Dissertations / Theses on the topic 'Insulation coordination'

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.

This thesis reviews the line insulation coordination practices of Turkish Electricity Transmission Company with special focus on E.H.V. transmission line towers&rsquo
top geometry and ground clearances. In respect of this, the national regulation, &ldquo
Elektrik Kuvvetli Akim Tesisleri Yö
netmeligi&rdquo
, is critically evaluated.The national regulation lags behind the modern world practice and the provisions of the regulation lead to uneconomical designs. The possible benefits of the modern practices are shown by application examples.

The present work was performed at HVDC ABB as an initial study on how to adopt probabilistic concepts into the VCSHVDC insulation coordination. Due to large voltage levels in HVDC applications the corresponding insulation need to be properly addressed to ensure a safe, economical and reliable operation. Traditionally, only the maximum overvoltage is considered, where no adoption to the shape of the overvoltage distribution is regarded. Use of probabilistic concepts in the insulation coordination procedure can ideally reduce insulation margins with a maintained low risk of flashover. Analysis and understanding of probabilistic concepts of AC systems is needed in order to implement the concepts into VSC-HVDC. With use of advanced VSC-HVDC models, faults are simulated with varied fault insertion time in PSCAD. The resulting overvoltages from the simulation is gathered using different statistical methods in order to obtain the approximated overvoltage distribution. It was found from the simulation results that use of a Gaussian distribution is inappropriate due to shape variety in the overvoltage distributions. Instead, Kernel Density Estimate can serve as a flexible tool to approximate overvoltage distributions with a variety in number of modes and shape. The retrieved approximated overvoltage distributions are compared with the insulation strength in order to calculate the risk of flashover. The comparison shows that the insulation can be tuned in order to match set requirements. The thesis work should be seen as pilot study, where key problems have been pointed out and recommended further studies are proposed.

Esta pesquisa apresenta uma metodologia, baseada em duas técnicas não invasivas para identificação e diagnóstico de pontos quentes em transformadores de potência durante plena operação ou em fase de projeto. A primeira técnica é baseada na medição de radiação infravermelha, emitida pelo equipamento em funcionamento e registrada por meio de análise termográfica. A segunda técnica é possível a partir do conhecimento prévio das características construtivas do transformador, fazendo uso do Método dos Elementos Finitos (MEF). A segunda técnica pode ser validada a partir das medições realizadas utilizando a primeira técnica. A formação de gases no interior dos transformadores de potência, devido à elevação da temperatura do óleo isolante em função dos pontos quentes, é discutida em detalhes com base nas normas técnicas estabelecidas pelo IEEE e IEC. As técnicas e procedimentos abordados ao longo dessa pesquisa foram obtidos a partir de um transformador com potência nominal de 120 MVA e relação de tensão 13,8/230 kV, projetado para integrar uma fazenda eólica ao Sistema Interligado Nacional (SIN).
This research presents a methodology based on two noninvasive techniques for identification and diagnostic of hot spots in power transformers during operation or project development. The first is based on measurements of infrared radiation from the equipment during operation and recording by thermography. The second technique is possible from the previous knowing of the constructive characteristics of the power transformer, by using the Finite Element Method (FEM). The second technique can be validated from measurements obtained using the first technique. The gas formation into the power transformers, because of the high temperatures in the insulating oil due to the hot spots, is discussed in details based on normative recommendations well established by the IEEE and IEC. All techniques and procedures to be approached in this research were obtained using a 120-MVA power transformer with voltage relationship of 13.8/230 kV that was projected to interconnect a wind farm to the Interconnected Brazilian System (Sistema Interligado Nacional - SIN).

Abstract Adding a dc circuit to an existing transmission line is one method of significantly increasing the power transfer capability of a transmission corridor. The resulting hybrid system has significant coupling between the ac and dc circuits, not only because of the proximity of the circuits, but also from the fact that they may share the same sending end or receiving end ac systems. The resultant interaction produces overvoltages on the dc system which can be somewhat higher than for a conventional dc scheme. This thesis investigates the overvoltages on a hybrid ac-dc transmission system and suggests some design considerations which could be taken into account to reduce stresses on certain critical components which result from such an arrangement. Blocking filters consisting of a parallel L-C combination in series with the dc converter were included to limit the flow of fundamental frequency current in the dc line. This thesis also investigates the proper blocking filter configuration to be used as an incorrectly chosen blocking filter can cause resonance overvoltages on the dc line at fundamental frequency. A method of eliminating dc components of the currents in the transformer windings of a dc converter is presented. The method uses the technique of firing angle modulation. It is shown that merely eliminating the fundamental frequency component on the dc side may not remove this dc component. The impact of such control action at one converter on the other converters in the dc transmission system is also presented. It is also shown that the undesirable side effects of such a scheme include increased generation of non-characteristic harmonies on both the ac and dc sides. The study is performed using an electromagnetic transients simulation program and theoretical calculations.

