Method and electrical device for locating short circuit in DC voltage system

Abstract

The invention relates to a method for locating a short circuit in a DC voltage system (100), the DC voltage system having a DC voltage line (104) and at least two components (110, 120, 130, 140), each having a capacitance and each being detachably connected to the DC voltage line by means of an electronic protection switch (111, 121, 131, 141). The electronic protection switches each have a current measuring means for measuring the current flowing through the respective protection switch. According to the method, a first point in time is determined at which the current flowing through the electronic protection switch which is first opened due to a short circuit in the DC voltage line corresponds to a reference current value. In addition, a second time point is determined at which the current flowing through the second open electronic protection switch due to a short circuit in the DC voltage line corresponds to a reference current value, and an approximate distance of the short circuit from one of the two electronic protection switches is calculated as a function of the determined time point.

Description

Technical Field

[0001] The invention relates to a method for locating a short circuit in a DC voltage system and to an electrical device having an electronic protection switch. Background Art

[0002] Modern semiconductor circuit breakers (English: Semiconductor Circuit Breaker, abbreviated SCCB, sometimes also called Solid State Circuit Breaker (solid state circuit breaker), abbreviated SSCB; the abbreviation SCCB is used below) can switch off the circuit much faster than conventional circuit breakers (English: Circuit Breaker) in the event of a short circuit. This advantageously leads to the fact that no further damage occurs in the circuit, especially at the short-circuit point, in addition to the damage that triggered the short circuit. In particular, the short-circuit current is quickly limited to a very small value, thereby feeding less energy into the short-circuit point.

[0003] Accordingly, in the circuit protected by the SCCB, the typical short-circuit characteristics caused by the conversion of short-circuit energy into heat energy, such as smoke or odor, discoloration or other visible damage, usually do not appear, which greatly increases the difficulty of subsequent fault finding. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a method for locating a short circuit in a DC voltage system.

[0005] This object is achieved by a method and by an electrical device having an electronic circuit breaker having the features of independent claim 1. Preferred embodiments of the invention are specified in the dependent claims.

[0006] One advantage of the invention can be seen in that a short circuit in a DC system can be located by evaluating two points in time. Modern electronic protection switches have current measuring components in the main current path and evaluation components, which (among other things) evaluate the current-time curve and determine whether the protection switch remains closed or is triggered. The invention makes use of this capability of modern electronic protection switches in order to preferably obtain the mentioned points in time from the evaluation of the current-time curve, which can be determined by modern electronic protection switches at a high sampling rate without additional sensors, or when the electronic protection switch detects a reference current value during a rising current curve that ultimately leads to the electronic protection switch switching off, and a corresponding time stamp is generated. Then, by evaluating the points in time of at least two electronic protection switches connected to the same DC voltage line, which can be determined with high accuracy, it is possible to locate the short circuit inexpensively depending on the topology, i.e. depending on the arrangement of the electronic protection switches along the DC voltage line.

[0007] The required calculation steps can advantageously be performed by a central component, such as a controller, or can be performed cost-effectively by one of the electronic circuit breakers. Alternatively, the calculation steps can be distributed to a plurality of electronic circuit breakers, or the calculation steps can be performed by all electronic circuit breakers that have the required data. This has the advantage that the approximate position of the short circuit can then be displayed on all circuit breakers of the system or can be read out by an external device that can be temporarily coupled wirelessly or by wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0009] Here, in the accompanying drawings:

[0010] Figure 1 A circuit schematic diagram of a DC voltage system according to an embodiment of the present invention is shown; and

[0011] Figure 2 A simplified flow chart of an embodiment of a method according to the invention is shown. DETAILED DESCRIPTION

[0012] Figure 1 The circuit diagram of a DC voltage system 100 according to an embodiment of the present invention is shown. The exemplary DC voltage system 100 has a DC voltage line (English: Busbar) 104, to which four components 110, 120, 130, 140 are connected in the example shown. Here, without limiting the generality, a representation that is typical in many application cases is selected: the central component 140 feeds electrical energy into the DC voltage system 100, which can be obtained by the first component 110 at the first connection 101, by the second component 120 at the second connection 102, and by the third component 130 at the third connection 103.

[0013] Each of the above-mentioned components is connected to the DC voltage line in a detachable manner via a fuse 111, 121, 131, 141. Preferably, for all fuses, an electronic semiconductor circuit breaker (SCCB) of the type mentioned at the beginning is used, which has a current measuring component for measuring the current flowing through the corresponding semiconductor circuit breaker. In other embodiments of the present invention, only selected fuses are designed as SCCBs, while other fuses are designed, for example, as conventional circuit breakers or fuses. The selection of conventional circuit breakers or SCCBs can be carried out here according to the components connected accordingly.

