main source of electric power的用法和樣例：
例句
- Turn on the main source switch, and the Control Unit is now put in work.
打開主電源開關時控制部件將開始工作。 - Three-phase UPS systems are used in most large data centers for power conditioning and battery back-up in the event of mains power failure.
當數據中心一旦發生主電源掉電的時候，三相不間斷電源系統是應用最廣泛的後備電池和供電條件。
