Current return channel and method for use of residual current device with differential current sensor in ungrounded DC power supply system

Abstract

The invention relates to a current return channel (20) and a method for using a residual current device (4) with a differential current sensor (8) in an ungrounded DC power supply system (2) using a current return channel (20). The current return channel (20) comprises an electronic circuit (22) coupled via two terminals between each of the active conductors (DC +, DC-) of the ungrounded power supply system (2) and ground (PE) and configured to be temporarily automatically activated when the low resistance insulation fault (1) instantaneously intermittently occurs, and temporarily automatically activated when the low resistance insulation fault (1) instantaneously intermittently occurs. In this way, a fault circuit in which a current-limiting fault current (If) flows, which triggers the residual current device (4), is formed.

Description

Technical Field

[0001] This invention relates to a current return path and method for the use of a residual current device with a differential current sensor (measuring current transformer) in an ungrounded DC power supply system with an active conductor. Background Technology

[0002] An ungrounded DC power supply system and a residual current device installed in an ungrounded DC power supply system represent a prerequisite application environment for the present invention, but are not part of the present invention.

[0003] When powering electrical operating equipment, ungrounded power supply systems—also known as isolated networks (IT networks)—are typically used to meet the growing requirements for operational, fire, and touch safety. Such networks are described in the standard DIN VDE 0100-410. The advantage of these networks is that the function of the electrical operating equipment is not impaired in the event of a first insulation failure (grounding fault or body fault).

[0004] Operating such networks typically requires the use of insulation monitoring systems to generate alarm notifications when a first fault occurs and to locate and eliminate insulation faults as quickly as possible before a second fault causes network shutdown. The requirements for applicable insulation monitoring devices (IMDs) are specified in the international standard IEC 61557-8.

[0005] Although insulation monitoring devices identify insulation faults, the location of the fault often remains unknown in widely distributed power supply systems. Therefore, to locate the faulty line outlet, selective insulation fault location (Branch) is initiated after the insulation fault is detected. For this purpose, an insulation fault location system according to standard IEC 61557-9 is primarily used. This system concentrates a test current into the power supply system at the feed point; the spatial flow of this test current can be traced by measuring current transformers distributed throughout the power supply system being monitored, as the test current closes (insulates) the fault location and is detected by all measuring current transformers located in the fault (test) circuit.

[0006] Measurement or response times for identifying insulation faults in ungrounded power supply systems that are significantly longer than 1 s (e.g., 5 s to 100 s) mean that so-called ground fault wipers—low-resistance insulation faults that occur momentarily and intermittently—are not detected. In grounded power supply systems, such as in TN networks, residual current devices are used for rapid disconnection, which can also perform disconnection or fault detection within milliseconds. In this context, residual current device is understood as a general term for protective devices with differential current sensors for detecting fault currents—these protective devices are primarily residual current devices (RCDs), modular residual current devices (MRCDs) with external disconnection mechanisms, and residual current monitoring devices (RCMs).

[0007] Such residual current devices are only applicable to ungrounded power supply systems, especially ungrounded DC power supply systems, to a limited extent, because in the case of a first fault, the flow of fault current is not large enough to enable selective disconnection or fault detection via differential current measurement.

[0008] Several methods are known that enable monitoring by appropriately adjusting measurement times and thresholds for certain network conditions, provided there is a sufficiently large network leakage capacitance in the IT network. In some cases, artificial network leakage capacitance is also inserted to serve as a current return path for fault current, thereby triggering residual current devices to disconnect or issue an alarm notification. However, this method only works reliably in ungrounded AC networks (AC IT networks) and not in ungrounded DC networks (DC IT networks). Furthermore, artificially increasing network leakage capacitance is counterproductive to the benefits of IT systems in terms of fire protection, personal and equipment protection, and impairs the functionality of the required insulation monitoring devices.

[0009] Patent application DE 10 2021 114 260 A1 describes a circuit arrangement for compliant insulation monitoring that rapidly disconnects upon detection of a ground fault in an ungrounded power supply system. In this context, an IMD is coupled to the neutral point of the ungrounded power supply system, and an AC / DC sensitive differential current sensor (measuring current transformer) is used to detect the fault current in the connected branch. This is evaluated in an assessment device that allows the power supply system to be disconnected using a separate switching device in the event of a fault.

