cut off electricity

shut off electricity

turn off electricity

black-out

power failure;

electric power cut

```Suddenly the electricity was off``` (突然停电了）

```electricity was broken off``` 可以涌来表达电源断掉了，这种说法用得比较少,表达突然断掉

break off 本身是一个比较形象上的词，表达的更像是circuit（线路）断掉了