FIELD OF INVENTION;
The invention relates to a water-cooled stator core design with axial insertion of
electrically insulated water-cooling pipes in to stator core for better heat
transfer.
BACKGROUND OF INVENTION AND PRIOR ART;
Stator core of turbo alternator experiences various types of losses like
Hysteresis and eddy current losses which in turn heat the stator core portion.
Heating of this core will reduce the operational limit of the turbo alternator.
Hence cooling of the stator core is very critical in the design for sizing of the
Turbo Alternator. Generally, Core cooling is done by providing ventilation ducts
in between the packets which allow flow of air radially from the air gap towards
the outer portion of stator core. In order to reduce the temperature of stator
core one can increase the number of spacers / width of spacers / size of the
stator lamination, but all these proposals lead to the increase in the space/
size of turbo alternator. In the proposed design, in addition to the ventilation
spacers pipe is provided in the core through which the cooling medium flows
Hence, Water cooled core aid in reducing the size and improve the performance
of the Turbo Alternator. Figure-1 shows the arrangement of stator core pipe
inside stator core. This method of stator core cooling reduces the temperature
of the core, reduces the space/ size of stator core and there by achieving
optimal utilization of turbo generator.
Prior-art
US005859482A relates generally to electric motors and, more particularly, to
a liquid cooled electric motor frame including a cast in place cooling conduit

and methods for fabricating Such a motor frame. However, in present invention
stator core is cooled by insulated water cooling pipes inserted in to stator core.
US007956500B2 teaches a machine that includes an inner air-cooled rotor
and an outer liquid-cooled stator, in which the stator includes a radial cooling
arrangement arranged to convey a cooling liquid radially in the stator to
dissipate heat from stator core and stator winding combined. However, in
present invention stator core is cooled by axial insertion of insulated water
cooling pipes in to stator core in addition, thisdesigned water-cooling circuit is
exclusively meant for stator core cooling, so better heat transfer effect.
OBJECT OF INVENTION;
An object of this invention is to make a water cooled stator core which will help
in reduction of temperature of stator core.
Another object is to reduce size of the stator core.
A still another object is optimum utilization of the turbo generator.
SUMMARY OF THE INVENTION:-
The stator cores of various rotating electrical machines are cooled by forced air
circulation. Stator core of turbo alternator experiences various types of losses
like Hysteresis and eddy current losses, which in turn heat the stator core
portion. Heating of this core will reduce the operational limit of the turbo
alternator. Hence cooling of the stator core is very critical in the design for
sizing of the Turbo Alternator. Generally, Core cooling is done by providing
ventilation ducts in between the packets, which allow flow of air radially from
the air gap towards the outer portion of stator core. In order to reduce the
temperature of stator core one can increase the number of spacers / width of

spacers / size of the stator lamination, but all these proposals lead to the
increase in the space/ size of turbo alternator.
In the proposed design, lamination segments are provided with a provision to
carry VPI insulated core cooling water pipes and after stacking of laminations
these coolingpipe are inserted into those slots through which cooling medium
flows. In this method of cooling the VPI insulated water cooling pipe circuit is
designed exclusively for dissipation of stator core heat load and considerably
there is no heat load from stator winding side. However, there is a separate
water cooling circuit is designed for dissipation of heat from stator winding.
Thus, the design with the proposed cooling method is novel to accommodate
the core cooling pipes in the core for cooling of stator core and thereby
reducing the temperature of stator and reducing the size of the generator
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: -
Figure-1 shows cross section of stator core assembly along with core cooling
water pipes(l) and stator core(2)
Figure-2 shows drive end side view of stator core assembly along with core
cooling water pipes(3)
Figure-3 shows Non drive end side view of stator core assembly along with core
cooling water pipe connection(4)
DETAILED DESCRIPTION OF INVENTION/PREFERRED EMBODIMENT:
The invention has a separate electrically insulated water cooling pipes
provision and is designed for cooling the stator core. In this arrangement there
is no heat load from stator winding side as stator-winding cooling is taken care
by separate water circuit.
The Vacuum Pressure Impregnated (VPI) insulation is used for these water
pipes for better electrical isolation and best thermal heat transfer from stator

core to cooling water. This VPI insulation also provides very good thermal
contact, as there is no air voids in contact zone due to Vacuum Pressure
Impregnation process, so the heat transfer is improved considerably.
As the water pipes are distributed on periphery of the stator core and cold
water is fed to these pipes in parallel for all the pipes at same pressure, so the
heat dissipation will be uniform and there is no chance to form hot spots in
stator core.
During assembly the "IT shaped insulated water pipe to be inserted from Non-
drive end side of the stator core and on drive end side these pipes are
connected to respective water headers as per the inlet/outlet scheme thereby
this invention provides simpler and effective solution for stator core cooling
compared to existing art.
Figure-1: shows cross section of stator core assembly along with core cooling
insulated water pipes (1) and stator core (2). The stator core is assembly is
made by using of Cold Rolled Non Grain Oriented (CRNGO) silicon steel
laminations in packets with proper ventilation gaps for air circulation also. In
the stator core, laminations provision is given for axial insertion of "U" shaped
insulated water-cooling pipes near to outer diameter. The water cooling pipes
are VPI insulated properly to avoid short circuit of laminations. This VPI
insulation will provide best electrical isolation and very good thermal contact
between laminations to cooling pipe. The Inlet and Outlet water headers are
assembled on drive end side of the Turbo alternator.
On drive end side of the alternator, the cold water from inlet water header is
passed through one side of already inserted insulated "U" shaped water pipe.
On non-drive end side of the alternator this water pipe will take "U" bend and it
will return to drive end of the alternator through another side of the insulated
water pipe. Later it will be connected to out let water header located on drive
end side of the alternator.

Figure-2: shows the drive end side view of stator core assembly along with core
cooling water pipes (3). Each pipe set will have "U" shape with one water inlet
side and one water out let side.
Figure-3: shows the Non-drive end side view of stator core assembly along with
core cooling "U" shaped water pipe(4) for making inlet water to return to outlet
header.

We claim: -
1. A water-cooled stator core of an electrical machine in which stator core
assembly is equipped with water pipes assembled in holes of the lamination
segments in which on the drive end cold water is injected through the one side
of the U-shaped water pipe and passes out from other side of the U-shaped
water pipe on the drive end of the machine itself.
2. The water-cooled stator core of an electrical machine as substantially
described and illustrated herein with reference to the accompanying drawings.
3. The water-cooled stator core as claimed in claim 1, wherein the electrical
machine may be a turbo alternator.