Analysis of transformer inrush transients in offshore electrical systems

Large transformers are electrically close to generators in an offshore power system. Energising such transformers causes significant inrush currents, which are sustained for several seconds. The voltage dip on the generator bus then initiates a response from the automatic voltage regulator (AVR). Using a numerical simulation, the lightly damped response of the AVR is shown to modify the inrush transient. Other on-line transformers can be sent into magnetic saturation. Site measurements confirm the features of the transient predicted by the simulation. The paper shows that a detailed model is required if the inrush current on an isolated offshore power system is to be correctly predicted.