Method and apparatus for detecting fuse failure

Abstract

The present invention provides a method and an apparatus for detecting a fuse failure. A method for detecting a failure of a protective fuse (5) for protecting an associated load (7) from overcurrent and / or overload comprises the following steps: measuring (S A ) The current I flowing through the protective fuse (5) to the load (7) is determined based on the measured current I (S B ) the thermal energy generated in the protective fuse (5), and automatically detecting (S) if the determined thermal energy exceeds a predetermined threshold and if the current I measured by the current sensor element (2) has stopped flowing through the protective fuse (5) C ) Failure of the protective fuse (5).

Description

Technical Field

[0001] The present invention relates to a method and a device for detecting a failure of a protective fuse capable of protecting an associated load from overcurrent and / or overload. Background Art

[0002] Fuses are widely used as overcurrent protection devices that disconnect circuits with a fusible element that heats and disconnects due to the passage of an overcurrent through the fuse. Different types of fuses can be used in power distribution systems. There are a wide variety of different types of electrical fuses.

[0003] An overcurrent is any current greater than the load is rated to carry under specific conditions. Unless removed promptly, even low overcurrents can overheat system components of the power distribution system, potentially damaging the system's insulation, conductors, and other equipment. Such overcurrents can even melt conductors and vaporize the insulation provided. Very high currents can generate magnetic forces and even bend and twist busbars.

[0004] Generally, there are two main types of overcurrent fault conditions: overload fault conditions and short-circuit fault conditions. In a short-circuit fault condition, an overcurrent flows outside of its normal current path in a circuit. A short-circuit fault can be caused, for example, by insulation breakdown or a faulty electrical connection. When a short-circuit fault does occur, the current can bypass the normal load and take a shorter path, hence the term "short circuit." An overload fault condition can be defined as an overcurrent that is confined to the normal current path; however, if the overcurrent is allowed to persist in the circuit for an extended period, it could cause damage to the equipment and / or connected wiring.

[0005] Protective fuses can be used to protect a variety of loads, including inductive, capacitive, and resistive loads, from overload and / or short-circuit fault conditions. For example, protective fuses can be used to protect an electric motor connected to a motor protective switch. The motor protective switch is adapted to protect the electric motor from overload and / or faults in external conductors. Motor protection can be used to prevent any damage to the electric motor, such as internal faults within the electric motor. A three-phase motor protective switch can be provided in parallel with the protective fuses. In the event of a fuse failure, the motor protective switch can take over the current flow for a period of time. Therefore, in many use cases, it is necessary to detect that a protective electrical fuse has failed or tripped due to overcurrent. Therefore, in many use cases, fuse failure supervision is required to increase the operational reliability and safety of the power distribution system. Fuse failure supervision for protective fuses can be implemented for critical loads of the power distribution system protected by the associated protective fuses. Other examples include emergency power systems or battery loading systems. In many cases of use, the protective fuse is connected in series to an additional protective switch, which may comprise a semiconductor protective switch or an electromechanical protective switch.

[0006] Conventional methods for detecting a protective fuse failure rely on measuring the voltage drop across the fuse, which requires measuring the potential on both sides of the fuse. To tap the potential difference at the fuse, two wires are required, which must be connected to both sides of the fuse. This increases the required technical effort and circuit complexity. Furthermore, in exceptional circumstances, the connecting wires on both sides of the fuse may be interrupted, increasing the possibility of a protective fuse failure going undetected. In this case, the operational safety of the power distribution system is compromised. Summary of the Invention

[0007] It is therefore an object of the present invention to provide a method and apparatus for detecting a fault of a protective fuse which increases the reliability of the fault detection without significantly increasing the complexity of the detection circuit.

[0008] According to a first aspect of the invention, this object is achieved by a method for detecting a failure of a protective fuse comprising the features of claim 1 .

[0009] According to a first aspect, the present invention provides a method for detecting a failure of a protective fuse for protecting an associated load from overcurrent and / or overload,

[0010] The method comprises the following steps:

[0011] measuring the current flowing through the protective fuse to the load by means of a current sensor element, determining the heat energy generated in the protective fuse from the measured current, and

[0012] If the determined thermal energy exceeds a predetermined threshold and if the current measured by the current sensor element has stopped flowing through the protective fuse, a failure of the protective fuse is automatically detected.

[0013] An advantage of the method according to the invention is that it can operate reliably even in harsh environments.Another advantage of the method according to the invention is that a failure of the protective fuse can be detected very quickly within a short detection time of less than 1 millisecond.

[0014] In a possible embodiment of the method according to the first aspect of the invention, a fuse failure detection signal is automatically generated if the determined thermal energy has exceeded the predetermined threshold value and the current measured by the current sensor element has stopped flowing through the protective fuse. The generated fuse failure detection signal indicates a possible failure of the protective fuse due to a short-circuit current.

[0015] This has the advantage that the fuse failure detection signal can be provided to a local or remote controller and can be taken into account for controlling the functionality of the power distribution system including the protected load.

