GB2132821A - Saturable transformer - Google Patents

Saturable transformer Download PDF

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Publication number
GB2132821A
GB2132821A GB08236776A GB8236776A GB2132821A GB 2132821 A GB2132821 A GB 2132821A GB 08236776 A GB08236776 A GB 08236776A GB 8236776 A GB8236776 A GB 8236776A GB 2132821 A GB2132821 A GB 2132821A
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United Kingdom
Prior art keywords
filament
transformer
core
winding
energisation
Prior art date
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Withdrawn
Application number
GB08236776A
Inventor
Peter Cross
Eric Barker
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ML Engineering Plymouth Ltd
Original Assignee
ML Engineering Plymouth Ltd
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Filing date
Publication date
Application filed by ML Engineering Plymouth Ltd filed Critical ML Engineering Plymouth Ltd
Priority to GB08236776A priority Critical patent/GB2132821A/en
Publication of GB2132821A publication Critical patent/GB2132821A/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F29/00—Variable transformers or inductances not covered by group H01F21/00
    • H01F29/14—Variable transformers or inductances not covered by group H01F21/00 with variable magnetic bias
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F29/00—Variable transformers or inductances not covered by group H01F21/00
    • H01F29/14—Variable transformers or inductances not covered by group H01F21/00 with variable magnetic bias
    • H01F2029/143—Variable transformers or inductances not covered by group H01F21/00 with variable magnetic bias with control winding for generating magnetic bias

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Circuit Arrangement For Electric Light Sources In General (AREA)

Abstract

A saturable transformer has first and second windings (16, 18) wound on first and second parts (17, 19) of a magnetic core. A control winding (15), also wound on the core, is energisable to bring about saturation of the second core part (19) whereby to destroy transformer action between the first and second windings (16, 18). The construction of the transformer is such that energisation of the control winding (15) does not cause saturation of the first core part (17); as a result, the impedance of the first winding (16) is not drastically reduced upon control winding energisation. The saturable transformer find application in apparatus for automatically bringing into operation a standby filament (21) of a multifilament lamp unit upon failure of the main lamp (20); in this application, the first and second windings (16, 18) are respectively connected to an a.c. energisation source (22) and to the standby filament (21), while the control winding (15) is arranged to be energised only for as long as current continues to flow through the main filament (20). <IMAGE>

