Line Switching Research Articles

UWB antenna with sweeping dual notch based on metamaterial SRR fictive rotation

AbstractIn this article, a novel frequency switchable method for Ultra‐Wide‐Band (UWB) microstrip antenna with dual notches is presented and discussed. This method is based on hexagonal‐shaped Split Ring Resonator (SRR) metamaterial cells located close to the 50‐Ω feed line and ideal switches inserted at the inner and the outer SRR of each cell. The incorporation of these ideal switches helps in changing the location of the opening of the inner ring (inner ring fictive rotation) and in activating or deactivating the filtering introduced by the metamaterial cells. The resulting radiating structure has an impedance bandwidth extending from 2.8 GHz to more than 11GHz accompanied with dual notched bands characteristic. It offers several cases by opening or closing the ideal switches. The obtained simulation results agree well with measurements carried out on the fabricated prototypes.

Group-Based Line Switching for Enhancing Contingency-Constrained Static Voltage Stability

A look-ahead contingency-constrained line switching problem is presented to enhance the static voltage stability of a look-ahead (say 30 minutes) base case, respecting a set of credible contingencies. This problem seeks to identify the ‘best’ network topology by switching out transmission lines to maximize the load margin of a look-ahead base case while ensuring the load margins of a set of credible contingencies are acceptable. Moreover, the voltage and thermal limitations are respected in the post-switching look-ahead base case. To solve the problem in an online environment, a group-based method is developed to reduce the complexity of the contingency constraints and enable tractable computation. Extensive numerical results on the IEEE 118-bus and the 1648-bus power systems examine the effectiveness of the proposed methodology.

Capacity Expansion of Wind Power in a Market Environment With Topology Control

Wind power integration is an essential problem for modern power industry. In this paper, we develop a stochastic bilevel mixed integer optimization model to investigate the wind power generation planning problem in an electricity market environment with topology control operations. Different from existing formulations, the lower level market clearing problem introduces binary variables to model line switching decisions, which have been proven very effective to improve transmission capability under different load profiles. To solve this challenging bilevel mixed integer program, a recent decomposition method is customized and a couple of enhancement techniques based on grid structure are designed. Numerical results on typical IEEE test beds show that 1) topology control could be very helpful in reducing wind energy curtailment and improving the wind penetration level, and 2) such advantage often can be achieved by applying topology control on a small number of lines in a coordinated fashion.

Switching attacks on smart grid using non‐linear sliding surface

A cyber-intruder uses the local knowledge of grid in order to develop and apply a coordinated switching sequence to attack and destabilise an otherwise healthy smart grid system. In this study, the attacker utilises the swing equation to discover the stable boundary limit of the target generator and applies non-linear sliding surface (NLSS) technique to compute switching sequences and perpetrate attacks through gained access over a target circuit breaker for the disruption of normal operation. The targeted generator in the Western Electricity Coordinating Council 3 machine, 9-bus system, and New England 10-generator, 39-bus system are attacked using a line switching event. An NLSS-based load switching triggered an attack is also executed in a single machine infinite bus system to compare against the linear sliding surface-based attack performance. The valour of an attack lies in its swift and fast action. Both these aspects are highlights of this work as the application of NLSS reduces chattering and achieves much faster spiralling out to instability.

Decentralized Topology Reconfiguration in Multiphase Distribution Networks

The cyber-physical nature of the modern power grid allows active power entities to exchange information signals with one another to make intelligent local actuation decisions. Exacting effective coordination amongst these cyber-enabled entities by way of strategic signal exchanges is essential for accommodating highly fluctuating power components (e.g., renewables, electric vehicles, etc.) that are becoming prevalent in today's electric grid. As such, in this paper, we present a novel decentralized topology reconfiguration algorithm for the distribution network (DN) that allows the system to adapt in real time to unexpected perturbations and/or congestions to restore balance in loads across the feeder and improve the DN voltage profile. For this, individual agents residing in DN buses iteratively exchange signals with neighbouring nodes to infer the current state (e.g., power balance and voltage) of the system and utilize this information to make local line switching decisions. Strong convergence properties and optimality conditions of the proposed algorithm are established via theoretical studies evoking potential games and discrete concavity. Comparative simulation studies conducted on realistic DNs showcase the practical properties of the proposed algorithm.

