Short circuit testing device

Abstract

An electrical equipment system for preventing an electrical load network (1) from being switched on in the event of a short circuit in the load network (1), the electrical equipment system comprising: a switch (2); an interlocking unit (6) coupled to the switch (2); a short-circuit test device (7) coupleable to the load network (1) wherein the short-circuit test device (7) comprises a voltage source (11), a measurement unit (12) and a control unit (13) connected to the voltage source (11) and to the measurement unit (12), the control unit (13) being adapted to cause the voltage source (11) to apply a test voltage to the load network (1), and for comparing a measurement signal recorded in response to the test voltage with a predefined short-circuit criterion and for outputting a protection signal to the interlocking unit (6) if the recorded measurement signal conforms to the criterion.

Description

[0001] This application is a divisional application of an application with an application date of June 7, 2021, application number 202110631623.9, and invention name “Short-circuit test device”. Technical Field

[0002] The present disclosure relates to a short circuit testing device. Background Art

[0003] The electrical load network or load grid is separated from the upstream network (usually the utility network or the grid) by means of a switch (especially a circuit breaker). With the switch or circuit breaker in the open state (usually after a short circuit shot down), the electrical state of the load network is unclear. Even if the electrical error seems to be repairable, it is not certain that this is the only error or that no new errors have occurred. Attempting to switch on the circuit breaker during a service life short circuit will generate a large amount of arcing at the contacts of the switch and corrode the contacts. The typical current in a short circuit state is 6000A in a 240V grid. Especially for grids with higher voltages above 600V, such incomplete switching actions under short circuit conditions can significantly shorten the service life of the low switch. Summary of the invention

[0004] The object of the present invention is to overcome the disadvantages of the prior art by providing a device which prolongs the service life of a switch, in particular a circuit breaker, and reduces contact corrosion.

[0005] According to the invention, this object is achieved by the following features.

[0006] A short circuit test device having a first line test conductor to be coupled to a first load line conductor of an electrical load network and a neutral test conductor to be coupled to a neutral conductor of the electrical load network, the short circuit test device comprising:

[0007] a voltage source which is switchable to the first line test conductor and the neutral test conductor to output a predefinable test signal,

[0008] a measuring unit adapted to measure voltage and / or current, the measuring unit comprising a measuring input connectable to the first line test conductor and the neutral test conductor, the measuring unit further comprising an output for providing a measurement signal, and

[0009] a control unit connected to the voltage source and the measuring unit, the control unit being adapted to cause the voltage source to apply a test voltage to the first line test conductor and the neutral test conductor and to output a protection command at a protection output terminal in order to compare the measurement signal provided by the measuring unit in response to the test signal with at least one predefined short-circuit criterion.

[0010] A method for checking a load in a circuit, the method comprising the following steps:

[0011] - checking whether the switch connecting the load to the utility network upstream of the switch is switched off or tripped,

[0012] - connecting the measuring unit to the load via a plurality of paired combinations of conductors of the electrical load network downstream of the switch if the switch is in the open state,

[0013] - for each of said pair combinations, applying a test signal to said load and comparing the response with a response indicative of a non-faulty load, and

[0014] - enabling the switch to be turned on if all of the responses indicate a non-faulty load, and disabling the switch to be turned on if any of the responses indicates a faulty load.

[0015] As a result, the service life of switches, especially circuit breakers, will be extended. Since switching can be prevented during short circuit conditions, excessive contact corrosion will not occur. Reducing or avoiding contact corrosion maintains low contact area resistance over a longer service life. Low contact resistance keeps the dissipated energy and the temperature inside the switch low. Low temperatures extend the service life of the electronic components inside the switch.

[0016] In general, it is advantageous in the context of the disclosed method if the result of the comparison forms the input of an OR logic, and if the output of the OR logic is false, the switch is allowed to be turned on, while if the output of the OR logic is true, the switch is prohibited to be turned on. Thus, the logic for allowing or prohibiting the turning on of the switch can be implemented using reliable means of low technical complexity. The OR logic can be implemented by software or hardware. In particular, the software can be run in a control unit of the short-circuit test device.

[0017] Advantageously, the response to the test signal comprises both a voltage response and a current response.Thus, the response allows multiple characteristics of the load to be examined.

[0018] Advantageously, checking the load involves a plurality of cascaded switches. Thus, the entire network of cascaded switches as well as the load can be checked. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention is described with reference to the accompanying drawings, which show preferred embodiments only.

[0020] Figure 1 A block diagram of a system according to the principles of the present invention is shown;

[0021] Figure 2 A schematic diagram showing a first specific embodiment of a system according to the present invention is shown;

[0022] Figure 3 A schematic diagram showing a second specific embodiment of a system according to the present invention;

[0023] Figure 4 shows a schematic diagram of a third specific embodiment of the system according to the invention in a first state;

[0024] Figure 5 The second state is shown according to Figure 4 A schematic diagram of an implementation scheme of

[0025] Figure 6 A fourth specific embodiment of the system according to the present invention is shown;

[0026] Figure 7 Possible solutions for correction algorithms are shown;

[0027] Figure 8 The first part of a possible test sequence is shown;

[0028] Fig. 9 shows a second part of a possible test sequence, which can be repeatedly performed, and

[0029] Fig.10 The last part of a possible test sequence is shown. DETAILED DESCRIPTION

