Based in Southern California, Dianoush Emami oversees complex electrical engineering projects that enable power plants to function at capacity reliably. Over the years, Dianoush Emami has managed electrical engineering projects involving the placement of high-voltage overhead and underground lines.
Underground transmission lines must overcome various technical challenges that make the cost per foot between four and seven times that of overhead lines. One major obstacle involves providing enough insulation that cables can be placed only inches from grounded material. In addition, the heat generated when operating electrical cables needs to be rapidly dissipated within a confined space. With overhead lines, engineers have the luxury of lines surrounded by insulating air and safely distant from each other.
Two basic underground transmission line configurations resolve these concerns. High-pressure fluid-or-gas-filled cables involve three high-voltage conductors encased within a steel pipe. Pressurized nitrogen or synthetic oil acts as an insulator, without itself conducting electricity, and prevents unwanted electrical discharges. The fluid, generally static and operating by conduction, also transfers heat from the conductors. Issues that can potentially arise include leaking oil that impacts groundwater and soil.
The other major option is a solid cable made of dielectric material, such as the XLPE cable, which has an aluminum or copper conductor and a semi-conducting shield at the core. Surrounding this core is cross-linked polyethylene insulation, with a metallic sheath and plastic jacket covering the entire cable. This effectively provides insulation and heat dissipation without fluid leakage risks.
