An electric substation and overhead transmission lines

Advancing Electric Transmission Systems, Part II

R&D projects to promote greater utilization of the transmission system.

A growing pool of research and development (R&D) activity is focused on new low-cost technologies to control transmission line power flows. Some of these R&D projects take the approach of dynamically managing the topology of the transmission grid in order to promote greater utilization of the transmission system. However, even at a reduced cost, their installation will force a more complicated optimization schema – this will also need to be solved at the same time. Distributed series reactors, sometimes called “smart wires”, are an example of potential advancement in this regard.

Numerous utilities are interested in accelerating the deployment of voltage source converters (VSCs). These are self-commuted high-voltage direct current (HVDC) converters. Contrary to “traditional” HVDC converters, the self-commuted HVDC converters do not have to rely on synchronous machines in the ac system for its operation. The increased controllability improves harmonic performance and provides VAR support. VSCs permit power flow to be reversed without reversing the polarity of the cable, thereby enabling the use of extruded cables (cables insulated with extruded polyethylene-based compounds, such as XPLEs). It makes undergrounding (cables, instead of overhead lines) more attractive. More VSCs are needed in the North American power system.

Advanced analytics and visualization applications are needed to maximize use of phasor measurement unit (PMU) data. PMUs, or synchrophasors, provide real-time information about the power system’s dynamic performance. Specifically, they take measurements of electrical waves (voltage and current) at strategic points in the transmission system 30 times per second. These measurements are time stamped with signals from Global Positioning System (GPS) satellites, which enable PMU data to be time-synchronized and combined to create a comprehensive view of the broader electrical system. Widespread installation of PMUs, which is occurring now, will enhance the ability to monitor and manage the reliability and security of the grid over large areas.

PMUs can provide system operators with feedback about the state of the power system with much higher accuracy than the conventional SCADA systems which typically take observations every four seconds. Because PMUs provide more precise data at a much faster rate, they can provide a much more accurate assessment of operating conditions and limits in real time. However, at this time, the actual visualization of this data and real-time feedback to operators is limited by available analytical tools for use in operating transmission systems.

What will it take to accelerate development of intelligent electronic devices (IEDs)? IEDs encompass a wide array of microprocessor-based controllers of power system equipment, such as circuit breakers, transformers, and capacitor banks. IEDs receive data from sensors and power equipment, and can issue control commands, such as tripping circuit breakers if they sense voltage, current, or frequency anomalies, or raise/lower voltage levels in order to maintain the desired level. Common types of IEDs include protective relaying devices, load tap changer controllers, circuit breaker controllers, capacitor bank switches, recloser controllers, voltage regulators, network protectors, relays, and so forth. Considerable development is needed to expand the family of IEDs available and, in turn, further enhance the functionality of the grid.

With available microprocessor technology, a single IED unit can now perform multiple protective and control functions, whereas before microprocessors, a unit could only perform one protective function. A typical IED today can perform five to 12 protection functions and five to eight control functions, including controls for separate devices, an auto-reclose function, self-monitoring function, communication functions and so forth. It can do this without compromising security of protection – the primary function of IEDs.

There are some important technologies which are undergoing significant research and development and in some cases are in very early stages of commercial use. In several cases, the R&D required to advance transmission technologies is being addressed by the Green Electricity Network Integration (GENI) program, which was founded inside the U.S. Department of Energy (DOE) Advanced Research Projects Agency.

Referring to its mission, Advanced Research Projects Agency-Energy (ARPA-E) said that it “advances high-potential, high-impact energy technologies that are too early for private-sector investment. ARPA-E awardees are unique because they are developing entirely new ways to generate, store, and use energy.”

ARPA-E was the Federal-level government agency tasked with promoting and funding research and development of advanced energy technologies. It’s modeled after the Defense Advanced Research Projects Agency (which many know by its acronym, DARPA).

