Dissertations / Theses on the topic 'Switching overvoltage'

This thesis analyses the controlled switching methods applied to modern SF6 type circuit breakers for the purpose of reducing switching overvoltages. Main emphasis is placed on controlled switching methods applied at extra high voltage level, since the cost of failures caused by switching overvoltages is highest in this voltage level. After a brief introduction about circuit breakers in general, switching overvoltages and controlled switching methods are analysed. Also a case study about controlled switching of an unloaded overhead line is provided, and success of controlled switching method is evaluated.

Hydropower plants contains a lot of vital electrical power technology such as generators and transformers. To prevent damage to this equipment due to overvoltage, they are often protected by surge arrester and in some cases also by surge capacitors. The design and dimension of these components vary between different sites and regions and are often done using a template without considering the actual conditions of the site. In this thesis Simulink and Simscape Power System are used to study the case when a hydropower station is exposed to overvoltage. One of Fortum’s hydropower stations is simulated when being exposed to lightning and switching overvoltage to see how the existing overvoltage protection handles this stress. The results show that the surge arresters mounted in front of the generator managed to keep it safe for all overvoltage scenarios it is exposed to. They also shows that the surge capacitors mounted in front of the generator reduces the gradient of the overvoltage surge. However, as the surge arresters already keeps the overvoltage at safe levels, there is no need of reducing the overvoltage gradient and the surge capacitors becomes excessive in this particular hydropower plant.<br>Vattenkraftverk innehåller många vitala komponenter så som generatorer och transformatorer. För att skydda dessa oftast väldigt dyra komponenter mot överspänningar, används ventilavledare och ibland också överspänningskondensatorer. Utformning och dimensionering av skydden varierar mellan olika anläggningar och regioner. Dimensioneringen av skydden görs ofta schablonmässigt, utan någon väsentlig anpassning till de faktiska förhållandena. I detta examensarbete används simuleringsverktyget Simulink tillsammans med tillägget Simscape Power Systems för att simulera vad som händer när ett vattenkraftverk utsätts för olika överspänningar. Ett av Fortums vattenkraftverk studeras när det utsätts för blixt- och kopplingsöverspänningar för att se vad ventilavledarna samt överspänningskondensatorerna i denna anläggning fyller för funktion. Resultaten visar att ventilavledarna monterade framför generatorn klarar av att hantera alla överspänningar de utsätt för under simuleringarna. Resultaten visade också att överspänningskondensatorerna monterade framför generatorn sänker spänningsgradienten, men eftersom ventilavledarna redan håller spänningen på en säker nivå blir överspänningskondensatorerna överflödiga i denna station.

Any switching action or lightning stroke on a transmission system causes excessive of voltage, which are propagated through the equipment. The withstand capability of the electrical equipment to these overvoltages is dependent on the rate of rise, peak value and the duration of these overvoltages and are especially critical to information technology (IT) equipment. Whenever there is a probability of these overvoltages appearing across the electrical equipment, they should be limited to a safe value by the application surge arresters of the metal oxide type. However, surge arresters are expensive, an optimal location for these should be found so as to minimise the number of surge arresters used.

Nesta dissertação, discorre-se sobre manobra sincronizada de disjuntores. Entre as atividades desenvolvidas para a sua elaboração estão a análise de transitórios causados por manobras em capacitores, reatores e linhas de transmissão, estudos de sobretensão e estudos para a determinação de instantes favoráveis às manobras, sob o ponto de vista de diminuição de sobretensões. Completa a dissertação a especificação de equipamento de sincronismo que, a partir de medições em tempo real de variáveis elétricas - que interferem nas sobretensões - e de variáveis climáticas - que interferem no tempo de acionamento dos contatos dos disjuntores - calculam o tempo de atraso necessário para o fechamento elétrico em instantes mais convenientes.<br>The scope of this dissertation is the study of synchronized switching of circuit breakers. The transients caused by capacitor, reactor and transmission line switching are analyzed, for overvoltage evaluation and to determined the favorable time in the wave that leads to smallest overvoltages. Finally the specification of an equipment is produced. The equipment acquire, in real time, the values of electrical variables (current and voltages) the ambient temperature and oil pressure in the circuit breaker operating mechanism, voltage in the auxiliary system and assign a delay in the breaker switching time in order to control overvoltages.

