Made available in DSpace on 2015-03-26T13:35:25Z (GMT). No. of bitstreams: 1 texto completo.pdf: 2832975 bytes, checksum: 755c3758e19c43f9d50b4a5fdc3052f6 (MD5) Previous issue date: 2007-07-20 / Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The objective of this work is to verify through an experimental research of the Randorn Fuse Model, how the orientation and disorder of the fuse network influence the process of fracture of a network. To execute the experirnents a circuit of size L x L was created, with the connections among the fuses orienteded by 45° with the direction of the applied potential difference. Two types of wires were used as fuses: copper wires and steel wool wires. The experirnents consisted in applying a potential difference V in the network and to measure the current I. The results were analyzed with the objective of determining their scaling laws changing the disorder or the network size. It was concluded that even for the totally disordered networks scaling laws were not observed. It was verified that for a fixed current above a certain critical current the electric resistance of the network intreases as a power law in time and also that the rupture time of the network decreases as a logarithmic law with the current for values slightly above the critical current, while for currents much larger than the critical current the rupture time decreases as a power law. / O objetivo deste trabalho é verificar, através de um estudo experimental do Modelo Aleatório de Fusíveis, como a orientação e a desordem da rede de fusíveis influenciam o processo de fratura da rede. Para a efetivação dos experimentos foi criado um circuito de tamanho L x L, com as ligações entre os fusíveis orientadas à 45° da direção de aplicação da diferença de potencial. Foram utilizados dois tipos de fios como fusíveis: fios de cobre e fios de palha de aço. Os experimentos consistiram em aplicar uma diferença de potencial V na rede e medir a corrente I. Os resultados obtidos foram analisados com o objetivo de se determinar suas leis de escala quando a desordem ou o tamanho da rede eram variados. Concluiu-se com os resultados que mesmo para as redes totalmente desordenada não foram observadas leis de escalas. Verificou-se ainda que para uma corrente fixa acima de certa corrente crítica, a resistência elétrica da rede aumenta como uma lei de potência do tempo e também que o tempo de ruptura da rede decai como uma lei logarítmica da corrente para valores de corrente pouco acima da corrente crítica, ao passo que para valores de corrente muito acima da corrente crítica o tempo de ruptura decai como uma lei de potência.

The determination of the pre-arcing time of a fuse given a specific current is crucial during the selection process if the fuse is to be effective for the given application. Often the data supplied by the manufacturer is enough to determine this time, however this is not always the case. For this purpose a fuse model of a diazed fuse has been developed in order to simulate the pre-arcing times in the range of 2 ms to 2 s. The model is implemented in MATLAB and simulates the pre-arcing time for a given current together with fuse parameters such as the materials and the geometry of the fuse. The model has been tested experimentally by running specific currents designed to represent a wide variety of currents which a fuse might be subjected to. The tests were done on 10A gG fuses for which the current through the fuse was logged and then used as input to the fuse model, the simulated time and the measured time was then compared. The simulated times are in general faster than the measured pre-arcing times, this is mainly due to the rate of change of thermal conductivity of the sand with respect to temperature being approximated in conjunction with thermal radiation not being taken into consideration. More testing needs to be done to validate the model for different current ratings and fuse-element designs. / Att bestämma smälttiden för en säkring som utsätts för en given ström är viktigt för att kunna avgöra om dess prestanda är tillräcklig för en viss applikation. I de flesta fall är det möjligt att använda tillverkarens data tillsammans med vågformen för att bestämma smälttiden, men det kan även inträffa att detta inte är möjligt. För dessa fall har en modell av en diazed säkring utvecklas för att simulera smälttiden inom 2 ms till 2 s. Modellen har implementerats i MATLAB och beräknar smälltiden för en given ström och parametrar för säkringen. Modellen har testats experimentellt genom att säkringar har utsatts för en mängd olika strömmar som representerar de olika strömmar som säkringen kan utsättas för. Testerna gjordes på 10 A gG säkringar där strömmen genom säkringen loggades för att sedan användas som ingångsvärde till modellen, tiderna för den uppmätta smälttiden och den beräknades smälltiden jämfördes sedan. De simulerade smälttiderna är lägre jämfört med de uppmätta, detta beror dels på att förändringen av värmeledningsförmågan med temperaturökning hos sanden är okänd och är uppskattad från referenser och dels på att värmestrålning inte har ingått i modellen. Mer tester behöver utföras för att validera modellen mot fler strömstyrkor och designer. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm