A method for monitoring a power grid uses power line sensors to measure time-stamped data representing AC current carried by the power grid at a multiple locations on the power grid, communicates the measured data from the power line sensors to a grid analysis device where the data measured by the power line sensors is synchronized and unwrapped to produce absolute phase data. The absolute phase data is then analyzed to generate predictions of instability of the power grid. The resulting unwrapped angle could also be called the “angle distance” from the reference.