Conselho Nacional de Desenvolvimento Científico e Tecnológico<br>A busca por soluções mitigatórias, no que tange aos efeitos das sobretensões transitórias atreladas às manobras de energizações e religamentos das linhas de transmissão, contemplam um tema desafiador e com fortes impactos sobre a coordenação de isolamento dos sistemas elétricos. Muito embora o reconhecimento de propostas clássicas e comerciais para a atenuação destes fenômenos, outras possibilidades, certamente, ainda são meritórias de destaque e investigações. Neste contexto, a presente dissertação encontra-se alicerçada na exposição dos fundamentos físicos e matemáticos de uma estratégia baseada em chaveamentos controlados, cujos instantes para o religamento da linha são pré-programados. A avaliação computacional da eficácia da metodologia é realizada utilizando o simulador ATP, no qual são efetuados estudos em um sistema elétrico típico submetido à curtos-circuitos sucedidos por desligamentos e subsequentes religamentos, sob a ação da tecnologia aqui focada e na ausência da mesma.<br>The search for mitigation solutions, with respect to the effects of overvoltages linked to the energization and reclosing maneuvers of transmission lines include a challenging subject with strong impact on the insulation coordination of electrical systems. Although the recognition of classical and commercial proposals to mitigate these phenomena, other possibilities are certainly still worthwhile highlighting and investigations. In this context, the present work is grounded in the exposure of the physical and mathematical foundations of a strategy based on controlled switchings, whose moments to the line reclosing are pre-programmed. The computational evaluation of the effectiveness of the methodology is made using the ATP simulator, which are studies in a typical electrical system subjected to the action of short-circuits fallowed by shutdowns and subsequent reclosing, under the action of technology here focused and lack thereof.<br>Dissertação (Mestrado)

Wound Field Synchronous Generators provide more than 95% of the electricity need worldwide. Their primacy in electricity production is due to ease of voltage regulation, performed by simply adjusting the direct current intensity in their rotor winding. Nevertheless, the rapid progress of power electronics devices enables new possibilities for alternating current add-ins in a more than a century long DC dominated technology. Damping the rotor oscillations with less energy loss than before, reducing the wear of the bearings by actively compensating for the mechanic unbalance of the rotating parts, speeding up the generator with no need for additional means, these are just few of the new applications which imply partial or total alternated current supplying of the rotor winding. This thesis explores what happens in a winding traditionally designed for the direct current supply when an alternated current is injected into it by an inverter. The research focuses on wound field salient pole synchronous machines and investigates the changes in the field winding parameters under AC conditions. Particular attention is dedicated to the potentially harmful voltage surges and voltage gradients triggered by voltage-edges with large slew rate. For this study a wide frequency band simplified electromagnetic model of the field winding has been carried out, experimentally determined and validated. Within the specific application of the fast field current control, the research provides some references for the design of the rotor magnetic circuit and of the field winding. Finally the coordination between the power electronics and the field winding properties is addressed, when the current control is done by means of a long cable or busbars, in order to prevent or reduce the ringing.

The purpose of this thesis is to introduce readers with design of a surge arresters in four different categories. In the first part of this thesis is described theory of overvoltage, surge arresters and testing. The second part of this thesis is focused on design of surge arresters to protect from overvoltage due switching capacitive loads. The thesis continued with design of surge arresters in medium voltage network. The next part is design of surge arresters to protect from overvoltage due switching inductive loads. The next point is protective distance of surge arresters in different lighting overvoltages. In the conclusion of this thesis is the appreciation of whole problems about surge arresters.

