I denna studie utforskar och analyserar vi olika numeriska metoder f?r att l?sa Helmholtz ekvation. Detta ?r av betydelse f?r att f?rst? det elektriska f?ltet i kroppen, vilket kan vara v?rdefullt f?r att identifiera cancertum?rer. Vi j?mf?r konvergensen, effektiviteten och tillf?rlitligheten av 13 l?sare fr?n paketet PETSc, vilka anv?nder olika f?rkonditionerare f?r att l?sa ekvationen.

On a request from the water sewage plant Gryaab in Gothenburg a power quality survey wasperformed. The voltages and currents have continuously been sampled in the incoming 10 kVsubstation HSP01 from April-August 2008. Power quality measurements were also performedin Gryaabs other 10 kV substation HSP04 fed from HSP01 and at the terminals of theinduction motor IN_PU4040 of 1.3 MW which controls one of the four large inflow pumps tothe plant. The reason for the latter measurement was due to registered negative transients eachtime the motor was connected to the grid. The cause of the transients could be explained by thecoupling in the substation, the ageing of the motor which could result in damage of thebearings or resonance in the motor circuit which amplifies high frequency harmonics.