US3896406A - Screen for core legs for transformers, reactors and the like - Google Patents

Screen for core legs for transformers, reactors and the like Download PDF

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Publication number
US3896406A
US3896406A US495112A US49511274A US3896406A US 3896406 A US3896406 A US 3896406A US 495112 A US495112 A US 495112A US 49511274 A US49511274 A US 49511274A US 3896406 A US3896406 A US 3896406A
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US
United States
Prior art keywords
tape
screen
core
core leg
sheets
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
US495112A
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English (en)
Inventor
Olle Andersson
Ellerth Ericsson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ABB Norden Holding AB
Original Assignee
ASEA AB
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by ASEA AB filed Critical ASEA AB
Application granted granted Critical
Publication of US3896406A publication Critical patent/US3896406A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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
    • H01F27/24—Magnetic cores
    • H01F27/245—Magnetic cores made from sheets, e.g. grain-oriented
    • 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
    • H01F27/34—Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
    • H01F27/36—Electric or magnetic shields or screens
    • H01F27/363—Electric or magnetic shields or screens made of electrically conductive material

Definitions

  • the Prior Art Close to the electrodes in an electrode gap there are risks of glow discharge occurring when the gap is under tension if the electrode surfaces show irregularities, sharp edges, and the like.
  • One type of electrode where this phenomenon frequently and easily occurs is the transformer-core.
  • the core legs of a transformer for strictly practical reasons cannot be made with purely circular cross-section, but its circumference is formed from a number of longitudinal surfaces which are perpendicular to each other and with sharp edges at their intersections.
  • Another reason is that the core is manufactured of shorn sheet and that there are always burrs along the shearing edges. Particularly at the edges of the core these burrs will form starting points for glow phenomena when the transformer is put under tension and an electric field arises between the innermost winding and the core leg.
  • FIG. 1 shows a cross-section through a core leg of a transformer core which is provided with a screen according to theinvention.
  • FIG. 2 shows how to apply the screen.
  • the core leg of a transformer or a reactor is providedwith a glow preventing screen of a material which, to a limited degree, is conductive, that is, is semiconducting.
  • a glow preventing screen of a material which, to a limited degree, is conductive, that is, is semiconducting.
  • the screen is manufactured of a tape 1 or the like with a structure or backing having great mechanical strength and is impregnated with an electrically semiconducting and thermosetting material.
  • the tape is wound with a good mechanical tension and with overlapping to make the screen complete. The degree of overlapping is determined by the thickness of the tape and the desired thickness of the finished screen. As is clear from FIG.
  • the screen will make contact with every protruding edge 3 of the core leg 2, and, since the tape is wound on so as to be well stretched, the tape as well as the finished screen will be in perfect mechanical and galvanic contact with the .core leg along all protruding edges of the leg.
  • the structure or backing of the tape may, for example, consist of glass fiber fabric giving the tape a very high mechanical strength.
  • the impregnating agent may contain resins of miscellaneous types, such as unsaturated polyesters and epoxy resins.
  • composition of suitable impregnating agents are given in the following:
  • EXAMPLE 1 33 parts by weight of an unsaturated polyester manufactured in a conventional manner of 1 mole maleic acid, 2 moles isophthalic acid and 3 moles 1,2-propane diol (acid value 30).
  • the components are mixed together to form a homogeneous compound.
  • This compound is applied to the glass tape on one or both sides. After curing the compound is electrically semiconducting.
  • EXAMPLE 2 60 parts by weight of an epoxy novolac with an epoxy chemical equivalent of l76l8l and a viscosity of 20-50 l0 cps at 52C,
  • amin-BF -complex compound for example BF-MEA from Allied Chemical Corp.
  • the components are mixed together to form a homo- I geneous compound.
  • This compound is applied to the tape on one or both sides. After curing the compound is electrically semiconducting.
  • EXAMPLE 4 30 parts by weight of an epoxy novolac with an epoxy chemical equivalent of 176-181 and a viscosity of 20-50 1O cps at 52C,
  • amin- BF -complex for example BF-MEA from Allied Chemical Corp
  • the components are mixed together into a homogeneous compound.
  • the compound is applied to the glass tape on one or both sides. After curing the compound is electrically semiconducting.
  • the components are mixed together into a homogeneous compound.
  • the compound is applied to the tape on one or both sides. After curing the compound is electrically semiconducting.
  • EXAMPLE 6 30 parts by weight of a polybutadiene resin with a vinyl content of at least 90 percent and a mole weight of at least 20,000,
  • the components are mixed together into a homogeneous compound.
  • the compound is applied to the tape on one or both sides. After curing the compound is electrically semiconducting.
