US3449703A - Current transformer having an accuracy unimpaired by stray flux from adjacent conductors - Google Patents

Current transformer having an accuracy unimpaired by stray flux from adjacent conductors Download PDF

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Publication number
US3449703A
US3449703A US714605A US3449703DA US3449703A US 3449703 A US3449703 A US 3449703A US 714605 A US714605 A US 714605A US 3449703D A US3449703D A US 3449703DA US 3449703 A US3449703 A US 3449703A
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United States
Prior art keywords
core
layer
current transformer
current
layers
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Expired - Lifetime
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US714605A
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English (en)
Inventor
Floyd L Steen
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General Electric Co
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General Electric Co
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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
    • H01F38/00—Adaptations of transformers or inductances for specific applications or functions
    • H01F38/20—Instruments transformers
    • H01F38/22—Instruments transformers for single phase ac
    • H01F38/28—Current transformers
    • H01F38/30—Constructions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
    • G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
    • G01R15/181—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using coils without a magnetic core, e.g. Rogowski coils
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F38/00—Adaptations of transformers or inductances for specific applications or functions
    • H01F38/20—Instruments transformers
    • H01F38/22—Instruments transformers for single phase ac
    • H01F38/28—Current transformers
    • H01F38/30—Constructions
    • H01F2038/305—Constructions with toroidal magnetic core

Definitions

  • the usual current transformer comprises a primary conductor carrying the current to be measured, a core surrounding the primary conductor, and a secondary winding wound about the core in which there is induced a secondary current representative of the measured primary current. If such a current transformer is applied in the vicinity of a bus carrying large currents through a path adjacent the core, the transformer accuracy may be seriously impaired by stray flux from the adjacent bus.
  • An object of my invention is to provide simple, inexpensive and effective means for maintaining the accuracy of the transformer substantially unimpaired by such stray flux from an adjacent bus.
  • I provide a core of nonmagnetic, electrical insulating material substantially surrounding the conductor carrying the current that is to be sensed.
  • a secondary conductor is wound about the core in an even number only of successive layers. Assuming that the layers are consecutively numbered from the core outward beginning with the number 1, each odd numbered layer extends from one point on the core along substantially the entire core length to a second point on the core closely adjacent the first point. Each even numbered layer extends from the second point along substantially the entire core length back to substantially said first point. Terminals are respectively connected to the first and last of these layers at said first point.
  • the turns in the adjacent layers are wound about the core in the same direction, and all the layers have a substantially equal number of turns distributed substantially uniformly along the length of the core.
  • FIG. 1 is a cross sectional view of an electric power system including a current transformer embodying one form of the present invention.
  • FIG. 2 is a sectional view along the line 2-2 of FIG. .1.
  • FIG. 3 is a schematic view of a portion of my current transformer.
  • bus bars 10 and 12 which are intended normally to carry high alternating currents, e.g., currents as high as several thousand amperes. Under fault conditions, the current through one or both of these bus bars can increase to values as high as 20 or 30 times this current.
  • I For measuring the current through conductor 10 under any of these current conditions, I provide a current transformer 20.
  • This current transformer comprises a toroidal core 22 suitably mounted in a position surrounding conductor 10 and a secondary winding 24 wound about the core.
  • Conductor 10 can be considered as the primary conductor of the transformer.
  • the core 22 is made of a material which is of constant permeability regardless of flux level or direction. Preferably, this material is a nonconductive, nonmagnetic material, e.g., a suitable resin.
  • the terminals of the secondary winding, which are located at point A, are designated 25 and 26.
  • the secondary winding 24 is Wound about the core in a plurality of layers, each having a substantially equal number of turns distributed substantially uniformly about the core along the length of the core.
  • the first layer is formed by winding the secondary conductor about the core beginning at a point A and extending over substantially the entire length of the core to a point B located closely adjacent point A.
  • a second, or next succeeding, layer is formed by winding the secondary conductor around the outer periphery of the first layer, beginning at point B and extending back along substantially the entire length of the core to point A.
  • the direction of winding of the turns in the first layer is the same as the direction of winding of the turns in the second layer.
  • the secondary conductor in the first layer is wound counterclockwise about the periphery of the core as considered in the transverse cross-sectional view of FIG. 2, then the secondary winding in the second layer is also wound counterclockwise about the core periphery.
  • the arrows in FIG. 2 depict the direction that the conductor is wound in each layer. If additional layers of secondary winding are applied, these are also wound in the same direction about the core periphery, as viewed in transverse cross section. Only an even number of layers are used, and the winding pattern is repeated for each succeeding pair of layers. That is, each odd numbered layer extends from A to B, and each even numbered layer extends from B back to A (assuming the layers are counted from the innermost layer outward).
  • primary current through the conductor 10 will induce a current in secondary winding 24 that is substantially proportional to the primary current.
  • No inaccuracies Will arise from core saturation or eddy current effects since the core, as described hereinabove, is of a nonmagnetic, insulating material.
  • the main problem that I am concerned with is reducing the inaccuracies caused by stray flux from the adjacent high current conductor 12 traversing the secondary winding of the current transformer. It can be shown that the current that will be induced by such stray flux in a given layer of secondary winding is proportional to the area enclosed by the conductor of that layer. For example, in the diagrammatic representation of FIG. 3, which shows a single layer of the secondary winding, the current that will be induced by the stray flux in this layer is proportional to the shaded area, which is the area enclosed by the secondary winding in this layer. This proportional relationship exists irrespective of the angle or direction at which the stray flux enters the shaded area.
  • the current induced by stray flux in the second layer of secondary winding of FIG. 1 will be in an opposite direction to that induced in the first layer, considered relative to the termi- 4D nals of the secondary.
  • I can make the current induced in the second layer substantially equal to that induced in the first layer, thereby reducing to substantially zero the net current induced by stray flux in the two layers.
  • third and fourth layers will likewise enclose areas of substantially the same size, differing only by the very slight amount resulting from the presence of the third layer beneath the fourth layer.
  • each layer of the secondary winding has relatively few turns. In one specific practical embodiment of the invention, each layer has over 400 turns on a core 3 inches in diameter. As a result, the conductor at each turn is disposed almost radially with respect to the center of the core, departing from a radius by less than one degree.
  • a current transformer for sensing the current through one of a plurality of closely adjacent high current buses comprising:
  • each odd numbered layer extending from one point on said core along substantially the entire core length to a second point on the core closely adjacent said first point
  • said secondary conductor comprising terminal portions respectively connected to the first and last of said layers at substantially said first point

