EP0864165B1 - Leistungstransformator hoher isolation - Google Patents

Leistungstransformator hoher isolation Download PDF

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Publication number
EP0864165B1
EP0864165B1 EP96940047A EP96940047A EP0864165B1 EP 0864165 B1 EP0864165 B1 EP 0864165B1 EP 96940047 A EP96940047 A EP 96940047A EP 96940047 A EP96940047 A EP 96940047A EP 0864165 B1 EP0864165 B1 EP 0864165B1
Authority
EP
European Patent Office
Prior art keywords
coupling
core
power transformer
windings
winding
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
EP96940047A
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English (en)
French (fr)
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EP0864165A1 (de
Inventor
John Robert Pickering
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.)
Metron Designs Ltd
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Metron Designs Ltd
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Publication date
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Publication of EP0864165A1 publication Critical patent/EP0864165A1/de
Application granted granted Critical
Publication of EP0864165B1 publication Critical patent/EP0864165B1/de
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
    • H01F30/00—Fixed transformers not covered by group H01F19/00
    • H01F30/06—Fixed transformers not covered by group H01F19/00 characterised by the structure
    • H01F30/16—Toroidal transformers
    • 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
    • H01F27/346—Preventing or reducing leakage fields
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F19/00—Fixed transformers or mutual inductances of the signal type
    • H01F19/04—Transformers or mutual inductances suitable for handling frequencies considerably beyond the audio range
    • H01F19/08—Transformers having magnetic bias, e.g. for handling pulses
    • H01F2019/085—Transformer for galvanic isolation

