Life Characterization of PEEK and Nanofilled Enamel Insulated Wires Under Thermal Ageing

This paper characterizes and develops life models for two different wire insulating materials: Poly-ether-ketone (PEEK) and nanofilled enamel (Allotherm wire). The article focuses on predicting the lifespan of PEEK and Allotherm wire insulating materials, specifically for use in low-voltage electrical machines. The study investigates the effects of thermal ageing in terms of dissipation factor, insulation capacitance, and partial discharge inception voltage (PDIV). Delamination of the insulation layer is observed in both wires during the ageing process, resulting in an increase in the differential dissipation factor and insulation capacitance. With respect to its unaged condition, Allotherm wire exhibits faster degradation, showing 2.4- and 4.5-times higher changes in the differential dissipation factor and insulation capacitance respectively compared to PEEK wire after the 16th ageing cycle. In addition, Allotherm wire experiences faster deterioration of the PDIV, with a 42% reduction compared to 32% in PEEK after the same ageing cycle. Using a single-stress Arrhenius life model, the study estimates the relative thermal index (RTI) for both materials as 245°C for PEEK and 226.25°C for Allotherm wire. These results indicate a 72.1% decrease in the lifetime of PEEK and a 25.5% decrease in the lifetime of Allotherm wire when compared to the manufacturer’s RTI specification

Torque Limiters for Aerospace Actuator Application

Safety and reliability of electrical actuators are essential for success of all electric and more electric aircrafts (MEA). Torque limiters improve the reliability of electromechanical actuators (EMA) by restricting the amount of force experienced by the actuator drive train components. If transmitted torque in the shaft exceeds a limit, it gives way in a controlled manner. This protects the actuator from potential failure and jamming. In this paper, different types of existing torque limiters are investigated for their suitability in aerospace EMA application and further integration within the electric motor. They classified based on the torque transmission mechanism and each type is described in detail. Operating principle and basic characteristics are reported. Comparative evaluation of commercially available devices is presented. It is found that those based on friction based and permanent magnet are most suitable due to their good torque density, reliability and high speed capability. Further, based on the characteristics, integration of torque limiter within the actuator motor is investigated in this paper. An example actuator motor is considered for integration. Different integration options suitable for the different types of torque limiting devices are described. Reduction in overall volume is shown for the integration options. Such integration can lead to improved reliability as well as higher power density resulting in next-generation actuator electrical drives for MEA

Practical Implementation and Associated Challenges of Integrated Torque Limiter

Evolving of aircraft design towards further electrification requires safe and fault-free operation of all the components. More electric aircraft are increasingly utilizing electro-mechanical actuators (EMA). EMAs are prone to jamming and subsequent failure due to large forces on the shaft. Large forces are generated due to the high reflected inertia of the electric machine rotor. To limit the force acting on the shaft, a torque limiting device is connected to the power train which can separate the rotating mass of the electric machine from the power train. In this paper, a concept of integration of torque limiter and the electric machine rotor is presented to reduce overall volume and mass. It is connected closely with the rotor, within the motor envelope. A commercially available torque limiter and an electric machine designed for actuator application are used to demonstrate the concept. While essential for safety, the torque limiter adds to the mass and size of the overall EMA. Conventionally, the torque limiter is connected externally to the motor shaft. Key performance requirements of the machine and torque limiter are provided. Structural analysis of the proposed integrated system is carried out to show the viability. Considering the high-speed operation of the motor, rotor dynamic is analyzed to ensure resonant modes are not encountered within operating speed. Mechanical design of the system, considering assembly, is presented. Integration is shown to reduce the overall mass and size of the system compared with a conventional system, as well as better dynamic behavior and higher bearing life