CA1272240A - Spider baffle for double end ventilation in dynamoelectric machine - Google Patents
Spider baffle for double end ventilation in dynamoelectric machineInfo
- Publication number
- CA1272240A CA1272240A CA000518555A CA518555A CA1272240A CA 1272240 A CA1272240 A CA 1272240A CA 000518555 A CA000518555 A CA 000518555A CA 518555 A CA518555 A CA 518555A CA 1272240 A CA1272240 A CA 1272240A
- Authority
- CA
- Canada
- Prior art keywords
- rotor
- baffle
- air
- passages
- stator
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K9/00—Arrangements for cooling or ventilating
- H02K9/02—Arrangements for cooling or ventilating by ambient air flowing through the machine
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
- H02K1/22—Rotating parts of the magnetic circuit
- H02K1/32—Rotating parts of the magnetic circuit with channels or ducts for flow of cooling medium
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Iron Core Of Rotating Electric Machines (AREA)
- Motor Or Generator Cooling System (AREA)
Abstract
SPIDER BAFFLE FOR DOUBLE END VENTILATION
IN DYNAMOELECTRIC MACHINE
ABSTRACT OF THE DISCLOSURE
In a double end ventilation dynamoelectric machine one side often runs at a higher temperature than the other side because the amount of air entering the rotor spider from each end is not equal. In addition there is turbulence and interaction where the two air streams meet. A vertical baffle is mounted between the rotor spider arms at an axial position to provide equal air flow from each end. This tends to equalize cooling as well as reduce the instability of the air. The sides of the baffle may be shaped to further improve flow and reduce pressure drop.
IN DYNAMOELECTRIC MACHINE
ABSTRACT OF THE DISCLOSURE
In a double end ventilation dynamoelectric machine one side often runs at a higher temperature than the other side because the amount of air entering the rotor spider from each end is not equal. In addition there is turbulence and interaction where the two air streams meet. A vertical baffle is mounted between the rotor spider arms at an axial position to provide equal air flow from each end. This tends to equalize cooling as well as reduce the instability of the air. The sides of the baffle may be shaped to further improve flow and reduce pressure drop.
Description
Case 2967 SPIDER BAFFLE FOR DOUBLE END VENTILATION
IN DYNAMOELECTRIC ~ACHINE
Background of the Invention This invention relates to the ventilation of dynamoelectric machines, and in particular it relates to an improvement in the ventilation of a double end ventilation machine by use of a spider baffle.
In a double end ventilation machine, air or other cooling gas enters at both ends of the machine and at least a portion of the air passes axially into the spider of the rotor from both ends. There are several spaced apart, radially extending, air passages through the rotor core and the air which has entered at both ends of the rotor passes through these radially extending passages into th~e air gap and may continue through radially extending passages in the stator. Because the air passages are usually not precisely uniform and may have different flow resistances, the air flow may not be balanced. That ~0 is, more air may flow into the rotor spider from one end than from the other, and air entering from one end may flow through more of the radially extending air passages than air entering from the other end. This imbalance is often more pronounced in series flow machines and tends to be particularly so in series flow machines that do not have fans and therefore tend ~1`~
. `:
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~' ' ,.
Case 2967 -- 2 ~
to move air at slower speeds. The result of this unbalance is that portions of the rotor and stator cores tend to be hotter on one end than on the other end.
In addition, when the cooling air enters from both ends, the air flow meets in the central region where there is turbulence. This turbulence tends to decrease the air flow in the radial ducts and to decrease cooling.
The present invention overcomes some of these problems by using a baffle between the spider arms of the rotor. This baffle is positioned axially to equalize or balance the air flow from both ends.
It is known to use various baffles in certain types of dynamoelectric machines. For example, in totally enclosed, fan cooled, explosion proof motors, it is known to use a vertical baffle between the spider arms to provide isolation between the two ends. This provides a seal which, if an explosion should occur~ isolates one end from the other end and keeps the trapped gas in the end where it was generated. There are no radially extending passages or ducts in this type of motor.
