Transmission Lines and Safety Considerations

 

A California-based electrical engineer, Dianoush Emami has significant experience designing power plants. Dianoush Emami has set up high-voltage transmission and electrical distribution systems that provide a consistent, safe energy source.

Transmission lines carry energy in large quantities from generating stations to substations, which can be distributed to individual businesses and households. The design and capacity of such lines vary widely, ranging from 44,000 volts to more than 750,000 volts.

Because of the high load capacity and extremely high voltage, transmission lines do not have an insulating sheath, as with the smaller loads involved with electrical lines and poles from substations. Instead, the air around the lines acts as an insulator, making it critical that nothing comes close to them, such as a tree branch, that might cause serious fire and outage. Because of the high voltages, a tree does not even need to touch the line for an electric arc to occur.

For this reason, all transmission lines are set up with right-of-ways that prevent vegetation from being planted in the vicinity. In addition, this cleared area enables personnel to access lines for inspections, repair, and maintenance.

Basic Types of Underground Transmission Lines

 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.

SF6 Circuit Breakers for High Voltage

 After receiving his bachelor's degree in electrical engineering from the University of Southern California, Dianoush Emami has accumulated several professional certifications in the electrical engineering sector. With over three decades of experience in his field, Dianoush Emami’s particular areas of expertise include quality control, safety, and high-voltage transmission work.

High-voltage circuit breakers protect electrical circuits from hazardous spikes. One common type of high-voltage circuit breaker is the SF6 circuit breaker. SF6 circuit breakers use a gas called sulfur hexafluoride as their dielectric material. The circuit breaker cuts power when there is an overload or a short circuit, protecting electrical systems and assets.

The three major types of SF6 circuit breakers are the single interrupter SF6 CB (designed for 220 kV systems), the two interrupters SF6 CB (designed for 400 kV systems), and the three interrupters SF6 CB (designed for 715 kV systems).

Circuit breakers are a more efficient alternative to fuses. Contrary to fuses, designed to protect against dangerous current only once, circuit breakers can be reused. One disadvantage of SF6 circuit breakers is that the constituent gas (sulfur hexafluoride) is a greenhouse gas and can contribute to global warming when it escapes into the atmosphere through the leakage.