Definitions

  • This invention concerns the design of power transformers to facilitate the construction of isolated power supplies that exhibit very low AC leakage currents between the primary and secondary sides.
  • Power Transformer is intended to mean a transformer utilised to transfer power in a power supply circuit. In particular it operates with primary and secondary voltages on its windings, normally greater than 1 Volt. This statement is intended to distinguish the application from that of Current Transformers which are used for measurement purposes and are intended to operate with very low winding voltages. Power supplies are used in many applications and are usually concerned with the conversion of voltage from an input level such as mains voltage or a DC voltage such as 12 Volts commonly present in motor vehicles to an output level required to operate the circuits or equipment to be powered.
  • a power transformer in accordance with the invention will normally comprise primary and secondary windings having different numbers of turns to provide a step up or step down of voltage.
  • the output of a power supply is required to be electrically isolated from the input for safety or other reasons related to measurement and these types incorporate a transformer, commonly referred to as the power transformer, to provide both the necessary voltage and current conversion and the isolation.
  • a plurality of outputs is required where each is isolated from the other and the invention is easily extended to this application.
  • a power transformer is known, see Canadian Patent No.982667, that comprises at least two independent magnetic paths provided by relatively high permeability magnetic cores each of which is surrounded by one or more windings individual to that core, and at least one coupling winding comprising one or more turns forming a closed circuit that encloses at least two of said magnetic paths.
  • the coupling winding is of variable impedance and is intended to enable variation of the output voltage of the transformer.
  • Other forms of transformer are also known that comprise such a coupling winding, but,in general, these are either not power transformers or are not intended for applications where electrostatic screening is a prime consideration.
  • the invention accordingly provides a power transformer of the known kind referred to characterised in that each said core together with the winding or windings individual thereto is enclosed by an electrostatic screen that is in turn enclosed by the or each coupling winding that encloses the respective magnetic path.
  • each core can thus be separately screened with an almost totally enclosing layer of conductive or slightly resistive material.
  • the slightly resistive material of say 0.1 to 500 Ohms per square has the advantage that it does not significantly increase losses when it constitutes what is generally known as a "shorted turn" whereas highly conductive materials such as metal foils need to have a gap or insulated overlap which generally lessens screening efficiency.
  • the separate wound and screened cores are magnetically coupled to provide transformer action by the coupling winding. This arrangement allows almost ideal electrostatic screens to enclose each winding and the windings to be separated by a far greater distance than if they were both on one similarly sized core. Using this method of transformer construction reduction of leakage currents to a few picoamperes is possible in line frequency transformers (50Hz-60Hz) and to a few nanoamperes in transformers used in switching supplies operating at 3kHz or above.
  • Figure 1 is a cross sectional drawing of a power transformer in accordance with a preferred embodiment of the invention.
  • Fig. 2 is a schematic representation of two conventional screened power transformers connected in series.
  • Fig. 3 is a schematic representation of an arrangement in accordance with the invention.
  • Fig. 4 is a schematic representation of three conventional power transformers connected in series, and
  • Fig 5 is a schematic representation of a further arrangement in accordance with the invention.
  • FIG 3 there is shown diagrammatically an arrangement according to one embodiment of the invention.
  • This resembles the schematic of figure 2 but differs in that the coupling winding is a single or multiplicity of conductive turns or paths that are closed around two or more separate magnetic cores as symbolically indicated. Since this winding encloses both magnetic cores and is a short circuit, that is its start is electrically connected to its finish, it tends to force the magnetic field in the secondary core to counterbalance that in the primary core such that the no load current in the coupling winding is minimised.
  • a primary winding is around one core and covered with an enclosing electrostatic screen and driven by a voltage that causes an alternating magnetic field to be present in that core then the coupling winding will cause an opposing field in the secondary core which will induce a voltage in the secondary winding.
  • the coupling winding is closed and encloses the vector sum of the flux in the two cores which approximates to zero and therefore has no net voltage induced regardless of the number of turns, which means that minimal currents flow into the primary or secondary screens or windings due to voltages induced in the coupling winding electrostatically coupling through the capacitance between coupling winding and either of the screens.
  • the turns ratio is simply the ratio of the number of turns of the primary to the number of turns of the secondary regardless of the number in the coupling winding.
  • FIG. 1 of the drawings there is shown a cross section depicting a practical construction of a power transformer embodying this principle of construction. It utilises two independent toroidal cores 7,8 of the type commonly used in transformer manufacturing. Each core is surrounded by one or more windings 1,4 in the manner well known to those versed in the art of transformer or inductor manufacture and each is further enclosed by a conductive or resistive electrostatic screen as previously described. Henceforth we will refer to core 7 as the primary core carrying the primary windings 1 and screen 2 and core 8 as the secondary core carrying the secondary windings 4 and screen 5.
  • the object of the construction is to provide near normal transformer behaviour between primary connections 9 and secondary connections 12 with minimal electrostatic coupling of the primary and secondary voltages to each other or of the primary voltage to secondary screen 5 or secondary voltage to primary screen 2.
  • Insulation 3 is placed on top of the windings 1,4 and conductive screens 2,5 placed on top of the insulation 3.
  • Each screen can be resistive in the range 0.1 to 500 Ohms per square as previously described or of very low resistivity material such as Copper but it will then need to be broken around its circumference and ideally overlapped with intervening insulation such that it does not constitute a shorted turn.
  • An example of a resistive screen may be a material such as conductive paint that has sufficiently high resistance to be a negligible load on the transformer when it encloses the core to give a shorted turn around the single core, but sufficiently low to be an effective electrostatic screen.
  • a connection 10,11 is made to each screen and can be brought out for connection to an external circuit as shown or can be connected internally to a point on a winding. Normally another layer of insulation 3 is placed over the screens 2,5 to protect them.
  • the two wound, screened cores are then stacked, as shown in Fig. 1, with insulation 3 between them. This can be fairly thick to minimise the capacitance between the screens of the two cores.
  • a coupling winding 6 is then wound around the two stacked cores, as if they were a single core as shown in Fig. 1, and the end of the coupling winding is connected to its start regardless of the number of turns.
  • the current in the coupling winding is inversely proportional to the number of turns and so its resistivity should be chosen to minimise losses caused by that current dissipating power in the resistance of the coupling winding.
  • the coupling winding may be of the type having an insulating coating or sleeve, preferably of a very high voltage breakdown and low dielectric constant material such as Polytetrafluorethylene (PTFE or "Teflon”) or Polyethylene.
  • PTFE Polytetrafluorethylene
  • Teflon Polytetrafluorethylene
  • FIG. 5 shows the schematic of such an arrangement utilising the invention whereas Figure 4 shows an inferior arrangement which uses an additional transformer in known manner. The latter arrangement has a higher voltage induced in the intermediate windings for a similar number of turns which then leads to additional electrostatically coupled current flow between primary and secondary.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Coils Of Transformers For General Uses (AREA)
  • Transformers For Measuring Instruments (AREA)
  • Regulation Of General Use Transformers (AREA)

Claims (7)

