EP1710812B1 - Fault-current circuit breaker and magnetic core for a fault-current circuit breaker - Google Patents

Abstract

The breaker has a summation current transformer with a soft magnetic core (2) made of nano-crystalline iron base alloy and with differential windings (4, 5) attached on the core. A relay (3) is connected with a measuring coil (7) of the transformer. The magnetic core exhibits a maximum permeability of more than 350 and a remanence ratio of more than 0.7, where the alloy has a structure, which consists of fine crystalline grains.

Description

The invention relates to an AC-sensitive residual current circuit breaker with a summation current transformer having a soft magnetic magnetic core of a nanocrystalline iron-based alloy and applied to the magnetic core differential windings and a measuring winding, and with a measuring winding connected to the switching element. Furthermore, the invention relates to a magnetic core for an AC-sensitive residual current circuit breaker.

Residual current circuit breakers (RCCBs) have been used for many years for both machine protection and personal protection and have significantly increased electrical safety. While FI switches with tripping currents of 300 to 500 mA are used for machine protection, FI switches with significantly lower tripping currents of 30 mA are used for personal protection.

FI switches are designed as purely passive components, wherein a current from the supply network to a consumer via a first winding and the current from the load to the supply network via a second winding of a magnetic core is performed and the two windings are designed as differential windings. The magnetic core thus operates as a summation current transformer. In error-free normal operation, the total current is zero considering the sign and the magnetic core is not magnetized. In the event of a fault, the total current is different from zero, so that the magnetic core is magnetized and a voltage is induced in a measuring winding. By means of the induced voltage, a relay is triggered, which interrupts the circuit to the consumer.

The magnetization of the magnetic core generated by the tripping current must therefore be sufficient to enable the relay to trigger via the induced voltage in the measuring winding. Furthermore, however, is also a compact Construction required. Finally, the functionality must be ensured over a temperature range of usually -25 ° C to + 80 ° C. For the magnetic core thus raises the demand for a sufficiently high constancy of the magnetic properties. This results in high demands on the magnetic material of the magnetic core used.

From the EP 392 204 A1 It is known magnetic cores made of an iron-based alloy having an iron content of more than 60 atomic%, the structure of which consists of more than 50% of finely crystalline grains with a grain size of less than 100 nm and having a saturation induction of more than 1.1 T and a Remanence ratio Br / Bs of less than 0.7, to use in residual current circuit breakers. Preference is given to magnetic cores having a remanence ratio Br / Bs between 0.4 and 0.7, ie with a so-called "round" hysteresis loop. The remanence ratio indicates the ratio of remanence Br to saturation induction Bs. According to one embodiment, the magnetic cores have a permeability of less than 120,000.

Furthermore, the FI-switches are adapted to different fault current forms. Thus, a distinction is generally made between pulse-current-sensitive and AC-sensitive FI switches. While AC-sensitive RCCBs are commonly used in AC networks, pulse-current-sensitive RCCBs are designed to respond to unipolar fault currents.

Depending on the application, so different magnetic materials are used.

Magnetic cores with a flat hysteresis loop are used for pulse current sensitive FI switches. From the EP 0 563 606 A2 are current transformer for pulse current sensitive residual current circuit breaker known that have a remanence ratio Br / Bs of less than 0.3 and consist of a nanocrystalline iron-based alloy. Furthermore, the use of crystalline Permalloy alloys for this purpose is known.

For AC-sensitive residual current circuit breakers come almost exclusively toroidal cores made of crystalline Permalloy alloys with a nickel content between 45 and 80% for decades. At the operating point of the FI switch, which is characterized by the field strength caused by the predetermined tripping current, these have a permeability of up to 350,000, the remanence ratio being between 0.3 and 0.7.

These Permalloy magnetic cores are very well suited for use in AC-sensitive FI switches. However, a disadvantage is the high nickel content, since the price for Rohnickel has risen sharply recently. There is therefore a desire for cheaper alternatives.

