Добірка наукової літератури з теми "Passive Snubbers"

Passive energy dissipating devices, such as elastoplastic dampers (EPDs) can be used for eliminating snubbers and reducing the response of piping systems subjected to seismic loads. Cantilever and three-dimensional piping systems were tested with and without EPD on shaker table. Using a finite element model of the piping systems, linear and nonlinear time-history analysis is carried out using Newmark’s time integration technique. Equivalent linearization technique, such as Caughey method, is used to evaluate the equivalent damping of the piping systems supported on elastoplastic damper. An iterative response spectrum method is used for evaluating response of the piping system using this equivalent damping. The analytical maximum response displacement obtained at the elastoplastic damper support for the two piping systems is compared with experimental values and time history analysis values. It has been concluded that the iterative response spectrum technique using Caughey equivalent damping is simple and results in reasonably acceptable response of the piping systems supported on EPD.

The switched reluctance machine (SRM) is the least expensive machine to produce yet it is very reliable. An SRM drive system has to be designed so that there is integration between the machine and the converter-controller configuration. This paper focuses on the resistor dump converter topology where most of the energy from the windings is dissipated in a resistor. A detailed analysis and simulation of the converter has been conducted and a design guideline for the proposed converter is laid out. The resistor dump converter has a low component count and this enables it to achieve a low cost converter. Simulation results show that for the resistor dump converter additional snubbers are required. This leads to an increase in complexity of the controller as more parameters need to be considered. Also, the addition of the passive components of the snubber makes the circuit less reliable and costly. For the purpose of just looking into detail on the behaviour of the converter, it is sufficient to look at the results of the simulation using a static inductor to model the SP-SRM. If cost is to be the priority, the most economical choice must be made but within limits of the application.

