当电力系统中发生不对称故障时，破坏三相系统运行状态的对称性，这时可采用()。（0.5）

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69421' and id < 4494916 and id<>'4494916' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69421' and id > 4494916 and id<>'4494916' order by id asc limit 5