Många elektriska apparater är i behov av reaktiv effekt för att kunna fungera. Transport av reaktiv effekt tar onödig plats av den tillgängliga kapaciteten i elnätet, därför används kondensatorbatterier nära slutanvändaren för att generera reaktiv effekt. Därmed genereras och förbrukas den reaktiva effekten i en avskild del av nätet. Tillkoppling av kondensatorbatterier ger upphov till transienter som kan skada andra närliggande komponenter. Utifrån det verkliga ställverket Stallbacka i Trollhättan har denna rapport analyserat de transienter som uppstår efter tillkoppling av ett kondensatorbatteri inom mellanspänningsområdet. Analysen har innefattat hur stora transienterna blir efter olika förutsättningar och scenarier. Resultatet visade att transienterna i detta fall aldrig nådde upp till några allvarliga nivåer, och därmed klarade komponenterna sig med god marginal. Huruvida transienterna påverkar elkvaliteten är oklart, då det inte finns några definierade krav. Slutligen skulle ett beräkningsverktyg för förutspådda transienter tas fram. Beräkningsverktyget blev aldrig fullständigt på grund av den ohanterliga lösningen som erhölls.<br>Many electrical devices need reactive power to operate. Transmission of reactive power occupies a proportion of the available capacity in the power system and therefore capacitor banks are used near to the end user to generate reactive power. Thus, the reactive effect is generated and consumed in a separate part of the power system. Capacitor banks switching causes transients which may damage the surrounding components. Based on the real substation Stallbacka in Trollhättan, this study has analysed capacitor banks switching transients within the medium voltage level. The analysis has covered the size of these transients according to different conditions and scenarios. The result showed that the transients in this case never reached serious levels, thus there was no impact on the components. It is not clear whether the transients affect the power quality because there are no defined limits.  A calculation tool to the predicted transients was supposed to be created in the process. This calculation tool was never completed due to the unmanageable solution that was obtained.

Cette thèse traite de l'étude analytique et numérique des surtensions de manoeuvre d'un réseau électrique comportant un transformateur à vide raccordé à l'extrémité d'une ligne de transport. Ce traitement permet d'établir des règles aussi simples que possibles pour identifier et éviter des manoeuvres dangereuses, lorsqu'il s'agit par exemple de remettre sous tension un réseau à l'issue d'un incident. Dans une première partie, une analyse de l'ensemble des surtensions de manoeuvre sur la ligne à vide est rappelée, puis une extension du problème avec transformateur à vide à son extrémité est considérée. Dans une deuxième partie, une configuration monophasés simple mais représentative d'un cas réel a été définie permettant d'effectuer une étude analytique des surtondons aux bornes du transformateur. Les résultats obtenus dans le cas linéaire comme dans le cas non linéaire sont qualitativement représentatifs. Ensuite, une simulation numérique triphasée a été réalisée à l'aide du logiciel Morgat. Pour cela, nous avons développé des sous-programmes de gestion des valeurs d'entrée et des résultats simulés permettant d'enchaîner les simulations en modifiant un ou plusieurs paramètres de manière déterministe ou statistique associée à un générateur aléatoire. Les paramètres ayant une influence importante ont été analysés et seuls trois d'entre eux ont été retenus : la fréquence propre du réseau vue des bornes du transformateur, la puissance de la source et la puissance du transformateur cible. L'une des conclusions auxquelles on aboutit est que le rapport des puissances transformateur cible et source doit être adapté si on désire limiter les surtensions. Enfin, une étude statistique de la fermeture aléatoire des trois pôles du disjoncteur autour d'une valeur moyenne a été faite. Ceci nous a permis de définir un critère simplifié caractérisant le domaine des surtensions admissibles en fonction des paramètres d'influence