[0016] In another possible embodiment of the method according to the first aspect of the invention, the thermal energy is calculated as an ampere-squared-second value and compared with the predetermined threshold value.

[0017] This has the advantage that the ampere squared second value used as the threshold value can be derived from the data sheet of the protective fuse.

[0018] In another possible embodiment of the method according to the first aspect of the invention, a failure of the protective fuse is detected if, as a further condition, the received switch status signal indicates that the associated load has not been switched off externally by the protective switch.

[0019] This has the advantage that, in the event that a protective switch connected in series with the protective fuse has been tripped by an external control signal, the cessation of the flow of current through the protective fuse does not cause the generation of a fuse failure detection signal which could be erroneously interpreted as a failure of the protective fuse.

[0020] In another possible embodiment of the method according to the first aspect of the invention, the energy input into the protective fuse caused by the flowing current is determined if the determined thermal energy does not exceed the predetermined threshold value, but the amplitude of the measured current is higher than a predetermined rated current.

[0021] In another possible embodiment of the method according to the first aspect of the invention, if the determined energy input into the protective fuse by the current does exceed a predetermined threshold, an overload fault warning signal is automatically generated indicating an impending failure of the protective fuse due to the overload current.

[0022] This offers the significant advantage of detecting an impending failure of a protective fuse before it actually occurs. This allows, for example, preemptive maintenance of a power distribution system that includes protective fuses to be performed. For example, if a protective fuse has already been damaged by an overcurrent, a possible failure of the protective fuse can be predicted, and corresponding countermeasures can be initiated before the protective fuse completely fails.

[0023] In another possible embodiment of the method according to the first aspect of the invention, the energy input into the protective fuse is determined by calculating the heat transfer balance of the protective fuse as the difference between the heat generated by the current flowing through the protective fuse and the heat dissipated by the protective fuse.

[0024] According to another aspect, the invention provides a fuse failure detection device comprising the features of claim 8 .

[0025] According to a second aspect, the present invention provides a fuse failure detection device provided for detecting a failure of a protective fuse for protecting an associated load from overcurrent and / or overload,

[0026] The fuse failure detection device comprises:

[0027] a current sensor element adapted to measure a current flowing through the protective fuse to the load,

[0028] a determination unit adapted to determine a thermal energy generated at the protective fuse from the current measured by the current sensor element, and

[0029] A fault detection unit is adapted to automatically detect a fault of the protective fuse if the determined thermal energy exceeds a predetermined threshold and if the current measured by the current sensor element has stopped flowing through the protective fuse.

[0030] In a possible embodiment of the fuse failure detection device according to the second aspect of the invention, the fault detection unit is adapted to automatically generate a fuse failure detection signal indicating a possible failure of the protective fuse due to a short-circuit current if the determined thermal energy has exceeded the predetermined threshold value and if the current measured by the current sensor element has stopped flowing through the protective fuse.

[0031] In another possible embodiment of the fuse failure detection device according to the second aspect of the invention, the determination unit is adapted to calculate an ampere squared second value representing thermal energy generated at the protective fuse in response to the current measured by the current sensor element.

[0032] In another possible embodiment of the fuse failure detection device according to the second aspect of the invention, the fault detection unit is adapted to compare the calculated ampere square second value with a predetermined ampere square second value to generate a fuse failure detection signal if the determined thermal energy has exceeded the predetermined threshold value and the current measured by the current sensor element has stopped flowing through the protective fuse and if the received switch status signal indicates that the associated load has not been externally switched off by the protective switch.

[0033] In another possible embodiment of the fuse failure detection device according to the second aspect of the invention, the determination unit is further adapted to determine the energy input into the protective fuse caused by the flowing current if the determined thermal energy does not exceed the predetermined threshold but the amplitude of the measured current is higher than a predetermined rated current.

[0034] In another possible embodiment of the fuse failure detection device according to the second aspect of the present invention, the fault detection unit is adapted to generate an overload fault warning signal if the determined energy input into the protective fuse by the current exceeds a predetermined threshold, wherein the generated overload fault warning signal indicates an impending failure of the protective fuse due to an overload current.

[0035] In another possible embodiment of the fuse failure detection device according to the second aspect of the invention, the determination unit is adapted to determine the energy input into the protective fuse by calculating the heat transfer balance of the protective fuse as the difference between the heat generated by the current flowing through the protective fuse and the heat dissipated by the protective fuse.

[0036] In a possible embodiment of the fuse failure detection device according to the second aspect of the invention, the current sensor element is adapted to measure a direct current.

[0037] In a further possible alternative embodiment of the fuse failure detection device according to the second aspect of the present invention, the current sensor element is adapted to measure alternating current.

[0038] In yet another possible embodiment of the fuse failure detection device according to the second aspect of the present invention, the current sensor element is connected in series to the protective fuse within the current supply path of the load, or is attached to the current supply path of the load.

[0039] In a possible embodiment, the current sensor element attached to the current supply path of the load can also be moved along a line or a strip of the current supply path.

[0040] In another possible embodiment of the fuse failure detection device according to the second aspect of the present invention, the failure detection unit comprises an interface for receiving a switch state signal from a protective switch connected in series with the protective fuse along a current supply path of the load.

