DETERMINATION OF CREEPAGE DISTANCE FOR MVDC SHIPBOARD POWER SYSTEMS
Abstract
19 APR 2018 The high-power demand of future U.S. Navy ships requires the utilization of Medium VoltageDirect Current (MVDC) architecture for powering shipboard propulsion, sensors, and weapons.Using MVDC on shipboard power system involves the knowledge of clearance and creepagedistance of electrical insulators for ungrounded-DC shipboard power systems. Also, in order toaddress the challenge of unprecedented levels of shipboard electrification through activelyswitching power electronic converters, it has been recognized that Navy???s existing standards forlow-voltage creepage and clearance are outdate, and, if applied to power electronic converters thestandards would lead to poor management of bus-interconnecting inductances and over-sizedequipment. As there are no existing standards on clearance and creepage distance for MVDC, thesedistances are extrapolated from medium voltage alternating current (MVAC) standards developedfor terrestrial power distribution systems. However, these extrapolations may not be accurate dueto the nature of space charge being different under AC and DC conditions. To account for thedifferences, MVDC clearance and creepage distance would have a large factor of safety which canunnecessarily increase the size of components in the system. Furthermore, as shipboard powersystems are usually ungrounded or a high-resistance ground, the voltage across the insulation canincrease in the event of a single-line-to-ground fault and cause additional stress in the insulation.Therefore, calculating the clearance and creepage distances for shipboard MVDC systems is notstraightforward and requires further investigation. The magnitude increase in voltage acrossinsulation upon fault depends on the location of the insulation in the power system. The eventualbreakdown of insulation upon increased voltage also depends on the amount of contamination oninsulator surface and degradation of insulation prior to the fault. As a result, a more comprehensivestudy is needed to determine the creepage distance in MVDC systems, which takes numerousfactors into consideration. The proposed research project consists of three stages, which are allnecessary to determine the creepage distance of MVDC systems: (1.) determine the voltage levelsacross bushings, cables and buses upon fault; (2.) build an experimental setup to determine the DCtracking degradation of the insulation used and measure the space charge across the insulatorsurface; (3.) develop a mathematical model that calculates/estimates the creepage distance basedon contamination and space charge. Accomplishment of stage (1.) requires system simulations andmodeling of equipment lowest replaceable units and interconnects within the cabinet. Work on(2.) and (3.) will be informed by and, in turn, inform present work on develop scaling laws formedium voltage connected power conversion and distribution equipment. The outcomes of theresearch will be recommendations for creepage and clearance requirements that the Navy canapply to future ships, development of methods and models for capturing creepage and clearanceimpacts to equipment sizing, and scaling and explorations into new methods that will increase thepower density of equipment while meeting the derived creepage and clearance standards. Thisproject is a collaboration between three Universities: Georgia Institute of Technology, Universityof Wisconsin-Milwaukee and Florida State University. The effort will be led by George Instituteof Technology.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 26, 2018
- Source ID
- N000141812623
Entities
People
- Lukas Graber
Organizations
- Georgia Tech Research Corporation
- Office of Naval Research
- United States Navy