Development of an improved low frequency transformer model for use in GIC studies
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Date
2004
Authors
Chandrasena, Waruna
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Abstract
Geomagnetically Induced Currents (GIC) are the ground effect of a complicated space
weather chain that originates in the sun. During a GIC event, the quasi dc current
that enters the transformers through the grounded neutral can cause severe half cycle
saturation in the iron core. This results in increased reactive power consumption
and generation of significant levels of harmonic currents. A severe GIC event in 1989
caused a complete blackout in the Hydro-Quebec system, and it shows how vulnerable
a power system can be.
There have been many simulation studies carried out to model the effects of GIC
in power systems using electromagnetic transient simulation programmes. Many of
these attempts have used curve fitting techniques to model the hysteresis characteristics
of power transformers. However, the correct representation of the hysteresis,
including the long term remanence and recoil loops is important, since the source of
the harmonic generation is the transformer itself. Therefore, the main objective of
this work is to develop a simulation model of a power transformer that represents
hysteresis characteristics including long term remanence and recoil loops. Further,
the new model is used in simulation studies to analyse the effects of GIC in รข power
system.
The new model is based on the Jiles Atherton (JA) theory of ferromagnetic hysteresis.
The eddy current effects are also incorporated into the same model, so that
the simulated B-H loop is frequency dependent. The new model is implemented using
the transient simulation software PSCAD/ENITDC, and it is validated by comparing
simulation results with recorded waveforms. A good agreement is achieved between
the simulated and recorded waveforms.
Effects of GIC on a power system are analyzed using a simulation model of a
power system. Simulation studies show that a transient simulation carried out to
model a GIC event requires not only the magnitude of the quasi dc current, but also
its history with respect to any particular point of interest. Further, simulation studies
demonstrate that it is important to accurately model the remanence effects of the iron
core of power transformers.