Circuit breakers and procedures

Abstract

Circuit breaker with at least one coil (L) for measuring the electrical current (I) of an electrical conductor of an electrical circuit, which is connected to a control unit (SE) which compares the measured current (I) or its equivalent with a first current limit value (I1) and, if the first current limit value is exceeded, initiates an interruption of the electrical circuit, characterized in that that the two terminals of the coil are connected to each other via a series circuit, comprising a first switch (S1) which is open in the basic state, a voltage source (U) and a voltage indicator (UII), and that the control unit (SE) is designed such that when a second current limit value (I2) is undershot for a first period (t1), the first switch (S1) is closed for a second period (t2), the voltage indicator (UII) compares the applied voltage with a first voltage value (U1) and, when the first voltage value is exceeded, provides information about the faultlessness of the coil.

Description

[0001] The invention relates to a circuit breaker with a coil for current measurement according to the preamble of patent claim 1 and to a method for a circuit breaker with a coil for current measurement according to the preamble of patent claim 14.

[0002] Circuit breakers are used as switching and protective devices in electrical circuits, particularly in multiphase power systems. They are particularly used in low-voltage networks, i.e., power systems with voltages up to 1000 V AC or 1500 V DC. Circuit breakers are specifically designed for currents starting at 63 amperes or 100 amperes, and for currents up to 1000 amperes, 6300 amperes, or 10,000 amperes.

[0003] Circuit breakers measure the electrical current in the electrical circuit and interrupt the circuit when current limits are exceeded, which occur, for example, in the event of an overload or short circuit in the electrical circuit.

[0004] Coils are often used to measure the electrical current in conductors. Rogowski coils, in particular, are widely used. These are also known as Rogowski transformers.

[0005] If the measuring unit for measuring the electrical current in a circuit breaker fails, the protective function in the electrical circuit is no longer guaranteed because overloads and short circuits can no longer be detected.

[0006] German patent application DE 10 2011 082 172 A1 discloses a circuit breaker and a method for testing a Rogowski transformer in a circuit breaker. To test a Rogowski transformer for wire breakage, a voltage is applied to the transformer, which is output by a digital-to-analog converter in response to a digital signal. The digital signal depends on the circuit breaker's rated current.

[0007] The American patent application US 2013 / 0 027 046 A1 discloses a method and device for testing solenoid valves. A device for testing a solenoid valve comprises: a voltage generator for applying a short voltage pulse to the windings of the solenoid valve, but not long enough to open the solenoid valve; an ammeter for measuring the current flowing through the windings of the solenoid valve; and an analysis device for analyzing the current measured by the ammeter to detect a possible fault in the solenoid valve.

[0008] German patent application DE 10 2005 036 769 A1 discloses a method for testing an inductive load. A full-bridge circuit comprises a first, second, third and fourth switching element (T1, T2, T3, T4). In the method, the testing comprises at least one measuring process. Within the at least one measuring process, either only the second or only the third switching element (T2, T3) is switched on, or only the first and second switching elements (T1, T2) or only the third and fourth switching elements (T3, T4) are switched on. At at least one recording time within the respective measuring process, a quantity is recorded which is representative of an electrical current flowing through a measuring resistor Rm. Depending on the recorded quantity and the respectively switched-on switching element orThe respective switched-on switching elements detect a fault or absence of faults in an inductive load of an electromechanical converter in the full-bridge circuit. The test period is specified such that the electromechanical converter remains in a rest position during this period.

[0009] The object of the present invention is to maintain the protective function in the electrical circuit.

[0010] This object is achieved on the basis of the preamble of patent claim 1 by a circuit breaker having the characterising features of patent claim 1 or by a method having the features of patent claim 14.

[0011] According to the invention, an electrical test voltage together with a voltage indicator can be connected to the coil for current measurement. The test voltage, for example from a voltage source, is connected in series with a voltage indicator and the coil to be tested. According to the invention, this series connection is connected to the coil when the current falls below a second current limit value, i.e., is relatively small or close to zero. For example, in an open circuit breaker, which can be designed for currents up to 10,000 amperes, this second current limit value can be 10 amperes or 1 ampere. Any value in the range from 500 mA to 20 A or even up to 80 A would be possible here.

[0012] Furthermore, the test of the current measurement coil is only carried out if no current has been measured for a certain period of time or if the current is below the second current limit value. In this case, i.e. if no current has been measured, there is a strong suspicion of a wire break in the current measurement coil, which should be eliminated according to the invention for safety reasons, so that a test according to the invention is carried out. If the current measurement coil is OK, a voltage is measured at the voltage indicator which roughly corresponds to the voltage of the voltage source, minus the relatively small voltage drop due to the coil resistance. This makes it possible to determine whether the coil is functioning properly or is faultless if a first voltage value is exceeded at the voltage indicator.

