POWER SWITCH

Description

[0001] The invention relates to a circuit breaker according to the preamble of claim 1.

[0002] Circuit breakers are protective devices or switching devices that function similarly to a fuse. They monitor the current flowing through them via a conductor and interrupt the electrical current or energy flow to a power sink or consumer. This interruption, known as tripping, occurs when protective parameters, such as current limits or current-time limits (i.e., when a certain current value is present for a specific period), are exceeded. The interruption is achieved, for example, by the circuit breaker's contacts opening.

[0003] Especially for low-voltage circuits or networks, there are various types of circuit breakers depending on the intended current in the circuit. Circuit breakers as defined in the invention refer specifically to those used in low-voltage installations for currents from 63 to 6300 amperes. More specifically, enclosed circuit breakers are used for currents from 63 to 1600 amperes, particularly from 125 to 630 or 1200 amperes. Open circuit breakers are used particularly for currents from 630 to 6300 amperes, and more specifically from 1200 to 6300 amperes.

[0004] Open circuit breakers are also known as Air Circuit Breakers, or ACBs for short, and closed circuit breakers as Moulded Case Circuit Breakers or Compact Circuit Breakers, or MCCBs for short.

[0005] Low voltage refers specifically to voltages up to 1000 volts AC or 1500 volts DC. It also includes voltages higher than extra-low voltage, defined as 50 volts AC or 120 volts DC.

[0006] For the purposes of this invention, "circuit breaker" refers in particular to circuit breakers with a control unit, such as an electronic trip unit (ETU). The control unit monitors the magnitude of the electric current measured by sensors, such as Rogowski coils, and, analogously, the voltage and / or other parameters of the electrical circuit, and interrupts the circuit. Electrical energy is required to operate the control unit, which is supplied by an energy converter, for example, a transformer. This transformer is connected on its primary side to the electrical circuit to be protected and on its secondary side to the control unit.

[0007] In the event of excessively high current flow, circuit breakers interrupt the circuit according to their protection parameters or response values. These protection parameters or response values ​​essentially define the current level and / or the current level and time after which the circuit should be interrupted if the current flow remains high. Unlike a fuse, these protection parameters or response values ​​are adjustable in a circuit breaker, for example, via a control unit such as an electronic trip unit.

[0008] Circuit breakers according to the prior art 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.

[0009] The energy converters serve as the so-called self-power supply for circuit breakers. They are based on the principle of magnetically coupled power transfer, which provides energy for the control unit, such as an electronic trip unit.

[0010] In this case, a conductor from the electrical circuit often forms the primary side of the energy converter. For example, the electrical conductor is the primary coil of the energy converter.

[0011] A problem with these converters is the high and low primary currents, which result in correspondingly high or low secondary currents (transformer principle). High primary currents can occur particularly with high load currents or short-circuit currents.

[0012] The control unit requires a certain minimum amount of energy to operate. To provide this energy, a certain current (input current threshold) is required in the AC circuit of such an energy converter. This means that the energy requirement of the control unit determines the minimum required current in the AC circuit. Therefore, the circuit breaker can only provide protection (according to its implemented functionalities) at or above this minimum required current (input current threshold).

[0013] Reducing the input current threshold at which the circuit breaker can provide protection is of great importance. The input current threshold (lowest current threshold) can be lowered by increasing the size of the energy transformer (current transformer). However, in compact devices like circuit breakers, this possibility is limited by space constraints.

[0014] On the other hand, the circuit breaker must also function reliably at high currents. In particular, the problem is that energy converters, which already supply sufficient energy at low currents, deliver too much energy to the control unit at high currents, which can impair its function.

[0015] Therefore, designing a power supply for the control units of a circuit breaker is not a trivial problem.

[0016] The apparent power of a current transformer increases linearly with the primary current amplitude and the mains frequency. This results in a minimum primary current required to meet the secondary-side power requirements of the control unit or ETU. This minimum primary current (input current threshold) is determined by the application requirements and dictates the magnetic dimensioning of the ferromagnetic core in the energy or current transformer (in particular, the material selection as well as the magnetic core length and cross-section). Essentially, this results in a minimum magnetic cross-section A for a magnetic operating point B, which is derived from a required secondary voltage U at the mains frequency f.

[0017] Above the minimum primary current, the apparent power increases due to the primary current amplitude. However, the power consumption of the control unit remains largely constant under all operating conditions, leading to a problem. The excess power is converted into heat in the input voltage regulator and / or the secondary winding. This heat must be dissipated, or critical self-heating will occur in the control unit and / or the energy converter.