The necessity of new and clean technologies for energy production from one hand and the carbon dioxide emission regulations on the other are inducing nuclear fusion research to speed towards a possible future energy source. So the next experiment, which is being built in France, called ITER (acronym for International Thermonuclear Experimental Reactor, an international collaboration between European Union, Japan, Russian Federation, India, China, South Korea and United States of America) has to give an answer on the real feasibility to achieve nuclear fusion, and in particular on the possibility to control the plasma stability for long time at high temperature, to maintain the stationary phase and to reach fusion temperature. One of the components necessary to heat the plasma is the Neutral Beam Injector; the concept has been developed for many years up to the present experiments. The principle is basic: the plasma is hit by a neutral atoms beam (not affected by the high magnetic field of the system) at high kinetic energy so that this energy is transferred by collisions to the ions of the plasma. Meanwhile the beam helps to drive the plasma current, necessary for the plasma confinement inside the vessel in a “tokamak” configuration. The engineering requirements for the ITER NBI are very demanding, as it is subjected by severe mechanical, thermic and electrical stress. In particular, the neutral beam power requested is 16.5 MW while the energy of the deuterium or hydrogen negative ions, accelerated before neutralization, is in the order of 1 MeV. This involves a total accelerating voltage equal to 1 MV. So one of the most critical topic for the whole system is the operation very close to the breakdown limits for the accelerating grids, so that breakdown is not considered as a fault but a common working condition for the system. The activity reported in this doctoral thesis, mainly carried out at Consorzio RFX, deals on this matter. In particular the effects of arc between the grids are analyzed, both in terms of arc energy deposition on the grids and in terms of the current and voltage transient propagation on different locations of the system. Arc energy has to be limited below a certain threshold value in order to avoid an irreversible grids damage; this would cause the de-conditioning and the loss of high voltage holding with a breakdown occurrence at lower voltage level. Instead the fast voltage transients are dangerous because they can induce overvoltages on some tricky points and therefore lead to unexpected insulation losses; in addition they are source of electromagnetic noise (EMI) due to high frequencies in the order of MHz, a problem if we consider the large number of diagnostic devices. In this thesis some design solutions to limit these effects are explained; they are supported by proper circuital simulations or experimental validation. The devices presented are alternative to the present adopted solutions, as they form a comprehensive protection strategy. Then, they are passive protections because we need an instantaneous intervention after breakdown to be effective, contrary to active protections which need some delay due to the signal acquisition demonstrating the arc occurrence. The thesis is organized as follows. In the chapter 1 the ITER neutral beam injector is presented, in the framework of the nuclear fusion research; the operation principles and the main components are basically described. Finally the test facility being built in Padua is shown; it is constituted by two experiments, a ITER full-scale negative ion sources, with a single -100 kV accelerating stage, and a full-scale injector, identical to that which will be installed in ITER. The chapter 2 shows at first the operating conditions, from the electrical point of view, foreseen for the neutral beam injector. In particular high voltage holding issues are presented, together with the conditioning process in vacuum; then a tentative vacuum arc modeling for long gap is described, considering arc energy dissipation due mainly to radiation phenomenon. At last present countermeasures against breakdown effects are shown, namely a concentrated core snubber at the injector transmission line ends and the active protections. In the chapter 3 two new concepts for passive protections are introduced. The first is a damping resistor connecting the last accelerating grid (the so called grounded grid) with the vacuum vessel (grounded) of the injector with the aim to damp the arc current involving this grid and the return conductor of the transmission line. Then the design and the assembly of a prototype are described; this is installed at the French laboratory of CEA (Commissariat à l’Énergie Atomique) in Cadarache, where it will be tested. The detailed circuital modeling of this test bed is reported; the model is useful to compare and understand experimental results. The second device is a distributed core snubber along the whole transmission line to damp the breakdown with a less cumbersome element and a simpler, more effective structure. The results on a small-scale example are presented to support this proposal. The chapter 4 outlines an integration of a comprehensive design for passive protections on a whole system. In particular, for the experimental negative ion source the positive effects of some devices are proposed, studied and optimized, i.e. a damper resistor, a distributed core snubber and a L–R parallel input impedance between the power supply and the transmission line. Finally the core snubber design is described, constituted by a series of magnetic cores evenly distributed on the transmission line and polarized by a proper biasing circuit.
