.两台变压器并联运行，空载时二次绕组中有一定大小的循环电流，其原因是(    )。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69521' and id < 4504021 and id<>'4504021' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69521' and id > 4504021 and id<>'4504021' order by id asc limit 5