A significant component to the reliable operation of any transmission line is in the specification and design of the insulators. While insulators and the associated hardware make up less than a few percent of the overall cost of a transmission line, they can account for a significant portion of the line’s reliable operation and overall performance. Insulators serve two roles. First, they provide a mechanical connection by which the electrical conductors are physically hung from the transmission structures. Second, insulators provide the electrical separation (insulation) between the energized conductors and the transmission structures which are grounded. The image below shows the placement of insulators on a typical high voltage direct current (HVDC) transmission structure.
Insulators can be manufactured from glass, ceramic/porcelain, and polymers (special composite materials). For HVDC, the preferred choice is a special formulation of glass insulators referred to as High-Resistivity Toughened Glass. For the Plains & Eastern project, Clean Line will purchase these insulators solely from Sediver partially because of their decision to expedite plans to locate a new insulator manufacturing facility in the U.S.; Sediver is currently constructing an assembly and high-tech test facility in West Memphis, AR. This new facility will bring more than 70 full-time jobs to the area.
Insulators are critical to the performance of any transmission line, so each assembly type must be tested to ensure it meets the appropriate design specifications and standards that promote high performance levels of the line. Insulator testing is comprised of two major facets; mechanical testing and electrical testing. Mechanical testing requires that each piece of steel hardware that connects the insulators to the tower and the conductor to the insulators is tested to ensure that it can withstand the stress that will occur on the insulator assemblies over the life of the project. Electrical testing insures that the electrical properties of the insulator assemblies perform according to international standards and design criteria. The electrical tests are done to ensure that the electrical properties of the insulator assemblies will perform as designed. These tests are conducted at voltage levels higher than the operating voltage to ensure that the assemblies will exceed expectations in the field.
Pictured below are some of our insulator assemblies during testing at a highly specialized high voltage laboratory. This set of Sediver insulators are assembled utilizing Hubbell Power Systems hardware. Hubbell is committed to providing half of the hardware on the project and will produce the components in Centralia, MO and in Birmingham, AL, the remaining hardware is being supplied by Salvi.
A single “vee” string undergoing a wet-withstand test to ensure that the insulator performs in expected conditions. Single “vee” strings will be on the majority of structures on the Plains & Eastern project.
Double “vee” strings will be used on some turning structures undergoing tests for Radio Interference Voltage (RIV) and corona. The assembly passed the tests with no concerns.
The Double “Vee” Assembly is disassembled after successful testing.
A Triple String Dead End Assembly, one of the largest insulator assemblies that will be used on the Plains & Eastern Clean Line, is assembled for testing. This insulator assembly’s total length will be 41 feet, it will have 102 insulator bells, and can support up to 270,000 pounds of tension from the conductors. Dead-end structures comprise about ten percent of the total number of structures for the Plains & Eastern project and are designed to handle full tension of the line on either side of the structure.
Once testing is complete and all assemblies are approved for manufacture, Clean Line can issue notice to proceed to Sediver, Hubbell, and Salvi in order to meet the Plains & Eastern Clean Line’s in-service date of late 2020.