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In this paper, the results obtained from lab tests on twisted pairs subjected to different voltage waveforms and atmospheric conditions are used to propose how to modify the IEC Std. 60034-18-41. The goal is to make the standard suitable for the More Electrical Aircraft (MEA). The results show that it is initially necessary to screen out materials through simple tests. The enhancement factors for temperature can be modified to consider reduced pressures and temperatures using a simple model. The aging enhancement factor can be reduced considering the reduced sensitivity of the partial discharge inception voltage (PDIV) at low pressures on the enamel thickness. Eventually, reference will be made to the drive discussed in Part I of this series to draw conclusions about the likelihood of partial discharge inception in a random wound stator and how to reduce it by modifying either the inverter or the stator insulation. Reference to a random wound motor is made throughout the paper.

Polyimide (PI) is an important insulation material due to its high thermal, chemical and electrical resistance along with good mechanical strength [1]. It has been widely used in equipment such as high voltage motors, wind turbine and aerospace craft [2]. [ABSTRACT FROM AUTHOR]

This paper is focused on the reliability evaluation of an electric vehicle (EV) motor based on hairpin technology. Besides bearings (not discussed here), the weak point of an electric motor is its insulating system. For inverter-fed motors, the inception of partial discharges might lead to failure in a matter of days, and thus, deserves particular attention. Qualification and lifetime evaluation of inverter-fed machines are described in IEC 60034-18-41, which specifies accelerated aging procedures and considers partial discharge inception as the end-of-life criterion. This standard was used as a reference for this paper. The only exception is that insulation models were subjected to the mechanical stress profile reported in the ISO 16750-3-2012 standard since an automotive motor is subject to significant vibrations during its operation. From the tests performed, we observed that, with the hairpin technology, turn-to-turn is the weakest link in the insulation system. All the insulation models were partial discharge (PD) free from the beginning of the tests to breakdown and the root cause for breakdown was, in all cases, traced back to cracks on the surface of the insulation. This suggests that, depending on insulating enamel thickness and conductor geometry, some insulation systems are intrinsically PD free by design, despite the effect of aging. Considering the severe vibration profiles typical of EVs, and the principal breakdown mechanism (cracking of the insulation), mechanical stress coupled with thermal stress appears as the main aging driver. Therefore, this paper spotlights the lack of proper standards for the qualification of automotive electric motors and hints at the possibility that IEC 60034-18-41 considers dealing with motors that might be intrinsically partial discharge free even after long-term exposure to operational stresses. [ABSTRACT FROM PUBLISHER]

High voltage equipment designed for DC applications is stressed differently from ac equipment. Most notably, the load conditions of the equipment play a major role in determining the electric field distribution in insulation under dc, due to the temperature dependence of conductivity. Additionally, polarization and space charge phenomena impose a time dependent behavior on the stress distribution. This has major consequences for the way in which degradation of the insulation under dc stress takes place. The nature of the stresses under dc may lead to accelerated degradation processes which could result in early breakdown of the insulation. This paper provides an overview of the stress conditions specific for dc application and highlights via which routes they may lead to failure. The stress distributions in converter transformers and dc cable systems will serve as typical examples. [ABSTRACT FROM AUTHOR]

In the framework of developing defect-based life models, in which breakdown is explicitly associated with partial discharge (PD)-induced damage growth from a defect, ageing tests and PD measurements were carried out in the laboratory on polyethylene (PE) layered specimens containing artificial cavities. PD activity was monitored continuously during aging. A quasi-deterministic series of stages can be observed in the behavior of the main PD parameters (i.e. discharge repetition rate and amplitude). The evolution of the parameters reflects the physicalchemical changes taking place at the dielectric/cavity interface during the aging process. PD activity shows similar time behavior under constant cavity gas volume and constant cavity gas pressure conditions, suggesting that the variation of PD parameters may not be attributed to the variation of the gas pressure. It is speculated that the change of PD activity is related to the composition of the cavity gas, as well as to the properties of dielectric/cavity interface. [ABSTRACT FROM AUTHOR]