Contingency Criteria Research Articles

Evaluation and Improvement of Power System Security with the Application of Machine Learning

The electricity grid has added many renewable and non-renewable energy sources to meet expanding demand. Sudden load variations exacerbate generator, transmission line, and distribution network issues. Load modelling choices are crucial for system prediction. This study indicates that ZIP load models with contingency criteria can accurately forecast load behaviour over time. The NR method predicts the contingency ranking with the High Bride Line Stability Ranking Index (HLSRI) under single line outage conditions, and an artificial neural network (ANN) is trained to predict the severity of the line outage and the system's behaviour. A mathematical model was utilised to analyse stability and cost with and without the UPFC and IPFC. Machine learning (ML) is used to rapidly predict the most affected transmission line during a contingency by clustering data using the J48 algorithm for the location of compensating devices. The PSO algorithm is used to develop an objective function to minimise fuel costs by maximising generating capacity. A transmission line failure and load variation might damage the electrical system. This study prioritises transmission line breakdowns and load changes. Power system security analysis provides power system status.

A generalised approach for efficient computation of look ahead security constrained optimal power flow

We consider a generalised comprehensive Look-ahead Security-constrained Optimal Power Flow (LASCOPF) formulation under the N−1 contingency criterion over multiple dispatch intervals. We observe that the number of decision variables varies quadratically with the number of intervals. To improve scalability, we propose a reduced LASCOPF formulation for which the number of decision variables varies only linearly. We extend these formulations to the N−k contingency criterion. For reduced LASCOPF we observe that the number of decision variables varies with the number of k-permutations of contingencies. To improve scalability, we propose a formulation that is further reduced to vary only with the number of k-combinations. Also, we show that our formulations can be extended simply to model recovery from the corresponding outages. Furthermore, we present LASCOPF under the N−1 contingency criterion using DC and AC power flow under generator contingencies. We prove that, barring borderline cases, solving the reduced formulation is equivalent to solving the comprehensive formulation. We extend these results to the N−k contingency criterion. Finally, we present numerical results on the IEEE 14 bus, IEEE 30 bus and IEEE 300 bus test cases, and the 1354 bus part of the European power system using AC power flow to demonstrate the computational advantage of the reduced formulations under the N−1 and N−2 contingency criteria.

Investigations on hybrid line stability ranking index with polynomial load modeling for power system security

Introduction. In recent years, numerous non-renewable and renewable energies are connected to the grid to meet the demand. Also, transient variation with loads poses the shortcomings for generating units, transmission and distribution networks. In this regard, the study on choice of suitable load modelling is essential to predict the system characteristics. The aspect of the research design is a ZIP load model, which, when combined with contingency criteria and constant-impedance, constant-current, and constant-power loads, produces realistic and long-term load representations. Purpose. The proposed technique, infers the single transmission line outage for obtaining the contingency ranking to ensure the system behavior. Methods. The proposed mathematical model with hybrid line stability ranking index has been used for observing the stability analysis with and without considering unified power flow controller. Results. The power system involves many unpredictable conditions or contingency conditions like single transmission line outage, double transmission line outage, generator outage and load variations. This paper mainly focuses on the single transmission line outage for obtaining the contingency ranking. Practical value. The recommended stability analysis has been very beneficial in establishing a secure transmission power system.

Voltage Stability Control Based on Angular Indexes from Stationary Analysis

This paper presents a novel methodology for the calculation of angular indexes of an electrical system from stationary analysis, using load flow and nose curves (P–V) in each of the buses of the system to perform control actions and preserve or improve voltage stability. The control actions are proposed considering a novel method based on the concepts of the cutset angle (CA) and center of angle (COA). The target is a fast estimation of voltage-stability margins through an appropriate angular characterization of the whole system and for each load bus with a complete network and N-1 contingency criteria. The most significant enhancement is that the angular characterization is based on the COA, which is related to the angular dynamics of the system, and indirectly reflects the inertia and the respective angles of the generator rotor, as well as the impact on the angular equivalent-system model. Simulations showed that the COA is an important index to determine the location of occurrence of the events. The COA can also help aim where control actions, like the amount of load shedding, should be carried out to remedy the voltage problems. The proposed method is assessed and tested in the benchmark IEEE 39-bus system.

