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Measuring Geomagnetically-Induced Currents Without De-Gaussing

January 22, 2018

Geomagnetically-Induced Current Measurement

One doesn’t naturally connect solar activity with Electric Utility disruptions, but Utility operators are keenly aware of the Sun’s impact on their systems and stability.

The Sun occasionally experiences Coronal Mass Ejections or CME’s. These “flares” release a shockwave of solar energetic particles, which in turn affect the Aural Electrojet Currents.These Currents can reach millions of Amperes and impact the Earth’s magnetic field by inducing electric fields along the surface of the earth, creating potentials on the Earth’s surface.

The field variations are slow in contrast to the system frequency and appear as quasi DC currents.

Grounded Neutral connections, common to many EHV transformers, complete a low resistance DC circuit that permits these DC currents to flow in the transformers. Unfortunately, the transformer’s cores saturate at very low levels of DC.

This saturation enables leakage flux, which in turn, produces eddy current heating in ferrous structural members that can lead to winding overheating and insulation damage. In extreme cases, transformer failure occurs. Replacement costs and lead times quickly become serious operational constraints.

Significant increases in harmonic content, absorption of VAR’s and the associate voltage stability problems can also create system problems.

All of which combine to make early detection of rising GIC’s critical.

GIC DC currents are normally detected in the neutral of the transformers, which in itself, is not difficult; however, it becomes challenging when the DC must be measured in the presence of significantly larger AC currents. In addition, fault conditions can result in AC currents that exceed 100 X the DC current detection level. Conventional detection methods have experienced significant residual after these events, which requires a physical site visit to De-gauss the device and remove the residual “set”.

OSI has created a device to simultaneously measure both the low-level DC currents associated with Solar events as well as the AC currents normally flowing in the neutral.

The device does not require de-gaussing following a fault event. The Utility maintains continuous monitoring without the delay and expense of a crew dispatch to de-gauss the device.

Interested in learning more?
Call or chat with us: www.OhioSemitronics.com