An online line switching methodology with look-ahead capability to alleviate power system overloads based on a three-stage strategy

An online line switching methodology to alleviate line overloads with look-ahead capability is proposed in this paper. This novel online methodology is based on a three-stage strategy, including screening, ranking, and detailed analysis and assessment stages for fast speed (online application) and accuracy. The proposed online methodology performs the tasks of rapidly identifying effective candidate lines, ranking the effective candidates, detailed analysis of the top ranked candidates, and supplying a set of effective line switching solutions for a current operating point. Both the current and the look-ahead post-switching power systems, after executing the proposed line switching action, meet the operational and engineering constraints. One distinguishing feature of the proposed methodology is that it provides a set of high-quality line switching solutions. The results provided by the exact AC power flow are used as a benchmark to compare the accuracy of the proposed three-stage methodology. The effectiveness and fast speed of the proposed line switching methodology with look-ahead capability are evaluated on the IEEE 39-bus and 2746-bus power systems with promising results.

Optimal capacity utilisation of transmission lines network in power flow operations: a survey

Purpose This paper aims to survey the need for full capacity utilisation of transmission lines in power systems network operations. It proposes a review of the N-1 security criterion that does not ensure reliable dispatch of optimum power flow during outage contingency. The survey aims to enlarge the network capacity utilisation to rely on the entire transmission lines network operation. Design/methodology/approach The paper suggests transmission line switching (TLS) approach as a viable corrective mechanism for power dispatch. The TLS process is incorporated into a constraint programming language extension optimisation solver that selects the switchable line candidates as integer variables in the mixed integer programming problem. Findings The paper provides a practical awareness of reserve capacity in the lines that provide network security in outage contingency. At optimum power flow dispatch, the TLS is extended to optimal transmission line switching (OTLS) that indicates optimal capacity utilisation (OCU) of the available reserve capacity (ARC) in the network lines. Practical implications Computational efficiency influenced the extension of the OTLS to optimal transmission switching of power flow (OTSPF). The application of OTSPF helps reduce the use of flexible AC transmission systems (FACTS) and construction of new transmission lines.. Originality/value The paper surveys TLS efforts in network capacity utilisation. The suggested ARC fulfils the need for an index with which the dispatchable lines may be identified for the optimal capacity utilisation of transmission lines network.

Cost-effective power grid protection through defender–attacker–defender model with corrective network topology control

Power grid vulnerability is a critical issue in power industry. In order to understand and mitigate power grid vulnerability under threats, existing research often makes use of defender–attacker–defender (DAD) models to derive effective protection plans and evaluate grid performances under various contingencies. Corrective topology control (also known as corrective line switching) can be used as an operation to mitigate outages or attacks. In this paper, we propose to extend the traditional defender–attacker–defender model with the post-contingency corrective line switching operations as an effective post-contingency mitigation method. The proposed new model cannot be solved by existing algorithms used to solve the traditional defender–attacker–defender models because of the introduced binary transmission switching variables in the inner level problem. To solve this complicated DAD with transmission line switching (DAD-TLS) model, we customized and developed an exact algorithm based on the nested column-and-constraint generation (NCCG) algorithm, to compute global optimal solutions. A set of numerical studies on IEEE RTS one-area system demonstrate the significant improvements of power system resilience under malicious attacks due to line switching, and highlight that hardening plans derived from this new DAD model are much more cost-effective compared with those obtained from traditional DAD models.

