Defining safe operating voltages for aerospace electrical systems

Increased electrical power demands are being experienced on the new generation of aircraft due to an increased reliance on electrical technology such as air conditioning, de-icing systems and electrical flight control actuation. Sustaining the transmission of hundreds of kilowatts of electrical power at low voltages, typical around 115 V, is not feasible owing to the penalties incurred due to high cable weights and issues relating to voltage drop. The use of higher voltages would reduce system weight but comes with a penalty in the increased likelihood of electrical discharge within the power system. This paper details studies of systems used to transmit power in aircraft. The studies examine the voltages at which systems could be used without the existence of partial discharge. This is done from a theoretical standpoint but is based on the results of tests of typical insulation systems. These tests have been carried out in an environmental chamber that can simulate an aircraft at altitude. It is shown that an increase to ever higher voltages does not lead to a continuous reduction in the power transfer to weight ratio of cabling systems. The optimum voltage is shown to depend on a number of factors.