[0041] According to another aspect, the present invention provides an adapter device comprising a fuse failure detection apparatus according to the second aspect of the invention.

[0042] In the following, possible embodiments of different aspects of the present invention are described in more detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 shows a block diagram for illustrating a possible exemplary embodiment of a fuse failure detection device according to an aspect of the present invention;

[0044] Figure 2 a flow chart showing the main steps of a possible exemplary embodiment of a method for detecting a failure of a protective fuse according to another aspect of the invention;

[0045] Figure 3 shows another flow chart for illustrating a possible exemplary embodiment of a method for detecting a failure of a protective fuse according to an aspect of the present invention;

[0046] Figure 4A 、 Figure 4B A signal diagram is shown to illustrate the operation of the protective fuse under a short circuit condition;

[0047] Figure 5 illustrates a simple schematic diagram for determining the definition of the ampere-squared-second value of thermal energy within a protective fuse by the method and apparatus according to the present invention; and

[0048] Figure 6A schematic diagram illustrating the operating behavior of a protective fuse for providing protection from overload and / or from overcurrent is shown. DETAILED DESCRIPTION

[0049] from Figure 1 As can be seen from the schematic block diagram of FIG, the fuse failure detection device 1 according to the present invention may include three main components. In the embodiment shown, the fuse failure detection device 1 includes a current sensor element 2, a determination unit 3 and a fault detection unit 4. The fuse failure detection device 1 is connected in series with a protective fuse 5, such as Figure 1 In a possible embodiment, the fuse failure detection device 1 can be connected in series in the current supply path between the power source 6 and the electric load 7, as shown. Figure 1 In a possible embodiment, the current supply path may further include an optional protective switch 8, as shown in FIG. Figure 1 The electric load 7 may include a resistive load, a capacitive load or an inductive load.

[0050] In a possible embodiment, the current sensor element 2 can be connected in series with the protective fuse 5 within the current supply path of the load 7. The current supply path can be adapted to carry either a DC supply current or an AC supply current. In a possible embodiment, the current sensor element 2 can also be attached to the current supply path of the load 7. In this embodiment, the current sensor element 2 can, for example, be clamped onto the wire that carries the current flowing through the protective fuse 5 and through the protective switch 8 to the load 7. The current induces a magnetic field that can be detected by the current sensor element 2 attached to the current-carrying wire or current-carrying busbar. This embodiment has the additional advantage that the current sensor element 2 can be moved along the current supply path between the power source 6 and the load 7. Therefore, the current sensor element 2 attached to the current supply path can also be manually fixed at different locations on the current-carrying wire between the power source 6 and the load 7. This provides greater flexibility when expanding an existing power distribution system by adding the fuse failure detection device 1 according to the present invention to the corresponding system. In other words, this embodiment does not require interrupting the existing current-carrying wire between the protective fuse 5 and the electrical load 7.

[0051] exist Figure 1 In the embodiment shown, the fuse failure detection device 1 is arranged after the protective fuse 5, i.e. on the output side of the protective fuse 5 at its load-facing side. In an alternative embodiment, the fuse failure detection device 1 according to the present invention can also be located on the side of the protective fuse 5 facing the power supply 6.

[0052] In a possible embodiment, Figure 1The illustrated current sensor element 2 may be adapted to measure a direct current provided by the power source 6 and supplied via the current supply path to the electrical load 7. In an alternative embodiment, the current sensor element 2 is adapted to measure an alternating current flowing from the alternating current source 6 to the electrical load 7 via the current supply path.

[0053] In a possible embodiment, the current sensor element 2 may comprise a shunt resistor connected in series to a protective fuse 5 within the current supply path of the load 7. The voltage across the shunt resistor is proportional to the current flowing through the shunt resistor.

[0054] In an alternative embodiment, the current sensor element 2 may include a coil suitable for measuring alternating current or high-speed current pulses, in particular a Rogowski coil. Due to its low inductance, the Rogowski coil can respond to rapidly changing currents of a few nanoseconds or so.

[0055] The current sensor element 2 may also comprise other types of current sensor elements, in particular a Hall effect current sensor or a giant magnetoresistance GMR sensor. A Hall effect sensor is suitable for measuring the magnitude of a magnetic field that may be caused by a current flowing along a current supply path. Therefore, in a possible embodiment, the attachment of the current sensor element 2 to the current supply path does not require a current connection. In such an embodiment, the fuse fault detection device 1 is galvanically isolated from the current supply path between the power supply 6 and the load 7. This increases the operational reliability of the fuse fault detection device 1 in the event that a high short-circuit overcurrent does occur. Furthermore, the expansion of existing power distribution systems can be facilitated, since the current sensor element 2 is only mechanically attached to the current supply path to measure the magnetic field, without the need to interrupt the current supply path when the fuse fault detection device 1 is installed on the current transmission line between the protective fuse 5 and the load 7.