The object of the invention is therefore to provide a magnetic core for use in AC-sensitive residual current circuit breakers, which is less expensive than the previously used Permalloy alloys, in particular no or only a small nickel content, and a replacement of Permalloy magnetic cores with little or no adjustments the residual current circuit breaker allowed. Another object is to specify a corresponding residual current circuit breaker.

The objects are achieved by an AC-sensitive residual current circuit breaker or a magnetic core having the features specified in the corresponding independent claims.

The FI switch has a summation current transformer, which contains a magnetically soft magnetic core of a nanocrystalline iron-based alloy. On the core differential windings and a measuring winding are applied in a known manner and the measuring winding is connected to a switching element. According to the invention, the magnetic core has a maximum permeability of more than 350,000 and a remanence ratio Br / Bs of more than 0.7.

It has been found that magnetic cores with a high remanence ratio of more than 0.7, which were previously not considered for use in residual current circuit breakers, in combination with a high permeability of more 350,000 are perfectly suited for use in AC-sensitive residual current circuit breakers and can replace the previously used Permalloy cores.

The magnetic cores according to the invention are also less expensive than highly nickel-containing Permalloy cores. However, due to the excellent magnet values, smaller and lighter magnetic cores can also be used than when using Permalloy alloys. Typically, a weight reduction of 40% can be achieved over permalloy cores.

The magnetic cores surpass those in the EP 0 392 204 A1 Cores proposed for use in FI switches in terms of permeability significantly and also have a higher remanence ratio. At the same time, the magnetic cores according to the invention fulfill the required low temperature dependence of the magnet values in the required temperature range of -25 ° C. to + 80 ° C.

The magnetic cores may in one embodiment have a permeability of greater than 400,000 and / or a remanence ratio greater than 0.8. These advantageous magnet values have a particularly favorable effect on the size of the cores used.

The magnetic properties of the magnetic cores and their temperature dependence are adjusted by a heat treatment under inert gas and magnetic field influence. Particular attention should be paid to the temperature and the duration of the heat treatment to adjust the nanocrystalline structure and the temperature of a subsequent heat treatment in the magnetic field. The heat treatment to adjust the nanocrystalline structure can be carried out at a temperature between 550 ° C and 620 ° C and for a period of, for example, 20 to 80 minutes. The subsequent heat treatment in a transverse magnetic field can be carried out at a temperature of 360 ° C to 400 ° C for a period of 20 to 150 minutes. Magnetic cores with a permeability of more than 600,000 can be realized. The appropriate parameters can be selected for each Alloy composition and core geometry can be determined experimentally with a few experiments.

The nanocrystalline iron-based alloys used have a structure which consists of more than 50% of fine-crystalline grains with a particle size of less than 100 nm. In addition to more than 60 at% iron, the alloy may contain 0.5 to 2 at% copper, 2 to 5 at% of at least one of the metals niobium, tungsten, tantalum, zirconium, hafnium, titanium and / or molybdenum, 5 to 14 at% boron and 14 to 17 at% silicon.

Magnetic core and winding turns of the winding can be coordinated so that with a predetermined fault current (trip current), which causes a triggering of the relay, a modulation of the magnetic core is achieved in which the permeability is more than 350,000, in particular more than 400,000. With a given fault current for triggering the relay of, for example, 30 mA is thus achieved by the dimensioning that in this operating point, the said magnet values are at least achieved and a safe triggering of the FI-switch is ensured.

If the magnetic core has a permeability maximum at a field strength between 5 and 15 mA / cm, then a permalloy core in a FI switch can be exchanged particularly easily for a core according to the invention, since a permalloy core in this field strength region also has a maximum permeability and therefore the preferred operating point of both cores is at comparable field strengths.

