EP0392204B1 - Use of a microcrystalline iron-based alloy as a magnetic material for a fault current-protective switch - Google Patents

Abstract

In magnetic core materials for fault current protective switches, a high constancy of the magnetic properties is required over the entire application temperature range from -25 DEG C to +80 DEG C. In the case of the known magnetic core materials with a high nickel content of the permalloy type, this requires a special additional anneal. This can be dispensed with if the magnetic core material used is an iron-based alloy with an iron content of more than 60 atomic %, more than 50% of whose structure consists of fine crystalline grains having a grain size of less than 100 nm and which has a saturation induction of more than 1.1 T and also a remanence ratio of less than 0.7. <IMAGE>

Description

The invention relates to the use of a fine crystalline iron base alloy as a magnetic core material for residual current circuit breakers.

Residual current circuit breakers (FI switches) have been used for many years to protect people and machines. An essential part of the RCDs is a soft magnetic core that acts as a residual current transformer. The tripping current for RCDs for machine protection is in the range of approximately 300 to 500 mA. In the case of RCDs for personal protection, however, the tripping current is only 30 mA. In the publication by Hilzinger and Boll "Soft Magnetic Crystalline and Amorphous Metals", Electronics, Issue 22, 1987, the requirements for the magnetic cores and the materials used for this are presented. In addition to the high maximum permeability or sufficient induction with small field strengths, the magnetic core materials must in particular have a low temperature dependence of the magnetic properties over the entire area of use. Essentially crystalline nickel-iron alloys with approx. 77% nickel (permalloy type) are used for 30 mA FI switches. The saturation of these materials is approximately 0.8 T. However, in order to achieve the required low temperature dependence of the magnetic properties of the materials, an additional, complex annealing treatment is required for the Permalloy alloys. This makes the manufacture of magnetic cores for RCDs complex and expensive. The requirement of Annealing treatment is discussed in more detail in the publication by Pfeifer and Boll in IEEE Transactions on Magnetics, Vol. MAG-5, No. 3, Sept. 1969, pages 365 to 370.

In addition to crystalline materials, amorphous materials for RCDs have also been proposed. Because of the required low magnetization field strength, only cobalt-rich alloys are suitable for 30 mA RCCBs whose saturation is in the range of 0.55 to 0.7 T. As explained in the previously mentioned publication by Boll and Hilzinger, however, when using the amorphous materials, problems arise with high requirements with regard to the temperature dependence.

The object of the invention is to provide a magnetic core material for RCCBs which, in addition to a high saturation induction, has a low temperature dependence of the magnetic properties.

The object is achieved by using an iron-based alloy with the features of claim 1.

Such fine-crystalline iron base alloys are known from EP-OS 271 657. These are in particular alloys which, in addition to iron, contain essentially 0.1 to 3 atom% of copper, 0.1 to 30 atom% of a further metal, such as Nb, W, Ta, Zr, Hf, Ti and Mo, have up to 30 atomic% Si and up to 25 atomic% B, the total content of B and Si being in the range from 5 to 30 atomic%. The iron can be partially replaced by cobalt and / or nickel. These materials are due their good magnetic high-frequency properties have been proposed for use in high-frequency transformers, chokes and magnetic heads. From EP-OS 299 498 a magnetic core made of a finely crystalline iron base alloy is known, which exhibits only slight changes in permeability over time. Magnetic cores with a remanence ratio of 0.3 and less or of 0.7 and more are used for the applications of the magnetic cores in chokes, filters and high-frequency transformers mentioned there. Furthermore, from a publication by Yoshizawa, Yamauchi, Yamane and Sugihara, Journal of Applied Physics, Vol. 64, Issue 10, 1988, pages 6047 to 6049, a magnetic core made of a fine-crystalline iron-based alloy for use in a choke coil is known. This publication also contains measurements of the temperature dependence of the saturation induction and the permeability for temperatures above freezing.

Surprisingly, it has now been found that fine-crystalline iron-based alloys have an extremely low dependence of the magnetic properties on the temperature, even at temperatures below freezing point down to the temperature of -25 ° C. which is of interest for use in residual current circuit breakers. A low temperature dependency of the magnetic properties above freezing point is not sufficient for use as a magnetic core material in residual current circuit breakers and, moreover, as is known from the materials previously used for residual current circuit breakers (see FIG. 4), there is no indication of a low temperature dependency at temperatures below freezing. As already explained in the publication by Pfeifer and Boll, nickel-iron alloys according to the prior art also show a lower permeability at higher temperatures, but a strong decrease at lower temperatures.

The fine-crystalline magnetic cores for RCCBs according to the invention have very good soft magnetic properties and a low temperature dependence of these properties. This is especially true for magnetic cores with a round hysteresis loop, i.e. H. with a remanence ratio of 0.4 and more and less than 0.7. The alloys are less expensive to manufacture, since an additional special annealing treatment to achieve the low temperature dependence of the magnetic properties is not necessary. The toroidal cores show a very good stability against pulse control as well as against small superimposed DC fields.