[0030] Figure 1 and Figure 5 The principle and preferred embodiments of the electrical equipment system are shown. Each system comprises a short-circuit test device 7 having a first line test conductor 8 to be connected to a first load line conductor 5 of an electrical load network and a neutral test conductor 9 to be connected to a neutral conductor 10 of the electrical load network 1, the short-circuit test device 7 comprising:

[0031] a voltage source 11 which can be switched to the first line test conductor 8 and the neutral test conductor 9 in order to output a predefinable test signal,

[0032] a measuring unit 12, which is suitable for measuring voltage and / or current, which comprises a measuring input which is connectable to the first line test conductor 8 and the neutral test conductor 9, and an output for providing a measurement signal, and

[0033] - A control unit 13, which is connected to the voltage source 11 and the measuring unit 12, and is suitable for causing the voltage source 11 to apply a test voltage to the first line test conductor 8 and the neutral test conductor 9, and in order to compare the measurement signal provided by the measuring unit 12 in response to the test signal with at least one predefined short-circuit criterion, the control unit 13 is also suitable for outputting a protection command at the protection output terminal when the recorded measurement signal meets the short-circuit criterion.

[0034] Figure 4 and Figure 5 The reference numeral 7 indicating the short circuit test device 7 is not included, and indeed no border line is shown for the short circuit test device 7. Including such a border line would make the figures more confusing. However, Figure 4 and Figure 5 The internal features of a short circuit test device 7 in one embodiment of the present invention are shown.

[0035] according to Figures 1 to 5 The electrical equipment system is implemented to prevent the load network 1 from switching on in the event of a short circuit in the load network 1. The system comprises an electrical utility network 3, an electrical load network 1 and at least one switch 2 located between the utility network 3 and the load network 1. The switch is particularly implemented as a circuit breaker to disconnect the load network 1 in the event of any fault cause (e.g. overcurrent and / or short-circuit current).

[0036] The switch 2 is located between the first public line conductor 4 of the public network 3 and the first load line conductor 5 of the load network 1, and the system further comprises:

[0037] an interlocking unit 6 coupled to the switch 2 to controllably lock the switch 2 in an off position and prevent the switch 2 from being turned on if the interlocking unit 6 receives a protection command; and

[0038] A short-circuit test device 7 , wherein the protection output is connected to the interlocking unit 6 .

[0039] As a result, the service life of the switch 2, and in particular the circuit breaker, will be extended. Since switching can be prevented during the short circuit condition, no excessive contact corrosion will occur. Reducing or avoiding contact corrosion maintains low contact area resistance over a longer service life. Low contact resistance keeps the dissipated energy and the temperature inside the switch 2 at a low level. The low temperature extends the service life of the electronic components inside the switch 2.

[0040] The short circuit test device 7 can be operated in a preventive manner after the switch 2 has been tripped or before any operation of the switch 2. In addition to extending the service life of the switch 2, preventing the operation of the switch 2 in the event of a short circuit can also prevent damage to equipment or people. This is especially true when the switch 2 is the main circuit breaker in a house or industrial facility, where closing the circuit breaker during the presence of a short circuit may seriously injure the operator or damage the remaining equipment.

[0041] A practical system comprising different units is described. Each of these units can be a separate device with its own housing. However, it is also suggested to place some or all of the described units and components in a single device.

[0042] The system is provided in particular for a low voltage network or electrical network. The network comprises a neutral conductor 10 and at least one or at least a first line conductor 4, 5. According to a particularly preferred embodiment, the network further comprises a second line conductor 18 and a third line conductor 19.

[0043] In case of a short circuit in the electrical load network 1, the short circuit test device 7 will prevent said load network 1 from being switched on. The load network 1 is distinguished from the upstream utility network 3 by a switch 2 which is part of the system. The switch 2 is located between the electrical utility network 3 and the load network 1. Another term for a network is a grid. According to the basic concept, only one switch 2 located in the first line conductor 4, 5 is sufficient to disconnect the load network 1. According to a preferred embodiment, as Figures 2 to 5 As shown, the neutral conductor 10 also passes through the switch 2 .

[0044] The electrical equipment system includes an interlock unit 6, which is coupled to the switch 2 to controllably lock the switch 2 in the disconnect position and prevent the switch 2 from being turned on. The interlock unit 6 can be an integral part of the switch 2. In one embodiment, the interlock unit 6 specifically includes a mechanical member that can engage a part of the switch mechanism of the switch 2 to prevent the contacts of the switch 2 from closing. For example, the interlock device 6 can include a pin that prevents the mechanism of the handle, crossbar or contact arm of the switch 2 from closing. The interlock device can also separate the handle or crossbar from the mechanism or contact arm. The interlock unit 6 can also or optionally include an electronic connection with the switch 2 to prevent the switch 2 from closing by locking the electronic release device. For example, the interlock device may be sending a trip signal to the trip latch of the switch 2 or activating the shunt of the switch 2. The interlock unit 6 usually has to be specially designed to lock for a specific switch 2 or a company's switch.

[0045] The interlocking unit 6 also comprises at least one control input to receive a protection command that can trigger the interlocking. In the case of electronic control, the interlocking device can only connect the protection output of the short-circuit test device 7 to the switch 2.

