Transcript Parallel Faults on DC Microgrids - The University of Texas at Austin

-Hunter Estes, graduate PhD student, NSF Fellow
The University of Texas at Austin
Department of Electrical & Computer Engineering
Research Advisors: Dr. Alexis Kwasinski & Dr. Robert Hebner
Research Group: Center for Electromechanics
http://www.utexas.edu/research/cem/dcmicrogridfaultexperiments.html
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The ONR’s next-generation, AES (all-electric ship) platform can be viewed
as an isolated microgrid. Many terrestrial microgrids are DC-based, and
DC is one of the voltage platforms currently being evaluated by the
ESRDC.
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While DC microgrids offer many advantages, a prime area of concern
relates to faults. Thus, quick fault recognition, identification, and control
strategy / fault management are a key research focus.
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The end-goal for DC systems is quick
fault remediation and/or branch
isolation of an affected circuit, while
impact on the remaining system
(ride through) is minimized.
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DC systems will likely need more
intelligence built into their system
for successful fault management
(i.e. DC smart grid)
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A microgrid was constructed in Center for Electromechanics power lab to
meet such testing protocol. This will allow for both connected & islandmode operation for the purposes of testing.
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The key component of fault testing was the design of a horizontal fault
mechanism. This allows for controlled separation or connection through
the use of an isolated stepper motor or a pneumatically-driven actuator.
Cathode (-)
Anode (+)
xgap
The focus of this research is to experimentally determine the
characteristics of horizontal series & parallel faults in DC systems, and to
explore the effects they have in terms of local and system disturbances.
 Note: Faults will also be studied in AC systems, as a basis for comparison
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Study: DC (280 – 750V) vs. AC systems of “quasi-equivalent” parameters
Monitor: AC & DC fault currents, gap voltages, arc fault transients, power
dissipated, bus disturbances, duration, re-strikes, loading effects
 Resolution: 50 – 0.5 μs data capture rates, 12 bit resolution
 Goals: DC arc modeling, arc fault detection, fault clearing strategies,
equipment designs, & safety recommendations
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DC horiz. series fault transients
AC horiz. series fault transients
DC horizontal parallel fault transients
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For series faults, DC systems did not show many fast-acting transients
(i.e. spikes) as compared to AC systems. However, DC series faults were
an order of magnitude longer in duration, and often damaged electrode
structures, locally.

DC series arcing faults are difficult to detect, for their voltages and
currents are very similar to pre-arcing conditions. However, equation
modeling for dynamic, DC series faults has been accomplished.
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AC series faults dissipated within a few cycles from the point of electrode
discontinuity. However, re-ignitions were possible. Additionally, fastacting transients were observed in both the gap voltage and current
waveforms. With magnitudes up to four times the bus voltage, these
spikes may be cause for alarm as this would exceed voltage ratings for
various passive components within system power electronics.
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DC parallel faults seem to show some disturbances at lower levels.
However, testing will continue to higher thresholds to observe such effects
in more detail. These will also be compared to AC systems.