From: deanhofman@clod.com   
      
   On 1/3/21 12:03 AM, Michael Moroney wrote:   
   > There is a long HVDC power line from northern Quebec Canada to Ayer,   
   > Massachusetts USA. It operates at either +/- 375 kV or +/- 450 kV   
   > depending on source.  As I understand it, it is grounded at exactly one   
   > point, near Saint-Claude, Quebec. You can see it on this Google   
   > satellite view: https://goo.gl/maps/bnsYcbv9Q3ewmkG49  where the power   
   > line ROW runs diagonally on the right side, and the actual grounding   
   > point is the weird circular shape at the upper right.  Additionally,   
   > multiple conductors (6) run from the ROW to the circle.  The street   
   > view at https://goo.gl/maps/K94ZceiRfUL2ePaU7 shows the huge towers   
   > as well as 4 grounding leads, two at the top of the towers and two   
   > others on wooden poles.  They are on rather substantial insulators.   
   >   
   > Does anyone know any details for this rather odd setup? Why multiple   
   > grounding conductors, and any details of the circular structure?   
   > Do the grounding conductors carry current during normal operation,   
   > perhaps with the line at half power with one side out of service and   
   > the grounding (neutral?) carrying the return current?   
   >   
        You might try the  sci.electronics.design group.  There are still some   
   knowledgeable people there.   
      
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