Inductor devices – With temperature modifier – Ventilating passages
Reexamination Certificate
2001-05-04
2003-05-13
Mai, Anh (Department: 2832)
Inductor devices
With temperature modifier
Ventilating passages
C336S173000, C336S177000, C336S182000, C428S544000, C428S546000, C148S400000, C148S304000, C148S306000, C420S121000
Reexamination Certificate
active
06563411
ABSTRACT:
FILED OF THE INVENTION
The invention concerns a current transformer for alternating current particularly mains alternating current with direct current components consisting of at least one transformer core with a primary winding and at least one secondary winding to which a burden resistor is connected in parallel and terminates a secondary circuit with low resistance.
BACKGROUND OF THE INVENTION
The power consumption of electrical instruments and apparatus in industrial and domestic use is measured by means of power meters. The oldest principle here utilized is that of the Ferraris wattmeter. The Ferraris wattmeter is based on measuring power through the rotation of a disk connected to a mechanical counter and driven by the current- or voltage-proportional fields of the respective field coils. In order to extend the capability of power meters, for instance for multiple tariff operation or remote control, use is made of electronic power meters in which current and voltage information is obtained by inductive current and voltage transformers. The output signals of these transformers are digitized, multiplied in-phase, integrated and stored. The result is an electrical dimension available for remote reading and other purposes.
On account of the frequently very high currents, that is currents in excess of 100A, the electronic power meters used for measuring power consumption in industrial applications operate indirectly. Special current transformers are connected in front of the current inputs so that only simple bipolar zero-symmetrical alternating currents have to be measured in the meter itself. The current transformers used for this purpose are designed with transformer cores made of highly permeable material. In order to obtain low errors in measurement over a small phase error, these transformers must be provided with very many secondary windings, that is typically more than 2500 secondary windings for 1 primary winding. These are unsuitable for use in domestic meters, which can also be installed in small industrial operations, because modern semiconductor circuits such as rectifier circuits or phase-angle circuits create current flows that are not zero-symmetrical and contain a direct current components This magnetically saturates the current transformer and thus falsifies the power reading.
Known current transformers for mapping such currents operate on the basis of open or mechanically applied air gaps and thus low-permeability magnetic circuits. Since, however, the noise immunity requirements of such current transformers must be very high in order to enable calibrated power measurement, these designs must be provided with costly shielding against external fields. This is demanding in terms of both material and assembly and hence is uneconomical for a wide range of domestic applications.
Another known possible concept is the use of current transformers with relatively impermeable transformer cores, that is transformer cores with permeability &mgr;=2000. Such permeability avoids saturation with small direct current components. A difficulty with these types of current transformers is the balance between the highest non-falsified transmittable effective value of the bipolar zero-symmetrical sine current to be measured and the highest non-falsified transmittable amplitude of a unipolar half-wave rectified sine current. The international standard IEC 1036 applicable in this case provides a ratio for these two dimensions of 1:1.
Achieving this ratio requires the lowest possible permeability. This however causes a high phase error between primary and secondary currents where a practical number of windings is used. As this must be compensated for in the power meter, it requires an appropriate electronic circuit.
In hitherto known current transformer designs the range of compensation is limited to a phase error of 5°. In practice this causes the highest transmittable effective value to be necessarily vastly oversized. Ratios occur of 3-4:1. This leads to very poor use of materials and thus to very high production costs.
In addition this phase error must be maintained with very high linearity over the entire current range to be transmitted in order to keep the cost of compensation as low as possible.
The goal of the present invention, therefore, is to present a current transformer for alternating current with direct current components of the type mentioned at the outset that provides high controllability for both alternating current and direct current components.
SUMMARY OF THE INVENTION
In addition it should provide a highly linear transmittance ratio for precise current measurement over a wide current range.
Moreover it should show high immunity against external magnetic fields without additional shielding precautions so that it can be used economically with simple means, particularly with low mass transformer cores and low winding turn counts, especially for measuring the power consumption of domestic electrical instruments and apparatus.
The goal is achieved according to the invention by means of a current transformer for alternating current with direct current components consisting of at least one transformer core with a primary winding and at least one secondary winding to which a burden resistor is connected in parallel and terminates a secondary circuit with low resistance, specially characterized in that:
1. the transformer core comprises a closed ring core with no air gap produced from a strip (strip ring core) made of an amorphous ferromagnetic alloy;
2. the amorphous ferromagnetic alloy has a magnetostriction value |&lgr;
s
|<0.5 ppm and a permeability &mgr;<1400; and
3. the alloy has a composition consisting essentially of the formula
Co
a
(Fe
1-x
Mn
x
)
b
Ni
c
X
d
Si
e
B
f
C
g
.
where X is at least one of the elements V, Nb, Ta, Cr, Mo, W, Ge and P, a-g are given in atomic % and whereby a, b, c, d, e, f, g and x satisfy the following conditions:
40≦a≦82; 2≦b≦10; 0≦c≦30; 0≦d≦5; 0≦e≦15; 7≦f≦26; 0≦g≦3;
with 15≦d+e+f+g≦30 and 0≦x<1.
These measures would produce a current transformer with excellent controllability for both alternating current and direct current components.
It would be further distinguished by a transmittance ratio with high linearity so as to ensure precise current measurement over a very wide current range. Moreover its design with no air gap would provide high immunity against external magnetic fields so that no additional shielding precautions would be necessary. The alloying system according to the invention would enable the achievement of very low mass transformer cores.
With a primary winding count of n
1
=1 current transformers can be produced with a secondary winding count of about 1500. Altogether according to the invention a current transformer can be produced at extremely low cost that tolerates direct current and is exceptionally suitable for the industrial and domestic applications mentioned at the outset
Particularly good current transformers can be produced through the use of amorphous ferromagnetic alloys having a magnetorestrictive value |&lgr;
s
|<0.1 ppm, and permeability &mgr;<1200 where the alloy has a composition consisting essentially of the formula
Co
a
(Fe
1-x
Mn
x
)
b
Ni
c
X
d
Si
e
B
f
C
g
.
where X is at least one of the elements V, Nb, Ta, Cr, Mo, W, Ge and P, a-g are given in atomic % and whereby a, b, c, d, e, f, g and x satisfy the following conditions:
50≦a≦75; 3≦b≦5; 20≦c≦25; 0≦d≦3; 2≦e≦12; 8≦f≦20; 0≦g≦3;
with 17≦d+e+f+g≦25 and x≦0.5.
The alloy systems mentioned above are characterized by linear, flat B-H loops up to a value of H=1 A/cm or greater. The alloy system according to the invention is practically free of magnetostriction. Magnetostriction is preferably suppressed by means of heat treatment whereby the actual saturation magnetostriction is obtained by fine adjustment of the iron and/or manganese content The saturation ma
Otte Detlef
Petzold Joerg
Kilpatrick & Stockton LLP
Mai Anh
Poker Jennifer A
Russell Dean W.
Vacuumschmelze GmbH
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