Selection of pilot relaying communication channels-a case study

Communications channels and channel devices for pilot relaying channels traditionally reside in the relay engineers´ domain. Today, many conventional communication channels are being replaced by digital communications networks, which are governed by other departments in the utility. The use of these channels for relaying requires the protective relay engineers to have a working knowledge of digital communications. Many relay engineers are responsible for specifying and/or designing protection schemes that include pilot communication channels. Some protection engineers have little expertise in the area of communications making it difficult to select or specify an acceptable criterion for a reliable channel in terms that are understood by the communications engineers. This paper will look at how one utility evaluated their options for pilot relaying communications channels. It will cover their selection criteria and the qualities they require in the products they use. It will address reliability concerns from substation environment to delay characteristics of communications equipment. The paper is deigned to enlighten the protective relay engineer in the area of communications as applied to protective relaying and the considerations one utility used to evaluate their choices