Perfect power system voltage stability is not possible in practice. Generally, the power grid is continually exposed to changes in its load and operating conditions. Therefore, dynamic stability analysis is one the most important and effective elements for greater security and reliability of planning, design, operation and economic aspects of electric power networks. This paper investigates and reports dynamic stability of power system with large-scale photovoltaic system (L-S PV). Two different scenarios with centralized PV power plants are considered at medium voltage level without voltage regulation capabilities. The simulation results offer details of the simulation investigations which show that voltage stability impact of L-S PV decreases based on the bus status, disturbance location, and disturbance duration. In addition, the paper discusses network terminal voltage, generator's rotor angle, generator's terminal current, generator's reactive power and output electrical power.