[2] Portable power system monitors (PPSMs) produced the data on voltage sags and responses at the Garrison and Malin 500-kV substations during the 2 July 1996 outages. Garrison, in western Montana, yielded the best overview of switching actions and dynamic performance in the area east of the Cascades. Malin, on the Oregon-California border, is a key Pacific AC intertie station.

An expansion of that data clarifies reactions to specific events. One example is the tripping of 1000 MW at the Jim Bridger generating station in southwestern Wyoming. Another is the tripping of the crucial Amps line between western Montana and Idaho. This last event prompted the plunge in voltage at Malin. Without the Amps line trip, capacitor banks at Malin would soon have injected the line with up to 400 MVAr, possibly stabilizing voltage at above 500 kV.