L’esigenza di nuove tecnologie per la produzione di energia, compatibili con l’ambiente, e le normative sulle emissioni di anidride carbonica stanno spingendo la ricerca sulla fusione nucleare come possibile alternativa futura. Da questo punto di vista il prossimo esperimento in via di costruzione in Francia, ITER (acronimo di International Thermonuclear Experimental Reactor, frutto di una collaborazione internazionale tra Unione Europea, Giappone, Russia, India, Cina, Corea del Sud e Stati Uniti d’America), dovrà dare delle risposte sull’effettiva fattibilità della fusione nucleare, e in particolare sul controllo della stabilità di plasma per lunghi tempi e ad alte temperature, sulla possibilità di funzionamento in regime stazionario e sull’effettivo raggiungimento della temperatura di fusione. Uno dei dispositivi necessari per il riscaldamento del plasma è l’iniettore di neutri, concetto sviluppato già in diverse macchine operanti fino ad oggi. Il principio è semplice: si tratta di “bombardare” il plasma con un fascio di atomi neutri (quindi insensibili ai forti campi magnetici presenti) ad alta energia cinetica in modo da trasferire mediante collisioni l’energia agli ioni del plasma stesso. Nel contempo il fascio aiuta anche il ostenimento della corrente di plasma, necessaria per il confinamento nella camera di scarica in configurazione “tokamak”. Le prestazioni ingegneristiche richieste all’iniettore di neutri di ITER sono molto gravose, sia dal punto di vista delle sollecitazioni meccaniche e termiche che da quelle elettriche. In particolare, la potenza del fascio di atomi neutri richiesto è di 16.5 MW mentre l’energia di accelerazione del fascio di ioni negativi di deuterio o idrogeno, a monte della neutralizzazione, è di 1 MeV. La tensione di accelerazione corrispondente è perciò di 1 MV. Uno dei punti più critici dell’intero sistema è dato dalle condizioni operative molto vicine ai limiti di scarica per le griglie di accelerazione, tanto che la scarica stessa non è considerata un fenomeno di guasto bensì una normale condizione di funzionamento del sistema. Il lavoro esposto in questa tesi di dottorato, svolto principalmente presso il Consorzio RFX, si inserisce in questo contesto. In particolare vengono analizzati gli effetti dell’arco tra le griglie sia in termini di energia d’arco depositata sulle griglie stesse che dei transitori di tensione e corrente che si propagano nei vari punti del sistema. Riguardo all’energia d’arco, essa dev’essere limitata al di sotto di un certo valore per evitare il danneggiamento irreversibile delle griglie stesse con conseguente decondizionamento del sistema, perdita delle proprietà di tenuta della tensione e quindi il verificarsi della scarica a tensioni più basse. I transitori di tensione invece possono essere dannosi, sia perché possono indurre sovratensioni in punti delicati del sistema con conseguente perdita dell’isolamento, sia perché sono fonte di disturbi elettromagnetici (EMI) per le varie apparecchiature diagnostiche presenti, legati alle alte frequenze in gioco dell’ordine dei MHz. Vengono in questa sede proposte alcune soluzioni progettuali per limitare tali effetti, corroborate da opportune simulazioni circuitali o da validazione sperimentale. I dispositivi esposti sono alternativi a quelli fino ad oggi impiegati, presentando una strategia d’insieme per la protezione. In più, sono di tipo passivo in quanto devono intervenire istantaneamente al verificarsi della scarica per poter essere efficaci, contrariamente alle protezioni attive che necessitano di un certo tempo di intervento legato all’acquisizione di un segnale comprovante la scarica. La tesi è articolata nel modo seguente. Nel capitolo 1 viene introdotto l’iniettore di neutri di ITER nell’ambito delle ricerche sulla fusione nucleare; ne vengono descritti schematicamente i principi di funzionamento e i componenti principali. Infine viene presentata l’installazione sperimentale in via di costruzione a Padova, costituita da due esperimenti, ovvero una sorgente di ioni negativi in scala 1:1 rispetto a quella di ITER, con un unico stadio di accelerazione del fascio a -100 kV, e un iniettore vero e proprio, identico a quello che verrà installato su ITER. Il capitolo 2 presenta dapprima le condizioni operative previste per l’iniettore di neutri dal punto di vista elettrico. In particolare vengono introdotte le problematiche della tenuta alla tensione e del processo di condizionamento in vuoto; quindi viene descritta una possibile modellazione circuitale per l’arco elettrico su lunghe distanze, considerando il fenomeno dell’irraggiamento come preponderante per la dissipazione dell’energia d’arco. Infine vengono presentate le attuali soluzioni contro gli effetti della scarica, ovvero uno snubber magnetico concentrato alle estremità della linea di trasmissione dell’iniettore e le protezioni di tipo attivo. Nel capitolo 3 vengono introdotti due nuovi concetti di protezioni passive. Il primo è un resistore di smorzamento che collega l’ultima griglia di accelerazione del fascio di ioni (la griglia di terra) con la cassa esterna dell’iniettore (messa a terra) in modo da smorzare la corrente d’arco che interessa tale griglia e si richiude sul conduttore di ritorno della linea di trasmissione. Vengono descritti il progetto e la costruzione di un prototipo installato presso il laboratorio francese del CEA (Commissariat à l’Énergie Atomique) di Cadarache, dove dovrà essere testato. L’impianto di prova di tale laboratorio viene poi modellato nel dettaglio per poter confrontare i risultati sperimentali e poterli interpretare. Il secondo dispositivo è uno snubber magnetico distribuito lungo tutto lo sviluppo della linea di trasmissione, in modo da smorzare al meglio ogni possibile guasto con un minor ingombro sul sistema e una struttura più semplice ed efficace. I risultati di una prova sperimentale su un modello in scala ridotta sono presentati a supporto della proposta. Il capitolo 4 delinea un esempio di progetto integrato di protezioni passive su un intero sistema. In particolare, per l’esperimento della sorgente di ioni negativi, vengono proposti, studiati e ottimizzati su un opportuno circuito equivalente gli effetti positivi del resistore di smorzamento, dello snubber magnetico distribuito e di un’impedenza L–R parallelo interposta tra alimentatore e linea di trasmissione. Infine viene descritto il progetto dello snubber, costituito da una serie di nuclei magnetici equispaziati lungo la linea e polarizzati da un opportuno circuito.

