dc arc

Introduction

DC distribution systems are becoming common in aircraft, ships, automobiles—but also in residential homes.  A critical unique feature of dc distribution is the self-sustaining series arc fault.  The focus in this work is to provide a reasonable model of this dc arc to assess its impact on dc systems. 
Additionally, an imminent problem is the detection, localization, modeling, and simulation of arc faults.  These arcs form when conductors (or connectors) fail, break, crack, or degrade.  The arcs that form in dc, since self-sustained, and are sources of fire, skin burn, electrical shock, and asset damage.
 The Center for Electromechanics operates a megawatt-level dc microgrid that operates connected to the grid or in island model.  An example configuration is shown in Fig. 1. To understand the impact of dc arcs in dc microgrids, our microgrid has been faulted several times to capture significant fault data.

dc_microMicrogrid at the Center for Electromechanics (one possible configuration)

Fig. 1 shows a photograph of an arc forming under accelerated conductor separation.  This situation is occurs when conductors break and fall.  Fig. 2 shows a sustained arc in the presence of slowly varying gap distance.

dc fault
Fig 1 . DC arc fault under accelerated separation (800 V, 200 A)

dc fault

Fig 2 . DC arc fault under steady separation (280 V, 50 A)

Modeling and Simulation

Because staging arc faults is destructive, it is important to simulate arc damages using a computer model before staging faults in practice.  The Center for Electromechanics has developed a simple and accurate dc arc fault model.  The model consists of a nonlinear resistance in series with a voltage source as shown in Fig. 4.

arc branch

Fig 4 . Left: arc branch model showing voltages and currents terms. Right: how the arc branch model relates to two separating electrodes.

The model has been validated experimentally on our microgrid by staging three types of faults: constant-speed gap, fixed-distance gap, and accelerated gap. Comparisons of experimental and simulated faults are shown in Fig. 5-Fig. 7.  These comparisons show how well the model can predict the arc’s instantaneous voltage, current, power, and energy.

case_01
Fig 5 .  Case study 1: constant speed fault (top row: instantaneous voltage and current; bottom row: instantaneous power and cumulative energy).


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05/12 "A dc arc model for series faults in low voltage microgrids”
A.L. Gattozzi, J.D. Herbst, F.M. Uriarte, and R.E. Hebner, “Analytical description of a series fault on a dc bus,” Proc. 2012 IEEE PES Innovative Smart Grid Technologies Conference (ISGT), Washington, DC, USA, Jan. 16-19, 2012.

01/12 "Development of a Series Fault Model for DC Microgrids"
F.M. Uriarte, H.B. Estes, T.J. Hotz, A.L. Gattozzi, J.D. Herbst, A. Kwasinski, and R.E. Hebner, “Development of a series fault model for dc microgrids,” Proc. 2012 IEEE PES Innovative Smart Grid Technologies Conference (ISGT), Washington, DC, USA, Jan. 16-19, 2012.

 

 

 

case 02
Fig 6 .  Case study 2: gap opened to a fixed gap-distance fault (top row: instantaneous voltage and current; bottom row: instantaneous power and cumulative energy).

case 03
Fig 7 .  Case study 3: accelerated fault (top row: instantaneous voltage and current; bottom row: instantaneous power and cumulative energy).

Contact:
Description: Herbst Description: C:\Users\Fabian\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\Defense.png

John D. Herbst

j.herbst@cem.utexas.edu
512-232-1645

Fabian M. Uriarte

f.uriarte@cem.utexas.edu
512-232-8079

 

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