Analysis of Fault Events in MVDC Architecture

Effective interruption of load currents under both normal and fault conditions presents major challenges in medium-voltage dc distribution systems. In a highly-integrated dc power system, the preponderance of power converters connecting several loads with power ranging from (W) to (MW) levels rises additional concerns about the effects of a dc fault on other loads connected to the same bus or adjacent buses. Equally critical are the interactions between these power converters during the fault isolation and clearance process. In order to address some of these issues, a basic but relevant model was constructed to study the behavior and effects of dc faults in an MVDC power system for an all-electric ship.

The results of the analysis appear in the paper, “Analysis of Fault Events in MVDC Architecture,” by A. Ouroua, J. Beno, and R. Hebner and were presented at the 2009 IEEE Electric Ship Technologies Symposium, April 20-22, 2009, in Baltimore, Maryland.

This team designed, built, and successfully ran a radial flux high temperature superconductor (HTS) trapped field magnet (TFM) motor. The motor was run in a zero field cooled mode. The paper, “Radial Flux High Temperature Superconductor Motor using Bulk Trapped Field Magnets,” by X. Feng, G. Gao, K. Davey, M. Werst, R. Hebner, R. Weinstein, D. Parks, and R. Sawh and presented at the IEEE International Electric Machines and Drives Conference in Miami, Florida, May 3-6, 2009, conveys several lessons learned about the use of TFMs in motor and generator applications. The state of the art of bulk TFM material is reviewed in the paper, with attention given to the difficulties of activating TFMs in a practical machine design. The difficulties are based on the cooling time needed to field-cool the TFMs; the maximum field which can be produced at the rotor using only MMF on the stator; and the maximum time for which the stator current can be high without sustaining insulation damage. The paper includes a prediction of improvements that can be expected using two significant departures from a conventional three-phase permanent magnet design. Both departures involve the addition of MMF on the rotor using a hybrid wound rotor design. Attention is given to predicting performance when no special activation is employed.