and dynamic thermal rating of power lines could increase capacity along existing lines.

Some storage technologies will be ready for deployment before 2020; however, significant room for improvement remains. At larger scales that may be needed to support large quantities of intermittent renewable energy sources, pumped hydroelectric power and CAES will be the only viable options before 2020. Batteries may also be used for large-scale storage in the T&D systems but are unlikely to be available for deployment at the hundreds-of-MW scales until after 2020. On a smaller scale (around 10 MW), batteries are already being deployed to enable islanding and load-leveling in the distribution system. Newer technologies (including ultracapacitors and flywheels) may not be ready for wide-scale use before 2035.

Measurements, Communications, and Controls

A modern electric T&D system will need measurement, communications, and control technologies to gather real-time data on the state of the grid, communicate those data, and process them to enhance system controlability. These technologies, including associated software, are the basis for “intelligence in the grid.” The following subsections discuss the status of several of these technologies, likely technology improvements, and the potential for their deployment in the U.S. T&D system.

Sensing and Measurements

Understanding and acting on the current state of the U.S. T&D system requires measuring the power characteristics at numerous points. The basic measurements needed are current (amperes) and voltage (volts) at every electrical connection and the status of all switches (on or off). These data provide information on the grid’s electrical condition and connectivity.27

Measurements are made at each T&D substation and are used to drive its controls and protective devices (relays).28 Supervisory control and data acquisi-


Connectivity of the electrical network can be changed by selectively opening or closing its many circuit breakers.


Protective devices can detect short circuits and isolate the faulty equipment by opening circuit breakers.

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