Short Circuits in Synchronous-Machine Armatures

An approximate solution is obtained for the current in a short-circuited coil or group of coils in the armature of a synchronous machine operating under load. The solution is expressed as the sum of a series of harmonics whose terms are in geometric ratio. The results obtained are similar in form to those previously obtained for the short circuit of a complete phase winding, and they reduce to that for the single-phase short circuit in the limiting case when the coil group comprises a complete phase. An experimental check of the theory is given for the case of a short circuit of a single armature coil, and it is shown that close agreement is obtained between theory and test with respect to the fundamental component of current, though not with respect to the small higher harmonics of current.