impacts of topology control on the European electricity network. To do this, we co-optimize unit commitment and transmission switching over 24 h, and we use a decomposition scheme to tackle the resulting large-scale problem. Our analysis is conducted on different scenarios of load and renewable power generation. We find that topology control results in significant cost savings within Europe which tend to be inversely related to net load. The robustness of our results is supported by an extensive sensitivity analysis.

Security-Constrained Transmission Topology Control MILP Formulation Using Sensitivity Factors

A transmission topology control (TC) framework for production cost reduction based on a shift factor (SF) representation of line flows is proposed. The framework can model topology changes endogenously while maintaining linearity in the overall Mixed Integer Linear Programming (MILP) formulation of the problem. In large power systems it is standard practice to optimize operations considering few but representative contingency constraints. Under these conditions and when tractably small switchable sets are analyzed, the SF framework has significant computational advantages compared to the standard B $\theta$ alternative used so far in TC research. These claims are supported and elaborated by numerical results on full models of PJM with over 13,000 buses. We finally present analytical investigations on locational marginal price (LMP) computation in our SF TC framework and their relation to LMPs computed for problems without TC. Also, we discuss practical implementation choices such as sufficient conditions on lower bounds that allow selection of large numbers employed in the MILP formulation.

Congestion management through topological corrections: A case study of Central Western Europe

The integration of an increasing amount of renewable generation within Europe is posing operational challenges that require various balancing actions. System operators therefore need to rely increasingly on the active control of the transmission network. Transmission topology control is a fast and economical option to add flexibility to the transmission system. We model the current methodology for controlling congestion in the Central Western European (CWE) market and quantify the benefits of topology control. We also compare the results with a nodal pricing model. Our computational results suggest that topology control can significantly reduce congestion management costs under the current market coupling regime whereas the benefits of topology control are limited under nodal pricing. Topology control emerges as an attractive and implementable means of managing congestion as it provides a significant percentage of the cost savings that would be achieved by overhauling the existing European market design and shifting to a nodal pricing regime.

Performance analysis of multiple-hop wireless body area network

There have been increases in the elderly population worldwide, and this has been accompanied by rapid growth in the health-care market, as there is an ongoing need to monitor the health of individuals. Wireless body area networks (WBANs) consist of wireless sensors attached on or inside the human body to monitor vital health-related problems, e.g., electrocardiograms (ECGs), electroencephalograms (EEGs), and electronystagmograms (ENGs). With WBANs, patients' vital signs are recorded by each sensor and sent to a coordinator. However, because of obstructions bythe human body, sensors cannot always send the data to the coordinator, requiring them to transmit at higher power. Therefore, we need to consider the lifetime of the sensors given their required transmit power. In the IEEE 802.15.6 standard, the transmission topology functions as a one-hop star plus one topology. In order to obtain a high throughput, we reduce the transmit power of the sensors and maintain equity for all sensors. We propose the multiple-hop transmission for WBANs based on the IEEE 802.15.6 carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol. We calculate the throughput and variance of the transmit power by performing simulations, and we discuss the results obtained using the proposed theorems.

A Decomposition Approach for Solving Seasonal Transmission Switching

Economic transmission switching has been proposed as a new control paradigm to improve the economics of electric power systems. In practice, the transmission switching operation itself is a disruptive action to the system. Frequently switching lines into or out of service can create undesirable effects on the security and reliability of power systems and may require new investments in the automation and control systems. In this paper, we formulate an economic seasonal transmission switching model where transmission switching occurs once at the beginning of a time period (season) and then the transmission topology remains unchanged during that period. The proposed seasonal transmission switching model is a large-scale mixed integer programming problem. The objective of the optimization model is to minimize the total energy generation cost over the season subject to loads and N-1 reliability requirements. We develop a novel decomposition method that decomposes the seasonal problem into one-hour problems which are then solved efficiently. We demonstrate our model and the decomposition approach on the 14-bus, 39-bus, and 118-bus power systems and show potential cost savings in each case.

Research on the WeChat Information Transmission Topology Based on Social Network Analysis

With the rapid development of mobile internet technology, Social Media has become an important way for us to communicate with others. Meanwhile, Social Media is regarded as the most popular information exchange and knowl- edge-sharing platformS by more and more people, making its network structure and information transmission topology at- tracted a wide attention. WeChat is one of the most commonly used Social Media in China, which was developed by Tencent in 2011. Due to the number of WeChat customer is very huge, traditional analytical methods become not applica- ble. In this paper, we try to use Social Network Analysis (SNA), which being capable of handling huge data, to reveal the relationship networks of WeChat. On this basis, we choose a WeChat user randomly, and listed part of groups that he par- ticipated in. Through analyzing its network architectures and data indicators, we found out three main information trans- mission topology of WeChat.

Impact of HVDC Transmission System Topology on Multiterminal DC Network Faults

This paper compares how a dc fault affects a multiterminal dc (MTdc) network depending on the HVDC transmission system topology. To this end, a six-step methodology is proposed for the selection of the necessary dc fault protection measures. The network consists of four voltage-source converters converters radially connected. The converters natural fault response to a dc fault for the different topologies is studied using dynamic simulation models. For clearing of the dc faults, four different dc breaker technologies are compared based on their fault interruption time, together with a current direction fault detection method. If necessary, the converters are reinforced with limiting reactors to decrease the peak value and rate of rise of the fault currents providing sufficient time for the breakers to isolate the fault without interrupting the MTdc network operation. The study shows that the symmetric monopolar topology is least affected by dc contingencies. Considering bipolar topologies, the bipolar with metallic return exhibits better fault response compared to the one with ground return. Topologies with ground or metallic return require full semiconductor or hybrid breakers with reactors to successfully isolate a dc fault.