碩士
國立中正大學
電機工程研究所
99
This thesis presents design and implementation of an isolated bi-directional converter for renewable power system applications, and the topology of this converter is a full-bridge type with high conversion ratio and high output power features. The use of active flyback and passive capacitor-diode snubbers can alleviate the voltage spike caused by the current difference between filter inductor and leakage inductance of the isolation tansformer, reduce the ringing due to leakage inductance of the isolation tansformer, while achieve near ZCS soft-switching features on the both-side power switches. A single-chip microcontroller dsPIC30F2020 is adopted to realize the controller which has the advantage of high reliability and easy to maintain. Finally, a 1.5 kW and a 3 kW bi-directional converters have been implemented to verify the feasibility of the converter.

The development of Wide Bandgap (WBG) devices has enabled power electronic converters to operate at much higher frequencies, voltages and high power. Working at a higher switching frequency minimises the size of magnetics but results in significant switching losses and electromagnetic interference (EMI) noise. Thus, it necessitates the use of soft-switching techniques to reduce these losses. Phase-Shifted Full-Bridge (PSFB) Converter is the most widely used soft-switching topology in the high-voltage and high-power, unidirectional, DC-DC conversion. The phase shift PWM control utilises the converter parasitics to achieve zero voltage switching (ZVS) turn ON. The gating technique allows the magnetic energy stored in the leakage inductance of the isolation transformer to charge and discharge the output capacitances of the inverter leg. However, the converter suffers from severe voltage overshoots across the rectifier bridge during the zero to the active state transition. The resonant circuit formed between the transformer leakage inductance and the parasitic diode capacitance of the rectifier is responsible for the high-voltage ringing. Many passive and active snubbers are presented in the literature to mitigate the high-voltage overshoots across the diode bridge. While passive snubbers are relatively simple to implement than active snubbers, they are lossy. On the other hand, the active snubbers require additional gate driver circuitry and complex control. The first part of the thesis proposes a novel passive regenerative snubber to overcome the mentioned drawbacks of the existing snubbers. The proposed snubber is ideally lossless with no control complexity. The work covers a detailed analysis of the PSFB operation with the proposed snubber while obtaining closed-form expressions for the converter state variables at the end of each topological stage. The study considers all the major converter parasitics, such as transformer leakage and magnetising inductances, and parasitic capacitances of the converter. Given the new snubber, the thesis also lays out a step-by-step PSFB design procedure utilising the analysis carried out in the first part of the work. The design aimed to develop a 100 kHz PSFB for an input voltage of 360-440 V in the output power range of 0.5-1.5 kW at a fixed output voltage of 48 V. The design approach focuses on two design objectives - All inverter switches must achieve ZVS turn ON and the desired converter gain for all possible operating conditions. A hardware prototype is built and tested. The experimental results validate the effectiveness of the snubber in reducing the voltage overshoot. Further, the analysis and design accuracy is verified using the measured state variables. The work, at last, presents the overall converter efficiency and the loss distribution among the converter components.

碩士
國立臺灣海洋大學
電機工程學系
96
With the ongoing development of power electronics technology, the inverter of IGBT are widely applied to power converting applications. It is well known that output over-voltage and energy loss during switching of inverter are the main causes for the damage of power electronic devices. To solve this problem, we first characterize the general behavior of IGBT with research, then energy loss of IGBT in both hard switching and soft switching is empirically studied. Based on these simulation results, this thesis proposes a new kind of snubber using passive lossless IGBT half-bridge inverter. Extensive simulations are carried out, and results of which verify that the snubber can suppress over-voltage and the switching loss can be effectively reduced.