  1. Leistungstransformator zur Leistungskopplung, mit mindestens zwei unabhängigen Kraftlinienwegen, die von zwei Magnetkernen (7, 8) mit relativ hoher Permeabilität bereitgestellt werden, die jeweils von einer oder mehreren Wicklungen (1, 4) umgeben sind, die dem jeweiligen Kern individuell zugeordnet ist bzw. sind, sowie mindestens einer Kopplungswicklung (6), die eine oder mehrere Windungen aufweist, die einen geschlossenen Kreis bilden, der mindestens zwei der Kraftlinienwege umschließt, dadurch gekennzeichnet, dass jeder Magnetkern (7, 8) zusammen mit der bzw. den ihm zugeordneten Wicklung(en) (1, 4) von einer elektrostatischen Abschirmung (5) umschlossen ist, die wiederum von der bzw. jeder Kopplungswicklung (6) umschlossen ist, welche den jeweiligen Kraftlinienweg umschließt.
  2. Leistungstransformator gemäß Anspruch 1, wobei die Kerne (7, 8) als ringförmige Kerne ausgebildet sind.
  3. Leistungstransformator, der eine Abwandlung des Transformators gemäß Anspruch 1 oder 2 bildet, wobei die oder jede Kopplungswicklung (6) durch zwei Kopplungswicklungen und einen zusätzlichen Magnetkern (Fig. 5) ersetzt ist, so dass einer oder mehrere der Kraftlinienwege und der zusätzliche Kern von einer der beiden Kopplungswicklungen umschlossen sind und der zusätzliche Kern und ein weiterer oder mehrere weitere der Kraftlinienwege von der zweiten Kopplungswicklung umschlossen sind.
  4. Leistungstransformator gemäß einem der Ansprüche 1 bis 3, wobei die elektrostatischen Abschirmungen (5) aus einem widerstandbehafteten Material mit einem spezifischen Widerstand von 0,1 bis 500 Ohm pro Quadrat gebildet sind.
  5. Leistungstransformator gemäß Anspruch 4, wobei das widerstandsbehaftete Material einen leitenden Anstrich aufweist.
  6. Leistungstransformator gemäß Anspruch 4, wobei das widerstandsbehaftete Material ein synthetisches Kunststoffmaterial aufweist.
  7. Leistungstransformator gemäß Anspruch 4, wobei das widerstandsbehaftete Material ein geformtes synthetisches Kunststoffmaterial aufweist.
EP96940047A 1995-12-01 1996-12-02 Leistungstransformator hoher isolation Expired - Lifetime EP0864165B1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9524566A GB2307795A (en) 1995-12-01 1995-12-01 Isolation transformer with plural magnetic circuits coupled by a winding
GB9524566 1995-12-01
PCT/GB1996/002976 WO1997021233A1 (en) 1995-12-01 1996-12-02 High isolation power transformer

Publications (2)

Publication Number Publication Date
EP0864165A1 EP0864165A1 (de) 1998-09-16
EP0864165B1 true EP0864165B1 (de) 2000-08-02

Family

ID=10784743

Family Applications (1)

Application Number Title Priority Date Filing Date
EP96940047A Expired - Lifetime EP0864165B1 (de) 1995-12-01 1996-12-02 Leistungstransformator hoher isolation

Country Status (4)

Country Link
EP (1) EP0864165B1 (de)
DE (1) DE69609625T2 (de)
GB (1) GB2307795A (de)
WO (1) WO1997021233A1 (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103035389A (zh) * 2013-01-16 2013-04-10 成都市亚丰电子技术有限责任公司 一种行波管环形变压器及其制作方法
US9711271B2 (en) 2012-11-16 2017-07-18 Phoenix Contact Gmbh & Co. Kg Planar transformer

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10138375C2 (de) * 2001-08-11 2003-08-21 Kurt Buehner Demodulator
EP1659413B1 (de) * 2004-11-23 2011-04-06 Liaisons Electroniques-Mecaniques Lem S.A. Trenntransformator
ATE550670T1 (de) 2008-07-11 2012-04-15 Lem Liaisons Electron Mec Sensor für eine hochspannungsumgebung
FR3134223A1 (fr) * 2022-03-31 2023-10-06 Safran Electrical & Power Transformateur de puissance à forte isolation galvanique

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4412957A1 (de) * 1994-04-17 1995-10-19 Schwan Ulrich Übertragungseinrichtung

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE848368C (de) * 1943-02-04 1952-09-04 Felten & Guilleaume Carlswerk UEbertrager
US3264592A (en) * 1962-05-07 1966-08-02 Paul A Pearson High voltage transformer
DE2529296A1 (de) * 1975-07-01 1977-01-20 Ferranti Ltd Impuls-transformator
US4338951A (en) * 1980-08-19 1982-07-13 Critikon, Inc. Magnetically coupled isolation interface circuit
AU3537589A (en) * 1988-04-28 1989-11-24 Fmtt, Inc. Matrix transformer having high dielectric isolation
GB9111535D0 (en) * 1991-05-29 1991-07-17 Measurement Tech Ltd Improvements in or relating to transformers

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4412957A1 (de) * 1994-04-17 1995-10-19 Schwan Ulrich Übertragungseinrichtung

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9711271B2 (en) 2012-11-16 2017-07-18 Phoenix Contact Gmbh & Co. Kg Planar transformer
CN103035389A (zh) * 2013-01-16 2013-04-10 成都市亚丰电子技术有限责任公司 一种行波管环形变压器及其制作方法

Also Published As

Publication number Publication date
GB9524566D0 (en) 1996-01-31
EP0864165A1 (de) 1998-09-16
GB2307795A (en) 1997-06-04
WO1997021233A1 (en) 1997-06-12
DE69609625T2 (de) 2001-04-12
DE69609625D1 (de) 2000-09-07

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