Spoofing tests against phasor measurement units demonstrate their vulnerability to attack. A generator trip in an automatic control scheme could be falsely activated by the GPS spoofing, possibly leading to cascading faults and a large-scale power blackout.

Cite and download the article:
D.P. Shepard, T.E. Humphreys, and A.Fansler, "Going Up Against Time," GPS World, August, 2012.