Transformer neutral blocking device to prevent the flow of geomagnetically induced currents in power systems

Joseph W. Porter, John G. Kappenman, Scott R. Norr, Stephen Simo

Research output: Contribution to journalConference articlepeer-review


Geomagnetically-induced currents (GIC), which cause detrimental effects to electrical equipment and power system operation, enter power systems through grounded neutral leads of wye-connected transformers. The Electric Power Research Institute (EPRI) has sponsored research into strategies which mitigate the effects of geomagnetic disturbances. One such strategy involves the use of a Neutral Blocking/Bypass Device (NB/BD) which can be inserted in power transformer neutral-ground connections to block the flow of GIC while maintaining a low-impedance AC grounding path. The device consists of distribution capacitors which provide the blocking function for the quasi-dc geomagnetically-induced currents. The capacitors are rapidly bypassed by a combination of a sparkgap and circuit breaker to solidly ground the neutral during power system disturbances. The sparkgap provides the fast operating response speed, while the circuit breaker provides a secure metallic bypass of the capacitor. In both simulation, and in rigorous field test, the bypass operation will occur rapidly (less than 1 msec) and will both prevent ferroresonant over-voltages and preserve proper protective device operation.

Original languageEnglish (US)
Pages (from-to)1640-1645
Number of pages6
JournalProceedings of the American Power Conference
Issue numberpt 2
StatePublished - Dec 1 1993
EventProceedings of the 55th Annual Meeting of the American Power Conference. Part 1 (of 2) - Chicago, IL, USA
Duration: Apr 1 1993Apr 1 1993


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