DE102019213154B4 - circuit breaker - Google Patents

Abstract

Circuit breaker for interrupting an electrical low-voltage circuit when current and/or current-time limit values are exceeded, with an energy converter (CT), the primary side (PS) of which has a conductor section of the low-voltage circuit and, on the secondary side, a power supply for at least one control unit (ETU) of the circuit breaker makes available,wherein a choke (L) is connected between the secondary-side output of the energy converter (CT) and the control unit (ETU) of the circuit breaker, characterized in that the energy converter (CT) and the choke (L) are arranged in a housing (GEH). are, wherein the choke (L) is at least partially surrounded by a metal sheet (BL) made of soft magnetic material.

Description

The invention relates to a circuit breaker for interrupting an electrical low-voltage circuit when current and/or current-time limit values are exceeded, with an energy converter, the primary side of which has a conductor section of the low-voltage circuit and the secondary side provides an energy supply for at least one control unit of the circuit breaker, wherein a choke is connected between the secondary-side output of the energy converter and the control unit of the circuit breaker.

Circuit breakers are protective devices that work in a similar way to a fuse. Circuit breakers monitor the current flowing through them by means of a conductor and interrupt the flow of electricity or energy to an energy sink or load, which is referred to as a trip, when protection parameters such as current limits or current time limit values, i.e. when a current value for a certain period of time present, are exceeded. The interruption occurs, for example, through contacts of the circuit breaker that are opened.

In particular for low-voltage circuits or networks, there are different types of circuit breakers depending on the magnitude of the electrical current provided in the electrical circuit. Circuit breakers in the context of the invention mean in particular switches such as are used in low-voltage systems for currents of 63 to 6300 amperes. More specifically, closed circuit breakers are used for currents from 63 to 1600 amperes, in particular from 125 to 630 or 1200 amperes. Air circuit breakers are used in particular for currents from 630 to 6300 amperes, more specifically from 1200 to 6300 amperes.

Open circuit breakers are also referred to as air circuit breakers, ACB for short, and closed circuit breakers as molded case circuit breakers, or compact circuit breakers, MCCB for short.

Low voltage means voltages up to 1000 volts AC or 1500 volts DC. Low voltage also means voltages that are greater than extra-low voltage with values of 50 volts AC or 120 volts DC.

Circuit breakers in the context of the invention mean in particular circuit breakers with a control unit, such as an electronic tripping unit, also referred to as an electronic trip unit, ETU for short. The control unit monitors the magnitude of the electrical current measured by sensors such as Rogowski coils or, in an analogous manner, the voltage and/or other parameters of the electrical circuit and causes the electrical circuit to be interrupted if threshold values are exceeded. Electrical energy, which is provided by an energy converter, for example a transformer, is required to operate the control unit. This is connected to the electrical circuit to be protected on the primary side and to the control unit on the secondary side.

If the current flow is too "high", circuit breakers interrupt the circuit according to their protection parameters or response values. The protection parameters or response values are essentially the magnitude of the current and/or the magnitude of the current and the time after which the circuit should be interrupted if the current flow is constantly “high”. In contrast to a fuse, these protection parameters or response values can be set in a circuit breaker, for example by means of the control unit, such as an electronic tripping unit.

The energy converters are used for the so-called internal energy supply of circuit breakers. They are based on the principle of magnetically coupled power transmission, which provides energy for the control unit, such as an electronic trip unit.

In this case, a conductor section or conductor of the electrical circuit often forms the primary side or primary coil of the energy converter, which is also referred to as the primary conductor section or primary conductor. As a rule, the phase conductor of the circuit is used as the conductor section, for example in a single-phase circuit with phase and neutral conductor or in a three-phase AC circuit with three phase conductors and, if necessary, neutral conductor. I.e. a conductor section (or conductor) is the primary coil of the energy converter.

Circuit breakers of the type mentioned are known, for example, from the following patent applications: DE 10 2014 217 292 A1 ; DE 10 2014 217 332 A1 ; DE 10 2015 217 108 A1 ; DE 10 2014 218 831 A1 ; DE 10 2014 218 910 A1 ; DE 10 2016 201 651 A1 ; DE 10 2015 226 475 A1 ; DE 10 2015 216 981 A1 ; DE 10 2016 202 827 A1 ; DE 10 2016 201 659 A1 ; DE 10 2015 210 479 A1 ; DE 10 2014 224 173 A1 ; DE 10 2015 216 023 A1 ; DE 10 2016 217 425 A1 ; DE 10 2016 205 196 A1 ; DE 10 2016 221 093 A1 ; DE 10 2017 211 900 A1 ; DE 10 2017 201 239 A1 ; DE 10 2017 205 003 A1 ; DE 10 2017 205 004 A1 ; DE 10 2017 212 477 A1 ; DE 10 2017 214 903 A1 ; DE 10 2017 214 907 A1 ; DE 10 2017 215 820 A1 .

