Last year, EPRI and its affiliate, the Electricity Innovation Institute (E2I), organized the Consortium for Electric Infrastructure to Support a Digital Society (CEIDS). The consortium's main goal is to improve the existing electricity infrastructure and create a new infrastructure that can meet the growing demands of a digital society. To achieve this goal, CEIDS members will work to develop the necessary technologies with financial contributions from public and private entities. Since its inception, CEIDS has initiated several projects, and it has conducted extensive research to help outline additional goals and identify specific challenges as well as up-and-coming solutions.
A host of challenges and opportunities face electrical power suppliers in the digital age. Fully realized distributed generation and self-healing transmission and distribution systems are just a few of the new technologies driving the market.
Such efforts have equally impressive objectives, ranging from strengthening the power delivery infrastructure to managing global sustainability (see Fig. 1). In order to improve the existing grid and create a new infrastructure to meet the highest power quality demands, CEIDS has developed the following goals:
- Develop technologies that increase the control, capacity, and reliability of power delivery systems. There are two underlying goals here: The first is to supply consumers with the quantity and quality of energy they need at competitive prices, and the second is to provide the necessary “hardening” that will allow systems to survive conceivable threats from natural and man-made disasters.
- Develop technologies that provide greater tolerance to power disturbances. Consumers can best meet their energy needs if they can choose from a variety of power options. These options may include power-system integration, distributed resources, and power conditioning equipment.
- Develop technologies that provide options for consumers to manage and use energy more efficiently. One such option would be the application of solid-state electronics for the control and utilization of electric power and load management programs.
- Develop and implement technologies that will enable consumers to access a variety of electricity-related business opportunities.
There are several ways to define power quality and reliability. Under a recent CEIDS project, a new approach has been developed that extends the traditional utility measures of reliability to include short-term power quality events. The result is a straightforward quality-level plan that helps characterize the security, quality, reliability, and availability (SQRA) of electric power supply systems.
Defining quality levels helps distinguish the caliber of the electrical supply and, conversely, it helps define the quality levels needed from a particular power system (i.e., the correct combination of utility and local-support equipment). Based on the recent CEIDS report titled, “Analysis of Extremely Reliable Power Delivery Systems,” the following quality levels have been proposed:
- Quality Level 1: Moderate voltage sags, ITI (CBEMA) curve
- Quality Level 2: Severe voltage sags
- Quality Level 3: Momentary power interruptions
- Quality Level 4: Long-duration power interruptions
Quality levels provide more than just a way to characterize events. If the industry standardizes quality levels, much more is possible. Vendors can claim a certain test-level quality for equipment. Users can specify requirements, such as a device with a specific ride-through (e.g., semiconductor manufacturers' SEMI F47). Additionally, utilities can advertise or guarantee levels of quality that are more meaningful than SAIDI or SAIFI. Together, these effects lead to less downtime for end-use equipment.
Over the past seven months, extensive industry research has been conducted under CEIDS, resulting in the identification of some major concerns facing the electrical industry. They are:
The existing electromechanically controlled transmission grid was not designed to meet the demands of competitive markets in terms of scale, transactional complexity, and power quality.
Because of rapidly increasing wholesale transactions, the North American grid system is experiencing unexpected power flows and bottlenecks. So far, the needed improvements in both capacity and reliability have not been made.
During the last decade, for example, total electricity demand in the U.S. rose by nearly 30%, but the nation's transmission network grew by only 15% . During the same period, expenditures by investor-owned utilities for distribution system construction fell by about 10% in real terms. The outlook for the next decade is even worse: Demand is expected to grow by 20%, but planned transmission growth is expected to reach only 3.5% . The result is constrained transmission capacity that contributes to price increases and serious reliability issues.
Given the current difficulty in obtaining permission to construct new high-voltage lines, the most promising strategy for quickly increasing transmission capacity is to upgrade existing systems using advanced technology. In order to support a competitive wholesale market and provide a high level of reliability and security, the grid should evolve into an electronically controlled, self-healing electricity network that integrates real-time monitoring, communications, self-diagnostics, and control strategies.
In basic PQ and reliability terms, utility supply is limited to 99.9% or 99.99% percent reliability — with varying levels of power quality. Currently, achieving ultrahigh reliability at a lower cost means installing extensive redundant onsite (customer-side) generation, static switches, and uninterruptible power supply (UPS) equipment, coupled with various enhancements to the grid.
It would be prudent to develop opportunities to enhance the grid without the need for extensive customer-side equipment. Of course, these enhancements only make sense if utilities can recover the costs for the added value of enhanced reliability.
The ideal solution would involve a combination of options ranging from advances in end-use equipment to improvements in high-voltage transmission networks.
By developing options that will improve the reliability of the entire power system, from generation fence-lines to end-use devices, digital quality power can be supplied at the lowest possible cost. Advances are needed that will enable the supply of a premium grade of power from the transmission or distribution system. These advances can also serve the purpose of “hardening” the power delivery systems against the threat of natural or manmade disasters.
The complexity of the electric power system, combined with its large geographic extent, makes it vulnerable to natural events, human error, and intentional attack. The industry has a great deal of experience in dealing with the first two, and it has recently begun considering the urgency of protecting the physical assets of the power system against attack by terrorists or saboteurs.
Perhaps even more difficult to protect against would be cyber attacks on the computers and software used to handle the growing number of power transactions and operate the grid. Trends toward standardization of computer and software systems may inadvertently increase vulnerability to cyber attacks.
