This uses "completed" as a past-participial adjective. The installation has completed. This uses "complete" as an intransitive verb like "finish" - a usage which is becoming more common. Traditionally it would be "has been completed".

Has been completed VS was completed?

Both are 'correct'. The first indicates the finished action; the second indicates the present condition. The work has been completed is it right or wrong?

Which is correct completed or completed?

Both are correct. Which you would use depends on what you are trying to say. I completed my undergraduate education at Columbia in 1966 is a simple statement about an act in the distant past. The verb is in the simple PAST.