[0046] The short-circuit test device 7 comprises a first line test conductor 8 which can be coupled to the first load line conductor 5 and a neutral test conductor 9 which can be coupled to the neutral conductor 10 of the load network 1. In this case, being coupleable means that the first line test conductor 8 is usually not connected to the first load line conductor 5, and they can be connected in the form of a physical connection, or the two conductors can be placed so close that an inductive or capacitive interaction occurs. According to a preferred embodiment, at least one first relay 14 is located in the first line test conductor 8 and the neutral test conductor 9. Usually more than one relay 14 is provided.

[0047] Advantageously, the switch 2 and the relay 14 are logically connected so that they are in opposite states. In this way, when the switch 2 is disconnected, the relay 14 is closed, thereby allowing the operation of the short-circuit test device 7. Once the switch 2 is closed, the relay 14 is disconnected, thereby disconnecting the short-circuit test device. This can be achieved in many ways. For example, the relay 14 can be a pair of auxiliary switches coupled to the handle of the switch 2. The relay 14 can also be a pair of auxiliary switches activated by a button. The movement of the button may also release the locking handle of the switch 2. In another embodiment, the switch handle can be protected with a cover that closes the relay 14 when disconnected.

[0048] The short-circuit test device comprises a power source, not shown, which is connected to the public network 3 or the grid, bypassing the switch 2 or the battery.

[0049] The short-circuit test device 7 comprises a voltage source 11 connectable to the first line test conductor 8 and the neutral test conductor 9. The voltage source 11 is adapted to generate a test signal having a high amplitude and a high rate of rise or slew rate. Relatively short voltage pulses, in particular in the range of a duration of half a cycle of the grid frequency of the utility network 3, may be sufficient. According to a preferred embodiment, the voltage source 11 comprises a boost circuit to generate a high amplitude signal. According to an alternative preferred embodiment, the voltage source 11 is implemented to generate a test signal comprising a frequency sweep.

[0050] The short-circuit test device 7 comprises a measuring unit 12 suitable for measuring voltage and / or current, the measuring unit 12 comprising a measuring input terminal, which can be connected to the first line test conductor 8 and the neutral test conductor 9, and the measuring unit 12 also comprises an output terminal for providing a measurement signal, which represents the measured voltage and / or current.

[0051] The short circuit test device 7 further comprises a control unit 13 connected to the voltage source 11 and the measuring unit 12. The control unit 13 is particularly implemented to include a microcontroller. The control unit 13 controls the test regarding a short circuit condition in the load network 1. The control unit 13 is adapted to cause the voltage source 11 to apply a test voltage to the first line test conductor 8 and the neutral test conductor 9. By applying the test voltage to the load network 1 and monitoring its behavior, a short circuit in the load network 1 can be detected.

[0052] The control unit 13 is adapted to compare the measurement signal recorded in response to the test signal provided by the measuring unit 12 with at least one predefined short-circuit criterion. A short circuit can be detected in different ways. By applying an almost perfect rectangular pulse or step, it will be possible to detect a short circuit condition by analyzing the step function response using methods known in the field of telecommunications. It can also work by using a swept signal as test signal. In both cases, the measurement signal is preferably analyzed in the frequency domain. According to a preferred embodiment, the control unit 13 comprises a transformation unit to perform an FFT or a wavelet transform or a Gabor transform on the measurement signal.

[0053] In the event that the recorded measurement signal complies with the stored short-circuit criterion, the control unit 13 outputs a protection command at the protection output to the interlocking unit 6. In the example described, the protection command triggers the interlocking unit 6, thereby preventing the switch 2 from closing and preventing the circuit from closing. In another embodiment, the switch 2 is always locked open, and the protection command will trigger the unlocking of the switch 2 when the short-circuit criterion is not met.

[0054] According to another embodiment, the short circuit test device 7 includes a communication interface to receive commands about the load network state and / or output measurement results and / or indicators about the load network state. The communication interface can be implemented according to any telecommunication process or standard. In particular, the communication interface is implemented according to at least one of the following standards: IEEE 802 including WiFi (IEEE 802.11) and Bluetooth (IEEE 802.15), Zigbee (based on IEEE 802.15.4), TCP / IP, GSM, GPRS, LTE. The communication interface is connected to the control unit 13.

[0055] As an advantage of the communication interface, the short-circuit test device 7 can be connected with at least one of the following components: PC or server, mobile device (such as smartphone), RTU (Remote Terminal Unit), cloud. The connection between the short-circuit test device 7 and one of the mentioned devices makes it possible to remotely and supervise the short-circuit test device 7. It provides the possibility to record fault events and visualize event graphics, all kinds of other information collected by the short-circuit test device 7 for fast location of the user or supervisor.

[0056] based on Figures 1 to 5 Details and specific implementations are described.

[0057] Figure 1 A block diagram of a basic system according to the present invention is shown. In addition to the components already described, Figure 1 A load 15 is also shown. Figure 1 In the basic system shown, the neutral line 10 does not pass through the switch 2. Figure 1 Also shown is the boundary between the utility network 3 , also called utility grid, and the load network 1 or load grid.

[0058] Figures 2 to 5 A system is shown in each case in which the three line conductors 5 , 18 , 19 and the neutral conductor 10 all pass through a four-pole switch 2 .

