Relay performance verification using fault event records

Introduction:Event reports recorded by intelligent electronic devices(IEDs)such as digital relays and fault recorders during disturbances depict the status and system parameters of the power system.Incorrect relay settings and unknown system parameters can lead to relay misoperation but information regarding these are available by performing a comprehensive analysis of fault records.Hence,it is necessary to regularly make a comprehensive assessment of the functioning of the relay to ensure reliable operation.Case description:The objective of this paper is to demonstrate various aspects of evaluating relay performance and verifying circuit parameters which are used in relay settings using field data in two case studies.Discussion and Evaluation:While scrutinizing the relay’s operation,this paper also presents key insights on verifying circuit parameters using the same relay event records.Conclusions:The lessons learned from the case studies presented in this paper will equip a protection engineer to inspect the operation of a relay during a transmission line fault,help gain a better understanding of the fault event and take possible actions to prevent future occurrence of similar events.

Estimating zero-sequence impedance of three-terminal transmission line and Thevenin impedance using relay measurement data

Current and voltage waveforms recorded by intelligent electronic devices(IEDs)are more useful than just performing post-fault analysis.The objective of this paper is to present techniques to estimate the zero-sequence line impedance of all sections of a three-terminal line and the Thevenin equivalent impedance of the transmission network upstream from the monitoring location using protective relay data collected during short-circuit ground fault events.Protective relaying data from all three terminals may not be always available.Furthermore,the data from each terminal may be unsynchronized and collected at different sampling rates with dissimilar fault time instants.Hence,this paper presents approaches which use unsynchronized measurement data from all the terminals as well as data from only two terminals to estimate the zero-sequence line impedance of all the sections of a three-terminal line.An algorithm to calculate positive-,negative-and zero-sequence Thevenin impedance of the upstream transmission network has also been presented in this paper.The efficacy of the proposed algorithms are demonstrated using a test case.The magnitude error percentage in determining the zero-sequence impedance was less than 1%in the test case presented.