Characterising the performance of selected electrical machine insulation systems

Abstract

Abstract-This paper presents results from an analysis of alternative slot liner materials used in the construction of electrical machines. The slot liner material has a vital safety critical function within a machine assembly, providing electrical insulation between the winding body and stator core pack. Performance measures for the slot liner material include the dielectric breakdown voltage, tensile strength, thermal conductivity and thermal class, amongst others. There is a large variety of slot liner materials available on the market with the material properties altered to suit a particular application. Some of these material properties are strongly dependent on the components and processes employed in construction of the complete winding assembly e.g. type of the winding impregnation and/or method used in impregnation of the stator/winding assembly. Consequently, the manufacturer provided data is usually inadequate when comparing various insulation systems and their individual elements for a particular machine construction. This research is focused on the conductive heat transfer phenomenon from the winding body into the machine periphery in context of the slot liner material used, for a given impregnation type and method. The repeatability of the winding manufacture process is also investigated. Three alternative slot liner materials with different thermal conductivity and ability of absorbing varnish impregnation have been chosen for prototyping of representative stator/winding hardware exemplars. This has been supplemented with a batch manufacture of the stator-winding hardware exemplar for a selected slot liner material. The proposed experimental approach allows for the complete insulation system to be evaluated accounting for the assembly and manufacture nuances. The results suggest that the use of a particular slot liner has an impact on the winding heat transfer and also implications regarding appropriate manufacture and assembly processes used, i.e. some of the materials require special handling. The experimental work has been supplemented with theoretical analysis to provide a more comprehensive insight into the winding heat transfer phenomena.

Characterizing the in situ Thermal Behavior of Selected Electrical Machine Insulation and Impregnation Materials

“…The SLM2 slot liner has the highest thermal conductivity and consequently provides the lowest thermal resistance across the stator-winding interface with SLM3 next and SLM1 the last. An insight into microscopic structure of the analysed slot liner materials has been provided in [24]. When comparing the analysed slot liner materials, it is evident that SLM3 has the most porous construction as compared with SLM1 and SLM2.…”

Experimentally Calibrated Thermal Stator Modeling of AC Machines for Short-Duty Transient Operation

“…This provides the opportunity to trial combinations of alternative materials to be used in the construction and assembly of the winding. As has been reported in the literature, the influence of the impregnation compound [22] and slot liner [23] have a significant impact on the thermal behaviour of a machine.…”

“…Also compared are three different types of slot liner, producing nine different combinations of impregnation material and slot liner type. The different viscosities of varnishes and potting compounds effect the degree of penetration of the impregnation material within the slot liner [23], and is difficult to predict the resultant thermal properties without experimental data. The insight gained from this study has been used to downselect the insulation system for the final machine prototype.…”

Experimental calibration in thermal analysis of PM electrical machines

“…Some of the thermal parameters that are obtained from tests on the machine hardware include contact thermal resistance [1]- [7], heat transfer coefficients [8]- [11], equivalent thermal conductivity [12]- [15] and loss components separation [16]- [20]. It is important to note that the thermal model parameters depend on the assembly and manufacturing factors along with the particular machine configuration and operating regime [1]- [3].…”

“…The second approach includes representative machine sub-assemblies, e.g. stator-winding sectors, so called motorettes [3]- [7], [11]. The custom designed experiments [8], [12]- [14] are also used.…”