  • the problem in the present case is to choose the maf terial components in the semiconducting impregnating agent with regard to the resistivity and the dielectric constant so that, on the one hand, the losses in the screen, caused by the currents having the operating frequency, are negligible in comparison with the iron losses in the leg and, on the other hand, a sufficient screening effect is obtained for the steepest voltage wave.
  • the upper permissible resistivity limit is determined by the capacity of the material to screen during transient phenomena, whereas its lower permissible limit is determined by the losses in the screen which can be accepted.
  • ID g the lowest permissible surface resistivity of the screen considering the losses therein (Q square) 8 thickness of screen p, resistivity of screen material a relative dielectric constant of screen material 6 dielectric constant for vacuum T the highest permissible electric time constant of screen material. This is determined from a comparison with the rise time T for the steepest surge volt age for which the screen is to have an acceptable screening effect.
  • the leg can never be quite straight in practice, but local irregularities will arise. It is therefore impossible to place a prefabricated circular screen around the core leg in such a way that the screen will be in galvanic contact with the edges of the core leg all around. In relatively large and randomly scattered areas there will be no contact between the screen and the leg, and the security against glow discharge can never be assured. The same phenomena also make it impossible to apply a prefabricated circular cylindrical screen around the leg to hold the sheets of the core leg together mechanically, since such a screen would never be in adequate mechanical contact with the core leg.
  • the screen is manufactured as described above, it will make an absolutely safe mechanical and electrical contact with all the protruding edges of the leg over its entire length. Since the tape is wound with a certain mechanical tension, which is of course kept so high that the desired mechanical contact pressure against the leg is obtained, it is assured that this contact will be permanent.
  • the hardening of the resin in the wound screen is suitably performed by means of infra-red radiation.
  • a tubular furnace can be used, surrounding the leg and the screen.
  • the furnace consists of a circular casing carrying on the inside a number of electrically driven infrared radiators which are directed towards the center of the furnace.
  • the infrared rays are radially displaceable so that the furnace may be used for different screen diameters.
  • the whole furnace is axially displaceable and its axial movement can be controlled with timing devices to ensure that the curing time is the same all over. The whole curing process can therefore be carried out automatically after starting and adjusting of the axial movement of the furnace.
  • the tape Since it is normal to use graphite as semiconducting ingredient in the impregnating agent, the tape is black in color. This causes the tape to absorb the infrared rays and the heating of the iron core is slight as there is an air gap between the screen and the core behind it (FIG. 1 Curing of resins in general by means of infrared radiation is well known. In this connection, however, said heating process is necessary because of the great thermal capacity of a core leg.
  • the tape can be wound on the core leg by hand or in a machine for compression of the sheet-metal packets.
  • the work can be performed with the core leg in vertical or horizontal position.
  • the uniting properties of the screen can be further strengthened by using a tape which shrinks during the curing.
  • a pressure on the screen which increases during the curing can also be obtained by winding a shrinkable foil outside the screen prior to curing. When the foil shrinks in response to heating, an increased pressure on the core leg is obtained and, in addition, the screen acquires a smooth and even outer surface.
  • a core leg for transformers, reactors and the like formed of a plurality of magnetic sheets with a surrounding tape to prevent the occurrence of glow disnated with an impregnant consisting essentially of an electrically semiconducting and thermosetting material, wound around the sheets with high mechanical tension and with overlapping so that a screen surrounding the core leg (2) is formed, said screen being cured by heat treatment and being quite stiff and having good mechanical and electrical contact with the core leg at least along the longitudinal edges (3) of the core leg.
  • a core leg according to claim 1 in which the material properties of the tape can be expressed in the formula:
  • R the lowest permissible surface resistivity of the screen considering the losses therein (Q/square) 8 thickness of screen I p resistivity of screen material 6 relative dielectric constant of screen material t dielectric constant for vacuum T the highest permissible time constant of screen material, which is determined out of a comparison with the rise time T for the steepest surge voltage for which the screen is to have an acceptable screening effect.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Insulating Bodies (AREA)
  • Insulating Of Coils (AREA)
  • Photoreceptors In Electrophotography (AREA)
  • Coils Or Transformers For Communication (AREA)
US495112A 1973-08-23 1974-08-06 Screen for core legs for transformers, reactors and the like Expired - Lifetime US3896406A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE7311463A SE385418B (sv) 1973-08-23 1973-08-23 Elektrisk skerm for att forhindra glimning invid metalliksa elektroder

