CA1091741A - Fluidly cooled flat plate neutral bus - Google Patents

Abstract

FLUIDLY COOLED FLAT PLATE NEUTRAL BUS

ABSTRACT OF THE DISCLOSURE
A fluidly cooled flat plate neutral bus for elec-trically connecting the neutral bushings on dynamoelectric machines. The current carrying flat plate is in heat trans-missive contact with a coolant carrying conduit which trans-fers heat generated in the neutral bus to the coolant flow-ing therethrough. The fluidly cooled flat plate neutral bus provides high heat flux while occupying a small volume.

Description

BACK~ROIJND OF THE I~EMTIOM
Field of the Invention:
This invention relates to the neut~al bushings on dynamoelectric electric machines, and more particularly to means for electrically connecting those neut:~al bushings and means for cooling the electrically connecting means.
Description of the Prior Art:
Large turbine generators often have several (three for a three-phase machine) neutral lead bushings which are electrically connected by a bus. Several schemes have been utilized in the past to remove the heat generated in the bus as a result of the current flow therethrough during gene-rator operation.
For some small generators satisfactory cooling of the bus was obtained by natural convection while larger machines required a forced convection air flow to maintain -; the bus at an acceptable ternperature. More recently, buses on certain, selected generators were altered to accommodate still higher amperage ratings in those generators. ~hese buses were typically water cooled members having rectangular .,5.

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~ 7~ 46,993 cross sectioned copper current carriers within which stain-less steel piping was brazed. Through the stainless steel piping or other suitable material coolant was transmitted which was effectlve in carrying away heat generated in the current carrier. This internally cooled neutral bus was acceptable for generators rated at less than 34,000 amperes.
However, this design was no longer practical for a variety of reasons in machines whose ratings were larger than 34,000 amperes. Space limitations set by attachment requirements between the bus and the bushings prohibit additional coolant carrying pipes. Enlargement of the current carrier to accommodate an increased number of coolant carrying tubes would cause an increased cantilever type load to be imposed upon the attached neutral bushings. Such increased load could damage the bushings or adversely affect the perform-ance of the entire generator. A neutral enclosure surrounds and isolates the neutral bushings and their connecting bus from the atmosphere. The purpose of the neutral enclosure is to prevent damage to and contamination of the bushings while shielding the electrically charged bushings and bus from any possible human contact. Any increase in the size of the rectangular current carrier bus must be reflected in a concomitant increase in the size of the neutral enclosure which surrounds that bus. Increasing the size of the neu-tral enclosure requires additional material and, more impor-tantly, additional space in the power plant central station.
A further method for increasing the heat transfer rate from the neutral bus is to increase the coolant velo-city through the stainless steel piping. However, for generator ratings higher than 34,000 amperes the required coolant velocity through the spatially limited maximum number of allowable stainless steel tubes becomes excessive resulting in possible tube erosion and drastically increased coolant pumping power. Such tube erosion can contaminate the nonconductive coolant and bring about forced turbine-generator outages while the excessive pumping power consump-tion can cause uneconomical operation.
It is thus apparent that a new design of bus is required which will increase the heat transfer capabilities and preferably decrease the space occupied by the old model bus.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved neutral bus is provided for electrically connecting the neutral bushings in dynamoelectric machines. This invention generally comprises an electrical winding which has internally cooled neutral bushings connected thereto, a multiple plate electrically conductive bus which is connected across those neutral bushings by flexible conductors disposed 20 between the plates, and a plurality of coolant conduits -attached to the plates for cooling the bus. -The conduits carry coolant therethrough and are joined to the plates in a heat conductive fashion. The coolant conduits are preferably joined to the bushing's internal coolant passages by flexible hoses. Further increases in generated heat from larger rated machines can be carried away by suitable selection of the number of conduits per bus plate members, size of the conduit, relative disposition of the B ~:

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` conduit and~s, and coolant velocity through each conduit.
The weight and volumetric requirements of the present inven-tion amount to 50% and 80% respectively of the previously utilized bus.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood from the following detailed description of a preferred embodi-ment, taken in connection with the accompanying drawings, in which:
Figure 1 is a transverse sectional view of a turbine generator in which the invention is incorporated;
Figure 2 is an elevation view of the present invention illustrating its connection with the neutral ~ bushings;
-~ Figure 3 is an elevation view of the invention taken 90 from Figure 2;
Figures 4A and 4B are elevation views taken 90 apart of a preferred embodiment coolant conduit which is shown utilized in Figures 1 through 3;
Figure 5A is a pictorial view of the prior art neutral bus, the attached bushings, and its enclosure;
Figure 5B is an elevation view of the prior art neutral bus; and Figure 5C is a pictorial view of the prior art coolant conduit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is concerned primarily with connecting means ~or the neutral bushings of dynamoelectric machines and cooling means used for transferring heat from the connecting means. Accordingly, in the description which ' ..

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follows the invention is shown embodied in a large water cooled turbine generator. It should be understood, however, that the invention may be used as a neutral bushing connec-tor in any dynamoelectric machine and also that the coolant utilized in the bus cooling means can be other than water.
In Figure 1 the invention is shown, by way of illustration, disposed in operating position on a large turbine generator 10. The generator 10 is a three-phase , machine of any rating with water cooled bushings.
As shown in Figure 1, the generator 10 has an outer gas tight housing 12 filled with a coolant gas which is normally hydrogen. The generator 10 has a laminated ` stator core 14 of usual construction which is supported within the housing 12 in any suitable manner. The stator ' core 14 is provided with longitudinal slots 16 in the usual manner for the reception of high voltage stator winding -coils 1~. Generator 10 also has a rotor member 20 of any * suitable type which is provided with a field winding (not shown). Neutral bushings 22, 24, and 26 receive their 20 coolant supply within housing 12. That coolant is directed radially outward to the extremity of each bushing from which the coolant makes a turn and travels radially inward.
During the course of the coolant's travel through the bush-ing, it absorbs heat from the bushing and is heat laden at its exit from the bushing.
Figures 2 and 3 illustrate the preferred embodiment of the present invention. Three separate plates 28, 30, and 32 are illustrated as being respectively connected with bush-ings 22, 24, and 26. Bus plate 28 is connected to bus plate 30 30 by a predetermined number of electrically conductive .' - . ., ,, : , ~. .