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Transformers For Measuring Instruments (AREA)
  • Coils Or Transformers For Communication (AREA)
  • Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
US714605A 1968-03-20 1968-03-20 Current transformer having an accuracy unimpaired by stray flux from adjacent conductors Expired - Lifetime US3449703A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US71460568A 1968-03-20 1968-03-20

Publications (1)

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US3449703A true US3449703A (en) 1969-06-10

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US714605A Expired - Lifetime US3449703A (en) 1968-03-20 1968-03-20 Current transformer having an accuracy unimpaired by stray flux from adjacent conductors

Country Status (5)

Country Link
US (1) US3449703A (ko)
CH (1) CH486758A (ko)
DE (1) DE1913553A1 (ko)
FR (1) FR2004314A1 (ko)
GB (1) GB1231108A (ko)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3754223A (en) * 1970-01-21 1973-08-21 Yeda Res & Dev Intruder detection system
US3806798A (en) * 1973-01-29 1974-04-23 Balsbaugh Labor Inc Electrodeless conductivity measuring system
US3867657A (en) * 1974-03-29 1975-02-18 Westinghouse Electric Corp Generator having shielded current transformers positioned therein
USRE29019E (en) * 1969-01-22 1976-10-26 Yeda Research & Development Co. Ltd. Intruder detection system
EP0279596A1 (en) * 1987-02-19 1988-08-24 Westinghouse Electric Corporation Electromagnetic contactor with lightweight wide range current transducer with sintered powdered metal core
US4887029A (en) * 1988-03-18 1989-12-12 Westinghouse Electric Corp. Mutual inductance current transducer, method of making and electric energy meter incorporating same
US5225769A (en) * 1992-02-21 1993-07-06 Zmd Corporation Defibrillation discharge current sensor
US5301096A (en) * 1991-09-27 1994-04-05 Electric Power Research Institute Submersible contactless power delivery system
US5341083A (en) * 1991-09-27 1994-08-23 Electric Power Research Institute, Inc. Contactless battery charging system
US5615075A (en) * 1995-05-30 1997-03-25 General Electric Company AC/DC current sensor for a circuit breaker
EP0866338A1 (en) * 1997-03-17 1998-09-23 Fluke Corporation Coil for an AC current sensor
FR2783085A1 (fr) * 1998-09-09 2000-03-10 Alstom Technology Bobinage torique sans noyau magnetique comportant deux enroulements superposes
US6356180B1 (en) * 1997-01-28 2002-03-12 Toyo Denso Kabushiki Kaisha High-voltage generating transformer
WO2011010972A1 (en) * 2009-07-23 2011-01-27 Cemalettin Denizoglu Windind means for purpose of destroying external magnetic effects in low power current transformers
EP2597658A3 (en) * 2011-11-22 2017-12-06 ABB Schweiz AG Current transformer
US20210265110A1 (en) * 2018-07-02 2021-08-26 Fluke Corporation Current transformer

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2471034A1 (fr) * 1979-12-04 1981-06-12 Merlin Gerin Capteur d'intensite a support souple deformable et son procede de fabrication
FR2564594B1 (fr) * 1984-05-21 1986-09-12 Merlin Gerin Capteur de courant a noyau amagnetique
FR2712423B1 (fr) * 1993-11-08 1996-02-09 Gec Alsthom T & D Sa Bobine de Rogowski utilisable dans une installation électrique avec enveloppe métallique à la terre et procédé de fabrication d'une telle bobine.

