This question of yours is as intriguing as it is inane and, attempting to answer this is fraught with the danger of giving a wrong answer to a right question or vice versa. First, let me put the question in perspective before I make any comment. Your question of wanting to be powerful is like someone wanting to be likeable. But for what? For a manager power or for that matter likeability is not an end in itself. They are means to achieve your end of becoming an effective manager. Becoming powerful (with all its negative connotations) cannot be a goal in itself.
Revisiting your question once again I find that you want to be powerful only in HR Department thereby limiting your own ambitions and aspirations. I am not sure if it is a Freudian Slip on your part. For a person looking for a formula to become powerful you should be looking at being a powerful manager and not just a powerful manager of a particular department.
Though I am not attempting to answer your query, I still wish to make a few comments on the same. The first observation is that there are no magic potion or scientific formula to become “powerful” as with any aspect dealing with matters related to human relations. If I am allowed to put it rather crudely, if you want to be powerful in your department you can curry favour with your boss or indulge in office politics. Both are double-edged swords with strong possibilities of generating negative outcomes. You may end up as a powerful boss, albeit a failed one.
Having said what I have, let me also add that power can mean different things to different people. Power is normally seen as an ability to control others. By inference, you get an opportunity to manipulate others. In a positive sense you can be powerful when you are respected for your knowledge and wisdom, a kind of power derived out of your sapiential authority. There are several qualities that have already been talked about by a number of contributors to this post that I do not wish to go over once again. However, for an HR Manager, in my opinion, Trust and Empathy comes on top of my bucket list of essential qualities. You should command respect based on your domain expertise but not demand it based on props like power.
Thank you.
,