Reliability evaluation of distribution systems with nonexponential down times

An overview of reliability models and methods for distribution systems with renewable energy distributed generation

This paper presents results of studies of the impacts of substation monitoring on reliability indices of distribution systems. It was detected that the fault detecting and repair time was the main cause of the prolonged outages experienced in the system which increases the poor reliability indices of the system. The intelligent monitoring device detect open circuit faults and relay to the base station in 30s compared with 3 to 24 hours it was taking to detect fault. The intelligent substation monitoring device reduced the fault detection time and hence improves the reliability of distribution systems. The system was simulated, and result showed that SAIDI was reduced from 244 hours of outage per annum to just 98 hours of outage per annum while CAIDI was improved from 10 hours of interruption per outage to 5 hours of interruption per outage. This paper demonstrated that the fault detection and reporting time can be greatly reduced by the use of intelligent monitoring system and reliability indices.

Probabilistic reliability evaluation of distribution systems considering the spatial and temporal distribution of electric vehicles

As solar photovoltaic (PV) systems are increasingly being incorporated into the electrical networks, many of their aspects are being studied, stability and reliability in particular. Extensive body of research is dedicated to the reliability of PV strings, inverters, and batteries. On the other hand, reliability of a comprehensive PV system and its interaction with the distribution network either standalone or connected to a network has not been modeled or analyzed. In this paper, a complete PV system model is proposed, including the PV string, battery, and inverter. The interaction between the PV and the distribution network is also considered. Moreover, the impact of integrating the PV system on the distribution system reliability indices is assessed. The Roy Billinton Test System (RBTS) bus-2 is used as a study system and several reliability indices are computed, namely SAIFI, SAIDI, CAIDI, ASAI, ASUI, ENS, and AENS.

A new reliability assessment method for distribution system with distributed generations (DGs) is proposed in this paper, aiming to quantitatively analyze the undesired impact caused by passive islanding detection failure. Firstly, the paper analyzes the impacts of DG interconnection on auto-reclosing operation and system reliability due to failure of anti-islanding detection when a transient or permanent fault occurs. Secondly, the power features in the moment of detection-failure are calculated and utilized for judging whether they exist in the nondetection zones (NDZ) of several common passive islanding detection methods. Then, the new reliability evaluation procedure is given and reliability indices of distribution system could be obtained considering passive islanding detection failure. In the end, the IEEE RBTS Bus6 test system, connected with photovoltaic and wind power, is built to prove the effectiveness of the proposed approach.

Reliability evaluation of electric power systems has traditionally been an integral part of planning and operation of electric power systems. The changes in the electric utility industry create a need for more realistic techniques for power system reliability evaluation. In this paper, we present a reliability analysis algorithm for radially operated, electrical distribution systems. The algorithm takes into account equipment performance history and converges in a matter of seconds for systems containing a number of components. The study presented here evaluates improvement in reliability evaluation scheme over the conventional process. A new reliability evaluation approach using Monte Carlo method is proposed to assess distribution system reliability. This exploration makes possible the comparison of alternative system designs to discover systems yielding desired reliability properties utilizing the reliability indices for load points and the overall system that have been computed . Basic features, algorithms and a variety of case studies are presented in this paper to illustrate the capabilities of the proposed method and its suitability for educational and research purposes.

Future smart electrical distribution systems could adopt switch remote control and advanced automation systems to operate in autonomous mode (islanding) some portions of the network in order to improve system reliability. In this perspective, a free code able to assess distribution reliability by using analytical or Monte Carlo simulation methods accounting for intentional islanding operation is presented. An effective network representation and data structure, which have led up to the implementation of two automatic and general procedures, are proposed. The procedures share common underlying information in order to speed up calculation. A further merit of the tool is that it enables the user to quickly and simply create the input files. The reliability indices of three distribution networks have been computed by means of the developed software for different scenarios, that is when island mode of operation is not permitted by regulation, and when island mode is permitted (intentional islanding) with the local load either partially or totally supplied by renewable distributed generators. The free code, the input files and the results related to the considered networks are available online at: http://www.dieei.unict.it/users/sconti/psrs.htm.

Reliability evaluation of distribution systems assesses the adequacy of the load points in regard to providing a suitable supply to customers. This area has received increased interest during the past few years. A considerable number of papers have been published describing the development and application of the available techniques for modelling the various features of a distribution system and for evaluating the reliability indices. Also a few publications have considered the evaluation of probability distributions of the reliability indices for radial systems. However, due to the complexity of the analysis and the need to consider overlapping outages in meshed networks, these techniques are not able to evaluate the probability distributions for such networks. Also, further considerations are still required in the evaluation of interruption costs/reliability worth in order to obtain true and more realistic values that reflect the behaviour of the system under study. This paper describes models and techniques for evaluating the probability distributions associated with the reliability indices in meshed networks. It also presents a procedure for combining costs of interruptions with the probability distributions of interruption durations and of CAIDI to assess the cost of interruptions in meshed networks. The proposed approaches are based on a combination of analytical techniques and Monte Carlo simulation. Finally the paper reports on the results obtained from sensitivity studies developed for bus 1 of the IEEE Reliability Test System. >

