A reliable power-line carrier-based relay system: Avoiding mistakes that cause PLC systems to misoperate or fail to operate

Power-Line Carrier (PLC) communications has been used since the 1930´s for protection functions. It was one of the first widely used communications for this purpose. Presently there are tens of thousands of terminals installed in the United States as well as over the world. The majority of the terminals in the United States are “dedicated” or narrowband type PLCs. While there are other and even newer technologies available such as broadband PLC, the dedicated PLC type is by far the most pervasive, particularly for protection functions. In order to have a reliable communication channel, the engineer must know the pros and cons of the channel, no matter what type of channel is used. PLC experience is diminishing in the industry as this “simple” communication scheme is overshadowed by the complexity of highly flexible microprocessor - based protective relays and more complex communication solutions. This paper will present topics that are helpful to understand power-line carrier problems in order to provide a reliable channel for protection functions. Topics will include such things as issues with design, installation and maintenance. Information will be presented to help the protection engineer avoid those mistakes that cause PLC systems to misoperate or fail to operate. For tutorial type of information the reader is encouraged to see IEEE 643-2004, IEEE Guide for Power-Line Carrier Applications as well as several other references listed in the back of this paper. What this paper does not cover are the PLC applications that are not dedicated to protective relay applications such as Broadband PLC, Single side band PLC, or Digital PLC. These technologies are multi-purpose - typically combining multiple applications into one channel or multiple channels. These are all technologies that are in use today, but for differing reasons may not be as applicable to protective relaying as the dedicated PLC.