[0014] It is only necessary for the present invention that at least two of the fuses 111-141 are designed as electronic protection switches and have current measuring components for measuring the current flowing through the corresponding semiconductor circuit breakers. Without limiting the generality, the following mainly focuses on the second component 120 and the third component 130 which are connected to the DC voltage line 104 in a detachable manner by means of two SCCBs 121, 131.

[0015] In the example considered, the first, second and third components 110-130 are electrical devices or loads, which obtain energy fed into the DC voltage system 100 by the central component 140. In other embodiments, some or all components 110-130 may be energy sources, and the central component 140 may be a component that outputs excess energy to a higher-level grid (not shown) in the event of excess energy in the DC voltage system 100.

[0016] Relevant to the present invention are the following components which, in addition to being coupled to the DC voltage line 103 by means of an electronic protection switch, also have capacitive elements, for example capacitors such as auxiliary capacitors. It is assumed below that the second and third components are such components. The remaining components, in particular the central component 140, can of course also have capacitive elements.

[0017] Capacitive elements are often present in DC voltage components. All types of voltage converters, such as DC to DC (DC / DC) converters or DC to AC (DC / AC) converters, practically always have capacitive elements in the form of capacitors, in particular in the DC intermediate circuit. In a typical application, the DC grid 100 is a so-called DC microgrid, in which Figure 1 All components 110 , 120 , 130 , 140 shown have corresponding capacitors.

[0018] Capacitance also occurs in grounded circuits, so-called earth boxes. Earth boxes for DC voltage applications are characterized in that both poles are connected to ground potential via capacitors. Accordingly, the earth box always has a certain amount of charge and thus a certain amount of releasable electrical energy. Figure 1 Some or all of the DC voltage lines leading to these components can be protected by means of a grounding box (not shown).

[0019] In the event of a short circuit along the DC voltage line 104, the electronic protection switches 121, 131 will generally also at least trigger or disconnect the components 120, 130 having capacitive elements, since these capacitors output their energy into the short circuit, the impedance of which is significantly lower than the impedance of the usual energy flow path away from the respective capacitor, regardless of whether the respective component 120, 130 is a load or an energy source.

[0020] For example, if a short circuit occurs at point 103, the capacitance / capacitor of the third component 130 starts to discharge into the short circuit. The third electronic protection switch 131 detects the current rise and the absolute value of the current by means of its current measuring component, and switches off according to the switch-off conditions stored in the third electronic protection switch, for example, when the current rise exceeds a certain value, and / or when the absolute value of the current flowing through the third electronic protection switch 131 exceeds a certain value.

[0021] Now, according to the present invention, the time point at which the current flowing through the third electronic protection switch 131 reaches a specific reference current value before or during the shutdown process is determined as the first time point. It is preferred to select a value lower than the current value when the electronic protection switch 131 is disconnected as the reference current value, which will be described in detail below, but can also be set to this value in the embodiment.

[0022] The capacitance / capacitor of the second component 120 will also discharge towards the short circuit in point 103. Due to the inductance of the section of the DC voltage line between the connection point 102 of the second component to the DC voltage line 104 and the short circuit at point 103, the drop of the line voltage at point 102 is slightly delayed compared to the drop of the line voltage at point 103, so that the discharge process of the capacitance / capacitor of the second component 120 towards the short circuit is delayed in time compared to the discharge process of the capacitance / capacitor of the third component 130. The second electronic protection switch 121 detects the current rise and the absolute value of the current by means of its current measuring means and switches off according to the switch-off conditions stored in the second electronic protection switch, for example when the current rise exceeds a certain value and / or when the absolute value of the current flowing through the second electronic protection switch 121 exceeds a certain value.

[0023] Now, according to the present invention, the time point at which the current flowing through the second electronic protection switch 121 reaches the reference current value before or during the shutdown process is determined as the second time point. The determination of these two time points does not need to be carried out in real time. For example, the current-time curve that causes the electronic protection switches 121 and 131 to be shut down can be (temporarily) stored in a storage component, and then the two time points at which the current flowing through the electronic protection switches 121 and 131 reaches the reference current value can be determined later based on the stored data, and if necessary, can be determined by interpolating the measured values ​​determined discretely in time. The storage component can be a component of the electronic protection switch, or it can also be a component of the control device (not shown) of the DC voltage system 100, which can itself be integrated into one of the electronic protection switches, which is thus a main protection switch (not shown). For the steps described below, it is only necessary to merge the time points in the processing unit and synchronize the clocks or time stamp generators of the electronic protection switches 121 and 131, or to consider possible clock deviations later. Data exchange and possible clock synchronization is shown by dashed line 105 and, as previously mentioned, may involve a central control or processing device.

