The diploma thesis presents a comparison of silver and copper fuse elements used in high-voltage fuse-links. Due to its very good electrical and thermal conductivity, chemical stability, and predictable behaviour under thermal loading, silver is used as a reference material for the production of fuse elements. However, because of the high price of silver, there is an increasing need in industrial practice to search for technically suitable and more cost-effective alternatives. Therefore, three types of copper were investigated in this thesis: Cu-ETP, Cu-OF, and Cu-PHC.
The theoretical part presents the basic operating principles of high-voltage fuse-links, their construction, and the key electrical, thermal, mechanical, and chemical properties of silver and copper. Special emphasis is placed on the influence of copper oxidation, microstructural changes, and the stability of electrical resistance under repeated thermal loading. Based on the theoretical properties, it was expected that Cu-OF would show the best results among the copper materials, mainly due to its very low oxygen content and high electrical conductivity.
For the analysis of the electro-thermal and mechanical behaviour of the fuse element, a numerical model was developed in COMSOL Multiphysics. The model was calibrated using experimental temperature measurements on the ceramic tube and on the fuse element. The model was used to determine the temperature conditions, mechanical stresses, and the conditions for accelerated cyclic testing. The simulation results showed that the highest mechanical stresses occur at the weakened sections or bridges of the fuse element, where the highest material loading is expected due to the reduced cross-section and local heating.
In the experimental part, 24 kV / 40 A high-voltage fuse-links were produced with fuse elements made of silver and selected copper materials. The samples were subjected to cyclic thermal loading, during which the voltage drop was monitored as an indicator of changes in electrical resistance and the stability of the fuse element. The results showed that, with appropriate geometry adjustment, copper fuse elements can approach the behaviour of a silver fuse element in basic electrical tests. However, greater differences between the materials appeared mainly during longer cyclic testing.
Among the analysed copper materials, Cu-PHC unexpectedly showed the best results. It exhibited the most favourable voltage drop behaviour, good stability throughout the cycles, and the longest service life among the copper samples. An additional tensile test showed that Cu-PHC withstands a significantly larger displacement before fracture than Cu-OF and silver, indicating greater mechanical compliance of the material. This property is important during cyclic heating and cooling, as the fuse element is subjected to repeated thermomechanical loads under such operating conditions.
Visual analysis of the fuse elements after testing showed that Cu-ETP exhibited the most pronounced oxidation changes, dark spots, and locally degraded areas. In Cu-OF, the oxidation changes were less pronounced, while Cu-PHC, despite undergoing a higher number of cycles, showed more uniform surface degradation and less pronounced locally oxidized areas. Even after cyclic testing, silver maintained the most stable surface condition and showed no characteristic signs of oxidation, which were present in the copper samples.
Based on the performed simulations, measurements, and analyses, it was found that silver remains the most reliable material for the production of fuse elements in high-voltage fuse-links. Nevertheless, the results show that, among the investigated copper materials, Cu-PHC is the most suitable alternative for further development testing. Due to its stable electrical behaviour, good mechanical compliance, less pronounced local oxidation, and the longest service life among the copper samples, Cu-PHC represents the most promising candidate for the possible replacement of silver in the selected design of a high-voltage fuse-link.
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