Insulation design of anchors and tower supports for 110,000-volt 4427-foot span over Carquinez straits

The first crossing of the Carquinez Straits by a high-tension transmission line was one of the stepping stones in the progress of the electrical industry. The pioneers built well, and the march of events, with its demands for greater and greater blocks of power, found the crossing structure adequate for the new requirements. Constructed in 1901 for one 60,000-volt circuit with a spare cable, two additional cables were added in 1914, making two 60,000-volt circuits. In 1922, coincident with the replacement of 60,000-volt pole lines by a 110,000-volt tower line, the crossing was modified to allow 110,000 volts on the two circuits, thus again practically doubling the transmission capacity. The original design made use of insulating materials in compression. A clear record for over 20 years led the company to adhere to the compression type in the reinsulation for the higher voltage, thus making the crossing unique among long high-voltage spans. The methods by which some of the problems were solved, the hinged anchor structure, the sturdy insulated support for the towers, the movable top for the middle tower support to allow for relative motion and the supplementary cable system to obviate crystallization at the supports, are described in the paper.