N211-069 TITLE: Medium Voltage Direct Current (MVDC) Partial Discharge and Space Charge Test Apparatus for Cable and Insulated Bus Pipe (IBP)
RT&L FOCUS AREA(S): Directed energy
TECHNOLOGY AREA(S): Ground / Sea Vehicles
OBJECTIVE: Develop an affordable test apparatus and test method for detecting Partial Discharge (PD), measuring Space Charge (SC), and estimating remaining service life of Medium Voltage Direct Current (MVDC) cable and Insulated Bus Pipe (IBP) installed on naval ships, and to develop a Health Index and method to estimate remaining service life.
DESCRIPTION: An Integrated Power and Energy System (IPES) offers the potential to provide revolutionary warfighting capability at an affordable cost. An IPES utilizes integrated energy storage and power along with advanced controls to provide a distribution bus suitable for servicing highly dynamic mission loads and propulsion demands while keeping the lights on. Additionally, such a system can enhance survivability, reliability, and flexibility while providing new capabilities such as the ability to quietly maneuver solely on energy storage. Currently, IPES development is focused on a MVDC system evolved from the DDG 1000 1kVDC Integrated-Fight-Through-Power system combined with shared and distributed energy storage as well as advanced controls with active state anticipation data linkage between machinery and combat systems. MVDC IPESs will be used on future surface combatants to affordably improve warfighting capability to meet evolving threats over the ship’s service life in an agile manner. As threat capabilities improve over the coming decades, the Navy is anticipated to rely more and more on high power, highly dynamic, and pulsed weapons and sensors. Because the need for generator synchronism is eliminated, MVDC is anticipated to be able to support these systems at lower cost, lower weight, and lower space requirements. Details on IPES are provided in the Naval Power & Energy Systems (NPES) Technology Development Roadmap.
As described in the NPES Technology Development Roadmap, ensuring service life of MVDC insulation is required for naval power and energy systems to support multiple future high power, pulsed sensors and weapons on future surface combatants. The ability to evaluate the health of MVDC insulation in installed cabling, insulated bus pipe (IBP) and their connections is critical to the successful implementation of MVDC and to avoid unplanned outages due to failed insulation systems. An important enabler to an MVDC system is a method to detect PD and measure the SC in the cable and/or IBP that has been installed onboard the ship during ship acceptance testing and periodically during the ship’s service life (Threshold) or continuously while the ship is operational (Objective). SC and voids in insulation of cables and IBP and their connections that operate above 1 kV can result in PD that can rapidly lead to failure of the cable / IBP insulation system. Traditional methods used for alternating current (AC) systems are not effective on MVDC systems. Existing methods for detecting PD in AC cables assume clean sinusoidal waveforms and are not suitable for MVDC systems with high frequency voltage ripple (See Ghosh, et al. [Ref 4] and Montanari, et al. [Ref 5]). SC in particular is unique to DC systems. Without an effective means to measure the health of the insulation system, the insulation system must incorporate large safety factors, resulting in thicker and heavier cables. Due to cable thickness limitations resulting from bend radius considerations, this conservative approach will require great expense and more cables of lower current capability to be paralleled together.
The power quality of MVDC on the shipboard distribution system shall be assumed to be in accordance with the "Preliminary Interface Standard, Medium Voltage Electric Power, Direct Current". The test apparatus shall be compatible with nominal system voltages of 6 kV, 12 kV, and 18 kV and steady-state current ratings up to 8,000 amps. The test is anticipated to be conducted shipboard during the acceptance testing of the ship and prior to ship delivery to the U.S. Navy, and periodically during the ship’s service life (Threshold) or continuously while operational (Objective) to verify continued PD-free operation and to measure SC.
MVDC systems are increasingly being used or considered for military and commercial applications (e.g., microgrids, offshore energy, wind farms, cruise ships). The test apparatus and test method will apply to these applications as well.
Initially, the test apparatus and test method are anticipated to be used by NSWC Philadelphia personnel to verify PD-free operation and to measure SC. Eventually, shipyards and repair facilities are anticipated to be required to use the test apparatus and test method on applicable MVDC systems. The test method is intended to be formalized in a Test Method Standard in accordance with MIL-STD-962. If the objective is met, PD-free operation and SC measurements will be continuously monitored onboard ship. Estimated remaining life of the insulation system will be presented to the operator for maintenance planning.
PHASE I: Develop a concept for an affordable method for detecting PD and measuring SC in MVDC distribution systems onboard naval ships. This concept must include a system design of the test apparatus and a draft test procedure. Develop and document a health index and method for estimating remaining service life of MVDC insulation in distribution system cabling / IBP. Demonstrate the feasibility of the concept through modeling and simulation. Identify the technical risks of the concept. The Phase I Option, if exercised, shall include the design of experiments to address the technical risks and the procurement of long lead experiment articles and associated test equipment for execution in Phase II.
PHASE II: Based on the results of Phase I efforts and the Phase II Statement of Work (SOW), conduct experiments to resolve technical risks. Employ the gained knowledge to develop a functional prototype of the test apparatus. Develop the test procedure, the health index calculation method, and the remaining service life estimate method. Validate performance of the test apparatus and test procedure initially through modeling and simulation, and then through testing.
PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology to Navy use. Develop the final production test apparatus suitable for use onboard naval ships and finalize the test method as a draft Test Method Standard in accordance with MIL-STD-962. Validate the performance of the production test apparatus and draft a Test Method Standard through testing. Deliver a test apparatus to the Government in accordance with the Phase III Statement of Work. Update and deliver to the Government the health index calculation method and the remaining service life estimate method.
KEYWORDS: Medium Voltage Direct Current; MVDC Partial Discharge; PD; MVDC Space Charge; SC; MVDC Insulation; MVDC Test Apparatus; MVDC Cable; MVDC Insulated Bus Pipe; IBP
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