[0018] International publication WO 98 / 13917 describes a power supply for electronic trip devices. This relates to a circuit arrangement for supplying power to electronic trip devices, in particular overcurrent releases for low- and medium-voltage applications. The current transformer assembly includes a voltage transformer (SPW) for supplying the trip devices with a second auxiliary voltage (UH2) when currents are absent or relatively low, and a current transformer (STW) for supplying the trip devices with a first auxiliary voltage (UH1) when currents are very high. A second voltage regulator (SR2) for generating the second auxiliary voltage (UH2) is connected downstream of the voltage transformer (SPW), and both auxiliary voltages (UH1, UH2) are fed to a common auxiliary voltage (UH) terminal via a diode decoupling device (DE).Such circuit arrangements are used to supply voltage to overcurrent releases in low and medium voltage technology.

[0019] U.S. Patent 3,526,812 describes a power supply for providing tripping energy to a circuit breaker connected in an electrical circuit. It consists of a capacitor charged by a unidirectional pulsating current, which is drawn from the circuit via a current transformer and rectifier. A low-impedance path is created through the secondary winding of the current transformer by a Zener diode-controlled short-circuit thyristor when the instantaneous voltage across the capacitor reaches a predetermined value, thus blocking a further increase in the capacitor voltage until the next half-cycle of the pulsating current.

[0020] German patent application DE 10 2019 213 154 A1 describes a circuit breaker for interrupting a low-voltage electrical circuit when current conductor and current-time interval limits are exceeded, comprising an energy converter (CT) whose primary side (PS) comprises a conductor section of the low-voltage circuit and whose secondary side provides a power supply for at least one control unit (ETU) of the circuit breaker, wherein an inductor (L) is connected between the secondary-side output of the energy converter (CT) and the control unit (ETU) of the circuit breaker. The energy converter (CT) and the inductor (L) are arranged in a housing (GEH), wherein the inductor (L) is at least partially surrounded by a sheet (BL) made of soft magnetic material.

[0021] German patent application DE 10 2006 022 223 A1 describes a component and system. The component and system comprise a protection module with a rectifier designed for charging a capacitor, to which a discharge resistor is connected in parallel.

[0022] The object of the present invention is to improve a circuit breaker of the type mentioned above, in particular to provide a power supply which, on the one hand, provides sufficient energy at low currents in the alternating current circuit and, on the other hand, operates safely at high currents in the alternating current circuit.

[0023] This problem is solved for a circuit breaker starting from the preamble of claim 1 by the characterizing features of claim 1.

[0024] According to the invention, a first and a second rectifier circuit are connected in parallel to the secondary output of the energy converter. The first rectifier circuit is connected to the secondary output of the energy converter via a capacitor. The second rectifier circuit is connected directly.

[0025] This has the particular advantage that the first rectifier circuit is optimally matched to the energy converter by the capacitor, thus supplying sufficient energy for the control unit or the loads of the power switch at low currents. At high currents, the first rectifier circuit is no longer optimally matched by the capacitor, resulting in low energy output.

[0026] Here, the second rectifier circuit takes over the power supply. According to the invention, the rectifier circuits are connected in parallel on the output side (to provide the power supply for the at least one control unit of the circuit breaker).

[0027] Further advantageous embodiments are specified in the dependent claims.

[0028] In an advantageous embodiment of the invention, a conductor of the electrical circuit forms the primary side of the energy converter.

[0029] This has the particular advantage of allowing for a simple setup.

[0030] In an advantageous embodiment of the invention, the capacitor forms a series resonant circuit with the inductance of the secondary side of the energy converter.

[0031] This has the particular advantage that maximum energy supply is ensured, thus achieving the minimum possible currents in the alternating current circuit for a safe energy supply.

[0032] In an advantageous embodiment of the invention, the capacitor is dimensioned such that its capacitive reactance at the operating frequency of the AC circuit is equal to the inductive reactance of the inductor, wherein the inductive reactance is set to a value that occurs for currents in the AC circuit up to a first current level. That is, the capacitive reactance cancels out the inductive reactance at the operating frequency (e.g., 50 Hz), and their magnitudes are equal. This has the particular advantage of ensuring optimal or maximum energy supply and thus achieving the minimum possible or defined currents in the AC circuit for a reliable power supply.