[0010] Patent application DE 10 2021 127 848 A1 describes a method and apparatus for detecting and locating periodic short-term insulation faults in an ungrounded power supply system. For this purpose, various process variables, such as those indicating machine activity, are correlated with differential currents measured by differential current sensors.

[0011] However, the solutions known to date are only applicable under certain technical conditions—for example, there must be a sufficiently large network leakage capacitance or there must be an AC IT network—and do not take into account the use of commercially available residual current devices such as RCDs, MRCDs, or RCMs. Summary of the Invention

[0012] Therefore, the object of the present invention is based on the ability to detect low-resistance insulation faults in ungrounded DC power supply systems—which occur at short intervals—so that commercially available residual current devices—which would otherwise not trip due to insufficient fault current—can be used for selective disconnection of line outputs.

[0013] This objective is achieved in the device by a current return path comprising electronic circuitry coupled via two terminals between one of the active conductors and ground, and configured to be temporarily and automatically activated when a low-resistance insulation fault occurs momentarily and intermittently, to form a fault circuit in which a current-limiting fault current flows, which triggers a residual current device.

[0014] The basic idea of ​​this invention is to automatically provide a current return path with a short but sufficiently long time interval when an insulation fault occurs momentarily and intermittently, thereby forming a fault circuit in which a finite but sufficiently large fault current can flow. This fault current is detected as a differential current by the differential current sensor of the residual current device and causes it to trip. Depending on the type of residual current device (RCD, MRCD, RCM), tripping is understood in this context as both triggering an alarm notification and performing a switching function.

[0015] Therefore, current-limiting return paths can utilize commercially available residual current devices in IT networks—typically intended for installation in TN networks—for selective ground fault brush detection, along with selective disconnection of line outputs affected by insulation faults. Simultaneously, the advantageous characteristics of ungrounded IT networks are not permanently compromised.

[0016] The current return path is implemented by electronic circuitry bipolarly coupled between each of the active conductors and ground. The electronic circuitry detects transiently intermittent low-resistance insulation faults and then provides a purely electronically activated current return path between the corresponding active conductor and ground to close the faulty circuit.

[0017] The electronic circuit according to the invention is simple in terms of circuit design and therefore robust (e.g., the electronic circuit does not have a microcontroller), forming a safe, current-limiting current return path over short time intervals.

[0018] In another embodiment, the electronic circuit has a coupling branch extending between the corresponding active conductor and ground, the coupling branch having a limiting resistor and a switching transistor switched in series with the limiting resistor, the switching transistor being controlled by interlocking logic via a trigger signal, the interlocking logic receiving a detection signal from an adaptive filter that detects and evaluates the displacement voltage to ground at each active conductor.

[0019] In the case of ground fault wiping, there is a very significant change in the displacement voltage, which has a characteristic voltage curve between the active conductor and the ground potential.

[0020] The adaptive filter detects the typical voltage offset and / or its characteristic voltage profile generated by ground fault wiping in a system-specific manner, and forwards this detection individually for each active conductor to interlocking logic for mutual interlocking of complementary switching transistors by means of the detection signal. If one of the switching transistors is selected, the interlocking logic prevents the forwarding of possible trigger signals for controlling the corresponding complementary switching transistor.

[0021] Each switching transistor forms a coupling branch that extends between the active conductor and ground, and now conducts a sufficiently large fault current through these branches. Limiting resistors in the respective coupling branches ensure that the current required by the ungrounded DC power supply system is limited to specified limits.

[0022] Existing additional protective devices such as circuit breakers and insulation monitoring devices will not be impaired by this additional electronic circuit.

[0023] The method steps described in the embodiment of the current return path implementation according to the present invention. In this respect, the foregoing technical effects are also reflected in the method-related advantages of the claimed method according to the present invention for use in an ungrounded DC power supply system with a residual current device having a differential current sensor. Attached Figure Description

[0024] Further advantageous features of the embodiments become apparent from the following description and accompanying drawings, which illustrate preferred embodiments of the invention in more detail using examples.

[0025] Figure 1 An ungrounded DC power supply system is shown.

[0026] Figure 2 An ungrounded DC power supply system with line output and current return path according to the present invention is shown.

[0027] Figure 3 An ungrounded DC power supply system with a current return path and disconnection device according to the invention is shown.

[0028] Figure 4An electronic circuit according to the invention is shown as a current return channel.

[0029] Figure 5 The time series is shown in the fault conditions of activation of the current return channel and triggering of the residual current device, as anticipated by the present invention.

