A peninsular power company's extra high voltage (EHV) transmission grid and the rest of the country behave as a two machine system for the following two types of disturbances loss of a large generator in the southern region of the peninsular power company faults on the 500 kV interconnections between the two systems Whether the two systems will remain stable relative to each other or go unstable depends on the following three factors • severity of the disturbance • loading on the peninsular power company's EHV transmission grid • amount of power imported from the rest of the country For stable oscillations the two systems must remain coupled at them 500 kV interconnections. For separations the two systems should be immediately isolated from one another at their 500 kV interconnections. Since these two systems behave as a two machine system for these two types of disturbances the extended equal area criterion(EEAC) is used to make an extremely quick and accurate prediction of the relative stability between them. For stable oscillations following a disturbance, circuit breakers at the 500 kV interconnections are blocked from tripping. For separations these circuit breakers are tripped. EEAC requires synchronized voltage phasor measurements at two specific locations within the overall electrical power system. The two sites are substations located on opposite sides of the electrical center of the two systems. The voltage angle at each location's electric bus will swing with respect to its equivalent machine. This information is constantly recorded to monitor the relative stability of the overall system. When a disturbance does occur, a prediction is made and the appropriate control actions are issued. / Master of Science