[0033] In an advantageous embodiment of the invention, the capacitor or series resonant circuit is designed such that, for currents up to the first current level, the energy delivered by the energy converter is essentially delivered to the control unit via the first rectifier circuit.

[0034] In a further advantageous embodiment of the invention, for currents above the first current level, the energy delivered by the energy converter is essentially delivered to the control unit via the second rectifier circuit.

[0035] This has the particular advantage that an optimal energy supply is ensured at both low and high currents.

[0036] In an advantageous embodiment of the invention, an overvoltage protection element is connected in parallel to the secondary-side output of the energy converter.

[0037] This has the particular advantage of limiting voltage spikes for currents above normal operating conditions.

[0038] In an advantageous embodiment of the invention, the first or (and) second rectifier circuit is a full-wave bridge rectifier circuit (also called a Graetz bridge).

[0039] This has the particular advantage of providing a particularly good rectification efficiency and trouble-free parallel connection of the outputs.

[0040] All embodiments, both in dependent form with reference to claim 1 and with reference only to individual features or combinations of features of claims, result in an improvement of a circuit breaker.

[0041] The described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawing.

[0042] The drawing shows: Figure 1 a schematic diagram of a circuit breaker, Figure 2 a circuit diagram for explanation, Figure 3 an equivalent circuit diagram of a secondary winding Figure 4 a circuit diagram of an embodiment according to the invention, Figure 5 a diagram of a bra curve, Figure 6 A further circuit diagram to explain the invention.

[0043] Figure 1 shows a representation of a basic circuit diagram of an exemplary circuit breaker. Figure 1Figure 1 schematically shows a low-voltage circuit breaker LS, with different units of the circuit breaker shown in a housing GEH. Figure 1 The diagram shows the electrical conductors L1, L2, L3 of a low-voltage circuit, for example, a three-phase AC circuit, where the first conductor L1 represents the first phase, the second conductor L2 the second phase, and the third conductor L3 the third phase of the three-phase AC circuit. A neutral conductor and a protective earth conductor may also be included.

[0044] In the example according to Figure 1The third conductor L3 is connected to an energy converter EW such that at least a portion of the current, i.e., a partial conductor current, or the entire current of the third conductor flows through the primary side of the energy converter EW. The energy converter EW is typically a core-type transformer, e.g., an iron-core transformer. In one embodiment, an energy converter EW can be provided in each phase or in each conductor of the electrical circuit. The secondary side of the energy converter EW, or of each provided energy converter, is connected to a power supply NT (or several power supplies) that provides a power supply—i.e., its own power supply, for example, in the form of a supply voltage—for the control unit ETU, for example, an electronic trip unit ETU. At least one additional component 9 can be connected to the control unit ETU.The power supply unit (NT) can also be connected to a first current sensor (SE) to supply power to the first current sensor, if required.

[0045] The first current sensor (SE) has at least one sensor element, such as a Rogowski coil, a measuring resistor / shunt, a Hall sensor, or similar, for determining the magnitude of the electric current in at least one conductor of the electrical circuit. In a typical configuration, the magnitude of the electric current in each phase conductor or conductor of the electrical circuit is determined.

[0046] The first current sensor SE is connected to the control unit ETU (electronic release unit ETU) and transmits to it the magnitude of the electric current of at least one conductor, the phase conductors or all conductors of the electrical circuit.

[0047] The control unit ETU can be a so-called Electronic Trip Unit.

[0048] The transmitted current values ​​are compared in the control unit ETU with current limits and / or current-time interval limits, which determine the triggering criteria. If these limits are exceeded, the electrical circuit is interrupted. This can be achieved, for example, by using an interruption unit UE, which is connected to the control unit ETU and has contacts K for interrupting conductors L1, L2, L3, or other conductors of the electrical circuit. In this case, the interruption unit UE receives an interruption signal from the control unit ETU to open the contacts.

[0049] Figure 2Figure 1 shows a first circuit diagram to illustrate the invention. An alternating current source EQ, serving as an energy source, supplies an energy consumer Load, which serves as an energy sink. A conductor of this circuit forms the primary side 20 of the energy converter EW. The conductor can have several turns of a primary coil of the energy converter EW. However, it can also simply be the conductor (without a turn) passing directly through or alongside a core 10 of the energy converter EW.

[0050] The core 10 of the energy converter EW further has a secondary-side output or a secondary side with secondary winding 15, which is formed by one or more turns of a secondary winding or coil 15.

