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 calculation of the striking distance can estimate the probability of lightning strike on a structure and thereby evaluate the effectiveness of a lightning protection system (LPS). The dimensioning and the positioning of air-termination on structures is often performed with the Rolling Sphere Method (RSM). RSM originated from the electric power transmission industry and is based on the well-known Electrogeometric Model (EGM). The EGM relates striking distance to the prospective peak stroke current. To apply this technique, an imaginary sphere is rolled over the structure. All surface contact points are deemed to require protection, whilst the unaffected volumes are deemed to be protected. The main drawback of this method is that it disregards the upward leadersiquest development and assumes the same probability for attachment to the ground, to a structure, and to a LPS. The proposed model is based on physical phenomena leading to the formation and the development of positive upward leader in the field produced by the negative downward leader charge distribution and by some other competing upward leaders. Its purpose is to develop a 3-D numerical model in order to improve the interception efficiency of the Lightning Protection System.

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.

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.

A new approach is proposed for designing coils free of partial discharges (PDs) for compact machines operating at high altitudes. The proposed method consists in using an enameled wire made with a thin additional resistive layer on the outer surface, which reduces strongly the electrical field in the voids between the wires of random coils. With such a wire, PDs occur only in specific zones situated near the wire connections and a local reinforcement of the insulation can increase strongly the partial discharge inception voltage (PDIV). The paper proposes a theoretical method for determining the properties of the resistive layer. The local reinforcement of the insulation is analysed with an electrostatic simulation and Paschen's law. Measurements confirm the effectiveness of the proposed method.

Lightning strikes create surge currents which generate overvoltages in the power distribution and data transmission networks. The spark gap surge protective device (SPD) Type 1 diverts high surge current harmlessly to the ground and limits overvoltage to acceptable values. The present paper aims to present the investigations on the spark gap technology and demonstrates the arc extinguishing method on the surge protective devicepsilas performances. Firstly, the association of the spark-gap with an extinguisher device will be presented. In a second stage, experimental and numerical results of the current density, the pressure, and the temperature of the arc during its propagation will be shown. Both the calculations and measurements have been done for a 10/350 mus pulse and various peaks current.