Clocks Trust: an Investigation of Recent 500KV Line Operations

The effect of sample synchronization on analog samples based differential protection is well known and understood. Sampling must be synchronized within an acceptable margin and samples taken at the same time, i.e., samples with equal timestamp values, are used in differential calculations. Given the importance of accurate synchronization, protective relays normally use supplementary information included with distributed time to determine time quality. But what if valid quality is sent with invalid time, and the relays are unaware of this ? An analysis of two 500KV line operations on California Oregon Intertie (COI) lines, both of which occurred on February 5, 2021, 15 minutes apart, led to answering the above question in great level of details. These events were re-created in multiple laboratories for testing and detailed investigations to determine the exact cause and effect sequence and the true root cause. Details of these investigations including field event records, synchronization and communication mechanisms, clock and relays behaviors, per the implemented algorithms are presented and explained in the paper. Thanks to the in-depth embedded debugging capabilities, root cause was conclusively determined for both events, using per message-based indicators and debugging data. Specifics of this detailed analysis, conclusions made, and corrective actions suggested are covered.