I made my master's thesis in the development department of switches in ETI d.d. My task was to design and optimize a new circuit of a differential circuit breaker EFI 003 type A. In the first part, I decscribed the importance and principal operation of the differential switch. Then I made measurements of parameters on the existing differential circuit breaker and used the results to build a model in Multisim. To optimize the final assebly procedure, I wanted to use only one primary turn on the differential transformer, so I used an appropriate core and then determined parameters of the circuit and also selected a suitable trigger relay. With appropriate selection of parameters, the breaking currents of the new differential circuit breaker are inside the limits, that are defined by standards (EN 61008 and IEC 61008), which was also verified with measurements on real differential circuit breaker.
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