Optimal operational scheduling and reconfiguration coordination in smart grids for extreme weather condition

With the increasing in frequency, intensity, and side effects of grid outages caused by weather based events, the importance of resiliency is also increased. This study presents a novel multi-objective optimization problem for improving the resilience of smart grid against natural disasters in the presence of a considerable amount of line outages occurring due to the weather conditions. The proposed model considers the management of distributed energy resources (DERs), energy storages (ESs), and dynamic topology reconfiguration of the distribution network. The main goal is based on a dynamic resilient operational planning using prediction of weather condition. The objectives in the proposed approach are defined as: to minimise operational cost of distribution network from the system operator's viewpoint, to minimise the penalty costs for energy not supplied and side effects of outages, and to maximise benefits of DER-ES owners by using flexible reconfiguration and dynamic operational planning considering weather conditions. A hybrid optimization algorithm based on genetic algorithm and ɛ-constraint method using fuzzy decision maker is employed to choose the best solution from a provided Pareto optimal set. The outcome of the Pareto solution specifies the best scheduling for DERs, ESs and switching of lines during the scheduling horizon.

Single-Phase Split-Inductor Differential Boost Inverters

In this paper, two single-phase single-stage split-inductor buck–boost inverters are proposed: type-I and II. The proposed type-I is unity power factor inverter, while the proposed type-II inverter is suitable for any power factor. Both topologies remove the shoot-through problem. Furthermore, the reverse recovery issues for all switches are eliminated; therefore, mosfet s are used to obtain higher efficiencies. The proposed inverters operated at higher switching frequencies confer the additional benefit of smaller passive components. The current stresses of the two switches in the proposed type-I and II inverters are lower of the conventional boost inverter. The dead time can be eliminated at both the high and line switching frequencies. In addition, the inductor conduction loss is minimized to improve efficiency. Moreover, the voltage stresses of the two switches in the type-I inverter can be much lower of its counterpart boost inverter. Most importantly, unlike the conventional high-reliability inverters, the magnetic volume of the proposed high-reliability type-I and II inverters is same of its counterpart boost inverter. The experimental results obtained for 500 W, 110 Vrms, 60 Hz hardware prototypes verify the analysis.

Broadcast Gossip Algorithms for Distributed Peer-to-Peer Control in AC Microgrids

This paper focuses on a fully distributed peer-to-peer control scheme for voltage regulation and reactive power sharing of multiple inverter-based distributed energy resources (DERs) in ac microgrids. The proposed peer-to-peer control strategy is fully distributed enabled through broadcast gossip communication, where each DER unit only requires local voltage and current measurement from its own and some (but not all) nearby neighbors for the voltage and reactive power sharing control. Employing the broadcast gossip communication protocol with attractive scalability and reliability properties, the control inputs can be updated to restore the voltage magnitudes at the point of common coupling to a desired value ensuring an accurate reactive power sharing for each DER. Since the proposed distributed controllers are implemented on local DERs, the central controller and hierarchy are no longer required. Accordingly, the microgrid system stability is preserved in the peer-to-peer requirements of line switches, which in turn, enables a plug-and-play operation of DERs and their robustness against microgrid topology change scenarios. Simulation studies in a modified IEEE 34-bus test network demonstrate the effectiveness and applicability of the proposed control strategy.

Corrective Control by Line Switching for Relieving Voltage Violations Based on A Three-Stage Methodology

An online line switching methodology to relieve voltage violations is proposed. This novel online methodology is based on a three-stage strategy, including screening, ranking, and detailed analysis and assessment stages for high speed (online application) and accuracy. The proposed online methodology performs the tasks of rapidly identifying effective candidate lines, ranking the effective candidates, performing detailed analysis of the top ranked candidates, and supplying a set of solutions for the power system. The post-switching power systems, after executing the proposed line switching action, meet the operational and engineering constraints. The results provided by the exact Alternating Current (AC) power flow are used as a benchmark to compare the speed and accuracy of the proposed three-stage methodology. One feature of the methodology is that it can provide a set of high-quality switching solutions from which operators may choose a preferred solution. The effectiveness of the proposed online line switching methodology in providing single-line switching and multiple-line switching solutions to relieve voltage violations is evaluated on the IEEE 39-bus and 2746-bus power system. The CPU time of the proposed methodology compared with that under AC power flow constitutes a speed-up of 9905.32% on a 2746-bus power system, showing good potential for online application in a large-scale power system.

