FIELD OF INVENTION
The invention relates to synchronous machines of the kind in which the rotor has
a direct current field winding. More particularly, the invention relates to a method
of providing insulation between prefabricated field coil and pole body of a
rotating machine.
BACKGROUND OF INVENTION
In large rotating machines, the field winding, mounted on rotor, is isolated from
ground, is supplied with a direct current from a DC source. The field winding is
carried by a rotor body, which is itself grounded and the winding is enclosed by
insulation, which electrically isolates it from the rotor body.
Since the field winding is to be electrically isolated from the rotor body, a
number of processes are used by different manufacturers for providing this
insulation. In such insulations processes, the main difficulty is faced in providing
insulation at the corners where two or three edges meet. In all the known
systems of insulation of field coils, corner insulation has been the weakest area.
It becomes much more difficult to conceive this insulation if the coil shape or
pole shape is not very regular.
In prior art, this insulation is provided with 0.25 thick nomex paper crafted in
various shapes. These pieces are stuck on the field coil and body prior to
assembly. Then field coil is mounted on the pole body and placed in such a way
to have uniform gap all round. Subsequently these gaps were packed with epoxy

glass sheets of various thickness to make a tight assembly. In the last step of
packing, since the activity is being carried out in a narrow gap of 2 to 3mm,
chances of the nomex getting torn off is quite common and this subsequently
results into failure of the assembly during high voltage test.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a fail proof insulation method for Field windings of rotating machines mounted on rotors.
SUMMARY OF THE INVENTION
According to the invention, there is provided an insulation method in which 1.0
mm thick epoxy glass molded components of suitable shapes have been
designed. These pieces have sufficient strength to withstand the abuse of
assembly. These molded components are assembled on the pole body and then
the field coil is lowered on it. Similar components are assembled on top side of
the field coils and then the packing is carried out with epoxy glass packers of
various thickness.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 - A schematic diagram showing the conventional arrangement for Field
coil insulation.

Fig. 2 - Illustrates a method for Field coil insulation according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in figure - 1, the insulation according to the prior art is made with the
help of a number of composite nomex papers cut and folded in various shapes to
suit the assembly.
As per prior art, there is provided a plurality of plain L bend pieces (1, 2, 3, 4) a
typical (three dimensional) shape cut piece (5) folded to cover two horizontal
edges meeting at corner. The L bend pieces (1 to 4) are used on all the twelve
edges, eight horizontal and four vertical edges, and the three dimensional piece
(5) is used at all the eight corners. Having pasted these pieces (1-5) on a field
coil (6) and a pole body (7), the field coil (6) is mounted on the pole body (7)
and then the gaps are filled up with epoxy glass laminates of various thickness
for making the assembly tight.
While driving the glass laminate pieces in the blind gap between the field coil (6)
and the pole body (7), there is a chance that the nomex piece placed earlier may
get torn off. This will not be known to the operator while completing the
assembly and this will only be revealed during subsequent high voltage test.
In fig -2, the modified design, two molded components (1, 2) have been
configured. Insulation is made with the help of these two components (1, 2) only.
Pieces of required length are cut from a first molded component (1). The second

molded component (2) has been designed in such a way that it covers all the
three edges meeting at a corner. Due to this no vertical corner piece is required.
Subsequently the assembly is tightened with the help of glass laminate sheets of
various thickness similar to existing the design.
Since in this design all molded pieces are used, chances of any insulation getting

torn off are not there. This makes the assembly fail proof. As per molded
components are used, productivity is improved.

WE CLAIM
1. A method of providing insulation between pre-fabricated field coil (6) and pole
body (7) of a rotating machine, comprising:
- providing a first molded component (1) formed out of epoxy glass having a
length and shape corresponding to the pre-fabricated field coil and the body of
the machine;
- providing a second molded component (2) configured in such a way that it
covers all the three edges of the pole body (7) and the field coil (6), meeting at a
corner;
- pasting the first (1) and second (2) molded component on the pole body (7)
including the field coil (6);
- lowering the field coil (6) to be disposed above the pole body (7); and
- filling-up the gaps between the pasted field coil (6) and the pole body (7) with
a plurality pieces of packers of several thickness formed of epoxy glass laminates
characterized in that the molded components and the glass laminate sheets in-
the blind gap make the assembly tight and insulation proof eliminating the use of
vertical corner pieces which were prone to damage.

2. The method as claimed in claim 1, wherein the thickness of the epoxy glass
molded components is selected as 1.0 mm.
3. The method as claimed in claim 1 or 2, wherein the second molded
component comprises straight edges and sharp corners.

According to the invention, there is provided an insulation method in which 1.0 mm thick epoxy glass molded components of suitable shapes have been designed. These pieces have sufficient strength to withstand the abuse of assembly. These molded components are assembled on the pole body and then the field coil is lowered on it. Similar components are assembled on top side of the field coils and then the packing is carried out with epoxy glass packers of
various thickness.