Fig. 1:

ein Schaltbild eines FI-Schalters

Fig. 2:

die Hysteresekurve eines erfindungsgemäßen Magnetkerns und eines Permalloy-Kerns nach dem Stand der Technik,

Fig. 3

die Abhängigkeit der Permeabilität von der Feldstärke für einen erfindungsgemäßen Magnetkern und einen Permalloy-Kern nach dem Stand der Technik,

Fig. 4

die Temperaturabhängigkeit der Ausgangsspannung eines FI-Schalters mit einem erfindungsgemäßen Mangetkern und mit einem Permalloy-Kern nach dem Stand der Technik

The invention will be described below with reference to an embodiment and the drawing. Show it:

Fig. 1:

a circuit diagram of a residual current circuit breaker

Fig. 2:

the hysteresis curve of a magnetic core according to the invention and a Permalloy core according to the prior art,

Fig. 3

the dependence of the permeability of the field strength for a magnetic core according to the invention and a Permalloy core according to the prior art,

Fig. 4

the temperature dependence of the output voltage of an FI-switch with a Mangetkern invention and with a Permalloy core according to the prior art

FIG. 1 shows a circuit diagram of a FI-switch 1. The FI-switch 1 contains as an essential element a wound magnetic core 2 and a relay 3 as a switching element. On the magnetic core 2, a first winding 4 and a second winding 5 are applied as differential windings. In each case a first end of the windings 4, 5 is connected to the conductors L1 and N of a power supply network. Furthermore, in each case a second end of the windings 4, 5 connected to a consumer 6. The consumer 6 is further connected to the grounding conductor PE.

Thus, a current flow takes place from the conductor L1 via the first winding 4 to the load 6 and from the load 6 via the second winding 5 to the conductor N. The currents flowing in the windings 4, 5 are equal in magnitude and the magnetic core 2 is due to the Forming the windings 4, 5 not controlled as differential windings. If an error occurs now, for example, as a person touches a current-carrying component of the consumer 6, the currents in the windings 4, 5 are of different sizes, since a partial current flows through the person. This has a remaining modulation and thus a magnetization of the magnetic core 2 result, whereby in a measuring winding 7 now a voltage is induced. Due to the induced voltage, a current is induced in the secondary circuit, which tripped the relay 3, and the circuit is interrupted to the load 6.

The triggering of the relay 3 must take place at a predetermined residual current of, for example, 30 mA for personal protection. A difference of 30 mA in the currents flowing through the windings 4, 5 must therefore result in a voltage induction in the measuring winding 7, which induces a current sufficient for triggering of the relay 3. By the According to the invention use of a magnetic core 2 of a nanocrystalline iron-based alloy with a permeability of more than 350,000 and a remanence ratio of more than 0.7, this requirement can be met with inexpensive magnetic cores and comparatively low material usage.

A magnetic core 2 according to the invention is produced from a thin strip of initially amorphous iron-based alloys as a ring strip core, the iron-based alloy containing, in addition to more than 60 at% iron, 0.5 to 2 at% copper, 2 to 5 at% of at least one of the metals niobium , Tungsten, tantalum, zirconium, hafnium, titanium and / or molybdenum, 5 to 14 at% boron and 14 to 17 at% silicon. The magnetic core is subjected to a heat treatment for adjusting the nanocrystalline structure, for example at a temperature of 580 ° C for a period of 30 minutes. Subsequently, a further heat treatment in a transverse magnetic field at, for example, 380 ° C for a period of also 30 minutes.

In Fig. 2 the dependence of the induction B of the field strength H is plotted in curve K1 for a magnetic core according to the invention with a remanence ratio Br / Bs of more than 0.7 and thus quasi Z-shaped loop and for a commercial Permalloy core with a round loop , About the ratio of remanence Br to saturation induction Bs is given a first distinguishing criterion of the cores according to the invention over previously used for FI switch cores.

