Description:‘A LIQUID COOLED STATOR FRAME FOR A ROTATING ELECTRICAL MACHINE’

FIELD OF INVENTION:
[001] 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 higher power density Rotating Electrical Machines. Particularly, the invention is directed to a Liquid cooled Stator frame for a higher power density Rotating Electrical Machine.

BACKGROUND/PRIOR ART OF THE INVENTION:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[003] Rotating Electric Machines, generally have an enclosure or housing which include a Stator frame and End covers. The heat generated during the operation of the Machine due to losses, travels from sources to the surrounding parts. The heat thus generated must be cooled in order to obtain desired and efficient operation of the machine. Efficient cooling or extraction of heat results in machines delivering designed power, reliable operation and further in offering high power density machines, which are of high demand in the markets.

[004] Generally, Electrical Machines are designed with internal and external air cooling circuits. Forced cooling is also done externally for efficient cooling. Apart from these cooling types, the heat is also extracted from the stator frame by circulating liquid, mostly water & ethylene glycol. Therefore, in a liquid cooled machine, the overall cooling is improved and better than air cooled machine of same rating. However, the design and incorporation of cooling circuit/path in the Electrical Machine is critical as coolant circuit should be compatible for manufacture and leak proof during operation withstanding the mechanical stresses/forces.

[005] The Patent EP0859447A1 discloses a liquid cooled electric motor which includes a stator frame having a cast in place cooling circuit and various casting processes. The cooling circuit is arranged in a helical configuration and the stator frame is cast around the circuit so that the circuit is embedded within, and integral with the frame. The said cooling circuit is formed from single circular tube and/or with straight & ring type tubes. The cooling circuit is not only limited to helical configuration but also of circumferential, serpentine or squirrel cage configurations.

[006] The Patent USOO7626292B2 discloses an electric motor/generator cooling mechanism which includes a hollow cooling jacket having an inner and outer co-axial surface. The inner case comprises of a cast spiral groove section with jogged cooling passages on outer surface. The disclosure includes an outer case having one or more inlet ports, an outlet port, and a vent for purging air, cooling fluid flowingly encased between the cooling jacket and the outer case, flowing through the jogged cooling passages. In this invention, the fluid flows in a continuous direction and does not require to make any 180 degree turns (i.e., the fluid is not required to reverse travel flow direction and go back toward an opposite direction), which may keep pressure drop to a minimum.

[007] The above two patents have not disclosed / revealed and claimed anything about the internal details of circuit such as geometrical shape and profile of ducts. Further not disclosed/ detailed about the possible ways of improving the thermal performance of cooling circuits by modifying their internal duct geometrical profiles.

[008] Therefore, the present invention has been proposed focusing on bringing up of improvement in the thermal behavior of the electrical machine by suitably designing the cooling circuit ducts with metallic projections called as fins. The presence of these metallic projections increases the thermal contact area for conduction and convection and results in better heat extraction from the sources. The present invention further results in high power density by the machine than those disclosed in the above two patents.

OBJECTS OF INVENTION:
[009] Primary object of the invention is to provide a Liquid cooled Stator frame for a Rotating Electrical Machine, which is simple in construction.

[0010] An object of the present invention is to develop an efficient liquid cooling circuit for stator frame of Rotating Electrical Machines to extract the heat generated inside the machine effectively.

[0011] Another object of the present invention is to develop a cooling circuit which results in improved thermal performance and better power density than those disclosed in the prior patents.

[0012] Yet another object is to maintain less temperature gradient throughout the liquid cooled stator frame periphery.

[0013] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:
[0014] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0015] 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 & ethylene glycol. The heat transfer coefficient using liquid is generally much higher, or better, than the heat transfer coefficient with air. Therefore, in a liquid cooled machine, the overall cooling typically is much better than a similar air cooled machine of same rating. Also, in a liquid cooled Machine, the internal and external fans can be eliminated which results in reducing noise.

[0016] The present invention is related to the cooling of Rotating Electrical Machines, specifically Liquid cooling methodology developed for the Stator frame. With effective cooling or heat extraction from the Electrical Machine, the machine becomes more power dense. As the heat from the source conducts mainly to the Stator frame, the cooling is limited only to the Stator frame.

[0017] The Liquid cooled Stator frame is a substantially cylindrical shaped body with hermetically located cooling circuit, formed between inner cylinder and outer cylinder when assembled.

[0018] These ducts are connected through connecting channels forming series cooling circuit with inlet at one end and outlet at other end of liquid cooled stator frame. With this arrangement a coolant flow path is established which is similar to that of a spiral path. To improve the thermal performance further, all cooling ducts are designed with metallic projection into it called as fin. The shape and size of the cooling ducts and profile of fin are designed to achieve uniform peripheral heat extraction from inside the machine resulting in less temperature gradient throughout the stator periphery. Further as the cooling circuit is hermetically sealed and secured inside, the said Liquid cooled Stator frame of Rotating Electrical Machine, is less susceptible to coolant leaks withstanding the mechanical stresses/forces during operation.