Description

value. The saturable transformer can thus be used in the above-mentioned filament changeover apparatus with its first winding connected directly across the a.c. energisation source of the apparatus and its second winding connected to the auxiliary filament.
A third winding can be wound on said first core part to establish a transformer action between the first and third windings which remains intact upon energisation of the control winding. This third winding could be used in the above-mentioned filament changeover apparatus for energising the main lamp filament thereby dispensing with the need for a separate main-filament transformer where one is required.
Preferably, the core of the saturable transformer of the present invention comprises a closed-loop outer member and a T-shaped inner member located within the outer member and connected thereto by its leg, the arms of the T-shaped member terminating short of opposite respective sides of the outer member. The control winding is wound on the leg of the T-shaped inner member. The said second core part carrying the second winding is constituted by the portion of the outer member which extends from opposite the end of one arm of the T-shaped member, to opposite the end of the other arm, past the base of the leg of this member; the first core part is constituted by the remaining portion of the outer core member.
Various other novel aspects and features of the invention will become apparent from the following description, given by way of example, of a saturable transformer and filament changeover apparatus incorporating the transformer, reference being made to the accompanying diagrammatic drawings, in which; Figure 1 is a diagrammatic representation of a saturable transformer embodying the invention; Figure 2 is a circuit diagram of a first form of filament changeover apparatus employing the Figure 1 transformer; and Figure 3 is a circuit diagram of a second form of filament changeover apparatus employing the Figure 1 transformer wound with a further winding.
The saturable transformer shown in Figure 1 comprises a core made up of an outer, closed-loop member 10 of rectangular form, and a T-shaped inner member 11 located within the outer member 10 to which it is connected by its leg 12. The two arms 13 of the T-shaped member 11 terminate short of opposite respective sides of the outer member 10, the ends of the arms 13 being spaced from the member 10 by air gaps 14 of predetermined width.
Typical dimensions for the core shown in Figure 1 are as follows: Core Thickness - 27 mm Outer Member 10: Overall Width -108 mm Overall Height-128mm Individual Width of top, bottom and sides; - 18 mm T-Shaped Member 10: Leg Height - 30 mm Vertical Width of arms - 19.5 mm SPECIFICATION Saturable transformer The present invention relates to a saturable transformer and, in particular, but not exclusively, to lampfilament changeover apparatus incorporating such a transformer.
Our co-pending U.K. patent Application No. 81.
35861 filed 27th November, 1982 describes the use of a saturable transformer in automatic filamentchangeover apparatus, this apparatus being arranged to bring into operation a standby, auxiliary filament of a multi-filament lamp installation upon failure of the main lamp filament. In the arrangement of the apparatus shown in Figure 3 of the aforesaid application, the primary and secondary of a saturable transformer are respectively connected to an a.c. energisation source and the auxiliary filament. A control winding of the saturable transformer is so arranged that when d.c. energised, the transformer core saturates, thereby destroying transformer action between the primary and secondary. During operation of the apparatus, while the main filament remains intact the control winding is energised thereby ensuring that the auxiliary filament is extinguished.However, upon main filament failure, the control winding is de-energised thereby allowing transformer action to take place between the primary and secondary of the saturable transformer; as a result, the auxiliary filament is brought into operation.
A characteristic of the saturable transformer described in our aforesaid co-pending Application is that d.c. energisation of the control winding results in the impedance of the transformer primary dropping to a very low value due to the saturation of the core around which the primary is wound.
As a consequence, the direct connection of the transformer primary across the a.c. energisation source is highly undesirable since it would result in a large current being drawn, to no useful purpose, while the main filament remains intact. Accordingly, various arrangements are described in our copending Application whereby the transformer primary current can be restricted during normal operation of the main filament. Such current-restricting arrangements, while workable, add substantially to the overall cost of the filament changeover apparatus. It is therefore an object of the present invention to provide a form of saturable transformer which would obviate the need for such current-restricting arrangements.
According to one aspect of the present invention, there is provided a saturable transformer comprising a core, first and second windings respectively wound on first and second parts of the core, and a control winding wound on the core and energisable to saturate said second part of the core while leaving the first core part unsaturated.
Saturation of the second core part collapses transformer action between the first and second windings; however, since the first core part carrying the first winding remains unsaturated, the impedance of this latter winding does not drop to a low Gap 14: - 0.5 mm A control winding 15 is wound on the leg 12 of the T-shaped core member 11.
Atwo-part primary winding 16 is wound on that portion 17 of the core member 10 which extends from adjacent one air gap 14 to adjacent the other air gap 14 via the part of the core member 10 furthest from the leg 12 of the T-shaped core member 11; this portion of the core member 10 will hereinafter be referred to a the first core portion 17.
Atwo-part secondary winding 18 is wound on the portion 19 of the core member 10 which extends from adjacent one air gap 14 to adjacent the other air gap 14 past the base of the leg of the T-shaped member 11; this core portion will be hereinafter referred to as the second core portion 19.
With the control winding 15 de-energised, the transformer exhibits normal transformer action between the primary winding 16 and the secondary winding 18 with a.c. fluxes being primarily established around the outer core member 17. However, this transformer action can be collapsed by d.c.
energising the control winding 15 to saturate the said second portion 19 of the core member 10, the d.c. flux passing from the leg 12, via the arms 13 and air gaps 14, into the second core portion 19 from where it returns into the leg 12.