[0024] If the components 110, 140 further away from the short circuit have capacitance, or the components 110, 140 are energy sources, the electronic protection switches 111, 141 of these components 110, 140 are turned off again later. The reason for this delayed turn-off has been explained in conjunction with the turn-off of the second electronic protection switch. In the design of the present invention, the time point at which the current flowing through them reaches the reference current value is also determined for these protection switches.

[0025] exist Figure 1 In the case of the component 140 shown by way of example in the figure for connecting the DC voltage system 100 to a higher-level grid, the electronic protection switch 141 associated with the component will generally have different dimensions and / or triggering characteristics than the electronic protection switches of the individual branches. In particular, its rated current and triggering current will be greater. It is unimportant here whether energy is obtained from the higher-level grid (that is, the components 110, 120, 130 are mainly electrical devices) or whether energy is output to the higher-level grid (that is, the components 110, 120, 130 are energy sources, for example renewable electrical energy such as photovoltaic devices or energy storage devices such as batteries or flywheels).

[0026] Below, according to Figure 2The method according to the invention is described in further detail. The method begins in step 210 with the determination of the already mentioned first time point at which the current flowing through the electronic protection switch which is first opened due to a short circuit in the DC voltage line 104 corresponds to the reference current value. In the case of a short circuit at point 103, which is considered here by way of example, this is the time point at which the current flowing through the third electronic protection switch 131 reaches the reference current value for the first time before or during the shutdown. As mentioned above, this determination can be carried out in real time or quasi-real time during the shutdown process, or can be carried out afterwards by evaluating stored measured values ​​and their time stamps.

[0027] In this case, the method can be started when a current rise indicating the occurrence of a short circuit is detected in one of the electronic circuit breakers of the DC voltage system 100. Alternatively, the method can be started by an operator who checks the device 100 after it has been switched off due to a short circuit, wherein in this case the method is run based on stored measured values. In step 220, the method continues with the determination of the second time point, which has also been mentioned, at which the current flowing through the second electronic circuit breaker that is switched off due to a short circuit in the DC voltage line 104 corresponds to the reference current value. In the case of a short circuit at point 103, which is considered here by way of example, this is the time point at which the current flowing through the second electronic circuit breaker 121 reaches the reference current value for the first time before or during the switching off. This determination can again be carried out in real time or quasi-real time during the switching off process, or can be carried out afterwards by evaluating the stored measured values ​​and their time stamps.

[0028] In one or more optional steps 230 , the substeps described in step 220 are carried out for other electronic protection switches of the DC voltage system 100 and further points in time are determined.

[0029] In step 240, the times determined in steps 210, 220 and optional step 230 are evaluated. In this case, in particular the relationship between the first and second times, optionally the relationship between the first time and each further time, is taken into account.

[0030] In a preferred exemplary embodiment, in particular, a difference is taken into account, ie, for example, a time difference Δt is determined between the second time t2 and the first time t1, ie, Δt=t2−t1. The sign of Δt is taken into account in this case.

[0031] In the presently observed case of a short circuit at point 103 , Δt is positive and corresponds to the maximum possible value.

[0032] If the short circuit is located in the middle between point 103 and point 102, then Δt=0. In this case, the inductive coating of the DC voltage line 104 The "center" is related to the length of the line between point 102 and point 103, provided that it remains constant or varies only slightly with length.

[0033] If the short circuit is located at the point 102 or at another point which is further away from the point 103 than the point 102 , Δt is negative and corresponds to the minimum possible value.

[0034] Therefore, in an embodiment, the position of the short-circuit point can be determined at least approximately based on Δt in step 240. If Δt=0, the short-circuit point is approximately located at the center between points 102 and 103, provided that the lengths of the connecting lines between points 102 and 103 and the corresponding SCCBs 121, 131 are approximately the same. If Δt>0, the short circuit is located between the center between points 102 and 103 and point 103; and if Δt<0, the short circuit is located between the center between points 102 and 103 and point 102 or between point 102 and point 101.

[0035] If more than two time points t1, t2 are ideally determined for all SCCBs 111-141 of the system 100, the timestamps may first be sorted in ascending order in step 240. The method described above is then performed with t1 corresponding to the first timestamp, i.e. the earliest timestamp, and t2 corresponding to the second timestamp, i.e. the second earliest timestamp.

