This month’s Featured Technical Paper is from the Proceedings of the 2018 International Conference of Doble Clients. The paper is titled: Addressing Localized Saturation of Generator Neutral Current Transformers.
An investigation was undertaken to determine the cause of an incorrect operation of a hydroelectric generator differential relay element that occurred during an external fault. Through analysis of the relay event reports and lab tests that simulated the fault conditions, it was determined that external magnetic fields at the generator neutral bus locally saturated a generator neutral current transformer, causing the differential trip. Mitigation options including a flux-shielded current transformer and a differential relay element utilizing a “high security mode” setting were evaluated and shown effective through lab tests. This paper summarizes the investigation results.
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