[0056] from Figure 1 As can be seen from the block diagram of FIG, the fuse failure detection device 1 does not require tapping of the potential on both sides of the protective fuse 5. The fuse failure detection device 1 according to the present invention is provided on the upstream side of the protective fuse 5 facing the power supply 6 or on the downstream side of the protective fuse 5 facing the electric load 7.

[0057] The current sensor element 2 measures the current I flowing through the protective fuse 5 and notifies the measured current I to the determination unit 3 of the fuse failure detection device 1, as shown in FIG. Figure 1 The determination unit 3 is adapted to determine the thermal energy generated at the protective fuse 5 based on the current I measured by the current sensor element 2. In a possible embodiment, the determination unit 3 is adapted to calculate an ampere-squared-second value representing the thermal energy generated at the protective fuse 5 in response to the current I measured by the current sensor element 2.

[0058] The fuse failure detection device 1 further comprises a failure detection unit 4 adapted to automatically detect a failure of the protective fuse 5 if the determined thermal energy does exceed a predetermined threshold and if the current measured by the current sensor element 2 has stopped flowing through the protective fuse 5 .

[0059] In a possible embodiment, the fault detection unit 4 is adapted to automatically generate a fuse failure detection signal FFDS indicating a possible failure of the protective fuse 5 due to a short-circuit current if the determined thermal energy has exceeded a predetermined threshold value and if the current I measured by the current sensor element 2 has stopped flowing through the protective fuse 5. In a possible embodiment, the fault detection unit 4 is adapted to compare the calculated ampere-squared-second value with a predetermined ampere-squared-second value to generate the fuse failure detection signal FFDS if the determined thermal energy has exceeded a predetermined threshold value and if the current I measured by the current sensor element 2 has stopped flowing through the protective fuse 5.

[0060] The I2t rating relates to the amount of energy a fuse element allows to pass when it clears an electrical fault. This term is typically used in the context of a short-circuit condition, and these values ​​can be used to perform coordination in electrical networks. I2t parameters are available for different types of fuses via charts in the manufacturer's datasheet. To coordinate fuse operation with upstream or downstream devices, both the melting I2t and the clearing I2t are specified. The melting I2t is proportional to the amount of energy required to begin melting the fuse element. The clearing I2t is proportional to the total energy the fuse allows to pass when clearing the fault. The energy depends primarily on the current and time of the fuse, as well as the available fault level and system voltage. Because a fuse's I2t rating is proportional to the energy it allows to pass, it is a measure of the thermal damage caused by the heat and magnetic forces generated by the fault.

[0061] In a possible embodiment, the fault detection unit 4 only generates the fuse fault detection signal FFDS if an additional condition is met, namely if the received switch state signal SWSS indicates that the associated load 7 has not been externally switched off by the associated protective switch 8 provided in the current supply path. In this embodiment, the fault detection unit 4 may include an interface for receiving the switch state signal SWSS from the protective switch 8, which is connected in series with the protective fuse 5 along the current supply path of the load 7. The protective switch 8 may include an electromechanical protective switch and / or a semiconductor protective switch.

[0062] In a possible embodiment, the fault detection unit 4 is further adapted to generate an overload fault warning signal OFWS if the determined energy input into the protective fuse 5 by the current flowing along the current supply path does exceed a predetermined threshold value. The generated overload fault warning signal OFWS may indicate an imminent (i.e. future) failure of the protective fuse 5 due to the overload current. In a possible embodiment, the determination unit 3 may determine the energy input into the protective fuse 5 by calculating the heat transfer balance of the protective fuse 5 as the difference between the heat generated by the current I flowing through the protective fuse 5 and the heat dissipated by the protective fuse 5. Thus, if the determined thermal energy does not exceed the predetermined threshold value, but the current of the measured current I is higher than a predetermined rated current, the energy input into the protective fuse 5 caused by the flowing current I may be determined. If this energy input does exceed the predetermined threshold value, the overload fault warning signal OFWS may be generated by the fault detection unit 4 and output via the interface of the fuse fault detection device 1. In Figure 1 In the illustrated embodiment, the fuse failure detection device 1 includes a data interface configured to output a generated fuse failure detection signal FFDS and an overload fault warning signal OFWS. The fuse failure detection signal FFDS indicates a failure of the protective fuse 5 due to a short-circuit current. In this case, the protective fuse 5 has already opened or melted due to the very high short-circuit overcurrent. In contrast, the overload fault warning signal OFWS indicates a possible future failure of the protective fuse 5 due to an overcurrent flowing along the current supply path.

[0063] Both the Fuse Failure Detection Signal (FFDS) and the Overload Warning Signal (OFWS) can be supplied to a local or remote controller to automatically trigger countermeasures. If the local or remote controller receives the Fuse Failure Detection Signal (FFDS), the protective fuse 5, which has tripped due to the short-circuit current, needs to be replaced. If the remote or local controller receives the Overload Failure Warning Signal (OFWS), the protective fuse 5 is still functional but may have been damaged by the flowing overload current, requiring replacement by a maintenance operator in the near future. The Overload Failure Warning Signal (OFWS) provides a warning of a possible future malfunction of the protective fuse 5 and, in a possible embodiment, can automatically trigger preemptive maintenance operations on the power distribution system.

