FIELD OF INVENTION
The present invention relates to salient pole type synchronous generators /
motors. More particularly, the invention relates to a salient pole machine with
improved in-built cooling system.
BACKGROUND OF THE INVENTION
In the case of salient-pole machines (generators / motors), the cooling of the
field winding is a critical area of concern. The coil is indirectly cooled and more
over only a small part of the coil surface comes into contact with the cooling
medium for example, air.
This severely limits the current capacity of the rotor coil. The problem is more
acute in the case of large capacity generators / motors, the rotor current density
being very low (<2.5 A/Sq. mm). Rotor coils are expected to operate within
lass-B limits of temperature to ensure full functioning life of the insulating
materials.

With the pole body (2) on two sides and the pole shoe (4) on the top of the coil
(1) completely block the rotor field coil (1) and the coil can come into contact
with air on only one of its four sides. (Refer Fig.l).
Even on this side, the pole winding retainers (3) are to be accommodated, which
occupy approximately 40% of the straight length of the coil. For this 40% length,
there is no contact with air, hence no codling can be affected.
Ultimately, only a small portion of the rotor field coil (1) is getting cooled.
In the case of pole windings of salient pole construction, according to the prior
art, about a third of the coils are extended by a few mm over the other coils,
that forming cooling fins. This increases the surface area of the coil exposed to
cooling air, thus improving the cooling. But this ultimately falls short of the
requirement.

WO 2005/078898 describes a salient pole machine comprising at least one filed
coil. In this arrangement, an axial cooling channel is created, through which
cooling medium can be supplied to the field coils. However, this machine
requires drilling an additional hole in the pole cap, thus weakening the strength
of a critical component. There are a number of holes in the pole shoe to
accommodate pole screws. Any additional holes are not desired.
GB 2453572 discloses a process by inter-winding ducts; and cooling ducts in pole
pieces. This invention is applicable for salient pole machines with more than 4
poles and rotor coils built up of wire type conductors. A cooling channel is
created in the coil through which air is passed, thereby improving the cooling.
However, this invention can not be applied for large salient pole synchronous
generators with rectangular conductors.
EP 0 415 057 B1 describes an arrangement for the forced supply of a cooling
medium into a gap between a pole core of the rotor body and the field coil, in
which a guiding device is provided in the gap between the pole core of

the field coil which splits the gap into .two areas which are freely connected
essentially only at that end of the gap which is on the pole-cap side and
otherwise have a flow passing through them successively. Such a guiding device
is comparatively complex in terms of manufacturing, however, and requires
special, correspondingly adapted fitting.
DE 198 10 628 Al discloses a ventilation system for the field winding or field coil
of large salient-pole machines, in which flow paths are also formed at the top of
flat copper conductors of the field coil parallel to the flow in the pole gap. The
parallel flow paths thus formed pass through all the flat copper conductors and
the associated insulating layers. However, the flow paths weaken the field coils
and, under certain circumstances do not result in the expected cooling
performance.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a salient pole type
synchronous machine with improved in-built cooling system, which eliminates the
disadvantages of prior art.

Another object of the invention is to propose a salient pole type synchronous
machine with improved in-built cooling system, which enhances cooling of the
field coils of the machine.
A still another object of the invention is to propose a salient pole type
synchronous machine with improved in-built cooling system, which reduces the
operating temperature of the rotor coil.
A further object of the invention is to propose a salient pole type synchronous
machine with improved in-built cooling system, which improves the efficiency of
the machine.
A still further object of the invention is to propose a salient pole type
synchronous machine with improved in-built cooling system, which increases the
operating life of the machine,

SUMMARY OF THE INVENTION
Accordingly there is provided a salient pole type synchronous machine
comprising a solid rotor with machined poles; a plurality of conductors with pole
shoes detachably attached to pole body; a plurality of retainers holding the pole
windings, characterized in that a cooling channel is configured between the pole
coils and the pole body, and in that a plurality of insulation pieces is provided on
the cooling channel to increase the surface area of the windings exposed to air.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 shows a schematic representation of the cross sectional view of a 4-pole,
solid rotor turbo-generator according to prior art.
Fig. 2 shows the machine of Fig.1, with the improvement incorporated according
to the invention.

Fig. 3 shows the detail of the insulation with cooling channels provided between
the pole coils and the pole body to increase the surface area of copper coil in
contact with cooling air.
DETAILED DESCRIPTION OF THE INVENTION
[0001] In the case of salient-pole generators / motors, the cooling of the field
winding is very critical and is crucial for sizing of the machine.
[0002] Though there exist a number of prior art for improving the cooling of the
field coils, the effectiveness of heat dissipation falls short of expectations. In
some cases, the provision of radial cooling holes in the pole shoe has been
proposed is unacceptable from strength point of view, as the pole shoe already
has many holes for fixing of the pole bolts and any extra holes will further
weaken the strength of the pole shoe.

[0003] Hence arises the need for an effective method of improving substantially
the cooling surface area of copper conductors in the field pole coils of salient
pole synchronous generators / motors, especially of large capacity.
[0004] While at the same time, care has been taken to avoid compromising on
the strength of the rotor components, which are continually subjected to heavy
stresses during rotation.
[0005] The proposed invention provides insulation pieces (6) as shown in Fig. 3.
Each channel (5) is 5mmx size out of the'total thickness of 10 mm.
[0006] By providing the insulated piece (6) in place of the pole body (2) on the
cooling channel (5) configured on the copper side of the pole (1), it is possible to
increase the copper surface area exposed to air on the other three sides by
almost two-fold the copper surface area that can be in contact with cooling air.

[0007] This will reduce the rotor coil (1) temperature on full load substantially,
thus allowing extraction of more output from the same frame size of the
machine.
[0008] Such a measure will have attractive commercial benefits for
manufacturers.

WE CLAIM:
1. A salient pole type synchronous machine comprising a solid rotor with
machined poles; a plurality of conductors (1) with pole shoes (4) detachably
attached to pole body (2); a plurality of retainers (3) holding the pole windings
(1), characterized in that a cooling channel (5) is configured between the pole
coils (1) and the pole body (2), and in that a plurality of insulation pieces (6) is
provided on the cooling channel (5) to increase the surface area of the windings
exposed to air.
2. The machine as claimed in claim 1, wherein each channel (5) is of size 5
mm x 5 mm.

3. A salient pole type synchronous machine substantially as hereinbefore
described and as illustrated in the accompanying drawings.

A salient pole type synchronous machine comprising a solid rotor with machined
poles; a plurality of conductors (1) with pole shoes (4) detachably attached to
pole body (2); a plurality of retainers (3) holding the pole windings (1),
characterized in that a cooling channel (5) is configured between the pole coils
(1) and the pole body (2), and in that a plurality of insulation pieces (6) is
provided on the cooling channel (5) to increase the surface area of the windings
exposed to air.