A problem with these converters are high primary currents, which cause a correspondingly high secondary current (transformer principle). Such high primary currents can occur in particular with high load currents or short-circuit currents. As a result, the apparent power of the current transformer is exceeded. This puts the energy converter in the state of magnetic saturation.

The apparent power of a current transformer increases linearly with the primary current amplitude and the grid frequency. This results in a minimum primary current that is necessary to meet the secondary-side power requirements of the control unit or ETU. This minimum primary current is determined by the requirements of the application and this results in the magnetic dimensioning of the ferromagnetic core in the energy converter or current converter (in particular the choice of material as well as the magnetic core length and cross-section). Essentially, there is a minimum magnetic cross-section A for a magnetic working point B, which is derived from a necessary secondary voltage U at the mains frequency f. This is described by the well-known transformer equation: $$\text{u}=4.4*\text{N2*}\cdot \text{A*B*f}$$

The secondary current I2 results from the number of secondary turns N2 / the turns ratio N2 to the primary current I1, whereby the magnetizing current Iu required to generate the magnetic flux must be subtracted from the primary current. $$\text{I2}=\left(\text{I1}-\text{I}\mathrm{\mu }\right)/\text{N2}$$

The product of both secondary variables defines the apparent power of the current transformer. If this apparent power is less than the secondary power consumption, the magnetic core becomes saturated because the magnetic flux density is limited by the core material.

Above the minimum primary current, the apparent power increases, driven by the primary current amplitude. However, the power consumption of the electronics remains largely constant for all operating conditions and this results in the above-mentioned mismatch between the source (energy converter or current converter) and sink (control unit or ETU). The excess power is converted into heat in the input voltage regulator and/or in the secondary winding. This heat must be dissipated or critical self-heating occurs in the control unit and/or in the energy converter.

In order to avoid this effect, a choke has recently been connected between the energy converter and the control unit of the circuit breaker.

The apparent power of the energy converter or transformer is determined by the primary current. The energy converter or transformer works without a fixed phase relationship between current and voltage on the secondary side. It is therefore not absolutely necessary to draw active power. If you also add a reactance in series, the apparent power of the transformer can be compensated by the reactive power at this impedance. For this purpose, a choke is inserted between the energy converter and the control unit (ETU).

The current-limiting effect of the choke in the energy converter design is a consequence of the inductive reactance of the choke. The inductance of this choke depends largely on the permeability of the soft magnetic core. Magnetic saturation in the core of the choke must be avoided under normal operating conditions, as this would result in very low inductance.

If the choke is in the vicinity of a primary conductor, the choke is influenced by the magnetic field of the primary conductor. The primary magnetic field causes a bias in the reactor core, which limits the operating range of the reactor.

One possibility is therefore to arrange the choke at a greater spatial distance from the primary conductor. However, this results in an increased space requirement, especially since one energy converter is generally provided per conductor of the low-voltage circuit, at least for the phase conductors. Furthermore, there is a significantly higher cost of routing the cables between the energy converter and the choke or control unit, since the insulation resistance of this cable route has to be significantly increased, since very high voltage peaks can occur between the energy converter (current converter) and the choke.

The German Offenlegungsschrift DE 10 2014 214 752 A1 discloses an inductor, power supply apparatus and methods of voltage regulation. A choke coil is specified with an electrical working winding for conducting alternating current, an electrical auxiliary winding for conducting direct current and a coil core made of a soft magnetic material. Both the working winding and the auxiliary winding are each arranged around at least part of the coil core, and at least the auxiliary winding comprises a superconducting conductor material. Furthermore, a device for supply a power grid with electrical alternating current with such a choke coil, and a method for controlling an ac voltage by means of a choke coil according to the invention is specified.

The German Offenlegungsschrift DE 10 2016 224 013 A1 discloses a differential current sensor. This application relates to a residual current sensor for an electrical circuit, comprising: a soft-iron core with an air gap, the soft-iron core being wound with a first and a second coil, a reed switch arranged in the air-gap of the soft-iron core.

The object of the present invention is to improve a circuit breaker of the type mentioned at the outset, in particular to maintain the effect of the choke, especially if it is to be arranged in the vicinity of a primary conductor.