Fig. 1

die Abhängigkeit der Induktion von der Feldstärke für einen erfindungsgemäßen Magnetkern mit runder Hystereseschleife

Fig. 2

die Abhängigkeit der Induktion B̂ (50 Hz), des statischen und dynamischen Induktionshubes von der Feldstärke

Fig. 3

die Temperaturabhängigkeit der magnetischen Eigenschaften eines erfindungsgemäßen Magnetkerns mit runder Hystereseschleife

Fig. 4

die Temperaturabhängigkeit der magnetischen Eigenschaften eines Kerns nach dem Stand der Technik

Fig. 5

die Temperaturabhängigkeit der magnetischen Eigenschaften eines erfindungsgemäßen Kerns mit flacher Hystereseschleife.

The invention will now be explained in more detail with reference to the exemplary embodiments and the figures. Show it:

Fig. 1

the dependence of the induction on the field strength for a magnetic core according to the invention with a round hysteresis loop

Fig. 2

the dependence of the induction B̂ (50 Hz), the static and dynamic induction stroke on the field strength

Fig. 3

the temperature dependence of the magnetic properties of a magnetic core according to the invention with a round hysteresis loop

Fig. 4

the temperature dependence of the magnetic properties of a core according to the prior art

Fig. 5

the temperature dependence of the magnetic properties of a core according to the invention with a flat hysteresis loop.

Embodiments

Both toroidal tape cores with a flat and a round hysteresis loop were produced. In particular, materials with a remanence ratio in the range from 0.4 to 0.7 have proven to be advantageous for use in 30 mA RCDs. The fine crystalline ribbons were produced by crystallizing an originally amorphous ribbon using a single heat treatment step and then cooling at a cooling rate of more than 0.4 K / min.

The production processes for the fine crystalline strips are known in principle from the European published documents already mentioned. The grain size of the fine-crystalline grains was always less than 25 nm in all of the exemplary embodiments. In addition to an iron content of 73.5 atom%, the magnetic cores of the exemplary embodiments also had 1 atom% copper, 3 atom% niobium, 13.5 atom% silicon and 9 atomic percent boron. The finished toroidal cores had the dimensions ∅ 19 x ∅ 15 x 5 mm. The hysteresis loops and the magnetization curves of B̂ as well as the static induction stroke ΔB _stat and the dynamic induction stroke ΔB _dyn with sinusoidal, one-way and two-way rectified current at room temperature were measured on the toroidal cores. In addition, the temperature dependence of the static and dynamic induction stroke and the permeability µ ₄ at 50 Hz was determined.

Example 1:

Those magnetic cores in which the heat treatment was carried out without a magnetic field had a remanence ratio of 0.65 (round hysteresis loop). 1 shows the quasi-static hysteresis loop of these magnetic cores. Fig. 2 shows the relationship between B̂, ΔB _stat , ΔB _dyn and the magnetic field strength. The induction B̂ of the magnetic cores according to the invention with a round hysteresis loop already reaches a value of 0.5 T at a field strength of 10 mA / cm and is therefore above the values of magnetic materials for RCDs according to the prior art. The cores according to the invention also have high values for the static and dynamic induction stroke. 3 shows the temperature dependence of the magnetic properties of the magnetic cores according to the invention. They have a very high constancy with little fluctuations over the entire temperature range of -25 ° C to + 80 ° C that is of interest for practical use.

For comparison, the temperature dependence of the magnetic properties for an alloy according to the prior art is shown in FIG. 4. This is a high nickel alloy that is sold under the name ULTRAPERM F 80 for residual current circuit breakers. This alloy also has a very good constancy of the magnetic values for temperatures above freezing point. However, there are significant changes here for temperatures below freezing.

Example 2:

A remanence ratio of 0.1 (flat loop) was measured on magnetic cores in which the heat treatment was carried out in a transverse magnetic field. They also showed good constancy of the magnetic properties with temperature changes, as can be seen from FIG. 5. However, the changes were greater than for the round hysteresis loop cores.

Claims (3)

1. Use of an iron-based alloy having an iron content of more than 60 atom %, the structure of which consists to the extent of more than 50% of finely crystalline grains having a grain size of less than 100 nm and which has a saturation induction of more than 1.1 T, as well as a remanence ratio B_r/B_s of less than 0.7 and a temperature-dependent variation in the induction excursion at the working point of less than ±10% in the temperature range of -25 to +80°C relative to room temperature, as a magnetic core material for fault-current circuit breakers.
2. Use of an iron-based alloy according to Claim 1, the iron-based alloy being further characterized by a remanence ratio of 0.4 and above.
3. Use of an iron-based alloy according to Claim 1, the iron-based alloy being further characterized in that the finely crystalline grains have a grain size of less than 25 nm.

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