Circuit breaker

Abstract

The disclosure relates to a circuit breaker (100), comprising: a first current branch (110) comprising a mechanical disconnector (111), the mechanical disconnector (111) having a first electrical contact (111a) and a second electrical contact (111b), wherein in a closed state of the mechanical disconnector (111) the first electrical contact (111a) electrically connects to the second electrical contact (111b) for electrically connecting a pair of bus terminals (101, 102), and wherein in an open state of the mechanical disconnector (111) the first electrical contact (111a) is electrically separated from the second electrical contact (111b); and a second current branch (120) electrically connected in parallel to the first current branch (110). Upon detection of a fault current between the bus terminals (101, 102) the mechanical disconnector (111) is transferred into the open state in order to disconnect the pair of bus terminals (101, 102) and to commute the fault current from the first current branch (110) to the second current branch (120), wherein in the open state the first electrical contact (111a) is separated from the second electrical contact (111b) by a predetermined distance within a micrometer range.

Description

[0001] CIRCUIT BREAKER

[0002] TECHNICAL FIELD

[0003] The disclosure relates to the field of fast interruption of fault currents in alternating current (AC) and direct current (DC) systems by using circuit breakers. The disclosure relates to a circuit breaker, for example a circuit breaker with mechanical disconnector for commuting a fault current from a first current branch to a second current branch. The disclosure relates to a hybrid circuit breaker.

[0004] BACKGROUND

[0005] Fast breakers are an emerging field. Normally such fast breakers are not needed since AC systems are dominant. However, due to the push of renewable energy technologies to reduce the emission of carbon dioxide gases, and increase efficiency, DC systems are becoming more and more important. Hence fast breakers are becoming very important. In many application scenarios, complete interruption speeds less than 1 ms are achieved by using solid-state breakers. However, solid-state breakers can suffer from high conduction losses, they are expensive and less reliable and do not provide isolation. Since solid-state breakers are made of semiconductor materials, they do not conduct well resulting in high conduction losses. This often results in the need to use a cooling system such as water cooling which is very expensive and not very reliable. Lastly, semiconductors do not offer a physical isolation and may have leakage currents limiting their use.

[0006] SUMMARY

[0007] This disclosure provides a solution for an ultra-fast circuit breaker for interrupting fault currents without suffering from the above-described problems. For example, a reliable non-expensive circuit breaker with an interruption speed less than 1 ms that does not suffer from conduction losses.

[0008] The disclosure presents an ultra-fast circuit breaker which can interrupt the circuit before any damage can happen to the circuit. In the event of a fault, the circuit breaker can open the bus terminals very fast before the current has a chance to increase in magnitude and becomes harder to interrupt.

[0009] The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. In this disclosure, a new circuit breaker, also referred to as hybrid circuit breaker, is introduced that is designed to be able to interrupt fault currents really fast without generating any arcs. The new circuit breaker is based on an actuator that is able to separate contacts with micrometers precision. This can only be done in the absence of arcs. If an arc is present, then the arc will ablate the contacts making it impossible to move small distances controllably and reliably.

[0010] Fault currents rise very fast in DC systems or in systems with low inductance. The circuit breaker presented in this disclosure operates very fast and is able to limit and interrupt fault currents. Such a breaker is currently not existing, since up to now AC systems dominate power networks.

[0011] The circuit breaker presented in this disclosure is based on an actuator with micrometers precision which is used in conjunction with a semiconductor device to be able to commutate the fault current very fast to the semiconductor branch that is ideally comprised of an insulated gate bipolar transistor (IGBT). Further details are described below with respect to Figures 1 to 4.

[0012] In order to describe the disclosure in detail, the following terms and notations will be used.