Advanced Control Techniques for Enhance the Power System Stability at OOS Condition

<p>The power system stability is the accurate operation of the electric grid by restoring balance after being subjected to an abnormal condition such as fault, line switching, load rejection, and loss of excitation. Protective equipment in high voltage substations should fast and precisely localize the faults. Some abnormal conditions in the power system such as out-of-step (OOS) condition which is not a real fault, but the protection equipment will consider it is. This misjudgment will cause the loss of synchronism between areas within the power system or between interconnected systems and will lead to blackout of the national grid. This paper studied the OOS condition, philosophy of protection relay device and how to avoid the false operation for distance function by Out of Step Blocking (OSB) by using the advanced protection relay, to improve the stability of power system. </p>

Polarization-Controlled Switching of Dual-Wavelength Lines with Orthogonal Polarization in Erbium-Doped Fiber Ring Laser.

By incorporating an inline switching filter, which is comprised of a polarization-diversified loop (PDL), two fiber Bragg gratings (FBGs) with different resonances, and three quarter-wave plates (QWPs), we propose a dual-wavelength-switchable erbium-doped fiber (EDF) ring laser that can select and switch between two lasing lines with orthogonal polarization. The proposed laser is composed of EDF, a 980 nm laser diode, a wavelength-division-multiplexing coupler, a rotatable linear polarizer, an optical isolator, a 3 dB optical coupler, and the inline switching filter. At a special combination of the orientation angles of the three QWPs, the inline filter can offer a different transmittance according to input polarization, e.g., reflection spectra of one and the other of the two FBGs for linear horizontally and vertically polarized input light, respectively. At this special combination of the QWPs, one of two different resonances of the two FBGs can be selected by varying laser cavity polarization through the adjustment of the orientation angle of the rotatable linear polarizer. Consequently, switching operation between two laser lines with orthogonal polarization at the two FBG resonance wavelengths could be obtained by properly controlling cavity polarization. The polarization extinction ratio of each lasing line was measured as more than 19.9 dB.

DC-Impulse Voltage-Dependent Electrical Tree Growth Characteristics of Epoxy Resin in LN2

This paper focuses on the electrical tree growth characteristics in epoxy resin with dc-impulse voltage caused by line fault and switching surges in liquid nitrogen (LN2). Electrical tree initiation tests were conducted on molded epoxy resin with a needle–plate system. The test samples were stressed with a dc voltage amplitude of 10 kV and an impulse voltage amplitude of 24 kV at 77 K. With a wide range of voltage frequencies and different impulse polarities, four different waveforms of dc-impulse voltage were used as applied voltage. Result shows that the electrical tree tends to grow longer when the dc and the impulse are of the same polarity. The impulse frequency plays a crucial role in tree initiation and growth process. The tree initiation probability increases with the frequency rising from 50 to 400 Hz in epoxy resin. Different charge transportation processes are discussed based on four different voltage waveforms. The collision ionization and charge recombination have a decisive effect on electrical tree initiation. The impulse voltage is worth regarding in the operation of a superconducting cable system.

Trap Distribution and Breakdown Characteristics of Direct-Fluorinated PI Film for DC-HTSFCL

High-temperature superconducting fault current limiter (HTSFCL) is an important application in the power industry. In high-voltage dc system, a polyimide (PI) is used as superconducting winding insulation in HTSFCL also withstands pulse voltage of lightning and operating voltage caused by line fault and switching. The combined dc-pulse voltage makes the electric field more deformed, which induces partial discharge and accelerates insulation failure. Direct fluorination is a good means of regulating the molecular structure and electrical properties of polymers. This paper studies the trap distribution and breakdown characteristics of direct-fluorinated PI film. The corona charging was implemented in an environment with a relative humidity of 40%, using a combined dc-pulse voltage. To calculate the trap distribution, the surface potential was obtained. The breakdown voltage was also measured in LN 2 under different voltages. The experimental results indicate that moderate fluorination can effectively reduce the depth of trap level, accelerate charge detrapping, and improve the breakdown voltage of the PI film.

