The "open-cage" design adopted by us have one of the highest mechanical strengths of the molded polymer arresters in the market. In the design Hitachi Energy has chosen silicone polymer which is highly hydrophobic and resistant to UV radiation.
Each arrester is built up of one or more units. Each unit is a polymeric housing containing a single column of ZnO disks, all individually extensively routine-tested during manufacture, dispersed with the necessary spacers as determined by the electrical design for the arrester.
Long arresters often require (and are supplied with) external grading rings to maintain a uniform and acceptable voltage stress along their length.
Silicone rubber is highly hydrophobic and resistant to UV radiation and has been shown to be the best insulation (compared to both porcelain and other polymers) based on worldwide independent laboratory and field tests. Hitachi Energy uses special fillers to enhance these properties as well as giving it high pollution resistance, tracking resistance and fire-extinguishing features.
For satisfactory performance, it is important that the arrester units are hermetically sealed. The HTV molding process under vacuum ensures this by efficient bonding between silicone and all internal parts along the entire length. Hence gaskets or sealing rings are not required.
When the arrester is stressed in excess of its design capability the arrester is short-circuited and an internal arc is established. Thanks to the open cage design, the arc burns through the soft silicone material, thereby permitting the resultant gases to escape quickly and directly. At the same time, the aramide fibers keeps all internal parts together and prevent the expulsion of the internal components. Hence, special pressure-relief vents are not required for the PEXLIM design.
The color of the silicon is grey. Seaworthy packing of the arresters is standard.