Reliability assessment and congestion management of power system with energy storage system and uncertain renewable resources

The high penetration of Renewable Energy Sources (RES) makes the power system unreliable due to its uncertain nature and to deal with this uncertainties installation of an Energy Storage System (ESS) is suggested. In this paper, the quantifying impact of ESS capacity on power system network reliability and relieving the congestion is analyzed. The proposed reliability assessment and congestion relief problem is formulated by considering generation cost and demand interruption cost for N-1 contingency criteria. The proposed algorithm manages the optimal charging and discharging of ESS to mitigate the uncertainties associated with RES and relieving the congestion. The impact of ESS capacity on reliability indices Expected Energy not Supplied (EENS) and Expected interruption Cost (ECOST) for Generating Companies (GENCOs), Transmission Companies (TRANSCOs), customers, and entire power system are calculated. The appropriate size of ESS is selected by the trade-off between investment cost of ESS and percentage change in EENS and ECOST value for the entire power system, GENCOs, TRANSCOs, and customers. The effectiveness of the proposed approach is tested on the modified IEEE RTS 24 bus system. The problem is modeled in the Generic Algebraic Solver (GAMS) environment and solved using CONOPT as an NLP solver.

Generation and Transmission Expansion Planning Towards a 100% Renewable Future

This paper proposes a novel modeling framework and decomposition-based solution strategy combining stochastic programming (SP) and robust optimization (RO) to deal with multiplex uncertainties in coordinated mid- and long-term power system planning. The problem is formulated as a multi-year generation and transmission planning problem from an independent system operator (ISO)’s perspective to minimize both expansion and operational costs under binary and continuous uncertainties, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\bf i.e.}$</tex-math></inline-formula> , system component contingency and load/generation variation. N- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\bf {k}$</tex-math></inline-formula> contingencies are captured in RO using the reformulated contingency criteria, while the load/generation uncertainty is considered in SP embedded with RO using operating scenarios generated from the historical data with spatiotemporal correlations. The original hybrid model is highly intractable, but the intractability can be relieved by the proposed decomposition strategy based on the column-and-constraint generation and L-shaped algorithms. We apply our model to perform long-term system planning under extremely high renewable penetration and investigate the case of 100% renewables in long-term planning. Numerical experiments on multi-scale test systems verify the efficacy of the proposed approach.

Sequential analysis of optimal transmission switching with contingency assessment

Optimal transmission switching (OTS) has been introduced as a persuasive approach for cost minimisation and the improvement of power system flexibility by utilising the lines’ existing conditions. Ordinary OTS based on optimal power flow (OPF) equations used in the previous studies may expose system security in some cases. This study proposes a novel sequential method to investigate the security of the system in post-OTS circumstances by considering N − 1 contingency criteria. The proposed method ranks the candidate lines as an operational strategy to reach the maximum reduction of the total operational cost by considering the security roles of transmission lines. The formulation of OTS and security assessment programs is based on alternating current OPF. The proposed approach provides more accurate solutions to a mixed integer non-linear programming model of the OTS program with N − 1 security criteria within a reasonable computation time. The obtained simulation results of the proposed method have been presented on IEEE 57-bus and IEEE 118-bus standard test systems. It is shown that the results of the ordinary OTS for lines’ outage ranking change because of system security consideration.

Ebola Preparedness in the Netherlands: The Need for Coordination Between the Public Health and the Curative Sector.

Context:During the Ebola outbreak in West Africa in 2014-2015, close cooperation between the curative sector and the public health sector in the Netherlands was necessary for timely identification, referral, and investigation of patients with suspected Ebola virus disease (EVD).Objective:In this study, we evaluated experiences in preparedness among stakeholders of both curative and public health sectors to formulate recommendations for optimizing preparedness protocols. Timeliness of referred patients with suspected EVD was used as indicator for preparedness.Design:In focus group sessions and semistructured interviews, experiences of curative and public health stakeholders about the regional and national process of preparedness and response were listed. Timeliness recordings of all referred patients with suspected EVD (13) were collected from first date of illness until arrival in the referral academic hospital.Results:Ebola preparedness was considered extensive compared with the risk of an actual patient, however necessary. Regional coordination varied between regions. More standardization of regional preparation and operational guidelines was requested, as well as nationally standardized contingency criteria, and the National Centre for Infectious Disease Control was expected to coordinate the development of these guidelines. For the timeliness of referred patients with suspected EVD, the median delay between first date of illness until triage was 2.0 days (range: 0-10 days), and between triage and arrival in the referral hospital, it was 5.0 hours (range: 2-7.5 hours). In none of these patients Ebola infection was confirmed.Conclusions:Coordination between the public health sector and the curative sector needs improvement to reduce delay in patient management in emerging infectious diseases. Standardization of preparedness and response practices, through guidelines for institutional preparedness and blueprints for regional and national coordination, is necessary, as preparedness for emerging infectious diseases needs a multidisciplinary approach overarching both the public health sector and the curative sector. In the Netherlands a national platform for preparedness is established, in which both the curative sector and public health sector participate, in order to implement the outcomes of this study.

