Jerk in Power plants due to breakdown of transmission line
When a transmission line suddenly becomes unavailable (trips due to fault) this can cause sudden frequency change in the system due to imbalance of supply to demand.  Some types of plant are very sensitive to frequency and a change of more than a few hz in system frequency can cause significant plant damage. For this reason they are usually equipped with frequency protection and the plant will trip if the system frequency becomes too high or low. The 'jerk' referred to here could be the mechanical effect on the plant caused by the change in frequency.