US3602631A - Electrical apparatus in an underground case - Google Patents

Electrical apparatus in an underground case Download PDF

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Publication number
US3602631A
US3602631A US43443A US3602631DA US3602631A US 3602631 A US3602631 A US 3602631A US 43443 A US43443 A US 43443A US 3602631D A US3602631D A US 3602631DA US 3602631 A US3602631 A US 3602631A
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United States
Prior art keywords
layer
electrical apparatus
casing
layers
corrosion
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
Application number
US43443A
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English (en)
Inventor
Harry R Sheppard
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Westinghouse Electric Corp
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Westinghouse Electric Corp
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Publication date
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/02—Casings
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00—Stock material or miscellaneous articles
    • Y10S428/922—Static electricity metal bleed-off metallic stock
    • Y10S428/923—Physical dimension
    • Y10S428/924—Composite
    • Y10S428/925—Relative dimension specified
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00—Stock material or miscellaneous articles
    • Y10S428/922—Static electricity metal bleed-off metallic stock
    • Y10S428/923—Physical dimension
    • Y10S428/924—Composite
    • Y10S428/926—Thickness of individual layer specified
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12556—Organic component
    • Y10T428/12569—Synthetic resin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12861—Group VIII or IB metal-base component
    • Y10T428/12951—Fe-base component
    • Y10T428/12958—Next to Fe-base component
    • Y10T428/12965—Both containing 0.01-1.7% carbon [i.e., steel]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12861—Group VIII or IB metal-base component
    • Y10T428/12951—Fe-base component
    • Y10T428/12972—Containing 0.01-1.7% carbon [i.e., steel]
    • Y10T428/12979—Containing more than 10% nonferrous elements [e.g., high alloy, stainless]