This thesis describes properties of windings of electric rotating machines and their insulation systems. There are winding and insulation low voltage machines tests listed with their procedures and criteria. Further it deals with coordination methodology and the last part contains execution and results assessment of tests conducted on stator samples.

碩士
中原大學
電機工程研究所
102
The thesis aims at the analysis of insulation coordination and protection coordination for 22.8kV overhead line in Taiwan. The voltages of distribution feeders used in Taiwan are divided into 22.8kV and 11.4kV levels, while the installations are divided into overhead and underground power distribution which 22.8kV voltage level is only implemented on underground distribution lines. To improve the power supply capacity, to reduce line losses and to simplify the voltage level, Taiwan Power Company intends to increase the distribution feeder voltage rating from 11.4kV to 22.8kV level comprehensively. Therefore, this project which studies on the installation of 22.8kV level overhead lines is proposed. The insulation coordination research focuses on the voltage of insulator that 11.4kV overhead line used in Taiwan. As for using Alternative Transients Program (ATP) to simulate the lightning surge, the thesis explains the modeling methods, parameters and the simulation results. Finally the thesis discusses the characteristics of overvoltage and evaluates the insulation coordination conditions of 22.8kV overhead lines according to simulation results. The protection coordination research focuses on the evaluation of whether the criteria adopted for estimating the short circuit currents of the 22.8kV distribution line. As the results of simulation, the research propose the methods of protection practice of 22.8kV overhead distribution lines.

碩士
國立中正大學
電機工程研究所
93
Abstract The insulation strength of electric power equipments should not only endure normal operation voltage for a long period time, but also endure the possible temporary overvoltages arisen in the systems. By means of understanding the insulation strength of electric power equipments, temporary overvoltags arisen in the systems, and the characteristics of surge protective devices, appropriate arresters may be selected to protect the overall system under on acceptable level of both security and economy. These are the major issues that insulation coordination concerns. This study also discusses the determination of protection margin under probabilistic lightning model. Based on the log-normal distribution lightning model, simulations are conducted using Electro Magnetic Transient Program (EMTP) to observe the protection margin for transformers at a 69 kV substation, as lightning strikes its nearby overhead lines. The simulation results show that whether or not the arresters are installed, the protection margin for transformers may be expressed as a random distribution. Therefore, under the probabilistic lightning model, the protection margin is better to be represented probabilisticly, not just a number. Generally speaking, the equipment’s withstanding voltage is in proportion to the system’s voltage class. So, under the same lightning conditions, the higher voltage class the system is, the higher probability satisfying the protection margin is. The results also show that the threat of lightning surge to 69kV systems is serious and is even more than that to 345kV and 161kV systems.

碩士
國立臺灣科技大學
電機工程系
102
A power company owns many power plants and extra high voltage (EHV) switchyards. Some power plants and EHV Switchyards after a period of time, because of their surrounding power demands, will add new facilities to their old ones in order to meet the power demands. Thus, the thesis studied the scenario of adding new facilities in an EHV switchyard. The thesis found that four 345kV power lines, which do not have disconnected switch (DS) in their outlets, once added one set of DS to their outlets respectively, this would increase flexibility when switchyard personnel operate facilities. The thesis also found that an EHV switchyard which has only one start-up transformer as its internal power supply, once added another start-up transformer, this would reach mutual backup functions. Those two new facilities mentioned above have changed its outfit of an EHV switchyard. An electromagnetic transient program (EMTP), which was used to establish a model of an EHV switchyard, simulated switching surges by operating its current facilities and lightning surges when a lightning occurs. Based on the results of the simulation and a comparison when new facilities were added, basic switching surge level (BSL) and basic impulse insulation level (BIL) were examined. The results of the examination should not affect its current insulation coordination design of an EHV switchyard.

碩士
國立臺灣科技大學
電機工程系
88
Stable power supply is the main task for power systems. The problem of overvoltage in power systems isn''t avoidable for electric equipment. However, to design an electric fixture which is able to sustain anomalous overvoltages without being destroyed is impossible and not economic. Consequently, there has to be a trade-off between safety and economy for electric equipment. To properly coordinate the insulation magnitude between power systems and protected electric equipment is called insulation coordination based on arresters. The aim of this paper focus on the use of arresters to protect distribution systems from the damages caused by overvoltages. By means of understanding the overvoltages which may cause by power systems and the insulation withstand voltages of electric equipment, adequate arresters may be selected to protect the full system.

