Power Network Configuration Research Articles

A Generalized Fault Location Approach for Any Type of Power Network

This paper presents a generalized fault location algorithm that can locate faults for any type of power network configuration. It enhances previous work presented by the authors by reducing the estimation steps but keeping its robustness and redundancy against traveling wave attenuation by power transformers, bad data, voltage signal errors and the impact of Inverter Based Power Sources (IBPSs). This is accomplished by forming arrays containing the network parameters and time-of-arrivals (ToAs) for fault signals captured by Digital Fault Recorders (DFRs), which are used as inputs to the algorithm to compute the accurate fault localization. The IEEE 39-bus system is used to validate the algorithm under different fault conditions using Electromagnetic Transients Program and Matlab as simulation tools.

Infrastructure planning for ride-hailing services using shared autonomous electric vehicles

Ride-hailing services using shared autonomous electric vehicles (SAEVs) are soon expected to serve a significant portion of the public transportation demands, especially in metropolitan cities. The transportation demands will arise randomly across all transportation nodes and during all hours of operation. This spatio-temporal nature of the transportation demand together with the constraints of trip length, battery size and consumption rate, and power network will guide the actions of the SAEVs. These actions are pair-with-demand, park, charge, and relocate, which in turn will determine the necessary infrastructure plan for ride-hailing services. The plan will comprise SAEV fleet size, charging hub locations across the nodes of the transportation network, and the number of charging stations in each hub. We formulate a profit-maximizing mixed integer linear model comprising a space-time-battery representation of the transportation network and a DC power flow representation of the power network. The model, intended for developing infrastructure plans for ride-hailing services, is robustified to accommodate randomness in travel and electric power demand. The model solution is demonstrated via an illustrative numerical case study representing the Tampa Bay region of Florida, USA. The results show how the infrastructure plans and their profitability depend on the demand fulfillment goal, battery size, battery consumption rate, and power network configurations. A linear relaxation of some of the integer variables of the model to reduce computational time is discussed.

On the Estimation and Reduction of the Frequency of the Loss of Offsite Power Event

Loss of offsite power (LOOP) contributes significantly to the estimated core damage frequency (CDF) for the majority of nuclear power plants (NPPs). Based on experience from some near-miss events around the world and especially in Japan from Fukushima Daiichi accident and several other NPPs it was proven the how important power supply is for nuclear safety. Therefore comprehensive description of the LOOP initiating event is given in this paper. Specific experience of the NPP Krško (NEK) related operation is also presented with comparison to the U.S. NPPs’ approaches and experience. Statistical data are given to explain main characteristics (frequency and duration) of the LOOP event. Important historical trends are also identified. LOOP event frequency is often calculated using generic data because of statistical data base. Thereat, many important factors that influence LOOP are neglected, such as the specific power network configuration, load profiles, climate conditions, and ageing of the equipment. Several different approaches that take these factors into consideration are therefore presented and discussed. Familiarity with the actual state of the NPP, power network and weather conditions helps in the proper planning process of the test and maintenance (T&M) activities and reducing of the risk. This is significant for better online risk estimate. Due to the Fukushima accident, it is necessary to review the safety of the NPPs from new different angles. This paper also shortly reviews planned modifications in NEK that will increase the electric power supply availability (i.e., reduce LOOP event frequency. Other, worldwide solutions that can help to avoid or mitigate LOOP effects are briefly presented.

Analysis of Akangba Transmission substation protection system

The challenges of the Nigeria power system have deprived the yearning electricity consumer access to stable power supply. Apart from the incessant load shedding due to inadequate power generation capacities, poor power system protection design, lack of constant protection system review after several changes to the power network is one of the contributing factors for unstable power system and unplanned outages. The network engineers must devise method of reviewing the protection settings as changes are made to power system components. This motivates the adoption of power system symmetrical fault analysis model presented herein. The model was applied to Akangba Transmission substation using the network planning software (NEPLAN software). The results show the fault current flowing through every part of the network. The effect of network expansion, switching Scenarios /Component changes on the fault current and protection scheme was also verified. Protection engineers must therefore take note of changes in the power network configuration when planning protection coordination and relay setting. The method is interesting and can be used as a template for reviewing protection scheme when changes are made on the power network. This will ensure better power protection management, enhance stable power supply and reduce damage to expensive power components.

Node-based valid inequalities for the optimal transmission switching problem

The benefits of transmission line switching are well-known in terms of reducing operational cost and improving system reliability of power systems. However, finding the optimal power network configuration is a challenging task due to the combinatorial nature of the underlying optimization problem. In this work, we identify a certain “node-based” set that appears as substructure of the optimal transmission switching problem and then conduct a polyhedral study of this set. We construct an extended formulation of the integer hull of this set and present the inequality description of the integer hull in the original space in some cases. These inequalities in the original space can be used as cutting-planes for the transmission line switching problem. Finally, we present the results of our computational experiments using these cutting-planes on difficult test cases from the literature.

