Operating Experience with Shaft-Driven Exciters in Air and Hydrogen [includes discussion]

Abstract

I N THE past several years papers have been presented covering new types of excitation for generators, and the major reason given for abandoning the customary shaft-driven or direct-connected exciter is that the latter is unreliable and requires too much maintenance. Since the American Gas and Electric Company has provided shaft-driven or directconnected exciters on all generators and large synchronous condensers purchased since 1936 and on most of the generators installed prior to 1931 on the basis that shaft-driven and direct-connected exciters are most reliable, it was decided that to demonstrate this, a very careful resurvey of exciter operating experience was in order. As a result data were obtained covering the operation and maintenance of practically all such exciters in service. The data confirm what was known already: that the experience has been most satisfactory and that outside of trying new developments for more or less experimental purposes, there is no good reason to consider at this time the use of special excitation schemes with the idea of eliminating commutator and brush difficulties.The survey which the company made covers 72 generator exciters installed from 1917 to December 31, 1951. Since 1937, 33 turbogenerators have been placed in service and these installations include 25 direct-connected main exciters, 9 gear-driven main exciteis, and 18 pilot exciters. The record of operation and maintenance on these machines has been reviewed in detail. The following information was obtained for each machine: 1. The operating hours. 2. The outages in which the exciter was involved. 3. All maintenance work, major and minor, which was performed. 4. Schedule of routine inspections. 5. Data on brush wear. In addition, discussions were held with the plant superintendents and plant electricians regarding the machines and the problems they have encountered with them. Twenty machines installed prior to H. B. MARGOLIS ASSOCIATE MEMBER AIEE 1931 also were studied and a discussion of these is included in this paper. For these machines, operating data and outage records were obtained. In these cases, however, the age of the machines made the accumulation of detailed and exact information difficult or impossible. Also, it was felt that the period from 1937 to date covers exciters which are more representative of modern-day practice and experience.In 1941, largely as a result of satisfactory perfonnance with direct-connected exciters, the first hydrogen-cooled exciter directly connected to an 18,750-kva hydrogen-cooled synchronous condenser was placed in service at Muncie, Ind. Since that time 10 similar units have been placed in service. Information on these exciters similar to that for the generator exciters was obtained. Experience with these exciters running in hydrogen has been even better than that with the aircooled machines. No forced outages have resulted and the brush wear has been extraordinarily low so chat the maintenance and inspection program has been relatively simple.In this paper several typical i...