## ARPA-E releases $10M for 6 projects developing electrical systems for fully-electric aviation applications ##### 27 February 2021 ARPA-E released$10 million in funding for 6 projects as part of the Connecting Aviation By Lighter Electrical Systems (CABLES) topic. CABLES is one of a set of projects supported by an ongoing funding opportunity for a range of the most innovative and unconventional ideas across the energy technology spectrum, exploring high-risk R&D that could lead to the development of disruptive technologies.

The projects selected under this opportunity and associated topics are not part of an existing ARPA-E program, but if successful could establish a new program area for ARPA-E to explore further.

CABLES teams will develop medium-voltage (> 10 kV) power distribution cables, connectors, and circuit breakers for fully-electrical aviation applications. Future all-electric, twin-aisle aircraft will require more than 50 MW of power distribution capability; the targeted outcome of this topic is to enable megawatt scale distribution with minimal impact on weight while maintaining the high reliability and safety requirements of aviation.

Projects will develop functioning prototypes tested to relevant aviation standards in order to broadly address the following critical technical challenges in this space:

• Identifying appropriate wiring materials with optimum gravimetric power densities and minimum electrical losses, and evaluating corresponding vacuum or cryogenic systems if necessary;

• Identifying insulating materials with high dielectric strength, good thermal conductivity, low specific weight, conformality, malleability, and air-void minimization;

• Assessing connector designs;

• Developing circuit breakers for aviation applications; and

• Addressing partial discharge related reliability issues that arise from low air pressure environments in aviation.

The funded projects are:

General Electric Company, GE Research. Megawatt Any-Altitude Gas Insulated Cable system for aircraft power distribution (MAAGIC) - $3,448,797. GE Research will develop a safe, lightweight, and altitude-capable megawatt power cable system with electromagnetic interference shielding capability for large aircraft. The proposed 10 MW cable system is expected to achieve ten times greater power density than conventional technology without degradation by partial discharge and is fire safe and oil resistant. This cable system will enable all-electric distributed propulsors for future large aircraft to achieve zero emissions by using aluminum conductors insulated and cooled with CO2, both of which are readily available, manufacturable materials. The proposed cable technology can also be used in other applications requiring high cable power density with a relatively small footprint including electric ships, submarines, and offshore wind turbine platforms. Illinois Institute of Technology. Superconducting Momentary Circuit Interrupter: Fault Protection with Ultralow Loss and Ultrafast Response for Future Electric Aviation -$779,374. Fault protection must be provided for future turboelectric aircraft’s medium-voltage direct current power systems, but not necessarily from conventional circuit breakers. Illinois Institute of Technology will develop a 10 kV/150A superconducting momentary circuit interrupter (SMCI) to provide fault protection with ultralow power loss (<1 W), ultrafast response (<10 μs or ten millionth of a second), and high-power density.

The architecture comprises an SMCI with a fast mechanical disconnect switch. Under normal operation, the SMCI conducts a DC load current through a high-temperature superconducting winding of a pulse transformer. Under a fault condition, the SMCI injects a high transient voltage via the transformer, drives the fault current to zero quickly, and holds the current as a small AC ripple current, allowing the mechanical switch to open safely and isolate the fault.

Virginia Tech. High Power Density Cost-Effective MV DC Aircraft Cable- $1,171,829. To make the power density of electric aircraft closer to conventional aircraft, an electric power system (EPS) with high power delivery and low system mass is necessary. As an essential component of aircraft EPS, cables are necessary to transmit power from one node to another. Virginia Tech will develop a high-power density, cost-effective ±5 kV cable for twin-aisle all-electric aircraft. Innovations include conductors with increased current-carrying capacity; a multilayer, multifunctional insulation system made of exceptionally high thermal conductivity materials; and a new insulation solution for higher voltages with superior mechanical strength and electrical reliability. Designed for DC voltage, the new insulator will allow fewer partial discharge events and provide improved electromagnetic interference protection. University of Tennessee. Ultra-Light Tightly-Integrated Modular Aviation-Transportation Enabling Solid-State Circuit Breaker (ULTIMATE-SSCB)-$1,400,000. A medium-voltage direct current (MVDC) system provides lower distribution losses, higher power carrying capacity, and reduced conductor material compared with its low voltage alternative current counterpart. These benefits are critical to meet stringent weight and size requirements for aviation applications.

The University of Tennessee will develop a lightweight, reliable, efficient, and flexible protection solution for future electrified aircraft propulsion systems that are expected to use a 1 kV to 10 kV MVDC distribution system. The team will develop a modular architecture with a highly integrated customized module, use advanced solid-state semiconductor devices cooled at cryogenic temperatures, and integrate protection intelligence to achieve project objectives.

Advanced Conductor Technologies LLC. Lightweight, High-power Density, Self-protecting Superconducting Power Cables and Connectors for Electric Aircraft Applications - $1,600,000. Advanced Conductor Technologies will develop two-pole, high-temperature, superconducting DC power cables and connectors with a power rating of up to 50 MW to enable twin-aisle aircraft with distributed electric propulsion to reduce carbon emissions. The cables and connectors will contain insulation independent of the cryogenic medium used as coolant and allow an operating voltage of 10 kV. Because they have intrinsic fault current limiting capabilities, the cables can protect the power distribution network from over-currents. This intrinsic capability will reduce the complexity of the power distribution network while improving its reliability. Hyper Tech Research. Power Transmission Cable for Electric Aircraft using Bio LNG for Cooling and Thermal Management -$1,600,000. There are two key engineering challenges in the development of 10 kV, 10 MW electric power distribution cables for double-aisle passenger aircraft. One is providing sufficient electrical insulation at high voltages and the second is transferring heat away from the conductors. Hyper Tech Research will decrease the resistivity of copper-clad aluminum conductors by a factor of three by maintaining the temperature of the conductors at around 120 Kelvin (-153 ˚C).

The goal of the technology is to reduce the conductor size, cryostat size, and cable volume and weight to significantly lower the mass-per-unit length of the cable. The team proposes to use available carbon neutral fuel, such as bio-liquefied natural gas (Bio-LNG), for electrical insulation and as a heat transfer medium. After cooling the cable, the Bio-LNG fuel will be consumed in an onboard turbogenerator or fuel cell.