As another example, in a mixed flow, single end ventilation motorl it is known to use a vertical baffle (i.e. a bafEle at right angles to the axis of the motor shaft) at one end of the rotor to prevent air entering the spider from the baffled end. In other words the baffle is used to direct air flow which enters the spider at the opposite or un-bafEled end and then flows radially outwards through radial ducts to join a parallel flow moving behind the stator core.
There is no flow from opposite ends in these examples and consequently there is no need to balance or equalize the air flow. The baffles in the examples do not equalize cooling.
Case 2967 Summary of the Invention The present invention is for use with double end ventilation dynamoelectric machinesO It provides a vertical baffle, that is a baffle extending substantially at right angles to the motor shaft, positioned between the spider arms, at an axial location which provides a balanced flow of air from both ends. The axial position of the baffle may be at the mid-point of the rotor or approximately at the mid-point, but not necessarily. Because the air flow paths from each end are not always symmetrical and identical, the location for the bafEle, in order to balance the flow, may be displaced from the mid-point. While the use of a plain vertical baffle will also reduce pressure drop which would otherwise occur where the oppositely directed air streams meet, the baffle may be shaped on both sides to further reduce pressure drop.
It is therefore an object of the invention to provide an arrangement for improved cooling in a double end ventilation dynamoelectric machine which balances the air flow from each end.
It is another object of the invention to provide a baffle between the arms of the spider of a rotor in a double end ventilation dynamoelectric machine for balancing or equalizing the flow of cooling gas.
~ ccordingly there is provided in a double end ventilation dynamoelectric machine having a rotor comprising a rotor shaft, a spider mounted on said rotor shaft and supporting rotor laminations forming a rotor core, said laminations being spaced apart in groups to provide radially extending ventilation passages between adjacent groups, and axially extending passages in said spider communicating at each end with an air inlet and communicating with said Case 2967 radially extending ventilation passages, the improvement comprising a baffle extending in a radial direction between said shaft and said core and located axially at a position providing a substantially equal flow of air from each air inlet.
Brief Description of the Drawin _ The invention will be described with reference to the drawings in which, Figure 1 is a sectional view of a prior art motor showing an unhalanced flow of air, Figure 2 is a sectional view of a similar electric motor having a vertical baffle according to the invention, Figure 3 is a plan view of one section of a vertical baffle, and Figures 4A and 4B are cross-sectional views of two embodiments or forms of baffle taken along line 4-4 of Figure 3.
Description of the Preferred Embodiment Referring first to Figure 1, there is shown a sectional view of a double end ventilated electric motor having a stator 10 and a rotor 11. Rotor 11 comprises a shaft 12 having a spider 14 which comprises a plurality of axially extending arms fixed to shaft 12. The spider arms extend in a radial direction from shaft 12 to support a plurality of rotor laminations 15 which form the rotor core. The spider 14 provides axially extending passages between the shaft 12 and the rotor laminations 15 for the circulation of cooling gas. The rotor laminations 15 are spaced apart in groups with radially extending ventilation passages 16 between adjacent groups. The laminations 15 have spaced peripheral slots to receive conductor bars 17 which extend axially from end to end and project beyond the laminations 15 where they are joined to end rings 18 and 20. Rotor flanges 21 Case 2967 -- 5 ~
and 22 hold laminations 15 in place on shaft 12 between a shoulder 19 on spider arms 14 and a rotor ring l9A welded to the spider arms 14.
The stator 10 comprises stator laminations 23 spaced apart in groups with radially extending ventilation passages 24 between adjacent groups. The ventilation passages 24 are shown aligned with the ventilation passages 16, however the passages 24 and 16 can be offset with one another to reduce the noise generated by the air passages or ducts when the motor is running. Offset passages reduce the noise level but this also tends to reduce air flow.
The stator laminations 23 are held in position on stator frame 25 by outside space blocks 26 and 27 and stator flanges 28 and 30. The stator laminations 23 have radially spaced slots at their radially inner edge to receive stator windings 31 which have end turns shown as 32 and 33. The stator winding connections are shown at 34. The stator frame 25 includes bracket covers 35 and 36, brackets 37 and 38 and bearings 40 and 41.
