What’s Energy Transmission Fiber

We are all aware fiber optics is the backbone of communications networks such as telecom, the internet, local area networks, cable television and more. It’s also the backbone of the electrical grid. For about three decades now, electrical utilities have been installing optical fiber to monitor and control the diverse elements of their transmission and distribution networks as well as provide for their communications needs.

The grid—the simple term we use to describe the complex network of power generating stations, substations and alternative-energy sources connected on transmission and distribution wires—requires management. Microgrids, city-block-sized managed areas, are being tested to see if they can increase security and efficiency. The growing supply of alternative-energy sources, such as solar, wind, geothermal and battery storage, complicates the grid-management problems due to their variations in supply of electricity over time.

The realization that the electrical grid is vulnerable to hacking and sabotage has increased the desire to develop secure, fiber-based management networks. Synchronization and management of electrical generation and distribution are complex functions that require comprehensive communications networks. Those networks are a combination of copper, fiber and wireless that have developed over more than a century of increasingly complex electrical grids.

Electric utilities also have extremely valuable resources, the rights-of-way that allow them to install fiber optic cables to connect and manage their grid. They also offer dark fibers and communications services to others and use the fibers for the benefit of their customer beyond providing electrical power. This has become an important source of revenue for utilities seeing a loss of profit because of conservation and the growth of alternative-energy sources.

Installing fiber optic cable along distribution lines using current towers is quite common among electrical utilities. There are many ways to install fiber optic cables on these towers. One choice is optical power ground wire (OPGW). This conductive cable is run at the top of the tower or pole to be the ground conductor and protect the power cables from lightning. OPGW is simply a metallic power cable with a stainless tube in the center that contains a number of fibers. The fiber, being a dielectric, is nonconductive and immune to electrical interference. OPGW is an obvious choice when installing a new transmission line.

Today, however, utilities that installed OPGW decades ago have discovered a problem with it. Older fibers may not be capable of handling modern communications speeds. There’s generally no problem with grid management and control signals that are not high-speed, but communications signals at greater than 10 gigabits per second may have problems with older fiber over long distances.

Upgrading OPGW generally requires taking a transmission line offline to remove and replace it. Unless a transmission line is down for other reasons, OPGW is rarely upgraded.

But those towers still offer plenty of options for adding optical fiber cables. Optical power attached cable is an all-dielectric fiber optic cable that is wrapped around the OPGW or power conductors already on the tower. This compact cable is just wrapped around the current power cables, even without turning off the power. It can span long lengths and at the heights common for power cables.

Another option utilities use widely is to run all-dielectric self-supporting (ADSS) fiber optic cable underneath the power conductors. This is a cheaper way to add fiber to a transmission line and does not disrupt the power delivery. All that is necessary is adding the ADSS supports to the towers and pulling the cable.

There are even instances of electric utilities installing underground cables on the rights-of-way of their transmission and distribution systems. But, it is very rare because of the higher cost of underground construction unless they are within metropolitan areas where underground cables are required.

Most of the fiber utilities install is used for grid management and control, but, as noted earlier, some lease dark fibers or partner with communications companies for other uses. One new use—pioneered by the Electricity Power Board of Chattanooga, Tenn., and now widely copied—is to build a fiber-to-the-home system on their fiber optic cable plants.

Perhaps the most complex problem addressed by fiber optic communications is integrating alternative-energy sources into the traditional grid. Instead of small numbers of large sources of power, alternative energy varies from kilowatts from residential solar-power systems to megawatts from commercial solar-power stations and wind farms. Such diverse sources of energy create new network-management problems that we will discuss next month.

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