North America’s electric power grid is a marvel of engineering, but it remains vulnerable to interruptions due to severe weather, heat waves, ice storms and other events.
Hurricanes Harvey, Irma and Maria in 2017 poked hard at those vulnerabilities in Texas, Florida and the Caribbean, especially Puerto Rico.
Nicholas Abi-Samra has devoted much of his career to engineering issues related to the grid, reliability and resiliency. He has more than 35 years of experience in power generation, transmission, distribution, retail and end-use energy applications. He is president of Electric Power & Energy Consulting (EPEC), an adjunct professor with UC San Diego and the author of a new book, “Power Grid Resiliency for Adverse Conditions” (Artech House, 2017).
During a phone conversation and email exchange with Engineering360 Editorial Director David Wagman, Abi-Samra outlined how the grid can be made more resilient and how tools no more complex than a saw and a ladder can reduce the possibility of power outages during a storm.
Many of the principles he has advocated in recent years — everything from battery energy storage to aggressive tree-trimming programs — are now included in a $17.6 billion plan released on December 11 to rebuild Puerto Rico’s electric power infrastructure.
Q. What are the basic principles to grid resiliency?
A. Making the power distribution system more resilient starts with changes in the design. It may be advantageous, for example, to split up a large network into smaller circuits, and to reexamine the circuit arrangements to enhance the speed of repair. Greater deployment of smart grid technology can also help.
When an electrical outage occurs, the smart grid’s intelligent switches can detect a short circuit, block power flows to the affected area, communicate with other nearby switches, and then reroute power around the problem to keep as many customers energized as possible. Because these intelligent switches can do all this automatically or under the control of remote operators, they can reduce the time it takes to restore power to just a few minutes.
Q. How do you define system resilience?
A. Resilience stands for the strength and fast recovery characteristics of utility infrastructure and operations to avoid or minimize interruptions during and after an extreme weather event, or, for that matter, any other extreme conditions.
While hardening existing power assets is an important strategy, utilities realized that they need to incorporate resilience into their long-term expansion plans. Thus, resilience starts with preventative and preparative measures to make outages from extreme events less likely or smaller in extent.
The wide destruction after Superstorm Sandy in 2012 and its impacts on the power grid enticed discussions about system resilience. It was proven by the destructive hurricanes of 2017 that stronger storms and longer and more intense heat waves will likely pose new challenges to energy infrastructure.
Q. What were the main difference between the response to Hurricane Harvey in Texas and Hurricane Maria in Puerto Rico?
A. We need to look at three issues: first, the nature or the hurricanes; second, the preparations for them; and third, the use of the smart grid in the response during and after the storms.
First, the nature of the two hurricanes was different. In Texas, and Houston in particular, Hurricane Harvey was mostly a "water" hurricane with a record-breaking rain 52 inches (1.32 m). Hurricane Maria that hit Puerto Rico had both high rainfall and storm surges as well as high winds, so the damage was from both.
Second, the preparations for the two hurricanes were different. The utilities in the states where Harvey was expected to hit had pre-positioned their response teams. And they could draw on hundreds who came from other utilities under mutual aid agreements that were agreed upon before the storm. This did not happen in Puerto Rico.
Third, utilities like CenterPoint made use of distribution system automation to respond to Harvey. CenterPoint operated more than 250 intelligent switches during the storm, and thus saved over 40 million outage minutes.
They also used smart meters to remotely disconnect customers who were ordered to evacuate. These measures contributed to minimizing the impacts and speeding up the restoration. Such smart grid resources may not have been available to PREPA (the Puerto Rico Electric Power Authority) due to its financial situation. On top of that, had they been in place, they may not have been as useful due to the damage inflicted by the storm.
(Read "Using Big Data to Predict Power Outages.")
Q. What factors contributed to the severity of Hurricane Maria on Puerto Rico’s power system?
A. PREPA has been operating under highly constrained financial circumstances for the last five years. Struggling with increasing debt, which reached $9 billion in 2017, PREPA filed for bankruptcy even before hurricanes Irma and Maria. Because of its financial situation, PREPA has performed few major upgrades to its grid.
PREPA's distribution system was operational, but with reliability concerns due to aging components. A high percentage of overhead distribution circuits used wooden poles that were in deteriorated condition. A number of underground distribution circuits had been “temporarily” replaced by overhead circuits that were vulnerable to high winds. Up until 2016, two thirds of the power was being generated by petroleum in aging power plants that were scarce on spare parts.
As a consequence of the financial situation, PREPA has incurred a 22 percent workforce reduction since 2014 (30 percent since 2012). The reduction shifted most preventative maintenance to reactive maintenance.
The power generators lie on the south side of the island, while the major loads are on the north side. Thus, transmission lines must pass through mountainous forest, making them difficult to repair.
Physical access to repair or replace damaged structures is difficult, leading to the long service interruptions and exposing the system to the potential risk of multiple contingencies and cascading outages.
Q. What solutions do you see as possible for Puerto Rico?
A. System hardening and resiliency cover the activities needed to make a system less susceptible to damage during major storms to decrease the number of customers who could experience power interruptions, or lack of essential services during major storms.
As Hurricane Maria and Superstorm Sandy before it have shown, no amount of reinforcement and preparation could completely avoid damage.
As I detail in my book, structural hardening of the distribution system should focus on two objectives: hardening of circuits which feed critical loads and load centers, and designing for quick restoration.
A cost-effective hardening approach should start with hardening substations, feeders and circuits which serve critical infrastructures such as hospitals. After these are hardened, an analytical approach should be used to prioritize the remaining feeders.
The most common hardening practices include replacing wooden utility poles with poles made of steel, concrete or a composite material, upgrading transmission towers from aluminum to galvanized-steel lattice or concrete, and installing guy wires and other structural supports.
Flying debris (such as roofs and road signs) and vegetation (such as falling trees and tree limbs) are the primary causes of distribution-pole damage during a storm, not strong winds themselves. In high-wind situations, the risk of airborne debris coming from trees outside the right-of-way can exceed the risk from trees within the right-of-way by a factor of three or four to one. Thus, vegetation management on the right-of-way alone is not enough.