In recent years, injection of renewable energy such as solar power in the power grid is increasing. However, inclusion of large-scale intermittent-type renewable energy requires better management in proper understanding of grid's variable characteristics and its protection systems. In this paper, the investigation on overvoltage issue is illustrated. Overvoltage in distribution feeder occurs when large amount of solar power is injected at low power demand. Another investigation is on false operation of overcurrent relays due to reverse power to the 33k V loads. The potential solutions to the two issues are illustarted in the small-sized power grid system using bi-directional inverters on AC buses in charging battery banks and adjusting the relay current settings. The benefits of solar power injection are illustrated whereby output power from generator is decreased and transmission looses are reduced. Electrical Transient Analysis Program (ETAP) was used for investigations.