[0019] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0020] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0021] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
[0022] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:

[0023] Figure 1 shows: a side & front elevation views of Liquid cooled Stator frame (100) according to present invention.

[0024] Figure 2 shows: a long sectional view along the axial length of Liquid cooled Stator frame (100) of rotating electrical machine shown in Figure 1.

[0025] Figure 3 (a) shows: a front elevation view of inner cylinder (101) of Liquid cooled Stator frame (100) as shown in Figure 1.
[0026] Figure 3 (b) shows: a front elevation view of outer cylinder (102) of Liquid cooled Stator frame (100) as shown in Figure 1.

[0027] Figure 4 shows: the isometric view of the entire cooling circuit (103) formed in the Liquid cooled Stator frame (100) shown in Figure 1.

[0028] Figure 5 (a) shows: the partial sectional view of the general cooling ducts profile on periphery of inner cylinder (101).

[0029] Figure 5 (b) shows: the partial sectional view of the cooling ducts profile (104) with fin (105) as shown in Figure 4 on periphery of inner cylinder (101).

[0030] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:

[0031] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0032] Electrical Machines generate heat during operation due to both electrical and mechanical losses and are to be cooled in order to ensure efficient operation of the machine. An excessively high temperature in the machine may result in 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.

[0033] Apart from these cooling types, the heat is also extracted/removed from the stator frame by circulating liquids, mostly water & ethylene glycol. The heat transfer coefficient using liquid is generally much higher, or better, than the heat transfer coefficient with air. Therefore, in a liquid cooled machine, the overall cooling is improved and better than air cooled machine of same rating. However, the design and incorporation of cooling circuit/path in the Electrical Machine is critical as coolant circuit should be compatible for manufacture and leak proof during operation withstanding the mechanical stresses/forces. Also, in a liquid cooled Machine, the internal and/or external fan can be eliminated which facilitates in reducing noise and fan losses.

[0034] The present invention covers the cooling of Stator frame only and End shields/covers are not cooled. The side and front elevation views of Liquid cooled Stator frame (100) of Rotating Electrical Machine in assembled condition with inner cylinder (101) and outer cylinder (102) are shown in Figure 1. The Liquid cooled Stator frame (100) is designed with a cooling circuit (103) present circumferentially for partial length of the stator frame.

[0035] Referring to Figure 2, the Liquid cooled Stator frame (100) is a substantially cylindrical shaped body with hermetically sealed cooling circuit (103) formed between inner cylinder (101) and outer cylinder (102). The outer cylinder (102) is assembled on to inner cylinder (101) through standard practices, forming the said cooling circuit (103) for fluid flow into the stator frame (100). The inner cylinder is designed with multiple cooling ducts present circumferentially on the outer surface. The cooling ducts (104) are distributed at equidistant for coolant flow and are present axially for partial length of the Liquid cooled Stator frame (100), where the heat conduction from the source is present. The multiple cooling ducts (104) are connected through connecting channels (106) forming series cooling circuit (103) with inlet at one end and outlet at other end of liquid cooled stator frame.

[0036] The outer cylinder has multiple ports (108 & 109) in line with the ends of cooling circuit to provide ports for liquid entry and exit. The presence of this outer cylinder (102) arrests the leakage of fluid flow at mating portion (107) from one cooling duct (104) to other. With this arrangement a continuous coolant flow path is established which is similar to that of a spiral path. Two ports are provided on the outer cylinder to serve as entry and exit for coolant respectively. The coolant from external cooling pump system can enter into any of the said ports and travels throughout the path created in the liquid cooled stator frame (100) and exits at the other port. The isometric view of the entire cooling circuit alone formed in the Liquid cooled Stator frame with the assembly of inner cylinder and outer cylinder and cooling ducts connected in series path through connecting channels is shown in Figure 4.

[0037] As per object of the invention and to improve further the thermal performance over the referred patents, the cooling ducts (104) of the circuit are designed with metallic projection called as fin (105) of same material as frame. Figure 5(a) & (b) shows the cooling ducts with and without fin configurations. The presence of these metallic projections in the cooling ducts increases the thermal area of contact for conduction and convection and results in better heat extraction from the sources. However, it may also lead to slightly higher pressure drop than the ducts without fin. The shape and size of the cooling ducts and profile of fin are designed to achieve uniform peripheral heat extraction from inside the machine resulting in less temperature gradient throughout the stator periphery.

[0038] The shape of cooling ducts is designed keeping in view of manufacturing simplicity. The geometrical size of the cooling duct depends on the flow rate of the coolant, inward heat flux, targeted cooling area and pressure drop. The profile of the fin is designed considering optimum/better heat extraction and for ease of manufacturing.

