Narrowband power-line carrier for use in protective relaying applications

The term power-line carrier is used to describe several different types of applications. In general use, it means using the 50/60 Hz power line for communications. The differentiation is in the line voltage and its application. Residential and commercial (120/220 Vac) applications are for home load control: Industrial (4 kV to 69 kVac) applications are for industrial process or metering reading and utility (4 kV to 765 kVac) applications are for system protection. There is interest in the present market for internet-high speed access via the power lines, which mainly pertains to residential access to the Internet via the lower voltage distribution lines. This paper discusses the use of power-line carrier in one of its oldest application - protection of the power transmission systems, using analogue techniques. We will cover the application of the equipment as well the theory behind the operation. A comparison of single - sideband PLC application, digital PLC, and narrowband PLC applications will be discussed, with emphasis on the narrowband PLC applications. A review of the some basic principals will be presented to help the reader refresh his understanding of those communication principles applicable.