同步发电机的励磁系统主要作用是（  ）？（0.5）

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69423' and id < 4495212 and id<>'4495212' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69423' and id > 4495212 and id<>'4495212' order by id asc limit 5