[0013] AC Alternating current

[0014] DC Direct current

[0015] PV Photovoltaic

[0016] LV Low voltage

[0017] IGBT Insulated gate bipolar transistor

[0018] MOSFET Metal oxide semiconductor field-effect transistor

[0019] According to a first aspect, the disclosure relates to a circuit breaker, comprising: a first current branch comprising a mechanical disconnector, the mechanical disconnector having a first electrical contact and a second electrical contact, wherein in a closed state of the mechanical disconnector the first electrical contact electrically connects to the second electrical contact for electrically connecting a pair of bus terminals, and wherein in an open state of the mechanical disconnector the first electrical contact is electrically separated from the second electrical contact; and a second current branch electrically connected in parallel to the first current branch; wherein upon detection of a fault current between the bus terminals the mechanical disconnector is transferred into the open state in order to disconnect the pair of bus terminals and to commute the fault current from the first current branch to the second current branch, wherein in the open state the first electrical contact is separated from the second electrical contact by a predetermined distance within a micrometer range of for example 1 to 20 um. The mechanical disconnector may be controlled by a controller which can transfer the mechanical disconnector between the closed state and the open state.

[0020] Such a circuit breaker allows for an ultra-fast interruption of fault currents without suffering from the problems of solid-state circuit breakers as described above. The circuit breaker is a reliable non- expensive device with an interruption speed less than 1 ms that does not suffer from conduction losses. The circuit breaker is able to interrupt the circuit before any damage can happen to the circuit. In the event of a fault, the circuit breaker is able to open the electrical contacts very fast before the current has a chance to increase in magnitude and becomes harder to interrupt.

[0021] In an exemplary implementation of the circuit breaker, the predetermined distance is a distance of several micrometers, e.g. 1 to 20 um. This is a very short distance for which the characteristics of the Paschen curve as described below are relevant, e.g. where the voltage withstand of the circuit breaker at such low distance is higher than with larger distances.

[0022] In an exemplary implementation of the circuit breaker, the predetermined distance should be derived from the left side of the Paschen curve characteristic for a predetermined pressure and a gaz. Gaz could be normal air, nitrogen, argon. The form of the curve changes based on the type of gaz. For such low predetermined distance, the voltage withstand of the circuit breaker is higher than for larger distances. At the left side of the Paschen curve characteristic, a voltage withstand of the first current branch is higher for lower distances of the two electrical contacts than for higher distances.

[0023] In an exemplary implementation of the circuit breaker, in the open state of the disconnector, an avalanche formation and successively electrical breakdown is hindered, and the first current branch is enabled to withstand several kilo Volts, e.g. 1 to 5 kV. Since avalanche formation and successively electrical breakdown is hindered, the circuit breaker can withstand high breakdown voltages.

[0024] In an exemplary implementation of the circuit breaker, the circuit breaker comprises: a piezoelectric drive or a supersonic piezoelectric drive configured to actuate the mechanical disconnector to move to the open state. Such piezoelectric drive or supersonic piezoelectric drive can be easily and precisely controlled by a controller, e.g., based on a semiconductor device. By utilizing a piezoelectric drive or supersonic piezoelectric drive, very precise movements can be initiated, in the order of micrometers.

[0025] In an exemplary implementation of the circuit breaker, the mechanical disconnector is configured for isolation and voltage withstand between the bus terminals. Isolation and voltage withstand between the bus terminals result in high breakdown voltages of the circuit breaker. In an exemplary implementation of the circuit breaker, the first current branch comprises a pair of antiseries connected semiconductor switches electrically connected in series to the mechanical disconnector; wherein the pair of anti-series connected semiconductor switches are switched-off before transferring the mechanical disconnector into the open state such that an arc-less commutation of the fault current from the first current branch to the second current branch is enabled; wherein the first current branch is configured to conduct a nominal current between the pair of bus terminals in the closed state of the mechanical disconnector. By such a pair of anti-series connected semiconductor switches, an arc-less commutation of the fault current can be realized, resulting in longer lifetime of the circuit breaker.

[0026] In an exemplary implementation of the circuit breaker, upon detection of a fault, the pair of anti-series connected semiconductor switches is turned off and subsequently the mechanical disconnector is activated. This enforces an arc -less current commutation between the first current path and the second current branch.

