當市電(dian)(dian)供電(dian)(dian)中斷或市電(dian)(dian)電(dian)(dian)壓(ya)超限 (±15%或±20%額定輸入電(dian)(dian)壓(ya))時,互投(tou)裝置將立(li)即投(tou)切(qie)至逆(ni)變(bian)器(qi)供電(dian)(dian),在電(dian)(dian)池組所提供的(de)直流能(neng)源的(de)支持下,此時,用戶負(fu)載所使用的(de)電(dian)(dian)源是通過EPS的(de)逆(ni)變(bian)器(qi)轉換的(de)交流電(dian)(dian)源,而不是來自市電(dian)(dian)