Air inlet passages 42 and 43 are formed generally by frame 25 with bracket cover 35 and intermediate frame plate 44 on one side and by frame 25 with bracket cover 36 and intermediate frame plate 45 on the other side. The outlet ventilation passages for air moving out of radial air passages 24 is between intermediate frame plates 44 and 45.
In Figure 1 the airflow, or flow of cooling gas, is indicated by arrows for a very unbalanced flow condition for purpose of illustration. In Figure 1 the major air flow is shown entering through air inlet passage 43. In this instance the flow ls so unbalanced that air from inlet 43 passes through all of the ventilation passages 16 and 24 thereby ~o Case 2967 virtually excluding the air entering a:ir inlet passage 42 from cooling the rotor or stator. ~hile this condition would be extreme, the effects of unbalanced conditions which are not so extreme will be indicated in subsequent examples.
Referring now to Figure 2, where like parts have the same designation numbers, a vertical baffle 46 has been added between the arms of spider 14. The baffle 46 is not necessarily located axially at the mid-point of the rotor core, but is located at an axial position where the air flow at air inlet passages 42 and 43 is balanced or equal. This achieves a more even cooling of the rotor and stator cores. It also prevents the mixing of the air flowing from either end and helps to reduce turbulence.
The use of a baffle 46 results in many cases in an increase in air flow. For example, on a large, series ventilated, high speed motor (4500 H.P. and 1800 RPM) the measured air flow through the motor before a baffle was installed was 7520 cubic ft./min.
or cfm. After a baffle was installed the measured air flow increased to 9478 cfm. The windage losses dropped by approximately one kilowatt after the baffle was installed.
As another exampie, on a smaller, slower speed motor having no rotor fans (350 Il.P. and 450 RPM) the measured airflow through the motor without a baffle was 927 cfm. After a baffle was installed the air flow increased to 988 cEm. While the airflow increased with improved cooling, the windage losses also showed a slight increase which appears to be because of the increased air flow.
It is believed that the increase in air flow when a baffle is installed as described, may be explained as follows. The air flowing axially from both ends meets and mixes in the annular air spaces case 2967 between the spider arms. As the two air streams meet they try to pass each other and create a turbu]ent region with possibly secondary flows. This causes higher friction losses. The baffle prevents any mixing action and reduces turbulence. It is also believed to provide a pumping action to move the air outwards in a radial direction.
Tests were also carried out on series type, double end ventilated motors with rotor mounted fans to assist air flow. Motors with fans develop a high pressure which apparently tends to overcome the small variations in pressure and in resistance to air flow, and consequently the unbalances in flow from the two ends is usually not as great. Consequently the use of a baffle does not result in as great an improvement.
Referring now to Figures 3 and 4~, Figure 3 is an elevation view of a section of vertical baffle 46. It was previously mentioned that the sides of the baffle could be shaped to further reduce turbulence.
In Figure 4A there is a baffle 46A, shown in section, with curved walls 47. The base portion of baffle 46A
is at the shaft, and the curved walls 47 very generally direct a portion of the axially moving air in a radial direction. Similarly, in Figure 4B there is a cross-sectional view of baffle 46B which has flat sloping sides 48, also intended to reduce turbulence and pressure loss in turning the axial flow to radial flow.
In conclusion, in any doubled end ventialted machine, air flow from either end can be balanced by a baffle placed between the spider arms at an appropriate axial location. The improvement in cooling that is achieved with a baffle tends to be greatest in series flow machines that do not have a rotor fan. However there may still be a significant improvement in series flow machines with rotor mounted fans and in parallel flow machines.
': ''~ ' i ,~
: , .
IN DYNAMOELECTRIC ~ACHINE
Background of the Invention This invention relates to the ventilation of dynamoelectric machines, and in particular it relates to an improvement in the ventilation of a double end ventilation machine by use of a spider baffle.
