Novel design and performance analysis of an external-rotor double-cage induction motor for high-efficiency jet fan systems

• Presents a novel Double-Cage Outer-Rotor to solve high starting current issues. • Fire-Resistance and Reliability: The external rotor design inherently protects stator winding, allowing safe and reliable operation up to 400°C in fire-like conditions. • The motor achieves strong starting torque and competitive IE3 efficiency for high-performance use. • Validated solution for safety-critical tunnels ventilation, offering robust performance under both normal and extreme thermal conditions. This paper presents the design, analysis, and experimental validation of a 30 kW three-phase double-cage outer-rotor induction motor for jet fan ventilation systems in underground tunnels. Conventional outer-rotor motors typically employ a single-cage configuration with large cross-section bars in order to maintain high efficiency; however, this design can lead to excessive starting currents. The proposed double-cage topology addresses this limitation by combining a high-resistance inner cage for enhanced starting torque with a low-resistance outer cage optimized for steady-state efficiency. The motor was parametrically modeled using ANSYS RMxprt and analyzed through 2D finite-element simulations in ANSYS Maxwell to evaluate electromagnetic performance, current distribution, and torque characteristics. A full-scale prototype was manufactured and tested, confirming the simulation predictions for current, torque, and efficiency. Additionally, thermal and high-temperature resistance test proved that the outer-rotor design inherently shields the stator winding, enabling safe operation in fire-like conditions and enduring temperatures up to 400°C for an extended duration. The results show that the double-cage outer-rotor motor achieves reduced starting current, strong starting torque, competitive IE3 efficiency, and robust thermal performance, while offering enhanced fire-resistance and operational reliability. This study establishes the technical feasibility of integrating advanced rotor architectures into outer-rotor motors, providing a viable solution for safety-critical tunnel ventilation applications requiring high performance under both normal and extreme thermal conditions.