Aircraft a.c. electrical systems using changeover contactors and rapid fault clearance

Conventional aircraft electrical systems are liable to interruptions or disturbances for up to several seconds under fault conditions. Such interruptions may be limited to substantially less than 100ms by the use of a very simple nonparalleled system employing changeover contactors and forms of undervoltage and overvoltage protection which do not depend on time delays to discriminate between real faults and switching transients. The overvoltage protection acts rapidly enough to prevent the voltage rising to destructive levels in the event of, say, a regulator fault. In its simplest form, with two generators or with four generators arranged in two subsystems, the total generator capacity must be twice the maximum load, to ensure, that the failure of one generator will not result in loss of load, in the 2-generator case, this can be reduced to four thirds if the load can be divided into three equal parts, one of which may be discarded in the event of a generator failure. In the 4-generator case, the factor may be four thirds, with no loss of load with one generator failure if it is possible to divide the load into six equal parts.