IEEE Electrification Magazine - December 2015 - 8

By Ramsis S. Girgis and Kiran B. Vedante

Impact of
GICs on Power
Transformers
Overheating is not the real issue.
HERE HAS BEEN SOME MISCONception in the electric power industry that geomagnetically induced
currents (GICs) can cause significant
overheating damage to the majority
of medium and large power transformers. Because
of the nature of GICs, the majority of power transformers would not experience damaging overheating because of them. This article presents the real
issue with GICs, which is that the combination of
the increase of reactive power absorption and injected current harmonics into the power system could
result in compromised grid stability.
To understand the effect of GICs on power transformers, this article starts by presenting the phenomenon of part-cycle saturation of transformer cores due to dc
and the resulting magnetizing current pulse. This is followed
by a description of the increase in transformer windings and
structural parts' temperature rises associated with dc. Calculated
values of these temperatures, considering the nature of the GIC pulses
in light of their short durations, are then presented.

T

basics of the effect of dc on Power Transformers
Phenomenon of Part-Cycle Saturation
of Transformer Cores When Subjected to dc
When a power transformer is subjected to dc, the result is a unidirectional dc flux in the core. The magnitude of the flux depends on the

Digital Object Identifier 10.1109/MELE.2015.2480355
Date of publication: 2 December 2015

8

I E E E E l e c t r i f i cati o n M agaz ine / december 2015

2325-5987/15©2015IEEE



Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2015

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