Usually, high power lines near a property will reduce its value. Lines running through a property almost certainly will. Further, in addition to reducing the value, those lines will make the property less desirable. So some people who might have bought the property now won't even consider it, regardless of price.
It's impossible to say whether the property you're looking at is already priced to reflect the power lines. Maybe yes, maybe no. Your Realtor can tell you. But if you buy it, you have to make sure you're getting a good value. And you have to recognize that it probably will be more difficult to sell when you want to sell it.
Finally, it's likely that the power company has an easement where the power lines run. Easements, too, can reduce the value of the property. Your Realtor can explain that in more detail.
Hope that helps.