Learn Arabic (Modern Standard): انقطعت الكهرباء أمس مساء. - The electricity was cut off yesterday evening.

You can spot a Form VII verb in the past tense by the prefix انـ (in-). The root of this word is ق-ط-ع (q-T-'), meaning "to cut." When you add the انـ prefix, you get the Form VII base انقطع (inqaTa'a). The ـت at the very end is just the "she" suffix for past tense.

Why does انقطعت translate to "was cut off" instead of "cut"?

Form VII verbs often give a reflexive or passive meaning to the original root. Since the standard Form I verb قطع means "to cut," the Form VII version انقطع means "to be cut" or "to get cut off." It does not need a special passive vowel pattern; the Form VII structure naturally carries this "happening on its own" meaning.

Why does the verb have the feminine ending ـت (-at)?

In Arabic, verbs must match the gender of their subject. The subject here is الكهرباء (the electricity). Even though it is not a person, الكهرباء is grammatically feminine, so the verb takes the "she" form in the past tense: انقطعت.

How do the time words أمس مساء work together here?

أمس means "yesterday" and مساء means "evening." In Arabic, you can combine time words simply by placing them next to each other. Together, they mean "yesterday evening" or "last night."