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Review
. 2016 May 20;8(5):201.
doi: 10.3390/polym8050201.

Mica/Epoxy-Composites in the Electrical Industry: Applications, Composites for Insulation, and Investigations on Failure Mechanisms for Prospective Optimizations

Natascha Andraschek  1 , Andrea Johanna Wanner  2 , Catharina Ebner  3 , Gisbert Riess  4
Affiliations
Review

Mica/Epoxy-Composites in the Electrical Industry: Applications, Composites for Insulation, and Investigations on Failure Mechanisms for Prospective Optimizations

Natascha Andraschek et al. Polymers (Basel). .

Abstract

The investigation of mica and mica/epoxy-composites has always been of high importance and has gained increased attention in recent years due to their significant role as insulation material in the electrical industry. Electrical insulation represents a key factor regarding the reliability and lifespan of high voltage rotating machines. As the demand for generating power plants is increasing, rotating machines are of intrinsic importance to the electrical energy supply. Therefore, impeccable functioning is of immense importance for both the producers of high voltage machines as well as the energy suppliers. Thus, cost reduction caused by shorter maintenance times and higher operational lifespan has become the focus of attention. Besides the electrical properties, composites should offer compatible chemical and mechanical, as well as thermal characteristics for their usage in insulating systems. Furthermore, knowledge of several occurring stresses leading to the final breakdown of the whole insulation is required. This review aims to give an overview of the properties of pure components, the composite, and the possible occurring failure mechanisms which can lead to a full understanding of insulation materials for high voltage rotating machines and therefore establish a basis for prospective optimizations.

Keywords: electrical insulation; failure mechanisms; insulation materials; mica; mica/epoxy-composites.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Construction of an electrical insulation. © copyright permission from Elsevier, 2014, Composites Part B: Engineering, New approaches towards the investigation on defects and failure mechanisms of insulating composites used in high voltage applications, License No. 3839281153636 [24].
Figure 2
Figure 2
Percentage of the particular damages (left), damages divided into 7 distinct groups (right). © copyright permission from IEEE, 2008, IEEE Electrical Insulation Magazine, Insulation Failure Mechanisms of Power Generators, License No. 3844180528249 [46].
Figure 3
Figure 3
Values of electric field strength and the duration of certain mechanisms causing insulation damage. © copyright permission from the author(s), this is an open access article distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/ [52].
Figure 4
Figure 4
Diglycidylether of Bisphenol A (DGEBA) n = 0–1.
Figure 5
Figure 5
4-Methylhexahydrophthalacid anhydride (MHHPA).
Figure 6
Figure 6
Zinc naphthenate (ZnNaph); structure example.
Figure 7
Figure 7
Opening of the anhydride ring due to reaction with an alcohol (R-OH).
Figure 8
Figure 8
Reaction of the opened anhydride with an epoxy upon formation of an ester and a hydroxyl group.
Figure 9
Figure 9
Network structure of an epoxy resin based on DGEBA/MHHPA.
Figure 10
Figure 10
Amine-accelerated reaction of anhydride with an epoxy.
Figure 11
Figure 11
Opened anhydride and zinc naphthenate (Naph− = R–COO−).
Figure 12
Figure 12
Zinc-naphthenate–MHHPA—dissociation at higher temperatures.
Figure 13
Figure 13
Epoxy-ring opening via free naphetenic acid H–Naph.
Figure 14
Figure 14
Equilibrium: non-dissociated and dissociated zinc salt of MHHPA.
Figure 15
Figure 15
Carboxylate–epoxy reaction.
Figure 16
Figure 16
Structure of dicyanate ester.
Figure 17
Figure 17
Structure of cyanate ester of bisphenol.
Figure 18
Figure 18
Structure of cyanate ester of tetra methyl bisphenol F.
Figure 19
Figure 19
Structure of cyanate ester of bisphenol M.
Figure 20
Figure 20
Structure of cyanate ester of phenol novolac resin.
Figure 21
Figure 21
Polycyclic trimerization of di-cyanate ester to triazine-structures.
Figure 22
Figure 22
Epoxidized novolac.
Figure 23
Figure 23
Hardening of epoxy/anhydride (simplified).
Figure 24
Figure 24
Hydrolysis of the ester structure.
Figure 25
Figure 25
Polyether structure of the cationic hardened epoxy resins.
Figure 26
Figure 26
TG/DTG curves of components obtained under N2 atmosphere (10 °C·min−1), PT pan, and β of 10 °C·min−1. © copyright permission Springer, 2011, Journal of Thermal Analysis and Calorimetry, Thermal characterization of mica–epoxy composite used as insulation material for high voltage, License No. 3837180507265 [83].
Figure 27
Figure 27
TG curves of mixtures: resin/hardener, hardener/N–Zn, and resin/N–Zn under N2 atmosphere (10 mL·min−1), Al2O3 pan, and β of 10 °C mL·min−1. © copyright permission Springer, 2011, Journal of Thermal Analysis and Calorimetry, Thermal characterization of mica–epoxy composite used as insulation material for high voltage, License No. 3837180507265 [83].
Figure 28
Figure 28
TG curves of resin, N–Zn and resin/N–Zn under N2 atmosphere (10 mL·min−1), Al2O3 pan, and β of 10 °C mL·min−1 and DSC curves under N2 atmosphere (50 mL mL·min−1), Al pan, and β of 10 °C min−1. © copyright permission Springer, 2011, Journal of Thermal Analysis and Calorimetry, Thermal characterization of mica–epoxy composite used as insulation material for high voltage, License No. 3837180507265 [83].
Figure 29
Figure 29
TG/DTG curves of resin and hardener with and without mice tape under N2 atmosphere (10 mL·min−1), Al2O3, pan, and β of 10 °C·min−1 .© copyright permission Springer, 2011, Journal of Thermal Analysis and Calorimetry, Thermal characterization of mica–epoxy composite used as insulation material for high voltage, License No. 3837180507265 [83].
See this image and copyright information in PMC

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