Discussion at spring convention: Use of frequency changers for interconnection of power system

R. W. Wieseman: I should like to ask Mr. Woodrow about the pull-out torque of this frequency-converter set; this is given as a little over 70,000 kw., or over twice the normal torque of the set. Is this pull-out torque the actual synchronous torque which the set can furnish for an appreciable time or is it the momentary torque of this set which includes the inertia torque of the rotors? The inertia torque is useful in a synchronous motor for a small fraction of a second only. The energy stored in the rotors of this frequency-converter set could furnish over twenty times normal load for but a few cycles. However, the limiting feature of the power output of the set is the ability of the generator to transmit power to its system. The power output of the generator, for a fraction of a second, is limited by the leakage impedance and not by the synchronous impedance because the generator magnetic flux can not change quickly and therefore it cannot be influenced by the opposing armature magnetomotive force. Thus, only two or three times normal load can be delivered by the generator for a small fraction of a second.