[0059] Figure 2 A first specific embodiment of the system according to the invention is shown. A first line test conductor 8 is permanently connected to the first load line conductor 5, a second line test conductor 16 is permanently connected to the second load line conductor 18, and a third line test conductor 17 is permanently connected to the third load line conductor 19. A neutral test conductor 9 is permanently connected to the neutral conductor 10.

[0060] The voltage source 11 comprises a transformer 36 , wherein a primary winding of the transformer 36 is connected to the step-up circuit and a secondary winding 37 of the transformer 36 is connectable to the first load line conductor 5 and the neutral conductor 10 via three relays 14 , 20 , 21 .

[0061] The measuring unit 12 is connected to the secondary winding 37 of the transformer 36 to measure the voltage via the voltage divider and the current via the shunt and amplifier 23, as shown in FIG. Figure 2 shown.

[0062] The first embodiment uses the transformer mutual inductance principle to provide the excitation signal. According to this principle, the voltage on the secondary winding of the transformer 36 and the current in the secondary winding are measured and analyzed by the measuring unit 12.

[0063] Figure 3 A second specific embodiment of the system according to the invention is shown. This embodiment uses the capacitive effect to couple the measuring unit 12 to the line and neutral conductors 5, 18, 19, 10.

[0064] The first hollow tube 24 surrounds the first load line conductor 5, the second hollow tube 25 surrounds the neutral conductor 10, the third hollow tube 26 surrounds the second load line conductor 18, and the fourth hollow tube 27 surrounds the third load line conductor 19. The first line test conductor 8 is connected to the first hollow tube 24, the second line test conductor 16 is connected to the third hollow tube 26, the third line test conductor 17 is connected to the fourth hollow tube 27, and the neutral test conductor 9 is connected to the second hollow tube 25. The hollow tubes 24, 25, 26, 27 or cylinders form a capacitor through which the lines 5, 18, 19, 10 pass.

[0065] The embodiment includes individual discrete capacitors 28, 29, 30, 31 located in each test conductor 8, 9, 16, 17. At least one first capacitor 28 is arranged in the first line test conductor 8 between the voltage source 11 and the first hollow tube 24, at least one second capacitor 29 is arranged in the neutral test conductor 9 between the voltage source 11 and the second hollow tube 25, at least one third capacitor 30 is arranged in the second line test conductor 16 between the voltage source 11 and the third hollow tube 26, and at least one fourth capacitor 31 is arranged in the third line test conductor 17 between the voltage source 11 and the fourth hollow tube 27.

[0066] The measuring unit 12 is connected to the first line test conductor 8 between the first capacitor 28 and the first hollow tube 24, to the neutral test conductor 9 between the second capacitor 29 and the second hollow tube 25, to the second line test conductor 16 between the third capacitor 30 and the third hollow tube 26, and to the third line test conductor 17 between the fourth capacitor 31 and the fourth hollow tube 27.

[0067] The second embodiment uses the capacitive voltage divider principle. The measuring unit 12 measures and analyses the voltage in the middle of the capacitor voltage divider circuit for each phase.

[0068] Figure 4 and Figure 5 A third specific embodiment of the system is shown in different states. This embodiment analyses the resistance behavior of the load network 3 .

[0069] The third embodiment comprises spring-loaded contacts 32, 33, 34, 35 to bring the short-circuit test device 7 into contact with the load network 3. Figure 4 and Figure 5 The first line test conductor 8 includes at least one first spring-loaded contact 32 arranged opposite to the first contact area of ​​the first load line conductor 5, the neutral test conductor 9 includes at least one second spring-loaded contact 33 arranged opposite to the second contact area of ​​the neutral conductor 10, the second line test conductor 16 includes at least one third spring-loaded contact 34 arranged opposite to the third contact area of ​​the second load line conductor 18, and the third line test conductor 17 includes at least one fourth spring-loaded contact 35 arranged opposite to the fourth contact area of ​​the third load line conductor 19.

[0070] The separate contact region can be embodied as a clamping region of the switch 2 .

[0071] Each of the spring-loaded contacts 32 , 33 , 34 , 35 is implemented to temporarily contact a corresponding contact area during application of a high-amplitude test signal by the voltage source 11 .

[0072] Figure 6 A fourth specific embodiment of the system according to the invention is shown. In this example, the switch 2 is connected to a three-phase system with phases L1..L3 and to a load 15. The short-circuit test device 7 is connected by Figure 6 The line test conductors 8 and 16 in are connected to two exemplary phases L1 , L2 .

[0073] The transformer 36 connected in series with the shunt 38 switches between the phases L1, L2 via electromechanical or electronic switches 20, 21, which can be implemented as relays in particular. The electromechanical or electronic switches 20, 21 are controlled by the control unit 13 via a driver 39. In addition, the electromechanical or electronic switch 40 connected to the interlocking unit 6 of the switch 2 is also controlled by the control unit 13 via the driver 39. In particular, the electromechanical or electronic switch 40 can also be implemented as a relay. Preferably, as Figure 6 As shown, an isolating electronic semiconductor component 45 , which can be embodied in particular as an optocoupler, is arranged between the control unit 13 and the driver 39 in order to isolate the control unit 13 from the driver 39 .

[0074] During the test, a test signal is generated by the control unit 13 and the DC to AC converter 41 and fed to the transformer 36. Thus, the test signal is also applied to the electrical circuit comprising the phases L1, L2, the load 15, the line test conductors 8 and 16, the electromechanical or electronic switches 20, 21, the transformer 36 and the shunt 38. Advantageously, the frequency of the test signal can be varied by the DC to AC converter 41 so that a frequency sweep can be generated.