In recent years, multilevel converters are becoming more popular and attractive than traditional converters in high voltage and high power applications. Multilevel converters are particularly suitable for harmonic reduction in high power applications where semiconductor devices are not able to operate at high switching frequencies or in high voltage applications where multilevel converters reduce the need to connect devices in series to achieve high switch voltage ratings. This thesis investigated two aspects of multilevel converters: structure and control. The first part of this thesis focuses on inductance between a DC supply and inverter components in order to minimise loop inductance, which causes overvoltages and stored energy losses during switching. Three dimensional finite element simulations and experimental tests have been carried out for all sections to verify theoretical developments. The major contributions of this section of the thesis are as follows: The use of a large area thin conductor sheet with a rectangular cross section separated by dielectric sheets (planar busbar) instead of circular cross section wires, contributes to a reduction of the stray inductance. A number of approximate equations exist for calculating the inductance of a rectangular conductor but an assumption was made that the current density was uniform throughout the conductors. This assumption is not valid for an inverter with a point injection of current. A mathematical analysis of a planar bus bar has been performed at low and high frequencies and the inductance and the resistance values between the two points of the planar busbar have been determined. A new physical structure for a voltage source inverter with symmetrical planar bus bar structure called Reduced Layer Planar Bus bar, is proposed in this thesis based on the current point injection theory. This new type of planar busbar minimises the variation in stray inductance for different switching states. The reduced layer planar busbar is a new innovation in planar busbars for high power inverters with minimum separation between busbars, optimum stray inductance and improved thermal performances. This type of the planar busbar is suitable for high power inverters, where the voltage source is supported by several capacitors in parallel in order to provide a low ripple DC voltage during operation. A two layer planar busbar with different materials has been analysed theoretically in order to determine the resistance of bus bars during switching. Increasing the resistance of the planar busbar can gain a damping ratio between stray inductance and capacitance and affects the performance of current loop during switching. The aim of this section is to increase the resistance of the planar bus bar at high frequencies (during switching) and without significantly increasing the planar busbar resistance at low frequency (50 Hz) using the skin effect. This contribution shows a novel structure of busbar suitable for high power applications where high resistance is required at switching times. In multilevel converters there are different loop inductances between busbars and power switches associated with different switching states. The aim of this research is to consider all combinations of the switching states for each multilevel converter topology and identify the loop inductance for each switching state. Results show that the physical layout of the busbars is very important for minimisation of the loop inductance at each switch state. Novel symmetrical busbar structures are proposed for multilevel converters with diode-clamp and flying-capacitor topologies which minimise the worst case in stray inductance for different switching states. Overshoot voltages and thermal problems are considered for each topology to optimise the planar busbar structure. In the second part of the thesis, closed loop current techniques have been investigated for single and three phase multilevel converters. The aims of this section are to investigate and propose suitable current controllers such as hysteresis and predictive techniques for multilevel converters with low harmonic distortion and switching losses. This section of the thesis can be classified into three parts as follows: An optimum space vector modulation technique for a three-phase voltage source inverter based on a minimum-loss strategy is proposed. One of the degrees of freedom for optimisation of the space vector modulation is the selection of the zero vectors in the switching sequence. This new method improves switching transitions per cycle for a given level of distortion as the zero vector does not alternate between each sector. The harmonic spectrum and weighted total harmonic distortion for these strategies are compared and results show up to 7% weighted total harmonic distortion improvement over the previous minimum-loss strategy. The concept of SVM technique is a very convenient representation of a set of three-phase voltages or currents used for current control techniques. A new hysteresis current control technique for a single-phase multilevel converter with flying-capacitor topology is developed. This technique is based on magnitude and time errors to optimise the level change of converter output voltage. This method also considers how to improve unbalanced voltages of capacitors using voltage vectors in order to minimise switching losses. Logic controls require handling a large number of switches and a Programmable Logic Device (PLD) is a natural implementation for state transition description. The simulation and experimental results describe and verify the current control technique for the converter. A novel predictive current control technique is proposed for a three-phase multilevel converter, which controls the capacitors' voltage and load current with minimum current ripple and switching losses. The advantage of this contribution is that the technique can be applied to more voltage levels without significantly changing the control circuit. The three-phase five-level inverter with a pure inductive load has been implemented to track three-phase reference currents using analogue circuits and a programmable logic device.

Switching of shunt reactors and capacitor banks is known to cause a very high rate of rise of transient recovery voltage across the circuit breaker contacts. With improvements in circuit breaker technology, modern SF6 puffer circuits have been designed with less interrupter per pole than previous generations of SF6 circuit breakers. This has caused modern circuit breakers to operate with higher voltage stress in the dielectric recovery region after current interruption. Catastrophic failures of modern SF6 circuit breakers have been reported during shunt reactor and capacitor bank de-energisation. In those cases, evidence of cumulative re-strikes has been found to be the main cause of interrupter failure. Monitoring of voltage waveforms during switching would provide information about the magnitude and frequency of small re-ignitions and re-strikes. However, measuring waveforms at a moderately high frequency require plant outages to connect equipment. In recent years, there have been increasing interests in using RF measurements in condition monitoring of switchgear. The RF measurement technique used for measuring circuit breaker inter-pole switching time during capacitor bank closing is of particular interest. In this thesis, research has been carried out to investigate switching transients produced during circuit breaker switching capacitor banks and shunt reactors using a non-intrusive measurement technique. The proposed technique measures the high frequency and low frequency voltage waveforms during switching operations without the need of an outage. The principles of this measurement technique are discussed and field measurements were carried out at shunt rector and capacitor bank installation in two 275 kV air insulated substations. Results of the measurements are presented and discussed in this thesis. The proposed technique shows that it is relatively easy to monitor circuit breaker switching transients and useful information on switching instances can be extracted from the measured waveforms. Further research works are discussed to realise the full potential of the measuring technique.