[0027] In an exemplary implementation of the circuit breaker, the pair of anti-series connected semiconductor switches comprises a pair of MOSFETs that is configured to withstand a voltage across the pair of bus terminals at least until activation of the mechanical disconnector. The MOSFETs can be precisely controlled to turn off the first current path and to commute the fault current to the second current branch.

[0028] In an exemplary implementation of the circuit breaker, the second current branch comprises a semiconductor device configured to at least temporarily absorb the fault current commuted from the first current branch to the second current branch. The fault current can be absorbed for some time in the second current branch before it can be commuted to a third current branch.

[0029] In an exemplary implementation of the circuit breaker, the semiconductor device comprises an Insulated Gate Bipolar Transistor (IGBT) and a diode bridge rectifier.

[0030] In an exemplary implementation of the circuit breaker, the IGBT is configured to at least temporarily withstand a voltage across the pair of bus terminals. The IGBT can temporarily withstand high breakdown voltages.

[0031] In an exemplary implementation of the circuit breaker, the circuit breaker comprises: a third current branch electrically connected in parallel to the first and second current branches; wherein the second current branch is switched off subsequently after commutation of the fault current from the first current branch to the second current branch in order to commute the fault current from the second current branch to the third current branch. The third current branch can receive the remaining fault current and efficiently drive it down to zero.

[0032] In an exemplary implementation of the circuit breaker, the third current branch comprises a Metal Oxide Varistor (MOV) device that is configured to drive the fault current down to zero based on generating a counter voltage counteracting the voltage across the pair of bus terminals. The MOV device can be used to efficiently drive the fault current down to zero based on generation of a counter voltage.

[0033] In an exemplary implementation of the circuit breaker, the MOV device is configured to drive the fault current down to zero based on the following relation: difauit= (VSyStem— Vmov)dt where difaultis the fault current derivative, Vsystemis the system voltage across the pair of bus terminals and Vmovis the counter voltage of the MOV device, L is an inductance between the pair of bus terminals. This relation best describes the phenomenon of counter voltage. The higher the build-up of the counter voltage, the faster is the decay of the fault current.

[0034] In an exemplary implementation, the circuit breaker may be configured to drive the fault current down to zero in less than 100 microseconds. In other examples, more time may be required, e.g., 150, 200, 250, 300, 350, 400, 450, 500 or more microseconds.

[0035] According to a second aspect, the disclosure relates to a method for handling a circuit breaker according to the first aspect described above, the method comprising: detecting a fault current between the bus terminals; and transferring the mechanical disconnector into an open state upon detection of the fault current in order to disconnect the bus terminals.

[0036] Such method allows an ultra-fast interruption of fault currents, thereby protecting the circuit from damage.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further embodiments of the disclosure will be described with respect to the following figures, in which:

[0039] Figure 1 shows a schematic diagram illustrating a circuit breaker according to the disclosure; Figure 2 shows an exemplary Paschen curve characteristic illustrating voltage over pressure and distance for a mechanical disconnector according to the disclosure;

[0040] Figure 3 shows an exemplary time diagram illustrating current and voltage overtime for a circuit breaker according to the disclosure; and

[0041] Figure 4 shows a schematic diagram illustrating a method for handling a circuit breaker according to the disclosure.

[0042] DETAILED DESCRIPTION OF EMBODIMENTS

[0043] In the following detailed description, reference is made to the accompanying drawings, which form a part thereof, and in which is shown by way of illustration specific aspects in which the disclosure may be practiced. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the disclosure is defined by the appended claims.

[0044] It is understood that comments made in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

[0045] In the following, AC systems and DC systems as used in this disclosure are described. Traditionally, AC systems dominated over DC systems mainly due to the reliance of transformers to deliver power over long distances. Transformers rely on AC and hence all electric utilities and most electric appliances relied on AC as an input. Phones or computers are such examples where they rely on an AC input that gets converted to DC to operate the PC. Datacenters are other such examples.