[0075] For evaluation, the voltage and current in the electrical circuit are sensed by means of a voltage amplifier 42 and a current amplifier 43 (note that the current is sensed by using a shunt 38). The signals of the voltage amplifier 42 and the current amplifier 43 are converted into digital signals by means of an analog-to-digital converter 44, which are fed to the control unit 13 and further processed there.

[0076] It should be noted that although Figure 6 Reference is made to a three-phase system with phases L1 .. L3, but a similar, equivalent or identical design of the system according to the invention is also possible in the context of another electrical system, such as a three-phase system with a neutral line (L1 .. L3, N) or a single-phase system with a neutral line (L1 / N, L2 / N, L3 / N).

[0077] Figures 7 to 10

[0046] A flow chart of the manner in which the operation of the hardware structure presented in this disclosure may be performed is now shown. Figures 7 to 10 In particular Figure 6 The hardware structure shown, but also refers to Figures 1 to 5 The hardware structure shown.

[0078] In detail, Figure 7 A possible solution for the correction algorithm is shown. In a first step 701, a power-on signal is received. Further, the short-circuit test device 7 is switched on in step 702. Next, the controller and the inputs and outputs are initialized in step 703. This essentially refers to the software running in the control unit 13. Next, the switch 2 is opened in step 704 to disconnect the load 15 from the phases L1..L3. Then, in condition 705, it is checked whether the test button associated with the correction routine is pressed.

[0079] If the check is positive (see branch Y), the electromechanical or electronic switch 20, 21 is closed in step 706 and a test signal is generated in step 707. If the check is negative (see branch N), the sequence continues with step 703. In addition, the output of the test button state subroutine A is fed into the condition 705.

[0080] In step 708, the voltage response to the test signal is stored. In particular, step 708 may include storing whether the voltage response is >1.5V, which means there is no isolation fault or short circuit in the load 15 and the load 15 is good, or whether the voltage response is ≤1.5V, which means there is an isolation fault or short circuit in the load 15 and the load 15 is not ready for operation. Figure 6 In the arrangement of , the voltage response is specifically sensed by the voltage amplifier 42 .

[0081] In step 709, the current response to the test signal is stored. In particular, step 709 may include storing the current response to the test signal. Figure 6 Whether the current response measured by the shunt 38 and current amplifier 43 in the arrangement is <200mV, which again means that there is no isolation fault or short circuit in the load 15 and the load 15 is good, or whether the current response is ≥200mV, which means that there is an isolation fault or short circuit in the load 15 and the load 15 is not yet ready for operation.

[0082] Generally, it should be noted that based on Figure 6 , one can get the impression that only the connection between phases L1 and L2 is sensed and checked for response. However, in reality, multiple checks can be performed on different connections. Thus, in addition to checking between phases L1 / L2, one can also check L2 / L3, L1 / L3, and in the case of a neutral line also between N / L1, N / L2, N / L3.

[0083] In step 710, the status of the various checks related to the voltage response are stored in associated registers. Equivalently, in step 711, the status of the various checks related to the current response are stored in associated registers. Next, the process jumps to "A" and thus to conditional 705. This sequence is repeated until all checks are completed.

[0084] Next, by using Figures 8 to 10 A possible test sequence is explained below. First, in condition 801, it is checked whether a power-on signal S is received from a switch 2. If the check is positive (see branch Y), in step 802, the short-circuit test device 7 is in the disconnected state and in step 803 the communication protocol is started so that another switch 2 can be tested. In step 804, a connection is made to the other switch 2 and the initialization subroutine B is started there. This option is useful if there are many cascaded switches 2 that must be checked to determine whether the circuit is faulty.

[0085] If the result of the check in condition 801 is negative, the short-circuit test device 7 is switched on in step 805. Next, the controller and the inputs and outputs are initialized in step 806. This essentially refers to the software running in the control unit 13. Next, the switch 2 is opened in step 807 to disconnect the load 15 from the phases L1..L3. Then, in condition 808, it is checked whether the test button associated with the correction routine has been pressed.

[0086] If the check is positive (see branch Y), the electromechanical or electronic switch 20, 21 is closed in step 809 and a test signal is generated in step 810. If the check is negative (see branch N), the sequence continues with step 807. In addition, the output of the test button state subroutine A is fed into the condition 808.

[0087] In step 811, the voltage response to the test signal is stored. In particular, this step 811 may include storing whether the voltage response is >1.5V, which means that there is no isolation fault or short circuit in the load 15 and the load 15 is good, or whether the voltage response is ≤1.5V, which means that there is an isolation fault or short circuit in the load 15 and the load 15 is not ready for operation. In particular, in Figure 6 In the arrangement of , the voltage response is sensed by a voltage amplifier 42 .

[0088] In step 812, the current response to the test signal is stored. In particular, step 812 may include storing the current response to the test signal. Figure 6 Whether the current response measured by the shunt 38 and current amplifier 43 in the arrangement is <200mV, which again means that there is no isolation fault or short circuit in the load 15 and the load 15 is good, or whether the current response is ≥200mV, which means that there is an isolation fault or short circuit in the load 15 and the load 15 is not yet ready for operation.