Switching of shunt reactors and capacitor banks is known to cause a very high rate of rise of transient recovery voltage across the circuit breaker contacts. With improvements in circuit breaker technology, modern SF6 puffer circuits have been designed with less interrupter per pole than previous generations of SF6 circuit breakers. This has caused modern circuit breakers to operate with higher voltage stress in the dielectric recovery region after current interruption. Catastrophic failures of modern SF6 circuit breakers have been reported during shunt reactor and capacitor bank de-energisation. In those cases, evidence of cumulative re-strikes has been found to be the main cause of interrupter failure. Monitoring of voltage waveforms during switching would provide information about the magnitude and frequency of small re-ignitions and re-strikes. However, measuring waveforms at a moderately high frequency require plant outages to connect equipment. In recent years, there have been increasing interests in using RF measurements in condition monitoring of switchgear. The RF measurement technique used for measuring circuit breaker inter-pole switching time during capacitor bank closing is of particular interest. In this thesis, research has been carried out to investigate switching transients produced during circuit breaker switching capacitor banks and shunt reactors using a non-intrusive measurement technique. The proposed technique measures the high frequency and low frequency voltage waveforms during switching operations without the need of an outage. The principles of this measurement technique are discussed and field measurements were carried out at shunt rector and capacitor bank installation in two 275 kV air insulated substations. Results of the measurements are presented and discussed in this thesis. The proposed technique shows that it is relatively easy to monitor circuit breaker switching transients and useful information on switching instances can be extracted from the measured waveforms. Further research works are discussed to realise the full potential of the measuring technique.

This master´s thesis deals with the designing process of surge protection for the object potentially explosive atmospheres and according to a set of standards ČEN EN 62305 and ČSN EN 60079. This work consists of four main parts. The first part deals with the theory of lightning and surges. Subsequently, in the second part is devoted to the theory of protection against these phenomena and proposals for external and internal lightning protection and surge. This chapter also deals with more demands on electrical installations in hazardous areas. The third part deals with the analysis of the risks to the subject paint and according to ČSN EN 62305-2 ed.2 and at the conclusion of the study is a proposal for external lightning protection and internal surge protection.

碩士<br>國立臺北科技大學<br>電機工程系所<br>98<br>This study presents the result of a case study on the switching over-voltage transients of AC electrified railroad trains equipped with switch-type rectifiers in Taiwan Railway Administration. It was found that new generation of switch-type converters could result in significant over-voltage of magnitude comparable to lightning surge if no proper snubber circuit is used. The switching surge could damage power equipment of nearby trains in the same service zone, as observed in the TRA system. It is recommended that maximum tolerance of switching overvoltage is clearly specified in the procurement phase of new trains with switch-type converters then is accurately verified in the commissioning phase to ensure proper preventive measure has been taken.

碩士<br>大同大學<br>電機工程學系(所)<br>94<br>This thesis will be utilizing ATP-EMTP as analytic tool, performing overvoltage analysis, regarding 345kV voltage grade level of the Mai-Liao Power Plant; especially its EHV No. 1 Station, concerning switching surge and lightening surge. The overall purpose is to evaluate whether the insulation strength of the 345kV system, is strong enough to withstand overvoltage threats of lightening surge and switching surge. Based on suggestions of ANSI/IEEE Std. C62.22 and outcomes of analysis of this research, relevant assessment will be made in regards to whether or not, the circuit breaker and transformer installations of the GIS system, possess sufficient protection margin; further alternation suggestions will also be made concerning the simulation methodologies and respective models to be applied, for lightening surge and switching surge. Various models for lightening surge simulation include: transmission line model, tower model, lightening current source model, archorn flashover model and substation model. Various models for switching surge simulation include: transmission line model, time-controlled switching model, statistic switching model and transformer model. Deriving from analytical results, one is made aware of the fact that, when conducting lightening surge overvoltage simulation, if one employs “Ramp 1/70μs” as lightening current waveform, as well as Multistory Tower Model as the tower model of lightening analysis, one can obtain much more rigorous outcomes. Furthermore, deriving from analytical results of energizing surge simulation, by using statistic switching model, provided that the simulation trials is over 100 times, the final results obtained are more accurate, when compared to using time controlled switching model. Whereas when conducting analysis for reclosing overvoltage simulation, if one applies the Bergeron Model as transmission line model, then a more reasonable decay phenomenon of residual voltage can be presented, which is much more realistic in relation to the actual reclosing overvoltage. The final outcome of this research study clearly shows that, the lightening surge overvoltage and the switching surge overvoltage derived from such operations of reclosing, as well as Jia-Min substation’s energizing, will not bear direct impact or damage, neither to the GIS system nor to the primary transformers at the Mai-Liao Power Plant. Nevertheless, when the Mai-Liao Power Plant and the Jia-Min substation are in shunt liaison, if the voltage phase angles at the 2 extremes of the circuit breaker are non-synchronous, then this will lead to an overcurrent invasion of the primary transformers at the Mai-Liao Power Plant.

