Network Resilience: The Grid
It is trendy these days to think we live in an interconnected world because of the existence of communications networks such as the Internet, but the truth is that modern society is grounded in less high profile infrastructure. These cat videos aren’t getting to your computer without the electrical grid. The servers in their heavily cooled datacenters, the myriad switching stations and routers that relay packets from one point to another in the tortuous path to your machine, and lastly your computer itself would not accomplish much without the continuing presence of the grid. In our engrossment with the high tech shell of our infrastructure, we have been neglecting its core to an increasing degree except during failures during which we are abruptly thrown back to the dark ages. This attitude to vital infrastructure is increasingly perilous as larger portions of the aging physical network reach obsolescence and inadequate funding is devoted to maintaining it.
In the graph of the electrical grid, the nodes are everything that produces (nuclear, solar, wind, hydroelectric, coal power plants) and manages (substations, residential transformers, switches) electricity, whereas the edges are the transmission lines themselves whose electrical potential can reach hundreds of thousands of kilovolts. The United States electrical grid consists of three vast components which are freely and strongly interconnected with themselves and loosely tied across their geographic boundaries – three usually separate grids, in fact: one in the East, one in the West, and the third covering the majority of Texas. These are referred to as “interconnections”, or “wide area synchronous grids”. In special circumstances, local bridges at their boundaries are enabled for load balancing purposes.
Map of the American electrical grid: NPR (http://www.npr.org/templates/story/story.php?storyId=110997398)
In the advent of electrification each of these vast interconnected blobs used to be discrete components serving isolated municipalities as the technology for high capacity power generation and long distance transmission was in its infancy. As demand soared and technology improved (high voltage transmission lines, etc), the grid began to coagulate for the sake of redundancy and convenience as resources for power generation such as rivers suitable for hydroelectric generation were not necessarily located near centers of demand. Overall costs of electricity decreased to the point where it was no longer a luxury but a vital commodity.
However, the interconnectedness of the network has proven to be hindrance as well as a blessing, due to the phenomenon of cascading failure. Isolated failures in the network now have the potential to wreak havoc on a scale unimaginable in the early 20th century. A watershed event in the power generation world was the 2003 Northeast blackout, which knocked out power for an estimated 55 million people in the Northeastern states and Ontario and costing . Due to the limitations of the hardware – there are no good ways to store large amounts of electricity for any length of time – the generation and distribution of electricity is necessarily a finely balanced maneuver and operators must constantly redirect the current flows. A lapse in judgement or too many simultaneous failures of critical links can leave the situation unsalvageable without a general shutdown. In this case the fault lay within Ohio, where several transmission lines overheated due to unusually high load, sagged, and shorted out due to contact with overgrown trees. The resulting surges of power as the network attempted to rebalance forced 256 power plants offline. As the system is always quite near its operating capacity, the uncontrolled propagation of unusual electrical conditions force increasing numbers of key nodes (i.e. power plants and switching stations) offline, causing a self-sustaining failure as the network ran out of redundant connections. Many local sections of the grid automatically isolated themselves due to automatic infrastructure protection routines, accepting short term blackouts to avoid even more expensive long term repairs. The extent of the blackouts can be seen in NOAA satellite imagery: http://www.noaanews.noaa.gov/stories/s2015.htm.
This incident revealed just how vulnerable the vital infrastructure of the United States really is. Although the consolidation of disparate electrical networks has undoubtedly increased the overall reliability of the grid, it remains a strictly hierarchical system that is vulnerable to catastrophic failure without a constant supply of power. As cheap petrochemical fuel dwindles and the nation is forced to switch to inconstant power generation methods such as wind and solar, it will become ever more necessary to have a buffer capacity – to build redundant nodes as well as redundant connections, and to increase the data and control available to operators. Proper routing is made far more difficult if operators are limited to the higher levels of the graph – the power stations and the high voltage transmission lines – and thus forced to make large and coarse adjustments. The ideal solution is to implement a nationwide “smart grid” – an umbrella term that encompasses many technologies that ultimately provide finer resolution control and feedback over the network. Under this system, neighborhoods and even individual households gain some centrality – i.e. gain some energy production/storage capabilities in the form of solar panels and batteries that will return unused power to the grid when necessary, and also constantly update the grid operators with vital information. The result will be a redundant network that is less reliant on a few large points of failure.
Sources/Further reading:
http://www.npr.org/series/103281114/power-hungry-reinventing-the-u-s-electric-grid
http://wwthey began to mergew.infrastructurereportcard.org/fact-sheet/energy
http://energy.gov/oe/technology-development/smart-grid
http://www.technologyreview.com/energy/23928/