[0089] As mentioned before, several checks can be performed for different connections, i.e. between phases L1 / L2, L2 / L3, L1 / L3, and in the case where there is also a neutral line between N / L1, N / L2, N / L3. The switch 2 can only safely connect the load 15 to the phases L1..L3 if each check indicates that there is no fault in the load 15. In other words, any negative check should prohibit switching the load 15 to the phases L1..L3. Advantageously, this function can be implemented by using an OR logic for all these tests, which means that any fault will generate a signal at the output of this OR logic. Generally, this OR logic can be implemented by hardware or software (in particular in the control unit 13).

[0090] According to the OR logic, if the result of the check of condition 811 is negative, a flag is set in step 813 to indicate that there is a short circuit in load 15. If the check is positive, the flag is cleared in step 814. Thus, if the result of the check of condition 812 is negative, the flag is set in step 815 to indicate that there is a short circuit in load 15, and if the check is positive, the flag is cleared in step 816.

[0091] Additionally, a voltage feedback check VF may be fed into the condition 811 and a current feedback check AF may be fed into the condition 812. The voltage feedback check VF gives an indication about the state of the voltage amplifier 42, such as whether the measurement has been completed, whether the measurement is valid (e.g. due to overload or saturation of the voltage amplifier 42), etc. Likewise, the current feedback check AF gives an indication about the state of the current amplifier 43, such as whether the measurement has ended, whether the measurement is valid (e.g. due to overload or saturation of the current amplifier 43), etc.

[0092] In step 817, the status of the various checks related to the voltage response are stored in the associated registers. Equivalently, in step 818, the status of the various checks related to the current response are stored in the associated registers. Next, for another connection between phases L1 / L2, L2 / L3, L1 / L3, and in the case where there is also a neutral line between N / L1, N / L2, N / L3, the process jumps to the next test sequence NT.

[0093] at last, Figure 8 A step 819 is shown of inhibiting the closing of the switch 2 due to the OR logic C and the initialization subroutine B which is run once when the test device 7 is switched on or powered on.

[0094] Fig. 9 A subroutine is shown which is carried out for the next test sequence NT for a further connection between the phases L1 / L2 , L2 / L3 , L1 / L3 and also in the case of a neutral conductor between N / L1 , N / L2 , N / L3 .

[0095] In step 901, for said next test sequence NT, the electromechanical or electronic switch 20, 21 is closed and a test signal is generated in step 902. In step 903, a voltage response to the test signal is stored. In particular, this step 903 may include storing whether the voltage response is >1.5V, which means that there is no isolation fault short circuit in the load 15 and the load 15 is good, or whether the voltage response is ≤1.5V, which means that there is an isolation fault or short circuit in the load 15 and the load 15 is not yet ready for operation. In particular, in step 904, the voltage response is stored. Figure 6 In the arrangement of , the voltage response is sensed by a voltage amplifier 42 .

[0096] In step 904, the current response to the test signal is stored. In particular, step 904 may include storing the current response to the test signal. Figure 6 Whether the current response measured by the shunt 38 and current amplifier 43 in the arrangement is <200mV, which again means that there is no isolation fault or short circuit in the load 15 and the load 15 is good, or whether the current response is ≥200mV, which means that there is an isolation fault or short circuit in the load 15 and the load 15 is not yet ready for operation.

[0097] If the result of the check of condition 903 is negative, a flag is set in step 905 to indicate that there is a short circuit in load 15, and if the check is positive, the flag is cleared in step 906. Thus, if the result of the check of condition 904 is negative, the flag is set in step 907 to indicate that there is a short circuit in load 15, and if the check is positive, the flag is cleared in step 908.

[0098] Additionally, a voltage feedback check VF may be fed into condition 903 and a current feedback check AF may be fed into condition 904 (see above for explanation of using voltage feedback check VF and current feedback check AF).

[0099] In step 909, the status of the various checks related to the voltage response are stored in the associated registers. Equivalently, in step 910, the status of the various checks related to the current response are stored in the associated registers. Next, for another connection between phases L1 / L2, L2 / L3, L1 / L3, and in the case where there is also a neutral line between N / L1, N / L2, N / L3, the process jumps to the next test sequence NT or the last test sequence LT. Thus, the process can be repeated for different test connections. Fig. 9 subroutine.

[0100] Fig.10 shows a subroutine that is similar to Fig. 9 The subroutine shown in is similar to that shown in and is performed for the last test sequence LT between phases L1 / L2, L2 / L3, L1 / L3 and in the case where a neutral line is also present between N / L1, N / L2, N / L3.

[0101] In step 1001, for said last test sequence LT, the electromechanical or electronic switch 20, 21 is closed and a test signal is generated in step 1002. In step 1003, a voltage response to the test signal is stored. In particular, this step 1003 may comprise storing whether the voltage response is >1.5V, which means that there is no isolation fault or short circuit in the load 15 and the load 15 is good, or whether the voltage response is ≤1.5V, which means that there is an isolation fault or short circuit in the load 15 and the load 15 is not yet ready for operation. In particular, in step 1004, the voltage response to the test signal is stored. Figure 6 In the arrangement of , the voltage response is sensed by a voltage amplifier 42 .

