An applied laboratory characterisation approach for electric machine insulation

Abstract

Insulation is a fundamental part of electric machines as it provides suitable electrical isolation between the different parts and sub-components. Developing techniques for analysing properties of insulation is extremely useful for the assessment of operating conditions, insulation quality and degradation (state of health). This paper investigates a novel non-invasive experimental approach to characterise phase-to-phase and phaseto-ground insulation by measuring electrical impedance and derived parameters (capacitance, dissipation factor) over a wide frequency range (100 to 2 MHz) at various different temperatures. Due to its simplicity the method lends itself better to an electrostatics interpretation compared with the typical twisted pair approach. Analysis is presented for the method which show its effectiveness under different operating conditions. This work has important applications in the area of condition monitoring of insulation using impedance based measurements.

Thermal Degradation Phenomena of Polymer Film on Magnet Wire for Electromagnetic Coils

“…Over time insulation materials may become severely degraded to the point where partial discharge occurs, leading to reduced dielectric properties and voltage resistance of the polymeric coatings [10], [11], as well as adhesion problems, delamination, surface erosion, oxidation as well as the formation of treeing and micro-cracks [3], [12]. The occurrence of repetitive partial discharge events greatly accelerates the ageing process further as it then moves from intrinsic ageing into a rapid extrinsic ageing process, which quickly leads to the catastrophic failure of the electric machine as the electromagnetic coils will quickly yield sustained shortcircuit conditions [6], [7], [8], [13], [2]. This type of fault mainly occurs in the stator coils, where resulting short circuits can include phase-to-ground, turn-to-turn and phase-to-phase.…”

“…In this context, the impact of water ingress on electrically stressed stator coils [9], accelerated ageing on wound model subsections of machines [4], the ageing of calendered insulation paper for for transformers [21] and the impact of fast switching of power electronic converters on insulation health [22], [23] have all been investigated. Suitable techniques for characterising and modelling insulation in terms of physical, chemical, dielectric and electrical properties are immensely valuable for quality assessment, diagnostics and degradation analysis to determine state of health and also for creating equivalent circuit models [24], [13], [25] for thermal analysis. Related approaches in the literature have investigated ageing on twisted insulation-coated wire pair set-ups [23], [26], motorettes or coils [27], [4] or even full machines [28], [29], [24], [25].…”

Thermally Induced Mechanical Stress in the Stator Windings of Electrical Machines

“…One main source of heat in an electrical machine is the power loss in the stator winding. Improper heat removal leads to reduced lifetime of the windings [6] and thus the machine, due to the degradation of copper wires and the coatings which is caused by rapid oxidization of the coatings [7]. For better heat transfer and removal, the windings in electrical machines are subjected to epoxy impregnation, which on one hand ensures improved heat removal and on the other hand prevents the coatings from being in direct contact with air, thus preventing oxidization of the coatings.…”

Investigation of traction motor windings' insulation capacitance at switching frequencies under accelerated thermal stress

“…Insulation monitoring and diagnostics along with multi-stress tests for different materials and coils were studied and thoroughly investigated in [51]- [56]. Finally, [57]- [61] contributed to this field of research with knowledge regarding the dielectric properties of new insulating materials for various applications, as well as diagnosis under a series of tests.…”