They do this with large mining machinery such as the drag lines and bucket wheel wheel excavators. They don't move very far so extension cords are acceptable.

They do this with large mining machinery such as the drag lines and bucket wheel wheel excavators. They don't move very far so extension cords are acceptable. And in mining they run portable medium voltage wiring through the tunnels to baby substations. They even make plugs and sockets rated to 15kV or possibly to 35kV, the upper limit for "medium voltage" in NA. Obviously you aren't going around plugging these cables in like they're attached to a reading lamp. They are on disconnects or circuit breakers and the circuit is de-energized before connection or disconnection. Otherwise arcing would destroy the connector. A faulted circuit would cause an explosion on connection likely killing or severely injuring an operator. Electricians working on medium voltage circuits must have medium voltage training and certifications.