[0102] In step 1004, the current response to the test signal is stored. In particular, step 1004 may include storing the current response to the test signal. Figure 6 Whether the current response measured by the shunt 38 and current amplifier 43 in the arrangement is <200mV, which again means that there is no isolation fault or short circuit in the load 15 and the load 15 is good, or whether the current response is ≥200mV, which means that there is an isolation fault or short circuit in the load 15 and the load 15 is not yet ready for operation.

[0103] If the result of the check of condition 1003 is negative, a flag is set in step 1005 to indicate that a short circuit exists in load 15, and if the check is positive, the flag is cleared in step 1006. Thus, if the result of the check of condition 1004 is negative, the flag is set in step 1007 to indicate that a short circuit exists in load 15, and if the check is positive, the flag is cleared in step 1008.

[0104] Additionally, a voltage feedback check VF may be fed into condition 1003 and a current feedback check AF may be fed into condition 1004 (see above for explanation of using voltage feedback check VF and current feedback check AF).

[0105] In step 1009, the status of the various checks related to the voltage response are stored in the associated registers. Equivalently, in step 1010, the status of the various checks related to the current response are stored in the associated registers. Next, the process jumps to condition 1011, in which a check is made whether the result of the OR logic with the flags of all the checks as inputs is positive. If the result of condition 1011 is positive (see branch Y), the process jumps to subroutine C, which results in the prohibition of turning on switch 2 (in this case, see also Figure 8 If the result of condition 1011 is negative (see branch N), the process jumps to the test button state subroutine A (in this case, see also Figure 8 condition in 808).

[0106] In summary, the proposed process can be described as follows:

[0107] 1) Calibration: First, a calibration is performed to store the characteristics of a fault-free load 15. In principle, this step only needs to be performed once, but it can of course also be repeated. This step can be performed at any time when the switch is in the open state, for example during preventive maintenance. When the power-on signal is received, the short-circuit test device 7 is switched on, i.e. powered on. This also leads to the initialization of the short-circuit test device 7. Next, the switch 2 is opened or tripped so that the load 15 remains disconnected from the phases L1..L3 and from the neutral line N if the neutral line is also present. This can be done by means of switching commands that can be sent to the switch 2. In addition, the switch 2 may also trip if a fault occurs (for example, overcurrent and / or undervoltage). Usually, the short-circuit test device 7 is turned off when the switch 2 is turned on and vice versa (this is also true when testing). At this stage, a command to switch 2 or a press of a test button or a time-based signal from control unit 13 injects a test signal into load 15, in particular by using a frequency sweep generated by DC to AC converter 41 and in particular by voltage source 11 to power an external power source (auxiliary power source or battery storage). Depending on load 15 (i.e. its capacitance and inductance), a suitable frequency sweep can be used. For testing phases L1 .. L3 and, in case a neutral line is also present, the neutral line N is switched to measuring unit 12. Then, based on the characteristics of load 15 (for example, the predetermined range may be: less than 200 mV for current feedback and / or greater than 1.5 V for voltage feedback), a timing loop is activated to generate a frequency sweep. This data is stored in registers for each check between phases L1 / L2, L2 / L3, L1 / L3, and in case a neutral line is also present between N / L1, N / L2, N / L3. When the test button is pressed later, the stored data, which is considered the health of load 15, is compared with the sensed test data.

[0108] 2) Testing: The short-circuit test device 7 is only activated when the switch 2 is open or tripped. The short-circuit test device 7 remains in the disconnected state as long as a power-on signal is received from the switch 2. When the switch 2 is open or tripped, a power-off signal is received from the switch 2 and the short-circuit test device 7 is switched on, i.e. powered on. This also results in the initialization of the short-circuit test device 7. At this stage, a switch-on command to the switch 2 or a press of a test button or a time-based signal from the control unit 13 injects a test signal into the load 15, in particular by using a frequency sweep generated by the DC to AC converter 41 and in particular by the voltage source 11 to power an external power source (auxiliary power source or battery storage). Based on the load 15 (i.e. its capacitance and inductance), a suitable frequency sweep can be used. In order to test the phases L1..L3, and in the case where a neutral line is also present, the neutral line N is switched to the measuring unit 12. Then, based on the characteristics of the load 15, a timing loop is activated to generate a frequency sweep. Next, an arithmetic comparison is used to check whether the output is within or outside a predetermined range, and the result is stored. If the measured values ​​are outside the predefined ranges of the current and voltage feedback (stored during the calibration process), the switch 2 is kept open by the interlocking unit 6. This data is stored in registers for each check between the phases L1 / L2, L2 / L3, L1 / L3, and also in case there is a neutral line between N / L1, N / L2, N / L3. The switch 2 can only safely connect the load 15 with the phases L1..L3 if each check shows that there is no fault in the load 15. If the test sequence shows that there is a fault between any of the phases L1 / L2, L2 / L3, L1 / L3, and if there is also a neutral line between N / L1, N / L2, N / L3, the switch 2 will remain in the open state or tripped state regardless of the results of the checks between the other pairs L1 / L2, L2 / L3, L1 / L3, N / L1, N / L2, N / L3.

[0109] It should be noted that Figures 7 to 10 The examples and the above summary apply equally to a three-phase system (L1 .. L3), a three-phase system with a neutral line (L1 .. L3, N) and a single-phase system with a neutral line (L1 / N, L2 / N, L3 / N).

