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PTP & Non-PTP Based End-to-End Dynamic Testing Methodology for Validation of Line Differential Protection - Test Consideration and Challenges

End-to-end testing is performed to validate protection schemes for transmission lines. In the case of line differential protection testing, this is performed by injecting the test values at the relay terminals on both sides of the line under test. The injection of the test values should be done simultaneously in order to properly simulate the system conditions during the time of the fault. Static tests typically involve the injection of test values known as System States. While this type of test is the norm for performing end to end tests in line differential schemes, they are not real representations of the system behavior during faults. Dynamic tests, on the other hand, involve the application of realistic faults typically in the form of properly simulated faults using COMTRADE playback. The ability to synchronize the test systems located on each end of the line is paramount. With the use of GPS-based, or other time sources now available, the synchronization of test systems, even when they are from different manufacturers or generations, can be properly achieved, and end-to-end tests can be performed successfully. In this paper, the theory of line differential protection, the importance of end-to-end testing, test considerations, and validation of differential characteristics using dynamic tests to perform End-to-End tests are discussed. The timing signals used have a great influence on the results of End-to-End tests and now typical time sources like GPS-enabled clocks are not always available due to the location of some of the elements to be tested. The evolution of Precision Timing Protocol (PTP) and the ubiquity of ethernet networks has made it even easier to access this kind of time source which can be reliably used for End-to-End tests in cases where other time sources are not available. In the paper, IRIG-B signals from GPS referenced clock as well as PTP timing signals are used to synchronize the test systems, and results are compared. Specifically, the 87L element is tested for pick-up accuracy, time of operation, and security by simulating internal and external faults for a short transmission line, and results are discussed. This paper proves that validation of line current differential by performing End-to-End tests using dynamic test methods successfully involving non PTP equipment as well as PTP equipment is achievable. This paper also sheds light on the challenges involved in end-to-end testing when using different models of test equipment with different current injection times. Recommendations are provided on how to calculate the time differences in injection time between different test sets and how to overcome the challenges associated with the synchronization of such test sets, for simultaneous injection.