FIELD OF INVENTION
The present invention relates to a device for supplying current from
stationary brushes to the rotor field circuit of traction alternator for
generating power in the stator winding for traction motors in the diesel
electric locomotive.
BACKGROUND OF INVENTION
The substantial parts of rail routes in India and abroad are not electrified.
Essentially diesel electric locos operate in these routes. The diesel engine
coupled with traction alternator work as mobile power house in these
diesel electric locomotives to provide power for traction motors.
The traction alternator mentioned above is a salient pole type 3 phase
synchronous alternator having field circuit in rotor. The current to the rotor
field coils is injected through carbon brushes and a slip ring assembly with
two slip rings fitted on alternator rotor. The pictorial view of alternator rotor
showing position of slip ring assembly is given as Fig. A.
Earlier the traction alternator was provided with mild steel slip ring
assembly (Fig. 1) which was prone to rusting. Also slip ring was developing
grooves & pit marks during service. In rainy season it was showing low
insulation resistance due to penetration of moisture in the hub insulation.

There was also problem of tracking between slip rings due to insulation
sleeve getting punctured due to carbon deposit on the surface of the
sleeve.
To overcome these issues, the new product stainless steel slip ring
assembly (Fig.2) has been developed which does not get rusted even
when not in use. The improved insulation system is capable to show good
insulation resistance even in monsoon period when humidity is 95%. The
insulation sleeve of slip ring stud is made of three layer insulation with
PTFE top which has very smooth surface; hence carbon dust doesn't get
deposited on it, thus eliminating the possibility of tracking between rings
during service.
OBJECTS OF INVENTION
It is an object of the present invention to provide a stainless steel slip ring
assembly instead of mild steel slip ring assembly so that customer does
not face surface rusting problem.
Another object of the invention is to develop a slip ring assembly with
improved insulation system so that the problem of low insulation
resistance is avoided during high humidity monsoon period and also
tracking due to carbon deposit on insulation sleeve does not occur.

Yet another object of the invention is to provide more reliable stainless
steel slip ring assembly by providing flexible fluonlex cable lead
connectors in brazed condition instead of flat copper strips in bolted
condition so as to avoid electrical failure due to overheating of loosened
bolted joints due to rotation of traction alternator rotor in service.
SUMMARY OF THE INVENTION
Accordingly, there is provided a slip ring assembly is a product which is
fitted on the rotor of traction alternator for collection of current from
stationery brushes and feed to the field circuit in the rotor. The current
going to the field circuit excites the windings and creates flux which
further generates power in the stator winding. The power generated in the
stator winding is taken out for end use.
Slip ring assembly consists of a mild steel Hub which is the base frame for
the slip ring assembly and the product is mounted over the rotor through
the hub. The hub has a round surface for sitting of slip rings. The round
surface is coated with an insulation layer before mounting of slip rings so
that the slip rings are isolated from the Hub. This isolation is necessary
because the hub is a part of ground potential and slip rings are at supply
potential to feed to the rotor windings. The slip rings are shrink fitted over
the insulation surface for proper grip so that the position is intact during

service. The access to slip rings for electrical connection is done through
copper studs which are brazed onto slip rings and brought out as
terminals. The copper stud of inner slip ring is insulated with a sleeve to
make it pass through the other slip ring. To extend the terminals, cables
are provided which go up to the rotor winding terminals to complete the
connection.
During operation, stationery carbon brushes slide over the slip rings
surface to supply current for excitation of rotor winding. The slip rings
collect the current and feed to rotor winding as per connection explained
above.
The stainless steel slip ring assembly has been designed based on
feedback from various diesel sheds and with innovative changes in
various assemblies to enhance the overall reliability of slip ring assembly
of traction alternator. Adoption of altogether new methodology of electrical
connections and improved insulation system with stainless steel surface of
slip ring assembly also makes the traction alternator highly reliable. The
invention is able to give trouble free service for many years without much
maintenance involved and also enhances the customer satisfaction.

CONSTRUCTIONAL DETAILS OF THE INVENTION:
The stainless steel slip ring assembly details are shown in Fig.2. The prior
art, i.e. mild steel slip ring assembly is also shown in Fig. 1.The
comparison of constructional features of the prior art and the invention is
as per table below:

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 shows the block diagram of existing mild steel slip ring assembly.
Fig. 2 shows a block diagram of stainless steel slip ring assembly of the
present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIEMNT OF THE
INVENTION
Fig. 1 shows the sketch of existing mild steel slip ring assembly, which
comprising a mild steel Slip rings (1), a fabricated hub bolted to rotor
assembly, (3) a hub insulation (3), an insulation sleeve made of epoxy
glass (4), a solid copper strap connectors (5); a brass studs bolted
arrangement (6).

Fig. 2 shows a block diagram of stainless steel slip ring assembly of the
present invention, comprising stainless steel slip rings (1); a fabricated
hub bolted to rotor assembly, (2); a hub insulation, (3); a 3-layer insulation
sleeve (4); a flexible copper connector and copper studs brazed
arrangement (6).


We claim
1. A device for supplying current from stationary brushes to the
rotor field circuit in the rotor of traction alternator for
generating power in the stator winding for traction motors in
the diesel electric locomotive consisting of an improved
stainless steel slip ring assembly (1) having two slip rings
fitted on alternator rotor, a modified insulation system for
slip ring assembly and Fluonlex cable based lead
connection for slip ring assembly.
2. A device as claimed in claim-1, wherein the slip ring is fitted
on the rotor through a mild steel hub (2) having a round
surface for sitting of the slip rings.
3. A device as claimed in claim-2, wherein the round surface of
the hub is coated with an insulation(3) before fitting of the
slip rings so that the slip rings are isolated from the hub
because the hub is at ground potential and the slip rings are
at supply potential and the slip rings are shrink fitted over the
insulation surface for proper grip so that the position is intact
during service.

4. A device as claimed in claim -3, wherein the access of the
slip rings for electrical connection is done through copper
studs which are brazed on to the slip rings, and are brought
out as terminals to which flexible cables are to go up to the
rotor winding terminals to complete the connection.
5. A device as claimed in claim - 4, wherein the copper stud of
the inner slip ring is insulated with a sleeve (4) to make it
pass through the other slip ring.
6. A device as claimed in claim-1, wherein the slip rings of the
slip ring assembly (1) are made of mild steel base rings
covered with stainless steel strips on the out side through
special welding process in order to optimize the weight and
to reduce the material costs, keeping the over all diameter
same, and making smoother top surface and harder than
mild steel alone and one cut mark of 45° angle is provided
for self cleaning of the carbon from the slip ring top surface.
7. A device as claimed in claim 3 wherein the hub insulation (3)
is made of layers of mica based insulation followed by layers
of epoxy prepeg cloth and hot ironing being carried out in

between the process of laying the insulation layers in order
to avoid slippage and wrinkles.
8. A device as claimed in claim 5, wherein the insulation sleeve
(4) is made of three layers of insulations consisting
micafolium, epoxy glass prepeg and finally PTFE sleeve
having extremely smooth surface over the first two layers.
9. A device for supplying current from stationary brushes to the
rotor field circuit of traction alternator for generating power in
the stator winding for traction motor in the diesel electric
locomotive as substantially described and illustrated in the
accompanying drawings.
10. A traction alternator for generating power in the stator
winding for supplying to traction motors in the diesel electric
locomotive provided with a device as claimed in any of the
claims 1 to 8.