Definitions

  • the present invention is anew andimproved fluid filled electrical'apparatus of the type suitable 'for vault or.
  • the electrical apparatus includes a. tankformed of a laminated material, havingatleastthree metallic layers.
  • the layer adjacent'the fluid in the tank, .i.e., the innermost or first layer of :the laminated'structure, is
  • this layer may be a.
  • the next or second layer, which forms the core of the sandwich, is selected for its overall corrosion resistance, such as a steel alloy containing at least 12 percent chromium, commonly called stainless steel. Since. the structural requirements of the tank are met by the inner-v most or first layer, this core or b'arrierlayer may be relativelythin and is'preferably so in order to minimize the-cost :oflthe laminated material.
  • the third or-outer-layer is selected to be anodic to the core or barrier layer, and is thus sacrificial to the barrier layer. Again, since the structural requirements of the tank are met by the first orinner layer, the thickness of the. outer layer may be selected strictly from the viewpoint'of'it's sacrificial action.
  • this third or outer. layer may be a mild orplain carbon steel. This sacrificial outer layer prevents, or at least delays, pitting cor-' rosion of the barrier layer, greatly extending the service life of the tank.
  • FIG; l is aperspective view of an electrical distribution transformer of the residential distributionetype, which maybe 1 constructed according-to the teachings of the invention
  • FIG. 2 is a perspective'view-of an electrical transformer of the network-type, disposed inanunderground vault, which may tion;
  • inven- FlG.'3 is a fragmenta ry', sectional view of the tank or casing .of electrical'apparatus constructed according to an embodiment of the invention. 7
  • FIGQ 4 is afragmentary, sectional view of a tank or casing of electrical apparatus constructed according to another embodiment of the invention.
  • FIG. 5 is a fragmentary, sectional view of the tank shown in FIG. 2, modified to include a protective outer coating of insulating material.
  • Electrical transformers filled with mineral oil. ask'arel, water, SFnor the like, may utilize theteachings of the invention, as wellras capacitors and protective ,apparatus, such as circuit breakers, which require a corrosion resistant tank or casing.
  • Transformer 10 shown inFlG. .1 is a distribution transformer of the type commonly used forunderground residential distribution,
  • Transformer 10 includes a casing 18. having a cover 20 which encloses the core-winding as sembly (not shown) of the transformer 10.
  • Asuitable insulatinggan'd cooling fluid, such as mineral oil, is also disposed in casing.v 18, to aid in insulating and cooling the electrical:
  • Transformer 10 is hermetically; sealed; with the electrical connections 'to theencased high voltage winding being made through the sealed high voltage.
  • the vault 14 has a heavy access'cover 34, which may be, 55
  • Transformer 12 shown in FIG. 2 is a power transformer of the network type, installed in a vault 40 which has a pluralityv of access covers thereon, such as cover 42.
  • the top of vault40 is'-usually at grade level 44.
  • Transformer 12 includes the main transformersection 46, a high voltage switch 48, and a .network protector 50.
  • An external high voltage electrical potential. is connected to the high voltage switch 48 through a multiple conductor single bushing 52, or through separate bushings, and the lower voltage distribution potential is obtained from thesecondary bushings, such as secondary bushing v54.
  • the main transformer portion 46 includes a tank 56 which encloses thecore-winding assembly of the transformer, and also an insulating and cooling fluid, such as mineral oil or askarel.
  • Transformers l0 and l2 are both subjected to highly corrosive environments, and must withstand flooding of their respective vaults with corrosive, polluted water for extended periods of time. Such environments have caused the failure of electrical transformers due to tank corrosion in periods much shorter than their normally expected service life.
  • the present invention is new and improved fluid filled electrical apparatus having a tank formed of a laminated structure.
  • the laminated tank structure includes at least first, second and third metallic layers, which will also be referred to as the inner, core and outer layers, respectively, from the viewpoint of the tank or casing construction.
  • the external surface of the inner layer is adjacent to the fluid inside the casing
  • the external surface of the outer layer is adjacent to the environment in which the electrical apparatus is placed
  • the core layer is sandwiched between the inner and outer layers.
  • Laminated metals for reducing corrosion are known in the prior art, but they have either been unsuccessful in arresting certain types of corrosion, too costly, or both.
  • cladding the external surface of a core material is known in which a relatively thick mild steel core has thin layers of stainless steel disposed on its two major opposed surfaces.
  • This approach however, at least for electrical apparatus disposed underground, suffers from the functional disadvantage of tanks formed of stainless steel, as the thin layers of stainless steel are subject to pitting and stress corrosion, exposing the mild steel core.
  • Another example of cladding known in the art utilizes a relatively thick core of stainless steel, clad with thin layers of steel containingabout 12 percent chromium. While this structure may be suitable functionally for the tanks of underground electrical apparatus, it is not economically attractive.
  • FIG. 3 is a fragmentary, cross-sectional view of fluid filled electrical apparatus having a tank or casing 60 constructed according to the teachings of the invention.
  • Casing 60 may be the tank 18 or cover 20 of transformer shown in FIG. 1, the tank 56 of transformer 12 shown in FIG. 2, or the casing of any fluid filled electrical apparatus having an electrically conductive member therein adapted for connection to an electrical potential.
  • Casing 60 has a first or inner layer 62 adjacent to the fluid 64, a second or core layer 66 and a third or outer layer 68.
  • the present invention economically solves the corrosion problem of underground electrical apparatus by selecting the material and thickness dimension of the first layer 62 only for its mechanical properties and cost, without regard to its ability to resist corrosion.
  • the thickness of layer 62 is selected to provide at least the structural requirements of the casing while it is in service. For distribution transformers of the residential type, this layer may be about 0.030 to 0.050 inch thick, while power transformers of the network type may have a first or inner layer of about 0.100 to 0.250 inch thick. Since.
  • the first layer is preferably a mild or plain carbon steel.
  • the second or core layer 66 of casing 60 is selected for its ability to resist corrosion and protect the structural layer 62.
  • One of the stainless steels'i.e., noncorroding alloys of iron and chromium, including at least 12 percent chromium in order to produce the required passivity, may be used.
  • suitable stainless steels are the A181 types 304 and 308, or the 18-8 stainless steels, such as AlSI type 302. Since stainless steel is relatively costly, compared with carbon steel, the thickness of the second layer 66 should only be that required to protect the structural layer. Thicknesses in the range of about 0.001 to 0.020 inch are suitable, .with the thickness selected depending upon the thickness of the structural layer 62. For example when the structural layer is about 0.030 to 0.050 inch thick, the core layer 66 may be about 0.006 inch thick.
  • Stainless steel while not subject to general attack by the usual environments surrounding underground electrical apparatus, is subject to localized attack, called pitting corrosion, which may be very severe, causing rapid penetration, especially when subjected to environments containing chlorides.
  • Chlorides promote the formation of active-passive electrolytic cells between the large passive or cathodic area and the small anodic area being attacked. Further, severe localized attack may cause failure of the core layer before perforation, as it promotes cracking of the stainless steel due to stress corrosion.
