FIELD OF INVENTION
The present invention relates to an improved system for anchoring stator
winding to stator frame of 3-phase traction motor in 6000HP 3-phase AC
drive locomotives.
BACKGROUND OF INVENTION
Indian Railways are running a number of passenger and goods trains to
move passengers and goods traffic across the country. Diesel electric and
AC locomotives are used to run the trains. Both of these employ
conventional DC traction motors as well as 3-phase AC Induction motors.
These motors are suspended on axle of wheels in the locomotive and hence
experience high level of vibration and shocks during running of train.
Presently 3-phase induction motors are used in 3-phase drive AC
locomotives for hauling of train. In the existing motors the stator coil
overhangs are only supported with each other by tying them with a glass
cord and not supported with the stator frame. These AC locomotives are in
service for the last 10-12 years and in this period many cases of failure of the
stator winding have been faced due to ground fault in overhang portion at
the slot exit. These type failures in stator winding have occurred due to
vibration of overhang portion of winding with respect to stator frame.

To solve the winding failure problem of traction motor therefore, there was a
need for a new system of anchoring stator winding to stator frame for 3-
phase traction motor.
SUMMARY OF THE INVENTION
The main object of the invention is to provide a robust design of stator
winding of 3-phase induction motor for traction application such that the
failure of stator winding on account of heavy vibrations and jerks is
eliminated.
One more object of the present invention is to provide strength to stator
overhang portion of stator winding of 3-phase induction motor.
Another object of the invention is to maintain the dimensions of the machine
so that proper fitment of the replacement motor in the bogie is not affected.
Yet another object of the present invention is to provide an improved design
3-phase induction motor thereby reducing the cost of maintenance and
increase serviceability and over all efficiency of locomotives.
These and other objects of the invention are achieved by designing the stator
frame to accommodate support rings and brackets for providing support to
stator coil overhangs.

Thus, in a preferred embodiment the present invention provides an improved
system for anchoring stator winding to stator frame of a 3-phase traction
motor comprising a stator winding with coil overhangs supporting each
other by a glass cord; wherein said stator winding is designed to
accommodate a support bracket; and a ring arrangement for providing
support to the stator coil overhangs by anchoring the stator coils to the stator
frame.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be described in detail with the help of figures of the
accompanying drawings where:
Fig-1 : shows long section of 3-phase induction motor.
Fig-2 : shows photograph of a stator assembly clamping at side of the
present invention.
Fig-3 : shows photograph of stator assembly clamping at end chamber of
the present invention.
Fig-4 : shows sketch of clamping side bracket.
Fig-5 : shows sketch of brackets clamped on end chamber
Fig-6 : shows sketch of epoxy moulding ring
Fig-7 : shows sketch of prior art winding overhang tied to glass cord
DETAILED DESCRIPTION
Locomotive are used to haul train. State of the art AC locomotive employs
3-phase induction motors, which are mounted on the axle of wheel of the
locomotives. When the motor is started the rotor rotates, which in turn
rotates axle through gear and pinion arrangement, thus driving the
locomotive.

As shown in Fig. 1 the 3-phase induction motor consist of a stationary part
called a stator 1 and a rotating part called a rotor 2.
The high permeability stator 1 made from sheet steel laminations 3 are
stacked together with two steel end chambers 4 at each end to form the stator
core. Over this stacked core laminations, tension segments are welded to
form the stator. The end chambers 4 are machined to ensure alignment of the
end shields 5, stator bore and axle ways.
The stator 1 is wound with 3-phase lap winding. The armature conductors
are insulated with polyimide and mica based class 200 Insulation system.
The coils 6 are held down in the core slots with Epoxy glass slot wedges,
and end windings are braced together with glass hose strips 11 (Fig. 2)
together with glass cord 12. The wound stator is finally vacuum pressure
impregnated in silicone varnish.
The rotor is a squirrel cage rotor. It consists of a core, which is formed by
stacking sheet steel laminations with end plates at both the ends. This core is
then assembled on the shaft 7 (Fig. 1). Copper bars 8 are inserted in the slots
provided and are shorted at the ends through short circuit rings.
The improved system of anchoring stator winding to stator frame of the
present invention shall eliminate the stator winding failure of 3-phase
traction motor used in 6000HP AC drive locomotives and also ensure
reliable operation of traction motor with increased service life. These motors
as described above are being used by Indian Railways for last 10-12 year for -
hauling trains. Many cases of ground fault in overhang portion of the stator
winding in these 3-phase induction motors have been reported during
service.