Publications (1)

Publication Number Publication Date
US3896406A true US3896406A (en) 1975-07-22

Family

ID=20318305

Family Applications (1)

Application Number Title Priority Date Filing Date
US495112A Expired - Lifetime US3896406A (en) 1973-08-23 1974-08-06 Screen for core legs for transformers, reactors and the like

Country Status (9)

Country Link
US (1) US3896406A (fr)
BR (1) BR7406833D0 (fr)
CA (1) CA1002138A (fr)
DE (1) DE2438631C3 (fr)
FR (1) FR2241863B1 (fr)
GB (1) GB1476491A (fr)
NO (1) NO137467C (fr)
SE (1) SE385418B (fr)
ZA (1) ZA745378B (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4388546A (en) * 1981-01-29 1983-06-14 Kraftwerk Union Aktiengesellschaft Arrangement for controlling the internal potential in generator rods
US4479890A (en) * 1982-10-05 1984-10-30 Rca Corporation Thick film resistor inks
US6242840B1 (en) 1998-06-15 2001-06-05 Alliedsignal Inc. Electrical machine including toothless flux collector made from ferromagnetic wire
US20040254294A1 (en) * 2003-06-11 2004-12-16 John Clulow Conductive adhesive sealant for bipolar fuel cell separator plate assemblies
CN101777416A (zh) * 2010-03-15 2010-07-14 贵阳新星变压器有限公司 壳式变压器矩形圆角铁芯
EP2667388A3 (fr) * 2012-05-25 2016-12-28 Hitachi Industrial Equipment Systems Co., Ltd. Transformateur SCOT à noyau enroulé

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2103426B (en) * 1981-08-08 1985-02-06 Marconi Co Ltd Transformers
GB2212670A (en) * 1987-11-24 1989-07-26 Vni Pk I Teknologichesky I Tra Bar for induction devices

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2399314A (en) * 1942-12-03 1946-04-30 Westinghouse Electric Corp Semiconducting composition and tape produced therefrom
US2705292A (en) * 1953-05-07 1955-03-29 Siemens Ag Slot conductor for dynamoelectric machines

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2399314A (en) * 1942-12-03 1946-04-30 Westinghouse Electric Corp Semiconducting composition and tape produced therefrom
US2705292A (en) * 1953-05-07 1955-03-29 Siemens Ag Slot conductor for dynamoelectric machines

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4388546A (en) * 1981-01-29 1983-06-14 Kraftwerk Union Aktiengesellschaft Arrangement for controlling the internal potential in generator rods
US4479890A (en) * 1982-10-05 1984-10-30 Rca Corporation Thick film resistor inks
US6242840B1 (en) 1998-06-15 2001-06-05 Alliedsignal Inc. Electrical machine including toothless flux collector made from ferromagnetic wire
US20040254294A1 (en) * 2003-06-11 2004-12-16 John Clulow Conductive adhesive sealant for bipolar fuel cell separator plate assemblies
US6933333B2 (en) * 2003-06-11 2005-08-23 Bulk Molding Compounds, Inc. Conductive adhesive sealant for bipolar fuel cell separator plate assemblies
CN101777416A (zh) * 2010-03-15 2010-07-14 贵阳新星变压器有限公司 壳式变压器矩形圆角铁芯
EP2667388A3 (fr) * 2012-05-25 2016-12-28 Hitachi Industrial Equipment Systems Co., Ltd. Transformateur SCOT à noyau enroulé

Also Published As

Publication number Publication date
FR2241863A1 (fr) 1975-03-21
CA1002138A (en) 1976-12-21
NO137467C (no) 1978-03-01
FR2241863B1 (fr) 1980-07-04
SE385418B (sv) 1976-06-28
NO743020L (fr) 1975-03-24
SE7311463L (fr) 1975-02-24
DE2438631C3 (de) 1978-10-05
DE2438631B2 (de) 1978-02-02
DE2438631A1 (de) 1975-03-06
GB1476491A (en) 1977-06-16
NO137467B (no) 1977-11-21
ZA745378B (en) 1975-09-24
BR7406833D0 (pt) 1975-06-17

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