Insulated Rotor Connection for Electric Machine Bearing Current Mitigation
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Solution Overview
Problem
Conventional hybrid-electric propulsion systems face challenges in mitigating bearing electric currents induced by common mode voltages, leading to premature bearing failures, especially when ceramic bearings or grounding brushes are not viable options.
Innovation Solution
A three-prong solution 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 like resolvers or seals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic bearings or grounding brushes are used to mitigate bearing electric currents, then bearing life is improved, but device complexity and ease of manufacture deteriorate
Solution Approach 1:
The patent extracts and eliminates the need for specialized bearing solutions (ceramic bearings, grounding brushes) by addressing the root cause of bearing current through insulated joints in the rotor connection assembly. This removes the problematic components while still achieving bearing current mitigation.
Solution Approach 2:
The patent introduces insulated joints as an intermediary element in the rotor connection assembly that blocks bearing current paths without requiring modification to the bearings themselves. This intermediary approach mitigates bearing current while maintaining simplicity.
2Reliability
If insulated joints are used to interrupt common mode current, then bearing current is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the rotor connection assembly into multiple components (rotor hub, connection members, insulated joints) that can be manufactured and assembled separately. This segmentation allows for standardized insulated joint components with achievable tolerances, reducing overall manufacturing precision requirements compared to a monolithic design.
3Reliability
If electromagnetic interference filters and shielded cables are used to reduce common mode voltage, then bearing current is reduced, but device complexity and cost increase
Solution Approach 1:
The patent implements preliminary action by addressing bearing current mitigation through the rotor connection assembly design (insulated joints) rather than adding downstream mitigation devices. This upstream approach prevents bearing current generation at its source, eliminating the need for additional filters and shielded cables.
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 mitigates bearing electric currents without shortening bearing life and with minimal modifications, enabling efficient fuel burn management between low-speed and high-speed spools.
Implementation Method 1
The rotor connection assembly has an insulated joint for interrupting common mode electric current from flowing between the rotor and the shaft
Implementation Method 2
A grounding device may be included to electrically ground the shaft
Data Source
AI summary
A hybrid-electric propulsion system is provided. In one example aspect, the hybrid-electric propulsion system includes a power converter and a propulsor. The propulsor includes a gas turbine engine having a shaft and one or more bearings supporting the shaft. The propulsor also includes an electric machine electrically coupled with the power converter. The electric machine includes a stator assembly and a rotor assembly. The rotor assembly has a rotor and a rotor connection assembly. The rotor connection assembly operatively couples the rotor with the shaft. The rotor connection assembly has an insulated joint for interrupting common mode electric current from flowing from the rotor of the electric machine to the shaft. A grounding device is included to electrically ground the shaft. The power converter includes an electromagnetic interference filter to reduce common mode voltage reaching the electric machine.