The
Toshiba Tosrich™ insulation system for low-voltage, small-capacity generators
with a relatively small number of insulation layers was based on a resin-rich
mica paper tape. The solvent containing synthetic resin was impregnated into the
mica tape, wound onto a coil and cured in a mold. Although used successfully
for many years for smaller machines, its replacement with a solvent less epoxy,
resin-rich mica paper tape during the 1990s allowed the improved Tosrich to be
applied to medium-capacity generators; it is still gaining manufacturing and service
experience.
For
larger machines, the Tostight-I™ insulation system was developed.A new
generation of the Tostight-I VPI insulation system was introduced in 1998. It
has been optimized to improve heat resistance and to be environmentally
friendly in materials, equipment, production methods, and disposal of waste.
The mica paper has been changed to replace the aramid fibrids with short glass
fibers. The new impregnating resin is principally a high-purity, heat-resistant
epoxy resin, employing a complex molecular capsule, latent hardening catalyst
that is activated by heat to quickly cure and produce a high-heat-resistant,
mechanically and electrically strong filling material for the mica. The revised
system is manufactured using new production equipment, including a fully
automatic taping machine and a new vacuum pressure impregnation facility and
curing oven. The VPI tank is equipped to control vacuum and impregnation as a
parameter of the coil capacitance. The new Tostight-I is intended to be usable
for all types of medium and large generators.
- Mitsubishi Electric Corporation
The
ground-wall insulation systems employed by Mitsubishi until the 1990s were
largely based on licenses obtained from Westinghouse. During the late 1990s,
Mitsubishi introduced a new global VPI insulation system for air-cooled generators
up to 250 MVA. The new system supplemented an older global VPI system, used for
air-cooled generators of up to 50 MVA rating. The new system uses a
glass-fabric-backed mica paper tape, bonded with a very small amount of
hardener-free epoxy resin as an adhesive. The global VPI resin is an epoxy
anhydride.
2.
Hitachi,
Ltd.: Hi-Resin™, Hi-Mold™, and Super Hi-Resin™
Hitachi
also introduced a pre impregnated or resin-rich mica paper insulation, called
the Hi-Mold™ coil in 1971 This press-cured system uses an epoxy resin to
impregnate glass-cloth-backed mica paper, which is partially cured to the B
stage. The high-performance resin was selected to obtain superior electric and
thermal characteristics for use in machines rated for up to Class F insulation
performance. The Hi-Mold system is used for hydro and gas turbine peaking
generators and for heavy duty or other unfavorable environments in synchronous and
induction motors.
3.
Summary
of Present-Day Insulation Systems:
A
review of subsections 4.2.1 through 4.2.8 shows that all of the world’s larger
OEMs are currently using various mixtures and types of epoxy resins and mica
paper to make their stator coil ground-wall insulation systems. The
compositions are adjusted or tailored to accommodate the exact process used in
their manufacture. The end results are comparable in terms of inherent
insulation quality as related to the machine and insulation design parameters,
provided that consistent quality control practices are routinely carried out.
This fact is recognized by some large suppliers of rotating machines, who will,
in times of extraordinary demand, out-source or purchase generators to their
own design from competitors, while allowing the supplier to use their own
insulation systems. We presented here the most efficient and reliable system of
insulation, the Micalastic insulation
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