A rede elétrica falhou durante a tempestade.

Because a is the feminine singular definite article, meaning the.

In Portuguese, definite articles are used more often than in English. So where English says The power grid failed..., Portuguese naturally says A rede elétrica falhou...

Here:

• a = the
• rede is a feminine singular noun

That is why it is a rede, not o rede.

In Portuguese, adjectives usually come after the noun.

So:

• rede elétrica = electrical grid / power grid
• noun: rede
• adjective: elétrica

This is the most normal word order. Putting the adjective before the noun is sometimes possible in Portuguese, but it usually sounds literary, emphatic, or changes the nuance. In this case, rede elétrica is the standard expression.

Because it agrees with rede, which is a feminine noun.

Portuguese adjectives must agree with the noun in:

• gender: masculine or feminine
• number: singular or plural

So:

• rede = feminine singular
• adjective must also be feminine singular → elétrica

Compare:

• a rede elétrica
• o sistema elétrico

The adjective changes because sistema is masculine, while rede is feminine.

The accent mark shows the stressed syllable and helps indicate pronunciation.

elétrica is stressed on lé:

• e-LÉ-tri-ca

Without the accent, a learner might stress it wrongly.

In European Portuguese, this word is pronounced differently from English and also somewhat differently from Brazilian Portuguese, but the accent clearly tells you where the stress goes.

Falhou is the pretérito perfeito simples, which is the normal simple past for a completed event.

It comes from the verb falhar:

• eu falhei
• tu falhaste
• ele/ela falhou
• nós falhámos
• vós falhastes
• eles/elas falharam

In this sentence, falhou presents the failure as a completed event that happened during the storm.

Because falhou refers to a specific completed event.

• falhou = failed / went out / stopped working at some point
• falhava = was failing, used to fail, or would fail, depending on context

So:

• A rede elétrica falhou durante a tempestade = one completed event
• A rede elétrica falhava durante as tempestades = it used to fail during storms / it was failing during storms

For a single incident, falhou is the natural choice.

Yes, but in this context it means something like:

• to fail
• to go down
• to stop working
• to cut out

For systems, machines, electricity, internet, brakes, etc., falhar often means malfunction or stop functioning properly.

Examples:

• O motor falhou.
• A internet falhou.
• Os travões falharam.

So in this sentence, falhou refers to the electrical system failing, not a person failing at a task.

Because rede elétrica is more specific.

• eletricidade = electricity in general
• rede elétrica = the electrical network, grid, or power supply system

So:

• A eletricidade falhou can be understood, especially in everyday speech, as the electricity went out
• A rede elétrica falhou sounds a bit more technical or formal, focusing on the system itself

Both can work, but rede elétrica points more clearly to the infrastructure.

Durante means during.

It introduces a period of time in which something happened:

• durante a tempestade = during the storm

It is followed directly by the noun phrase:

• durante o jogo
• durante a noite
• durante a reunião

It is a very direct equivalent of English during in this kind of sentence.

Sometimes, but the meaning is not exactly the same.

• durante a tempestade = during the storm, focusing on time span
• na tempestade = literally in the storm or during the storm, but it can feel less precise here

For time expressions with events, durante is often the clearest choice.
So A rede elétrica falhou durante a tempestade is the most straightforward version.

Because tempestade is a feminine singular noun.

So it takes:

• a tempestade = the storm

Like many Portuguese nouns ending in -dade, it is feminine:

• a cidade
• a liberdade
• a tempestade

Yes. A very common alternative is:

Durante a tempestade, a rede elétrica falhou.

This is also correct. It simply puts the time expression first.

Both are natural:

• A rede elétrica falhou durante a tempestade.
• Durante a tempestade, a rede elétrica falhou.

The difference is mostly one of emphasis and information flow, not grammar.

A careful European Portuguese pronunciation would be roughly:

a rred(ə) e-LÉK-tri-kɐ fa-lyô du-RAN-t(ə) a təm-pə-STAD(ə)

A few useful points:

• rede often sounds closer to rede with a reduced final vowel
• elétrica has the stress on lé
• falhou contains lh, which is like the lli in some pronunciations of million, but smoother
• unstressed vowels are often reduced in European Portuguese
• tempestade is stressed on the last strong syllable: -sta-

If you want a simpler learner-friendly guide:

• a RE-de e-LE-tri-ca fa-LHOU du-RAN-te a tem-pes-TA-de

Not exactly.

• rede elétrica = the electrical network/grid
• energia elétrica = electrical energy / electric power

So in this sentence:

• rede elétrica focuses on the system or infrastructure
• energia elétrica would focus more on the electricity itself as a type of energy

That is why rede elétrica is the better match when talking about a grid failure.