Contingency-Constrained Unit Commitment With Intervening Time for System Adjustments

The $N$ -1-1 contingency reliability criterion considers the consecutive loss of two components in a power system, with intervening time for system adjustments between the two losses. In this paper, we consider the problem of optimizing generation unit while ensuring the $N$ -1-1 criterion. Due to the coupling of time periods associated with consecutive component losses, the resulting problem yields a very large-scale mixed-integer linear optimization model. For efficient solution, we introduce a novel branch-and-cut algorithm using a temporally decomposed bilevel separation oracle. The model and algorithm are assessed using multiple IEEE test systems, and a comprehensive analysis is performed to compare system performance across different contingency criteria. Computational results demonstrate the value of considering intervening time for system adjustments in terms of total cost and system robustness.

Geotechnical risk management approach for TBM tunnelling in squeezing ground conditions

Historically, attempts to use tunnel boring machines (TBMs) in Himalayan geology have been unsuccessful, particularly where weak rocks exist at the significant depths often required for hydroelectric hydraulic tunnels resulting in squeezing ground conditions. The use of segmental tunnel linings erected by shielded TBMs presents additional risk, such that the advantages of potentially high rates of advance using this form of construction have not previously been realised. Programme demands for the 330MW Kishanganga Hydroelectric Project in India required that 15km of the 23km headrace tunnel be constructed using a double-shield TBM erecting a segmental lining. Preliminary studies suggested difficult ground due to squeezing conditions along the 1400m deep tunnel through weak meta-sedimentary rocks. To allow planning and construction to commence, a risk management approach to design and construction was formulated with contingency procedures and criteria developed to allow the risks to the TBM and the lining to be managed effectively. Advanced numerical modelling included analysis of the tunnel with the ground represented by a Stress Hardening Elastic Viscous Plastic (SHELVIP) model to take account of time dependent loading. The Kishanganga tunnel represents the first segmentally lined TBM tunnel to be successfully constructed in the Himalaya. This paper describes the risk-mitigation approach, the special measures developed to address the risks, the numerical modelling and laboratory testing undertaken, and includes results from the segmental lining monitoring. Recognition of the risks, the development of an innovative methodology and the provision of the means by which geotechnical risk could be managed effectively during construction, gave confidence to all stakeholders to proceed with a method of construction that had not previously been implemented successfully in the Himalaya.

First trimester screening cut-offs for noninvasive prenatal testing as a contingent screen: Balancing detection and screen-positive rates for trisomy 21.

To provide data on how screen-positive and detection rates of first trimester prenatal screening for fetal Down syndrome vary with changes in the risk cut-off and maternal age to inform contingency criteria for publicly funded noninvasive prenatal testing. First trimester screening and diagnostic data were collected for all women attending for first trimester fetal aneuploidy screening in Western Australia between 2005 and 2009. Prenatal screening and diagnostic data were linked to pregnancy outcomes, including data from the Midwives' Notification System and the Western Australian Registry of Developmental Anomalies. The prevalence of Down syndrome and performance of screening by risk cut-off and/or for women >35 years were analysed. The current screening risk cut-off of 1:300 has screen-positive and detection rates of 3.5% and 82%. The screen-positive rate increases by 0.7-0.8% for each 100 point change in risk, up to 19.2% at 1:2500 (96% detection rate). Including all women >35 years as screen positive would increase the screen-positive rate and detection rates to 30.2% and 97.2%. Variation in screening risk cut-off and the use of maternal age to assess eligibility for noninvasive testing could significantly impact the demand for, and cost of, the test. A contingent first trimester screening approach for risk assessment is superior to the use of a combination of screening and maternal age alone. These data will inform decisions regarding the criteria used to determine eligibility for publicly funded noninvasive prenatal testing.

