FIELD OF INVENTION
This invention relates to an improved insulation and a process for making the same
for manufacturing high voltage AC or DC electrical coils suitable for operation in highly
humid and polluted environment.
BACKGROUND OF THE INVENTION
The present requirement of mass rapid movement in metropolitan cities requires
various modes of transports and the one that is being preferred world wide Is of
electrical multiple unit or EMU locomotives employing 3 phase AC traction motors for
efficient operation. The conversion of single phase overhead traction power to three
phase requires high voltage electronic inventors and high voltage reactors or inductors
to have smooth three phase sinusoidal AC voltage to drive the three phase traction
motors.
To have increased efficiency it requires that the total electrical equipment is made as
low in weight as possible. The reactors or inductors are bulky and heavy electrical
components and contribute significantly to the overall weight of the electrical
equipment thus, a reduction in weight of these inductors makes possible substantial
higher efficiency.
A US patent 4273829 discloses an insulation system for wire and cable in which the
electrical conductor is insulated with a film selected from ethylene tetra-fluoroethylene
co-polymer film and fluorinated ethylene-propylene co-polymer coated polyimide film
and a top coat insulation system comprising a first layer of polyimide, a second layer of
polyvinyl: dene fluoride with a third layer of cross linked acrylic polymer.
Normally the inductors and reactors are made oil cooled along with the main traction
transformer, due to the requirement of handling of large amount of power and
operation at high voltage and inert atmosphere. To achieve reduced weight, while
delivering the maximum output, the present invention describes an improved
insulation that enables operation of inductors and reactors in air cooled environment
resulting in significant reduction in weight and improvement of traction efficiency.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose an improved insulation
and a process of making thereof the same which eliminates the disadvantages of prior
art.
Another object of the present invention is to propose an improved insulation and a
process of making the same which is electrically-sufficient to withstand high voltage
irrespective of operating temperature.
A still another object of the present invention is to propose an improved insulation
and a process of making the same which is water resistant.
A further object of the present invention is to propose a process of making the same
which reduces the weight of the insulator.
DETAILED DESCRIPTION OF THE INVENTION
The inductor and reactor coils can be made of various constructions, like coils wound
in disc shape or spirally wound in cylindrical shape. The coil windings material
employed can be copper/ aluminium depending up on the overall rating space
requirement and user preference.
To have lowest weight it is needed to have maximum possible current density in the
winding without exceeding the insulation temperature. To achieve this it is also
required that the insulation should be of suitable thickness so that it provides
sufficient electrical insulation while allowing proper heat dissipation. Unlike oil cooled
equipment, where the insulation is protected by sealed oil filled tank, when the
windings are air cooled, the insulation is also required to be resistant to moisture and
conductive layers of contamination that settle on the winding during operation. In the
present invention all the above goals are achieved by using a layer of special moisture

Resistant polymide insulation (2), followed by a layer of fibre glass insulation (3) on the
winding conductor (1).
The special water resistant polyimide insulation (2) is suitable for operating temperature
of more than 200°C and is having a radial insulation thickness of 0.15mm. Combined
with glass insulating layer (3), provided for mechanical protection of polyimide film (2),
the total radial insulation thickness on the conducting wire (1) is of only 0.2mm. This
allows proper heat dissipation while providing sufficient electrical insulation. The
conductor wire (1) with this insulation is wound with required no. of turns into complete
coils.
After winding of coils these are assembled, with or without core, as per the design, and
the same are impregnated with high temperature resistant insulating varnish by using
VPI, vacuum pressure impregnation process. A further layer of silicone conformal
coating is provided on the coils after vacuum pressure impregnation.
The overall radial insulation layer thickness over the main electrically charged current
carrying conductors, with the above process, is about 0.3mm to 0.35mm only. This
insulation is electrically sufficient to withstand high voltage while limiting the desired
operating temperature. The water resistant insulation makes the windings and the
inductors or reactors suitable for continuous operation under most humid coastal
conditions, having very high humidity of more than 95% to perpetual continuous
precipitation. The windings remain intact, unaffected and impervious to corrosive
effects of layers of moisture absorbing conductive insulation, which becomes highly
conductive under high humid conditions, ever after long service life.
The overall design make it possible to reduce the weight of heavy inductors and
reactors resulting in efficient operation of the associated utilities.

WE CLAIM
1. An improved insulation and the process of making the same comprising:-
- applying a preliminary layer of special moisture resistant polyimide insulation
(2) followed by a layer of fibre glass insulation (3) on the conductor (1);
- winding conductor wire (1) with this insulation with required number of turn
into complete coils;
- the coils are impregnated with insulating varnish by using VPI, vacuum
pressure impregnation process for better dissipation of heat in high
temperatures;
- providing a final layer of silicone conformal coating on the coils.
2. The improved insulation as claimed in claim 1, wherein overall radial insulation
layer thickness is 0.3 mm to 0.35 mm.
3. The improved insulation as claimed in claim 1, which is workable even over
200° C.

ABSTRACT

TITLE: AN IMPROVED INSULATION AND THE PROCESS
FOR MAKING THEREOF
This invention relates to an improved insulation and the process of
making the same comprising:-
-applying a preliminary layer of special moisture resistant polyimide
insulation (2) followed by a layer of fibre glass insulation (3) on the
conductor (1);
-winding conductor wire (1) with this insulation with required number of
turn into complete coils;
-the coils are impregnated with insulating varnish by using VPI, vacuum
pressure impregnation process for better dissipation of heat in high
temperatures; .
-providing a final layer of silicone conformal coating on the coils.