16. Westinghouse Electric Co.: Thermalastic™

Westinghouse Thermalastic™, the first modern synthetic insulation system. The first Thermalastic insulated generator went into service in 1950, in the 1960’s minor changes that were made included introduction of glass cloth as a backing material for the mica, resin modifications to help VPI resin tank stability, and improvements in the partial discharge suppression treatments on generator coil surfaces. Although large turbine generators continue to use the individual bar impregnation and cure method, motors and smaller generators shifted to the global VPI method in the early 1970s. The hybrid epoxy VPI resin used for turbine generators was optimized for the previously developed processing equipment and insulation requirements. It is comprised of a modified epoxy resin, prepared in a resin cooker to create polyester linkages, and is compatible with styrene for viscosity control. The final resin cure was achieved by cross-linking through the epoxy or oxirane group.

After Siemens acquired Westinghouse in the late 1990s, the Thermalastic system underwent many refinements in materials and processing while maintaining the same resin system. Now a days there are not much changes though.

    General Electric Co. :Micapals I and II™, Epoxy Mica Mat™, Micapal HT™, and hydromat

It was introduced to the industry in an IEEE Technical paper in 1958, after several years of limited production. Micapal 1 contained approximately 50% GE Micamat™ (paper), made with calcined muscovite, and 50% muscovite splitting.

winding operation.

After a 12-year development program, General Electric announced the MICAPAL II™ insulation for large turbine generator stator windings in 1978. This solvent less, resin-rich, second-generation epoxy mica paper insulation system has been used on most large steam turbine generators since that time.

In 1999, GE began to offer a reduced-build strand-and-turn insulation, using similar metal oxide fillers in the large-motor business. These machines use the global epoxy VPI process to make the glass-fabric-supported Mica-mat insulation systems for machines at least up to 13.8 kV ratings. Several generations of VPI resins have been used by GE for motor manufacture. Two of these epoxy resin systems have been based on controlled reactivity chemistry. The most recent improvement creates polyether linkages in cured Di-Glycidyl ether Bis-Phenol, an epoxy resin provides high reactivity at curing temperatures with excellent shelf life at room temperature.

 

2.      Alsthom, GEC Alsthom, Alstom Power: Isotenax™, Resitherm™, Resiflex™, Resivac™, and Duritenax™

During the 1950s, Alsthom licensed the resin technology used in the GE Micapal I system to create the first Isotenax™ system. There were several differences in materials and processes between the two systems. Isotenex used only mica paper, not mica splittings. The resin-rich impregnating epoxy contained significant amounts of a solvent mixture that had to be removed after the glass-backed mica paper tape was wrapped around the stator bars. Since the 1980s the UK operations of Alsthom have also worked with global VPI processing and an insulation system called Resivac™. Recent advances in the VPI system have used bisphenol epoxy resins with a latent Lewis acid catalyst system

3.      Siemens AG, KWU: Micalastic™

Siemens began using the individual-bar VPI process with polyester resins and mica splittings as early as 1957 for hydro and steam turbine generators, with initial help from Westinghouse. This system was trade named Micalastic. Production continued with this combination of resins and processes for at least 10 years. Except for indirect cooled generators and direct-cooled generators rated at more than about 300 MVA or so, which still use the individual bar epoxy VPI methods, the global VPI process has been standard for all motor and turbo generator stators since 1986. For its large global VPI stators, this manufacturer avoids difficulties due to shear stress at the interface of the bar to the stator core by employing a slip plane. The slip plane consists of mica splitting sandwiched between two semi conductive tapes.

    ABB Industrie AG: Micadur™, Micadur Compact™, Micapact™ and Micarex™

Brown Boveri AG started changing from resin-rich asphalt mica flake ground-wall insulation about 1953, first using modified polyester resins and then switching to epoxy resins to make resin-rich tapes. The ABB Group name for bars and coils manufactured from the epoxy resin-rich system is Micarex™. Initially, these tapes were applied by hand and later by machine taping, followed by hot-press consolidation and curing. New machine production with this system will stop with the end of turbo generator production in Sweden, although some repair licensees will continue using Micarex for some time.

The Micadur™ insulation system was introduced in 1955 by Brown Boveri as an individual bar VPI method before the merger of ASEA with Brown Boveri to form ABB in the mid 1980s, ASEA also developed the technology for individual bar VPI production, using similar materials. The result was Micapact™, introduced in 1962 for the stator insulation of large rotating machines. It was made with glass-backed mica paper, impregnated with a special mixture of an epoxy resin, curing agent, and additives. Unlike most other VPI tapes, the glass backing and mica paper lack any impregnant or bonding resin. The adhesion between mica paper and glass was accomplished by an extremely thin layer of material, which was melted at a high temperature during formation of the tape. The tape did not contain any volatile matter, which means that the completed machine taped bar insulation was more easily evacuated and impregnated.