City transportation network vulnerability to disasters: the case of Hurricane Hermine in Florida

ABSTRACT Hurricanes affect millions of people in the U.S. every year and cause billion-dollar economic losses. Florida is one of the states in the U.S. which is vulnerable to hurricanes and major infrastructure damages were reported due to these extreme events such as Hurricane Hermine (2016). This study aims to assess the impacts of Hermine on the transportation network of Tallahassee, the capital of Florida, using a spatial-analytical approach and real-world hurricane data on roadway closures, power outages, power network configuration, and other storm-related variables. First, a geographic information systems (GIS)-based analysis was utilised to obtain the spatial patterns of hurricane-induced roadway closures along with power outages, power lines, downed trees, and the city’s flood hazard zones. Second, a statistical model was developed to understand the association between the aforementioned variables and roadway closures. The spatial model results revealed that the roadway closures and power outages almost have the same patterns, and the city centre experienced more disruptions than other areas. The statistical model findings indicated that the power outages and power lines have strong relationships with roadway closures. The obtained knowledge of this study can provide valuable information for city officials to prepare better emergency policies for future potential hurricanes.

Lightning-Induced Voltages on Complex Power Systems by Using CiLIV: The Effects of Channel Tortuosity

Recently, Andreotti et al. (2015) have presented a new tool for lightning induced voltage calculations on power networks. This tool, named Circuit for Lightning Induced Voltage (CiLIV), has been initially developed for straight and vertical lightning channels; afterwards, the tool has been extended to evaluate induced voltages produced by tortuous lightning channels. However, in the aforementioned studies, only simple power network configurations have been examined. Therefore, aim of this paper is twofold: 1) to apply CiLIV to more complex network configurations, that is, complex networks equipped with transformers, surge arresters, groundings, and so on; 2) to investigate the effects of channel tortuosity on the voltages induced in these complex networks.

Successive-over-relaxation based recursive Bayesian approach for power system configuration identification

PurposeThe purpose of this paper is to propose successive-over-relaxation (SOR) based recursive Bayesian approach (RBA) for the configuration identification of a Power System. Moreover, to present a comparison between the proposed method and existing RBA approaches regarding convergence speed and robustness.Design/methodology/approachSwift power network configuration identification is important for adopting the smart grid features like power system automation. In this work, a new SOR-based numerical approach is adopted to increase the convergence speed of the existing RBA algorithm and at the same time maintaining robustness against noise. Existing RBA and SOR-RBA are tested on IEEE 6 bus, IEEE 14 bus networks and 48 bus Danish Medium Voltage distribution network in the MATLAB R2014b environment and a comparative analysis is presented.FindingsThe comparison of existing RBA and proposed SOR-RBA is performed, which reveals that the latter has good convergence speed compared to the former RBA algorithms. Moreover, it is robust against bad data and noise.Originality valueExisting RBA techniques have slow convergence and are also prone to measurement noise. Their convergence speed is effected by noisy measurements. In this paper, an attempt has been made to enhance convergence speed of the new identification algorithm while keeping its numerical stability and robustness during noisy measurement conditions. This work is novel and has drastic improvement in the convergence speed and robustness of the former RBA algorithms.

Service Restoration for a Renewable-Powered Microgrid in Unscheduled Island Mode

This paper deals with the service restoration problem in renewable-powered microgrids that are driven islanded by an unscheduled breakdown from the main grid. The objective is to determine the maximum of the expected restorative loads by choosing the best arrangement of the power network configurations immediately from the beginning of the breakdown all the way to the end of the island mode. The intermittency nature of the renewable power, as well as the uncertainty of the duration of the breakdown pose new challenges to this classic optimization scheduling task. The proposed two scenario-splitting methods can be solved in a two-step solving procedure, in which a Lagrangian technique and dynamic programming are utilized to provide an analytical sub-optimal yet efficient solution to the original problem. Simulation results demonstrate that both methods can find solutions very close to optima effectively; the scheduling plan should be adjusted when the time evolves, especially when the renewable power generation takes a large portion in the power supply; and the energy storage system plays a significant role to reduce the risk of unreliability in the wind power forecasting, even with a small amount of capacity. Finally, the proposed approach can be applied to radially configured systems with other types of distributed generators.

CPIndex: Cyber-Physical Vulnerability Assessment for Power-Grid Infrastructures

To protect complex power-grid control networks, power operators need efficient security assessment techniques that take into account both cyber side and the power side of the cyber-physical critical infrastructures. In this paper, we present CPINDEX, a security-oriented stochastic risk management technique that calculates cyber-physical security indices to measure the security level of the underlying cyber-physical setting. CPINDEX installs appropriate cyber-side instrumentation probes on individual host systems to dynamically capture and profile low-level system activities such as interprocess communications among operating system assets. CPINDEX uses the generated logs along with the topological information about the power network configuration to build stochastic Bayesian network models of the whole cyber-physical infrastructure and update them dynamically based on the current state of the underlying power system. Finally, CPINDEX implements belief propagation algorithms on the created stochastic models combined with a novel graph-theoretic power system indexing algorithm to calculate the cyber-physical index, i.e., to measure the security-level of the system's current cyber-physical state. The results of our experiments with actual attacks against a real-world power control network shows that CPINDEX, within few seconds, can efficiently compute the numerical indices during the attack that indicate the progressing malicious attack correctly.

