This month’s Featured Technical Paper is from the Proceedings of the 2017 International Conference of Doble Clients. The paper is titled: Transformer Investments: Potential Equipment and System Impact of Severe Harmonic Distortion during Geomagnetic Disturbance.
Geomagnetic disturbances (GMD) can force large quasi-dc geomagnetically induced currents (GIC) through power transformers, resulting in severe part-cycle saturation. In addition to the direct thermal impacts of the saturation on transformers, which have been widely discussed in the industry, the saturation also causes large reactive power demand and harmonic current injections. This paper addresses the latter issue; the potentially extreme levels of harmonic distortion that can result from simultaneous saturation of many transformers in a transmission system. Far more than a routine power quality issue, voltage distortion levels of several tens of percent can interfere with protection systems and subject transformers, capacitors, cables, generators, and other equipment to severe duty. In many cases, the protection systems of the equipment might not adequately address this harmonic duty. The paper describes the sensitivity of equipment and systems, the protection gaps, and how these vulnerabilities can be assessed to comply with the recent NERC TPL-007-1 standard.
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