The accident that household electrical appliances in dozens of private houses failed happened several years ago. It seems to be caused by the abnormal voltage rise which resulted from a self-excitation phenomenon due to a condenser installed for power factor improvement of three-phase induction generators. In order to make this case clear, we considered theoretically and experimentally the outbreak of a self-excitation phenomenon of a condenser by using an experimental machine in this paper. The result made it clear that a self-excitation phenomenon was easily generated in single-phase alternating current load compared with in three-phase one. Therefore, it is possible to consider that the self-excitation is promoted by new electromotive force induced by the magnetic field for a component of negative-phase sequence.