Slashing Transmission Wildfire Risk Using High-Capacity Low-Sag Conductors

Introduction:

In the Western United States, dry vegetation, strong winds and sagging powerlines have been blamed for hundreds of wildfires causing billions of dollars in damages and lost lives. While efforts are underway to improve vegetation management, underground distribution lines and upgrade other equipment, upgrading the transmission backbone is key to improving grid reliability and resilience while slashing the risk of transmission wildfires.

Background:

Much of the existing transmission system in the Western United States was built between 1950 and 1980 using conductor technology developed in the early 1900’s. These conductors consisted of steel core strands wrapped with aluminum wires. The steel provided tensile strength while the aluminum carried electrical current. In transmission voltages (above 69 kV), most of these conductors were suspended on steel lattice structures. While electrical demand varies within any given 24 hour period, many of the existing transmission lines are running at their upper limits and sagging beyond safe clearances as identified in the 2010 NERC Alert. Excessive conductor sag (and aged conductors) not only increases the risk of wildfires, they also reflect that the lines are most likely unable to carry additional current under emergency conditions.

Solution:

Modern conductors, such as ACCC®, use a high-strength, light-weight carbon fiber core that mitigates thermal sag due to its very low coefficient of thermal expansion (about ten times less than steel). The core’s light weight allows the incorporation of nearly 30 percent more aluminum. These characteristics enable the conductor to carry twice the current of legacy ACSR conductors and are ideally suited to upgrade the existing grid without the need to remove and replace existing structures – an otherwise very costly and environmentally impactful proposition.

Example:

In 2019 Southern California Edison used high-capacity, low-sag ACCC® Conductor to increase line capacity and resolve sag infractions on their double-circuit 230-kV Rector to Vestal lines and the adjacent 230-kV Vestal to Magunden lines in the Big Creek Transmission Corridor. Implementing the ACCC Conductors saved customers more than $85 million dollars in lieu of a project that uses larger, heavier conventional ACSR conductors and new larger, taller structures to increase line capacity and fully resolve clearance issues.

Reconductoring with the ACCC also reduced construction time from an estimated 48 months to 18 months — freeing up SCE resources and crews to focus on other projects. Mustafa Ali, SCE stated: “This reconductor project increased line capacity from 936 amps to 1,520 amps, which has huge transmission grid reliability impacts at the independent system operator level.”

Why it Matters:

The severity and impact of transmission wildfires over the last decade in the Western United States has forced many utilities to shut power down during high-risk conditions in an attempt to prevent starting more fires. This has created substantial difficulties for consumers. The use of high-capacity, low-sag conductors such as ACCC can not only reduce the risk of fire initiation, its high-capacity can also allow utilities to reroute power around high-risk areas during severe conditions. This offers a direct improvement to reliability and fire-risk mitigation. The ACCC Conductor can also handle very high temperatures without degradation. This, coupled with its improved clearance can improve survivability and resilience.