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Litz wires operating in a cryogenic environment can potentially improve both the efficiency and power density of electrical machines and passive components. However, due to the low resistivity and high magnetic fields, eddy-current losses may become significant in cryogenically cooled windings, especially in airgap winding arrangements or in the case of significant slot leakage fields, unless the litz wire parameters are carefully chosen. A framework for litz wire loss performance optimization and experimental characterisation at cryogenic temperatures is provided. An optimum operating temperature for minimum loss is derived based on analytical expressions, which highlights the role of litz wire parameters, current density and external field. The proximity loss model, used to calculate the optimum operating temperature, is validated experimentally. Two test rigs with different magnetic cores were designed and built. Copper and aluminium litz wires with a strand diameter down to 0.1 mm were tested in a liquid nitrogen bath with a uniform harmonic external magnetic field up to 0.5 T peak and a frequency up to 1 kHz. Measurements show good agreement with the theoretical results and confirm that the proposed model can be confidently used during the preliminary design of cryogenic windings.

Electrical propulsion has been identified as a key enabler of greener, quieter, and more efficient aircraft. However, electrical propulsion aircraft (EPA) will need to demonstrate a level of safety and fault management (FM) at least equal to current aircraft. This will rely heavily on the capability and design of the electrical FM system. Given the functional limitations and current lack of FM technologies suitable for a future EPA application, strategic development of FM devices is required. While there are a variety of roadmaps for EPA concepts and key electrical components, the necessary development of FM solutions targeted toward EPA has yet to be established. This article proposes FM strategy maps that go beyond projections of expected development in FM technologies to scope the feasibility of key FM solutions. This method can then be used to present FM technology projections, electrical oversizing, and wider system redundancy alongside the EPA concepts in development. These strategy maps capture the impact of any FM technology barrier on the viability of a given EPA concept, enabling critical FM solutions to be integrated into the wider electrical system development. This marks a significant contribution to the development of robust, strategic electrical FM for future EPA concepts.

This paper provides the concept of design, implementation, and system integration of energy efficient power management solution for a fault-tolerant more electric engine/aircraft (MEE/MEA). The power management solution consists of three components, i.e., the power management system (PMS), the stability analysis module, and the condition-based control (CBC) module. The PMS is to optimize the electrical power system (EPS) level efficiency based on constraints with consideration of power limits of the dc system in the MEE/MEA architecture, which are calculated by the stability analysis module, and system reconfiguration, which is provided by the CBC module. This paper focuses on the design and implementation of PMS algorithm for EPS of a fault-tolerant MEE/MEA architecture. A PMS solution to optimize EPS level efficiency optimization is proposed, which is based on multiple objective optimization problem (MOOP). The proposed MOOP is solved with a modified nondominated genetic algorithm with local search mechanisms. The proposed power management solution are implemented in the MEE/MEA simulation model as well as hardware-in-loop virtual testbed and results show the effectiveness of the proposed algorithm. National Research Foundation (NRF) This work was conducted within the Rolls-Royce @ NTU Corporate Lab with support from the National Research Foundation Singapore under the Corp Lab @ University Scheme. (Corresponding author: Yicheng Zhang.)

Superconductors have a potential application in future turboelectric distributed propulsion (TeDP) aircraft and present significant new challenges for protection system design. Electrical faults and cooling system failures can lead to temperature rises within a superconducting distribution network, which necessitates a reduction or temporary curtailment of current to loads to prevent thermal runaway occurring within the cables. This scenario is undesirable in TeDP aircraft applications where the loads may be flight-critical propulsion motors. This article proposes a power management and control method that exploits the fast-acting measurement and response capabilities of the power electronic interfaces within the distribution network to maximize current supply to critical loads, reducing the impact of a temperature rise event in the superconducting distribution network. This new algorithm uses the detection of a resistive voltage in combination with a model-based controller that estimates the operating temperature of the affected superconducting cable to adapt the output current limit of the associated power electronic converter. To demonstrate the effectiveness of this method and its impact on wider system stability, the algorithm is applied to a simulated voltage-source converter supplied aircraft dc superconducting distribution network with representative propulsion motor loads.

