When the conventional simplified hunting discriminant having x_q, δ and so on is used, the hunting limits of the series capacitor transmission system and equivalent transmission system without a series capacitor are in agreement. But hunting is apter to occur in the series capacitor transmission system judged by detailed calculation of the inverse vector locus. This discriminant is obtained by assumption of no quadrature damper winding. But it has great hunting preventive effects. So, exact hunting discrimination results cannot be obtained in the case of assumption of no quadrature damper winding. As stated above, the conventional simplified hunting discriminant has weak points.
Hunting discrimination should be made at the frequency where the inverse vector locus passes through an imaginary axis. But it has become clear that hunting discrimination can be made roughly accurately by the damping torque coefficient of 0Hz. Based on this fact, the authors have introduced a new simple hunting discriminant for the series capacitor transmission system. The direct and quadrature damper windings have been considered in this discriminant. Naturally this discriminant sometimes gives different results to the series capacitor transmission system and equivalent transmission system without a series capacitor.