Fall 2004 Issue

Broadband over Power Lines (BPL) Interference: Fact or Fiction?

The following, which originally appeared in the July/August 2004 issue of
The Canadian Amateur, appears here courtesy the author and the Radio Amateurs of Canada. Its contents were summarized in a presentation the author made at the Central States VHF Society conference, which was held in Mississauga, Ontario, Canada on July 23–24, 2004. Because VE4MA is both an active amateur radio operator and an electrical engineer in the field of power systems telecommunications, he brings a unique perspective to the BPL controversy.

By Barry W. Malowanchuk,* VE4MA

BPL is an exciting new variation of an old idea. This old idea proposes to use the wires of electric power systems through neighborhoods and in buildings to transport high-speed Internet (broadband) data signals for public customers and for utility applications. These modern power-line carrier-current system variants are in the process of undergoing technical trials and limited implementation in Canada and in the USA. Concerns have been raised as to possible interference to users of the radio spectrum between 1.7 and 80 MHz. This article will attempt to give some technical information concerning the systems being proposed, the user applications, the nature of the possible interference, the control measures being proposed, the testing activities underway to evaluate possible interference, and the state of BPL deployments in Canada and in the USA.

System Technical Description

To understand the technical issues associated with interference, a basic understanding of how BPL systems are created and the differences among them is necessary. The differences lead to significant changes between system characteristics as they are implemented, and consequently, will greatly vary the potential impact on the radio amateur.
From a world perspective, BPL is not new. For at least a decade, BPL has been widely deployed in the United Kingdom. The reasons for early deployment there are not obvious, but consider that the heavily populated centers of Europe have already been “wired” for telephones. To rewire in order to deliver new or additional telecommunication services based on coaxial or fiber-optic cable is a very costly undertaking, which consequently would be unlikely to occur. The electric power system is, of course, already in place, and any technology that could make use of existing wires to deliver new services to customers is going to be a desirable option. This was also the motivation for the deployment of Digital Subscriber Line (DSL) modems on conventional telephone lines by the telephone companies.

European BPL

The electric systems of Europe are different from the electric systems in North America, and this goes beyond the standard use of 220 volts at 50 Hz, but rather is in the basic configuration. Each distribution transformer that converts the medium-voltage (MV) line voltage (4 to 40 kV) down to the low-voltage (LV) 220 volts has 200 to 250 customers who are connected to the LV side through coaxial supply cables. In the use of BPL, the distribution transformer is a significant obstacle, because the transformer, which is intended to pass low frequencies near 50 Hz, appears as an open circuit to the passage of higher frequency signals. Therefore, in order to provide telecommunications services to a large number of electricity system customers, a means of bypassing the transformer is necessary. This bypass operation is costly, as there are large voltages to deal with on the MV side of the transformer, and there are concerns with the transient voltages that are produced by lightning hits on the MV lines. The fact that 200 to 250 customers can be reached from the LV side of each transformer is the main reason for its early deployment in Europe, as the source of broadband data only needs to be delivered to each transformer by fiber-optic cable, DSL lines, or even broadband microwave radio. From the onset, this made the economics and practicality of BPL very attractive to reach European customers.

North American BPL

In North America, the situation is different, with a maximum of about 20 customers being served by a single distribution transformer, and in most cases the number of customers typically will vary from 1 to 8. Thus, providing BPL service to a large number of customers in NA will have a significantly higher cost than in Europe because of the need to attach to the LV side of a proportionately larger number of transformers at a much higher cost per customer. Otherwise, the transformer barrier needs to be crossed in order to get a better utilization of the high-speed data line. The NA BPL manufacturers have had to concentrate on transformer bypassing. Consequently, they have a number of options to choose from, which ultimately defines the major differences in their systems.

 

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