Selection of Capacitors for the Self Excited Slip ring Induction Generator with External Rotor Capacitance

Abstract

The self regulating feature of a Self Excited Induction Generator (SEIG) by connecting additional capacitors is examined with the slip ring induction generator. The system consisting of external rotor capacitors at rotor has been analyzed. A methodology has been explained to choose appropriate set of values of these rotor capacitors for desired voltage regulation. Based on the steady-state equivalent circuit model, consideration of the circuit conductances yields a 7th-degree polynomial in the frequency. The polynomial can be solved for real roots, which enables the value of C, to be calculated. Critical values of load impedance and speed, below which the machine fails to self-excite irrespective of the capacitance used, are found to exist. Closed form solutions for C are derived for different loads. Using the Same numerical approach, an iterative procedure is also developed for predicting the capacitance required for maintaining the terminal voltage at a preset value when the generator is supplying load. Results of a detailed investigation on a conventional 3.5 kW induction motor operated as a SEIG are presented to illustrate the effectiveness of the proposed method. Close agreement between predicted and test results has been observed thereby establishing the validity of the analysis carried

Keywords: capacitance requirements, self-excitation, slip ring induction generator, external rotor capacitance