[0036] Alternatively or additionally, in particular when Δt≠0, the time t0 of the short circuit can be determined or at least estimated, from which the time difference between the time stamp t1 or t2 on the one hand and t0 on the other hand can be determined and linked to one another, using the formula: Δt1=t1-t0 and Δt2=t2-t0 and r=Δt1 / Δt2 or r'=Δt2 / Δt1.

[0037] Here, in order to simplify the view, as already described above, t1 and Δt1 are associated with the SCCB that is triggered first, and t2 and Δt2 are associated with the SCCB that is triggered second.

[0038] It thus holds that, if the ratio is derived from r=Δt1 / Δt2, then r=1 corresponds to the case of Δt=0, i.e. the distances from the short circuit to the two SCCBs that are triggered first are approximately the same, and r<1 represents a measure of how far the short circuit is from the center in the direction of the SCCB that is triggered first.

[0039] If, on the other hand, the ratio is derived from r'=Δt2 / Δt1, then r=1 also corresponds to the case of Δt=0, i.e. the distances of the short circuit to the two SCCBs that are triggered first are approximately the same, and r'>1 represents a measure of how far the short circuit is from the center in the direction of the SCCB that is triggered first. Using the known distance between points 102 and 103 and the inductive coating, the geometric distance can be approximately derived from the value r or r'.

[0040] In an embodiment of the present invention, the time point t0 can be determined or estimated based on the rise of the current in the first triggered SCCB, for example, by linear interpolation of the current values ​​stored in the first triggered SCCB before and during the shutdown due to the short circuit. For example, the time point at which the linearly interpolated current rise begins can be approximately determined as t0.

[0041] In an embodiment of the present invention, as described above, a value lower than the current value at which the SCCB is switched off at the lowest rated current value in the DC voltage system 100 in the event of a short circuit is preferably selected as the reference current value, and reaching the reference current value is determined at least at the time points t1, t2 during the SCCB disconnection. In many practical applications of the DC voltage system 100, SCCBs 111, 121, 131, 141 with different rated current values ​​are used. As described above, Figure 1 In the case shown in the example in FIG. 1 , the assembly 140 is used to connect the DC voltage system 100 to a higher-level grid. Therefore, the SCCB 141 associated with the assembly usually has a higher rated current than the SCCBs 111 , 121 , 131 of the respective branches 110 , 120 , 130 .

[0042] Without limiting the generality, it is assumed that the SCCBs 111, 121, 131 of the various branches 110, 120, 130 have the same rated current In, for example In=50 A. Before the associated SCCB is switched off, it is often possible to tolerate a certain value exceeding the rated current for a certain time, for example, an overcurrent of 20% within 30 seconds or 1 minute. In the SCCB, this triggering behavior can be precisely parameterized, for example, the allowed number of repetitions of such a tolerable overcurrent event within a certain time unit can also be parameterized, so that even if a single event itself can be considered tolerable, when this number is exceeded, it is also triggered or switched off.

[0043] This tolerable overcurrent value forms a lower limit for selecting the reference current value Ir, ie, Ir>1.2*In in the example described above.

[0044] The upper limit of Ir is obtained from the maximum current value reached by the SCCBs 111, 121, 131 during short-circuit shutdown. This value also depends on the parameterization of the selected SCCB. For example, the SCCB can be parameterized to tolerate very high on-currents and must accordingly be able to distinguish between on-currents and short-circuit events, e.g., based on the rise of the current flowing through the SCCB and / or the duration of the current event. In many practical applications, the current value for short-circuit shutdown may be approximately 4 to 5 times the rated current In, simply put, Ir < 4*In.

[0045] Therefore, a value that satisfies the following conditions can be selected as the reference current value for the present invention: 1.2*In < Ir < 4*In, where In is the lowest rated current value of the SCCBs 111, 121, 131, 141 connected to the DC voltage line 104.

[0046] A reference current value that has a certain margin from the above-mentioned limit values has proven to be particularly suitable, especially 1.5*In < Ir < 3*In, preferably Ir = 2*In.

[0047] In step 250, the result of the calculation described in detail above is output to the operator or prepared for output, and the method ends.

[0048] As described above, the method can be performed in real time or after a short-circuit event based on the data stored in the SCCB. Here, in a particularly preferred embodiment, the data exchange and clock synchronization 105 between the SCCBs can be omitted. This embodiment will be described below.

