الفهرس 
Review of The Available LiteratureOnly 14 pages are availabe for public view
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Abstract
Presence of the brushes in the field circuit of aconventional synchronous machine gives rise to number of problems and disadvantage8 which can be summarized in the following points :
1) Limitation of output power ssociated with brush design which means building of high ratings is limited by the esign of field circuit.2) Need for frequent maintenance and brush replace¬ment due to wear in both brushes and slip rings.
3) The maoh1neis not suited for service in hazar¬dous areas due to possibility of sparking For avoiding these roblems, research work was devoted to furnich the synchronous machire with the required D.C. field ezo~tet10n through other means rather than the con¬-ventional brushes.Severalinvestigators(1,~,3,4,5,6,7,8,9jlO,11;12), dealt with the mentioned aspects.Some of them(1,2) have engaged themselves in resenting brushless -alternators, in which D.C.current needed for the field excitation is sup-plied to the field oircuit via no brushes, others (3,4)have