Power system at transient stability limits

Power system at transient stability limits:  A 220kV double circuit parallel grid power transmission line-1 and line-2 were supplying to an integrated steel plant with a maximum demand of 500MW. Each 220kv grid incomer PCC was connected to 2sets of 155mva, 220kv/33kv grid transformers.  Power Quality measurements were carried-out at the common 33kv secondary bus, wherein all four grid transformers were connected in parallel. High wind swayed a tree over line-1, about 5km upstream of the steel plant.