Luvata - Stator Direct Cooling
Our copper hollow conductors provide new possibilities to cool down electric motors. The internal cooling hole on the stator windings enables efficient thermal transfer out from the core, exactly from the source where the heat is generated. Cooling with air improves the performance significantly and liquid cooling even more. As a result increased power and torque are achieved by direct cooling with Luvata’s hollow conductors.
In electric motors, the current flows in the windings, which are made of copper because of its low resistance. Electrical losses are an unavoidable obstacle and increase with the amount of current; for example, doubling the current quadruples the losses, which increases heat in the motor. In addition, magnetic losses heat both the stator and the rotor, further increasing the heat load. This heat can be extracted by direct or indirect cooling. The big benefit of direct cooling is that it treats the heat where it is generated, in the winding itself instead of in the housing. Effective cooling of the stator also ensures a lower rotor temperature, nabling the use of less expensive lower temperature graded permanent magnets.
Direct cooling offers the highest power density for an electric motor – especially continuous power output – alongside excellent efficiency over a broad range. Partial load is the most realistic use case for an electric motor, and tests conducted have shown that a direct-cooled motor offers approximately twice the power output at peak load and three times the power output at continuous steady-state operation compared to a standard, indirect-cooled motor.
The higher efficiency of direct-cooled motors means that smaller power units can be used in EVs, saving both weight and costs. It also enables the use of electric powertrains in larger vehicles such as trucks. Direct-cooled motors can use standard, cost-effective materials, including magnets, providing higher performance at a lower cost – a key enabler for the wider adoption of EVs.
All impurities reduce the electrical conductivity of copper, which is why we make Luvata hollow conductors from OF-OK® high purity oxygen-free copper. As a result of its purity, Luvata OF-OK has typical electrical conductivity of 100-102 %IACS and thermal conductivity of 390 W/Km.
The maximum oxygen content of 5 ppm (0.0005%) makes the material immune to hydrogen embrittlement and ensures safe joining with all brazing and welding methods.
The OF-OK used in our hollow conductors is cast in our own foundry in electric furnaces using selected high purity raw materials. This means we can control the whole manufacturing process from casting to signing the inspection certification, and ensure the consistency of our product from batch to batch.
When necessary OF-OK is alloyed with silver (Ag) to increase both the softening temperature and creep resistance of the alloy without any significant sacrifice of its other properties.