碩士
國立臺北科技大學
電機工程系
107
Nowadays, the power system is developing rapidly with the tendency towards smart grid. Various voltage level substation will be equipped with weak-voltage systems and equipment. It may cause various electromagnetic impacts between over-voltage and over-current. The lightning surge, switching surge and transient over voltages owing to power system fault on the low voltage electronic apparatuses is quit baddest. To improve its impacts, installing surge protection devices in the low-voltage system. However, the expected benefit of low-voltage SPD isn’t work because of not setting some installation regulars and data standards.This thesis research about some problems of low-voltage surge protection devices. First of all, the system modeling is analyzed by using Alternative Transient Program of Electromagnetic Transient Program (EMTP/ATP), analyze the affections of lightning surge, switching surge and transient over voltages owing to power system fault on the low voltage electronic apparatuses in various voltage level substation and evaluate the protection requirement by whether installing SPD or not at low voltage side in the substations.Based on the EMTP/ATP simulation results for effectiveness of low-voltage SPD, and thereby determine the installation opportunity and best location. Furthermore, voltages and currents of low-voltage SPD are further surveyed and comparied with the Basic Impulse Insulation Level (BIL), interrupt capacity (IC) of molded-case circuit breaker and the protection characteristic curves of fuse to evaluate the disadvantage of insulation coordination and protection coordination. Finally, the improved strategy will be proposed to upgrade the protection performance as well as improve the reliability and safety of power feeding for users.

碩士
國立臺北科技大學
電機工程系
107
Large photovoltaic (PV) plant with capacity over several hundreds mega watts need to be interconnected to the very high voltage (VHV) transmission system. In general, the fault impact of large PV plant on the power system is very serious. Good protection coordination and insulation coordination are required for reducing the fault impact on power system, where the system grounding is a key affection factor in the large PV power plant; the system grounding of VHV system is determined by the grounding of main transformer neutral point, while for high voltage system, the solid grounding or low resistance grounding can be used. However, the system grounding of low voltage system shall be compatible with inverter design, which may be the solid grounding, non-grounding and ground-potential-transformer (GPT) grounding. The system ground fault and surge characteristics will be different under different system grounding such that it has large affection on ground fault protection coordination and surge protection coordination (insulation coordination). In this thesis, the relative problems of system grounding are surveyed. At the first, system modeling for the simulations of ground fault and surge characteristics is constructed based on the alternative transient program of electromagnetic transient program (EMTP-ATP). For the ground fault characteristic, the fault currents, phase voltage and ground potential rise (GPR) on VHV system, high voltage system and low voltage system are analyzed, while the surge characteristic aim to surge phase voltage and surge GPR from lightning surges. Based on these analysis results, the affections of various system groundings on the ground fault protection coordination and insulation coordination at high and low voltage systems are reviewed. Furthermore, the advantages and defects of various system grounding are compared and the risks are evaluated. Finally, the strategies for improving the associated defects are proposed including the selection of system grounding type and the suggestion of protection coordination and insulation coordination planning. Thereby, the performances of ground protection and surge protection are reinforced such as upgrading the power supply safety and reliability of large PV power plants.

碩士
國立臺北科技大學
電機工程系
107
The single-phase pole transformer of the power distribution system is generally used for supplying low-voltage users. It always outage by a fault caused by lightning, which is close relationship with the lightning and fault characteristics and the insulation coordination and protection coordination of a transformer. It is necessary to further discuss for proposing an improved strategy. In this thesis, the lightning and fault characteristics of an existent single-phase pole transformer are analyzed considering different installation positions of main protection devices (arrester and current-limiting fuse) under different lightning strike points and lightning strength. In addition, the transformer is fed by phase and neutral conductors from a three-phase four-wire (3Φ4W) distribution system with a multi-grounded neutral line. The influence of different grounding resistance levels of each neutral grounding point is also discussed. Furthermore, the defects of the existent protection coordination and insulation coordinationon of the single-phase pole transformer are evaluated, and the improved strategy is proposed for upgrading protection performance of the transformer and the reliability of power feeding. First of all, the Alternative Transient Program of Electromagnetic Transient Program (EMTP/ATP) is used for modelling and simulating a system under normal operation, lightning, and ground fault situations, respectively. Based on the EMTP/ATP simulation results, the voltages and currents of transformers, arresters and current limiting fuses are further surveyed. Furthermore, the Basic Impulse Insulation Level (BIL) and current damage curve of the transformer are comparied with the protection characteristic curves of arrester and fuse, and the setting of protection relay on an upstream substation to evaluate the disadvantage of insulation coordination and protection coordination. Finally, the improved strategy will be proposed to upgrade the protection performance as well as improve the reliability and safety of power feeding for users.