[0013] If the coil is broken, no current can flow through it, the circuit is interrupted, and the voltage indicator cannot detect a voltage. This identifies a coil fault and provides appropriate information about the presence of a fault.

[0014] The measurement can be carried out briefly, for example in the millisecond range, in order to detect a wire break in the coil.

[0015] The invention has the particular advantage that a test can be performed to determine the functionality of the current-measuring coil during operation of a circuit breaker, particularly when no or very low current is measured. It is irrelevant whether the control unit, which evaluates the coil's electrical current or voltage as a measured variable, is connected in parallel. Typically, the coil connection is high-impedance, often in the megaohm range, so that no or very low current flows through it, which does not affect the test.

[0016] Advantageous embodiments of the invention are specified in the subclaims.

[0017] In an advantageous embodiment of the invention, the coil is a Rogowski coil. This has the particular advantage of enabling particularly accurate measurement of the electrical current, both small and large, and across a wide frequency range. Fault detection in Rogowski coils is not straightforward, but is particularly easy with the method according to the invention.

[0018] In an advantageous embodiment of the invention, a second switch, which is open in the basic state, is provided in the series circuit for two-pole connection and disconnection of the series circuit to the coil. In a further embodiment, one terminal of the first switch is connected to the first terminal of the coil and one terminal of the second switch is connected to the second terminal of the coil, and the series-connected voltage source and voltage indicator are located between the other two terminals of the switches. This has the particular advantage that in the basic state there is no one-sided connection of a series circuit to the coil, which could change the symmetry of the coil for current measurement and thus falsify the current measurement result or cause an offset.The coil is often connected to a symmetrical differential input, which could change the symmetry if components are connected to the coil at one side.

[0019] In an advantageous embodiment of the invention, the voltage source is a direct voltage source. This has the particular advantage of allowing for particularly simple implementation, particularly due to the use of simple voltage indicators.

[0020] In an advantageous embodiment of the invention, the voltage indicator has a Schmitt trigger. This has the particular advantage of enabling a simple, standardized implementation of the voltage indicator.

[0021] In an advantageous embodiment of the invention, the control unit comprises a microprocessor. This has the particular advantage of enabling a particularly simple implementation of the control unit that can be adapted via firmware.

[0022] In an advantageous embodiment of the invention, the control unit has a high-impedance input to which the coil is connected. This has the particular advantage that a particularly unaffected test of the coil for faults can be performed, since a very low current flows through the control unit.

[0023] In an advantageous embodiment of the invention, an output unit connected to the control unit is provided, which provides information about the lack of freedom from errors visually, acoustically, and / or wirelessly. This has the particular advantage of informing an operator about a wire break or a fault in the current measurement coil.

[0024] In an advantageous embodiment of the invention, the control unit is designed such that, in the event of a coil fault, an interruption of the electrical circuit is initiated. This has the particular advantage of preventing unprotected operation of a system, such as a low-voltage switchgear.

[0025] In an advantageous embodiment of the invention, the first and / or second time periods are parameterizable. This has the particular advantage that the user can adapt the function very flexibly and optimally to their application.

[0026] In an advantageous embodiment of the invention, the control unit is designed such that an interruption of the electrical circuit is prevented when the series circuit or test voltage is connected. This has the particular advantage that the circuit breaker does not mistakenly interrupt or trip the electrical circuit during the brief test of the coil. The test voltage could cause the control unit to falsely detect a current flow, which could lead to undesired tripping. When the series circuit is connected, the interruption or tripping should be prevented for the duration of the connection of the series circuit, i.e., the test voltage. Since the series circuit is only connected for a short period of time, this is acceptable.

[0027] In an advantageous embodiment of the invention, the second current limit value is in the range of 500 mA to 20 A and / or the first time period is in the range of 5 ms to 50 s and / or the second time period is in the range of 10 microseconds to 10 seconds. These specified time periods have proven particularly advantageous for the practical application of the invention in a circuit breaker, in particular in an open circuit breaker.

[0028] All embodiments further develop the invention in an advantageous manner.

[0029] The described properties, features and advantages of this invention and the manner in which they are achieved will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0030] An embodiment of the invention is explained in more detail with reference to the drawing. It shows: Fig. 1 a first block diagram to explain the invention Fig. 2 a further second block diagram to explain the invention Fig. 3 a further third block diagram to explain the invention Fig. 4 a flow chart to explain the invention

[0031] Fig. Figure 1 shows a section of a circuit breaker LS, comprising a coil L for measuring the electrical current I of an electrical conductor (not shown) of an electrical circuit (not shown). The coil L is connected on both sides to a control unit SE. The coil L supplies a current or a voltage corresponding to the measured current of the electrical conductor (not shown). This means that the coil L supplies a value for the measured electrical current, i.e., an equivalent.

