be addressed regarding their selection and application and to reduce costs.

Equipment That Allows Greater Control of Energy Flows

Greater control of energy flows reduces the risk of cascading failures and may speed restoration of power after a major outage. Medium-voltage (4-13 kV) and high-voltage (>69 kV) high-power electronic-based controllers can provide flexibility and speed in controlling the flow of power over transmission and distribution lines. New energy storage units can help level loads and improve system stability. Some specific examples of these equipment technologies are given below.

Flexible AC Transmission System (FACTS) Devices

High-voltage power electronic-based controllers are currently being demonstrated. FACTS controllers can increase the power transfer capability of transmission and distribution lines and improve overall system reliability by reacting almost instantaneously to disturbances. The unified power flow controller and the convertible static compensator are key examples of FACTS technology. They control both real and reactive power flows among transmission corridors and maintain the stability of transmission voltage. More research, design, and development is needed to reduce the cost and enhance the performance of FACTS technologies. The next steps should include the development of the fourth generation of FACTS controllers using advanced power electronics devices.

Advanced Power Electronic Devices

The next major step in the development of power electronic devices would be to replace the silicon-based thyris-tors used in current devices with thyristors based on wideband-gap semiconductor materials, such as silicon carbide, gallium nitride, or very-thin-film diamond materials. These materials have the potential to reduce the cost of power electronic controls.

FACTS Integrated with Storage

Fast-response devices for energy storage could be used with FACTS controllers to provide ride-through capability for transient and brief outages. One promising technology, superconducting magnetic energy storage (SMES), responds to disturbances in less than one AC cycle and provides ride-through capability for multi-second outages. Research is needed to adapt the high-temperature superconducting materials described above for cables for use in the high-field SMES environment, potentially lowering the cost so that these units can be used to support the electric power transmission system.

Voltage-sourced Converters

Voltage-sourced converters can be used to connect independent asynchronous AC transmission systems. Other thyristor-based controllers can supply reactive power (i.e., volt-ampere-reactives) for voltage support and reactive power management in transmission systems. Connection of systems that now cannot be connected might lead to increased power flow.

Intelligent Universal Transformers

The intelligent universal transformer concept involves a state-of-the-art power electronic system and is not a transformer device in the traditional sense. It would be designed to replace conventional transformers with a power electronic system that steps voltage as traditional transformers do, but can also manage and control consumer demand and power flows, and compensate for reactive power.

Advanced Monitoring and Communications Equipment

Substantial improvements in the cost and performance of sensors and communications media and equipment offer the prospect of increasing the capacity of existing power system facilities by monitoring and compensating for the operating conditions of numerous devices simultaneously. Examples include the following.

Integrated Communication Architecture

Overlaying a communication architecture on the existing power delivery system could be a foundation for enhancing the functionality of the power system and, therefore, its resilience. This requires an open standards-based systems architecture for an infrastructure for data communications and distributed computing. Several technical elements of this infrastructure include, but are not limited to, data networking, communications over a wide variety of physical media, and embedded computing technologies. Challenges remain in fully deploying such an architecture while meeting cyber security challenges.

Wide Area Measurement System

The Wide Area Measurement System (WAMS), based on a combination of satellite communications employing time-stamping with fiber or wireless, will provide the real-time information needed for integrated control of large, highly interconnected transmission systems. By constantly monitoring the health of a network across a wide geographical area, WAMS can detect abnormal system conditions as they arise.

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