  • the function of the third or outer layer 68 is to protect the core layer 66 from pitting and stress corrosion. lt accomplishes these functions by forming a sacrificial anode for the core layer, and as such the material of which the outer layer is formed must be higher in the galvanic series than the material of which the core layer is formed. Since stainless steel is the preferable material for the core layer 66, the outer layer may be formed of such materials as carbon steel, magnesium, aluminum, or zinc. In order to prevent the outer layer from being sacrificed too rapidly, however, it will usually be preferable to select a material which'is higher than the core material in the galvanic series, but not too much higher. Thus, carbon steel, which is above, but close to stainless steel in the galvanic series, is an excellent material for the third layer 68, and it additionally has the benefit of being relatively low in cost.
  • the thickness dimension of the third layer 68 depends upon the corrosiveness of the intended environment. Since the I outer layer will be sacrificed, it'eventually will provide reduced structural strength for the casing and its thickness need not be influenced greatly by strength requirements. As hereinbefore stated, the inner layer 62 is selected to provide adequate structural requirements of the casing while the transformer is in service. The third layer 68 will provide additional structural strength for the casing during manufacturing and shipment of the transformer, when it requires the greatest strength. Thus, the inner layer 62 must be selected to at least provide the in-service strength requirements of the casing, and the inner and outer layers together must provide adequate structural strength for manufacture and shipment.
  • the outer layer 68 When theouter layer 68 is attacked to the point where the core or barrier layer is exposed, the outer layer 68 will continue to be attacked in preference to the core layer 66 due to their relative locations in the galvanic series, thus stopping the penetration of the corrosion through the tank wall.
  • the outer layer will continue to be sacrificial in preference to the core layer, as long as the area of the third layer material exposed by the corrosion, i.e., the sides of the craters produced by the corrosion, plus a predetermined surfacearea of the third layer immediately adjacent the crater, such as about a 2 inch radius about the center of the corrosive attack for carbon steel, is greater than the area of the core material exposed by the corrosion.
  • the thickness of the outer layer is selected with the corrosiveness of the intended environment in mind. If the third layer is selected to be a metal higher in the galvanic series than carbon steel, such as zinc, more core area may be exposed before the core layer is attacked.
  • FIG. 3 illustrates a fragmentary sectional view of a tank or casing in which the first andthird layers have different dimensions.
  • Like reference numerals in FIGS. 3 and 4 indicate like components, and like reference numerals with a prime mark indicates similar but modified components.
  • FIG. 4 illustrates a tank 60' having first and second layers 62 and 66, such as illustrated in FIG. 3, but having a third layer 68 which is substantially thinner than the third layer 68 shown in FIG. 3, as functionally itwill usually not be necessary to make the third layer as thick as the structural layer.
  • FIG. 5 is a fragmentary, cross-sectional view of the tank60 shown in FIG. 3, including a protective coating 70 disposed on the outer surface of the third layer 68.
  • Protective coating 70 may be selected from a large number of organic coatings specially developed to protect metals against corrosion, such as coatings formed of the epoxies, acrylics, asphaltics, alkyds, or polyesters.
  • the thickness of the outer protective coating depends upon the particular coating selected, with about 0.001 to 0.020 inch being the usual range. With the laminated tank construction disclosed herein, however, it would be suitable to use one of the lower cost protective coatings, such as an alkyd, which allows a slow diffusion of moisture. A coating which alwhich apparatus would be severely damaged or rendered uselows a slow diffusion of moisture is actually better than one i which is more moisture resistant, as pinholes and scratches in g the coating will not cause the'underlying metal to be as severely and rapidly attacked as would occur at openings in a more perfect coating.
  • FIG. 5 also illustrates a corrosion crater 72 in the tank 60, and shows how the crater is stopped by the barrier layer 66.
  • the corrosion penetrates the outer layer 68 through an open ing in the coating 70, and proceeds inwardly until the barrier layer 66 is exposed.
  • the outer layer 68 becomes sacrificial to the barrier layer 66, and the corrosion attacks the outer layer, usually along the surface of the barrier layer, enlarging the size of the crater without pitting or otherwise attacking the barrier layer.
  • the area of the wall 74 plus a predetermined surface area about the crater, does not exceed the area 76 of the barrier layer which is exposed, the outer layer will corrode in preference to the barrier layer.
  • the laminated structure of which the casings or tanks are formed may be produced by any suitable method, such as by heating metal slabs of the layer materials to welding temperature, and then rolling them together to bond the slabs together.
  • the laminated material when being fabricated into the tank or casing structure, may be welded by conventional methods, with stainless steel welding rods generally being preferable if the core layer is stainless steel, although mild steel rods may also be successfully used.
  • the third or sacrificial layer be at least as sacrificial to the welding material used as it is to the core layer. Welded joints in which the core layers are tied together via the weld material are most desirable, but overlap welds are suitable if the overlap dimen- I ing in highly corrosive environments, such as underground,
  • the electrical apparatus includes a tank or casing constructed of a laminated metallic structure which greatly extends the useful service life of the tank, without undue economic penalty.
  • the tank material includes three layers of metal, with the outer layers functioning properly even if constructed of plain carbon steel, such as commonly used for tanks and casings of similar apparatus mounted in noncorrosive environments, and the core material, which may be selected from one of the stainless steels, while being more costly per pound than carbon steel, is a relatively thin layer, such as form about 0.001 to 0.020 inch.
  • the additional cost of the thin layer of core material, and the cost of producing the laminated structure IS substantially less than a tank constructed completely of stainless steel, and is easier to fabricate.
  • the additional cost of the laminated tank, compared with a tank constructed of mild steel, is more than offset by the increased service life of the apparatus when disposed in corrosive environments.
  • I claim as my invention: 1. Electrical apparatus comprising: acasing, I i an electrically conductive element disposed in said casing, said electrically conductive element being adapted for connection to an electrical potential; and fluid means disposed in said casing, said casing being at least partially constructed from a laminated metallic structure having at least first, second and third layers, said first layer being a structural layer, in
  • said second layer being a barrier layer, disposed between. said first and third layers, to protect said first layer from corrosion, and said third layer being anodic to said second layer, forming a sacrificial anode to reduce pitting corrosion of the second layer.
  • the electrical apparatus of claim 1 wherein at least the first layer is a carbon steel and the second layer is a steel alloy containing at least 12 percent chromium.
  • first and third layers are carbon steels and the second layer is a stainless steel.
  • the electrical apparatus of claim 1 including an insulating coating disposed on the third layer.
  • first and third layers are carbon steels and the second layer is a stainless steel, and the first layer is substantially thicker than the second layer.
  • first and third layers are carbon steels and the second layer is a stainless steel, and the second and third layers are each thinner than the first layer.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Prevention Of Electric Corrosion (AREA)
US43443A 1970-06-04 1970-06-04 Electrical apparatus in an underground case Expired - Lifetime US3602631A (en)

