Communication Channel Requirements for Pilot Protection

Introduction

Pilot relaying has been applied for transmission line protection since the 30's. The well known communication channels (pilot wire or Power Line Carrier) are increasingly being replaced by digital channels.  Dark fiber (dedicated fiber optic cable), multiplexed fiber optic systems (T1 and SONET) and 56 kbps phone lines are now made available for pilot protection purposes. The new channels provide much higher data transfer rate but reliability and security performance criteria developed for the telecommunications industry are not easily translated to teleprotection applications.

The demand for Information Technology and Telecommunications has grown exponentially over the last decade. Industries with critical infrastructure organizations, including electric utilities, are working to integrate their IT and telecom strategies in order to reduce costs, improve efficiency, and strengthen the information backbones within their corporations.

Teleprotection, or relaying, channels conventionally reside with the Utility Relaying group, as a relaying communications channel forms part of the Protection System. Relaying channels have traditionally been point-to-point connections but it seems logical and cost effective to use an existing digital communications network instead of installing or replacing a dedicated relay communications channel. The relaying demands, at first glance, seem to easily fit into the telecommunications network that generally provides high redundancy and high bandwidth.  However, due to a lack of understanding between the relaying group and the telecommunications group, the special requirements for teleprotection are not always clearly stated and, as a result, not fully considered in the communications network's design.  At the same time, the relay engineer does not have a clear picture of how the relay's data is transported from the local relay to the remote, receiving relay.  Consequently, any problems relating to the communications link can be hard to resolve due to lack of understanding of the entire teleprotection system, including both relays and communications.

Several working groups are active in this area. The new IEEE C37.94 "Standard for N times 64 kilobit per second Optical Fiber Interface between Tele-protection and Multiplexer Equipment" addresses connectivity between relays and multiplexers on an optical level.  PSCC (Power System Communications Committee) as well as WECC have groups working on guides to provide communications system designers with basic performance criteria for communication circuits carrying protective relaying applications.  The need for these guides was precipitated by the recognition of potential relay problems due to channel timing delays arising from the application of digital communications and switching technologies.

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