High Current Cooled Flexible Bus Work Systems
Navy SBIR 2019.2 - Topic N192-125
ONR - Ms. Lore-Anne Ponirakis - loreanne.ponirakis@navy.mil
Opens: May 31, 2019 - Closes: July 1, 2019 (8:00 PM ET)


TITLE: High Current Cooled Flexible Bus Work Systems


TECHNOLOGY AREA(S): Electronics, Materials/Processes, Weapons ACQUISITION PROGRAM: Electromagnetic Railgun

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.


OBJECTIVE: Develop an innovative flexible bus work design with an integrated cooling system that supports small effective bend radii and high heat removal rates, while retaining structural robustness.

DESCRIPTION: The United States Navy is actively developing the Electromagnetic Railgun, which requires transfer and consolidation of large pulsed current operating at a high repetition rate. Thus, the design of integrated cooling of the current transfer system becomes a significant component of the design. A subset of this pulsed current transfer system has the additional design challenge of relative motion between components in the circuit. Examples of this are the training, elevation, and recoil in the Electromagnetic Railgun.


The combination of motion and cooling in the current transfer system presents a challenge. Existing cooled hard bus designs are efficient for transferring current and cooling, but do not support the motion. Flexible coaxial cables have long been used to transfer current and to accommodate the recoil in a Railgun, but these are typically uncooled.

Cooled coaxial cables do exist, but have not yet been proven to fully support the required training and elevation needs of a tactical Electromagnetic Railgun mount.


While flexible bus work is often implemented through flexibility in the conductors themselves, there is no requirement here on how the bus work flexibility is implemented. Flexible conductors, articulating hard bus work with joints, sliding contacts, and any other proposed solution that satisfies requirements are acceptable. The proposed designs can be composed of multiple parallel conducting paths carrying a subset of the current, or a single conducting path carrying the total current.


The minimum bend radius for any proposed solution is required to be less than 0.5 m, with an objective of less than

0.25 m. The proposed solution should scale to greater than 5 m in length, and the desire is to minimize the cross sectional area. The proposed system must conduct pulsed current with peak current of up to 5 million amperes with total electrical action up to 250e9 A2s, at a repetition rate of up to 20 pulses per minute, and operate at voltages of up to 10,000 volts. Inflow coolant temperatures expected to range from 10 to 40 °C.


Furthermore, this bus work design must be structurally robust, able to survive installation, handling, shipboard environment, and the Lorentz forces that occur during operation. Methods of terminating the bus work must be considered, including both electrical connections and connections to the cooling system. Typical electrical connections will terminate either to a fixed coaxial parallel plate bus work.


The proposed system shall meet all requirements after exposure to transportation vibration per MIL-STD-810G. The proposed system shall perform as intended and without degradation while experience Type I vibration in accordance with MIL-STD-176 for frequency range 4-15 Hz. Finally, the component interfaces requiring an electrical bond in the proposed system shall be in accordance with MIL-STD-464, using MIL-STD-1310 as a guide.


PHASE I: Develop a flexible bus work concept design with integrated cooling the meets the U.S. Navy’s needs. Demonstrate the feasibility of this approach through modeling, simulation, and scaled testing; and the potential to scale the technology to a relevant scale. Develop a Phase II plan.


PHASE II: Advance the concept design into a full-scale demonstration design prototype to be manufactured and tested in a repetition rated capable Railgun system at NSWCDD Dahlgren. Government furnished equipment will be used for pulsed power and for the electrical load.


PHASE III DUAL USE APPLICATIONS: Perform a final design iteration on the Phase II demonstration design prototype, taking advantages of any lessons learned in Phase II. Integrate the new flexible, cooled bus work design into a tactically relevant Railgun system. This final design will be manufactured and tested in the selected Railgun system.



1.   Carpenter, C.J. "Action-reaction forces between current-carrying conductors." Science, Measurement and Technology, IEE Proceedings - Volume 153, Issue 2, 9 March 2006, pp. 73-80. https://ieeexplore.ieee.org/document/1608697


2.   Kerrisk, J. "Railgun conductor heating from multiple current pulses." IEEE Transactions on Magnetics, Volume 22, Issue 6, Nov 1986, pp. 1561-1566. https://ieeexplore.ieee.org/document/1064727

3.   Lombardi, A.; Donazzi, F.; Taralli, C.; Tencer, C.; and Lima, A.J.O. "Heat transfer in forced cooled cables." IEEE Transactions on Power Delivery, Volume 5, Issue 1, Jan. 1990, pp. 8-13. https://ieeexplore.ieee.org/abstract/document/107248


KEYWORDS: Flexible Bus Work; Pulsed Current Transfer; Cooled Bus Work; Electromagnetic Railgun



Joel Mejeur





Tom Boucher





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