abstract: With the penetration of distributed renewable energy and the development of semiconductor technology, power electronic devices could be utilized to interface re- newable energy generation and the distribution power grid. However, when directly connected to the power grid, the semiconductors inside the power electronic devices could be vulnerable to the power system transient, especially to lightning strikes. The work of this research focuses on the insulation coordination of power elec- tronic devices connected directly to the power distribution system. The Solid State Transformer (SST) in Future Renewable Electric Energy Delivery and Management (FREEDM) system could be a good example for grid connected power electronic devices. Simulations were conducted in Power Systems Computer Aided Design (PSCAD) software. A simulation done to the FREEDM SST showed primary re- sults which were then compare to simulation done to the grid-connected operating Voltage Source Converter (VSC) to get more objective results. Based on the simulation results, voltage surges caused by lightning strikes could result in damage on the grid-connected electronic devices. Placing Metal Oxide Surge Arresers (MOSA, also known as Metal Oxide Surge Varistor, MOV) at the front lter could provide eective protection for those devices from power transient. Part of this research work was published as a conference paper and was presented at CIGRE US National Conference: Grid of the Future Symposium [1] and North American Power Symposium [2].
Dissertation/Thesis
Masters Thesis Engineering 2017

碩士
國立臺北科技大學
電機工程系
106
This thesis is to study the affections of neutral grounding of main transformer on protection coordination and insulation coordination and to assess the risks for the customers supplied by very high voltage system (VHV customers). Two neutral grounding types for main transformer namely resistor-grounding and solid-grounding are surveyed, respectively. The resistor-grounding type was used for all the existing VHV customers in Taiwan, where the neutral point of main transformer secondary windings is grounded via a resistor for suppressing the ground fault current, and thus reduce the current flowed into grounding system for decreasing human hazards during ground fault on secondary. Furthermore, the interrupting capacity of breaker can be only specified by three phase short circuit current. The resistor-grounding, however, has detrimental effects on the system protection coordination and insulation coordination owing to low single-phase-to-ground fault (1-ΦGF) current and high floating neutral potential. It is difficult to reach fast primary protection and better selectivity for 1ΦGF just only by ground over current relay, and the surge voltage on VHV side is easily transferred to high voltage side. Furthermore, the 1-ΦGF on high voltage side will cause to very high phase-to-ground over voltage to threaten the insulation of equipment and surge arrester damage. These drawbacks are not the problems for solid-grounding system but the interrupting capacity of breaker and the human hazards of grounding system are need to be reviewed. In this thesis, all of these problems are further studied based on the electromagnetic transient characteristics analysis for the VHV customer distribution system. First of all, the customer distribution system model is constructed and analyzed by the alternative transient program (ATP) of electromagnetic transient program (EMTP). Then, the ground fault and lightning surge characteristics of system with different grounding types of main transformer neutral point are analyzed. Based on the analysis results, the affections of these different characteristics on the protection coordination and insulation coordination are reviewed and the derived risks are evaluated. Finally, the overall comparisons between advantages and disadvantages of resistor-grounding and solid-grounding of main transformer are showed based on the development of power apparatuses of today. The recommendations for planning the system grounding of VHV customer are proposed.

碩士
中原大學
電機工程研究所
103
The Taipei Rapid Transit Corporation (TRTC) is going to upgrade the power supply reliability by upgrading from the originally N-1 design criterion to N-2. The former refers to the power system design which allows the outage of one 161kV Bulk Supply Substation (BSS) and the latter allows the simultaneous outage of two BSS’s in the same Wen-shan or Nei-hu Line. That is, under the outage of two BSS’s in the Wen-shan Line, the closest BSS of Nei-hu Line must be able to supply power to Wen-shan, and vice versa for the outage of Nei-hu and the power supply from Wen-shan. This thesis focuses on relay coordination and the insulation coordination of the 22kV power system under the aforementioned load transfer between Wen-shan and Nei-hu Lines due to the N-2 conditions. The thesis is comprised of two parts. The first part presents the relay coordination calculation results, where the present settings on the directional overcurrent relays for the 22kV power system protection are evaluated under the N-2 load transfer condition, which includes the evaluation on the tripping sequence and on the coordinating time intervals of relays. The second part presents the insulation coordination results by constructing the electro-magnetic transient simulation model for the 22kV power system under the N-2 load transfer condition, and by evaluating the switching surge impact on the 22kV power system equipments, which includes the evaluation on the BSL (Basic Switching Surge Insulation Level) and on the overvoltage protection tolerance of the 22kV system equipments. Both evaluations point out the limitations of 22kV power systems presently existing in the Wen-hu Line on their overcurrent and overvoltage protections, and make suggestions on the counter measures.