Electric utilities have vast numbers of protective relays in their fleets, including generation, transmission, and distribution systems. It is very important to maintain an accurate database that stores the actual in-service settings for each and every relay. Off-the-shelf software already exists for storing and keeping track of all relay settings (Figure 1). It is vital to download the relay settings while on site because — due to federal regulations — it is not practical or easy to maintain remote access to relays protecting the bulk electric system (BES). Access to this information is necessary to meet requirements such as NERC’s critical infrastructure protection (CIP) standard.
Actual in-service relay settings are needed to develop proper test routines for maintenance and construction projects, to analyze system events when a misoperation occurs, and to perform arc flash studies. Using incorrect settings for any of these tasks can lead to dire unwanted results.
Relay technology ranges from older electromechanical to modern numerical relays. Note that the term “microprocessor-based” does not always apply to numerical relays. Some static relays use microprocessors but operate on analog secondary voltage and/or current signals. Numerical relays, on the other hand, operate on digitized secondary signals.
One of the many advantages numerical relays provide is the ability to save the settings in a file by downloading them with communications software as shown in Figure 2. This is not possible for electromechanical relays.
As-Found Versus As-Left Relay Settings
As-found relay settings are the pre-existing settings stored in the relay found on site. As-left settings are settings left after changing settings as tasks such as testing are completed. The best practice is to save both sets of settings whenever any testing (for example, routine maintenance) is conducted or a setting is changed for whatever reason. This method ensures an accurate history for each and every relay.
This article explains the importance of maintaining an accurate relay settings database. The actual on-site settings stored in the relay are necessary for developing test routines and conducting relay operation analysis.
Steve Turner is in charge of system protection for the fossil generation department at Arizona Public Service Company in Phoenix. After working with Beckwith Electric Company, Inc. for 10 years, Steve spent two years as a consultant in San Diego. His previous experience includes positions as an Application Engineer at GEC Alstom and in the international market for SEL focusing on transmission line protection applications. Steve also worked for Duke Energy (formerly Progress Energy), where he developed the first patent for double-ended fault location on overhead high-voltage transmission lines and was in charge of all maintenance standards in the transmission department for protective relaying. Steve has BSEE and MSEE degrees from Virginia Tech University. He has presented at numerous conferences including Georgia Tech Protective Relay Conference, Western Protective Relay Conference, ECNE, and Doble User Groups, as well as various international conferences. Steve is a senior member of IEEE and a member of the IEEE PSRC.