During detailed investigation of the failure of the stator winding of 3-phase
traction motor it was found that in most cases, the failure had occurred at the
slot exit 13 (Fig. 2) on both connection as well as drive end.
Prima facie, this failure at slot exit 13 is due to relative vibration between
stator coils 6 and stator frame 2 during operation due to electrical stresses,
machine vibrations and jerks and vibrations encountered during service due
to track conditions.
To overcome this failure at slot exit 13 a new design had to be developed for
anchoring coil overhangs 14 (Fig. 2) to stator frames through support
brackets and rings arrangement. One coil support ring is assembled at each
end to tie each coil with the support ring using glass cords. The coil support
ring is further tightly anchored with support brackets at different locations of
the stator frame. The support brackets are preferably steel support brackets.
A major constraint in this was the space available to accommodate the rings
and support brackets as the outer dimensions of the frame had to remain
unchanged. In order to overcome these constraints the present invention
provides an improved system for anchoring the stator coil overhang to the
stator frame, which is mentioned below.
In the existing design there is no provision for any bolting arrangement of
the clamps to support the support rings. In the present invention the stator
frame has been designed to accommodate the clamps. Special clamps used
(Fig. 4) are designed to be bolted through a tapped hole provided in the end
chamber as shown by bolting arrangement 21 in Fig. 3 enabling dismantling
of the same if required.

Also special brackets as shown in Fig. 5 were designed to fit on the inner
portion of the sides of the frame through bolting as shown in bolting
arrangement 15 (Fig. 2). The design of these support brackets is such that no
portion of it fouls with the end shields on the outside and also there is
enough clearance with the overhangs on the inside. Special fibre rings 22
(Fig. 3) made of epoxy glass as shown in Figure 6 is designed to support the
end windings through anchoring.
To ensure the strength of winding overhang portion of wound stator
assembly with support brackets and rings vibration response measurement
test has been carried out on both new designs wound stator and prior art
design would stator assembly. Significant improvement has been observed
in the vibration pattern of new design.
The distinguishing features of the invention over prior art are explained in
tabular form as under.


WE CLAIM
1. An improved system for anchoring stator winding to stator frame of a
a 3-phase traction motor, said system comprising a stator winding
with coil overhangs supporting each other by a glass cord; wherein
said stator winding is designed to accommodate a support bracket; and
a ring arrangement for providing support to the stator coil overhangs
by anchoring the stator coils to the stator frame.
2. The system as claimed in claim-1, wherein said support rings
are epoxy glass moulding ring.
3. The system as claimed in claim-1, wherein said support brackets
are steel support brackets.
4. The system as claimed in claim-3, wherein said steel support brackets
are designed such that no portion of the brackets fouls with the end
shield and there is enough clearance with the overhangs on the inside.
5. The system as claimed in claims 1 or 2, wherein one said epoxy glass
moulding ring is assembled at each end to tie each coil with the
support ring with the help of glass cords.
6. The system as claimed in claim 5, wherein said epoxy glass
moulding ring is tightly anchored with said steel support blocks at
different locations of the stator frame.

7. The system as claimed in claim-1, wherein the end chamber of the
stator is provided with a tapped hole for bolting special clamps to
support the epoxy glass moulding ring.
8. An improved system for anchoring stator winding to stator frame of a
three phase traction motor, substantially as herein described and
illustrated in the accompanying drawings.

The main object of the invention is to provide a robust design of stator winding of 3-phase induction motor for traction application such that the failure of stator winding on account of heavy vibrations and jerks is eliminated. One more object of the present invention is to provide strength to stator overhang portion of stator winding of 3-phase induction motor.
Another object of the invention is to maintain the dimensions of the machine so that proper fitment of the replacement motor in the bogie is not affected. Yet another object of the present invention is to provide an improved design
3-phase induction motor thereby reducing the cost of maintenance and increase serviceability and over all efficiency of locomotives. These and other objects of the invention are achieved by designing the stator frame to accommodate support rings and brackets for providing support to stator coil overhangs. Thus, in a preferred embodiment the present invention provides an improved system for anchoring stator winding to stator frame of a 3-phase traction motor comprising a stator winding with coil overhangs supporting each other by a glass cord; wherein said stator winding is designed to accommodate a support bracket; and a ring arrangement for providing support to the stator coil overhangs by anchoring the stator coils to the stator frame.