Hybrid electric propulsion could be the solution to the ambitious environmental targets of the aerospace industry. Fully-superconducting machines have the potential to deliver the step-change in specific torque, power, and efficiency capabilities required for large civil transport aircraft applications. However, fully-superconducting machines are still in their infancy. This article investigates the electromagnetic design of two different stator design concepts for an ac fully-superconducting machine for an aerospace distributed fan motor application. A benchmark aerospace specification of 1 MW was chosen and the design of a conventional permanent-magnet machine was used to assess the performance of the two equivalent fully-superconducting ac motor designs. Following the guidelines from an experimental study of the losses in a small ac stator prototype with MgB 2 coils, a fully-superconducting air-cored stator design and a new yokeless stator design are proposed. Both ac superconducting machine designs use superconducting bulk magnets mounted on a rotor core and an MgB 2 superconducting stator winding. This article discusses the key design issues of the two stator layouts in relation to the current aerospace targets for efficiency and power density.

This paper addresses the concept of designing and implementing the power management system (PMS) for electrical power system (EPS) of more electric engine/aircraft (MEE/MEA). An optimization model for the PMS in MEE/MEA is formulated. Various PMS solutions are required to meet different performance expectations. In order to have least possible electrical network losses, two types of PMS solutions are proposed, i.e., to optimize the generator efficiency and to optimize the EPS level efficiency, as single objective optimization problem (SOOP) and multiple objective optimization problem (MOOP), respectively. The SOOP is solved as a mixed integer programming problem while the MOOP is solved with a modified non-dominated genetic algorithm. The proposed PMS algorithm is implemented in the MEE/MEA simulation model and results show the effectiveness of the proposed algorithm.

The demand of More Electric Engine/ Aircraft (MEE/ MEA) increases with the need of on-board electrification system for future aircraft. Also, moving towards More Electric Engine/Aircraft (MEE/MEA) concept can achieve better fuel benefit in the engine by controlling the split ratio of the power off-take from each of Low Pressure (LP) and High Pressure (HP) spools. Due to the trend of MEA and MEE integration with the power electronic driven technology, a higher reliability level of electrical power system is required to meet the minimum safety requirement during fault condition. A concept of intelligent system for mitigating the faults by identifying the best fault tolerant system configuration with the minimum load shedding is proposed in this paper. The proposed method not only mitigates the fault elimination from the electrical system but also maintains continuous mechanical power output from LP and HP spools in order to maintain optimum fuel benefit of the engine.

Modern day advancements in electrical engineering especially power generation and management has enabled the path for More Electrical Aircrafts (MEAs) and hybrid propulsion systems. The electrical power generation in aerospace system is in itself an isolated micro grid with ac and dc components operating in either series or parallel or in hybrid mode. Uninterrupted and stable operation of these systems is of utmost importance. Known stability methods based on Lyapunov are difficult to implement as generalized on-line stability assessment procedure for such complex power network. In this paper a detailed and systematic small signal stability analysis of a More Electric Aircraft electrical power generation system is presented based on the eigen value analysis. The effect of different control algorithms on the MEE/MEA power network stability is studied using the proposed method. Also, it is shown that the stability is improved by using optimal gain feed-forward information of dc-bus currents. The stability matrix for the whole operating regime is developed and the stability margin variation for different operating conditions and control variations is presented. The efficacy of the estimated stability margin for MEE/MEA power network is verified using an Opal-RT Virtual test bed for all the control configurations.

