My initial guess would be the immense electric field around the lines, that causes hair to get charged and due to each hair having the same charge they start to repel each other.
So what is exactly happening here?
I believe the mechanism is somewhat different: the electric field polarizes, rather than charges, hair, and then acts on the resulting electric dipoles, judging by the formulas in: "Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference, Shanghai, China, September 1-4, 2005", p. 4266. "Analysis of Body Hair Movement in ELF Electric Field Exposure", H. O. Shimizu, K. Shimizu. According to the formulas, it is essential that the electric field is not uniform. The authors claim good agreement with experimental results.