Electrical power generation systems have inherent inefficiencies due to electrical and mechanical loss mechanisms. These inefficiencies mostly stem from generator core and copper losses, eddy current losses, and mechanical losses (bearings, rotating seals and windage). These inefficiencies raise the generator temperature, mostly the stator and rotor, as well as increase the aircraft heat load, requiring larger and heavier heat exchanging systems. Heat, which is the direct product of inefficiency, is the main reason for limiting generator output. The insulating and encapsulating materials inside the generator, are limited to operating at a maximum temperature of 220C. Therefore, the key to increasing power density lies in improving efficiency and improving cooling. Improved efficiency is the outcome of the generator electromagnetic design combined with the type of cooling method chosen for the specific application. IPS has developed several oil cooled generators utilizing improved cooling techniques to maximize power density. IPS has a patent for cooling rotors in conduction oil cooled generators. This patent is used in the Global Hawk UAV generator, and allows continuous operation at elevated temperatures to 700F, and is also used to increase the power rating of a 650 Amp, 28 Vdc generator to 1000 Amp in the same envelope.
Benefit: The technology developed as a result of the proposed effort will provide substantial increase in power density for electromagnetic devices that will result in smaller size and weight or increased power output out of a given envelope. Potential applications for this technology are any aircraft that requires increased power and where the new generator is driven by the existing engine/gearbox. Immediate examples are the Joint Strike Fighter. Other military applications are megawatt size generator for DEW application, where size and weight play a major role in the project feasibility. Commercial airlines are using significantly increased electric power because of the incorporation of entertainment and communication systems to every seat in the aircraft. Furthermore, future aircrafts will have the generator directly mounted to the engine Low Pressure Turbine prompting issues of size, weight and overhung moment, which could all be alleviated by higher power density generators.
Keywords: High Speed, High Speed, Power Density, Aircraft, Current Density, Electromagnetic, Cooling, Electrical Systems, starter generator