In a double end ventilation machine, air or other cooling gas enters at both ends of the machine and at least a portion of the air passes axially into the spider of the rotor from both ends. There are several spaced apart, radially extending, air passages through the rotor core and the air which has entered at both ends of the rotor passes through these radially extending passages into th~e air gap and may continue through radially extending passages in the stator. Because the air passages are usually not precisely uniform and may have different flow resistances, the air flow may not be balanced. That ~0 is, more air may flow into the rotor spider from one end than from the other, and air entering from one end may flow through more of the radially extending air passages than air entering from the other end. This imbalance is often more pronounced in series flow machines and tends to be particularly so in series flow machines that do not have fans and therefore tend ~1`~
. `:
'` ' '' .,- ~
~' ' ,.
Case 2967 -- 2 ~
to move air at slower speeds. The result of this unbalance is that portions of the rotor and stator cores tend to be hotter on one end than on the other end.
In addition, when the cooling air enters from both ends, the air flow meets in the central region where there is turbulence. This turbulence tends to decrease the air flow in the radial ducts and to decrease cooling.
The present invention overcomes some of these problems by using a baffle between the spider arms of the rotor. This baffle is positioned axially to equalize or balance the air flow from both ends.
It is known to use various baffles in certain types of dynamoelectric machines. For example, in totally enclosed, fan cooled, explosion proof motors, it is known to use a vertical baffle between the spider arms to provide isolation between the two ends. This provides a seal which, if an explosion should occur~ isolates one end from the other end and keeps the trapped gas in the end where it was generated. There are no radially extending passages or ducts in this type of motor.
As another example, in a mixed flow, single end ventilation motorl it is known to use a vertical baffle (i.e. a bafEle at right angles to the axis of the motor shaft) at one end of the rotor to prevent air entering the spider from the baffled end. In other words the baffle is used to direct air flow which enters the spider at the opposite or un-bafEled end and then flows radially outwards through radial ducts to join a parallel flow moving behind the stator core.
There is no flow from opposite ends in these examples and consequently there is no need to balance or equalize the air flow. The baffles in the examples do not equalize cooling.
Case 2967 Summary of the Invention The present invention is for use with double end ventilation dynamoelectric machinesO It provides a vertical baffle, that is a baffle extending substantially at right angles to the motor shaft, positioned between the spider arms, at an axial location which provides a balanced flow of air from both ends. The axial position of the baffle may be at the mid-point of the rotor or approximately at the mid-point, but not necessarily. Because the air flow paths from each end are not always symmetrical and identical, the location for the bafEle, in order to balance the flow, may be displaced from the mid-point. While the use of a plain vertical baffle will also reduce pressure drop which would otherwise occur where the oppositely directed air streams meet, the baffle may be shaped on both sides to further reduce pressure drop.
It is therefore an object of the invention to provide an arrangement for improved cooling in a double end ventilation dynamoelectric machine which balances the air flow from each end.
It is another object of the invention to provide a baffle between the arms of the spider of a rotor in a double end ventilation dynamoelectric machine for balancing or equalizing the flow of cooling gas.
~ ccordingly there is provided in a double end ventilation dynamoelectric machine having a rotor comprising a rotor shaft, a spider mounted on said rotor shaft and supporting rotor laminations forming a rotor core, said laminations being spaced apart in groups to provide radially extending ventilation passages between adjacent groups, and axially extending passages in said spider communicating at each end with an air inlet and communicating with said Case 2967 radially extending ventilation passages, the improvement comprising a baffle extending in a radial direction between said shaft and said core and located axially at a position providing a substantially equal flow of air from each air inlet.
Brief Description of the Drawin _ The invention will be described with reference to the drawings in which, Figure 1 is a sectional view of a prior art motor showing an unhalanced flow of air, Figure 2 is a sectional view of a similar electric motor having a vertical baffle according to the invention, Figure 3 is a plan view of one section of a vertical baffle, and Figures 4A and 4B are cross-sectional views of two embodiments or forms of baffle taken along line 4-4 of Figure 3.
