There are a couple of things to consider here. Since there are power lines located on an easement, I personally (for valuation purposes as a buyer) would not consider the land on the easement as part of the property. In other words, pretend the lot is only a ~1/2 acre lot. Some may argue this is not correct, but it is a conservative approach as a buyer.
The other thing to consider is that some people don't like to live next to power lines so it could definitely limit the marketability of the home in the future if you try to resell.
In my opinion, the best thing to do if you definitely want to buy this home would be to find comps in the same area that are also next to the power lines. Feel free to contact me and I would be glad to put together a market report for you on the property and help you find some good comps to review.
If you do go through with the purchase, you can certainly attempt to get a tax abatement, but there are no guarantees so I personally think it would be better to factor everything into your purchase price up front and make sure you are not overpaying for the property.