1~ 9 17 ~ ~ 46,993 flexible connectors which are, preferably, braided wire - straps. Current carrying requirements dictate the number and size of the previously mentioned flexible connectors.
Bus plates 30 and 32 are similarly connected with the flexi-ble connectors. Use of flexible connectors 34 in attaching the separate bus plates together have several advantages:
easier handling characteristics during assembly than a single bus plate; larger allowable tolerances are permitted for the relative assembly position between each bushing and each bus plate since the bus plates may be electrically interconnected after assembly with the bushings; and removal and replacement of individual bus plates is facilitated by the easily connectible and disconnectible characteristics of flexible connectors 34. Additional design freedom can be obtained by using a double layer of flexible connectors 34 as illustrated in Figure 3. Each bus plate is shown embo-died as having a separate coolant conduit 36, 38, and 40.
Each conduit is firmly attached to its respective bus plate to provide a heat conduction path of low resistivity. To aid in the formation of an effective heat transfer joint, square cross sectioned conduit, illustrated in Figure 4B, is used. Any conduit, however, preferably having at least one flat side can be effectively utilized.
The coolant conduit's disposition on the face of each bus plate can be optimized by actual testing to deter-mine the most effective positioning for maximum heat trans- O
fer between the bus plate and the coolant flowing through the attached coolant conduit.

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Although not shown, it is to be understood that multiple layers of bus plate can be utilized with coolant conduit "sandwiched"
between adjacent plates.
Flexible coolant hoses 42, preferably polytetra-fluroethylene, are illustrated as connecting the ends of each coolant conduit to the bushing coolant nipples (not shown). By making such connection the existing coolant supply may be utilized without resorting to additional external connections with the coolant conduits. The arrows , 10 shown in Figure 2 indicate the direction of coolant flow through each of the coolant conduits 36, 38, and 40. No - preference as to the direction of coolant flow is to be inferred from the arrows since the arrows are only used to show one possible direction of flow.
Figure 3 shows the same elements of the present invention as does Figure 2, but Figure 3 is rotated 90 from the vantage point of Figure 2. It is to be further under-stood that the neutral bushings illustrated in Figure 1 can be pointed in any direction while still utilizing the pre-sent invention.
Figures 4A and 4B illustrate a sectional and elevation view respectively for a coolant conduit into which is brazed stainless steel nipple 44. Nipple 44 provides the ; entrance and exit terminal points for each coolant conduit's connection through coolant hoses 42 to the neutral bushings.
By way of example, bus plates 28, 30 and 32 are made of material having a high electrical conductivity while ~91741 46,993 `
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, coolant conduits 36, 38, and 40 are made from material having a high heat transfer conductivity. In the present case the materials of both elements, bus plate and coolant conduit, is copper. For neutral bushings which are located on 48" centerlines, bus plates of 17" in width and 1.25" in thickness are used with the length of each bus plate being chosen by referencing the bushing separation distances and using other design considerations. Coolant conduits 36, 38, and 40 have standard pipe wall thicknesses and are 2" by 2"
10 outside dimension. Joining coolant conduits 36, 38, and 40 .:
to bus plates 28, 30, and 32 respectively is accomplished by brazing. Other suitable means of ~oining may be used to obtain the typically highly conductive (electrical and heat) ~oints attained by brazing. ~
Figure 5A is a pictorial illustration of a prior -art neutral bus. Flexible connectors 34 are shown attached '~ between the enclosed rectangular cross sectional bus sec- ;
tions 46, each of which is attached to a separate bushing.
Figure 5B illustrates an elevation view of the . 20 prior art neutral bus and cooling system therefor. The ; complex shapes of the cooling conduits 48, better illus-trated in Figure 5C, used in cooling the attached rectangu-lar-cross sectioned bus 46, necessiate an intricate fabri-cation procedure and a complicated assembly process into the bus. In Figure 5C it can be seen that adding cooling con-duits to the existing configuration or increasing the size of the existing conduits reduce access to the interior of the bus and result in increased difficulty in bolting the bus to the bushings.
It will now be apparent that an improved neutral bush-., `

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~3 ~4 1 46,993 ~ ing bus has been provided in which greater heat transfer is realized, smaller space is required, and greater assembly and disassembly freedoms exist. These features provide generators of higher rating, less space requirements, less material, and easier maintainability.

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Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A dynamoelectric machine comprising: an electrical winding having a plurality of neutral bushings which include internal coolant passages; an electrically conductive bus electrically connected across said neutral bushings, said bus comprising:
a plurality of discrete plate members equal in number to the neutral bushings, each plate member being electrically connected to a corresponding bushing; and a series of flexible electrical connectors dis-posed between said plate members for electrically inter-connecting said plate members; and a plurality of coolant conduits joined in heat transfer relationship to said plate members for passing coolant therethrough, each conduit being joined to a cor-responding plate member.

2. The dynamoelectric machine of claim 1, further comprising: means for providing fluid communication between said neutral bushings, cooling passages and said coolant conduits, said fluid communication means having more flexi-bility than said coolant conduits.

3. me dynamoelectric machine of claim 2, wherein each of said coolant conduits is fluidly connected to its corresponding bushing's cooling passage.