[0032] This measured value is evaluated by the circuit breaker's control unit SE, and at least when a first current limit I1 is exceeded, an interruption of the electrical circuit (not shown) is initiated. This is indicated by an arrow labeled "Trip," which initiates an interruption, for example, by an interrupting device (not shown), such as contacts that open an electrical circuit.

[0033] The current measurement quantity supplied by coil L, for example, a voltage proportional to the measured current, is usually recorded in the control unit SE using a high-impedance resistor. Advantageously, coil L is a Rogowski coil, which allows for a wide current measurement and frequency range of the current to be measured.

[0034] According to the invention, a series circuit of a voltage source U, advantageously a DC voltage source, for example, with a voltage of 3.3 volts, a voltage indicator UII, and a first switch S1 are connected to the two terminals of coil L. Switch S1 is open in the basic state and is closed for the test procedure. Advantageously, a second switch S2 can also be provided, which is also open in the basic state, whereby both switches S1 and S2 are actuated simultaneously. The switches are preferably arranged at the coil terminals.

[0035] If no current is measured in the electrical circuit, the coil, for example a Rogowski coil, can be tested. For this purpose, Fig. 1 both switches S1, S2 are briefly closed, for example by a signal from the control unit SE, and the voltage indicator determines whether a voltage is present. If this voltage exceeds a first voltage value U1, which is selected so that it corresponds to the voltage of the voltage source U less the voltage drop due to the coil resistance less any contact and line resistances and tolerances, the coil is OK for measurement and is working correctly. Otherwise, there is a coil fault that prevents current measurement and thus prevents the circuit breaker from functioning properly. Corresponding information or a message can be issued by an output unit A connected to the control unit. This can be visual information (LED, lamp), acoustic information (buzzer) and / or wireless information, for example via a radio message.

[0036] Furthermore, if a wire break occurs in the coil, the control unit can initiate an interruption of the electrical circuit to ensure that the electrical circuit is not left unprotected. Furthermore, the control unit can prevent the circuit breaker from being reclosed as long as there is no wire break or lack of continuity in the coil.

[0037] With a voltage source voltage of 3.3 volts, a voltage value U1 of 2.1 volts is practical. This also has the advantage that standard digital inputs can be used to evaluate the voltage level.

[0038] The test or measurement should be performed especially when no current flow is detected. Experience has shown that in such a case, a wire break in the current measuring coil could also be present. This means that if the current falls below a certain value I2 for a certain period of time t1, a test is performed for a period of time t2, which can be relatively short.

[0039] During this time, the control unit can prevent or suppress the circuit breaker from tripping or interrupting. For example, the SE control unit initiates the test procedure and suppresses the interruption of the electrical circuit for the same period.

[0040] Fig. 2 shows a figure according to Fig. 1, with the difference that the switches S1, S2 are controlled by the voltage indicator UII, in which part of the control is realized, and that the control unit SE comprises a measuring unit ME and a microprocessor MP.

[0041] The measuring unit ME performs various functions for converting measured values. For example, it can act as an analog front-end, and it can also perform analog-to-digital conversion. The output of this measuring unit ME is fed to the microprocessor MP.

[0042] The microprocessor MP can, for example, take over all or part of the control functions that are implemented in firmware, for example.

[0043] Fig. 3 shows an arrangement according to Fig. 2, with the difference that the measuring unit ME is designed as a standalone unit, and the control unit SE also provides a test voltage and performs the function of the voltage indicator. The control of switches S1 and S2 is also handled by the control unit SE.

[0044] For example, the voltage indicator can be implemented directly via an input of a microprocessor contained in the control unit, which switches from low to high when a voltage greater than 2.1 volts is present. The control unit provides a voltage of 3.3 volts in this case.

[0045] If the control unit contains a microprocessor running on firmware, a suitable firmware algorithm can be run to test the coil for functionality.

[0046] Fig. Figure 4 shows a flowchart for such an algorithm.

[0047] In step 100 a check is made to see whether the coil, for example a Rogowkis coil, has already been marked as faulty. If this is the case, the algorithm ends with step 200. If it is not, it continues with step 110, in which it is checked whether the current is below a second current limit value I2, for example in the case of an open circuit breaker, less than 10 A. If it is not, the algorithm ends with step 200. If the current is small enough, it continues with step 120, in which a test process is initiated and a test voltage is applied. Then in step 130 the corresponding voltage information is read, for example by querying the input connection. In step 140 the test voltage connection is ended. In step 150 a check is made to see whether the first voltage value U1 was reached or whether the input connection was high. If this is the case, an error counter for the coil is reset to zero orreset and the algorithm ends with step 200. If the answer is negative, an error counter is incremented in step 160. This means that an error is not reported immediately, but only when the error, i.e. lack of voltage, which indicates a wire break in the coil, occurs repeatedly or in a reproducible manner. In step 170, a check is then made to see whether the error counter has reached a value of 3, for example, i.e. the test was negative 3 times, so that there is definitely a fault in the coil. If this is not reached, the algorithm ends with step 200. If the error counter is greater than or equal to 3, for example, the coil is marked as faulty in step 180 and further actions (tripping the circuit breaker, information about the error via the output unit) can take place.

