Simolap Mini-hydro Power Plant (MHPP) is one of the power plants that will be built in Humbanghasundutan Regency in North Sumatra Province. The MHPP will operate by injecting its power to Humbanghasundutan distribution power system. The interconnection of Simolap HPP, require in-depth technical grid study to see the impact of the interconnection of the Simolap MHPP to the performance of the electrical system, especially in North Sumatra. Several parameters that will be analyzed in detail are Generator Synchronization, Load Flow Analysis, Losses Reduction, Short Circuit Analysis, Protection Study, Drop/ Over Voltage Study, Network Analysis, Grounding Review, and Anti-islanding Scheme. All of those studies were conducted to analyze the impact of the MHPP operation to the distribution system of North Sumatra power system.