Is it normal that what I studied in my bachelor's and master's is rarely useful to my PhD?
It's quite normal for your bachelor's and master's studies to have little, if any, influence on your PhD research, particularly in the sciences and engineering. I think this is especially true in engineering, as the contents of engineering curricula tend to be more "conservative" than the research ongoing in most departments. 

Moreover, though, one of the skills you need to learn to survive as a research professional is the ability to learn a brand new topic to which you have not previously been exposed. This is because it's quite likely that you'll move into another research area multiple times during your professional career, and the only way to figure out what makes for good research in the field is to become an expert in it. So studying something brand new in your PhD is not only not a problem, it represents a great opportunity for your future career.