[0049] Assume that at least two of the SCCBs have been disconnected or triggered due to a short-circuit event. Consistent with the above description, these are the SCCBs 121 and 131. The operator uses a portable device, such as a smartphone with a suitable application, which can be temporarily connected to these SCCBs (wirelessly or wired, e.g., via radio or a Blinksignal) for data exchange and calls the current-time curve related to short-circuit shutdown stored in the SCCB 121. In addition, the deviation between the clock of the portable device and the clock of the SCCB 121 is determined and stored.

[0050] This process is repeated for the SCCB 131. The timestamps of the asynchronous clocks of the SCCBs 121, 131 can be correlated with each other afterwards based on the deviation of the clocks of the two SCCBs relative to the clock of the portable device. Of course, if the clocks of the SCCBs are synchronized, this step can be omitted.

[0051] The portable device then determines t1 and t2 according to the method described above. Here, a preset value can be used as a reference current value. Alternatively, however, the portable device can also first analyze the called current-time curve and determine a reference value specifically for the corresponding evaluation based on the analysis result, for example if the deviation of the rated current value of the SCCB is so great that the standard value Ir=2*In is too close to the current value that the SCCB with a higher rated current value can tolerate when temporarily exceeded. In general, for Ir, only the values ​​that the two observed SCCBs experience during the corresponding short-circuit-induced shutdown process and preferably only once during the current rise are taken into account.

[0052] After Ir has been determined or a suitable standard value for Ir has been determined, the combined operation can be performed on the portable device based on the (possibly subsequently synchronized) timestamps of the two SCCBs reaching Ir, which are obtained, if necessary, by interpolation of the sampled values ​​of the current. Figure 2 The method is described and the results are displayed to the operator.

[0053] Of course, the evaluation described above can also be performed by a central device or a control center instead of by means of a portable device.

[0054] It should be noted that the embodiments described above can be arbitrarily combined with each other. In addition, it should be noted that the term "controller" used herein includes controllers, processors and processing units in the broadest sense used in SCCB, i.e., for example, general-purpose processors, digital signal processors, application-specific integrated circuits (ASICs), programmable logic circuits (e.g., FPGAs), discrete analog or digital circuits and any combination thereof, including all other processing units known to those skilled in the art or developed in the future. Here, the processor can be composed of one or more devices. If the processor is composed of multiple devices, these devices can be configured to process instructions in parallel or sequentially.

Claims

1. A method for locating a short circuit in a DC voltage system (100), wherein: The DC voltage system comprises at least two components (110, 120, 130, 140), each of which comprises a capacitor and is connected to the DC voltage line (104) in a detachable manner by means of an electronic circuit breaker (111, 121, 131, 141), wherein the electronic circuit breaker comprises a current measuring component for measuring a current flowing through the corresponding circuit breaker; The method comprises the following method steps: - determining a first point in time at which the current flowing through the electronic protection switch which is first opened due to a short circuit in the DC voltage line corresponds to a reference current value; - determining a second point in time at which the current flowing through the second electronic protection switch which is opened due to the short circuit in the DC voltage line corresponds to the reference current value; and - Based on the determined time, the approximate distance of the short circuit from one of the two electronic circuit breakers is calculated.

2. The method according to claim 1, wherein: The two points in time are differentiated and the approximate distance of the short circuit from one of the two electronic circuit breakers is calculated from the difference.

3. A method according to any one of the preceding claims, wherein: The distance of the short circuit is calculated starting from the circuit breaker that is tripped first due to a short circuit.

4. A method according to any one of the preceding claims, wherein: A current value between a minimum overcurrent that one of the electronic protection switches can tolerate within a predeterminable short time and a maximum current flowing through the electronic protection switch that opens first during a short circuit, preferably a current value between 1.5 times and 3 times the minimum rated current value of one of the electronic protection switches, is selected as the reference current value.

5. An electrical device (100), comprising: - a DC voltage line (104); at least two components (110, 120, 130, 140), each of which has a capacitor and is connected to the DC voltage line in a releasable manner by means of an electronic circuit breaker (111, 121, 131, 141), wherein: The electronic protection switch has a current measuring component for measuring the current flowing through the corresponding protection switch; - means for implementing a method according to any of the preceding claims.

6. The electrical device according to claim 5, wherein: The components for implementing the method are part of a control unit which has components for exchanging data with the electronic circuit breaker.

7. The electrical device according to claim 5, wherein: The components for carrying out the method are components of one of the electronic circuit breakers.

8. The electrical device according to claim 5, wherein: Components for implementing the method are distributed on the electronic protection switch.

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