同步发电机励磁绕组的作用是（   ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69444' and id < 4497155 and id<>'4497155' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69444' and id > 4497155 and id<>'4497155' order by id asc limit 5