Robust Differential Protection with Intermittent Cable Faults for Aircraft AC Generators

Differential protection is a popular method to protect aircraft generators against winding faults. Traditional relay-based systems have a limited capability to distinguish between differential current resulting from a winding fault, and the one resulting from measurement noise or current saturation, resulting in false alarms and unnecessary equipment shutdown. Modern aircraft generators are monitored and controlled by advanced generator control units, and therefore, sophisticated signal processing algorithms can be implemented to enhance the differential protection performance. We propose and compare four different differential detector designs, based on the available information about measured currents, for detection of persistent, short circuit faults in the protected windings. Also, current sensors are subject to intermittent, open circuit, cable faults, resulting in degradation in the differential detection performance. We propose an optimal differential protection architecture, based on the Neyman-Pearson criterion, to detect winding short circuit faults in the presence of intermittent cable faults. In this architecture, the system switches between two different detectors, depending on the cable health state.