[0064] In the illustrated embodiment, the fuse failure detection device 1 may include a control interface for receiving a switch state signal SWSS from a protective switch 8, which may be connected in series with the protective fuse 5 within the current supply path. The protective switch 8 may be a separate component, in particular a semiconductor device such as an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), or other semiconductor switching devices such as a bipolar junction transistor (BJT) or a junction gate field effect transistor (JFET). Other possible embodiments include thyristors or integrated gate commutated thyristors (IGCTs). Once the protective switch 8 has disconnected the electrical load 7, the switch state signal SWSS may be set to logic high, indicating that the associated load 7 has been disconnected by the protective switch 8. As long as the switch state signal SWSS is logic low and indicates that the associated load has not been disconnected externally by the protective switch 8, the fault detection unit 4 may automatically generate a fuse failure detection signal FFDS if the determined thermal energy has exceeded a predetermined threshold and the fault detection unit 4 detects that the current measured by the current sensor element 2 has ceased flowing through the protective fuse 5. In this embodiment, the fault detection unit 4 can monitor the amplitude of the current measured by the current sensor element 2. If the amplitude of the current drops to zero within a short predetermined time, the fault detection unit 4 can determine that the current I has stopped flowing through the protective fuse 5. Therefore, in a preferred embodiment, the fault detection unit 4 only generates the fuse fault detection signal FFDS when three conditions are met. The first condition is that the calculated ampere-squared-second value has exceeded a predetermined ampere-squared-second value. The second condition is that the current I flowing through the protective fuse 5 and measured by the current sensor element 2 has stopped flowing. The third condition is that the received switch state signal SWSS clearly indicates that the protective switch 8 has not yet been shut down, for example, the received switch state signal SWSS is logically low.

[0065] In a possible embodiment of the fuse failure detection device 1, the current sensor element 2, the determination unit 3 and the fault detection unit 4 can be integrated into the housing of the corresponding device. In an alternative embodiment, the different units of the fuse failure detection device 1 (especially the determination unit 3 and the fault detection unit 4) can be distributed in different locations within the power distribution system. In another possible embodiment, the housing of the fuse failure detection device 1 can also include Figure 1 The protective switch 8 is shown in the block diagram.

[0066] Figure 2 A method for detecting protective fuses such as Figure 1 Flowchart of a possible exemplary embodiment of a method for detecting a fault of a protective fuse 5) as shown in the block diagram of FIG. In the embodiment shown, the method comprises three main steps S A 、S B 、S C.

[0067] In the first step S A In the embodiment, the current flowing through the protective fuse 5 to the load 7 is detected by means of the current sensor element 2. The current sensor element 2 can be integrated into the housing of the fuse failure detection device 1, such as Figure 1 The current sensor element 2 may further comprise a separate element connecting the determination unit 3 and the fault detection unit 4 to the sensor signal line. The measured current I may comprise a direct current and / or an alternating current.

[0068] In another step S B In the embodiment, the thermal energy generated in the protective fuse 5 according to the measured current is determined. In a possible embodiment, the thermal energy can be calculated as an ampere squared second value and then compared with a predetermined threshold value.

[0069] In another step S C In step S, if B The heat energy determined in step S A If the current I measured by the current sensor element 2 has stopped flowing through the protective fuse 5, a failure of the protective fuse 5 is automatically detected. If such a failure is detected, a fuse failure detection signal FFDS indicating a possible failure of the protective fuse 5 due to the short-circuit current may be generated.

[0070] Figure 3 A flow chart showing a possible embodiment of the method for the failure of the protective fuse 5 is shown.

[0071] The process begins at step S0. In another step S1, a determination is made as to whether current can be detected. If the magnitude of the flowing current I measured by the current sensor element 2 exceeds a predetermined threshold for a predetermined minimum time span, current flow is detected. If current flow is detected in step S1, the ampere-squared-second value of the measured current I is calculated and compared to a predetermined ampere-squared-second threshold in step S2. This predetermined ampere-squared-second threshold comprises a parameter that can be set in the configuration memory of the determination unit 3 during initialization. In a possible embodiment, the ampere-squared-second threshold stored in the configuration memory can also be adjusted by a user or operator via a user interface, or by an external controller via a data interface of the fuse failure detection device 1. Another parameter that can be set in the configuration register or configuration memory can include the rated current visible to the load 7. In a possible embodiment, the comparison of the calculated ampere-squared-second value with the predetermined ampere-squared-second threshold can be performed by a comparator of the fault detection unit 4. In a possible embodiment, the ampere-squared-second value can be calculated based on the measured current, in a possible embodiment, every ten milliseconds. This time period can vary depending on the application. In a possible embodiment, the time period for calculating the ampere squared second value is adjustable. If the ampere squared second value does not exceed a predetermined threshold, a further comparison is performed in step S3, such as Figure 3 , as shown in the flowchart. In step S3, a determination is made as to whether the measured current exceeds a predetermined rated current, which can be read from the configuration memory of the fuse failure detection device 1. If this is not the case, the protective fuse 5 is still within the normal operating range and no critical condition has occurred. Conversely, if the measured current exceeds the predetermined rated current, the energy input into the protective fuse 5 due to the flowing current I can be calculated or determined in step S4. In a possible embodiment, the determination unit 3 determines the energy input into the protective fuse 5 in step S4 by calculating a heat transfer balance for the protective fuse 5. The heat transfer balance comprises the difference between the heat generated by the current I flowing through the protective fuse 5 and the heat dissipated by the protective fuse 5. If the energy input into the protective fuse 5 due to the current I does exceed a predetermined threshold, in a preferred embodiment, the fault detection unit 4 can generate an overload fault warning signal OFWS in step S4, indicating a possible impending failure of the protective fuse 5 due to the overload current.

