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The interconnection of the Central Interconnected System (SIC for its initials in Spanish) with the Northern Interconnected System (SING) have been one of the trending topics in the year 2013 in the Chilean electric industry. Two are the projects that are on target for the interconnection; a high voltage alternating current (HVAC) 500 kV connection, proposed by the French utility GDF SUEZ, and a high voltage direct current (HVDC) ±500 kV planned by the CNE, the Chilean electric regulator entity. Both projects have important differences in technology and there's not too much technical evidence of the problems that could arise in the operation, caused by the SIC-SING interconnection. Low frequency oscillations are studied in this work, using modal analysis for both interconnection projects. A SIC-SING model is developed using DigSilent software, considering 2019 as the year of a possible union of the networks. Two generation scenarios are studied; one where the central system (SIC) sends 1.000 MW to the northern system (SING), and another one where the SING sends 800 MW to the SIC. The modal analysis results show that interconnecting both systems with the HVAC gives arise to a 0.5 Hz unstable oscillation mode. This unstable mode has it origin on the interconnection and it's related to a group of steam machines on the SING system. Whether the SIC-SING system is connected with the HVAC or the HVDC, 0.9 Hz weakly damped modes are observed in both systems. These modes are related to the evolution of the systems at 2019. [ABSTRACT FROM AUTHOR]