[0046] Another reason for the justification of AC systems is due to breakers. It is much easier to interrupt an AC system than a DC system. It is very difficult to interrupt a DC system due to the absence of a current zero crossing. In AC systems, the current crosses zero three times in one period. Hence, every 10 ms (for 50 Hz systems), the breaker has a chance to interrupt the current. However, in DC systems, since the current is constant, it poses a big challenge. The current has to be forced and taken down to zero artificially. Besides, in DC systems, the system inductance is much lower than comparable AC systems. Hence, fault currents can rise very rapidly leading to high current magnitudes and further away from a zero current crossing. This complicates the interruption process further and clearly shows the difficulty in interrupting a current that goes in the wrong direction.

[0047] In AC systems, the speed of the breaker is not so critical since the current will eventually go to zero regardless of the system and the breaker has a chance to interrupt fault currents every 10 ms. Consequently, AC breakers are not built for speed since it is expensive, complex, and unnecessary to do so.

[0048] However, for DC systems, speed plays a major role. The faster the breaker, the faster it can react and limit fault currents. The smaller the short circuit current, the easier it is to interrupt, and the smaller is the energy that needs to be absorbed by the breaker. This results in a smaller footprint and leads to cost reduction in breaker design.

[0049] Another major advantage is maintenance and lifetime. The faster the mechanical breaker is at interrupting a fault current at low current magnitudes, the less are the contacts ablated. This results in a prolonged lifetime and much less maintenance increasing reliability.

[0050] The circuit breaker presented in this disclosure provides a solution to the above-described problems. It utilizes a circuit breaker, also referred herein as hybrid circuit breaker, with high power density to accelerate the contacts of the breaker very fast. The breaker is so fast that even AC systems seem as a DC system to the breaker since it is able to completely interrupt fault currents within 100 us in a preferred embodiment. It does not wait for a current zero but creates its own by generating a counter voltage that is high enough to counteract the system voltage and drive the fault current down to zero. This principle is not only fast and has low on-state losses, it is arc-less. It is able to interrupt fault current without generating any arcs.

[0051] The following figures illustrate the circuit breaker and a method for handling the circuit breaker in detail.

[0052] Figure 1 shows a schematic diagram illustrating a circuit breaker 100 according to the disclosure.

[0053] The circuit breaker 100 comprises: a first current branch 110 comprising a mechanical disconnector 111. The mechanical disconnector 111 comprises a first electrical contact 11 la and a second electrical contact 11 lb. In a closed state of the mechanical disconnector 111 the first electrical contact I l la electrically connects to the second electrical contact 111b for electrically connecting a pair of bus terminals 101, 102. In an open state of the mechanical disconnector 111 the first electrical contact 11 la is electrically separated from the second electrical contact 11 lb.

[0054] The circuit breaker 100 comprises: a second current branch 120 electrically connected in parallel to the first current branch 110.

[0055] Upon detection of a fault current between the bus terminals 101, 102 the mechanical disconnector 111 is transferred into the open state in order to disconnect the pair of bus terminals 101, 102 and to commute the fault current from the first current branch 110 to the second current branch 120. In the open state the first electrical contact I l la is separated from the second electrical contact 111b by a predetermined distance within a micrometer range, e.g. 1 to 20 um.

[0056] The mechanical disconnector 111 may be controlled by a controller (not shown in Figure 1).

[0057] The predetermined distance can be a distance of several micrometers, e.g. 1 to 20 um.

[0058] In particular, the predetermined distance can be a distance at a left side 201 of a Paschen curve characteristic 200 as exemplarily shown in Figure 2 for a predetermined pressure. At the left side 201 of the Paschen curve characteristic, a voltage withstand of the first current branch 110 is higher for lower distances of the two electrical contacts than for higher distances.

[0059] In the open state of the disconnector 111, an avalanche formation and successively electrical breakdown can be hindered, and the first current branch 110 may be enabled to withstand several kilo Volts, e.g. 1 to 5 kV.

[0060] The circuit breaker 100 may comprise: a piezoelectric drive or a supersonic piezoelectric drive configured to actuate the mechanical disconnector 111 to move to the open state.

[0061] The piezoelectric drive or the supersonic piezoelectric drive may be controlled by a controller (not shown in Figure 1). It can be the same or a different controller than the controller controlling the mechanical disconnector 111.

