We consider the impulse surge voltages acting on alternators running in the block with the elevating transformer. The alternators' insulation is not stable, particularly when the block alternators are placed in more severe conditions because the surge voltage waves coming from the line and through the step-up transformer have a direct effect on them. It is interesting to know whether the limitation of the surge voltage waves at the input of the HV winding of the transformer, by means of lightning arresters is sufficient to protect the alternators' insulation. According to the collected results we observe that this limitation is not efficient in the case of alternators and that it is important to connect lightning arresters across the LV winding.