Today’s electrical transmission System—including the giant power lines and transmission towers that snake across our landscapes—operates much like a System of interconnected streams. Power flows through the transmission System along the path of least resistance, finding multiple paths between the power plants and the cities that are demanding the power. Grid operators actually have very little control over today’s System. Their primary task is to make sure that as much power is being generated as is being used—if not, the grid’s voltage could drop, causing the grid to become unstable. Operators generally know which lines are in service and when relays have opened to protect lines against faults, but they have limited control capabilities. Unfortunately, like water in a bathtub, power can “slosh around” within the grid, developing oscillations that, under the worst of conditions, could lead to widespread blackouts. To compound the problem, grid operators also have limited information about how the power is flowing through the grid. The Smart Grid will help solve this problem by adding new capabilities for measurement and control of the transmission System. These technologies will make the grid much more reliable and will minimize the possibility of widespread blackouts.
The 2003 Blackout
August 14, 2003, is a date that few grid operators in North America will ever forget. Although power demand was high that day, the situation seemed under control until a relatively insignificant power line in Ohio overheated and tripped offline. Like throwing a rock in a pond, that power line failure triggered oscillations in the transmission systems that line the shores of the Great Lakes and provide power to the Northeast and parts of Canada. Those oscillations eventually overloaded the System, causing a massive blackout that stretched from Michigan and Ohio, through the Northeast, and into Canada. With subways down, many commuters in New York City struggled to find a way home. The blackout affected an estimated 10 million people in Ontario, Canada, and 45 million people in eight U.S. states.
The Smart Grid Solution
Smart Grid technologies offer a new solution to the problem of monitoring and controlling the grid’s transmission System. New technologies called Phasor Measurement Units (PMU) sample voltage and current many times per second at a given location, providing a snapshot of the power System at work. PMUs provide a new monitoring tool for the Smart Grid. In our current electric grid, measurements are taken once every 2 or 4 seconds, offering a steady-state view into the power System behavior. Equipped with Smart Grid communications technologies, measurements can be taken many times a second, offering dynamic visibility into the power System. This makes it easier to detect the types of oscillations that led to the 2003 blackout.
The “Self-Healing” Grid
Smart Grid technologies also offer new means of controlling the transmission System. New high-power electronics function essentially as large-scale versions of transistors, adding a new level of control to the transmission System. New technologies could also help dampen unwanted power oscillations and avoid unproductive flows of current through the grid that only serve to waste energy. The combination of new measurement and control technologies also enables a new automated approach to controlling the grid. Software could potentially monitor the grid in real time for potential disturbances that could lead to blackouts, and it could take actions to check the disturbances. Such monitoring software could act to dampen out oscillations in the power grid, or it could even reroute power through the grid to avoid overloading a transmission line. In the event that a power line needs to be removed from service, control software could reroute the power in a way that causes minimal disruptions to the grid. This approach is often referred to as the “self-healing” grid. The ideal self-healing grid will involve a combination of transmission System monitoring and control software and comparable measures for the local distribution systems that deliver the power to individual homes and businesses. These distribution System measures are sometimes referred to as distribution intelligence.
“Seeing” the Smart Grid
Another contributor to the 2003 blackout was the limited situational awareness of the various grid operators involved. At the time, there was limited data sharing and transparency among the grid operators in different regions of North America, making it hard for the individual grid operators to see the big picture. By including new standards that make it easier for grid systems to interact with one another, the Smart Grid will make data sharing among regional grid operators easier to accomplish. Potentially, grid operators will be able to explore the state of the grid at the national level and switch within seconds to explore specific details at the local level. These technologies will provide rapid information about blackouts and power quality as well as insights into System operations for utilities.