Advances in distribution system reliability assessment

Traditionally, reliability of power systems has been an important measure of system performance and a key factor in system planning. Recently, the large-scale changes in the regulations governing the power industry have lead to a growing emphasis on distribution system reliability. Further, the shift towards a more technical and computerized society requires that power supply be increasingly reliable. Advanced models and methods are needed to obtain an improved understanding of the distribution system reliability. Monte Carlo simulation is one such method that can be used to find the statistical distribution of the reliability indices. This dissertation presents a computationally efficient Monte Carlo simulation algorithm for assessing the distribution reliability indices. Several state regulatory agencies have started to prescribe minimum reliability standards to be maintained by the distribution companies. The effect of these regulations has not been fully explored. In this work, a detailed analysis of the impact of various regulatory standards on a practical distribution system is presented. Storms cause a significant fraction of the distribution customer interruptions. While the impact of wind storms on distribution system reliability has been studied earlier, the effect of lightning storms on the reliability indices is not fully understood. Momentary interruptions caused by lightning storms may severely disrupt production at automated manufacturing facilities and other sensitive loads resulting in a loss of millions of dollars per incident. An analysis of lightning storm data is presented in this dissertation along with a method for calculating the impact of lightning storms on distribution system reliability. Finally, several topics for future research are discussed

Insulation Coordination in Modern Distribution Networks

The appropriate analysis of the response of distribution networks against Lightning Electro Magnetic Pulse (LEMP) – originated by nearby strikes – requires the availability of accurate coupling models in order to reproduce the real and complex configuration of distribution systems. The above models represent a fundamental tool for estimating the number of protective devices and their most appropriate location in order to guarantee a given minimum number of flashovers and outages per year. When dealing with real networks, such an optimization could require huge computational efforts due to the vast number of power components and feeders. This thesis thoroughly analyzes many of the possible engineering simplifications that, without losing accuracy, can be adopted in the statistical evaluation of the lightning performance of distribution networks in order to limit computational times. Particular attention is devoted to the effect of the ground conductivity on the LEMP and on the line parameters; two new analytical expressions for the evaluation of the inverse Laplace transform of the ground impedance matrix elements of multiconductor overhead lines are derived. The first expression is the inverse Laplace transform of Sunde’s logarithmic formula and is given in two equivalent forms. The second expression is the inverse Laplace transform of Sunde’s general integral expression. Finally, a procedure able to evaluate the lightning performance of a real medium-voltage distribution network, which includes several lines, transformers and surge protection devices is developed and proposed for the analysis of some real cases. Such a procedure allows inferring the characteristics of the statistical distributions of lightning-originated voltages at any point and phase of the network. The analysis aims at assessing the expected mean time between failures of transformers caused by both direct and indirect lightning strikes.L'analisi della risposta di una rete elettrica di distribuzione a un campo elettromagnetico esterno generato da una scarica atmosferica richiede l'utilizzo di accurati modelli in grado di riprodurre la reale e complessa configurazione della rete. Tali modelli rappresentano uno strumento fondamentale per la stima del numero di dispositivi di protezione ed il loro appropriato collocamento al fine di garantire il numero minimo annuo di “flashovers” e interruzioni. In una rete di distribuzione reale, tale ottimizzazione può richiedere sforzi computazionali proibitivi a causa dell’elevatissimo numero di componenti di potenza e linee presenti. Questa tesi analizza in maniera esaustiva molteplici semplificazioni ingegneristiche adottabili, al fine di ridurre i tempi computazionali, nella valutazione statistica del numero annuo di guasti di una rete di distribuzione. Particolare attenzione è dedicata agli effetti della conducibilità finita del suolo sul campo irradiato dal fulmine e sui parametri delle linee. Nella tesi sono derivate due nuove espressioni analitiche per il calcolo della trasformata di Laplace inversa dell’impedenza del terreno. La prima è la trasformata di Laplace inversa dell’espressione di Sunde logaritmica ed è proposta in due forme equivalenti. La seconda è la trasformata di Laplace inversa della più generale espressione integrale di Sunde. Infine, si è sviluppata una procedura in grado di valutare la “lightning performance” di una rete di distribuzione in media tensione avente configurazione realistica, che comprende “feeder” principali e laterali, pali, cabine secondarie e dispositivi di protezione contro le sovratensioni. La procedura messa a punto, basata sull’applicazione del metodo di Monte Carlo, permette di calcolare l'ampiezza delle tensioni indotte da fulminazione in qualsiasi punto e in ogni fase della rete. L’attività ha riguardato anche la valutazione del tempo medio fra i guasti (MTBF) di ogni trasformatore MT / BT causati da fulminazione indiretta e diretta, parametro di fondamentale rilevanza per l’ente distributore

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

Evaluation of Geostationary Lightning Mapper performance using the Colombia-Lightning Mapping Array

The Geostationary Lightning Mapper (GLM) on the Geostationary Operational Environmental Satellites - R (GOES-R) series satellites is the first operational lightning mapper flown in a geostationary orbit, which provides continuous observations of lightning. In order to make use of these data for improving nowcasting of severe weather and for data assimilation, it is important to characterize and understand the detection capabilities of GLM. Observations from 3-dimensional VHF Colombia Lightning Mapping Arrays (COL-LMA) provide a valuable basis for evaluating the spatial accuracy and detection efficiencies of observations from the recently launched, optical-based Geosynchronous Lightning Mapper (GLM). This Bachelor Final Thesis results of comparing spatially and temporally the individual event (pixel) level for sets of individual discharges from the LMA and GLM observations. The focus is on a representative sample of case studies encompassing different forms of convective organization at different times of day and night. The detection efficiency of GLM relative to LMA will be characterized in terms of the flash number, size, power and height among others

