Investigation of starting dynamics of electrical submersible pumps with soft starting

Numerical simulation is utilised to investigate the starting dynamics of electrical submersible pumps (ESPs) with soft starting. The shaft torsional oscillation during start-up is emphasised in this study. The effect of negative damping from the induction motor is demonstrated and explained from a theoretical point of view. A comparison is made with direct online starting and it is concluded that properly designed soft starting is able to attenuate the self-excited torsional oscillation which has been a serious problem associated with ESPs. The impact of supply harmonics introduced by soft starting is also analysed