S? d?ng cho h? th?ng ?i?n h? th? khi ngu?n c?p ph? t?i b? gián ?o?n B? chuy?n m?ch t? ??ng, giám sát và chuy?n ??i gi?a hai ngu?n ?i?n Chuy?n m?ch 3 v? trí I - O - II  – It pressured the trustworthiness by adopting a streamlined type which is a straightforward and clear form.– T? ??ng kh?i ??ng ho?c d?ng ho?t ??ng ( c?a DG ) khi ngu?n ?i