Aircraft Electric Machine Pressurization for Breakdown Prevention
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Solution Overview
Problem
Electric machines in aircraft face electrical breakdown and arcing issues at low altitudes due to reduced dielectric strength of air, which cannot be mitigated by voltage derating in high-thrust applications, necessitating alternative measures to prevent catastrophic failure.
Innovation Solution
An electric machine with a pressurized casing using a dry gas seal and a pressurization system that increases gas pressure above external pressure, reducing the mean free path and energy acquisition of free electrons, thereby increasing the voltage required for electrical breakdown beyond operational levels, preventing arcing and corona.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage derating is applied to prevent electrical breakdown, then reliability improves, but power output deteriorates
Solution Approach 1:
The patent changes the pressure parameter of the gaseous environment inside the casing from ambient pressure to pressurized condition. This parameter change increases the dielectric strength of the gas, allowing high voltage operation without electrical breakdown, thus maintaining both high power output and reliability simultaneously
2Power
If high voltage is used to meet thrust demand, then power output improves, but electrical breakdown risk worsens
Solution Approach 1:
The patent creates a pressurized gaseous environment inside the casing that acts as an inert barrier against electrical breakdown. The pressurized gas suppresses electron avalanche and ionization processes, effectively creating a protective atmosphere that allows high voltage operation without arcing or corona discharge
Solution Approach 2:
The pressurized gas inside the casing serves as an intermediary medium between the high voltage electrical components and the external low-pressure environment. This intermediary pressurized atmosphere prevents direct electrical breakdown while allowing the high voltage system to operate at full power
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
The pressurization system effectively prevents electrical breakdown within the electric machine, allowing it to operate safely at low altitudes by raising the pressure inside the casing, thus enhancing the voltage threshold for electron avalanche initiation and reducing the risk of arcing and corona.
Implementation Method 1
a pressurisation system configured to pressurise the casing above an external gas pressure to prevent electrical breakdown within the gas the casing
Implementation Method 2
An increase in the gas pressure within the casing, however, results in a smaller mean free path between molecules within the gas within the casing, thereby increasing the likelihood of collisions
Implementation Method 3
a dry gas seal to seal the casing around the shaft
Data Source
AI summary
An electric machine (101) for use in an aircraft is shown. The electric machine comprises a casing (104) containing electromechanical components, a shaft (106) which extends outside of the casing, a seal (107) to seal the casing around the shaft, and a pressurisation system (102) configured to pressurise the casing above an external pressure to prevent electrical breakdown within gas in the casing.