The onset of a ferroresonance phenomenon in power systems is commonly caused by the reconfiguration of a circuit into the one consisting of capacitances in series and interacting with transformers. The reconfiguration can be due to switching operations of de-energisation or the occurrence of a fault. Sustained ferroresonance without immediate mitigation measures can cause the transformers to stay in a state of saturation leading to excessive flux migrating to transformer tanks via internal accessories. The symptom of such an event can be unwanted humming noises being generated but the real threatening implication is the possible overheating which can result in premature ageing and failures.The main objective of this thesis is to determine the accurate models for transformers, transmission lines, circuit breakers and cables under transient studies, particularly for ferroresonance. The modeling accuracy is validated on a particular 400/275 kV transmission system by comparing the field test recorded voltage and current waveforms with the simulation results obtained using the models. In addition, a second case study involving another 400/275 kV transmission system with two transformers is performed to investigate the likelihood of the occurrence of sustained fundamental frequency ferroresonance mode and a possible quenching mechanism using the 13 kV tertiary connected reactor. A sensitivity study on transmission line lengths was also carriedout to determine the probability function of occurrence of various ferroresonance modes. To reproduce the sustained fundamental and the subharmonic ferroresonance modes, the simulation studies revealed that three main power system components which are involved in ferroresonance, i.e. the circuit breaker, the transmission line and the transformer, can be modeled using time-controlled switch, the PI, Bergeron or Marti line model, and the BCTRAN+ or HYBRID transformer model. Any combination of the above component models can be employed to accurately simulate the ferroresonance system circuit. Simulation studies also revealed that the key circuit parameter to initiate transformer ferroresonance in a transmission system is the circuit-to-circuit capacitance of a double-circuit overhead line. The extensive simulation studies also suggested that the ferroresonance phenomena are far more complex and sensitive to the minor changes of system parameters and circuit breaker operations. Adding with the non-linearity of transformer core characteristics, repeatability is not always guaranteed for simulation and experimental studies. All simulation studies are carried out using an electromagnetic transient program, called ATPDraw.

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ABSTRACT Federal regulations have recognized that arc flash hazards are a critical source of potential injury. As a consequence, in order to work on some electrical equipment, the energy source must be completely shut-down. However, power distribution systems in mission critical facilities such as hospitals and data centers must sometimes remain energized while being maintained. In recent years the Arc Flash Hazard Analysis has emerged as a power system tool that informs the qualified technician of the incident energy at the equipment to be maintained and recommends the proper protective equipment to wear. Due to codes, standards and historically acceptable design methods, the Arc Flash Hazard is often higher and more dangerous than necessary. This dissertation presents detailed methodology and proposes alternative strategies to be implemented at the design stage of 600 volt facility power distribution systems which will decrease the Arc Flash Hazard Exposure when compared to widely used code acceptable design strategies. Software models have been developed for different locations throughout a power system. These software model simulations will analyze the Arc Flash Hazard in a system designed with typical mainstream code acceptable methods. The model will be changed to show implementation of arc flash mitigation techniques at the system design level. The computer simulations after the mitigation techniques will show significant lowering of the Arc Flash Hazard Exposure.

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Circuit breakers are used in the power system to break or make current flow through power apparatus. Reliable operation of circuit breakers is critical to the well- being of the power system and can be achieved by regular inspection and maintenance. A low-cost automated circuit breaker monitoring system is developed to monitor circuit breaker control signals. An interface is designed on top of which different local and system-wide applications can be developed which utilize the data recorded by the system. Some of the possible applications are proposed. Lab and field evaluation of the designed system is performed and results are presented.

