采用Yd连接的三相变压器空载运行时，产生主磁通的电流为（   ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69321' and id < 4487851 and id<>'4487851' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69321' and id > 4487851 and id<>'4487851' order by id asc limit 5