In multi-machine power systems, it is practically impossible to represent the entire system in detail, thus there is a necessity to resort to some equivalency to suppress detail. The most common practical method used to derive reduced models of large power grids is based on the concept of coherency and aggregation. This paper presents a newly proposed technique to identify the coherent groups of generators, which is suitable for real-time application, using the synchronization coefficients. The technique is based on a proposed coherency criterion introduced by using the weighted complete graph model that reveals the relationship between the synchronization coefficient and the integrity of the connection grid lines in power systems. The presented technique is applied on the IEEE 39 bus system. The obtained results proved that the proposed technique is fast, simple and highly effective in determining the coherent groups of generators and the integrity of connection grid lines.