CHOICE OF SHORT-TERM CONSTANT CONFIGURATION OF THE DISTRIBUTION NETWORK

The work studies a possibility of choice for a given interval of changing the load power and the capacity of renewable generation sources of such a constant configuration of the primary distribution network, at which the energy losses differ minimally from the losses at the optimal hourly reconfiguration The study was carried out using the fast algorithm of the primary distribution network reconfiguration by the losses minimization criterion that was worked out by the authors. The algorithm efficiency is proved by comparing the results obtained on study basis with the results of other methods. After emergency cut-out of the sectionalizing switch the reconfiguration algorithm based on the methods known in the graph theory allow us to determine the line switch required for restoration. For the final choice of such switches feasibility of the post-emergency is tested and the controls are chosen, if the conditions are not met. The work of the proposed methods is demonstrated by the example of the 33 nodal IEEE scheme.

Adequate Topology for Efficient Energy Resources Utilization of Active Distribution Networks Equipped With Soft Open Points

Active distribution networks concerned with providing efficient control technologies for large-scale integration of distributed generation (DG) units into the distribution systems. This research proposes a methodology for distribution networks reconfiguration by controlling number, sharing, size, and location of DG units. Also, the soft-open points (SOPs) are added instead of the tie line switches. The SOPs are benefited with its high capability in controlling active/reactive power flow to enhance transmission system performance. The main target of this work is to increase the efficiency of energy utilization through minimizing the power system losses and improving system voltage profile while preserving all system constraints within permissible limits with reliable and flexible networks in normal and abnormal conditions with a suitable penetration level of DG. A modified particle swarm optimizer is developed to find the best system configuration, size, and placement of DG units as well as the size and allocation of SOPs. Research methodology is tested on two standards: the IEEE 33-node and 69-node distribution networks under different operating cases. This paper compares the obtained results with those in the literature to prove the capabilities of the proposed work. Finally, the suggested work pursues the optimal number of DG units with their appropriate penetration levels and selects the most convenient location of SOPs for adequate network reconfiguration.

Predictive Risk Analytics for Weather-Resilient Operation of Electric Power Systems

Day-to-day operation of the electricity grid generation, transmission, and distribution is environmentally driven and closely dependent on evolving weather patterns. This paper introduces several new weather-driven analytics for accurate spatial–temporal electricity generation forecasts, asset health and reliability assessment, probabilistic load forecasts, and electricity market simulations. A new risk metric is suggested, which accounts for the weather hazards, grid vulnerability, and financial consequences in the face of changing weather patterns and associated meteorological predictions over time. New mitigation formulations for power system topology control through transmission line switching for fast and timely recovery of the weather-caused electricity outages are suggested. The proposed decision support tool enables the operators to predictively evaluate the high-risk weather threats and consequently plan on how to safeguard the grid when exposed to forecasted weather-driven incidents. The efficiency of the proposed toolset is illustrated by application to a part of the IEEE 73-Bus test system.

Comparison of the characteristics of three kinds of HVDC systems with ABB, SIMENS, and Cigre Benchmark

This study presents the comparison among three control systems: Cigre Benchmark model, ABB model, and SIMENS model based on PSCAD. Firstly, the control systems which refer to Cigre Benchmark control model, ABB control model, and SIMENS control model are introduced, respectively. Analysis and comparison are done on these control systems about their design theories, control logic, and functional models, and the advantages and disadvantages of each control system are concluded. Secondly, simulations in both normal and fault conditions are done in order to verify the conclusions. On the one hand, the steady-state response characteristics of these three high-voltage direct current (HVDC) models are obtained and compared by setting different voltage of the receiving terminal AC bus. On the other hand, the transient response characteristics of these three HVDC models under different operating conditions are obtained, such as symmetrical and asymmetrical short-circuit fault, line switching on or off etc. The research results will provide experiences and references for the future optimisation of the HVDC control system.