In FIG. 3 the course of the permeability over the field strength H is plotted in curve K3 for the magnetic core according to the invention of a nanocrystalline iron-based alloy and in curve K4 for the commercially available Permalloy core. A comparison shows that the magnetic core according to the invention has a much higher permeability than the permalloy core. Consequently, with identical winding to achieve the same induction voltage in the measurement winding of the FI-switch by the fault current, a correspondingly smaller iron cross-section of the nanocrystalline magnetic core is sufficient.

It should also be noted that the maximum permeability for both cores occurs at approximately the same field strength. This simplifies the replacement of the permalloy core with a core according to the invention. A resizing is not necessary in principle, but nevertheless advisable because of the possible material savings.

In FIG. 4 is plotted with the temperature dependence of the measured output voltage on the measuring winding 7 of another important parameter for FI-switches and in curve K5 for a FI-switch with the nanocrystalline magnetic core according to the invention and in curve K6 for the Permalloy core. Both cores show sufficient constancy of the output voltage within the required temperature range of -25 ° C to + 80 ° C.

It can be seen from the exemplary embodiment that magnet cores made of a nanocrystalline iron-based alloy and the specified magnetic properties can be advantageously used in AC-sensitive FI switches and can replace the permalloy cores used for this purpose without problems directly for decades. In particular, a significant weight, volume and cost reduction can be achieved.

Claims (10)

1. Residual current device which is sensitive to alternating current and has a summation current transformer which contains a soft-magnetic magnet core (2) composed of a nanocrystalline iron-based alloy as well as differential windings (4, 5), which are fitted to the magnet core (2), and a measurement winding (7), and having a switching element (3) which is connected to the measurement winding (7), characterized in that the magnet core (2) has a maximum permeability of more than 350 000, and a remanence ratio Br/Bs of more than 0.7.
2. Residual current device according to Claim 1, characterized in that the magnet core has a maximum permeability of more than 400 000.
3. Residual current device according to one of the preceding claims, characterized in that the magnet core (2) has a remanence ratio Br/Bs of more than 0.8.
4. Residual current device according to one of the preceding claims, characterized in that the nanocrystalline iron-based alloy has a structure, more than 50% of which is composed of fine-crystalline grains with a grain size of less than 100 nm, and in addition to having more than 60% by atomic weight of iron, the iron-based alloy also has 0.5 to 2% by atomic weight of copper, 2 to 5% by atomic weight of at least one of the metals niobium, tungsten, tantalum, zirconium, hafnium, titanium and/or molybdenum, 5 to 14% by atomic weight of boron, and 14 to 17% by atomic weight of silicon.
5. Residual current device according to one of the preceding claims, characterized in that a predetermined tripping current results in a drive for the magnet core (2) for which the permeability is more than 350 000, in particular more than 400 000.
6. Residual current device according to one of the preceding claims, characterized in that the magnet core (2) has a maximum permeability at a field strength of between 5 and 15 mA/cm.
7. Magnet core for a summation current transformer for a residual current device (1) which is sensitive to alternating current, with the magnet core (2) being composed of a nanocrystalline iron-based alloy, and with the magnet core (2) having a maximum permeability of more than 350 000 and a remanence ratio Br/Bs of more than 0.7.
8. Magnet core according to Claim 7, characterized in that the magnet core (2) has a maximum permeability of more than 400 000.
9. Magnet core according to Claim 7 or 8, characterized in that the magnet core (2) has a remanence ratio of more than 0.8.
10. Magnet core according to one of Claims 7 to 9, characterized in that the nanocrystalline iron-based alloy has a structure, more than 50% of which is composed of fine-crystalline grains with a grain size of less than 100 nm, and in addition to having more than 60% by atomic weight of iron, the iron-based alloy also has 0.5 to 2% by atomic weight of copper, 2 to 5% by atomic weight of at least one of the metals niobium, tungsten, tantalum, zirconium, hafnium, titanium and/or molybdenum, 5 to 14% by atomic weight of boron, and 14 to 17% by atomic weight of silicon.

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