Electronic – Why the arc when bonding-on during high voltage repairs

groundinghigh voltagerepair

When working on high voltage power-lines via helicopter the technician will "bond-on" with a steel wand called a hot-stick. During this process an arc is conducted from the line to the wand. Now, since the helicopter is floating both literally and electrically, why is there any potential between the line and the wand?

My guess is that because of the alternating electric current in the power-line there is therefore an alternating expanding and collapsing magnetic field present in close proximity to the helicopter. This sets up a charge polarization in the frame of the helicopter 180 degrees out of phase with the current and therefore an electrical attraction occurs which produces an electric potential.

If this is true, even though the electrons are not free to move in a bird (as they are in the metal helicopter frame) they are able to rotate and still set up a charge polarization (much like a charged balloon sticks to a wall) and therefore when a bird "bonds-on" to a wire don't you think they feel a little tingle at first?

One other thing. Is it true that by virtue of the fact the the helicopter circuitry is an isolated one, they can bond-on to either line and that line will be the ground reference for the ground of the helicopter circuitry?

Best Answer

This question is somewhat related to yours.

The phenomenon has nothing to do with magnetic fields. There is an intense electric field around any high-voltage wire (AC or DC), and the intensity is inversely proportional to the distance from the wire. At very close distances, the intensity exceeds the breakdown threshold for the air itself.

The presence of the conductive helicopter (and the repairman with his metal mesh suit) distorts this field, concentrating it even further in the space between the wire and the helicopter. When the bonding strap gets close enough, an arc forms. The current in this arc is limited by the overall capacitance of the helicopter.

Once the bonding connection has been made, the helicopter and the mesh suit are all at the same potential as the line itself. The electric field is still distorted, but now the concentrated areas are moved away from the repairman and the connection between the wire and the helicopter.

And regarding the birds, when have you ever seen a bird sitting on one of these high-tension transmission lines?