Dynamics of a Turbo-generator Driven by DC Motors During Off-line Three-phase Sudden Short Circuit

Abstract

This article reports the responses of a turbo-generator driven by separately excited DC motors when the former is subjected to a sudden short-circuit test. Such setups are usually arranged in test rigs of generator manufacturers and electrical machines laboratories, where DC motors are used as the prime mover. Sudden short-circuit tests on turbine generators offer a short-circuit current spectrum that can be used to extract operational impedances and time constants of the generator. The sets of differential equations representing the DC motors, coupling system, and generator are appropriately solved together to obtain the responses. The results show the machine and system dynamics under damped and undamped shaft coupling. Transient parameters of the generator are extracted in each case and compared. The influence of speed departures on shaft torques and current waveforms are also studied. These results suggest that short-circuit tests can be performed at rated voltages if the couplings can be designed so as to absorb the high short-circuit torques developed during sudden short-circuit tests.

Keywords:

• turbo-generator
• sudden short-circuit test
• shaft torques
• transient behavior