This paper presents transient performance of an isolated three-phase self-excited series connected synchronous generator (SESCSG) subject to sudden switch off an excitation capacitor. The SESCSG has its stator windings and rotor windings connected in series but with different phase sequences. The Y-connected excitation capacitor bank is assumed to be properly connected at the machine's stator terminals. An approach based on a three-phase induction machine model is employed to derive dynamic equations of the studied SESCSG. Experimental results obtained from a laboratory 1.1 kW induction machine driven by a DC motor are also performed to confirm the feasibility of the proposed method. An eigenvalue scheme is also employed to examine the dynamic characteristics of the SESCSG when one of the excitation capacitors is lost. It can be concluded from the simulated and experimental results that the unstable oscillations of the SESCSG may happen when one of the excitation capacitors is suddenly switched off.