International audience; Hybrid electric propulsion has been identified as a potential solu-tion to the ambitious environmental emissions and noise targets of the aerospace industry. Superconducting machines may be the key component of that topology enabling the high power densities and efficiencies needed in aerospace. Fully superconducting ma-chines, however, are not a mature technology. This paper looks at the different machine design configurations focusing on the stator magnetic circuit of a fully superconducting motor. The motor has been designed for an aerospace distributed fan propulsion motor with an aerospace benchmark specification of 1 MW. The AC ful-ly superconducting machine includes superconducting bulk magnets mounted on a conventional rotor core and an MgB2 su-perconducting wire wound stator. The AC losses in the stator winding are particularly sensitive to exposure to the main rotor field so different screening solutions were used to shield the su-perconducting windings from the rotor field. The effectiveness of the screening techniques for the stator coils and the impact on the machine performance and weight were evaluated for different stator designs, such as full stator core and air core with and without flux diverters. Various combinations of pole numbers, diverter geometries and magnetic materials have been checked. Results show that there is a trade-off between stator iron losses and superconducting losses.

The aerospace industry has ambitious environmental emissions and noise reduction targets that have led to some radical proposals for future aerospace transportation technologies. One of the disruptive technologies identified is hybrid electric propulsion. The use of electrical machines for aerospace propulsion is not a new concept. Fully superconducting machines have the potential to deliver the step-change in specific torque, power and efficiency capabilities required for large civil transport aircraft applications. However fully superconducting machines are still in their infancy. This paper looks at the electromagnetic design of two different stator design concepts for an AC fully superconducting machine for an aerospace distributed fan motor using a benchmark aerospace specification. A benchmark aerospace specification of 1 MW was chosen and the design of a conventional permanent-magnet machine was used to assess the performance of the two equivalent fully superconducting AC motor designs. The AC fully superconducting machine includes superconducting bulk magnets mounted on a conventional rotor core and an MgB2 superconducting wire wound stator in a non-magnetic core. The paper looks at a fully superconducting air-cored stator design to reduce weight and a new yokeless stator design is proposed to reduce the armature losses. The paper will look at the key design issues of the different motor designs in relation to the current aerospace targets for efficiency and power densities.

This study presents the development, analysis, manufacture and testing of a demonstrator multiple-can line-start rim-drive induction motor for use as a bi-directional electric thruster on-board a tidal stream turbine. A simple ‘canned’ rotor construction was used to eliminate the requirement for a conventional squirrel-cage rotor, to minimise the rotor size and weight and improve reliability, all the while providing compatibility with the sub-sea operating environment. The experimental test results on a demonstrator 30 kW rim-drive motor show good agreement with finite-element analysis predicted results.

Superconducting fault-current limiters are being considered as a potential technology for restricting fault current to acceptable levels without extensive and costly network asset replacement. Such an issue currently arises primarily from the connection of a distributed generation. This paper first investigates the fault studies of an active medium-voltage distribution network with several superconducting fault-current-limiter deployment strategies and then considers their impact on circuit-breaker transient recovery voltage. These circuit-breaker characteristics at various voltage levels have been studied, and it is demonstrated that the superconducting fault-current limiter is capable of reducing both the magnitude and the rate of rise of the transient recovery voltage.

This paper reports results of tests on several MgB2 round wire samples wound with small bend diameters. Wire suitability for use in a resistive type superconducting fault current limiter with a practical aspect ratio is assessed in terms of current limiting performance and tolerance to mechanical process handling. A fully controllable low current supply was used to determine the variation of the wire impedance against frequency and temperature. The frequency response enabled the calculation of coil inductance and superconducting resistance. Critical temperatures measured were in the range of 34 K-39 K. A high current supply was used to test the coil current limiting properties in the temperature range 25-32 K in self field at 50 Hz. Good, repeatable current limiting properties were observed with quench currents in the range 95-390 A. Good tolerance to mechanical process handling was also evident.

