Effect of Armature Resistance Upon Hunting of Synchronous Machines

The ability of systems to withstand shocks, such as faults or switching operations, is much greater for small operating angles. The present paper has to do with system stability for small oscillations as contrasted with the more usual concept of stability as being its ability to withstand shocks. The analysis shows that synchronous machines without amortisseur windings and with no resistance in the armature are inherently stable for small oscillations in prime mover input or load output. With resistance in the armature, stability for such conditions is dependent upon load. A new proof is given for the relation previously derived by Nickle and Pierce which states that the limiting angle at which a machine becomes stable is tan ¿1 r/xq. Arguments are presented which show that any standard type of damper which may have been installed in generators for other incidental reasons, possesses the property of preventing spontaneous hunting except for the most abnormal conditions met in practise.