Rosenberg dynamo with fixed polarity

The design, construction, and experimental data, of a generator are shown which, while retaining the properties of the Rosenberg cross-field design, ensure fixed polarity by means of a permanent magnet and magnetic shunt. The field and mechanical parts of the machine are of welded mild steel, the only cast part being the permanent-magnet bar. The drooping part, the peak part, and the no-load point, of the current/voltage curve are discussed and the small influence of the regulating pole setting on the no-load voltage is explained. The result of paralleling two machines without an equalizing bar is that one machine is generating and the other, with lower setting of the regulating pole, is motoring with temporarily reversed field. After disconnecting, the correct polarity is re-established owing to the action of the fixed pole. The fixed-pole design can also be used in ordinary plant for exciters.