Improving transient stability of a synchronous machine by electronic commutation of a neutral capacitor bank

Single pole switching is selected for a radial 200 km, 400 kV transmission line which connects a 270 MVA hydroelectric synchronous motor to the power system. Transient stability of the synchronous motor cannot be maintained when one phase of the circuit is out of service for the length of time required for arc extinction. In this paper, it is shown that inserting a capacitor in the neutral of the motor transformer bank will increase considerably the power transfer during the open phase operation and therefore, the probability of retaining synchronism is greatly increased. The capacitor is inserted in the transformer neutral ground circuit during the open phase period by action on a power electronic device synchronized to the opening-reclosing sequence.