Among the options for building more resiliency into power grids to withstand the vagaries of the weather, putting the distribution infrastructure underground is an obvious if potentially costly option. [Engerati-Preparing the Grid for Failure]
The issue has been under discussion in Virginia for several years with studies taking an all-or-nothing approach to replacing all overhead power lines, making such a project cost prohibitive. For example, a 2005 study by the Virginia State Corporation Commission (SCC) placed the cost of undergrounding all overhead electric distribution lines in the state at US$83.3 billion, or about US$27,000 per customer.
But under new legislation, which became effective July 1, 2014, utilities may bury part of their overhead 69kV or less network, with cost recovery via a special rate adjustment that is approved by the SCC. Such annual incremental increase in the level of investments in such facilities may not exceed 5% of the utility's distribution rate base.
Most outage prone overhead lines
Under the plan Dominion Virginia Power intends to install new underground equipment, burying approximately 6,400km (4,000 miles) of its most outage prone overhead lines, focusing on the tap lines – out of the almost 93,000km (58,000 miles) of distribution lines – over the next 10-12 years.
The cost is estimated at US$175 million/year, but Dominion intends to request a small, gradual increase over time to cover the costs of the program.
Dominion is currently analyzing the overhead distribution system to determine which overhead tap lines throughout its service area are most vulnerable during major storms. The tap lines, the overhead wires that go into neighborhoods, typically sustain the most damage during storms and require the highest number of repairs, because of the proximity of trees.
Benefits of undergrounding
Key benefits will include a reduction in the frequency and duration of outages in the most damage-prone neighbourhoods, with a reduction in the power restoration time due to the smaller number of repairs potentially necessary after a storm. In fact Dominion expects that by the end of the program in 2026, the restoration time during major storms could be cut in half.