by Pablo Paz Sagues - Development Engineer on Jul 01, 2021
Advanced Electronics Solutions
During the past years, electric automobiles have evolved from conceptual prototypes to a booming trend, overcoming great challenges on the way and occupying a growing portion of the automotive market. E-aircrafts are now in the concept phase, getting ready to take off. Several companies, ranging from small start-ups to large traditional aircraft manufacturers, are developing the next generation of flying machines.
Due to operating conditions, airborne components must comply with strict reliability and safety requirements. Atmospheric conditions at 8000 meters are very different than at sea level and not all components are inside the pressurized volumes of the aircrafts. The low density of air at high altitudes have two main negative effects on electric systems. First, it reduces the cooling properties of air and second, it decreases the dielectric strength of air, following the Paschen curve. Both phenomena have a strong influence in the performance and lifetime of insulated electrical conductors, such as laminated busbars.
Laminated busbars represent the best solution for most solid-state power converters. In e-aircraft, it applies to the main inverter which powers the electric motors. Rogers also offers ROLINX® CapLink Solutions that combine capacitors with ROLINX laminated busbars for low inductance and high-power density specially designed for high power inverters.
Rogers Corporation, ROLINX CapLink Solutions
As air density decreases, so does its heat transfer capability. This is the reason why many electric components must be adapted and/or derated for operating altitudes above 2000 meters. ROLINX busbars are custom designed for each project and optimized based on operating conditions, including ambient air temperature and density.
Rogers engineers’ most powerful tools are their design experience and FEM simulations. In the case of high-altitude designs, FEM simulates the busbar's power dissipation and heat transfer to the environment at different ambient conditions. Once a 3D model is developed, its thermal response to outside temperatures and pressures can be studied virtually. This allows a quick iterative design that leads to the optimal conductor thickness, while preventing overheating in all operating scenarios.
Rogers Corporation, ROLINX Busbars, FEM simulations
The FEM simulation above shows the current thermal distribution for a busbar model (on the left). For given ambient conditions (temperature, density, …) it is possible to obtain the busbar´s operating temperature, in order to, as necessary, optimize the design.
Another challenge for airborne electrical equipment is the decreasing dielectric strength of gases at lower pressures. This relationship was experimentally discovered by Friedrich Paschen who created the law that bears his name.
Paschen curves for different gases (Wikipedia, June 2021, retrieved from:https://en.wikipedia.org/wiki/Paschen%27s_law).
In the case of air, the breakdown voltage is 3.1kV/mm at sea level pressure but decreases to 2.0 kV/mm at 0.5bar (pressure corresponding to 5500m) and even lower at higher altitudes. This phenomenon has two main implications:
The evolution to cleaner transportation is pushing the development of e-aircrafts and is already reality in development phase. Operation at high altitude and other demanding specifications creates many challenges, pushing all electrical components a step further in performance. Operating at high altitude with low air density has many implications on the design of laminated busbars. Technical requirements, ambient conditions and physical phenomena are studied case by case at Rogers to deliver the safest and most optimized ROLINX busbar solution.
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