[0062] The mechanical disconnector 111 may be configured for isolation and voltage withstand between the bus terminals 101, 102.

[0063] The first current branch 110 may comprise a pair of anti-series connected semiconductor switches 112, 113 electrically connected in series to the mechanical disconnector 111. This pair of anti-series connected semiconductor switches 112, 113 can be switched-off before transferring the mechanical disconnector 111 into the open state such that an arc-less commutation of the fault current from the first current branch 110 to the second current branch 120 can be enabled.

[0064] The first current branch 110 may be configured to conduct a nominal current between the pair of bus terminals 101, 102 in the closed state of the mechanical disconnector 111. Upon detection of a fault, the pair of anti-series connected semiconductor switches 112, 113 may be turned off and subsequently the mechanical disconnector 111 can be activated. The pair of anti-series connected semiconductor switches 112, 113 may comprise a pair of MOSFETs 112, 113 that is configured to withstand a voltage across the pair of bus terminals 101, 102 at least until activation of the mechanical disconnector 111.

[0065] The second current branch 120 may comprise a semiconductor device 121, 122, 123, 124, 125 configured to at least temporarily absorb the fault current commuted from the first current branch 110 to the second current branch 120. The semiconductor device 125 may comprise an Insulated Gate Bipolar Transistor (IGBT) 125 and a diode bridge rectifier 121, 122, 123, 124 as shown in Figure 1. The IGBT 125 may be configured to at least temporarily withstand a voltage across the pair of bus terminals 101, 102.

[0066] The circuit breaker 100 may comprise a third current branch 130 electrically connected in parallel to the first and second current branches 110, 120.

[0067] The second current branch 120 can be switched off subsequently after commutation of the fault current from the first current branch 110 to the second current branch 120 in order to commute the fault current from the second current branch 120 to the third current branch 130. The third current branch 130 may comprise Metal Oxide Varistor (MOV) device 131 that is configured to drive the fault current down to zero based on generating a counter voltage counteracting the voltage across the pair of bus terminals 101, 102.

[0068] The MOV device 131 may be configured to drive the fault current down to zero based on the following relation: where difaultis the fault current derivative, Vsystemis the system voltage across the pair of bus terminals 101, 102 and Vmovis the counter voltage of the MOV device 131, L is an inductance between the pair of bus terminals 101, 102. In an exemplary implementation, the circuit breaker 100 may be configured to drive the fault current down to zero in less than 100 microseconds. In other examples, more time may be required, e.g., 150, 200, 250, 300, 350, 400, 450, 500 or more microseconds.

[0069] While traditional breakers have electromagnetic coils and iron plungers, they are slow and rely on a current zero crossing to interrupt fault currents. This newly introduced circuit breaker 100 described in this disclosure allows to create a counter voltage that is higher than the system voltage forcing a current zero crossing. The breaker is able to interrupt both AC or DC systems extremely fast, in less than 100 us. It will force a current zero crossing. It is not only very fast and comparable to solid state breakers in terms of speed, it has very low on-state losses and is arc-less. This means it is very reliable and is able to perform a very large number of electric operations without any damage.

[0070] By operating on the left side of the Paschen curve (see Figure 2) the interruption speed can be accelerated significantly. The mechanical disconnector 111 is then allowed to open more, for example several millimeters afterwards to ensure a decent voltage withstand reliability.

[0071] Further embodiments of the circuit breaker 100 are described in the following.

[0072] The nominal current path (referred herein as first current branch 110) is composed of at least one ultrafast mechanical disconnector 111 and a pair of anti-series low voltage connected MOSFETs 112, 113. One disconnector 111 will aim to have a travel distance of micrometers, e.g. 1 to 20 um. The second branch 120 consists of a diode bridge rectifier 121, 122, 123, 124 and a semiconductor device such as an IGBT 125. The third branch 130 consists of a metal oxide varistor (MOV) 131 as shown in Figure 1.

