Case Study Comparison of Serial and Ethernet Digital Technologies for Remedial Action Schemes

This presentation is a case study of a performance comparison of multiple communications technologies and architectures available via protection and automation IEDs for use in a remedial action scheme (RAS). Discussion includes design description and implementation issues of several popular and standardized technologies available today to perform high-speed, digital communication of data among IEDs. Discussion of the characteristics of each type of communication is combined with test results from an actual installation in a customer facility. Tests were performed in a lab environment and then also over a wide-area communications system with the goal of understanding the benefits of using protective relays and automation IEDs as RAS controllers. The objective was to improve the customer RAS monitoring and control capabilities, while, at the same time, enhancing diagnostics and reliability and reducing costs. The customer used the test results to evaluate the best method to provide relay-to-relay communications for internal and intertie RAS systems. The results are applicable to any use of high-speed, digital communications to transfer data among IEDs.The test consisted of installation and observation of each technology over long-distance and short-distance communications channels. Communication consisted of both EIA-232 serial ports and/or Ethernet connection (10/100BASE-T) and measurements identifying the performance and reliability characteristics of each communications method. The various technologies are compared based on the customer selection criteria of reliability, simplicity, speed, expandability, and cost. Measurements were made of the RAS message transfer time between line monitor IEDs and the central RAS controller and then from the central RAS controller to the IED performing the trip command. Timing was measured and recorded with accuracy assured by using satellite clocks to synchronize the IED clocks. Consideration was given to the ability of each technology to permit ongoing test and measurement of performance and reliability online without the need to schedule an outage and test offline as was necessary in the past. Reliability of the installed equipment is monitored using a continuous self-test and monitoring capability within the IEDs. This innovation eliminates the need to manually verify IED power supplies, communications quality, and I/O monitoring. The results of this online IED performance monitoring generates RAS equipment alarms that provide plant operators with real-time reliability indicators from each RAS plant IED and replaces the present method of manual inspection. When communicated via the digital communications methods, this information alerts the central RAS controller about the status of the RAS IEDs. Dependability and availability tests demonstrate the features of each protocol that provide the capability to detect both instantaneous channel failures and channel availability over extended periods of time.