(John Kemp is a Reuters market analyst. The views expressed are his own)
By John Kemp
LONDON Nov 13 Much as the anger at continued power outages in New York and other states hit by storm Sandy is understandable, past experience shows a two-week wait is far from unusual.
Thirteen days after the post-tropical cyclone hit the East Coast, almost 90,000 customers were still without mains power on Monday, the vast majority in New York state (80,000).
More than 8 million customers have already had their supply restored. But for those still without light, power and in some cases heat, lengthy delays restoring electric service have become a source of mounting frustration and anger.
The Long Island Power Authority (LIPA) and Consolidated Edison of New York (Con Ed), have borne the brunt of that anger as the principal suppliers in New York City and Long Island.
However, lengthy re-connection delays for customers on small, remote or badly damaged circuits are unfortunately common after big storms.
On June 29, 2012, a major storm system known as a derecho formed over Illinois and moved down the Ohio valley to the Mid-Atlantic, with winds gusting up to 80-100 miles per hour.
The derecho blacked out power to 4.2 million customers across 11 states and the District of Columbia, according to a review of the outages compiled by the Infrastructure Security and Energy Restoration (ISER) Division of the U.S. Department of Energy.
Five days later, more than 400,000 customers were still without power in West Virginia (198,000), Ohio (97,000), Virginia (72,000), Maryland (33,000) and other states. Small groups of unlucky customers were still power-less 9 days after the storm ("A review of power outages and restoration following the June 2012 derecho" August 2012).
RESTORATION CURVE ANALYSIS
In the aftermath of a major outage, power suppliers and policymakers study "restoration curves" to derive lessons from the experience. Restoration curves plot the number of customers still without power, or those reconnected, each day after the storm hits (Charts 1 and 2).
Chart 1: link.reuters.com/haf93t
Chart 2: link.reuters.com/kaf93t
"There is no normal restoration curve following major storms, as each event offers a unique set of conditions and circumstances," ISER warns.
"However, utilities typically focus initial efforts on repairing utility-owned power plants, substations and transmission lines that serve them. Next utilities work to restore customers that provide essential services to the community, such as hospitals, police stations and fire departments."
"Once essential customers are restored, utilities focus on completing repairs to circuits that serve the largest number of customers and can be restored in the least amount of time."
"After large circuits are repaired, restoration efforts typically experience diminishing returns, as crews turn their attention to circuits serving fewer customers. The final stages of restoration often take the longest, as utilities restore power to small groups and individual customers."
This is precisely the pattern which has been observed in New York, New Jersey and Pennsylvania since Sandy hit (Chart 1).
On Nov 1, almost 350,000 customers had power restored in New York state, but by Nov 7 daily restorations had fallen to 115,000, and by Nov 11 it was just 61,000.
In Pennsylvania, power was restored to 415,000 customers on Oct 31, but by Nov 4 restorations had fallen to 81,000 and by Nov 8 to 4,000.
Given that post-tropical storm Sandy took out power to roughly twice as many customers as the June derecho, it is not surprising some customers have so far had to wait about 1.5 times as long to have their power restored.
HARDENING AND RESILIENCY
Following the storm and flooding, many customers, utilities and public utility commissions (PUCs) in the Northeast are asking whether more could be done to strengthen the transmission and distribution system to reduce outages from future storms.
In fact much has already been done in states along the U.S. Gulf Coast and in the Southeast on making electricity systems harder and more resilient following the devastating hurricanes in 2005 (Katrina and Rita) and 2008 (Gustav and Ike) which devastated the city of New Orleans and wreaked widespread havoc on the region's oil refineries and communities.
The results are summarised in a lessons-learned report on "Hardening and resilience: U.S. energy industry response to recent hurricane seasons" published by ISER in August 2010.
The report documents measures which can be used to harden power networks to make them less susceptible to damage from extreme wind, flooding and flying debris: raising substations and control rooms on the flood plain or relocated them to higher ground, upgrading power poles from wood to steel, strengthening poles with guy lines, and burying power lines underground.
Officials also talk about making networks more "resilient" essentially a measure of their ability to recover more quickly after a major storm. For example that can be bolstered by conducting preparedness and training exercises, participating in regional mutual aid groups to share linemen and equipment, stockpiling spare transmission and distribution equipment, and even purchasing or leasing mobile transformers and substations that can be delivered by road.
GULF COAST HURRICANE LESSONS
As the Northeastern states contemplate how to harden their electricity system in case of future storms, the question is how much customers and utility commissions are prepared to order the utilities to spend and recover through higher rates.
Following 2005 and 2008 hurricanes, public utility commissions in traditional hurricane states Florida, Louisiana and Texas have all introduced stringent new reporting requirements and regulations for power companies covering reliability, storm and flood preparations.
It is entirely understandable that New York, for which Sandy was a once in a century occurrence, was less prepared.
The storm surge last month also appears to have done at least as much damage as high winds, though in general wind damage poses a greater threat to electrical assets according to ISER.
A category 1 hurricane (74-95 miles per hour) is likely to result in "extensive damage to power lines and poles that will likely result in power outages that could last a few to several days" says ISER.
A category 3 storm (111-130 miles per hour) will mean "electricity is unavailable for several days or a few weeks." Any region hit by a category 4 or 5 storm is likely to see some customers without power for months.
Even if transmission and distribution lines, poles and towers are designed to withstand high winds, they are unlikely to survive a strike by a 3 tonne tree flying at 120 miles per hour.
Public utility commissions in Texas, Louisiana and Florida have all demanded that poles in coastal areas be upgraded to withstand winds of 140 or even 150 miles per hour. Poles can also be guyed to cope with extreme winds at a cost of about $1,500-3,000 per pole.
In the case of the high-voltage transmission circuits, Gulf Power company guyed 300 transmission towers and other vulnerable assets, and replaced wooden cross arms with steel ones, for a total cost of about $600,000, according to ISER.
BURYING LINES, CUTTING TREES
Burying power lines is an extreme option. The frequency of outages on buried lines is 50 percent less than for overhead wires, but when they do go wrong outages last 58 percent longer.
But the catch is that burying does not necessarily protect power lines from flooding and storm surges. It is also very costly.
"Southwestern Electric Power Company estimated a 79 percent premium for undergrounding, with the cost of overhead wires at $250,000 per circuit mile and undergrounding at $447,200 per circuit mile," ISER explained.
For major transmission circuits, the extra cost could be much more. Louisiana power companies warned the state utility commission that undergrounding high-voltage circuits would cost 5-10 times as much as overhead lines, $500,000 to $2 million per mile, plus coolants and pumping stations to prevent the system overheating (wires give off a lot of warmth). The state's utilities put the total cost of conversion at $1,500-4,500 per customer.
More cost effective is raising substations and control centres to protect them from flood damage. The Public Utility Commission of Texas (PUCT) recommends all new substations located on a 100-year floodplain be raised so the floor of the control house and all water-sensitive components above the 100-year flood level.
The single most useful resiliency measure, however, is keeping trees and vegetation near power lines well trimmed.
"Tree and vegetation-related damage to power lines is the most common cause of electricity outages," ISER warns, not just for local low voltage circuits but for the major inter-regional distribution system as well.
Uncontrolled tree growth was significantly responsible for the giant August 2003 blackout that left 50 million people without power in the Northeast for up to four days. Every utility, says ISER, should have a formal vegetation management programme. (Editing by Patrick Graham)
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