July 2010 Vol. 65 No. 7
Features
‘Hardening’ Power Lines
“Why don’t they just put everything underground?” It’s a question heard repeatedly after major storms knock out vital power and communications services, and one that utilities often were asked after last winter’s storms left hundreds of thousands of Americans without electrical power.
Most everyone considers both electrical and telephone service “essential,” but most storm victims will say they can do without telephones longer than electricity which means no lighting, refrigeration or air conditioning. Homes heated with natural gas or oil require electric-powered fans to distribute heat. Last winter, in parts of the country there were residences and businesses without electrical power for weeks.
Replacing overhead systems with new underground infrastructure seems to make sense to property owners, who don’t recognize that immediately after a major storm is not the time for service providers to put distribution cable underground — the priority is restoring service, and the only way to do that is to repair and rebuild damaged poles and overhead wires.
In the short term, replacing downed power lines with underground cable is impossible and impractical. In the long run, cost makes it unrealistic to consider replacing all electrical distribution lines with underground cable.
“Multiple studies have shown that broad-based conversion of existing overhead distribution to underground is neither feasible nor cost effective,” said Richard Brown, PhD, P.E., senior vice president at Quanta Technology, a utility infrastructure consulting company based in Raleigh, NC.
“Typically,” Brown continued, “such action would cause rates to double and require a large scaling up of the utility workforce for about 20 years. This does not even consider indirect costs associated with third-party attachments and customer-owned equipment.”
$ difference
The cost difference between aerial and underground can vary widely based on a variety of factors, said Brown, but new construction of three-phase primary distribution system underground typically costs from three to five times that of equivalent overhead.
“It is typically much cheaper,” he said “to harden an existing overhead system against extreme weather than to convert to underground. In addition, underground systems also can be susceptible to storm surge damage, and can actually take longer to restore should damage occur.”
He said typical elements of a “storm hardening tool kit” include: stronger poles, storm guying, push braces, pole class uprating, shorter spans, smaller conductor sizes, fewer attachments, increased vegetation management — and undergrounding.
Placing power cable underground is not new to the electrical industry. In fact, two of the first compact horizontal directional drills sold went to a Georgia electrical utility to replace aging service lines. For decades, power companies have served new developments with underground cable, and office parks, educational institutions, and government facilities have limited or no aerial infrastructure. Undergrounding used in a hardening program usually is in older neighborhoods most susceptible to damage from high winds and ice.
“Underground conversion,” said Brown “is best coordinated with new construction and with relocations. For example, a roadway widening may require the relocation of overhead lines. At this time, a utility can consider whether the incremental cost of underground conversion is warranted based on hardening and aesthetic benefits.”
For utilities in areas subject to extreme weather, Brown said the best practice is to develop a storm-hardening roadmap.
“This,” he said, “is a multi-year plan that gradually hardens the system in a targeted and cost-effective manner. A typical roadmap will identify and harden certain critical poles, upgrade to Grade B construction in certain cases, and address critical customers such as hospitals and police stations. The addition cost of undergrounding can typically only be justified by aesthetic considerations.”
To date, he added, the most proactive states with regards to hardening are Florida and Texas, due to their high exposure to hurricanes.
Power utilities and regulators in states affected by the severe winter of 2009-2010 surely are evaluating hardening options now.
“Achieving the proper level of infrastructure performance during major storms at the lowest possible cost is a challenging task, but will increasingly be demanded of utilities by their regulators and customers,” concluded Brown.
Quanta Technology is an independent consulting arm of Quanta Services which provides business and technical expertise to energy utilities and industry and assists in deploying strategic and practical solutions to improve their business performance.
FOR MORE INFORMATION:
Quanta Services Inc., (713) 629-7600, www.quantaservices.com
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