[0072] Therefore, in the event that the thermal energy represented by the calculated ampere-squared-second value does not exceed the predetermined threshold value but the current flowing through the protective fuse 5 is higher than the predetermined rated current, that is, in the event of an overload current, an overload fault warning signal OFWS is generated. In a preferred embodiment, if the calculated heat transfer balance indicates that a critical energy input into the protective fuse 5 may cause damage to the protective fuse 5, the overload fault warning signal OFWS is automatically generated.

[0073] In step S5, it is determined whether the current I flowing through the protective fuse 5 and measured by the current sensor element 2 has stopped. If the current I is still flowing, the process loops back to step S2, as shown in FIG. Figure 3 On the contrary, if the monitored current I has stopped flowing, it is determined in step S6 whether the interruption of the current I is caused by an external protective switch (such as Figure 1 In a possible embodiment, the received switch state signal SWSS is evaluated to determine whether an external shutdown has been performed. If the received switch state signal SWSS indicates an external shutdown, the process loops back to step S1, as shown in FIG. Figure 3 However, if the switch state signal SWSS indicates that no external shutdown has been performed, then in step S7 it is determined that the protective fuse 5 has been tripped due to the high short-circuit current. In this case, the fault detection unit 4 may also automatically generate a fuse failure detection signal FFDS in step S7 to indicate a possible failure of the protective fuse 5 due to the short-circuit current.

[0074] from Figure 3 It can be seen that there are two parameters that can be set externally, namely the predetermined ampere-squared-second threshold I 2 t max and rated current I R In a possible embodiment, both parameters can be set during the initialization phase. In another embodiment, the parameters can also be adjusted during operation of the fuse failure detection device 1 via a user or a data interface. The data interface can connect the fuse failure detection device 1 to a remote or local controller that can set the parameters during operation of the distribution power system. Furthermore, the rated current I can be adapted according to the load 7 to be protected by the protective fuse 5. R In a possible embodiment, the permissible rated current I can be read from a database or from a local memory integrated in the load 7 to be protected. R .

[0075] The protective fuse 5 includes a fusible element. These fusible elements within the protective fuse 5 can melt to protect the downstream load to which the protective fuse 5 is connected. The protective fuse can also be referred to as a sacrificial device in the circuit. The fusible element within the protective fuse 5 is specifically designed to continuously carry a specific amount of current without opening the circuit. This is referred to as the rated current I of the protective fuse 5. R If current I flows through these element bridges or limiting portions of the electrical fuse 5, heat is generated. The fuse element continues to carry current as intended until a balance is achieved in the heat transfer. Balance in heat transfer is achieved when the amount of heat generated equals the amount of heat dissipated.

[0076] If, on the other hand, there is an imbalance in the heat transfer due to an overcurrent condition (such as an overload or a short circuit occurring), the heat generated is greater than the heat dissipated. This in turn causes a temperature increase at the fusible element of the protective fuse 5, which is performed by the limitation or weakness. If the temperature increase does reach the melting point of the fusible element (e.g. 1085°C for copper or 962°C for silver), the element bridge within the protective fuse 5 does begin to melt and open, resulting in an interruption of the current I flowing through the protective fuse 5 to the protected load 7. In the event of a short circuit condition, the fusible element within the protective fuse 5 begins to melt and then separates the protected load 7 from the power supply 6 in only a few milliseconds. During this time period, an arc can be generated within the fuse 5, also as shown in FIG. Figure 4A 、 Figure 4B The signal diagram is shown in the figure.

[0077] The heat energy generated during the interruption of the fault current by the protective fuse 5 can be expressed in joules and is usually referred to as ampere squared seconds. During the operating time t, the heat energy is proportional to the square of the current I.

[0078] The heat energy generated can be expressed as melting ampere-seconds squared, arcing ampere-seconds squared, and clearing ampere-seconds squared.

[0079] Melting ampere-squared second value I 2 t is the heat energy transferred by the protective fuse 5 after the occurrence of an overcurrent until the fuse element actually melts.

[0080] The arcing ampere-seconds squared value is the heat energy transferred by the protective fuse 5 during its arcing time.

[0081] The clearing amp-seconds value is the sum of the melting amp-seconds value plus the arc discharge amp-seconds value.