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2241127A (en) * 1938-04-14 1941-05-06 Westinghouse Electric & Mfg Co Protective relay
US2975384A (en) * 1954-09-24 1961-03-14 Sprague Electric Co Toroidal inductor combinations
CH419329A (de) * 1964-04-06 1966-08-31 Siemens Ag Kombinierter Strom- und Spannungswandler
US3299384A (en) * 1964-07-01 1967-01-17 Ibm Wide-band transformer having neutralizing winding
US3353132A (en) * 1965-05-27 1967-11-14 Gen Electric Leakage flux suppressor windings for transformers

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2241127A (en) * 1938-04-14 1941-05-06 Westinghouse Electric & Mfg Co Protective relay
US2975384A (en) * 1954-09-24 1961-03-14 Sprague Electric Co Toroidal inductor combinations
CH419329A (de) * 1964-04-06 1966-08-31 Siemens Ag Kombinierter Strom- und Spannungswandler
US3299384A (en) * 1964-07-01 1967-01-17 Ibm Wide-band transformer having neutralizing winding
US3353132A (en) * 1965-05-27 1967-11-14 Gen Electric Leakage flux suppressor windings for transformers

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE29019E (en) * 1969-01-22 1976-10-26 Yeda Research & Development Co. Ltd. Intruder detection system
US3754223A (en) * 1970-01-21 1973-08-21 Yeda Res & Dev Intruder detection system
US3806798A (en) * 1973-01-29 1974-04-23 Balsbaugh Labor Inc Electrodeless conductivity measuring system
US3867657A (en) * 1974-03-29 1975-02-18 Westinghouse Electric Corp Generator having shielded current transformers positioned therein
DE2512369A1 (de) * 1974-03-29 1975-10-09 Westinghouse Electric Corp Elektromechanischer generator
EP0279596A1 (en) * 1987-02-19 1988-08-24 Westinghouse Electric Corporation Electromagnetic contactor with lightweight wide range current transducer with sintered powdered metal core
US4887029A (en) * 1988-03-18 1989-12-12 Westinghouse Electric Corp. Mutual inductance current transducer, method of making and electric energy meter incorporating same
US5341083A (en) * 1991-09-27 1994-08-23 Electric Power Research Institute, Inc. Contactless battery charging system
US5301096A (en) * 1991-09-27 1994-04-05 Electric Power Research Institute Submersible contactless power delivery system
US5225769A (en) * 1992-02-21 1993-07-06 Zmd Corporation Defibrillation discharge current sensor
WO1993017349A1 (en) * 1992-02-21 1993-09-02 Zmd Corporation Defibrillation discharge current sensor
US5615075A (en) * 1995-05-30 1997-03-25 General Electric Company AC/DC current sensor for a circuit breaker
US6356180B1 (en) * 1997-01-28 2002-03-12 Toyo Denso Kabushiki Kaisha High-voltage generating transformer
US6566994B1 (en) * 1997-03-17 2003-05-20 Fluke Corporation Coil for an AC current sensor
KR100317876B1 (ko) * 1997-03-17 2002-04-24 맥나이트 더글라스 쥐 교류전류센서용코일
EP0866338A1 (en) * 1997-03-17 1998-09-23 Fluke Corporation Coil for an AC current sensor
WO2000014551A1 (fr) * 1998-09-09 2000-03-16 Alstom France S.A. Bobinage torique sans noyau magnetique comportant deux enroulements superposes
FR2783085A1 (fr) * 1998-09-09 2000-03-10 Alstom Technology Bobinage torique sans noyau magnetique comportant deux enroulements superposes
WO2011010972A1 (en) * 2009-07-23 2011-01-27 Cemalettin Denizoglu Windind means for purpose of destroying external magnetic effects in low power current transformers
EP2597658A3 (en) * 2011-11-22 2017-12-06 ABB Schweiz AG Current transformer
US20210265110A1 (en) * 2018-07-02 2021-08-26 Fluke Corporation Current transformer

Also Published As

Publication number Publication date
CH486758A (de) 1970-02-28
DE1913553A1 (de) 1969-10-09
GB1231108A (ko) 1971-05-12
FR2004314A1 (fr) 1969-11-21

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