Although the second core portion 19 can be saturated by d.c. energisation of the winding 15, the first core portion 17 carrying the primary winding 16 is not saturated byenergisation of the winding 15 and a.c. fluxes set up by the primary winding 15 will circulated round the core portion 17 and through the arms 13 (these latter being dimensioned such that they are not saturated upon d.c. energisation of the winding 15). As a result, the inductive reactance of the primary winding 16 does not decrease dramatically upon d.c. energisation of the winding 15, as would be the case if the first core portion 17 were to become saturated.
In summary, the saturable transformer shown in Figure 1 enables transformer action between primary and secondary windings to be selectively collapsed by energisation of a control winding 15, the inductive impedance of the primary winding remaining high even when the transformer action is collapsed.
A copper slug 29 ca be provided around the leg 12 to inhibit the passage of a.c. fluxes through this leg.
Figure 2 illustrates the use of the Figure 1 transformew in automatic filament changeover apparatus arranged to bring into operation a standby auxiliary filament 21 of a multi-filament lamp installation upon the failure of the main lamp filament 20.
During normal operation of the installation, the main lamp filament 20 is selectively energised by an a.c. energisation source (not shown) via terminals 22 and a step-down transformer23).
The filament changeover apparatus comprises a current transformer 24, a rectifier bridge 25 connected on its a.c. side to the output of the current transformer 24 and on its d.c. side to a smoothing capacitor 27, and a saturable transformer of the Figure 1 form. The primary of the current transformer 24 is connected in series with the main filament 20. The primary and secondary windings 16 and 18 of the saturable transformer are respectively connected to the terminals 22 and to the auxiliary filament 21. The control winding 15 of the transformer is connected across the d.c. output side of the rectifier bridge 25.
So long as the main filament 20 remains intact, a.c.
energisation of the terminals 22 will result in energisation of the filament 20 via the transformer 23.
During such energisation ofthe main filament 20, the current flowing through the transformer 24 results in a d.c. potential appearing across the d.c.
side of the bridge 25, the magnitude of this potential being such that the consequential d.c. energisation of the control winding 15 is sufficient to saturate the transformer core portion 19 carrying the secondary winding 18. As a result, there is no transformer action established between the primary and secon dary windings 16 and 18 so that the auxiliary filament 21 is de-energised (and remains so as long as the main filament 20 is intact).
Upon failure of the main filament 20, current flow through the transformer 24 ceases so that the control winding 15 becomes de-energised. As a result, transformer action between the primary and secondary winding 16 and 18 is established and the auxiliary filament 21 is automatically energised.
From what has already been said in relation to Figure 1, it will be appreciated that during normal energisation of the main filament 20, even though part of the core of the saturable transformer is held in saturation, the primary winding 16 has substantial inductive impedance due to the fact that the associated core portion 17 is not saturated.
The second form of filament changeover apparatus shown in Figure 3 is similar to that of Figure 2 except that the main filament transformer 23 has been replaced by a second secondary winding 26 wound on the first core portion 17 of the saturable transformer. Since the core portion 17 remains unsaturated regardless of the state of energisation of the control winding 15, transformer action between the primary winding 16 and the secondary winding 26 will exist even when the core portion 19 is saturated. The operation of the Figure 3 apparatus upon failure of the main filament is the same as that described above for the Figure 2 apparatus.
Clearly the Figure 3 apparatus is advantageous over that shown in Figure 2 since it requires only one transformer rather than two.
Various modifications to the form of saturable transformer described with reference to Figure 1 are, of course, possible. Thus, the shape of the core members 10 and 11 can be varied from that shown, the core member 10 being, for instance, annular in form.
CLAIMS (Filed on 11 April 1983) 1. A saturable transformer comprising a core, first and second windings respectively wound on first and second parts of the core, and a control winding wound on the core and energisable to saturate said second part of the core while leaving the
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. Gap 14: - 0.5 mm A control winding 15 is wound on the leg 12 of the T-shaped core member 11. Atwo-part primary winding 16 is wound on that portion 17 of the core member 10 which extends from adjacent one air gap 14 to adjacent the other air gap 14 via the part of the core member 10 furthest from the leg 12 of the T-shaped core member 11; this portion of the core member 10 will hereinafter be referred to a the first core portion 17. Atwo-part secondary winding 18 is wound on the portion 19 of the core member 10 which extends from adjacent one air gap 14 to adjacent the other air gap 14 past the base of the leg of the T-shaped member 11; this core portion will be hereinafter referred to as the second core portion 19. With the control winding 15 de-energised, the transformer exhibits normal transformer action between the primary winding 16 and the secondary winding 18 with a.c. fluxes being primarily established around the outer core member 17. However, this transformer action can be collapsed by d.c. energising the control winding 15 to saturate the said second portion 19 of the core member 10, the d.c. flux passing from the leg 12, via the arms 13 and air gaps 14, into the second core portion 19 from where it returns into the leg 12. Although the second core portion 19 can be saturated by d.c. energisation of the winding 15, the first core portion 17 carrying the primary winding 16 is not saturated byenergisation of the winding 15 and a.c. fluxes set up by the primary winding 15 will circulated round the core portion 17 and through the arms 13 (these latter being dimensioned such that they are not saturated upon d.c. energisation of the winding 15). As a result, the inductive reactance of the primary winding 16 does not decrease dramatically upon d.c. energisation of the winding 15, as would be the case if the first core portion 17 were to become saturated. In summary, the saturable transformer shown in Figure 1 enables transformer action between primary and secondary windings to be selectively