Patent ID: 8340931

Claim:
A method for monitoring the stability of a power transmission system at a monitoring location by referencing geographically remote nodes; comprising: (a) taking a first sample of an AC power line parameter at a first node location using a first monitor to produce a first phasor representing the AC power line parameter at the first node, (b) taking a second sample of an AC power line parameter using said first monitor after a first time interval to produce a second phasor representing the AC power line parameter at the first node, (c) calculating from the first and second phasors, the product of one times the complex conjugate of the other, and using the result to produce a phase difference indicator for the first node; (d) sending the phase difference indicator for the first node to the monitoring location over an electronic network; (e) taking a third sample of an AC power line parameter at a second node location geographically remote from the first using a second monitor to produce a third phasor representing the AC power line parameter, (f) taking a fourth sample of an AC power line parameter at the second node using said second monitor after a second time interval to produce a fourth phasor representing the AC power line parameter at the first node, (g) calculating from the third and fourth phasors, the product of one times the complex conjugate of the other, and using the result to produce a phase difference indicator for the second node; (h) sending the phase difference indicator for the second node to the monitoring location over said electronic network; and (i) calculating a first relative phase change rate indicator using at least a first processor at the monitoring location from the phase difference indicators of the first node and the second node.