碩士
國立臺灣科技大學
電子工程系
95
In this thesis, three kinds of representative snubbers are discussed, including R-C, R-C-D and L-C-D snubbers, respectively. R-C snubber, a dissipative snubber, associating with circuit leakage inductance is to form a R-L-C circuit to eliminate overvoltage and ring wave around the power device so as to suppress ring wave EMI. R-C-D snubber, a dissipative and polarized snubber, acts as a capacitor to prolong the rise time of voltage waveform around the power switch so as to suppress EMI resulted from rise time changed by voltage variation in power regulation. The last L-C-D snubber, a lossless snubber, uses inductor and resonant circuit to prolong rise time of current waveform around the power device, in which the capacitor is used to prolong rise time of the voltage waveform. It is appropriate for suppressing EMI resulted from rise time changed by voltage and current variations in power regulation. The investigation for R-C snubber is appropriate for all kinds of converters about ring wave suppression. R-C-D snubber is appropriate for all kinds of converters about voltage rise time change. L-C-D snubber is appropriate for buck and boost converters about rise time changes of current and voltage. Three kinds of snubbers are respectively applied in PFC, forward and flyback converter topologies by way of mathematics analysis and simulation for achieving a unified relationship between the mentioned snubbers, including waveform comparison and spectrum distribution. In this thesis, experiments for the three kinds of snubber circuits applied in PFC, forward and flyback converters are examined. Their performances are quite close to the theoretical predictions.

At Entergy River Bend Station (a 978 MWe BWR located near Baton Rouge, Louisiana) snubber examination and testing have become unwanted expenses with the potential to lengthen planned outages and increase ALARA concerns. This paper presents a new concept for snubber replacement which can be used to expand the “Snubber to Strut” methodology. The E-BAR is a passive gapped support fabricated to be a “drop-in” replacement for snubbers. During normal plant operation the E-BAR functions like a box support, and during dynamic loading the E-BAR limits pipe motion and functions as a seismic restraint. Combining the guidance of WRC-300 [1] (snubber to strut criteria) and the industry practice of installing box supports with 1/16″ gaps between the pipe face and steel frame, generic criteria were developed to facilitate drop in snubber replacements. Replacements based on these criteria do not require re-analysis of the piping system. At the River Bend Station 102 snubbers were identified with thermal movements between 1/16″ and 3/8″. Sixty four snubbers (> 60%) met the generic criteria and were shown to be located at appropriate locations for snubber replacement. Development and explanation of the generic criteria and their applications are discussed here-in.

Passive energy dissipating devices like Elasto-plastic dampers (EPDs) can be used for eliminating snubbers and reducing the response of piping systems subjected to seismic loads. Cantilever and 3-dimensional piping systems were tested with and without EPD on shake table. Using a finite element model of the piping systems, linear and nonlinear time history analysis is carried out using Newmark’s time integration technique. Equivalent linearization technique such as Caughey method is used to evaluate the equivalent damping of the piping systems supported on Elasto-Plastic damper. An iterative response spectrum method is used for evaluating response of the piping system using this equivalent damping. The analytical maximum response displacement obtained at the Elasto-Plastic damper support for the two piping systems is compared with experimental values and time history analysis values. It has been concluded that, iterative response spectrum technique using Caughey equivalent damping is simple and results in reasonably acceptable response of the piping systems supported on EPD.

