BROADBAND OVER POWER LINES

The principle behind broadband-over-power-line is deceptively simple:

because electric currents flow over just the low-frequency portions of power lines , there is ample room for data to stream over the unused higher frequencies inherent in alternating current.

To be sure, this idea of coupling data in radio frequencies with electricity on the same line, known as a carrier-current system, is not new. Utilities already take advantage of this fact by transmitting very basic network-maintenance and -monitoring data across their lines [12]. There are even home networking systems, called in-building BPL, available today that exploit a building's electrical wiring [8]. BPL is simply a more sophisticated, higher bandwidth version of these technologies. More about radio frequency and alternating current later, but first, we need to understand how electricity is produced and transmitted.

The Power Transmission and Distribution Grid

Naturally, we start our discussion at the electrical power plant. Here, energy is generated and distributed across a geographical region via powerful high voltage power lines that form the basis of the power distribution grid [5]. High voltage lines transmit between 155,000 to 765,000 volts of electricity. Like the Internet, the power grid is a network connected by wires (in this case, power lines; see Figure 1).

Figure 1. Power transmission and distribution grid [5].

At some point, the high voltage electricity will need to be converted by transformers, located at power substations, into a reduced voltage (7,200 volts) to be carried over medium voltage lines. This process, called a step-down, is necessary for areas unable to handle high voltage electricity.

Then, shortly before it enters a customer's home or business, a transformer drum steps down the voltage down even further to a more manageable, not to mention safer, voltage (240 volts) for consumer use. This power is usually carried over low voltage lines, which are held up by the wooden or steel electric poles you see overhead on many streets.