Nine days after Sandy made landfall, power outages are not over yet. 8.5 million customers lost power from the storm, and hundreds of thousands still remain without power. Those numbers may be worse by the end of today; a nor’easter is already striking parts of the northeast and is expected to last into tomorrow with winds strong enough to tear though temporary repairs and uproot trees weakened by last week’s storm. Instead of getting ready to go home, line crews borrowed from other parts of the country are gearing up for another round of repairs.
The “Frankenstorm” of October 2012 started as Hurricane Sandy, but developed unique challenges for those in its path as it became a fusion of several weather events. The largest Atlantic hurricane on record would, under most conditions, have turned out to sea in the northern Atlantic, were it not for a blocking pattern caused by an extremely high pressure system over Greenland. As a result, Sandy turned west and made landfall in the most populated part of the U.S. There, instead of weakening as such storms usually do on landfall, it was fed new energy from a Jet Stream lower pressure trough associated with cold air from the arctic. The storm that began with the wind velocity and storm surges of a hurricane became an engine for blizzards. Instead of struggling with deadly heat and a lack of air conditioning as after Katrina, people found themselves without a way to keep warm.
Storms such as this one do provide utilities the opportunity to stage crews and materials in advance. This can greatly reduce restoration times, but it is only the beginning. Restoring power after a major storm becomes a disentangling of both obvious and nested problems. An accurate damage assessment is crucial. The electric power system uses transmission lines to deliver power from generators to distribution substations, and distribution lines carry the power outward from the substations to customer sites. Repairing downed distribution lines will not restore anyone’s power if the transmission system serving the local distribution substation is also down. So determining what the major problems are and a strategic order for addressing those means everyone gets their power back faster. This takes experience and team work to accomplish and is often not as obvious as the general public may assume.
Any given trouble location may have a number of obstacles to remove before repairs can begin. If roads are washed out or bridges gone, crews have to find a way to get to the site. Roads may have to be cleared of a number of fallen trees before the crews can get through. At the same time, downed trees near power lines cannot safely be cleared until a utility crew has verified that any downed lines are not electrified. Water may have to be pumped from sites doused in storm surge. This past week, there were even incidents reported where angry onlookers prevented crews from working.
As a general rule, utilities will attempt to restore critical facilities first: Distribution circuits that serve hospitals usually are among the first to get electric service restored. However, there is no hard-and-fast rule since the order of repairs and the order of restoration will depend on the specific locations and types of damage. After critical facilities, the utility’s goal is to restore the greatest number of customers possible as fast as possible, and repairs are ordered accordingly. As a result, repairs after a major storm rarely look like they make sense to an onlooker. For example, you may never see the crews that perform the repair that gets your power back online if that repair takes place on a transmission line miles away. Or power may come back to a whole part of town at once except one neighborhood. That isn’t because that neighborhood was passed by, but because the circuit that feeds it needs additional repairs that its neighbors didn’t.
So how can the electric infrastructure be made more resilient against these storms? It depends. Restoring services to areas with overhead distribution lines usually takes longer than for areas with underground cable. High winds wreak havoc on overhead distribution systems, particularly in areas with trees; broken tree limbs become projectiles that tear down power lines. A line doesn’t even have to be down; a tree limb lying across the wires will often short out the line. So in general, reducing the overhead exposure of the power system would help in most storm situations, and the obvious fix is undergrounding: bury the lines. However, putting the infrastructure underground isn’t a perfect fix everywhere; this past week has seen a number of substations deluged by storm surge and buried electric equipment shorted out by floodwater. Another way to reduce exposure for overhead lines is tree trimming; but the preference of the general public – and understandably so – is “Don’t trim my trees.” Yet, statistically, tree conditions are among the highest causes of outages, and in storms such as Sandy the toll to the distribution system is severe. Simply stated, we cannot have it both ways.
In a storm as devastating as Katrina or Irene or Sandy, it is simply not possible to rebuild large portions of distribution systems in two or three days, when it may have taken weeks to build those portions originally, without the of the debris of downed trees and other encumbrances. Sandy and other recent storms are clearly demonstrating how our dependency on the electrical infrastructure has outgrown the design criteria of the existing systems, many of which date back 50 or more years. Making electric service more secure against long outages after storms is not technologically difficult, but it is expensive, ultimately translating into higher electric bills. In the U.S. we have preferred to keep our electric bills low. But as the cumulative costs from storm damage keeps mounting, it may be that we are not saving as much as we think.