From early times adding auxiliary mass to the main mass has been done to mitigate vibration events. And much research of the structure by adding an equivalent mass using fluid or functional fluid has been done. On the other hand, the research and development of a new damper using rotating inertia mass began in the early 1970s in Japan. The new type damper was termed the “Mechanical Snubber” when it was used for piping and equipment systems in nuclear power plants. Tens of thousands of Mechanical Snubbers are used in Japanese domestic light water reactor and also in foreign countries. As one of the only surviving developers, the author would like to report the development process. This Mechanical Snubber has a large equivalent inertia mass and it accords with the design criteria of high stiffness of seismic method of nuclear power plant. In recent years, in the field of civil engineering and construction, studies using rotating inertia mass or negative stiffness of mechanism have come into favor. These studies are expected to be applied in structure and bridge engineering. This paper describes the historical background of inertia mass dampers, the theory of the inertia mass damper (I.M.D.) applied as a product, and the electromagnetic inertia mass damper (E.I.M.D.) developed as a passive and/or semi-active damper. Some experimental studies using shaking table in the National Center for Research on Earthquake Engineering (NCREE) in Taiwan and theoretical studies are introduced.

The nuclear industry is preparing for the licensing and construction of new nuclear power plants in the United States. Several new designs have been developed and approved, including the “traditional” reactor designs, the passive safe shutdown designs and the small modular reactors (SMRs). The American Society of Mechanical Engineers (ASME) provides specific Codes used to perform preservice inspection/testing and inservice inspection/testing for many of the components used in the new reactor designs. The U.S. Nuclear Regulatory Commission (NRC) reviews information provided by applicants related to inservice testing (IST) programs for Design Certifications and Combined Licenses (COLs) under Part 52, “Licenses, Certifications, and Approvals for Nuclear Power Plants,” in Title 10 of the Code of Federal Regulations (10 CFR Part 52) (Reference 1). The 2012 Edition of the ASME OM Code defines a post-2000 plant as a nuclear power plant that was issued (or will be issued) its construction permit, or combined license for construction and operation, by the applicable regulatory authority on or following January 1, 2000. The New Reactors OM Code (NROMC) Task Group (TG) of the ASME Code for Operation and Maintenance of Nuclear Power Plants (NROMC TG) is assigned the task of ensuring that the preservice testing (PST) and IST provisions in the ASME OM Code to address pumps, valves, and dynamic restraints (snubbers) in post-2000 nuclear power plants are adequate to provide reasonable assurance that the components will operate as needed when called upon. Currently, the NROMC TG is preparing proposed guidance for the treatment of active pumps, valves, and dynamic restraints with high safety significance in non-safety systems in passive post-2000 reactors including SMRs.

The nuclear industry is preparing for the licensing and construction of new nuclear power plants in the United States. Several new designs have been developed, including more traditional evolutionary designs, passive reactor designs, and small modular reactors (SMRs). ASME (formerly the American Society of Mechanical Engineers) provides specific codes used to perform inspections and testing, both preservice and inservice, for many of the components used in the new reactor designs. The U.S. Nuclear Regulatory Commission (NRC) reviews information provided by applicants related to inservice testing (IST) programs for design certification (DC) and combined license (COL) applications under Part 52, “Licenses, Certifications, and Approvals for Nuclear Power Plants,” of Title 10, “Energy,” of the Code of Federal Regulations (10 CFR Part 52) (Reference 1). The 2012 Edition of the ASME OM Code, Operation and Maintenance of Nuclear Power Plants, defines a post-2000 plant as a nuclear power plant that was issued (or will be issued) its construction permit, or combined license for construction and operation, by the applicable regulatory authority on or after January 1, 2000. The ASME New Reactors OM Code (NROMC) Task Group (TG) is assigned the task of ensuring that the preservice testing (PST) and inservice testing (IST) provisions in the ASME OM Code are adequate to provide reasonable assurance that pumps, valves, and dynamic restraints (snubbers) for post-2000 plants will operate when needed. Currently, the NROMC TG is preparing proposed guidance for the treatment of active pumps, valves, and dynamic restraints with high safety significance in nonsafety systems for passive post-2000 plants, including SMRs. (Note: For purposes of this paper, “post-2000 plant” and “new reactor” are used interchangeably throughout.) Paper published with permission.