Outages Of Elements Research Articles

OPEX of hybrid DC/AC power systems with large penetration of offshore wind taking into account spinning reserves

This study presents a method to analyse the secure and optimal operation of transmission systems consisting of both HVDC (high-voltage direct current) and high-voltage alternating current interconnections under a scenario of high penetration of offshore wind and taking into account the system spinning reserves. Different reliability management strategies are assumed, accounting for a single AC element and/or a single DC element outage and taking into consideration the probability of failure of the different power system components. The cost of operation of the system and the wind energy curtailed over the operating time are determined. This method is applied to a study case, based on the CIGRE HVDC Test System. The system behaviour over a complete year is modelled using realistic wind generation and demand based on scaling data from the Belgian power system.

Probabilistic transmission network planning based on risk criteria

The proposed methodology introduces the risk concept, which takes into consideration the probability of the occurrence of different operating states, the probability of the outage of system elements, and the impact such outages would have on the electric power system (EPS). The impact on the EPS is assessed on the basis of a new indicator called impact on the grid, which takes into consideration all overloads caused by the outage of a particular element. The new methodology, based on a risk index, demonstrates the reliability of the EPS and provides background and arguments, useful for transmission system operators taking decisions regarding new investments on the transmission network (TN). The new methodology also contributes multi-selection criteria for determining priorities among individual investments, based on investment costs and on maintaining a sufficient level of reliability.

Early detection of network element outages based on customer trouble calls

This paper deals with the issue of early detection of network element outages. Timeliness of outage detection as well as accuracy in finding outages on equipment in a telecommunication network depend on the monitoring system used and its performance. The intent of this paper is to investigate and propose a complementary solution to improve the performance of the existing systems in detecting faults earlier than it was able to do before. In developing our approach two constraints are given. The existing operational environment cannot be changed; threshold tuning and parameter changing cannot be done; furthermore no additional infrastructure investment has been planned. Hence, our approach relies on an alternative method based on a two-stage hybrid statistical and diagnostic detector which we designed in a way that exploits additional available data and avoids alarm monitoring system imperfections. The role of this detector is twofold: early detection of network element outages based on customer trouble calls and rule-based decision making for faulty-element isolation based on knowledge derived from fault and network management data. In this paper we present results of statistical analysis of trouble-reporting data. The analysis showed that the timing of customers' trouble reports and their content have information potential that can be utilized for early detection of outages. The detector is explained in detail and its accuracy and reduction delay is evaluated. The method presented can reduce the outage detection delay time by 2.33h on average observed in relation to the performance of an existing fault management process which was designed to detect outages solely on the basis of an alarm monitoring system, for the “difficulties in work” type of malfunction. We attained an overall probability of correct detection of 95.3%. Out of the total number of outages that hypothetically could be detected, by using this method we were able to detect 77.5% of cases 1h before the alarm was raised in the existing alarm system, while 23% of cases were detected 4h before the actual alarm. The approach has been tested on real telecommunication network data over the period of one year.

Generator Outage Identification by Use of Electromechanical State-Space Model Analysis

In this paper, a theory is developed that relates the natural response of an electric power system to sudden outages of transmission elements. The key development is in determining, via state-space analysis, the anticipated spectral content of either frequency or phase angle measurements as observed immediately following the sudden outage. This theoretical development mainly focuses on frequency measurements and the elements subjected to sudden outages are generators. For any sudden generator outage, the power system exhibits a very specific natural response in terms of its kinetic and potential energies. Kinetic energy in the system is directly related to each specific generator's rotational speed. It is shown that the effect can be seen directly in bus frequency measurements. Each remaining generator on the system has its own unique response to the sudden outage which contributes to the overall system natural response. This overall response is generally composed of oscillatory components which have specific frequencies. These oscillations, as measured by frequency meters, can be used to identify sudden element outages via their spectral content.

Stochastic generation-expansion planning and diversification of energy transmission paths

The paper addresses a stochastic generation-expansion planning model in the interdependent operation of an electric power system (EPS) and a natural gas system (NGS). The objective of the proposed optimization model is to provide consumers with a reliable electric energy supply by proper generation-expansion planning and diversification of energy transmission paths with minimal investment and operating costs. The proposed method takes into account constraints in the EPS and NGS. The Monte Carlo simulation method is applied to consider random outages of EPS and NGS elements and inaccuracies in the long-term electric load forecasting. A scenario reduction technique is used for reducing the computational burden of a large number of planning scenarios. The EPS and NGS are presented by a direct current (DC) model and a transportation model. The optimization problem is decoupled into a master problem and a subproblem using the Benders decomposition to cope with large-scale problems. The master problem deals with the optimization of investment in new generation units and energy transmission paths. The subproblem comprises a two-level optimization with a decomposed EPS reliability check as the master problem of the subproblem, and a NGS reliability check as the final subproblem. The case studies illustrate the applications of the proposed stochastic method in a coordinated generation-expansion planning problem when considering uncertainties.

