Synchronized phasor measurements have become an important technology with several international manufacturers offering commercial phasor measurement units (PMUs) which meet the prevailing industry standard for synchrophasors. With the occurrence of major blackouts in many power systems around the world, the value of data provided by PMUs has been recognized, and installation of PMUs on power transmission networks of most major power systems has become an important current activity. This paper presents a transmission line protection scheme based on synchronized phasor measurement units to detect (predict) out of step condition using equal-area criterion which is consistent with transient energy function method for single machine-infinite bus system or two machines system. This scheme uses the measured values of voltages and currents, as complex values, at the generator bus and at the infinite bus. These values of voltage and current are measured in time domain and transformed into phasor domain by using Discrete Fourier Transform to calculate the required areas. The proposed scheme can be used for the detection of out of step condition using equal area criterion with different types of faults at different locations and different models of transmission lines.