abstract: Switching surges are a common type of phenomenon that occur on any sort of power system network. These are more pronounced on long transmission lines and in high voltage substations. The problem with switching surges is encountered when a lot of power is transmitted across a transmission line/network, typically from a concentrated generation node to a concentrated load. The problem becomes significantly worse when the transmission line is long and when the voltage levels are high, typically above 400 kV. These overvoltage transients occur following any type of switching action such as breaker operation, fault occurrence/clearance and energization, and they pose a very real danger to weakly interconnected systems. At EHV levels, the insulation coordination of such lines is mainly dictated by the peak level of switching surges, the most dangerous of which include three phase line energization and single-phase reclosing. Switching surges can depend on a number of independent and inter-dependent factors like voltage level, line length, tower construction, location along the line, and presence of other equipment like shunt/series reactors and capacitors. This project discusses the approaches taken and methods applied to observe and tackle the problems associated with switching surges on a long transmission line. A detailed discussion pertaining to different aspects of switching surges and their effects is presented with results from various studies published in IEEE journals and conference papers. Then a series of simulations are presented to determine an arrangement of substation equipment with respect to incoming transmission lines; that correspond to the lowest surge levels at that substation.<br>Dissertation/Thesis<br>Masters Thesis Electrical Engineering 2018

<p> This thesis investigates the nature and magnitude of switching transient overvoltages that can be expected in inductively grounded underground coal mines. Computer models of power system equipment have been developed to analyse single-phase fault isolations; motor starts (including prestriking) and motor turn offs. The computer models that were developed have been validated against field recordings. The "Alternative Transients Program" (ATP) software was used to conduct the computer simulation studies. </p> <p>The underground substations used in Central Queensland coal mines are grounded through a Neutral Earthing Reactor (NER). The primary purpose of a NER is to limit earth fault currents. However, when a single -phase -to -ground fault occurs, energy is stored in the NER. Consequent to the isolation of such a fault, the energy stored in the NER is released. The release of this energy manifests itself as a transient overvoltage. This thesis investigates the effect of the rating of the NER and the value of the electric current at the instant of earth fault isolation on transient overvoltages. </p> <p>Two alternate earthing schemes were investigated in an attempt to reduce the severity of the transient overvoltages consequent to the isolation of earth faults. The first alternative that was investigated was the addition of a Resistor -Capacitor Snubber in parallel with a NER. Computer simulations indicate that the proper choice of Snubber parameters is very effective in reducing transient overvoltages following the isolation of earth faults. Consequently, a decision was made to manufacture a R -C Snubber and conduct field tests on the same. A summary of the field tests results has been included in the thesis. </p> <p>The other alternate grounding scheme that was investigated was the substitution of a Neutral Earthing Reactor with a Neutral Earthing Resistor. Computer simulations indicate that transient overvoltages following the isolation of earth faults are virtually eliminated if a Neutral Earthing Resistor is used. </p> <p>Consequent to this research work, the use of R -C Snubbers has become a recommended practice at various coal mine sites in Australia which use NER grounded, container type substations. The R -C Snubber is the preferred alternative at such installations as it is very compact and also eliminates the heating/reliability problems associated with resistance grounding. </p> <p>Vacuum contactors are used throughout the Central Queensland mines to frequently turn motors on and off. One of the most significant characteristics of vacuum contactors is their ability to interrupt high frequency currents. The consequence of this is that a considerable number of high frequency prestriking transients can be generated whenever a motor is turned on. These high frequency transients can lead to the premature aging of insulation. This thesis presents a computer model that was developed to simulate prestriking transients using the TACS (Transient Analysis of Control Systems) programming feature of the ATP software. Further investigation of prestriking transients was considered to be beyond the scope of the present research project. However, the unique TACS based prestriking model of a vacuum contactor that has been developed will be a useful tool for conducting further research.   </p>