A large body of research is currently being conducted into superconducting power system applications, targeting improved efficiency and reductions in system size and weight. In order to attain the required levels of safety and reliability of the superconducting power system, effective protection systems, tailored to the specific fault behaviour of the novel components must also be in place. This paper presents a review of relevant literature concerning the dynamic and transient characteristics of superconducting DC networks and key associated components (such as superconducting cables and machines). This first part of a two stage Failure Modes and Effects Analysis (FMEA) is presented, which provides a conceptual consideration of expected physical failure modes and mechanisms. The effects on the wider network are discussed from which various protection considerations are drawn. A number of key research questions are drawn from this study, which will form the starting point of the second stage of the FMEA. The outputs from the FMEA will shape the protection requirements for a superconducting DC network.

et al., Cost-effective highly efficient nanostructured n-type Mg2Si 1-x Sn x and p-type higher manganese silicide (HMS) compositions were prepared for the development of practical waste heat generators for automotive and marine thermoelectric applications, in the frame of the European Commission (EC)-funded PowerDriver project. The physical, mechanical, and structural properties were fully characterized as part of a database-generation exercise required for the thermoelectric converter design. A combination of high maximal ZT values of ~0.6 and ~1.1 for the HMS and Mg2Si1-x Sn x compositions, respectively, and adequate mechanical properties was obtained. © 2013 TMS., The work was supported by the EC FP7 Power-Driver Project.

The linear viscoelastic behavior of a poly(paraphenylene) with a benzoyl substituent has been examined using tensile, dynamic mechanical, and creep experiments. This amorphous polymer was shown to have a tensile modulus of 1–1.5 Msi, nearly twice that of most common engineering thermoplastics. The relaxation behavior, which is similar to that of common thermoplastics, can be described by the WLF equation. Outstanding creep resistance was observed at low temperatures, with rubbery-like behavior being exhibited as the temperature approached Tg. Physical aging was shown to interact with long-term creep, rendering time–temperature superposition invalid for predicting the long-term properties. The effect of physical aging on the creep behavior was characterized by the shift rate μ. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 70: 2971–2979, 1998

In order to minimise the environmental impact of increased air traffic substantial developments in civil aircraft electrical power systems must occur. NASA have set a target to reduce noise by 71dB, NOx emissions by 80% and fuel consumption by 60% for the N+3 generation of aircraft entering into service sometime between 2030 and 2035. Turboelectric Distributed Propulsion (TeDP) is expected to enable these goals to be met. NASA's N3-X concept aircraft comprises gas turbine engines which drive electrical generators and a DC network distributes power to an array of fans, which provide thrust. Interconnection and protection technologies will also be included to achieve desired levels of reliability of supply to the propulsion motors. This paper outlines the architecture of a generic TeDP system, explores its benefits, describes technical challenges that will need to be overcome and discusses the technical implications of implementing TeDP with regards to electrical system power density and safety.

The design of a line-start rim-driven induction motor specifically for use in a marine propulsor/thruster is described. This paper explores the use of a hybrid ‘canned’ induction rotor design in which a conventional ‘deep-bar’ cage is replaced by a simple cage with a low radial depth, along with a series of air-gap cans to provide environmental shielding, and a conducting rotor can to simplify the rotor design. An overview of the design process to the ‘final’ design for the proposed induction rim-drive is explained, along with details of the two-dimensional finite element models and simulation results. An appraisal of the merits of the rim-driven design, compared to a benchmark industrial induction motor, is also discussed.

A process for determining the aging characteristics of solid rocket propellants by measuring their dynamic mechanical properties is described. Samples of rocket propellant are tested using a mechanical spectrometer at low strain levels and low frequencies. The change in the dynamic storage modulus of the propellant with aging time and temperature is used to determine the aging rate anf the likely mechanisms occuring during aging. The technique is advantageous is several respects: (1) because the tests are non-destructive and use small test specimens, and entire aging program can be conducted using much less propellant than is required ihn traditional aging programs (propellant requirements are reduced by more than an order of magnitude) (2) the technique can be applied to samples with unusual or unique geometries which cannot be tested using traditional methods; (3) test specimens can be obtained directly from live, operational solid rocket motors, and service life and mechanical property degradation can be determined.

A resistive superconducting fault current limiter (SCFCL) based on MnB 2 has been investigated as a means of reducing network fault level. The deployment strategy of this device has been discussed and its performance as a fault current limiter has been analysed with the aid of network simulation results. It has been demonstrated that a resistive SCFCL can reduce all three components of fault currents: peak make, peak break and rms break. In turn reduced peak make leads to reduced electromagnetic forces on conductor carrying fault current, reduced torques on generator and prime mover and less damage at the point of fault.