[0039] The Liquid cooled Stator frame of the present invention comprising of multiple cooling ducts, which by suitable connecting channels result in single or multiple cooling circuits with multiple inlets and outlets.

ADVANTAGEOUS FEATURES OF INVENTION:
[0040] As the cooling circuit is hermetically sealed and secured inside, the Liquid cooled Stator frame of rotating Electrical Machine, is less susceptible to coolant leaks withstanding the mechanical stresses/forces during operation. Therefore, as the coolant flows through the cooling circuit, the coolant takes the heat conducted into the Stator frame from the inside heat source.

[0041] The present invention, i.e. Liquid cooled Stator frame for Electrical Machines also provides an efficient cooling, making the Electrical machine more power dense than the conventionally cooled Machine of same rating. The Liquid cooled Stator frame comprises of the liquid cooling circuit which will extract the heat generated inside the Machine. The circuit is designed such that it maintains less temperature gradient across the stator periphery.

TEST RESULT:
Sl. No. Parameter Present invention Prior art
1 Temperature rise of coolant (DegC) 7.21 6.98
2 Average velocity of streamlines (m/s) 1.35 1.12
3 Maximum Stator outer surface temperature (DegC) 75.74 77.17
4 Average temperature of DE side Bearing location (DegC) 71.49 72.79
5 Average temperature of NDE side Bearing location (DegC) 75.74 77.17
WORKING OF THE INVENTION:
[0042] The present invention is related to the cooling of the rotating electrical machine by pumping coolant into the cooling circuit designed in the stator frame of electrical machine. During actual operation of the Electrical machine, the coolant will be pumped into the said Liquid cooled stator frame through inlet by the external cooling pump system. As the coolant flows in the Liquid cooled stator frame, it picks up the heat generated in the machine. The hot coolant at outlet will be guided to the heat exchanger which is part of the pump system. With this arrangement of heat exchanger and pump system, coolant will always be pumped into the Liquid cooled stator frame at particular temperature.

[0043] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0044] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0045] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0046] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0047] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0048] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0049] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
, Claims:WE CLAIM

1. A Liquid cooled Stator frame for a Rotating Electrical Machine, comprising of a substantially cylindrical shaped body with hermetically sealed cooling circuit (103) formed between inner cylinder (101) and outer cylinder (102), wherein the outer cylinder (102) is assembled on to inner cylinder (101) forming the cooling circuit for fluid flow into the stator frame (100), wherein the inner cylinder (101) is provided with multiple cooling ducts (104) placed circumferentially on the outer surface, in which the cooling ducts (104) are positioned at equidistance for coolant flow and are disposed axially for partial length of the Liquid cooled Stator frame (100), where the heat conduction from the source is located;
the multiple cooling ducts (104) are connected through connecting channels (106) forming series cooling circuit with inlet at one end and outlet at other end of liquid cooled stator frame (100).

2. The Liquid cooled Stator frame (100) for a Rotating Electrical Machine as claimed in claim 1, wherein the outer cylinder (102) has multiple ports (108 & 109) in line with the ends of the cooling circuit to provide ports for liquid entry and exit, in which the outer cylinder (102) arrests the leakage of fluid flow at mating portion (107) from one cooling duct (104) to other and the coolant flow path forms a spiral path.

3. The Liquid cooled Stator frame (100) for a Rotating Electrical Machine as claimed in claim 1 or 2, wherein two ports are provided on the outer cylinder (102) to serve as entry and exit for coolant, in which the coolant from external cooling pump system enters into one of the said ports and travels throughout the path created in the liquid cooled stator frame (100) and exits at the other port.

4. The Liquid cooled Stator frame (100) for a Rotating Electrical Machine as claimed in claims 1-3, wherein the cooling ducts (104) of the circuit are provided with projection i.e. fin (105).
5. The Liquid cooled Stator frame (100) for a Rotating Electrical Machine as claimed in claims 1-4, wherein said inner cylinder (101) comprises of circumferentially located multiple cooling ducts (104) with a fin (105) on outer surface thereof and the outer cylinder (102) with plain inner surface is provided so as to arrest leakage of fluid after assembly.

6. The Liquid cooled Stator frame (100) for a Rotating Electrical Machine as claimed in claims 1-5, wherein each circumferentially located cooling duct (104) is having multiple fins (105) on outer surface of inner cylinder (101) for better heat transfer.

7. The Liquid cooled Stator frame (100) for a Rotating Electrical Machine as claimed in claims 1-6, wherein the shape and size of the cooling ducts (104) and profile of fin (105) are designed to achieve uniform peripheral heat extraction from inside the machine resulting in less temperature gradient throughout the stator periphery.