Electric Machine Rotor Isolation for Gas Turbine Bearing Currents
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Solution Overview
Problem
Conventional hybrid-electric propulsion systems face challenges in mitigating bearing electric currents induced by common mode voltages, which can lead to premature bearing failures, and existing solutions like ceramic bearings or grounding brushes may not be viable in all scenarios.
Innovation Solution
A three-pronged approach involving reducing common mode voltage using electromagnetic interference filters and shielded cables, interrupting common mode current with insulated joints, and grounding the shaft using integrated devices within existing engine components, such as resolvers or carbon seals, to mitigate bearing electric currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic bearings or grounding brushes are used to mitigate bearing electric currents, then bearing current damage is reduced, but device complexity increases and adaptability is limited
Solution Approach 1:
The patent extracts and eliminates the harmful common mode current path by introducing an insulated joint that disconnects the electrical connection between the rotor and shaft, thereby removing the source of bearing current damage without adding complex mitigation components
Solution Approach 2:
The insulated joint serves multiple functions: it provides mechanical support for the rotor while simultaneously blocking harmful electrical currents, and it maintains electrical continuity for normal operational currents, making the solution universally applicable without requiring additional specialized components
2Reliability
If insulated joints are used to interrupt common mode current, then bearing electric currents are reduced, but device complexity increases
Solution Approach 1:
The patent merges the electrical insulation function with the existing mechanical rotor connection structure, integrating the insulated joint into the rotor support system so that it becomes a unified component rather than an separate addition, thereby minimizing increases in device complexity
3Reliability
If grounding devices are integrated into existing components, then bearing electric currents are mitigated, but manufacturing precision requirements increase
Solution Approach 1:
The grounding device is designed to be integrated into existing engine components such as the resolver or carbon seal, allowing it to serve multiple functions (grounding and either signal processing or sealing) simultaneously, which distributes the precision requirements across existing tolerances rather than requiring new high-precision interfaces
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces bearing electric currents without shortening the life of bearings and with minimal modification to the spool rotor structure, enabling fuel burn gains and extended bearing lifespan.
Implementation Method 1
reducing common mode voltage using electromagnetic interference filters
Implementation Method 2
The rotor connection assembly has an insulated joint for interrupting common mode electric current from flowing from the rotor to the shaft
Implementation Method 3
A grounding device may be included to electrically ground the shaft
Data Source
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AI summary
A hybrid-electric propulsion system (150) is provided. In one example aspect, the hybrid-electric propulsion system (150) includes a power converter (188A) and a propulsor (200A). The propulsor (200A) includes a gas turbine engine (210A) having a shaft (246) and one or more bearings (290) supporting the shaft (246). The propulsor (200A) also includes an electric machine (300A) electrically coupled with the power converter (188A). The electric machine (300A) includes a stator assembly (340) and a rotor assembly (310). The rotor assembly (310) has a rotor (312) and a rotor connection assembly (316). The rotor connection assembly (316) operatively couples the rotor (312) with the shaft (246). The rotor connection assembly (316) has an insulated joint (322) for interrupting common mode electric current from flowing from the rotor (312) of the electric machine (300A) to the shaft (246). A grounding device (360) is included to electrically ground the shaft (246). The power converter (188A) includes an electromagnetic interference filter (189A) to reduce common mode voltage reaching the electric machine (300A).