The GENI program’s mission has been to modernize the way in which we transmit electricity through advances in hardware and software to enable greater control over power flows in order to better manage peak demand and cost.

HVDC converters and other controllers are based on power electronic semiconductor devices. These devices exploit the properties of semiconductor materials, principally silicon, germanium, and gallium arsenide. Semiconductor materials can be manipulated by “doping,” the addition of impurities, and can be controlled by the introduction of an electric field, light, or pressure. Power semiconductor devices are those intended for high-current and/or high-voltage applications.

Silicon (Si) is the most widely used material in the manufacture of semiconductor devices. It has low raw material cost, requires relatively simple processing, and offers good temperature range. Other, more advanced devices are being researched which could reduce the cost and increase the functionality of converters. A new set of potentially “game-changing” switches has evolved. These switches fall into the category of “wide band gap” semiconductors. Among these, silicon carbide (SiC) and gallium nitride (GaN) have increased in reliability and dramatically decreased in cost. They hold a promise for significantly increased high-value applications across the electric utility industry in power generation, delivery, and end-use and should be actively supported by the U.S. DOE.

Advanced electric energy storage has become the focus of intense effort inside the United States and around much of the rest of the world. Bulk storage is one of the major limitations in today’s “just in time” electricity delivery system and one of the great opportunities for smart grid development in the future. Only about 2.5% of total electricity in the United States is now provided through energy storage, nearly all of it from pumped hydroelectric facilities used for load shifting, frequency control, and spinning reserve.

The U.S. DOE has supported research and the initial development of storage technologies ranging from improved battery chemistries to new approaches for compressed air storage. However, the cost and performance of today’s electric energy storage is well below that which will be needed to witness widespread adoption. The DOE plans to continue and enhance research on new storage technologies, the development of early stage commercial technologies and the demonstration of various applications.

Investments in robotics and unmanned aerial vehicles (UAVs) can reduce inspection cost and increase safety. The Electric Power Research Institute (EPRI) says that “with over 300,000 km (186,000 miles) of transmission lines in the United States, transmission line inspection is a costly, and sometimes dangerous, proposition. Robotic transmission line inspection involves various technologies that inspect transmission lines (as well as substation equipment and potentially distribution equipment) using robots rather than humans. The idea is to reduce inspection costs and improve safety by using robots in potentially hazardous environments.”

Likewise, the use of either fixed-wing or rotary-wing UAVs is being studied today in conjunction with the U.S. Federal Aviation Administration, for use during facility inspections. This technology also has potential to assist in the quick evaluation of facilities after a major storm, which would then allow for more efficient, and safe, restoration efforts.

Modernizing transmission operations requires a new suite of advanced grid management (AGM) tools. Transmission system operators (TSOs) include traditional utility transmission owners/operators, independent system operators (ISOs), regional transmission organizations (RTOs), and others. TSOs are making investments in an increasingly robust communications infrastructure as well as an enhanced analytical and forecasting capability. These investments are being made in response to requirements for TSOs to incorporate increasing functionality in order to maintain reliability, meet load growth, and to comply with new regulations that are increasing grid compliance with the U.S. Federal Energy Regulatory Commission’s (FERC) rules, enhancing the use of distributed resources, demand response, and energy efficiency. At the same time, market operations are becoming increasingly more complex, the threat of cyber security is increasing, and pressures are continuing to mount to maintain costs and improve the use of assets.

A number of these investments was made as part of sustaining core capabilities even before the United States began to evolve the concept of a “smart grid.” For example, the development of techniques for real-time simulation of transmission operations and enhanced visualization have been under development since the 1990s. Today, they are considered part of the smart grid, but would have simply been viewed as necessary improvements a decade ago.

In order to further the ability of TSOs to take advantage of these investments, there is significant research and development underway that’s focused on AGM. This involves several leading-edge areas of R&D: data analytics, advanced mathematical algorithms, data management, and others that allow system operators to use “faster than real-time data” to manage the transmission system.

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