Date of Award

2019

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering (PhD)

Administrative Home Department

Department of Electrical and Computer Engineering

Advisor 1

Bruce A. Mork

Committee Member 1

Sumit Paudyal

Committee Member 2

Leonard J. Bohmann

Committee Member 3

R. Andrew Swartz

Abstract

Power transformers are key components in the power grid and any unexpected failure can cause widespread blackouts with substantial downtime, loss of revenue, and costs to repair or replace. Detection and discrimination of a short circuit in the early stages of fault origin provide fast relaying operation and save equipment from further damage. This research deals with two such disturbances. The first is a short circuit internal to the transformer windings and the second is a Geomagnetic Disturbance (GMD), an external cosmic event that may magnetically saturate the transformer core and impact the power grid on a larger scale.

In order to model an internal winding fault for both turn-to-turn and turn-to-ground, a methodology was developed to obtain the leakage inductances using Finite Element Analysis. Various challenges were addressed, and advances were made in the modeling and implementation in the EMTP time-domain environment. Further, with the help of developed techniques, winding fault characterization was made and simplification to equivalent mathematical relations was achieved. Benchmarking of this new EMTP model vs. a manufacturer's proprietary model provides excellent confidence in the developed methodology. A wide range of simulations of complex winding faults was performed to compare the performance of conventional differential approaches and inferences were drawn. Laboratory implementation of Park's vector-based approach was achieved. Relay tests were performed to compare the response of the conventional (phase and negative sequence) algorithm to the Park's approach. The Park's approach worked well as an alternative to negative sequence for detecting single-turn turn-to-turn winding faults.

Geomagnetic Induced Currents (GICs) and their possible ill effects have been a concern to the power system operator. In recent times, various utilities, regulators, ISO and industrial partners have shown interest in combating the problems of GIC/GMD when it occurs. Today, empirical phasor analysis-based methods are prevalent. As an improvement on this, time-domain modeling approaches for studying and analyzing the disturbances are devised and developed. These new models are tested, validated and inferences from the study are presented. This time-domain approach captures nonlinear and frequency-dependent effects that are typically linearized or simplified by prevailing phasor-domain simulation tools. This method shows great promise as an improved alternative for GMD analyses.

Available for download on Thursday, December 31, 2020

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