Description of the Preferred Embodiment Referring first to Figure 1, there is shown a sectional view of a double end ventilated electric motor having a stator 10 and a rotor 11. Rotor 11 comprises a shaft 12 having a spider 14 which comprises a plurality of axially extending arms fixed to shaft 12. The spider arms extend in a radial direction from shaft 12 to support a plurality of rotor laminations 15 which form the rotor core. The spider 14 provides axially extending passages between the shaft 12 and the rotor laminations 15 for the circulation of cooling gas. The rotor laminations 15 are spaced apart in groups with radially extending ventilation passages 16 between adjacent groups. The laminations 15 have spaced peripheral slots to receive conductor bars 17 which extend axially from end to end and project beyond the laminations 15 where they are joined to end rings 18 and 20. Rotor flanges 21 Case 2967 -- 5 ~
and 22 hold laminations 15 in place on shaft 12 between a shoulder 19 on spider arms 14 and a rotor ring l9A welded to the spider arms 14.
The stator 10 comprises stator laminations 23 spaced apart in groups with radially extending ventilation passages 24 between adjacent groups. The ventilation passages 24 are shown aligned with the ventilation passages 16, however the passages 24 and 16 can be offset with one another to reduce the noise generated by the air passages or ducts when the motor is running. Offset passages reduce the noise level but this also tends to reduce air flow.
The stator laminations 23 are held in position on stator frame 25 by outside space blocks 26 and 27 and stator flanges 28 and 30. The stator laminations 23 have radially spaced slots at their radially inner edge to receive stator windings 31 which have end turns shown as 32 and 33. The stator winding connections are shown at 34. The stator frame 25 includes bracket covers 35 and 36, brackets 37 and 38 and bearings 40 and 41.
Air inlet passages 42 and 43 are formed generally by frame 25 with bracket cover 35 and intermediate frame plate 44 on one side and by frame 25 with bracket cover 36 and intermediate frame plate 45 on the other side. The outlet ventilation passages for air moving out of radial air passages 24 is between intermediate frame plates 44 and 45.
In Figure 1 the airflow, or flow of cooling gas, is indicated by arrows for a very unbalanced flow condition for purpose of illustration. In Figure 1 the major air flow is shown entering through air inlet passage 43. In this instance the flow ls so unbalanced that air from inlet 43 passes through all of the ventilation passages 16 and 24 thereby ~o Case 2967 virtually excluding the air entering a:ir inlet passage 42 from cooling the rotor or stator. ~hile this condition would be extreme, the effects of unbalanced conditions which are not so extreme will be indicated in subsequent examples.
Referring now to Figure 2, where like parts have the same designation numbers, a vertical baffle 46 has been added between the arms of spider 14. The baffle 46 is not necessarily located axially at the mid-point of the rotor core, but is located at an axial position where the air flow at air inlet passages 42 and 43 is balanced or equal. This achieves a more even cooling of the rotor and stator cores. It also prevents the mixing of the air flowing from either end and helps to reduce turbulence.
The use of a baffle 46 results in many cases in an increase in air flow. For example, on a large, series ventilated, high speed motor (4500 H.P. and 1800 RPM) the measured air flow through the motor before a baffle was installed was 7520 cubic ft./min.
or cfm. After a baffle was installed the measured air flow increased to 9478 cfm. The windage losses dropped by approximately one kilowatt after the baffle was installed.
As another exampie, on a smaller, slower speed motor having no rotor fans (350 Il.P. and 450 RPM) the measured airflow through the motor without a baffle was 927 cfm. After a baffle was installed the air flow increased to 988 cEm. While the airflow increased with improved cooling, the windage losses also showed a slight increase which appears to be because of the increased air flow.
It is believed that the increase in air flow when a baffle is installed as described, may be explained as follows. The air flowing axially from both ends meets and mixes in the annular air spaces case 2967 between the spider arms. As the two air streams meet they try to pass each other and create a turbu]ent region with possibly secondary flows. This causes higher friction losses. The baffle prevents any mixing action and reduces turbulence. It is also believed to provide a pumping action to move the air outwards in a radial direction.
Tests were also carried out on series type, double end ventilated motors with rotor mounted fans to assist air flow. Motors with fans develop a high pressure which apparently tends to overcome the small variations in pressure and in resistance to air flow, and consequently the unbalances in flow from the two ends is usually not as great. Consequently the use of a baffle does not result in as great an improvement.
