变压器差动保护的差动元件通常采用比率制动特性，引入外部（   ）作为制动量。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69380' and id < 4491629 and id<>'4491629' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69380' and id > 4491629 and id<>'4491629' order by id asc limit 5