高频保护的载波频率低于50kHz时，将对保护信号（    ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69378' and id < 4491491 and id<>'4491491' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69378' and id > 4491491 and id<>'4491491' order by id asc limit 5