Last month we looked at how electric utilities were planning to transform the North American power grid from a dumb network to a smart, responsive and self-healing system—in short, an "Energy Internet."
Electric utilities are focusing on four main areas of improvement. First, as covered last month, they are looking for ways to produce and store power closer to points of consumption.
Second, utilities are looking at ways to move more power through existing transmission lines. Third, utilities are investigating installation of real-time sensors to monitor the grid in real time. Finally, they are evaluating control systems and power transmission hardware that can control the flow of power fast enough to avoid blackouts.
"A more practical, proven, and less expensive solution is upgrade of transmission network control and sensing systems."
There are various ways to push more power through existing transmission lines. Because of the current lack of real-time monitoring and control, many lines run at just 50% of capacity. But as the grid gets smarter in various ways, EPRI officials reckon that it may be possible to squeeze perhaps a third more juice through today's wires.
Alternative power cables are another way to move more power through the grid. Aluminum and carbon-glass fiber composites could carry twice as much power as conventional cables. Superconducting cables can carry five times as much power as ordinary wires.
One of the simplest, most effective methods for increasing transmission line capacity is to switch from AC to DC. "A DC transmission system can deliver almost four times more power than an AC system on an existing right of way—an important consideration for areas undergoing significant load growth," says Randy Schreiber, the vice-president of strategic marketing and operations at ABB (www.abb.com/us).
Upgrading transmission lines and producing and storing power closer to points of consumption both require expensive investments, often in somewhat speculative or unproven technology. A more practical, proven, and less expensive solution is upgrade of transmission network control and sensing systems.
Both ABB and Siemens (www.usa.siemens.com/energy) have a variety of hardware and software products that address this market. Many of these products are also used in process control applications. Intelligent alarm processing, system simulation, and historical data analysis are familiar tools both within and outside of the power industry.
But some sensors, final control elements, and control system software are unique to the monitoring and control requirements of the nation's electrical grid. Much of this uniqueness occurs because, unlike most real-time process control applications, control of the grid must encompass many different control systems and span a wide area geographically.
"Hierarchical SCADA systems like the one we applied to control Mexico’s national grid are the heart of any transmission system. Historically, these systems were designed to serve the control area of the regulated utility, and as such they lacked the capability to "see" beyond their boundaries. This very constraint came into play during the August 2003 blackout," observes Schreiber.
"Our hierarchical SCADA system allows data to be shared between neighboring regions and aggregated for supervisory entities. This is perhaps the most "Internet-like" aspect of the technologies that we apply to power grid control and monitoring," adds Schreiber.
Siemens’ uses state estimation in its hierarchical SCADA system. "Our State Estimator provides a simple and cohesive view of the real-time state of the entire transmission system, including a look into the health of neighboring networks," says Tom Garrity, the vice-president of sales and business development for Siemens Power Transmission & Distribution.
"The State Estimator also identifies and compensates for failures in the SCADA software subsystem, data telemetry and local metering so that issues obscuring a proper view of the transmission system may be corrected proactively, not discovered during system emergencies or post-mortem analyses. New innovations in State Estimation include phase-angle measurements provided by GPS devices," adds Garrity.
Rockwell Automation (www.rockwellautomation.com) is developing a technology called CIP Sync that will bring time synchronization to DeviceNet, EtherNet/IP, and other networks built on the Common Industrial Protocol (CIP). Based on the recent IEEE-1588 standard--Precision Clock Synchronization Protocol for Networked Measurement and Control Systems--CIP Sync provides a mechanism to synchronize the clocks across a distributed network.
"ODVA (www.odva.org) is developing the technology, and the CIP Sync specification is expected to be complete within the next 12 months. Initially, it will provide synchronization enhancements for EtherNet/IP, followed by other CIP networks," says Steve Zuponcic, a program manager with Rockwell.
Another unique requirement for power grid control is the need for very fast-acting, solid-state switches. Today's electro-mechanical switches take tenths of seconds or longer to divert power—usually far too long to avoid a problem. But several firms have devised solid-state systems that can switch massive amounts of power in milliseconds.