Revamping of the making switch protecting the magnetizing winding of the RFX-mod2 experiment

The objective of the thesis is the revamping of the making switch protecting the magnetizing winding of the RFX-mod 2 experiment. The RFX-mod2 machine is briefly introduced, and then the focus is centred on the magnetizing windings supply system. One of the principal units of the system is the PP making switch, that is made for closing impulsive DC currents up to 50kA with voltages up to 35kV, with closing time in the order of few mus. It is currently composed of 3 parallel switches and one of them lacks support from the manufacturer, and replacement with an equivalent is not possible because there are no compatible components commercially available. As a part of necessary RFX-mod upgrades, the switch needs to be substituted, revamping the PP unit. The objective of the thesis is the design of a new solution. The development process requires identification of the appropriate specifications and performance analysis of the current design, as the making switch is an emergency system and as such requires high reliability and internal fault tolerance. In order to identify specifications for the project, a numerical model of the making switch is developed. The numerical model is validated through comparison with data collected from Consorzio RFX on the operation of the current making switch. Initially the experimental data picked to validate the model excludes fault conditions. But the system behaviour under normal operating conditions represents only a part of the requirements for a new solution, so a failure rate/mode analysis in carried out in the next chapter. After the failure rate/mode analysis, the numerical model is validated again using fault operating conditions data. This process is crucial as it provides data on electrical and thermal stresses on components with both normal or faulty initial conditions, and so it provides all requirements for the design of a new solution. After a market inspection, a solution based on commercially available light-activated thyristors is presented. Another device called Ultra Fast Earthing Switch (UFES) is coupled with thyristors in order to enhance fault tolerance. Simulations are used to test the proposed solution, providing i^2t of components and temperature of thyristors. With the use of a four sector model, performance under assorted conditions is compared to the previous solution: results obtained show significant lower temperatures under normal operation and better fault tolerance.