Maintaining the security of electric power supplies to these systems will become increasingly important in years to come. An EPRI survey of electric utilities revealed real concerns about grid and communications security. The most likely threats were bypassing controls, integrity violations, and authorization violations, with four in ten rating each as either a 5, or 4 out of 5. Concern about the potential threats generally grew as the size of the utility (peak load) grew.
Generally, there are two main utility-side approaches that increase overall power quality and reliability to customers.
The first involves the use of medium-voltage devices that improve voltage sags and, possibly, momentary interruptions. These devices are generally configured to supply improved quality to a fixed location — either one customer or a power quality park. Typically, utilities employ medium-voltage devices in these configurations:
- Static series compensators provide ride-through for sags by injecting a signal to offset the voltage lost during a sag.
- Stored energy backup provides ride-through for sags and momentary interruptions by using stored energy, including batteries, superconducting coils, and ultra-capacitors.
- Static transfer switches provide ride-through for momentary interruptions and most voltage sags by quickly switching between two different utility feeders.
The second utility-side approach for addressing voltage sags and momentary interruptions requires the development of more reliable distribution configurations, such as spot networks. Fig. 1 shows a “sag-resistant spot network” configuration. Although currently in the conceptual stage, this configuration could be implemented with existing technologies.
Significant investments in the grid system and customer-side equipment will be needed to determine optimal solutions for digital end users' SQRA requirements. At this stage, however, it's not clear what balance of investment in the supply side versus the customer side is required to most cost effectively meet the needs of the growing digital power market. The ideal approach will be based upon the characteristics of the existing power system and nature of the load at each specific site.
Locations with more reliable utility supply systems (such as urban areas where networks could be used) will need to rely less on customer-side equipment to reach high performance levels. Locations with poorer reliability (such as rural areas where radial distribution is used) will need to place more dependence on customer-side solutions and invest in such equipment as distributed generation (DG) and UPSs.
In some cases, it may be desirable to have an off-grid solution that is totally dependent on DG and customer-side solutions.
Some key factors that determine the optimal solution on the utility system side are the number of customers that demand high reliability, the amount they are willing to pay for it, the size of these loads, and the spatial distribution of such loads within the service territory. These and other factors will determine the optimal balance of investment between supply-side and customer-side solutions.
Despite the significant challenges facing the electrical industry, engineers are working on a variety of advanced power electronics solutions to ensure power quality and reliability.
Based on new materials and processing concepts, advanced power electronics devices will enable precise control and tuning of all power circuits for maximum performance, cost-effectiveness, and reliability. Within the electrical industry, they hold the potential to increase asset utilization and power throughput; reduce capital, operating, and maintenance costs; and create value-added services and other business opportunities. Defense, industrial, transportation, and other sectors will also benefit from the precise control and tuning capabilities of advanced high-power devices.
In addition, introducing integrated circuit-like control capabilities to the power grid will protect and enhance reliability in the deregulated energy market as the volume and magnitude of bulk power transactions grow. Advanced power electronics will enable more complete use of the existing energy infrastructure while ensuring adequate safety margins. This will free up society's resources for uses other than the capital-intensive upgrade or construction of transmission facilities. Some of these advanced power electronics solutions include:
Dual-sided control for gate turnoff thyristors (GTOs)
GTO thyristors with control circuits on both sides of the wafer will require smaller control signals, leading to power controllers that are less costly and more reliable.
Silicon carbide for power components
Silicon carbide can operate at much higher temperatures than silicon, which means that more power can be pumped through a single device. These devices will lead to lower-cost, more reliable solid-state power controllers.
A large flexible AC transmission system (FACTS) that uses silicon carbide GTOs will be approximately 50% less expensive than silicon-based devices. For example, a STATCOM currently costs $50/kVA. A silicon carbide-based device would cost $25/kVA. This substantial cost reduction will result in more installed devices. It is projected that, beginning in 2010, 2000 MVA in FACTS devices will be installed annually.
The primary benefit of a FACTS device is to increase the capacity of an existing line, thus avoiding or deferring the construction of a new line and/or substation. The Tennessee Valley Authority (TVA) has documented that it saved $14 million by installing a 100 MVA STATCOM and avoiding the expansion of a substation .
Similarly, distribution FACTS devices, such as the DSTATCOM, allow utilities to avoid or defer new additions to their distribution system. For example, American Electric Power (AEP) projects the savings of installing a DSTATCOM to be $600,000 . They anticipate that 100 of these devices will be installed annually starting in 2010.
A technological revolution is sweeping modern society, creating a new era of economic and social change driven by microprocessors and the digitally based technologies they enable. Programs such as CEIDS strive to ensure that electricity will continue to be the engine that drives economic progress. To do so, however, requires the active participation of representatives from all of the key stakeholder communities including utilities, energy providers, manufacturers, end users, and governmental and quasi-governmental organizations. If you would like to learn more about CEIDS or join the consortium, visit http://ceids.epri.com or call 800-313-3774 (option 4).
Marek Samotyj is the program director for CEIDS. He works at EPRI's affiliate, the Electricity Innovation Institute (E2I), in Palo Alto, Calif. You can reach him at [email protected].
Karen Forsten is a business development manager at EPRI PEAC's Greenville, Miss., office. She can be reached at [email protected].
Edison Electric Institute. EEI Statistical Yearbook, 1998 and 1999.
North American Electric Reliability Council, NERC Reliability Assessment (1999-2008). Princeton, N.J., 1999.
Innovator In-107577. “Statcom Provides Cost-Effective Voltage Support for TVA's Growing Load.” June, 1997.
Innovator In-111241. “AEP Applies DSTATCOM to Help Industrial Customer Expand Operations.” Oct., 1998.