This system consists of 5 substations, the real-time data and control commands are transmitted between substations through a microwave telecommunication system. The Global Positioning System (GPS) is used to provide an accurate time signal to all substations so that all data can be sampled synchronously at each station. As a result, all recorded data and measured phasors can be analyzed by referring to a common time axis. This system was put into service in 1996 to monitor the Heilongjian Eastern Electric System and to increase its stability by determining the amount of generation to be cut off through the measured frequency. It is the first time China has carried out such a large GPS application in a power system. The field tests show that the strategy based on "off-line simulation and on-line search" can be finished within 180 ms after the fault occurred. This paper shows and analyzes some fault data recorded over two years and estimates the performance of this system. This paper also introduces the methodology to monitor operating states of the power system by using the PQ figure in the generator, the space vector diagram for voltage and phasor diagram based on synchronized phasor measurement (SPM)