Inductor devices – Interlinked coils or windings – Coil surrounding linear conductor
Reexamination Certificate
2000-02-23
2001-11-06
Donovan, Lincoln (Department: 2832)
Inductor devices
Interlinked coils or windings
Coil surrounding linear conductor
C336S175000, C336S178000, C336S212000, C336S234000
Reexamination Certificate
active
06313727
ABSTRACT:
DESCRIPTION
The invention relates to a current transformer for three phase current systems and serves for the capturing of currents, for example, for three phase current meters or electronic trigger devices of low voltage circuit breakers.
PRIOR ART
On the one hand current converters are known as current transformers, wherein the main disadvantage of the current transformer comprises the saturation properties of the core material limiting precision and current ranges. On the other hand, ironless transformers (Rogowski-converters) are known, wherein the ironless transformers are suitable for a wide current region and require an integrating further processing of the current transformer signals. The use of toroid coils is a disadvantage in connection with ironless transformers, wherein the production and mounting of the torpid coils around the three phase conductors generally is associated with a high expenditure. For avoiding expensive round winding machines, a method for production of a current transformer formed of a Rogowski-coil and having a bendable non-magnetic winding support is proposed in the German printed patent document DE 42 29 678 A1. Accordingly a thermally deformable winding support is predeformed and is shifted onto a winding spindle formed as a straight line and is wound with the transformer coil. The hollow body returns into its anullar shape after pulling from the winding spindle. When using such coil in a three phase current system, the high technological care required for producing the current transformer and for mounting the current transformer is a disadvantage.
PRESENTATION OF THE INVENTION
Therefore, is an object of the invention to furnish a current transformer for three phase systems according to the Rogowski principle, where the current transformer can be produced and mounted easily and economically and which current transformer at the same time allows metering the sum current.
The object is accomplished according to the invention by the complete set of features of the independent claim, while advantageous embodiments of the invention can be gathered from the subclaims.
The support of the converter coils by soft magnetic yokes allow a simple and an uncomplicated production of the current transformer relative to the symmetry of the converter coils. On the one hand the measurement sensitivity of the current transformer is increased based on a bundling of the magnetic fields derived from the three phase current conductors and on the other hand the sensitivity to interference is decreased based on the shielding effect by the soft magnetic yokes. The magnetic effect of the yokes also balances dissymmetries between the transformer coils to a substantial degree. Since the sum current in a symmetric three phase systems is zero outside of a case of interference, the yokes to not reach even approximately the region of their magnetic saturation, wherefore the current transformer according to the present invention has to be considered operating according to the Rogowski principle. The conductor currents to be captured result in a conventional way from the difference or, respectively, the sum of the measurement voltages in each case of two transformer coils surrounding the corresponding three phase current conductor, depending on whether these converter coils are disposed relative to each other in the same or in an opposite winding sense. The current transformer is suitable for the capturing of the sum current of the three phase systems from the difference of the measurement voltages of the two outer converter coils to be integrated.
The yokes comprise ferrites or other suitable soft magnetic neck materials. Advantageously recesses are furnished in the yokes for supporting the converter coils.
Since the sum current normally is zero in a symmetrical three phase current system, according to an advantageous embodiment of the invention the magnetic circuit can be closed on two sides by cross yokes, which leads to a further increase of the shielding against magnetic interfering fields and to an improvement of the symmetry of the current converter. The yokes and cross yokes advantageously can be performed in two L-shaped or I-shaped, or, respectively, U-shaped parts but also as a complete unit.
According to an advantageous embodiment of the invention it is disclosed for a simplified mounting relative to so-called bushing transformers that one of the yokes is afterwards connectable to the remaining components of the current converter. The converter coils can be slipped without problem between the three phase current conductors thereby in order to complete thereafter the current transformer by connection with still missing soft magnetic parts.
A very stable further embodiment of the invention results by sideways disposed soft magnetic structures of the yokes in part covering the converter coils, wherein the embodiment is protected substantially against external mechanical as well as magnetic influences. The structures can start oppositely disposed or alternatingly disposed from the two yokes or only from one of the yokes while maintaining sufficient air gaps. An alternative further embodiment comprises the arrangement of soft magnetic webs framing the converter coils on the sides, where the soft magnetic webs are connected to the two yokes.
The invention is by no means limited to the described further embodiments and such embodiments, in particular combinations to be formed reasonably therefrom, shall be clearly included.
REFERENCES:
patent: 3575677 (1971-04-01), Fink
patent: 4258348 (1981-03-01), Belfer et al.
patent: 5424899 (1995-06-01), Scott et al.
patent: 5521572 (1996-05-01), Goodwin et al.
patent: 1079192 (1960-04-01), None
patent: 3707707 (1988-09-01), None
patent: 4229678 (1994-03-01), None
patent: 195 05 812 C2 (1995-02-01), None
patent: 0 758 749 A1 (1996-08-01), None
patent: 2027669 (1970-10-01), None
Donovan Lincoln
Kasper Horst M.
Moeller GmbH
Nguyen Tuyen
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