N25A-T012 TITLE: Medium Voltage Direct Current Protection Relays and Associated Sensors

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Directed Energy (DE)

OBJECTIVE: Develop a Fault Protection relay and associated sensors for 1 kV, 6 kV, and 12 kV Medium Voltage Direct Current (MVDC) distribution systems to implement overcurrent and differential / directional protection in both breaker and breakerless architectures.

DESCRIPTION: MVDC systems are an evolution of the DDG 1000 1 kV DC Integrated-Fight-Through-Power (IFTP) system combined with shared and distributed energy storage as well as advanced controls with active state anticipation data linkage between machinery and combat systems. 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. Once technically mature, MVDC IPESs are intended for Future Surface Combatants (FSCs) to affordably improve warfighting capability to meet evolving threats over the ship’s service life in an agile manner. The Navy is anticipating relying more and more on high power, highly dynamic, and pulsed weapons and sensors on FSCs. 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.

One of the key enablers of an MVDC IPES is reliable and affordable MVDC fault protection systems compatible with both breaker and breakerless fault protection strategies [Refs 1-2]. One of the primary functions of a fault protection system is to sense a fault (such as line to line short circuit) and act quickly to localize and initiate isolating the fault. This function may be performed in both circuit breakers and in protection relays. Circuit breakers typically must decide whether to open or close using only locally measured voltages and currents. Also, protection relays can use more remote current and voltage sensors at the edge of a protection zone to determine if a fault has occurred, and if so, if the fault is within the protection zone. The protection relay initiates action to isolate the fault by sending commands to active rectifiers, circuit breakers, and/or disconnect switches. Designs of future MVDC systems are anticipated to require the use of protection relays to achieve power reliability requirements.

In differential protection, the currents on all conductors of the same polarity entering or leaving the protection zone are summed by the protection relay; if they do not sum to zero, then a fault is within the zone. For directional protection, protection relays examine the direction of current flow to determine if a fault is within the zone. One challenge is minimizing false alarms by coordinating multiple current readings when fault currents rise with high di/dt, particularly in a bus topology supporting pulsed power loads. If the current readings do not occur near simultaneously when currents are quickly ramping up, the sum of the current readings may not sum to zero even if the fault is not within the zone. An additional challenge is proving robustness and reliability of MVDC current and voltage sensors.

The Navy seeks protection relay and associated voltage and current sensors to detect a fault, determine if the fault is within the protection zone, and initiate commands to isolate the fault (if the fault is in the protection zone) within 8 microseconds (threshold) and 1 microsecond (objective). These times are to prevent solid state circuit breaker overcurrent protection from activating without coordination with other circuit breakers. The threshold requirement may require insertion of system inductance to slow the current ramp rate; added inductance can result in stability issues that then must be addressed. The protection relay and associated voltage and current sensors should be designed for use in a shipboard environment (as defined in MIL-DTL-917) for a design life of forty years (threshold) or fifty years (objective). If there is a fault within the zone, the protection relay and associated sensors should operate as desired at least 99% of the time (threshold) or 99.9% of the time (objective). The protective relay should experience a false positive (initiating fault protection when no fault is present in the protection zone) on average no more than once every 30,000 operating hours (threshold) or 300,000 operating hours (objective). The protection relay should be able to differentiate between a fault and a pulsed load. Currently this application does not commercially exist.

PHASE I: Provide a concept design of an MVDC Protection Relay and associated sensors fulfilling the desired functionality listed in the Description. The feasibility of the MVDC Protection Relay and associated sensors should be demonstrated through circuit simulation.

The Phase I Option, if exercised, should include the identification of key knowledge gaps and risks, knowledge gap closure plans/risk mitigation steps, initial design specifications, and capabilities description. Provide a Phase II test plan and test procedures for a prototype solution that addresses the key knowledge gaps and risks. Deliver a draft procurement specification for the production system including the initial design specifications and capabilities description to build a prototype solution in Phase II.

PHASE II: Provide updated initial design specifications (if necessary) developed during the Phase I Option and produce a prototype system for testing in accordance with the test plan and test procedures. Include, if necessary, component testing to close knowledge gaps prior to updating the design specifications. Conduct the tests and update the system design and draft procurement specification for the production system based on lessons learned from testing. Deliver a fully tested prototype system to the Government.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology to Navy use. Any naval ship with elements of a MVDC distribution system (including CVN-78 class, DDG-1000 class, DDG-51 flight III, FFG-62, and DDG(X)) is a candidate for transitioning the technology.

In addition to naval warships, MVDC systems using the protection relays are anticipated to apply to commercial ships such as ferries, cruise ships, and ice breakers. Commercial applications are likely to increase in the upcoming years as international treaties enforce lower emissions from commercial ships; MVDC systems enable more efficient operation of diesel generator sets and easier integration of energy storage systems. Any terrestrial process control industrial application (oil refining, plastic production, chemical manufacturing, etc.) or renewal energy system employing MVDC could also benefit from the protection relay and associated sensors.

REFERENCES:

1. Doerry, Norbert H. and Amy Jr., John V. "Medium Voltage Direct Current (MVDC) Fault Detection, Localization, and Isolation." SNAME Maritime Convention 2022, Houston TX, Sept 27-29, 2022.

http://doerry.org/norbert/papers/SNAME-SMC-2022-073.pdf

2. Doerry, Norbert and Amy Jr., John V. "System Inductance for MVDC Circuit Breakers." IEEE Virtual ESTS 2021, July 27-August 6, 2021.

http://doerry.org/norbert/papers/20210601%20MVDC%20system%20inductance%20Doerry%20Amy.pdf

3. 2019 Naval Power and Energy System (NPES) Technology Development Roadmap.

https://www.navsea.navy.mil/Resources/NPES-Tech-Development-Roadmap/

KEYWORDS: Medium Voltage Direct Current; Fault Protection Relay; Current Sensor; Fault Detection and Localization; Differential Protection; Directional Protection

TPOC 1: Dr. Norbert Doerry
(301) 227-188
Email: [email protected]

TPOC 2: John Amy
(215) 897-130
Email: [email protected]

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