[0073] During nominal operation, the mechanical disconnector 111 and the low voltage MOSFETs 112, 113 conduct the nominal current. The on-state losses are very low. In the event of a fault, the MOSFETs 112, 113 are turned off and the mechanical disconnector 111 is triggered shortly after. This enforces an arc-less current commutation between the nominal branch 110 and the IGBT 125. After waiting for a certain period of time depending on the technology of the mechanical disconnector 111, a turn-off command is sent to the IGBT 125 to turn it off. Hence another current commutation is enforced to the MOV 131. The MOV 131 generates a counter voltage counteracting the system voltage and hence driving the fault current down to zero.

[0074] The equation that best describes this phenomenon is as follows: The higher the buildup of the counter voltage, the faster is the decay of the fault current. Two contacts are used in this design to speed up the interruption process. Increasing the number of series connected contacts will increase the interruption speed further at the expense of adding resistance and more losses. This is a tradeoff.

[0075] The mechanical disconnector may consist of one of the following devices:

[0076] 1) Actuator powered drive

[0077] 2) Thomson or double-sided coil

[0078] 3) Supersonic piezoelectric drive.

[0079] The Thomson coil (TC) is composed of a flat spirally shaped coil consisting of several turns, with an electrically conducting armature in its proximity. The armature has a flat profde and can be situated directly on top or at the bottom of the coil, as close as possible to minimize the air gap. To generate such large currents, capacitors are connected in series and in parallel to increase the charging voltage and increase the capacitance respectively. The main difference between a double-sided coil and a Thomson coil is the currents in the armature. The armature of a DSC consists of yet another coil that is connected in series with the primary coil such that currents of the opposite direction flow. Currents in proximity to each other flowing in opposite directions cause a repulsive force similar to the phenomenon explain above.

[0080] A piezoelectric drive is an amplifier-type power supply for stable driving of the amount of displacement and the amount of vibration for each piezo element based on its purpose. Piezo elements have the characteristics of capacitive elements.

[0081] A supersonic piezoelectric drive is a piezoelectric drive that operates at high power, high current and high voltage. These drives usually operate at ultrasonic frequencies.

[0082] In this disclosure, a supersonic piezoelectric drive is preferred due to its high accuracy in conjunction with its speed. Due to the complete absence of arcs, the contacts remain intact. The contacts do not ablate and are very reliable. By utilizing a piezoelectric drive, very precise movements can be done, in the order of micrometers. Separating the contacts by as little as micrometers enables operation to the left of the Paschen curve (see Figure 2) where the voltage withstand of the breaker at such low distance is higher than at larger distances.

[0083] As already described above, in AC systems, the current crosses zero every 10 ms. Every time it crosses zero, the circuit breaker has the potential to interrupt the fault current. Traditional AC breakers do not need to be fast. They just need to be reliable and robust. However new more efficient systems require DC and not AC. DC has numerous benefits and also low inductance and no current zero crossing. Due to the raw speed of the breaker described in this disclosure, it can interrupt both DC or AC currents extremely fast. Since it is so fast, it can act as a fault current limiter also protecting all equipment downstream. Moreover, since it is able to interrupt fault currents without any arcs, it has a large lifetime.

[0084] The number of electrical and mechanical operations in this case can be matched without any problem regardless of the magnitude of the fault current. This means the damage inflicted on the breaker is limited leading to more reliability and longer lifetimes without maintenance.

[0085] The circuit breaker 100 presented in this disclosure has similar performance as a pure solid-state circuit breaker. However, it exhibits very low conduction losses and is able to conduct large currents. Furthermore, it has similar interruption speeds, is more reliable, and even provides galvanic separation. In principle, it can be made as fast as a semiconductor-based device while conducting large currents and not exhibiting any conduction losses. Moreover, this principle does not require a cooling system and costs a fraction of the cost of solid-state breakers.

[0086] Application scenarios of the circuit breaker 100 are datacenters, DC systems especially LVDC up to 1500 V, renewables such as PV, or electric vehicles and charging stations. The circuit breaker 100 is highly useful in DC systems or in any system where complete fault current interruption in less than 1 ms is mandatory.