collapsed by energisation of a control winding 15, the inductive impedance of the primary winding remaining high even when the transformer action is collapsed. A copper slug 29 ca be provided around the leg 12 to inhibit the passage of a.c. fluxes through this leg. Figure 2 illustrates the use of the Figure 1 transformew in automatic filament changeover apparatus arranged to bring into operation a standby auxiliary filament 21 of a multi-filament lamp installation upon the failure of the main lamp filament 20. During normal operation of the installation, the main lamp filament 20 is selectively energised by an a.c. energisation source (not shown) via terminals 22 and a step-down transformer23). The filament changeover apparatus comprises a current transformer 24, a rectifier bridge 25 connected on its a.c. side to the output of the current transformer 24 and on its d.c. side to a smoothing capacitor 27, and a saturable transformer of the Figure 1 form. The primary of the current transformer 24 is connected in series with the main filament 20. The primary and secondary windings 16 and 18 of the saturable transformer are respectively connected to the terminals 22 and to the auxiliary filament 21. The control winding 15 of the transformer is connected across the d.c. output side of the rectifier bridge 25. So long as the main filament 20 remains intact, a.c. energisation of the terminals 22 will result in energisation of the filament 20 via the transformer 23. During such energisation ofthe main filament 20, the current flowing through the transformer 24 results in a d.c. potential appearing across the d.c. side of the bridge 25, the magnitude of this potential being such that the consequential d.c. energisation of the control winding 15 is sufficient to saturate the transformer core portion 19 carrying the secondary winding 18. As a result, there is no transformer action established between the primary and secon dary windings 16 and 18 so that the auxiliary filament 21 is de-energised (and remains so as long as the main filament 20 is intact). Upon failure of the main filament 20, current flow through the transformer 24 ceases so that the control winding 15 becomes de-energised. As a result, transformer action between the primary and secondary winding 16 and 18 is established and the auxiliary filament 21 is automatically energised. From what has already been said in relation to Figure 1, it will be appreciated that during normal energisation of the main filament 20, even though part of the core of the saturable transformer is held in saturation, the primary winding 16 has substantial inductive impedance due to the fact that the associated core portion 17 is not saturated. The second form of filament changeover apparatus shown in Figure 3 is similar to that of Figure 2 except that the main filament transformer 23 has been replaced by a second secondary winding 26 wound on the first core portion 17 of the saturable transformer. Since the core portion 17 remains unsaturated regardless of the state of energisation of the control winding 15, transformer action between the primary winding 16 and the secondary winding 26 will exist even when the core portion 19 is saturated. The operation of the Figure 3 apparatus upon failure of the main filament is the same as that described above for the Figure 2 apparatus. Clearly the Figure 3 apparatus is advantageous over that shown in Figure 2 since it requires only one transformer rather than two. Various modifications to the form of saturable transformer described with reference to Figure 1 are, of course, possible. Thus, the shape of the core members 10 and 11 can be varied from that shown, the core member 10 being, for instance, annular in form. CLAIMS (Filed on 11 April 1983)
1. A saturable transformer comprising a core, first and second windings respectively wound on first and second parts of the core, and a control winding wound on the core and energisable to saturate said second part of the core while leaving the
first core part unsaturated.
2. A saturable transformer according to Claim 1, wherein the core of the transformer comprises a closed-loop outer member and a T-shaped inner member located within the outer member, the T-shaped inner member being connected by its leg to the outer member and the arms of the inner member terminating short of opposite respective sides of the outer member; the control winding being wound on the leg of the inner member, the said second core part carrying the second winding being constituted by the portion of the outer mem bey which extends from opposite the end of one arm of the T-shaped inner member, to opposite the end of the other arm, past the base of the leg of this member, and the first core part being constituted by the remaining portion of the outer core member.
3. A saturable transformer according to Claim lor Claim 2, wherein a third winding is wound on said first core part to establish a transformer action between the first and third windings which remains intact upon energisation of the control winding.
4. Apparatus for automatically bringing into operation a standby auxiliary filament of a multifilament lamp unit upon the failure of the main lamp-unit filament, said apparatus comprising: - a saturable transformer according to any one of the preceding claims, the said first and second wingings being respectively arranged for connection across an a.c. filament-energisation source and for connection to the said auxiliary filament, and - saturation control means responsive to current flow through the said main filament, to supply a direct current to the control winding of the saturable winding whereby to cause saturation of the said second core part during normal operation of the main filament.
5. In a multi-filament lamp installation, filamentchangeover apparatus for automatically bringing into operation a standby auxiliary lamp filament upon failure of a main lamp filament of the installation, said apparatus comprising: - a saturable transformer according to Claim 3, the said first, second and third windings of the transformer being respectively connected to an a.c. energy sation source of the installation, to the said auxiliary lamp filament, an to the said main lamp filament, and - saturation control means, responsive to current flow through the main filament, to cause a direct current to flow through the control winding of the saturable transformer of a magnitude sufficient to saturate the said second core part and thereby prevent energisation of the auxiliary filament during normal functioning of the main filament.
6. A saturable transformer substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.
7. Filament-changeover apparatus substantially as hereinbefore described with reference to Figure 2 or Figure 3 of the accompanying drawings.
GB08236776A 1982-12-24 1982-12-24 Saturable transformer Withdrawn GB2132821A (en)

