FIELD OF INVENTION: -
The present invention is related to the cooling methods of rotating Electrical Machines for various applications, specifically to the liquid cooled Machines. The present invention is also related to the liquid cooling methodology developed for the Stator frame of rotating Electrical Machines. The present invention is further related to the End Shields design compatible with the Stator frame for the liquid cooling circuit.
BACKGROUND OF INVENTION AND PRIOR ART:
Electric Machines generally have an enclosure or housing which include a Stator frame and End Shields. The heat generated during the operation of the Machine, because of both electrical and mechanical losses, will flow from the sources to the surrounding parts. Electrical losses due to the copper winding housed in the stator core contribute to the major portion of the heat generated.
This heat will flow from the Stator core to the Stator frame either through conduction or convection. The heat thus generated must be typically cooled to ensure the desired and efficient operation of the machine. An excessively high temperature may result in machine's bearing failure or damage to the stator winding insulation. This will reduce the operating life of the Machine and demands for the maintenance at regular intervals. Efficient cooling or extraction of heat effectively will result in increasing the power density of machines and reliability which are of high demand in the markets.
Generally, Electrical Machines are designed with internal and external air cooling circuits. Forced air cooling is also done externally for effective cooling. Apart from these cooling types, the heat is also extracted/removed from the stator frame through fluids, mostly water. The liquid is circulated in the stator frame. The heat transfer coefficient for forced convection cooling using liquid is generally much higher, or better, than the heat transfer coefficient for air. Therefore, in a liquid cooled machine, the overall cooling is typically much better than a similarly sized, substantially similar air-cooled machine.

OBJECTS OF INVENTION: -
An object of the present invention is to develop a Liquid cooled Stator for Electrical Machines to remove/extract the heat generated inside the Machine effectively.
Another object of the present invention is to develop such a Liquid cooled Stator which will have less coolant pressure drop and maintain less temperature gradient throughout the stator periphery.
Yet another object of the present invention is to develop a Liquid cooled stator, which is less susceptible to corrosion, coolant liquid leaks withstanding the mechanical stresses/forces during operation.
Further object of the invention is to develop End shields compatible for the Liquid cooled stator frame.
SUMMARY OF THE INVENTION: -
The present invention is related to the cooling of Electrical Machines, specifically Liquid cooling methodology. The more the cooling or heat extraction from the Electrical Machine more it becomes power dense. Therefore, the Liquid cooled stator for electrical Machine is designed consisting of stator frame and End Shields fitted at the ends of stator frame. The cooling conduit/circuit is designed to have less pressure drop and extract the heat generated inside the Machine effectively. The Stator frame is designed with built-in multiple (six) cooling segments distributed peripherally. Each cooling segment is designed with metal projections into it called fins, which will increase the heat transfer surface area and better cooling. The shape and size of the cooling segments are designed to have uniform peripheral heat extraction from inside the Machine. As these segments extend to the ends of Stator frame, the End Shields are designed with connecting channels and cooling segment slots, which will help or guide liquid/coolant flow from one segment to the other. With this arrangement, all the cooling segments will be connected in series and the liquid/coolant entry and exit are designed on the same End Shield for better compatibility.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:-
Figure 1 is a side elevation view of the Electrical Machine
Figure 2 (a) is a side elevation view of the Liquid cooled Stator frame of Electrical Machine shown in Figure 1.
Figure 2(b) is a front elevation view of the Liquid cooled Stator frame of Electrical Machine shown in Figure 1 with the cooling segments distributed circumferentially.
Figure 3 is a partial cross-sectional view through the Liquid cooled Stator of Electrical Machine shown in Figure 1.
Figure 4 (a) and (b) are the front views of the inner side and outer side of the Non-Drive side End Shield with the connecting channels utilized in connection with the Liquid cooled Stator frame of Electrical Machine shown in Figure 2.
Figure 5 (a) and (b) are the front views of the inner side and outer side of the Drive side End Shield with the connecting channels utilized in connection with the Liquid cooled Stator frame of Electrical Machine shown in Figure 2.
Figure 6 (a) and (b) are the Non-Drive End and Drive End isometric views of the complete Liquid cooling conduit of the Electrical Machine shown in Figure 1.
DETAILED DESCRIPTION OF INVENTION/PREFERRED EMBODIMENT:
Figure 1 is a side elevation view of a Electrical Machine including a Liquid cooled Stator frame 100 with built-in cooling segments 202 in plurality throughout the length of the Stator frame and two End Shields 500 and 600 with the connecting channels, fitted each to one side of the Stator frame, as described hereinafter in more detail. The said Liquid cooled Electrical Machine, will provide many advantages than known air cooled Machines.
More particularly and referring to Figures 2 (a) and (b) and 3, Stator frame 100 includes a substantially cylindrical shaped body section 201 having an outer surface 214 and an inner surface 215. The cylindrical shaped body section 201, has built-in cooling segments 202 in plurality and opposed ends 203 and 204.