Zugl.: Freiberg (Sachsen), Techn. Univ., Diss., 2005

Le disjoncteur modulaire protège les installations électriques basse-tension contre les défauts de court-circuit. L’arc électrique, généré dans la chambre de coupure du disjoncteur lors de l’ouverture du circuit, est fractionné en plusieurs arcs dans un assemblage de multiples plaquettes métalliques, afin de limiter l’intensité du courant et d'isoler le défaut. Le travail exposé dans ce document se concentre sur la phase de limitation de l’intensité du courant de court-circuit. Une chambre d’arc modèle représente de façon simplifiée l’environnement de l’arc électrique durant cette phase. L'arc est amorcé par une impulsion haute-tension entre deux plaquettes métalliques fixes, l'onde de courant est transitoire et de forte intensité. La pertinence du montage expérimental est validée par la confrontation des phénomènes qu'il permet d'observer à ceux rencontrés dans le disjoncteur. Une attention particulière est portée à la tension d'arc, qui est une caractéristique déterminante pour la performance de la limitation. L’influence du matériau des électrodes est étudiée, en distinguant le substrat d’un éventuel revêtement. / The modular circuit breaker protects low-voltage lectrice installations against short-circuit faults. The electric arc generated in the arc chamber of the circuit breaker upon opening of the circuit is divided into several arcs in an assembly of multiple metallic plates, in order to limit the current and isolate the fault.The work set out in this paper focuses on the short-circuit current limitation phase. A model arc chamber represents in a simplified way the environment of the electric arc during this phase. The arc is initiated by a high-voltage pulse between two fixed metal plates, the current wave is transient and of high intensity.The relevance of the experimental setup is validated by comparison of the phenomena that it allows to observe with those encountered in the circuit breaker. Particular attention is paid to the arc voltage, which is a determining feature for the performance of the limitation. The influence of the material of the electrodes is studied, distinguishing the substrate from a possible coating.

En strömbrytare är en säkerhetsanordning som är utformad för att bryta strömmen om ett problem uppstår. Det finns ett flertal olika typer av brytare beroende vilket spänningsområde som avses. Brytare för lågspänning används för hushållsapparater, medan högspänningstyper används för överföring av spänning i elnätet. Högspänningsbrytare använder idag svavelhexafluorid (SF6)-gas, som ett isolerande medium för att släcka den elektriska ljusbåge som bildas när strömmen bryts. SF6 är dock problematiskt för miljön, då dess globala uppvärmningspotential (GWP) är 23 500 gånger högre jämfört med koldioxid (CO2). Företaget Hitachi ABB Power Grids har utvecklat AirPlus™-tekniken som ersätter SF6-gasen med en koldioxidbaserad gasblandning. Examensarbetet fokuserade på att utvärdera möjligheten att minska användningen av SF6 genom AirPlus™-tekniken och hur tekniken skulle kunna en introduceras på marknaden. Slutligen så utvecklades en strategi för hur detta skulle kunna ske. Studien innefattar den bakomliggande informationsinhämtningen och analysen av data, marknadsutvärdering och utvecklingen av marknadsstrategin. Detta utfördes genom att utvärdera AirPlus™-tekniken och dess konkurrenter, samt genom en kvalitativ och kvantitativ analys av implementeringen av LTA 420 kV-brytaren på marknaden. Sammanfattningsvis så visar studien att marknadsintroduktionen av strömbrytaren LTA 420 kV är genomförbar. Även om koldioxid tekniskt inte har samma prestanda som SF6, är tekniken fortfarande bra och ger starka kundfördelar: GWP minskar med över 99,9%, användningen överensstämmer med miljöregler, den ger lägre ägandekostnader, färre kontroller, lägre kostnad för hantering av koldioxidgasen, och fungerar väl vid extremt låga temperaturer. De viktigaste utmaningarna för Hitachi ABB Power Grids relaterar till konkurrensen på marknaden. Det är därför tillrådligt att företaget arbetar med en effektiv marknadsintroduktion för att säkerställa en stor marknadsandel. / A circuit breaker is a safety device designed to interrupt power if a problem is detected. There are several kinds of circuit breakers for different applications. Low-voltage circuit breakers are used for household appliances, while high-voltage types are used for transmission networks. High-voltage circuit breakers use sulfur hexafluoride (SF6) gas as an insulating medium, which extinguishes the electric arc that is formed when power is cut. However, it is a huge hazard for the environment, as its global warming potential (GWP) is 23,500 times higher than that of CO2 gas. The company Hitachi ABB Power Grids developed the AirPlus™ technology, which replaces the SF6 gas with a carbon dioxide (CO2) based gas mixture. The presented degree project has evaluated the feasibility of reducing the use of SF6 through the AirPlus™ technology and then developed a strategy for the company Hitachi ABB Power Grids for the market introduction of the eco-efficient LTA 420 kV circuit breaker. This study covers the background research, market evaluation, and market strategy.  It was done through research about the AirPlus™ technology and its competitors, so as qualitative and quantitative analysis of the LTA 420 kV circuit breaker implementation in the market. In conclusion, the study shows that the market introduction of the LTA 420 kV circuit breaker is feasible. Although CO2 is not as good an insulation medium as SF6, it is still good and presents strong customer benefits: GWP reduced by over 99.9%, compliance with new regulations, lower cost of ownership, fewer regulatory controls, reduced cost of handling the gas, and well-functioning at extremely low temperatures. The main concerns for Hitachi ABB Power Grids are related to market competition. Thus, it is advisable that the company works on an effective market introduction to assure a large market share.