I'm not a professional, and I don't know the course of the second interview. In this case, you'd better come to Polytechnic University to find a tutor and have an interview with him. If he wants you, he will help you in the second interview. The second interview is simple. Don't worry too much. The most important thing is the interview. There is no advantage in foreign professional interviews, so if the tutor helps you, your interview results will be easy to get. The proportion of interview in the second interview is much greater than that of written examination. There is a buddy in my dormitory who is a cross-major He came to the University of Technology in advance and contacted a tutor, so it was easy to get on.
Don't choose too good a tutor. A good tutor doesn't want to be interdisciplinary. Teachers who can take graduate students are not much different. The only difference is that there are many projects. When you come, find a graduate student from the School of Power and ask which tutor is good. You have recruited interdisciplinary students before, so you have a better chance to go to graduate school.
By the way, did the University of Technology let you pay the deposit for the second interview?