Short circuit or electrical fault analyses are performed with the motor speed adjusted so that the applied electrical frequency is coincident with the torsional resonant frequency to produce the maximum dynamic torque (conservative assumption). For the short circuit analysis, the motor air gap torque as a function of time is usually obtained from the motor manufacturer.
A line-to-line short circuit is a short between two of the phase circuits while the motor is running. It produces a braking torque which has fundamental and second order frequency components. On the other hand, a three phase short circuit produces a braking torque at the fundamental with no second order.
A non-synchronous short circuit is a short that occurs when the generator is synchronized when a phase difference between the generator and network voltages exists. It produces a braking torque which has a fundamental electrical frequency component. Proper controls can prevent the occurrence of a non-synchronizing short circuit.