This object is achieved by a circuit breaker having the features of patent claim 1 or an energy and measurement converter for a circuit breaker having the features of patent claim 15.

In order to minimize the influence of the magnetic field, it is provided according to the invention that the choke is at least partially surrounded by a metal sheet made of soft-magnetic material. Soft-magnetic material means, in particular, material with a coercive field strength between 1 and 1000 A/m.

Advantageous configurations are specified in the dependent claims.

In order to minimize the influence of the magnetic field, in an advantageous embodiment the choke is protected by a shield made of soft-magnetic sheet metal.
This has the particular advantage that the magnetic field lines of the primary conductor are collected in this shield and guided around the choke, in addition to a simple design.

In an advantageous embodiment of the invention, the choke is encapsulated in a sheet metal housing made of soft magnetic material, ie completely surrounded.
This has the particular advantage of providing maximum shielding. In this configuration, the interior of the sheet metal housing is practically free from external magnetic fields and pre-magnetization is suppressed. However, this configuration is complex in terms of manufacturing technology.

In an advantageous embodiment of the invention, the throttle is surrounded or enclosed in a tube section or tube profile, for example with a rectangular or round cross-section, made of soft-magnetic material, such as soft-magnetic steel. In this embodiment, a residual magnetic field penetrates into the interior only at the two open ends of the tube. The field strength decreases with the penetration depth in the pipe.
This has the particular advantage that a design that is more practicable in terms of manufacturing technology is provided.

In an advantageous embodiment of the invention, the sheet metal wall of the tubular profile facing away from the primary conductor can be omitted. That is, the sheet of soft magnetic material is designed in a U-shape. In particular, that the base of the U-plate is arranged parallel or approximately parallel to the primary conductor section, ie the open side of the U-plate faces away from the primary conductor.
This results in a stronger penetration of the magnetic field from the open side into the space towards the choke. However, the residual field strength in the interior is reduced due to the greater distance between the open side and the primary conductor. This has the particular advantage that there is an even more practicable design in terms of production technology, since the throttle does not have to be introduced into a tube but only has to be surrounded and is also very space-saving. With this arrangement, the magnetic field strength in the interior of the magnetic U-plate can be reduced by 50%.

In an advantageous embodiment of the invention, the choke is arranged in particular lying to the conductor section (or primary conductor).
A horizontal arrangement means, in particular, an arrangement in which the area enclosed by the inductor core, in particular the area of greatest extent of the inductor core, is arranged parallel to the conductor section (primary conductor or current-carrying conductor track).
This has the particular advantage that the magnetic field enclosing the conductor section (primary conductor) acts homogeneously on the inductor core and the parasitic influence of the primary conductor field on the inductor is thus minimized.

In an advantageous embodiment of the invention, the choke has a magnetic powder core, in particular in a closed form.
This has the particular advantage that the permeability of the inductor core is reduced by the air gap distributed in the core material, so that the magnetic saturation of the core is shifted towards high secondary currents.

In an advantageous embodiment of the invention, the choke has a Sendust powder core on. Sendust is a soft magnetic metal powder for magnetic cores. In particular, the Sendust alloy typically consists of 85% iron, 9% silicon and 6% aluminum. The powder is sintered into magnetic cores for coils.
This has the particular advantage that high magnetic permeability, low magnetic losses and good temperature stability of the choke behavior can be achieved with Sendust cores.

In an advantageous embodiment of the invention, the powder core is a toroidal core; U-shaped or E-shaped half-core in double execution or with a final I-shaped connection core.
This has the particular advantage that the design can be optimally selected based on the available installation space in the device.

In an advantageous embodiment of the invention, the conductor section (primary conductor section) is surrounded by a transformer core, which in turn is wound with a secondary winding.
The transformer core can consist of a soft magnetic material. The transformer core can in particular be designed as a wound nanocrystalline core.
The transformer core can be approximately rectangular, the corners are often rounded. The secondary winding can be arranged on one long side of the rectangle. The choke is arranged approximately parallel to the conductor section or to the secondary winding. Advantageously, the choke can be arranged on the side of the secondary winding.
This has the particular advantage of short cable paths and an advantageous design with optimum properties. In particular, low magnetic core losses can be achieved at higher frequencies using nanocrystalline material.

A nanocrystalline core has in particular a residual flux density which is less than 30%, in particular less than 20%, of the saturation flux density. The coercive field strength should be less than 10 A/m, in particular less than 5 A/m. The nanocrystalline core can in particular have the elements Fe, Si, B, Nb and/or Cu.