[0082] Figure 5The calculation of the ampere-squared second value is illustrated. There is a melting time and an arcing time. The melting time covers the time span from the onset of the overcurrent condition to the moment arcing begins within protective fuse 5. This is followed by the arcing time, which is the time span between melting of the fuse element and interruption of the overcurrent. If the point of no return is reached, protective fuse 5 melts and interrupts the current supply path.

[0083] Figure 6 The operation of the protective fuse 5 for short-circuit overcurrent protection and overload current protection is shown.

[0084] An overcurrent is any current greater than the current that the connected load, device, or apparatus is rated to carry under specified conditions. Even moderate overcurrents can cause system components to overheat rapidly unless the overcurrent is removed promptly.

[0085] An overload fault condition involves an overcurrent that is confined to the normal current path. Typically, it is less than the rated current I of the protected load or application. R An overcurrent of 600% is called an overload fault current. An overload condition often occurs in an application or system when a temporary surge current persists in the system, such as due to a mechanical blockage or stuck equipment condition.

[0086] Usually, it is greater than the rated current I of the protected device or load. R An overcurrent of 600% of the rated current is called a short-circuit fault current. A short-circuit condition may occur due to, for example, an accident, incorrect application, or insulation breakdown.

[0087] Figure 6 A diagram showing the characteristic curve of the protective fuse 5 is illustrated. There are three main operating regions of the protective fuse 5. As long as the measured current I is below the rated current I R , there is normal operating behavior and the protective fuse 5 is not affected. If the current I exceeds the predetermined rated current I R In a possible embodiment, lead provided in the copper limiter or bridge can diffuse into the bridge element, thereby lowering the melting temperature of the fuse element bridge. The lowered melting temperature can be, for example, 170°C. Consequently, an overcurrent that causes diffusion of material into the connecting bridge element can, over time, cause a decrease in the melting temperature and ultimately lead to a rupture of the bridge element. In the event of a short circuit, very high currents almost immediately cause the copper bridge element to break due to the rapidly reached initial melting temperature of copper, approximately 1083°C.

[0088] The determination unit 3 of the fuse failure detection device 1 can continuously determine the heat energy generated in the protective fuse 5 based on the current measured by the current sensor element 2. As long as the protective fuse 5 is within the normal operating range, no detection or warning signal is generated. Overload conditions can be detected by continuously monitoring the calculated heat transfer balance.

[0089] The heat transfer balance indicates the difference between the heat incoming and the heat dissipated by the protective fuse 5 .

[0090] Heat entry can be calculated as ΔQ + =R*I 2 *Δt.

[0091] The dissipated heat can be calculated as ΔQ - =λ(T n –T0)*Δt,

[0092] Where Δt is the incremental time unit,

[0093] T0 is the ambient temperature, for example, 35°C.

[0094] T n is the extrapolated temperature,

[0095] R is the resistance at the fuse element, and

[0096] I is the current.

[0097] T n+1 =T n +ΔT,

[0098] Where ΔT is the temperature difference and can be calculated as follows:

[0099] ΔT=(ΔQ + -ΔQ - )*C*Δt,

[0100] where C is the heat capacity.

[0101] The calculation of the heat ingress may be performed separately for the lead and the limited fuse element of the protective fuse 5. The calculation may be performed by a calculation unit, ie a processor or a microprocessor.

[0102] In a possible embodiment, Figure 1 The shown fuse failure detection device 1 may further comprise at least one temperature sensor element adapted to measure the instantaneous temperature T at the protective fuse 5. The measured temperature may be used to verify the calculated extrapolated temperature or for calibration purposes.

[0103] In a possible embodiment, the fuse failure detection device 1 can be integrated into other devices. In a possible embodiment, the fuse failure detection device 1 can be integrated into an adapter device. The adapter device can be used to connect an electrical load or an electrical load control device to a line or busbar of a power system. In a possible embodiment, the adapter device can also include a protective switch 8 and a protective fuse 5.

[0104] In another possible embodiment, the fuse failure protection device 1 may further include a user interface having a graphical display unit. In this embodiment, if the fuse failure detection signal FFDS or the overload fault warning signal OFWS is displayed to the operator of the power system, the fuse failure detection signal FFDS and / or the overload fault warning signal OFWS may be displayed to the operator to help him / her take necessary countermeasures. The display unit of the user interface may also display parameters set for the fuse failure detection device 1, in particular the rated current I R and a predetermined ampere-squared-second threshold. In a possible embodiment, as Figure 2 、 Figure 3 The method according to the present invention shown in the exemplary flow chart can be executed by a processor FPGA integrated in a fuse failure detection device 1. The fuse failure detection device 1 can be a mobile handheld device 1 with an integrated current sensor element 2, which can be clamped on a wire or bus bar of a power supply path of a load 7.

Claims

1. A method for detecting a failure of a protective fuse (5) for protecting an associated load (7) from overcurrent and / or overload, The method comprises the following steps: - measuring the current I flowing through the protective fuse (5) to the load (7) by means of a current sensor element (2); - determining the heat energy generated in the protective fuse (5) based on the measured current I; as well as - Automatically detecting a failure of the protective fuse (5) if the determined thermal energy exceeds a predetermined threshold and if the current I measured by the current sensor element (2) has stopped flowing through the protective fuse (5).