[0087] The circuit breaker 100 presented in this disclosure thus provides a solution for a novel ultra-fast circuit breaker to interrupt fault currents in at least less than 1 ms. The circuit breaker 100 is a device for limiting and interrupting fault currents really fast with no (significant) conduction losses. The circuit breaker 100 can be deployed in datacenters, PV, battery systems, electric vehicles, or DC microgrids, for example.

[0088] Figure 2 shows an exemplary Paschen curve characteristic 200 illustrating voltage over pressure and distance for a mechanical disconnector according to the disclosure.

[0089] The Paschen curve characteristic 200 (simply called Paschen curve 200) shows a parabolic-like curve illustrating voltage V over pressure P times distance d. The Paschen curve characteristic 200 has a minimum 203 that divides the curve in a left side 201 section and a right side 202 section. As described above, the predetermined distance for separating the first electrical contact I l la of the mechanical disconnector 111 from the second electrical contact 11 lb is a distance at the left side 201 of the Paschen curve characteristic 200 for a predetermined pressure, e.g., atmospheric pressure.

[0090] The y axis of the Paschen curve 200 shows the voltage breakdown V. The x axis of the Paschen curve 200 shows the variable pressure P multiplied by contact distance d. Assuming constant pressure P, the x axis can also be simplified to a distance parameter d. The shape of the Paschen curve 200 is like a parabola.

[0091] At short contact separations, the voltage breakdown V of contacts is very high since it is not easy to accelerate electrons in such a short gap. As the gap (i.e., distance d) increases, the voltage breakdown V decreases and then increases again. Operating reliably at such low separation distances reliably and very accurately hinders the avalanche formation and hence hinders the electrical breakdown. Therefore, the circuit breaker 100 will be able to withstand several kilovolts, e.g. 1 to 5 kV even at distances as low as 20 um. This concept only works as long as there are no arcs ablating or damaging the contacts. Otherwise, a movement with micrometer precision is not possible.

[0092] Figure 3 shows an exemplary time diagram illustrating current I and voltage V over time t for a circuit breaker 100 according to the disclosure.

[0093] A time tO, a fault occurs.

[0094] At time tl, the mechanical disconnector 111 commutates current to the IGBT 125: IIGBT, 302 increases while Ibreaker, 301 decreases.

[0095] At time t2, the IGBT 125 commutates current to the MOV device 131 : IMOV, 303 increases while IIGBT, 302 decreases.

[0096] At time t3, the MOV counter voltage is generated.

[0097] At time t4, the current is completely interrupted.

[0098] Itotai, 310 increases from tO to t3 and decreases from t3 to t4 down to zero.

[0099] Io denotes the nominal current. Fault current limitation can be performed at t3 in less than 100 us.

[0100] As shown in Figure 3, breakdown voltage Vb, 304 is much larger than system voltage Vs, 305.

[0101] Figure 4 shows a schematic diagram illustrating a method 400 for handling a circuit breaker according to the disclosure.

[0102] The circuit breaker 100 may correspond to the circuit breaker 100 as described above with respect to Figure 1.

[0103] The method 400 comprises detecting 401 a fault current between the bus terminals 101, 102 (shown in Figure 1). The method 400 comprises transferring 402 the mechanical disconnector 111 (see Figure 1) into an open state upon detection of the fault current in order to disconnect the bus terminals 101, 102. Such method allows an ultra-fast interruption of the fault current, thereby protecting the circuit from damage.

[0104] While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similarto the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms “coupled” and “connected”, along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

[0105] Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.

[0106] Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence. Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the disclosure beyond those described herein. While the disclosure has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the disclosure. It is therefore to be understood that within the scope of the appended claims and their equivalents, the disclosure may be practiced otherwise than as specifically described herein.

