I am from Nigeria and I was given a month visa to join my husband and children in the UK. I was given a resident permit that will expire in 2019. I want to travel to Portugal with my husband. Do I need a visa extension for my traveling and coming back to the UK?
The 30-day visa is only relevant for your first entry, since your residence permit (BRP) can only be collected in the UK.
Now that you have a valid BRP, you only need that and a valid passport.
Should you lose your BRP sometime, you have to obtain a temporary visa to get back in.
No. With a valid residence permit, you do not need a visa.