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GB08236776A GB2132821A (en) 1982-12-24 1982-12-24 Saturable transformer

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GB08236776A GB2132821A (en) 1982-12-24 1982-12-24 Saturable transformer

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GB2132821A true GB2132821A (en) 1984-07-11

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2143434A (en) * 1983-07-01 1985-02-13 Oreal Hair-care composition and hair treatment process
GB2146492A (en) * 1983-07-14 1985-04-17 Blum Gmbh & Co E Controllable transformer
WO1994020332A1 (en) * 1993-03-01 1994-09-15 Tunewell Technology Limited An electrical arrangement
RU2641292C2 (en) * 2016-09-19 2018-01-17 Геннадий Леонидович Багич Method for improving efficiency of transformer operation
EP4102523A1 (en) * 2021-06-08 2022-12-14 Katholieke Universiteit Leuven, KU Leuven R&D Variable transformer

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1085526A (en) * 1964-02-07 1967-10-04 Ass Elect Ind Improvements relating to controlled transformers

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1085526A (en) * 1964-02-07 1967-10-04 Ass Elect Ind Improvements relating to controlled transformers

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2143434A (en) * 1983-07-01 1985-02-13 Oreal Hair-care composition and hair treatment process
GB2146492A (en) * 1983-07-14 1985-04-17 Blum Gmbh & Co E Controllable transformer
WO1994020332A1 (en) * 1993-03-01 1994-09-15 Tunewell Technology Limited An electrical arrangement
US5465010A (en) * 1993-03-01 1995-11-07 Tunewell Technology Ltd. Electrical [arrangement] distribution system for vehicle
USRE36037E (en) * 1993-03-01 1999-01-12 Tunewell Technology Ltd. Electrical distribution system for vehicle
RU2641292C2 (en) * 2016-09-19 2018-01-17 Геннадий Леонидович Багич Method for improving efficiency of transformer operation
EP4102523A1 (en) * 2021-06-08 2022-12-14 Katholieke Universiteit Leuven, KU Leuven R&D Variable transformer

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