[0051] The two terminals of the secondary winding 15 form the secondary-side output of the energy converter EW, which provides a power supply for the two inputs of the at least one control unit ETU. Further components of the power supply NT, not shown, may be included, for example, in block 30. Each output is electrically connected to each input.

[0052] Figure 3 Figure 1 shows an equivalent circuit diagram of the secondary-side output or secondary winding 15 of the energy converter EW. The equivalent circuit diagram of the secondary winding 15 has a voltage source VQ (the voltage induced in the secondary winding) in series with an inductance L1 (the inductance of the secondary winding) and a resistance R1 (the wire resistance of the secondary winding).

[0053] Figure 4 shows a representation according to Figure 3, with the difference that a first and a second rectifier circuit D1, D2 are connected to the secondary-side output of the energy converter EW and to the secondary winding 15 respectively (represented by the equivalent circuit diagram).

[0054] The rectifier circuits D1 and D2 are connected in parallel on the input side. According to the invention, the first rectifier circuit D1 is connected to the secondary winding 15 via a capacitor C1. That is, according to the invention, a capacitor or capacitance is provided in at least one connection between the secondary winding 15 and the first rectifier circuit D1.

[0055] The second rectifier circuit D2 is directly connected to the secondary winding 15.

[0056] The first and second rectifier circuits D1, D2, i.e. the rectifier circuits, are connected in parallel on the output side to provide a power supply for the at least one control unit ETU of the circuit breaker LS.

[0057] Advantageously, capacitor C1 forms a series resonant circuit with the inductance L1 of the secondary winding 15 of the energy converter EW. Advantageously, capacitor C1 is dimensioned such that its capacitive reactance (XC = 1 / ωC) (ω = 2 * Pi * f = angular frequency) (C = capacitance of capacitor C1) (XC = capacitive reactance) at the operating frequency of the AC circuit is equal to the inductive reactance (XL) of inductor L1, i.e., the magnitude of the inductive reactance equals the magnitude of the capacitive reactance (|XL|=|XC|). This cancels out the reactive components at the rated frequency (which should correspond to the operating frequency of the AC circuit, e.g., 50 Hz). (XL = ωL = inductive reactance) (L = inductance of inductor L1)

[0058] For the inductive reactance XL, for example, a value is assumed that occurs for currents up to a first current level.

[0059] This will be explained again below in the context of further additions and in other words. The control unit ETU is supplied by energy converters (current transformers) located in the circuit breaker LS. These energy converters EW have, for example, a toroidal construction with a complete flux path formed by, for example, the iron core 10. The primary conductor of the primary side 20 is guided through, for example, a core 10 shaped as a ring (toroid). The electromagnetic energy generated by the primary conductor is captured by the iron core 10. The secondary windings 15 wound around the iron core 10 convert the electromagnetic energy into electrical energy (voltage source VQ).

[0060] Depending on the current level on the primary side 20, the energy converter exhibits different behavior. At low currents, up to a certain initial current level, the energy converter EW operates essentially linearly.

[0061] At high currents, starting from a certain initial current level, the energy converter EW operates in an essentially non-linear manner.

[0062] This dual behavior is due to the core 10, implemented as an iron core, which is used to transmit electromagnetic energy.

[0063] The properties of the iron core are characterized by a so-called BH curve, as shown in Figure 5 depicted.

[0064] Figure 5 This shows a BH curve. This shows the flux (Wb) on the vertical axis, which is generated by the iron core in response to the input line current (Coil Current, AT) on the horizontal axis.

[0065] At low coil currents (low H), the curve is approximately linear, as shown in the diagram as the linear region LM (circle).

[0066] In this operating range up to a first current level, the energy converter EW behaves like a current-dependent voltage source VQ with a series inductance L1, as shown in the equivalent circuit diagram (as well as a resistance component of the resistance R1).

[0067] At higher input currents, the energy converter EQ deviates from this model and behaves like a non-linear voltage source VQ. According to the invention, the linearity of energy converters EW is utilized at low line currents (up to a first current level). Here, more energy is extracted at lower line currents using a capacitor that forms a series resonant circuit, i.e., by utilizing resonance (resonant capacitor C1 connected in series).

[0068] At lower line currents (on the primary side 10), the capacitance of capacitor C1 cancels out the inductance L1 (of the secondary winding 15). This contributes to the fact that, according to the equivalent circuit diagram, the voltage source VQ of the secondary winding 15 directly supplies energy to the first rectifier circuit D1, thus achieving an impedance match (reduced source impedance) to extract more power for the control unit. The energy flows to the first rectifier circuit D1.