Claims

CLAIMS1. A circuit breaker (100), comprising: a first current branch (110) comprising a mechanical disconnector (111), the mechanical disconnector (111) having a first electrical contact (11 la) and a second electrical contact (11 lb), wherein in a closed state of the mechanical disconnector ( 111) the first electrical contact (I l la) electrically connects to the second electrical contact (11 lb) for electrically connecting a pair of bus terminals (101, 102), and wherein in an open state of the mechanical disconnector (111) the first electrical contact (I l la) is electrically separated from the second electrical contact (11 lb); and a second current branch (120) electrically connected in parallel to the first current branch (HO); wherein upon detection of a fault current between the bus terminals (101, 102) the mechanical disconnector (111) is transferred into the open state in order to disconnect the pair of bus terminals (101, 102) and to commute the fault current from the first current branch (110) to the second current branch (120), wherein in the open state the first electrical contact (11 la) is separated from the second electrical contact (11 lb) by a predetermined distance within a micrometer range.

2. The circuit breaker (100) of claim 1, wherein the predetermined distance is a distance of several micrometers.

3. The circuit breaker (100) of claim 1 or 2, wherein the predetermined distance is a distance at a left side (201) of a Paschen curve characteristic (200) for a predetermined pressure.

4. The circuit breaker (100) of any of the preceding claims, wherein in the open state of the disconnector (111), an avalanche formation and successively electrical breakdown is hindered, and the first current branch (110) is enabled to withstand several kilo Volts.

5. The circuit breaker (100) of any of the preceding claims, comprising: a piezoelectric drive or a supersonic piezoelectric drive configured to actuate the mechanical disconnector (111) to move to the open state.

6. The circuit breaker (100) of any of the preceding claims,wherein the mechanical disconnector ( 111) is configured for isolation and voltage withstand between the bus terminals (101, 102).

7. The circuit breaker (100) of any of the preceding claims, wherein the first current branch (110) comprises a pair of anti-series connected semiconductor switches (112, 113) electrically connected in series to the mechanical disconnector (111); wherein the pair of anti-series connected semiconductor switches (112, 113) are switched-off before transferring the mechanical disconnector ( 111) into the open state such that an arc-less commutation of the fault current from the first current branch (110) to the second current branch (120) is enabled; wherein the first current branch (110) is configured to conduct a nominal current between the pair of bus terminals (101, 102) in the closed state of the mechanical disconnector (111).

8. The circuit breaker (100) of claim 7, wherein upon detection of a fault, the pair of anti-series connected semiconductor switches (112, 113) is turned off and subsequently the mechanical disconnector (111) is activated.

9. The circuit breaker (100) of claim 7 or 8, wherein the pair of anti-series connected semiconductor switches (112, 113) comprises a pair of MOSFETs (112, 113) that is configured to withstand a voltage across the pair of bus terminals (101, 102) at least until activation of the mechanical disconnector (111).

10. The circuit breaker (100) of any of the preceding claims, wherein the second current branch (120) comprises a semiconductor device (121, 122, 123, 124, 125) configured to at least temporarily absorb the fault current commuted from the first current branch (110) to the second current branch (120).

11. The circuit breaker (100) of claim 10, wherein the semiconductor device (125) comprises an Insulated Gate Bipolar Transistor, IGBT (125) and a diode bridge rectifier (121, 122, 123, 124).

12. The circuit breaker (100) of claim 11,wherein the IGBT (125) is configured to at least temporarily withstand a voltage across the pair of bus terminals (101, 102).

13. The circuit breaker (100) of any of the preceding claims, comprising: a third current branch (130) electrically connected in parallel to the first and second current branches (110, 120); wherein the second current branch (120) is switched off subsequently after commutation of the fault current from the first current branch (110) to the second current branch (120) in order to commute the fault current from the second current branch (120) to the third current branch (130).

14. The circuit breaker (100) of claim 13, wherein the third current branch (130) comprises a Metal Oxide Varistor, MOV, device (131) that is configured to drive the fault current down to zero based on generating a counter voltage counteracting the voltage across the pair of bus terminals (101, 102).

15. The circuit breaker (100) of claim 13 or 14, wherein the MOV device (131) is configured to drive the fault current down to zero based on the following relation:where difauitis the fault current derivative, Vsystemis the system voltage across the pair of bus terminals (101, 102) and Vmovis the counter voltage of the MOV device (131), L is an inductance between the pair of bus terminals (101, 102).

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