It is now established that the turn-to-turn capacitance variation of electrical motor windings can be used as an insulation system aging indicator: turn insulation aging causes a significant increase of the corresponding capacitance and a decrease of several resonance frequencies in the upper part of the impedance spectrum of the motor windings. To set up a monitoring system based on this indicator, it is necessary to consider the whole system including the cable used to connect the motor to the electronic converter. The paper highlights the cable influence on the whole system. Aging tests were made on samples of a three-wire shielded cable used in the aircraft industry in order to analyze the cable aging influence on the monitoring system dedicated to get data on the motor insulation aging. This analysis shows that the series resonance situated at higher frequencies gives better results. It should be used by the monitoring system in order to get useful data on the motor aging, independently of the slight variations of the cable capacitances.

The paper deals with a new indicator for monitoring the turn-to-turn insulation aging of ac motors. Measurements of capacitance and Partial Discharge Inception Voltage (PDIV) were performed on a large number of twisted pairs of enameled wires between standard thermal accelerated aging cycles. A significant increase of the capacitances and a reduction of the PDIV were noted on all the samples for three different diameters of enameled wires. The correlation of the capacitance increase with the degradation of the insulation quality opens perspectives for preventive maintenance applications.

The proposed paper is focused on the definition of an aging diagnostic method by an analysis of the winding behavior at high frequencies, which strongly depends on the turn-to-turn capacitances. Firstly, it is shown that the thermal aging define variations of the turn-to-turn capacitances which determine changes in winding frequency resonances at high frequencies. These frequencies variations will be used as an aging indicator. A PSpice model is used to simulate the real coil behavior and shows the variation of several high frequency resonances which can be used as indicators for AC machine preventive maintenance program.

The presented paper concerns the insulation of cables providing the link between the converters and electrical machines in aircraft. It focuses on thermal aging tests performed on cables with the analysis of the capacitance variation. The tests were conducted on samples of a three-wire shielded cable, insulated with polyimide and polytetrafluoroethylene (PTFE). This study shows that the capacitance between the conductors of a cable is correlated with the aging of its electrical insulation.

The presented paper focuses on monitoring of turn-to-turn insulation quality. It is based on the measure of the variation of the winding turn-to-turn capacitance and the Partial Discharge Inception Voltage (PDIV). The test methods is defined and described. Twisted pairs of three different diameters of enameled wires were tested. The PDIV is measured with an adequate system properly calibrated to minimize background noise to an acceptable value. Finally, it is shown an increased capacitance and a reduction PDIV between aging cycles. The correlation of these two parameters opens perspectives for preventive maintenance applications.

The aim of the paper is to present a new prospective method for on-line monitoring of partial discharge (PD) in large AC motors. The principle of this system consists to measure the weak magnetic high frequency field, due to PD, in the space between the magnetic core and the machine external frame of large generators. Special sensors, trimmed to the machine winding resonances, may perform such field measurements. With several sensors, it will be possible to localise PD activity corresponding to insulation weaknesses.