[0069] At higher current levels, above a certain initial current threshold, when the energy converter EW does not operate linearly, the capacitor C1 cannot compensate for the inductance L1 due to its change in value. The energy is then extracted via the second rectifier circuit D2.

[0070] In summary, source impedance Z: Z=R1 at low line currents (|XL|=|XC|) Z = √ XL 1 ∧ 2 + R 1 ∧ 2 at higher line currents

[0071] The source impedance Z is reduced at low line currents, allowing higher power to be drawn from the energy converter EW. Thus, even at low primary currents, 20 watts of energy can be provided for a control unit ETU.

[0072] Figure 6 shows a representation according to Figure 4 , with the energy flow shown according to the invention.

[0073] The capacitor C1 or the series resonant circuit consisting of the series connection of capacitor C1 and inductor L1 is designed in such a way that for currents up to a first current level, the energy supplied by the energy converter EW is essentially supplied to the control unit ETU via the first rectifier circuit D1.

[0074] For currents above the first current level, the energy supplied by the energy converter EW is essentially transferred to the control unit ETU via the second rectifier circuit D2.

[0075] An overvoltage protection element can be connected in parallel to the secondary-side output or the secondary winding 15 of the energy converter EW.

[0076] The first or (and) second rectifier circuit can be a full-wave bridge rectifier circuit.

[0077] Core 10 can be a nanocrystalline magnetic core, for example to reduce current harmonics.

[0078] Additional components of the power supply unit (PSU) may be included.

[0079] The invention utilizes the linearity of energy converters at low currents to increase the power delivered by a capacitor. A dynamic change in the energy flow path is achieved using two rectifier circuits, one for resonance and one without resonance, without (significantly) increasing the system's complexity. The invention thus reduces the current required on the primary side to provide energy (e.g., for a control unit). Two rectifier circuits connected in parallel eliminate the need for complex switching mechanisms.

[0080] Although the invention has been illustrated and described in detail by the exemplary embodiment, the invention is not limited by the disclosed examples and other variations can be derived by the person skilled in the art without departing from the scope of protection of the invention as defined by the claims.

Claims

1. Circuit breaker (LS) for interrupting an AC electrical circuit when current and / or current / time period limit values are exceeded, having an energy transducer (EW), the primary side of which is connected to the electrical circuit and the secondary side of which provides an energy supply for at least one control unit (ETU) of the circuit breaker (LS), characterized in that a first and a second rectifier circuit (D1, D2) are connected to the secondary-side output (15) of the energy transducer, in that the first rectifier circuit (D1) is connected to the secondary-side output (15) of the energy transducer (EW) via a capacitor (C1), in that the output sides of the rectifier circuits (D1, D2) are connected in parallel in order to provide an energy supply for the at least one control unit (ETU) of the circuit breaker (LS).

2. Circuit breaker (LS) according to Patent Claim 1, characterized in that a conductor of the electrical circuit forms the primary side (20) of the energy transducer (EW).

3. Circuit breaker (LS) according to Patent Claim 1 or 2, characterized in that the capacitor (C1) forms a series resonant circuit with the inductor (L1) of the secondary winding (15) of the energy transducer (EW).

4. Circuit breaker (LS) according to Patent Claim 3, characterized in that the capacitor (C1) is dimensioned such that its capacitive reactance for the operating frequency of the AC circuit corresponds identically to the inductive reactance of the inductor (L1), wherein in particular a value that occurs for currents up to a first current level is set for the inductive reactance.

5. Circuit breaker (LS) according to Patent Claim 3 or 4, characterized in that the capacitor (C1) or series resonant circuit is designed in such a way that, for currents up to the first current level, the energy delivered by the energy transducer is essentially delivered to the control unit (ETU) via the first rectifier circuit (D1).

6. Circuit breaker (LS) according to Patent Claim 5, characterized in that, for currents from the first current level upward, the energy delivered by the energy transducer (EW) is essentially delivered to the control unit (ETU) via the second rectifier circuit (D2).

7. Circuit breaker (LS) according to one of the preceding patent claims, characterized in that an overvoltage protection element is connected in parallel with the secondary-side output (15) of the energy transducer (EW).

8. Circuit breaker (LS) according to one of the preceding patent claims, characterized in that the first or second rectifier circuit (D1, D2) is a full-wave bridge rectifier circuit.