Setting up a French national flash flood warning system for ungauged catchments based on the AIGA method

Occurring at small temporal and spatial scales, flash floods (FF) can cause severe economic damages and human losses. To better anticipate such events and mitigate their impacts, the French Ministry in charge of Ecology has decided to set up a national FF warning system over the French territory. This automated system will be run by the SCHAPI, the French national service in charge of flood forecasting, providing warnings for fast-responding ungauged catchments (area ranging from ~10 to ~1000 km2 ). It will therefore be complementary to the SCHAPI’s national “vigilance” system which concerns only gauged catchments. The FF warning system to be implemented in 2017 will be based on a discharge-threshold flood warning method called AIGA (Javelle et al. 2014). This method has been experimented in real time in the south of France in the RHYTMME project (http://rhytmme.irstea.fr). It consists in comparing discharges generated by a simple conceptual hourly hydrologic model run at a 1-km2 resolution to reference flood quantiles of different (e.g., 2-, 10- and 50-year) return periods. Therefore the system characterizes in real time the severity of ongoing events by the range of the return period estimated by AIGA at any point along the river network. The hydrologic model ingests operational rainfall radar-gauge products from Meteo-France and takes into account the baseflow and the initial soil humidity conditions to better estimate the basin response to rainfall inputs. To meet the requirements of the future FF warning system, the AIGA method has been extended to the whole French territory (except Corsica and overseas French territories). The calibration, regionalization and validation procedures of the hydrologic model were carried out using data for ~700 hydrometric stations from the 2002-2015 period. Performance of the warning system was evaluated with various contingency criteria (e.g., probability of detection and success rate). Furthermore, specific flood events were analysed in more details, by comparing warnings issued for exceeding different critical flood quantiles and their associated timing with field observations. The performance results show that the proposed FF warning system is useful, especially for ungauged sites. The analysis also points out the need to account for the uncertainties in the precipitation inputs and the hydrological modelling, as well as include precipitation forecasts to improve the effective warning lead time.

Using the UPFC and GUPFC Controllers to Maximize Available Transfer Capability (ATC)

This paper focuses on studying the effect of the unified power flow controller (UPFC) and generalized unified power flow controller (GUPFC) to maximize the Available Transfer Capability (ATC). The normalized sensitivity factors technique is used, can be approximately computed, to determine the ATC of a test system, considering a variety of system limits. The basic Voltage Stability Constrain Optimal Power Flow (VSC-OPF) solution that does not consider contingencies is used for determining the sensitivity of power flows with respect to the critical loading parameter. Then, based on this solution and assuming a small variation of the loading parameter, compute the power flows again by solving critical power flows function. Then the sensitivity of system loading factor and N-1 contingency criteria technique is used to determine an optimal location of the UPFC and GUPFC controller. Finally, using proper models of the UPFC and GUPFC controllers, the effects of this Flexible AC Transmission System (FACTS) controller on the system ATC are studied. The IEEE 57- bus and 118-bus is used as the test system for validity, computing the system ATC for a given generation and loading pattern. All realistic control limits, as well as voltage dependent loads, are used in the ATC computation, with and without FACTS controller. The GUPFC can so strong influence the system in controlling or enhancement the ATC as good as power flow possible is compared with the UPFC. Keyword: UPFC, GUPFC. ATC, loading parameter, VSC-OPF

An optimal pricing scheme in electricity markets by parallelizing security constrained optimal power flow based market-clearing model

To improve economic efficiency of electricity markets, the market-clearing model must be designed to give transparent information for pricing system security and to quantify the correlation between the market operations and the power systems operations, which is an immensely provocative and challenging issue in electricity markets. This paper sets out to propose a novel approach to pricing the system security by parallelizing the security constrained optimal power flow (SCOPF) based market-clearing model, while providing market solutions as a function of complying with the required voltage security margin and N-1 contingency criteria. The proposed SCOPF based market-clearing framework also takes into consideration the bilateral transaction information and, at the same time, optimal pricing expressions through computing locational marginal prices (LMPs) and nodal congestion prices (NCPs) for ensuring voltage security are derived. The results from a 129-bus model of the Italian HV transmission system turn out to be the validity of the proposed market-clearing model for managing and pricing the system security.