This paper discusses the increasing requirements for an effective means of controlling fault levels on electrical networks and describes the work by Rolls-Royce and partners to develop a practical superconducting fault current limiter. Practical superconducting fault current limiters require materials with a high tolerance to mechanical process handling and must be sufficiently robust not to be damaged by the severe electro-magnetic and thermal stresses imposed when restricting a fault current. Magnesium diboride (MgB 2 ) is amongst the most promising materials under consideration for superconducting fault current limiters. This paper reports tests which have been carried out on several MgB 2 round wire samples wound with small bend diameters. Electrical characteristics and fault current limiting abilities were determined of a number of MgB2 samples when cooled to below their critical temperature. During these tests strong and repeatable current limiting properties were observed for 50Hz ac applications. Furthermore, MgB 2 exhibited unusually high tolerance to mechanical process handling, clearly differentiating itself from other superconducting materials.

A study has been conducted to investigate the relationship between binder molecular structure and the mechanical/rheological properties of solid propellants. Beginning with the mechanical property requirements dictated by the motor grain operating conditions as well as rheological constraints imposed by available processing technology, the approach taken was to work backwards to obtain the ideal molecular structure of a solid propellant binder. Structural/processing requirements were determined from the demands of three typical rocket motor applications: space transfer, launch vehicle/ballistic missile, and tactical air-to-air. Three general formulation approaches to meet the demands of these applications were considered. These include traditional composite and nitrate ester plasticized formulation approaches, in addition to a hypothetical all-binder propellant. For each of these three formulation approaches, a variety of polymer molecular characteristics were defined in terms of molecular weight, crosslink density, solubility parameter, chain stiffness, monomeric friction coefficient, volume fraction filler, and volume fraction plasticizer. Characterization data for ten polymeric binder systems are reported to show how their molecular architecture influences the resulting propellant properties.

Superconducting machines offer the significant advantage of smaller volume, lighter weight, and increased operating efficiencies compared with traditional electrical machines. To date, superconducting machines have utilized a superconducting dc field winding on the rotor of a synchronous machine. This increases the system complexity because it requires cryogenic cooling on the rotating part of the machine. The stator in these machines is generally composed of a set of conventional ac copper wire coils. Round magnesium diboride (MgB2) wire however has the potential to form low-cost ac stator coils for a superconducting machine. This could enable a stationary superconducting ac stator winding to be fabricated, reducing the complexity associated with the cryogenic cooling. This paper presents initial test results on a prototype ac solenoidal coil to represent a typical ac stator coil for a superconducting machine using MgB2 wire. The diameter of the wire with insulation was 1 mm and the coil was wound in a double-layer solenoidal arrangement. The magnetic flux density distribution, quench current level, long duration operating current level, and the ac losses of the coil were measured and discussed. This paper demonstrates the potential of MgB2 wire to develop a superconducting ac stator winding for a superconducting machine.

A prototype resistive superconducting fault current limiter (SFCL) was developed using single-strand round magnesium diboride (MgB2) wire. The MgB2 wire was wound with an interleaved arrangement to minimize coil inductance and provide adequate inter-turn voltage withstand capability. The temperature profile from 30 to 40 K and frequency profile from 10 to 100 Hz at 25 K were tested and reported. The quench properties of the prototype coil were tested using a high current test circuit. The fault current was limited by the prototype coil within the first quarter-cycle. The prototype coil demonstrated reliable and repeatable current limiting properties and was able to withstand a potential peak current of 372 A for one second without any degradation of performance. A three-strand SFCL coil was investigated and demonstrated scaled-up current capacity. An analytical model to predict the behaviour of the prototype single-strand SFCL coil was developed using an adiabatic boundary condition on the outer surface of the wire. The predicted fault current using the analytical model showed very good correlation with the experimental test results. The analytical model and a finite element thermal model were used to predict the temperature rise of the wire during a fault.