This paper presents a further step in the development of accurate and consistent techniques for the reliability evaluation of transmission and distribution systems. A theoretically accurate Markov approach6is limited in application because of computer storage requirements and the rounding errors which occur in the solution of relatively large systems. This paper extends the modified approximate technique presented in reference (P) to permit evaluation of the contribution to the system reliability indices of different modes of component outage. The equations developed give results which compare very closely those predicted by the Markov approach. A three state weather model is developed to illustrate the effect of severe adverse weather periods on the system reliability performance. The load point failure modes considered are those which arise due to component permanent, temporary, maintenance and overload outages.

??This paper presents a new approach to evaluate reliability indices of electric distribution systems using genetic Algorithm (GA). The use of reliability evaluation is an important aspect of distribution system planning and operation to adjust the reliability level of each area. In this paper, the reliability model is based on the optimal load transferring problem to minimize load generated load point outage in each sub-section. This approach is one of the most difficult procedures and become combination problems. A new approach using GA was developed for this problem. GA is a general purpose optimization technique based on principles inspired from the biological evolution using metaphors of mechanisms such as natural selection, genetic recombination and survival of the fittest. Test results for the model system with 24 nodes 29 branches are reported in the paper.

A non-simulation-based linear model for analytical reliability evaluation of radial distribution systems considering renewable DGs

Smart grid is a power grid consists of extensive monitoring systems which deal with the monitoring of attributes such as current, voltage, power, and energy at distribution transformers, substations transformers, distribution switching devices and smart meters. Smart grid with advanced communication technologies can be used for several purposes such as efficiency and reliability improvement. IEC 61850 is the core standard in the smart grid domain for distribution and substation automation. This paper introduces a vision of modern substation and distribution systems using the IEC 61850. Network operators mainly assume that the modern substation and distribution systems based on the IEC 61850 are reliable for a long-time of operation. However, similar to any other systems, the implemented IEC 61850 might fail because of the operational failures or aging failures. This paper proposes a novel method for reliability evaluation of modern substation and distribution systems. A typical IEC 61850 based distribution and substation system is developed and analyzed using the proposed method. The fault tree analysis (FTA) is used to quantify the reliability of the system. The technique is implemented and demonstrated on the Roy Billinton test system (RBTS). The analysis is further extended on a 400/63 kV substation with a breaker-and-a-half configuration. In addition, the technique proves to be robust under different operations. The results verify the feasibility and applicability of the proposed method.

Interest in distributed generation (DG) arose in the 1990s with the deregulation of the electricity industry and the development of improved DG technologies. Furthermore, the appearance of high-technology loads requires an increase in the reliability of the power system. In this new scenario, it is important to consider DG in the planning of distribution networks. For example, a utility can install DG to provide additional capacity to feeders or substations. Additionally, DG can be used to improve the restoration capability of the distribution networks, that is, DG can eliminate network constraints (voltage drop or feeder loading) during the restoration process. Consequently, DG can improve the reliability indices associated with the restoration time. In this paper, a methodology to estimate the impact of DG on the reliability indices of distribution networks is proposed. This impact is assessed considering that DG can be connected to an isolated feeder (isolated operation) or to a feeder with tie-lines (interconnected operation). The network constraints model used in this paper is based on a simplified version of the power summation load flow method and compensation techniques. The results with the proposed methodologies, to model the isolated and interconnected operation of DG, demonstrate that DG has a significant impact on the reliability indices of distribution networks. The proposed methodologies have been validated and tested in a large distribution test system. The results show the importance of considering the impact of DG on the reliability indices of distribution networks

The aim of this paper is to discuss some operating procedures available in distribution systems which permit local generating plants to supply the load which can not be supplied by the system bulk supply points during outage conditions. The paper describes analytical and computational techniques which simulate the operational behaviour of these local generating facilities. The increased information that can be gained from these improved techniques is illustrated by the analysis of a typical distribution system.

Using the Exponentiated approach and three-parameter Weibull distribution as baseline function, a newly generalized distribution was formed called the Exponentiated Generalized Modified Weibull distribution. One of the properties of a proper probability density function was used to ascertain that the resulting function is a proper probability density function. Statistical properties of the newly generated distribution were studied and graphs of probability density and cumulative density functions of the distribution were plotted using varying parameter values. Monte Carlo simulation approach was used for the test of homogeneity of the distribution and it was observed that the parameters in the distribution approach the true value as sample size increases. The distribution was compared with some of the existing distributions in its category and it was observed that the distribution outperformed the existing distributions using secondary data. Therefore, it was concluded that Exponentiated Generalized Modified Weibull distribution can be adopted in modeling events involving distributions of its category