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US4344370A 1970-06-04 1970-06-04

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4030058A (en) * 1976-03-30 1977-06-14 Westinghouse Electric Corporation Inductive coupler
US5412304A (en) * 1993-08-09 1995-05-02 Hughes Aircraft Company Cooled primary of automobile battery charging transformer
US20100013586A1 (en) * 2006-07-03 2010-01-21 Claudio Ceretta Power Reactor for Energy Transfer
US20120212312A1 (en) * 2011-02-22 2012-08-23 Abb Technology Ag Dry-type network transformer

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4030058A (en) * 1976-03-30 1977-06-14 Westinghouse Electric Corporation Inductive coupler
US5412304A (en) * 1993-08-09 1995-05-02 Hughes Aircraft Company Cooled primary of automobile battery charging transformer
US20100013586A1 (en) * 2006-07-03 2010-01-21 Claudio Ceretta Power Reactor for Energy Transfer
US8228153B2 (en) * 2006-07-03 2012-07-24 Societa' Elettromeccanica Arzignanese, S.P.A. Power reactor for energy transfer
US20120212312A1 (en) * 2011-02-22 2012-08-23 Abb Technology Ag Dry-type network transformer
WO2012115902A3 (fr) * 2011-02-22 2013-08-01 Abb Technology Ag Transformateur de réseau du type non immergé
CN103443881A (zh) * 2011-02-22 2013-12-11 Abb技术有限公司 干式网络变压器
US8884732B2 (en) * 2011-02-22 2014-11-11 Abb Technology Ag Dry-type network transformer
CN109036776A (zh) * 2011-02-22 2018-12-18 Abb瑞士股份有限公司 干式网络变压器

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Publication number Publication date
BE768027A (fr) 1971-12-03

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