Saddle Node Bifurcation and Voltage Stability Analysis of Sri Lanka

In electrical power systems, saddle node bifurcation (SNB) is the voltage stability margin at which voltage collapse takes place. It plays an important role in power system planning and operation as economic and environmental pressures force to operate always closer to the limit of stability. Voltage collapse is associated with the reactive power demands not being met because of limitations in the generation and transmission of reactive power. Determination of the SNB point greatly assists planning and operation of power system. Among various voltage stability analysis (VSA) methods, this paper specifies the continuation power flow (CPF) method as it accurately identifies the SNB point and the critical or the weaker bus. In this paper, power system of Sri Lanka is assessed for diverse applications of VSA by concerning about single element outage or (N-1) criterion and the role of voltage compensation devices. Furthermore, the optimum at the SNB point is verified by eigenvalue analysis.

Supercomponentes Contingency Modeling for Security Assessment in Power Systems

The utilization of the power systems to its maximum capacity is a condition that produces economic benefits to all agents involved in the chain of energy supply and thus to society. However, under these conditions, operators can take risks that could cause the loss of system stability and, in the worst case, blackouts. Thus, operators require analysis tools that give them information in order to take preventive and corrective actions, to operate the system in a reliable way and to check the behaviour of the same. Generally, in this type of analysis, simple component's contingencies are used. However, the practice has shown that more than one component (generation unit, circuit line, single transformer, among others) of the system can fail, either by simultaneous outages; events in cascade or by a major outage that means a complete installation with several components gets out of service. So, a super component refers to complex electrical facilities as: substations, generation plants and multiple circuit transmission lines. An outage of the super component implies the multiple and simultaneous outages of many elements. These kinds of events are not, generally, considered in the mentioned analyses; however, it would be very important to keep them in mind in the security evaluation of power systems. This paper presents a methodology to evaluate the severity of this kind of contingencies in the operative planning scenario. The super components that are taken into account are the multiple circuit lines (in the same structure), generation plants and substations. The impact of contingency on power system security is evaluated in a 24-hour ?day ahead? planning horizon through the computation of the energy not supplied, the number of overloaded lines and the percentage of load loss The Energy not supplied is computed as function of a load shedding based on operator's rules.

Probabilistic performance indexes for small signal stability enhancement in weak wind-hydro-thermal power systems

Deterministic strategies are still largely used for small signal stability (SSS) assessment and enhancement in most power systems worldwide. However, the solutions obtained with such strategies are very limited since they are correct just around the particular conditions analysed. Therefore it is essential to develop comprehensive strategies to cope with more operating conditions and random factors in SSS studies. This paper presents the development and application of a probabilistic methodology for SSS assessment and enhancement. The approach accounts for uncertainties of generation and nodal load demands as well as the effects of system element outages. Probabilistic performance indexes based on a combination of Monte Carlo method and fuzzy clustering are calculated. It is shown how properly statistical processing of output variables of interest can be adapted to evaluate the proposed indexes, which are the instability risk index and two additional indexes concerning power system stabiliser location and transfer capability as affected by SSS. The results obtained using a 18-power plant power system are analysed and compared against the results obtained through a deterministic approach. Relevant discussion highlights the viewpoint and effectiveness of the proposed methodology in providing instability risk assessment and useful information that aims at minimising the occurrence and impacts of electromechanical oscillations in the context of power system operation around uncertain load conditions.

Common supply failures in linear multi-state sliding window systems

Abstract This paper considers a linear multi-state sliding window system (SWS) that consists of n linearly ordered multi-state elements. Each element can have different states: from complete failure to perfect functioning. A performance rate is associated with each state. The system fails if the sum of the performance rates of any r consecutive elements is lower than demand w . Different groups of elements (common supply groups (CSGs)) share some common resources. Failures in the resource supply system (common supply failures (CSF)) result in the simultaneous outage of several elements belonging to corresponding groups. Different groups of elements are affected by different CSF. This paper presents an algorithm for evaluating the reliability of SWS that is the subject of CSF. It also introduces the CSG reliability importance measure and suggests an algorithm for its estimation. Further, it formulates a problem of optimal element distribution among CSGs and presents a method for solving it. An illustrative example shows the application of the suggested algorithms.