Probabilistic life cycle analysis model for evaluating electric power infrastructure risk mitigation investments

One effect of climate change may be increased hurricane frequency or intensity due to changes in atmospheric and geoclimatic factors. It has been hypothesized that wetland restoration and infrastructure hardening measures may improve infrastructure resilience to increased hurricane frequency and intensity. This paper describes a parametric decision model used to assess the tradeoffs between wetland restoration and infrastructure hardening for electric power networks. We employ a hybrid economic input–output life-cycle analysis (EIO-LCA) model to capture: construction costs and life-cycle emissions for transitioning from the current electric power network configuration to a hardened network configuration; construction costs and life-cycle emissions associated with wetland restoration; and the intrinsic value of wetland restoration. Uncertainty is accounted for probabilistically through a Monte Carlo hurricane simulation model and parametric sensitivity analysis for the number of hurricanes expected to impact the project area during the project cycle and the rate of wetland storm surge attenuation. Our analysis robustly indicates that wetland restoration and undergrounding of electric power network infrastructure is not preferred to the “do-nothing” option of keeping all power lines overhead without wetland protection. However, we suggest a few items for future investigation. For example, our results suggest that, for the small case study developed, synergistic benefits of simultaneously hardening infrastructure and restoring wetlands may be limited, although research using a larger test bed while integrating additional costs may find an enhanced value of wetland restoration for disaster loss mitigation.

Budget constrained optimal security hardening of control networks for critical cyber-infrastructures

Competing schemes for security-hardening the power grid differ in their installation costs and the amount of coverage they provide against cyber attacks. Manually mapping schemes to vulnerable assets, where each asset has a unique degree of criticality in an arbitrary power network configuration, is a cumbersome process. Moreover finding an optimal scheme combination so as to maximize overall network security under a fixed budget constraint is an NP hard problem. In this paper we describe a dynamic programming solution to this problem and implement it along with logic-based models of the power grid, its control elements and best security practices as a tool-chain. The tool-chain takes, as input, a power network configuration, and the budget constraints and security schemes described in logic, determines the critical assets and automatically selects an optimal scheme combination to apply to maximize security. We demonstrate the feasibility of the tool chain implementation by security hardening the IEEE power system 118-bus test case from a pool of five different best-practice schemes.

An Interactive Power System Analyzer with Graphics Display for Educational Use

The paper presents a student-oriented power-system analyzer with an interactive graphics display. Its capabilities include studies of (1) load flow, (2) load and generation, (3) voltage level control, (4) economic dispatch, and (5) contingency and planning analysis. Power network configurations of up to 30 buses can be presented clearly on one screen. The interactive nature of this program makes such studies effective and easy to use. With the support of a computer with graphics software and many graphics terminals, this program can be a useful teaching tool for power system studies. The object of this work is to produce a computer/graphics facility for power-system studies that the junior and senior students can use. The computer available for student use is the IBM 4381, which is linked with an interactive graphics system. The Tektronix 4014 display terminal is a CRT storage display device with an enhanced resolution of 4096* 3120. This system is supported by many software packages including TCS, which has been chosen for this study. The power-system analyzer is designed to include the following features: 1. Interactivity The most common outstanding feature of this analyzer is that it is interactive. The potential saving in time by achieving the solution within a few seconds rather than a few hours or days is important. 2. Easy graphics display Two kinds of graphics displays are used. For a small system, an automatic display mode is available. No graphics data are needed.

An Interactive Power System Analyzer with Graphics for Educational Use

The paper presents a student-oriented power system analyzer with an interactive graphics display. Its capabilities include studies of (1) load flow, (2) load and generation , (3) voltage level control, (4) economic dispatch, and (5) contingency and planning analysis. Power network configurations of up to 30 buses can be presented clearly on one screen. The interactive nature of this program makes such studies effective and easy to use. With the support of a computer with graphics software and many graphics terminals, this program can be a useful teaching tool for power system studies.

An indirect method for the detection of changes in power network configuration

This paper presents an indirect procedure for determination of power network topology. The procedure applies the methods of state and parameter estimation, using redundant and noisy measurements, and a power system model in the steady state for some known basic network topology. Detection of changes in a network topology related to a basic topology is done by monitoring a suitably selected performance index during the process of static state estimation, while the location of changes requires additional criteria. The paper describes the development of a mathematical algorithm and gives some simulation results obtained on a real power network.