Each cooling segment has plurality of fins/metal projections 2O5 for increasing the surface area and effective heat transfer. The liquid/coolant will flow from one end of Stator frame to the other end through these cooling segments 202, extracting the heat generated inside the Machine. The coolant/fluid flow from one cooling segment 202 to the other will happen through the cooling slots 401 and 501 and connecting channels 402 and 502 provided in the End Shields 400 and 500 fitted to the Stator frame 100. Bolt openings 206 are provided at indicated locations in Figure 2(b), so that the End shields 400 and 500 can be bolted with the Stator frame 100. This will connect all the cooling segments 202 in series. Sometimes, assembled End shields 400, 500 and Stator frame 100 is referred to as the enclosure or Machine housing.
Figure 3 is a partial cross-sectional view through the Liquid cooled Stator frame 100. As shown in Figure 3, bearing assemblies 308 are supported by End Shields 400 and 500 and include bearings 309 for supporting Rotor shaft 107. Grease inlet tubes 311 enable an operator to supply grease to bearings 309. Stator core and windings (not shown in Figure 3) are secured within the Machine housing. A Rotor shaft 107 is rotatably mounted within the housing and rotates relative to Stator frame 100. A terminal box (not shown in Figure 3) is secured to Stator frame 100, and terminal box includes openings for lead cables and sensor leads (not shown in Figure 3), which are electrically connected, for example, to the stator windings.
Figure 4 (a) and (b) are front views of inner side and outer side of the Non-Drive side End Shield utilized in connection with the Liquid cooled Stator frame of Electrical Machine shown in Figure 2, comprising of the multiple cooling segment slots 401 distributed throughout the End Shield periphery as indicated on one side, and multiple (two) connecting channels 402 on the other side. These cooling segment slots 401 are located geometrically at same position as the cooling segments 202 of Stator frame 100. Further comprises of two ports positioned as indicated in Figure 4(a) are used as inlet 403 and outlet 404 for the

liquid/coolant. The coolant liquid flows from one cooling slot to the other in the end Shield through these connecting channels.
The liquid/coolant will flow from the external cooling pump system through the inlet 403 into the cooling segment slot 401 of the End Shield 400 and further flows/enters into the cooling segment 2O2 of the Stator frame 100. These cooling segment slots 401 will aid in transfer or flow of the coolant/liquid into the cooling segments 202 of Stator frame 100 or from Stator frame 100 into the End Shields 400 through the cooling segment slots 401. Figure 5 (a) and (b) are front views of the inner side and outer side of Drive side End Shield utilized in connection with the Liquid cooled Stator frame of Electrical Machine shown in Figure 2, comprising of the multiple cooling segment slots 501 distributed throughout the End Shield 500 periphery as indicated on one side, and multiple (three) connecting channels 502 on the other side. These cooling segment slots 501 are located geometrically at same position as the cooling segments 202 in the Stator frame 100. The coolant/liquid flows from one cooling slot to the other in the End Shield through these connecting channels 502.
Figure 6 (a) and (b) are the Non-Drive End and Drive End isometric views of the complete Liquid cooling conduit of the Electrical machine shown in Figure 1, consisting of the multiple cooling segments 202 built in the Stator frame 100, multiple cooling segment slots 401 and 501, and multiple connecting channels 402 and 502. Further the Figures show the series connection of the cooling segments 202 with the aid of the provisions made in the End Shields 400 and 500. Further, the inlet and the outlet ports 403, 404 for the liquid/coolant are also shown.
Electric Machines generate heat during operation as a result of both electrical and mechanical losses and must be typically cooled in order to ensure the desired and efficient operation of the machine. An excessively high machine temperature may result in machine's bearing failure or damage to the stator winding insulation. Therefore, the Electrical Machines are designed with internal and external cooling circuits, conventionally with the air. Forced cooling is also

