115,000-Kw. Turbo-Alternator

Due to the increasing use of large single-shaft steam turbine units, it has been necessary to design very large generators operating at 1,800 r.p.m. The present paper describes a 115,000-kw. unit recently placed in operation. The generator is wound for 18,000 volts and the whole output of the machine, with the exception of a small part used for the operation of auxiliaries, is stepped up to 182 kv. and all switching is done on the high-voltage side of the transformers. It was possible, therefore, to design the generator for a voltage that would permit a simple two-conductor per slot winding. On account of the great axial length of the machine, ventilation required careful study and a new scheme of rotor ventilation was developed to secure uniform cooling throughout the length of the long rotor body. The stator ventilation is of the inward-outward parallel flow type with fourteen parallel paths in each half of the stator. Air circulation is provided by four single inlet motor-driven blowers mounted under the generator. A fin type radiator cooler is mounted under the generator yoke and condensate is circulated through the cooler. Excitation is furnished from a 350-kw., 250-volt coupled, shunt-wound exciter and a 7½-kw. overhung pilot exciter is used to excite the fields of the main exciter.