In an advantageous embodiment of the invention, the conductor section (primary conductor section) is surrounded by a Rogowski coil, which is arranged in the housing.
The energy converter, in particular its transformer core, and the Rogowski coil can be arranged one above the other in the housing. For example with a tour.
This has the particular advantage that a compact combined energy and measurement converter is made possible for a circuit breaker.

According to the invention, a combined energy and measurement converter for a circuit breaker is also proposed.
It has a housing that can be slid onto a conductor section. The housing can be made of plastic. The conductor section forms the primary side of the energy converter. In the housing, the transformer core surrounds the conductor section.
The transformer core has the secondary winding. This can be arranged on one long side of an (approximately) rectangular transformer core. The secondary winding is connected in series with the choke, which is located near the secondary winding in the housing to allow for short cable runs. The choke is shielded by a soft-magnetic metal energy converter. The Rogowski coil is arranged in the housing parallel to the transformer core, for example made of nanocrystalline material. Further advantageous configurations mentioned above can be integrated.

All of the configurations, both in a dependent form related back to patent claim 1 and also related only to individual features or combinations of features of patent claims, bring about an improvement in a circuit breaker or an energy converter.

The characteristics, features and advantages of this invention described and the manner in which they are achieved will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawing.

• 1 ein erstes Schaltbild mit einer Drossel zur Erläuterung der Erfindung,
• 2 ein Simulationsbild mit einer erfindungsgemäß vollständig geschirmten Drossel,
• 3 ein Simulationsbild mit einer erfindungsgemäß u-förmig geschirmten Drossel,
• 4 ein kombinierter Energie- und Meßwandler für einen Leistungsschalter in einer ersten Ansicht,
• 5 ein kombinierter Energie- und Meßwandler für einen Leistungsschalter in einer zweiten Ansicht.

The drawing shows:

• 1 a first circuit diagram with a choke to explain the invention,
• 2 a simulation image with a choke that is completely shielded according to the invention,
• 3 a simulation image with a U-shaped shielded choke according to the invention,
• 4 a combined energy and measurement converter for a circuit breaker in a first view,
• 5 a combined energy and measuring transducer for a circuit breaker in a second view.

1 shows a first circuit diagram to explain the invention. An alternating current source AC serving as an energy source supplies an energy consumer Load serving as an energy sink. A (phase) conductor section or (phase) conductor of this circuit, for example a low-voltage three-phase alternating current circuit, forms the primary side PS of an energy converter CT, also known as Pri termed conductor section or primary conductor. In this case, the primary side PS, which has a primary coil or primary winding, can be configured by one or more turns of the conductor or conductor section. In a typical configuration, only the conductor section or conductor can be routed straight through or past a core KCT or transformer core KCT of the energy converter CT (number of turns equal to one or 0.5).
The core KCT of the energy converter CT also has a secondary side SW, which is formed by one or more turns of a secondary winding or coil.
The two connections of the secondary winding SW form the secondary-side output of the energy converter CT, which provides an energy supply for the two inputs of the at least one control unit ETU of the circuit breaker, which is not shown.
Each output is electrically connected to an input. A choke L is provided in at least one connection between the output and input, ie connected in series with the secondary winding SW.
The circuit may be a low voltage circuit.

2 shows a simulation image with a choke L that is completely shielded according to the invention. 2 shows a conductor section as a primary conductor PS, which is surrounded by a soft-magnetic transformer core KCT. In the example, the transformer core KCT is almost rectangular, the corners are rounded. The transformer core KCT has a secondary winding SW. The secondary winding can be arranged on a long side of the rectangular transformer core KCT as shown.
The choke L is offset (laterally) above the secondary winding SW.
The choke L is completely surrounded by a soft magnetic sheet BL. The soft magnetic sheet BL serves as shielding.
In 2 simulated magnetic field lines are also shown. These ends and begin at the soft-magnetic shielding plate BL of the choke L. In the interior formed by the closed soft-magnetic plate BL (sheet metal housing), in which the choke L is located, there is no magnetic field.

3 shows a figure according to 2 , with the difference that the sheet metal housing is replaced by a U-shaped sheet metal BL. The throttle L is surrounded by a U-shaped metal sheet BL.
The open side of the U faces away from the primary conductor PS, the transformer core KCT and the secondary winding SW. The base of the U faces these.
Inside the U there is only a residual magnetic field. This is based on the in 3 shown simulated magnetic field lines.