Conceptual framework for evaluation and interpretation of the reliability of the composite power system

This paper presents a conceptual framework for power system reliability evaluation which is based on the principles which underlie the procedures used in practice to achieve reliability of operation. Based on this framework, the paper discusses: the interpretation of the meaning of security and adequacy: the observability of security and adequacy interruptions; the different nature of interruptions due to security and adequacy and their impacts on the customer interruption costs; the interdependence of security, adequacy and operating costs; the nature of forced outages of generation and transmission elements and how they impact security and adequacy; and a practical procedure for the calculation of adequacy and security.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pertinent factors in the adequacy evaluation of an overall electric power system

Reliability evaluation of generating facilities, composite generation and transmission systems, and of distribution systems, are usually conducted independently, and the reliability indices obtained for each assessment are used to make decisions on the facilities concerned. These assessments often assume the other parts of the system to be fully reliable and capable of performing their intended function. This form of analysis therefore gives an optimistic appraisal of the overall system behaviour. The paper considers the influence of element outages in all parts of an electric power system in order to obtain a more practical appraisal of the overall system indices. The relative contributions to the system indices of composite generation and transmission failures and distribution zone failures are also assessed. In particular, the impact on the system performance indices of pertinent factors such as load curtailment philosophy, contingency level, terminal station outages, additional generation and/or transmission and/or distribution facilities etc., are evaluated. The concepts associated with overall electric power system adequacy assessment are illustrated by application to a comprehensive test system.

System loadability and load shedding

Abstract System loadability is evaluated using a nonlinear programming technique, and a loadability margin is determined for purposes of static voltage stability assessment. The margin is either in terms of voltampere load or VAR load. Generation participation is adjusted in order to produce higher system loadability. The effect of the forced outage of transmission elements on system loadability is studied. The method is also used to obtain the complete nose curve (upper and lower sides) for particular load buses. The curves indicate the system's strength in terms of potential voltampere or reactive system load as a function of voltage magnitude at a particular bus. A load shedding strategy that maximizes the system reactive security margin is introduced.

Overall adequacy assessment of an electric power system

Reliability evaluation of a complete electric power system, including generation, transmission and distribution facilities, is normally not conducted because of the enormity of the problem. Instead, reliability evaluations of generating facilities, of composite generation and transmission systems, and of distribution system segments alone are conducted independently and the reliability indices obtained for each segment are used to make decisions. These assessments, however, often assume the other parts of the system to be fully reliable and capable of performing their intended function. This kind of analysis therefore gives an optimistic appraisal of the system performance. The paper considers the influence of outages of elements in all parts of an electric power system to obtain a more comprehensive appraisal of the overall system. Some of the factors that affect the overall system performance are highlighted. The relative contributions to overall system indices from composite generation and transmission failures and distribution zone failures are also illustrated. The concepts involved in the reliability evaluation of a complete power network are presented using an educational test system developed at the University of Saskatchewan.

Meeting the challenge of assuring dependable telecommunication services in the '90s

Assuring the dependability of telecommunication services in the face of increasing customer expectations, revolutionary changes being made or proposed in networks, and recent disruptive disasters are discussed. Work focused on reducing vulnerability to network element outages is described and examined for three new technologies: fiber network architectures, common channel signaling, and intelligent network architectures. A comprehensive service dependability management process to be established by service providers is recommended. >

PROBABILISTIC VOLTAGE ASSESSMENT AND VAR COMPENSATION

Abstract The system voltage profile subject to system elements' forced outage is assessed. Two system voltage reliability indexes are evaluated: the loss of voltage probability, and the expected voltage violation. A similar set of two voltage reliability indexes are also calculated for every load bus in the system.A simple VAR compensation approach is introduced. It enhances the voltage profile assuming a maximum of three overlapping element outages can occur.For purposes of demonstration, the system and load bus voltage reliability indexes are calculated for the AEP 30-bus system. Results of applying the proposed VAR compensation scheme to the 30-bus system are also presented and discussed.

Efficient Simulation of Line and Transformer Outages in Power Systems

A method of simulating single and multiple transmission element (line and transformer) outages is discussed in the paper. The method simulates the outaged system states assuming the scheduled demands of the end buses of the outaged elements are still met. Sensitivity relationships of power systems are used both to determine the required power injections into the end buses, and to determine the corresponding corrections to the phase angles and magnitudes of bus voltages. The proposed method has been applied to the 30-bus and 118-bus IEEE standard test systems. Relevant results are presented and discussed.