Transient performance of series-compensated three-phase self-excited induction generator feeding dynamic loads

Abstract

This paper presents the transient performance of a series-compensated three-phase self-excited induction generator (SEIG) feeding a dynamic load such as a three-phase squirrel-cage induction motor (IM). Mathematical modeling and simulation study of SEIG and an induction motor (SEIG-IM) combination is carried out using MATLAB/Simulink. An exhaustive experimental study is conducted using a Mawdsley's generalized machine operating as a SEIG and a three-phase squirrel-cage IM as the dynamic load. The simulated results are compared with the experimental results under various operating conditions of the SEIG such as the following: 1) its voltage and current buildup at no-load; 2) switching of a three-phase squirrel-cage IM to the SEIG terminals without series-compensating capacitors (resulting failure to start an IM); and 3) switching on the same motor with the series capacitors (resulting in successful starting of the IM). A sudden switching of the IM as a dynamic load on the SEIG without the series compensation causes severe transients in electrical and mechanical variables of the SEIG and due to large starting current requirement of the IM, there is a collapse of the terminal voltage of SEIG. However, the use of series compensation in short-shunt configuration of SEIG results in the successful starting of the IM with an improved voltage regulation of SEIG. The phenomenon of subsynchronous resonance (SSR) is observed due to the large variations in the impedance of the SEIG-IM combination and the presence of series capacitors. It causes low frequency oscillations in the IM stator voltages, currents, and its speed. The SSR phenomenon restricts the IM to attain the rated speed. A detailed study of the SEIG-IM system is made to select proper combination of shunt and series capacitors to avoid the SSR phenomenon.