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About this Article
Written by: Philip Rendina
Written on: October 24th, 2003
Tags: computer science
Thumbnail by: Jeffrey G. Katz/Wikimedia Commons
About the Author
Philip W. Rendina was a junior currently pursuing a Bachelor's Degree in Electrical Engineering at Rose-Hulman Institute of Technology in Terre Haute, Indiana in the fall of 2003. He enjoys spending leisure time with family and friends, listening to music, photography, and video editing.
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Volume VI Issue I > Broadband over Power Lines
In order to bring high-speed internet to areas where developing a traditional broadband infrastructure would be cost prohibitive, engineers have recently begun working on developing techniques for delivering broadband internet signals over the existing power supply grid. By using an entirely different frequency range, power lines can carry traditional AC power and data signals simultaneously. Although modifications to the current infrastructure are necessary to deliver the signals and minimize interference, the technology looks promising, as tests have yielded results comparable to other methods of broadband delivery.

Introduction

Imagine living in a rural area of Wyoming and desiring to connect to the internet. Most likely, your only option is a dial-up connection at less than 56K speeds. Since there are relatively few subscribers in this area, cable and DSL (digital subscription lines) broadband internet service providers choose not to offer service, instead opting to focus on larger markets (Fig. 1).
Jeffrey G. Katz/Wikimedia Commons
Figure 1: High voltage lines in Washington State.
With the recent realization that high speed broadband internet signals can be carried over the power supply grid, public utility companies have developed and are now implementing such a service, PLC (power line communication). Because the utility companies have existing infrastructure in place to transmit BPL (broadband over power lines) signals, they have a significant advantage over cable and DSL providers: whereas traditional broadband providers need to set up an entire infrastructure to tap into a market, utility companies need only to make slight modifications to the power supply grid to allow transmission. Yet, these slight modifications have proven to be very problematic.
Although implementation of BPL is not without its problems, the potential benefits of such technology have driven engineers to develop various techniques to overcome these problems. Once fully operational and problem-free PLC systems implementing BPL are in place, everyone who has an electrical outlet will be able to have a high-speed internet connection.

The Power Supply Grid and How It Works

In power plants across the United States, three-phase AC (alternating current) power is generated at 60 Hz. Three-phase power refers to the three 120 degree phase shifts in the AC power sine wave between 0 and 360 degrees [1]. After generation, the power leaves the plant and travels a short distance to a transmission substation where the voltage component of the power is increased to anywhere from 36 to 300 kV to reduce the current, thereby reducing overall loss in the power lines. Leaving the transmission substation, the power is transmitted up to a distance of 300 miles on HV (high voltage) lines until reaching a power substation. At the power substation, the voltage is stepped down by transformers to a voltage in the range of 1 to 36 kV and also "split" by buses to be delivered along multiple MV (medium voltage) lines into cities and towns. Once in the city or town the voltage is again stepped-down by MV/LV (low voltage) pole transformers to 120 V. Taps are used to filter out two of the three phases of power that are to be delivered to the customer. At the customer's residence, the two phases are fed to a panel board that acts as a bus bar. All devices in the customer's residence utilize only one phase of power except for water heaters and similar devices, which use both phases to deliver 240 V [2] (Fig. 2).
Illumin
Figure 2: Take a tour of the different components along the power line that help to deliver electricity and data to one's home. (Flash)