2. The method according to claim 1 , wherein a fuse failure detection signal (FFDS) is automatically generated indicating a possible failure of the protective fuse (5) due to a short-circuit current if the determined thermal energy has exceeded the predetermined threshold value and the current I measured by the current sensor element (2) has stopped flowing through the protective fuse (5).

3. The method according to claim 1 or 2, wherein the thermal energy is calculated as ampere squared seconds (I 2 t) value, and compare it with the predetermined threshold.

4. The method according to claim 1, wherein a failure of the protective fuse (5) is detected if, as a further condition, the received switch state signal (SWSS) indicates that the associated load (7) has not been switched off externally by the protective switch (8).

5. The method according to claim 1 , wherein if the determined thermal energy does not exceed the predetermined threshold value, but the magnitude of the measured current I is higher than a predetermined rated current (I R ), the energy input into the protective fuse (5) caused by the flowing current I is determined.

6. The method according to claim 5, wherein if the determined energy input into the protective fuse (5) by the current I exceeds a predetermined threshold, an overload fault warning signal (OFWS) is automatically generated indicating an impending failure of the protective fuse (5) due to an overload current.

7. The method according to claim 6, wherein the energy input into the protective fuse (5) is determined by calculating the heat transfer balance of the protective fuse (5) as the difference between the heat generated by the current I flowing through the protective fuse (5) and the heat dissipated by the protective fuse (5).

8. A fuse failure detection device (1) provided for detecting a failure of a protective fuse (5) for protecting an associated load (7) from overcurrent and / or overload, The fuse fault detection device (1) comprises: - a current sensor element (2) adapted to measure the current I flowing through the protective fuse (5) to the load (7); - a determination unit (3) adapted to determine the thermal energy generated at the protective fuse (5) from the current I measured by the current sensor element (2); as well as - a fault detection unit (4) adapted to automatically detect a fault of the protective fuse (5) if the determined thermal energy exceeds a predetermined threshold and if the current I measured by the current sensor element (2) has stopped flowing through the protective fuse (5).

9. A fuse failure detection device (1) according to claim 8, wherein the failure detection unit (4) is adapted to automatically generate a fuse failure detection signal (FFDS) indicating a possible failure of the protective fuse (5) due to a short-circuit current if the determined thermal energy has exceeded the predetermined threshold value and if the current I measured by the current sensor element (2) has stopped flowing through the protective fuse (5).

10. The fuse failure detection device (1) according to claim 8 or 9, wherein the determination unit (3) is adapted to calculate ampere squared seconds (I 2 t) value, the ampere square second (I 2 The value of t) represents the heat energy generated at the protective fuse (5) in response to the current I measured by the current sensor element (2).

11. A fuse failure detection device (1) according to claim 10, wherein the failure detection unit (4) is adapted to convert the calculated ampere squared second (I2) to a value which is greater than the predetermined threshold value if the determined thermal energy has exceeded the predetermined threshold value and the current I measured by the current sensor element (2) has stopped flowing through the protective fuse (5) and if the received switch status signal (SWSS) indicates that the associated load (7) has not been switched off externally by the protective switch (8). 2 t) value and the predetermined ampere square second (I 2 t) value to generate the fuse failure detection signal (FFDS).

12. The fuse failure detection device (1) according to claim 8, wherein the determining unit (3) is further adapted to determine if the determined thermal energy does not exceed the predetermined threshold value but the magnitude of the measured current I is higher than a predetermined rated current (I R ), the energy input into the protective fuse (5) caused by the flowing current I is determined.

13. The fuse failure detection device (1) according to claim 8, wherein the fault detection unit (4) is adapted to generate an overload fault warning signal (OFWS) if the determined energy input into the protective fuse (5) by the current I exceeds a predetermined threshold, wherein the generated overload fault warning signal (OFWS) indicates an impending failure of the protective fuse (5) due to an overload current.

14. The fuse failure detection device (1) according to claim 8, wherein the determination unit (3) is adapted to determine the energy input into the protective fuse (5) by calculating the heat transfer balance of the protective fuse (5) as the difference between the heat generated by the current I flowing through the protective fuse (5) and the heat dissipated by the protective fuse (5).

15. The fuse failure detection device (1) according to claim 8, wherein the current sensor element (2) is adapted to measure direct current and / or alternating current.

16. The fuse failure detection device (1) according to claim 8, wherein the current sensor element (2) is connected in series to the protective fuse (5) within the current supply path of the load (7) or attached to the current supply path of the load (7).

17. The fuse failure detection device (1) according to claim 8, wherein the fault detection unit (4) comprises an interface for receiving a switch state signal (SWSS) from a protective switch (8), the protective switch (8) being connected in series with the protective fuse (5) along the current supply path of the load (7).

18. An adapter device comprising a fuse failure detection apparatus (1) according to any one of the preceding claims 8 to 17.

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