[0048] When the algorithm is finished, it can start again from the beginning.

[0049] The invention will be briefly presented again below.

[0050] The control unit SE is designed in such a way that when a second current limit value I2, e.g. 1 ampere, is undershot and a first period t1, e.g. 200 ms, is exceeded, the test voltage is switched on for a second period, e.g. 20 ms, in order to determine the functionality of the coil.

[0051] This allows a continuity test of the coil to be performed. The result of the continuity test is determined by the control unit, for example, via the control unit's firmware. The result is advantageously available within a very short time, e.g., within 1 ms.

[0052] If the coil is OK and a current flows through the electrical conductor to be measured at the moment of the continuity test, the measured values ​​will only be imperceptibly affected.

[0053] If the coil has no continuity, e.g., the coil wire is broken, meaning a fault has occurred, a configurable action can be executed. For example, the electrical circuit can be interrupted, meaning the circuit breaker can be tripped. Furthermore, a visual indicator, e.g., an LED or display, can be activated to indicate the fault. Furthermore, the fault can be reported via a communication unit, e.g., to a monitoring and / or management system.

[0054] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

[1] Circuit breaker with at least one coil (L) for measuring the electric current (I) of an electrical conductor of an electrical circuit, which is connected to a control unit (SE) which compares the measured current (I) or its equivalent with a first current limit value (I1) and initiates an interruption of the electrical circuit when this limit value is exceeded, characterized by , that the two terminals of the coil are connected to each other via a series circuit, comprising a first switch (S1) which is open in the basic state, a voltage source (U) and a voltage indicator (UII), and that the control unit (SE) is designed such that when a second current limit value (I2) is undershot for a first period (t1), the first switch (S1) is closed for a second period (t2), the voltage indicator (UII) compares the applied voltage with a first voltage value (U1) and, when the first voltage value is exceeded, provides information about the faultlessness of the coil. [2] Circuit breaker according to claim 1, characterized by that the coil is a Rogowski coil. [3] Circuit breaker according to claim 1 or 2, characterized by that a second switch (S2), which is open in the basic state, is provided in the series circuit for the two-pole connection and disconnection of the series circuit to the coil. [4] Circuit breaker according to claim 3, characterized bythat one terminal of the first switch (S1) is connected to the first terminal of the coil (L) and one terminal of the second switch (S2) is connected to the second terminal of the coil (L) and the series-connected voltage source (U) together with the voltage indicator (UII) is located between the two other terminals of the switches (S1, S2). [5] Circuit breaker according to one of the preceding claims, characterized by that the voltage source (U) is a DC voltage source. [6] Circuit breaker according to one of the preceding claims, characterized by that the voltage indicator (UII) has a Schmitt trigger. [7] Circuit breaker according to one of the preceding claims, characterized by that the control unit (SE) has a microprocessor. [8] Circuit breaker according to one of the preceding claims, characterized bythat the control unit (SE) has a high-impedance input to which the coil (L) is connected. [9] Circuit breaker according to one of the preceding claims, characterized by that an output unit (A) connected to the control unit (SE) is also provided, which outputs information about the lack of freedom from errors optically, acoustically and / or wirelessly. [10] Circuit breaker according to one of the preceding claims, characterized by that the control unit is designed in such a way that an interruption of the electrical circuit is initiated in the event of a fault in the coil. [11] Circuit breaker according to one of the preceding claims, characterized by that the first and / or second period (t1, t2) is parameterizable. [12] Circuit breaker according to one of the preceding claims, characterized bythat the control unit is designed in such a way that an interruption of the electrical circuit is prevented when the series circuit or test voltage is connected. [13] Circuit breaker according to one of the preceding claims, characterized by that the second current limit value (I2) is in the range 500mA to 20A and / or the first period (t1) is in the range 5ms to 50s and / or the second period (t2) is in the range 10 microseconds to 10 seconds. [14] Method for a circuit breaker with a coil (L) for measuring the electric current (I) of an electric conductor of an electric circuit, wherein the measured current (I) or its equivalent is compared with a first current limit value (I1) and, if exceeded, an interruption of the electric circuit is initiated, characterized bythat when a second current limit value (I2) is undershot and a first time period (t1) is exceeded, a test voltage is applied to the coil with a series-connected voltage indicator for a second time period (t2), and when a first voltage value (U1) is exceeded, information about the functionality of the coil is available at the voltage indicator. [15] Method for a circuit breaker according to claim 14, characterized by that the connection is two-pole.

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