Insulator strings supporting a 225 kV power transmission line near Fessenheim nuclear power station, France.  The metal rings around the top and bottom of the insulators are called <a href="https://en.wikipedia.org/wiki/corona_ring" class="extiw" title="en:corona ring">corona rings</a>.  They serve to reduce the potential gradient at sharp points to prevent <a href="https://en.wikipedia.org/wiki/corona_discharge" class="extiw" title="en:corona discharge">corona discharge</a>, a leakage of current into the air.
<ul><li>original: Jean-Pierre Daniel</li>
<li>derivative work: <a href="//commons.wikimedia.org/w/index.php?title=User:Chetvorno&amp;action=edit&amp;redlink=1" class="new" title="User:Chetvorno (page does not exist)">Chetvorno</a> (<a href="//commons.wikimedia.org/wiki/User_talk:Chetvorno" title="User talk:Chetvorno"><span class="signature-talk">talk</span></a>)</li></ul>
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