Multiobjective transmission expansion planning considering security and demand uncertainty

This paper presents a methodology for resolving the transmission expansion planning problem by considering single contingency criteria (N-1). Each bus bar in the power system considered future demand uncertainty. The planning problem was divided into an investment problem (calculating investment costs) and an operative problem (resolving power flows). A modified evolutionary elitist non-dominated sorted genetic algorithm (NSGA-II) was used for resolving the investment problem, determining several investment proposals where feasibility was evaluated by solving the operative problem. On the other hand, a high order interior point (HOIP) method was proposed for solving load flow problems. The methodology was tested by using two systems found in the specialised literature: IEEE-24 bus and Garver or IEEE-6 bus systems. The results, when compared with traditional ones, showed the proposed method’s power and the multiobjective technique’s convenience.

Distribution Planning Based on Reliability and Contingency Criteria

Conductor layout plays a vital role in distribution planning. Here in this paper we suggest the distribution planning by the means of Analytical Hierarchy Process (AHP) where we take into consideration some aspects of reliability such as miles of conductor, feeder failures, customer interruption, maximum interruption, estimated relative cost. The results of the discussed techniques will lead to a configuration of substation that will minimize substation construction cost. It will further lower long range distribution expenses as it will lead to optimum feeder path. The application of the proposed methodology to a case study is presented.

Transmission Expansion Planning Using Contingency Criteria

This paper proposes a methodology for choosing the best transmission expansion plan considering various types of security (operating reliability) criteria. The proposed method minimizes the total cost that includes the investment cost of transmission as well as the operating cost and standby cost of generators. The purpose of the study is development of new methodology for solving transmission system expansion planning problem subject to contingency criteria which are essentially extensions of the (N-1) contingency criterion. The transmission expansion problem uses an integer programming framework, and the optimal strategy is determined using a branch and bound method that utilizes a network flow approach and the maximum flow-minimum cut set theorem. The characteristics of the proposed method are illustrated by applying it to a five-bus system and a 21-bus system. The results of these case studies demonstrate that the proposed method provides a practical way to find an optimal plan for power system expansion planning.

Reliability assessment for taipower's composite system‐case studies

This paper studies the reliability assessment of Taiwan Power Company's (Taipower's) system. The systems for the years 2003 and 2006 are investigated in accordance with the existing N‐1 and N‐2 planning criteria. The reliability assessment is achieved by both the power‐flow based deterministic analysis and the Markovmodel based probabilistic analysis. It is found that the reliability of the system will be enhanced in 2006 compared to the system in 2003 due to the sixth transmission and substation project. This paper also explores the generalized N‐1 and N‐2 contingency criteria by taking generator, transformer, or transmission outages into account. In addition, the possibility of raising the N‐1 and N‐2 contingency criteria to the level of N‐2 and N‐3 contingency criteria is considered. It is found that the N‐2 criteria are stricter for the 161 kV transmission system while the 345 kV transmission system is still robust and conforms to the N‐3 criteria in 2006. Furthermore, the sequential N‐1–1 and N‐1–2 contingencies are less severe than the simultaneous N‐2 and N‐3 contingencies.

05/02143 Voltage stability constrained OPF market models considering N-1 contingency criteria

05/02143 Voltage stability constrained OPF market models considering N-1 contingency criteria

Voltage stability constrained OPF market models considering [formula omitted] contingency criteria

This paper proposes two novel techniques for including contingencies in OPF-based electricity market computations and for the estimation of a “system-wide” available transfer capability (SATC). The OPF problem formulation includes voltage stability constraints and a loading parameter in order to ensure a proper stability margin for the market solution. Two methods are proposed. The first technique is an iterative approach and computes an SATC value based on an N − 1 contingency criterion for an initial optimal operating condition, to then solve an OPF problem for the worst contingency case; this process is repeated until the changes in the SATC values are below a minimum threshold. The second approach solves a reduced number of OPF problems associated with contingency cases according to a ranking based on a power transfer sensitivity analysis of the transmission lines. Both methods are tested on a 6-bus system and on a realistic 129-bus Italian network model considering supply and demand side bidding. Local marginal prices and nodal congestion prices resulting from the proposed solutions as well as comparisons with results obtained by means of a standard OPF technique are also presented and discussed.