A gearbox and flexible shaft system is used to link a testing generator to a load commuted inverter (LCI) driven multi-phase motor. The generator sudden short circuit test normally causes severe electric and mechanical oscillations. A sudden short circuit may cause a significant torque oscillation. This oscillation may break the shaft and gearbox. Hence a system level electromechanical model is built and its analysis is conducted. The system natural frequency, required damping factor, and electric/mechanical torque flow and distribution can be observed. The system analysis as presented is also important for other electromechanical system, such as wind turbine system.