Claims

1. A short circuit test device (7) having a first line test conductor (8) to be coupled to a first load line conductor (5) of an electrical load network and a neutral test conductor (9) to be coupled to a neutral conductor (10) of the electrical load network (1), wherein at least a first relay is arranged in the first line test conductor (8) and the neutral test conductor (9), and wherein the first relay is logically connectable to at least one switch located between the electrical load network and an electrical utility network so that in use the first relay and the at least one switch are in opposite states, the short circuit test device (7) comprising: a voltage source (11) which can be switched to the first line test conductor (8) and the neutral test conductor (9) to output a predefinable test signal, a measuring unit (12) adapted to measure voltage and / or current, the measuring unit (12) comprising a measuring input connectable to the first line test conductor (8) and the neutral test conductor (9), the measuring unit (12) also comprising an output for providing a measurement signal, and - a control unit (13), which is connected to the voltage source (11) and the measuring unit (12), and is suitable for causing the voltage source (11) to apply a test voltage to the first line test conductor (8) and the neutral test conductor (9), and for comparing the measurement signal provided by the measuring unit (12) in response to the test signal with at least one predefined short-circuit criterion, and the control unit (13) is also suitable for outputting a protection command at a protection output terminal if the recorded measurement signal complies with the short-circuit criterion.

2. The short circuit test device (7) according to claim 1, characterized in that: The voltage source (11) comprises a voltage boost circuit.

3. The short circuit test device (7) according to claim 1 or 2, characterized in that: The voltage source comprises a transformer (36), wherein a secondary winding (37) of the transformer is connected to the first load line conductor (5) and the neutral conductor (10).

4. The short circuit test device (7) according to claim 1 or 2, characterized in that: The first line test conductor (8) is connected to a first metal hollow tube (24) to be placed around the first load line conductor (5), and the neutral test conductor (9) is connected to a second metal hollow tube (25) to be placed around the neutral conductor (10).

5. The short circuit test device (7) according to claim 4, characterized in that: At least one first capacitor (28) is arranged in the first line test conductor (8) between the voltage source (11) and the first hollow tube (24), and at least one second capacitor (29) is arranged in the neutral test conductor (9) between the voltage source (11) and the second hollow tube (25).

6. The short circuit test device (7) according to claim 5, characterized in that: The measuring unit (12) is connected to the first line test conductor (8) between the first capacitor (28) and the first hollow tube (24), and the measuring unit (12) is connected to the neutral test conductor (9) between the second capacitor (29) and the second hollow tube (25).

7. The short circuit test device (7) according to claim 1 or 2, characterized in that: The first line test conductor (8) comprises at least one first spring-loaded contact (32) for temporarily contacting the first load line conductor (5) during application of a test signal by the voltage source (11), and the neutral test conductor (9) comprises at least one second spring-loaded contact (33) for temporarily contacting the neutral conductor (10) during application of a test signal by the voltage source (11).

8. The short circuit test device (7) according to claim 1 or 2, characterized in that: The short-circuit test device (7) further comprises a communication interface for receiving and / or outputting commands and / or measurement results and / or indicators about the state of the load network, and the communication interface is connected to the control unit (13).

9. The short circuit test device (7) according to claim 1 or 2, characterized in that: The voltage source (11) is implemented to generate a test signal comprising a frequency sweep, and the control unit (13) is implemented to analyze a measured response signal in the frequency domain.

10. An electrical equipment system, comprising an electric power utility network (3), an electric load network (1), and at least one switch (2) located between the utility network (3) and the load network (1), wherein the switch (2) is located between a first utility line conductor (4) of the utility network (3) and a first load line conductor (5) of the load network (1), the system further comprising: - an interlocking unit (6) coupled to the switch (2) to controllably lock the switch (2) in an off position and prevent the switch (2) from being turned on if the interlocking unit (6) receives a locking command; as well as - A short-circuit test device (7) according to one of claims 1 to 9, wherein the protection output is connected to the interlocking unit (6).

11. The electrical equipment system according to claim 10, characterized in that: The switch is implemented as a circuit breaker in order to disconnect the load network (1) in the event of an overcurrent and / or a short-circuit current.

12. A circuit breaker comprising an interlocking unit (6) and a short-circuit test device (7) according to one of claims 1 to 9, wherein the protection output is connected to the interlocking unit (6).

13. A method for checking a load (15) in an electric circuit, the method comprising the steps of: - checking whether the switch (2) connecting the load (15) to the utility network (3) upstream of the switch (2) is disconnected or tripped, - providing that the switch (2) is in the open state, connecting the measuring unit (12) to the load (15) via a plurality of paired combinations of conductors (L1 .. L3) of the electrical load network (1) downstream of the switch (2), wherein at least a first relay is arranged in a paired combination of test conductors coupled to the paired combinations of conductors, and wherein the first relay can be logically connected to the switch (2) so that in use the first relay and the switch (2) are in opposite states, - for each of said pair combinations, applying a test signal to said load (15) and comparing the response with a response indicative of a non-faulty load (15), and - enabling the switch (2) to be turned on if all of the responses indicate no faulty load (15), and prohibiting the switch (2) from being turned on if any of the responses indicates a faulty load (15).

14. The method according to claim 13, characterized in that The result of the comparison forms the input of the OR logic, and if the output of the OR logic is false, the switch (2) is allowed to be turned on, while if the output of the OR logic is true, the switch (2) is prohibited to be turned on.

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