I accounted a problem I have a big base and now I get a lot of the purple bubbles(accid bombs?) what when spawn in my base and explode my towers are not attacking it and you can do it only with your personal weapons what still caused an explosion.

so how do i defend against them or is it possible to turn them off because they are really annoying.

And where did they come from ?

It just make no scenes to me to have a unit that it does not matter what you do it destroy your base special when they come in my case every 5 min 3 to 4 bubbles over time your base will be destroy

You need the small observer radars. They let you turrets in an 32 area around the radars attack the bubbles. (I think a better tooltip would be a good thing to make it more clear what they are used for).

They are spawned by the enemy main buildings above a certain level.