4 shows a housing GEH with a transformer core KCT, which is wound with a secondary winding SW. A throttle L is arranged in the housing, analogously to 2 or. 3 . The choke has a core or choke core. For example, a magnetic powder core or Sendust powder core. The core or dust core can be a toroidal core, as shown. The choke L is wound on the toroidal core. The throttle L is surrounded by a U-shaped plate BL.
The open side of the U faces away from the transformer core KCT and the secondary winding SW. The base of the U is oriented towards the transformer core KCT or the secondary winding SW.
The housing has an opening OF. The opening OF is provided for a conductor section or conductor of the low-voltage circuit. This forms the primary side/the primary conductor PS of the energy converter CT.
The transformer core KCT encloses the opening OF, housing material of the housing GEH being provided between the transformer core KCT and the primary conductor PS, which consists of non-conductive material, for example plastic such as polyethylene or PVC. The Rogowski coil RS, which is located in the housing GEH parallel under the transformer core KCT, is only indicated.

5 shows a representation according to 4 , in a plan view, of the in 4 illustrated combined energy and measurement converter for a circuit breaker.

The disclosed invention optimizes the design for the high primary short circuit current operating range.

The high magnetic field strength associated with the primary current leads to pre-magnetization in the choke that is located close by. This pre-magnetization reduces the storage effect of the choke and thus the working range of the design due to magnetic saturation effects in the soft magnetic core of the choke. The disturbing external magnetic flux within the choke can be guided around the choke by being guided in a soft-magnetic shield arranged surrounding it. In this way, the working range of the design is extended to the area of the highest short-circuit currents.

Claims (15)

Circuit breakers for interrupting an electrical low-voltage circuit when current and/or current-time limit values are exceeded, with an energy converter (CT), the primary side (PS) of which has a conductor section of the low-voltage circuit and, on the secondary side, provides a power supply for at least one control unit (ETU) of the circuit breaker, with between the secondary-side output of the energy converter (CT) and control unit (ETU) of the circuit breaker a choke (L) is connected, characterized in that the energy converter (CT) and the choke (L) are arranged in a housing (GEH), the choke (L) being at least partially surrounded by a metal sheet (BL) made of soft-magnetic material is. circuit breaker after Claim 1 , characterized in that the sheet metal (BL) made of soft magnetic material is designed as a shield which is arranged between the energy converter (CT) and the inductor (L). circuit breaker after Claim 1 , characterized in that the sheet metal (BL) of soft magnetic material completely surrounds the inductor (L). circuit breaker after Claim 1 , characterized in that the sheet metal (BL) made of soft magnetic material is designed as a tube section with a rectangular or round cross section, the throttle (L) being arranged inside the tube section. circuit breaker after Claim 1 , characterized in that the metal sheet (BL) made of soft magnetic material is U-shaped, in particular that the base of the U-shaped metal sheet is arranged parallel or approximately parallel to the conductor section. Circuit breaker according to one of the preceding patent claims, characterized in that the choke (L) is arranged lying to the conductor section. Circuit breaker according to one of the preceding patent claims, characterized in that the choke (L) has a magnetic powder core. Circuit breaker according to one of the preceding patent claims, characterized in that the choke (L) has a Sendust powder core. Circuit breaker according to any of the preceding Claims 7 or 8th , characterized in that the powder core is a toroidal core; U-shaped or E-shaped half-core in double execution or with a final I-shaped connecting core. Circuit breaker according to one of the preceding patent claims, characterized in that the conductor section is surrounded by a transformer core (KCT), which in turn has a secondary winding (SW) wound on it. circuit breaker after Claim 10 , characterized in that the transformer core (KCT) consists of a soft magnetic material, in particular a nanocrystalline material. circuit breaker after Claim 10 or 11 , characterized in that the transformer core (KCT) is approximately rectangular, that the secondary winding (SW) is arranged on a long side of the rectangle, that the choke (L) is arranged approximately parallel to the secondary winding (SW). circuit breaker after Claim 12 , characterized in that the choke (L) on the side of the secondary winding (SW) is arranged approximately in parallel. Circuit breaker according to one of the preceding patent claims, characterized in that the conductor section is surrounded by a Rogowski coil (RS) which is arranged in the housing (GEH), so that a combined energy and measurement converter is formed. Energy and measurement converter for a circuit breaker, with a housing (GEH) that can be slid onto a ladder section, the conductor section forms the primary side (PS) of the energy converter (CT), A transformer core (KCT) with a secondary winding (SW) surrounding the conductor section is arranged in the housing (GEH), a Rogowski coil (RS) surrounding the conductor section is arranged as a measuring transducer in the housing (GEH), A choke (L) is arranged in the housing (GEH), which is connected in series with the secondary winding and is shielded by a soft-magnetic sheet metal (BL).

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