A Network for the Smart Grid

Ron Wilson, Altera Corporation

Say the words Smart Grid, and many people will think first of the new electric meter that recently appeared outside their home. But ask a power engineer, and she will talk about the most profound change in electricity distribution since AC conquered DC.

The Smart Grid will take the international power network from a collection of regional monitors and local electromechanical controls into an unknown new world of real-time, software-defined networks. In this article we will look at one piece of that giant transformation: the measurement-and-control network that will interconnect the intelligent elements of the grid.

Mapping the Grid

The world’s power grids weren’t designed—they grew. Most regional grids began as point-to-point connections between generating stations and loads. The loads could be specific large consumers such as a factory or streetcar line, or they could be substations that distributed power to residences. Siting decisions for power plants and the locations of customers determined the topology of the network.

From the beginning, these connections had a hierarchy: the greater the power being transported and the longer the distance, the greater the voltage. The interfaces between segments required switches, circuit-breakers, and transformers. Over time, these connections evolved into star topologies with a substation at the hub of each star, and then added redundant links in the higher levels of the hierarchy.

A control network evolved in parallel with the power-transmission network. Initially it used mechanical switches; electromechanical meters for voltage, current, phase, and volt ampere reactive (VAR) measurements; and humans for control. Because humans couldn’t always be fast enough to prevent damage to the network, the grid used automatic circuit breakers at key points. As the technology developed, the network added telemetry, remotely activated switches, centralized control rooms, and local intelligent devices such as reclosers—circuit breakers that would automatically make timed attempts to close and restore the circuit.

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