Referring now to Figures 3 and 4~, Figure 3 is an elevation view of a section of vertical baffle 46. It was previously mentioned that the sides of the baffle could be shaped to further reduce turbulence.
In Figure 4A there is a baffle 46A, shown in section, with curved walls 47. The base portion of baffle 46A
is at the shaft, and the curved walls 47 very generally direct a portion of the axially moving air in a radial direction. Similarly, in Figure 4B there is a cross-sectional view of baffle 46B which has flat sloping sides 48, also intended to reduce turbulence and pressure loss in turning the axial flow to radial flow.
In conclusion, in any doubled end ventialted machine, air flow from either end can be balanced by a baffle placed between the spider arms at an appropriate axial location. The improvement in cooling that is achieved with a baffle tends to be greatest in series flow machines that do not have a rotor fan. However there may still be a significant improvement in series flow machines with rotor mounted fans and in parallel flow machines.
': ''~ ' i ,~
: , .
Claims (7)
1. In a double end ventilation dynamoelectric machine having a rotor comprising a rotor shaft, a spider mounted on said rotor shaft and supporting rotor laminations forming a rotor core, said laminations being spaced apart in groups to provide radially extending ventilation passages between adjacent groups, and axially extending passages in said spider communicating at each end with an air inlet and communicating with said radially extending ventilation passages, the improvement comprising baffles each extending in a radial direction between said shaft and said core and located within a corresponding one of the axially extending passages axially at a position providing a substantially equal flow of air from each air inlet.
2. The invention of claim 1 in which the baffle has sides sloping inwardly from the shaft towards the core to reduce turbulence.
3. The invention of claim 2 in which the sloping sides are cured concavely.
4. A double end, series flow ventilation dynamoelectric machine, comprising a stator including a stator core having a plurality of spaced apart groups of radially extending laminations defining at inner edges thereof a rotor receiving space the spaces between adjacent groups of stator laminations defining radially extending stator ventilation passages, a rotor mounted on an axially extending shaft for rotation within said rotor receiving space in said stator core, said rotor having a rotor spider mounted on said shaft with radially projecting, axially extending spider arms for supporting a rotor core, - 9 - Case 2967 said spider arms defining axially extending ventilation passages having an air inlet at each end hereof, said rotor core having a plurality of radially extending laminations in spaced apart groups defining between adjacent groups radially extending ventilation passages in communication with said axially extending passages, said inner edges of said stator laminations and the periphery of said rotor laminations defining an air gap, and a baffle extending in a radial direction around said shaft between said spider arms, said baffle being located axially at a position providing substan-tially equal flow of air from each air inlet.
5. A dynamoelectric machine as defined in claim 4 in which said radially extending stator ventilation passages and said radially extending rotor ventilation passages are aligned.
6. A dynamoelectric machine as defined in claim 4 in which said radially extending stator ventilation passages are offset from said radially extending rotor ventilation passages.
7. A dynamoelectric machine as defined in claim 4 in which said baffle has shaped side walls converging generally from a wider portion adjacent said shaft to a narrower portion adjacent said rotor laminations.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000518555A CA1272240A (en) | 1986-09-18 | 1986-09-18 | Spider baffle for double end ventilation in dynamoelectric machine |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000518555A CA1272240A (en) | 1986-09-18 | 1986-09-18 | Spider baffle for double end ventilation in dynamoelectric machine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1272240A true CA1272240A (en) | 1990-07-31 |
Family
ID=4133970
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000518555A Expired - Lifetime CA1272240A (en) | 1986-09-18 | 1986-09-18 | Spider baffle for double end ventilation in dynamoelectric machine |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1272240A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102299582A (en) * | 2011-08-22 | 2011-12-28 | 卧龙电气集团股份有限公司 | Passive cooler for motor |
-
1986
- 1986-09-18 CA CA000518555A patent/CA1272240A/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102299582A (en) * | 2011-08-22 | 2011-12-28 | 卧龙电气集团股份有限公司 | Passive cooler for motor |
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| MKEX | Expiry |