Utility Automation & Engineering|T&D - April 2007

Attenuation on MV Lines

A BPL device is attached to the power line via an MV overhead coupler ( capacitive or inductive). It transmits its data over the coupler onto the power line. The signal travels the circuit, encountering utility equipment along the way that weakens it. Obviously, the overhead line itself tends to attenuate the signal the further it goes, but, for the most part, other devices such as capacitor banks and transformers tend to impact the separation distance between two neighboring devices significantly more, unless of course, it is in a rural setting with limited number of utility devices per mile.

Eventually the signal will become too weak to be useful. At some distance closer to the upstream device, another BPL device can be installed that can repeat the signal it received from the previous device and then send it down the line

to the next device. Signals on the higher frequencies (closer to 30MHz) usually experience higher attenuation.

Capacitor banks and transformers are two major contributors to signal attenuation. Other factors that attribute to signal attenuation include reflected signals caused by impedance mismatches, but typically these two devices tend to outweigh the impact of the other factors.

Normally, a single capacitor bank won’t attenuate the signal sufficiently to where it becomes useless; however multiple capacitor banks between two BPL devices (in relatively close proximity to each other) can. In some cases, there may not be a pole between two capacitor banks where an additional BPL device could be installed, which will make it difficult—but not impossible— to overcome. BPL vendors are working

on solutions to this problem and some may have already solved this.

Noise and attenuation problems can impact a BPL installation in a significant way if not addressed properly. Before any BPL equipment is deployed, the RF noise should be assessed to gain a better understanding of what to expect. The BPL industry has come a long way in solving many of the issues encountered on MV circuits, but there are many lessons yet to be learned. BPL equipment manufacturers as well as the utilities that are deploying this technology are constantly looking at new ways to address these challenges as they gain better understanding of the MV distribution networks. ❮❮

Ray Blair is vice president, Broadband over Power Line Initiatives, IBM. Charlie Arteaga is chief architect, Broadband over Power Line Initiatives, IBM.

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