Congestion Management Through Topological Corrections: A Case Study of Central Western Europe (CWE)

The integration of increasing amount of renewable generation within Europe is posing operational challenges that require various balancing actions. System operators therefore need to rely increasingly on the active control of the transmission network. Transmission topology control is a fast and economic option to add flexibility to the transmission system. We model the current methodology for controlling congestion in the CWE market and quantify the benefits of topology control. We also compare the results with a nodal pricing model. Our computational results suggest that topology control can significantly reduce congestion management costs under the current market coupling regime whereas the benefits of topology control are limited under the nodal pricing. Topology control emerges as an attractive and implementable means of managing congestion as it provides a significant percentage of the cost savings that would be achieved by overhauling the existing European market design and shifting to a nodal pricing regime

Tool-driven Design and Automated Parameterization for Real-time Generic Drivetrain Models

Real-time dynamic drivetrain modeling approaches have a great potential for development cost reduction in the automotive industry. Even though real-time drivetrain models are available, these solutions are specific to single transmission topologies. In this paper an environment for parameterization of a solution is proposed based on a generic method applicable to all types of gear transmission topologies. This enables tool-guided modeling by non- experts in the fields of mechanic engineering and control theory leading to reduced development and testing efforts. The approach is demonstrated for an exemplary automatic transmission using the environment for automated parameterization. Finally, the parameterization is validated via vehicle measurement data.

Towards Optimal Transmission Switching in Day-Ahead Unit Commitment

Co-optimizing transmission topology with generation dispatch, and leveraging grid controllability could be a viable way to improve economic efficiency of system operations in control centers. In particular, day-ahead unit commitment is a typical business process that electric utilities deploy to ensure enough generation capacity is committed day-ahead to meet the load for the next day. In a market environment, day-ahead reliability unit commitment (DA-RUC) performs a simultaneous solution of minimizing the cost of commitment for resources to meet forecasted load, net scheduled interchange and operating reserve requirements using security constrained unit commitment (SCUC). The commitment may then be further checked by running security constrained economic dispatch (SCED) to verify that the commitment solution can be feasibly dispatched subject to system constraints and activated transmission constraints for each hour identified in the study period. This paper applies Optimal Transmission Switching (OTS) in DA-RUC using some heuristic pre-screening techniques to reduce the dimension of the OTS problem. Various pre-screening methods of candidate transmission lines for switching are proposed and compared. Simulation results will be presented to demonstrate generation dispatch combined with OTS in each hour could reduce congestion cost and significantly lower generation cost.

Transmission Switching With Connectivity-Ensuring Constraints

This paper seeks to improve the computational time needed to solve transmission switching problems. Transmission switching provides an effective way to reduce operating costs in power system operations by altering the topology of the trans- mission network. However, determining the optimal set of lines to switch creates an enormous computational burden. Trans- mission switching formulations add binary decision variables for many transmission lines in the system to indicate if they are switched. This creates a very weak formulation that is difficult to solve. Altering the transmission topology by switching lines can affect the reliability of the network, for instance, by creating islands. Additional reliability constraints need to be added to the problem formulation. These constraints can potentially make an already difficult problem even harder. This paper takes a different approach to the transmission switching problem. Rather than preventing islanding by using constraints in the problem formulation, we look at how they can be used to improve the solution process. Specifically, we develop a cutting plane algorithm to generate valid inequalities and fi xv ariables based on the fact that optimal solutions to the transmission switching problem that do not contain islands exist.

Special Issue on Smart Grid and Emerging Technology Integration

Special Issue on Smart Grid and Emerging Technology Integration

Technology and Topology Optimization for Multizonal Transmission Systems

This paper presents a method to optimize equipment investments in multizonal transmission systems, considering spatial properties of the areas of focus. Together with a probabilistic technique for assessing nodal injection capability, the method in the paper completes the methodology of a long term transmission system planning tool. Transmission topology, line route and technology are optimized through iterative application of linear integer programming and Dijkstra's shortest path algorithm. By optimizing the transmission route, the spatial properties of the area of focus are taken into account, which in turn can significantly influence the installation costs of transmission equipment. The optimization method considers both AC and DC technology and takes the N-1 security criterion into account.

Configuration Analysis of RV Transmission Based on Topology Graph Theory

This paper puts forward the method of obtaining new types of RV transmission. Research shows that the topological graph can effectively express the topology unit and topological structure of RV transmission; the process that through topology degradation and evolutionary method to Obtain the RV transmission of topology map and through the topology inversion to get the new organization is practical and feasible. The topological evolution methods have tie bar evolution, tree, increasing gear tooth ring and mixing superimposed evolution. The RV transmission topology inversion is implemented by the way of gear ring, Gear meshing, the gear, the shaft, tie rod and the frame. Method was developed to get the evolutions of a variety of RV transmission, and the evolution of a graph of the inverse mapping was enumerated. The topology graph theory methods used in the RV transmission for the structure of RV transmission innovation provides an important theoretical method.