单速交流控制 single speed AC control

直流单线制 DC single wire system

控制单播流量 Unicast traffic flow control ; Unicast traffic control ; Control for unicast traffic

单管回流制 one pipe circuit system

单相工频交流制 single-phase industrial frequency AC system

单相低频交流制 single-phase low frequency AC system

换流单元控制 convertor unit control

电子电流限制单元 electronic current-limiting unit

电子式电流限制单位 electronic current-limiting unit