Good question. I've been googling and found nothing. I think it means that they had regional power grids running with emergency links between them (nearest nei

Good question. I've been googling and found nothing. I think it means that they had regional power grids running with emergency links between them (nearest neighbour basis?) already in case a large part of the generating capacity in one region was lost or in case a site near the boundary of one region became disconnected from that region's main line. One night they decided to try to activate all the inter-regional links so that power from all the power stations was available across the whole country. I got confused by the 'in parallel' bit, but then you would hardly be connecting them in series! The grids would have been 3-phase and the frequency was controlled to be near exactly 50 Hz, but then you would have to synchronise the phase of each pair of grids before you made the link active... Any electrical engineers around? This historical incident would make a good magazine article I think.