Research and technology

As the NASA Center responsible for assembly, checkout, servicing, launch, recovery and operational support of Space Transportation System elements and payloads, Kennedy Space Center is placing emphasis on its research and technology program. In addition to strengthening those areas of engineering and operations technology that contribute to safer, more efficient, and more economical execution of our current mission, we are developing the technological tools needed to execute the Center's mission relative to future programs. The Engineering Development Directorate encompasses most of the laboratories and other Center resources that are key elements of research and technology program implementation, and is responsible for implementation of the majority of the projects in this Kennedy Space Center 1988 Annual Report

Portuguese transmission grid incidents risk assessment

Documento confidencial. Não pode ser disponibilizado para consultaTese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 201

Using probability density functions to analyze the effect of external threats on the reliability of a South African power grid

Includes bibliographical references.The implications of reliability based decisions are a vital component of the control and management of power systems. Network planners strive to achieve an optimum level of investments and reliability. Network operators on the other hand aim at mitigating the costs associated with low levels of reliability. Effective decision making requires the management of uncertainties in the process applied. Thus, the modelling of reliability inputs, methodology applied in assessing network reliability and the interpretation of the reliability outputs should be carefully considered in reliability analyses. This thesis applies probability density functions, as opposed to deterministic averages, to model component failures. The probabilistic models are derived from historical failure data that is usually confined to finite ranges. Thus, the Beta distribution which has the unique characteristic of being able to be rescaled to a different finite range is selected. The thesis presents a new reliability evaluation technique that is based on the sequential Monte Carlo simulation. The technique applies a time-dependent probabilistic modelling approach to network reliability parameters. The approach uses the Beta probability density functions to model stochastic network parameters while taking into account seasonal and time-of- day influences. While the modelling approach can be applied to different aspects such as intermittent power supply and system loading, it is applied in this thesis to model the failure and repair rates of network components. Unlike the conventional sequential Monte Carlo methods, the new technique does not require the derivation of an inverse translation function for the probability distribution applied. The conventional Monte Carlo technique simulates the up and down component states when building their chronological cycles. The new technique applied here focuses instead on simulating the down states of component chronological cycles. The simulation determines the number of down states, when they will occur and how long they will last before developing the chronological cycle. Tests performed on a published network show that focussing on the down states significantly improves the computation times of a sequential Monte Carlo simulation. Also, the reliability results of the new sequential Monte Carlo technique are more dependent on the input failure models than on the number of simulation runs or the stopping criterion applied to a simulation and in this respect gives results different from present standard approaches. The thesis also applies the new approach on a real bulk power network. The bulk network is part of the South African power grid. Thus, the network threats considered and the corresponding failure data collected are typical of the real South African conditions. The thesis shows that probability density functions are superior to deterministic average values when modelling reliability parameters. Probability density functions reflect the variability in reliability parameters through their dispersion and skewness. The time-dependent probabilistic approach is applied in both planning and operational reliability analyses. The component failure models developed show that variability in network parameters is different for planning and operational reliability analyses. The thesis shows how the modelling approach is used to translate long-term failure models into operational (short-term) failure models. DigSilent and MATLAB software packages are used to perform network stability and reliability simulations in this thesis. The reliability simulation results of the time-dependent probabilistic approach show that the perception on a network's reliability is significantly impacted on when probability distribution functions that account for the full range of parameter values are applied as inputs. The results also show that the application of the probabilistic models to network components must be considered in the context of either network planning or operation. Furthermore, the risk-based approach applied to the interpretation of reliability indices significantly influences the perception on the network's reliability performance. The risk-based approach allows the uncertainty allowed in a network planning or operation decision to be quantified

Rationales for the Lightning Flight-Commit Criteria

Since natural and artificially-initiated (or "triggered") lightning are demonstrated hazards to the launch of space vehicles, the American space program has responded by establishing a set of Lightning Flight Commit Criteria (LFCC), also known as Lightning Launch Commit Criteria (LLCC), and associated Definitions to mitigate the risk. The LLCC apply to all Federal Government ranges and similar LFCC have been adopted by the Federal Aviation Administration for application at state-operated and private spaceports. The LLCC and Definitions have been developed, reviewed, and approved over the years of the American space program, progressing from relatively simple rules in the mid-twentieth century (that were inadequate) to a complex suite for launch operations in the early 21st century. During this evolutionary process, a "Lightning Advisory Panel (LAP)" of top American scientists in the field of atmospheric electricity was established to guide it. Details of this process are provided in a companion document entitled "A History of the Lightning Launch Commit Criteria and the Lightning Advisory Panel for America s Space program" which is available as NASA Special Publication 2010-216283. As new knowledge and additional operational experience have been gained, the LFCC/LLCC have been updated to preserve or increase their safety and to increase launch availability. All launches of both manned and unmanned vehicles at all Federal Government ranges now use the same rules. This simplifies their application and minimizes the cost of the weather infrastructure to support them. Vehicle operators and Range safety personnel have requested that the LAP provide a detailed written rationale for each of the LFCC so that they may better understand and appreciate the scientific and operational justifications for them. This document provides the requested rationale

Summary Report Comparing High Voltage Overhead and Underground Transmission Infrastructure

This report summarises the findings of an independent systematic literature review of high voltage overhead and underground transmission infrastructure, which was undertaken by The University of Queensland and Curtin University. This is the summary report for the study which is complemented by more detailed reports provided separately in Chapters 1 to 8 which cover the themes and cases studies in more detail