Static electricity is due to the relative movement of 2 materials. I am not sure this would explain your experiences. Perhaps you are experiencing capacative coupling to the 500 kv transmision line. The voltage induced on items placed near the transmission line will be a function of the capacitance from 500 kv line to item and capacitance between item and ground similar to the voltage divider principle. This voltage can be controlled by how well the item in question is grounded. Even poor grounding can be enough to control this induced voltage ( capacitance to ground is typically a very big number so even a poor ground in parrallel can effectively reduce the induced voltage to near zero.)
I have heard of this before from people who get a shock when they touch truck door handles that are parked under high voltage power lines.