done externally for efficient cooling. Electric Machines generally have an enclosure or housing which include a frame and end shields. Apart from these cooling types, the heat is also extracted /removed from the stator frame through fluids, mostly water. The liquid is circulated in the stator frame and end covers. The heat transfer coefficient for forced convection cooling using liquid is generally much higher, or better, than the heat transfer coefficient for air. Therefore, in a liquid cooled machine, the overall cooling typically is much better than a similarly sized, substantially similar air-cooled machine. Further, in a liquid cooled Machine and by using a remotely mounted heat exchanger such as an evaporative water chiller, the immediate surroundings of the Machine are not heated as with an air-cooled Machine. The remotely mounted heat exchanger therefore further facilitates improving Machine's operation. Also, in a liquid cooled Machine, the external fan can be eliminated which facilitates in reducing noise.
A Liquid cooled Stator for Electric Machine comprises of a Stator frame and two End shields for fixing to the ends of the Stator frame. The Stator frame is designed with built-in multiple (six) cooling conduit/segments distributed circumferentially independently as shown in Fig 2. The angle between all the segments is same except the first and the last segments leaving a solid portion. This surface will be used for taking the winding terminals out to the terminal box. These cooling segments are present axially throughout the length of the Stator frame, enabling the liquid flow from one end to the other without any interconnections. Therefore, every cooling segment forms an independent segment and as the coolant/liquid flows through them, the coolant/liquid takes the heat conducted into the Stator frame from the inside heat source. The design and profile of these cooling segments is such that the maximum Stator inner periphery cooling is covered, enabling to achieve lesser temperature gradient.
Inside every cooling segment multiple fins are designed as shown in Figure 2, for increasing the thermal contact surface area and effective heat transfer instead of plane/smooth surface. As these cooling segments are independent without

any interconnections, the coolant fluid flow from one segment to the other through the provision made in the End Shields fitted at the ends of Stator frame. Both the End Shields are designed with cooling slots and connecting channels for guiding the liquid/coolant from segment to segment thus closing the entire cooling conduit/circuit. Figures 4 and 5 show the End Shields with the designed cooling slots and the connecting channels. As all the cooling segments would be connected in series through the End Shields, the liquid/coolant entry and exit, called inlet and outlet ports are provided on the same End Shield which will be fitted to the Non-Drive side of the Machine. This will ease the access of the ports to the coolant pumping system.
As per the objective of developing a Liquid cooled Stator with low pressure drop/loss and less temperature rise, the shape, profile and dimensions of the flow path of the cooling conduit/circuit are designed accordingly with the liquid/coolant operating conditions. The isometric view of Non-Drive End and Drive End entire closed loop cooling circuit/conduit is shown in Figure 6.
Further bolt openings are provided suitably for fixing End Shields to the Stator frame. At the inner diameter side, provision for mounting bearing, bearing housings and grease path are also designed for ease of assembly. Each End Shield is designed with multiple ribs 406, 504 on both sides which will not only strengthen but also reduce the weight of the End Shields.
EXAMPLES/ PREFERRED EMBODIMENT: -
Most of the Electrical Machines are designed with internal and external cooling circuits, conventionally with the air for cooling them. Forced cooling is also done externally for efficient cooling. Apart from these cooling types, the heat is also extracted/removed from the stator frame through fluids, mostly water. The heat transfer coefficient for forced convection cooling using liquid is generally much higher, or better, than the heat transfer coefficient for air. Therefore, in a liquid cooled Machine, the overall cooling typically is much better than a similarly

sized, substantially similar air cooled machine. Also, in a liquid cooled Machine, the external fan can be eliminated which facilitates in reducing noise.
The present invention, i.e. Liquid cooled Stator for Electric Machines also provides an efficient cooling, making the Electrical machine more power dense than the conventionally cooled similar rating Machine. The Liquid cooled Stator comprises of the Stator frame and End Shields fitted at the ends. They carry the liquid conduit/circuit as detailed in the description and figures which will extract the heat generated inside the Machine. The circuit is designed such that it will have less pressure drop and maintains less temperature gradient across the stator periphery.

WE CLAIM: -
1. A Liquid cooled Stator frame (100) for an Electric Machine, comprising a cylindrical shaped body section having plurality of cooling segments 202 along the length of the stator frame in which the body section comprises a wall having an outer surface and an inner surface and said cooling segments are placed inside the said wall between said inner surface and said outer surface wherein the cooling segments have projected multiple fins(205) throughout the length of the said segments of the Stator frame.
2. A Liquid cooled Stator frame for an Electric Machine as claimed in claim 1, wherein integral cooling slots and connecting channels of End Shields connects the cooling segments of the said Liquid cooled Stator frame for coolant flow in series.
3. A Liquid cooled Stator frame for an Electric Machine as claimed in claim 1, comprising End Shield that comprises of two ports positioned at two separate locations aligned with the cooling segments, serving as an inlet port and an outlet port for the fluid/coolant.
4. A Liquid cooled Stator for Electric Machine as claimed in claim 1, wherein a Non-Drive side End Shield is secured to the Non-Drive side of the said Stator frame and a Drive side End Shield is secured to the Drive side of the said Stator frame.