[0030] Figure 6 An ungrounded DC power supply system with an activated current return path according to the invention is shown under fault conditions. Detailed Implementation

[0031] Figure 1 An ungrounded DC power supply system 2 with active conductors DC+ and DC- and a voltage source U0 is shown to illustrate the problem. Between the active conductors DC+ and DC-, the ungrounded DC power supply system 2 has an unavoidable leakage impedance relative to ground PE (ground potential), which itself manifests as an insulation resistance R. f and leakage capacitance C e For fault current monitoring, a residual current device 4 is installed according to the requirements of the specification. This residual current device is designed, for example, as an RCM or MRCD, and has a differential current assessment unit 6 and a differential current sensor 8.

[0032] In the case of insulation fault 1, which is a type of fault in the body or grounding, the short-circuit current cannot flow as it would in a grounding network. Instead, due to the absence of a (resistive) return path, a fault current I will be generated. f The magnitude of the fault current is determined by the insulation resistance R. f and leakage capacitance C e Confirmed. However, in this underlying ungrounded DC power supply system 2 (DC network), the leakage capacitance C e They have proven ineffective in terms of their conductivity. Because their resistance is very high under fault-free conditions, the insulation resistance R... f Only very low fault currents are allowed. However, this fault current I... f Insufficient to trigger residual current device 4.

[0033] Figure 2 An ungrounded DC power supply system 2 is shown, comprising a main system 12 and a line output 14 connected to the main system 12. The line output 14 is monitored by a residual current device 4 for fault current detection by means of differential current measurement (differential current sensor 8).

[0034] According to the present invention, the current return channel 20 in the form of electronic circuit 22 is coupled between one of the active conductors DC+ and DC- in the main system 12 and ground PE via two terminals.

[0035] exist Figure 3 In this design, the residual current device 4, designed as an RCM or MRCD, has an external disconnect device 10 that is directly connected to the differential current assessment unit 6 of the RCM 4 or MRCD 4 and acts as an external circuit breaker, capable of selectively disconnecting the branch of the faulted line outlet 14. This enables selective fast tripping. Alternatively, the switching function can be integrated into the residual current device 4 in the form of a residual current device (RCD).

[0036] Figure 4 The invention illustrates its use as fault current I. f ( Figure 1 Electronic circuit 22 of the reverse current channel 20.

[0037] Electronic circuit 22 has the following task: detecting the displacement voltage U between the active conductor DC+, DC and ground PE. DC+, PE U DC-, PE The process involves evaluating the detected process and deriving the necessary switching action of the switching transistor 28.

[0038] For example, the necessary instructions for electronic circuit 22 can be described as follows:

[0039] An adaptive filter 30 is used to detect the corresponding displacement voltage U of the active conductor DC+ and DC to ground (PE). DC+, PE U DC-, PE And by comparing it with a threshold, for example, the displacement voltage U DC+, PE U DC-, PE Whether it is greater than 80% of the conductor-to-conductor voltage, or by relating it to the voltage pattern, assess whether there is a low-resistance insulation fault occurring at short intervals. Figure 1 The displacement-voltage curve characteristics of ).

[0040] If the voltage exceeds or displacement voltage U is detected DC+, PE U DC-, PE The characteristic curve of the displacement voltage in the adaptive filter 30 will forward the detection signal 32 from the adaptive filter 30 to the interlock logic 34.

[0041] The switching transistors 28 of the active conductors DC+ and DC- affected by the insulation fault 8 are controlled by a trigger signal 36 from the interlocking logic 34 for a time interval of, for example, 50 ms, which is longer than the trigger time of the residual current device 4 used, while the corresponding complementary switching transistors 28 are interlocked via the interlocking logic 34.

[0042] Figure 5 The time series is shown in the case of a fault (ground fault brushing event), wherein the activation of the current return channel 20 and the triggering of the residual current device 4 are as expected in this invention.

[0043] When a ground fault brushing event 1 occurs at time T1 (see...) Figure 1 and Figure 6 When the fault current I is small f1 The flow begins immediately, and the magnitude of the fault current is determined by the network's leakage impedance R. f C e This leads to and determines the outcome. At a certain reaction time T, for example, 1 ms. d1 Subsequently, due to the current component of electronic circuit 22, an increased fault current I appears at time T2. f2 This allows the residual current device 4 to be triggered. The triggering occurs at another reaction time T. d2 The time after that is at point T3.

[0044] Figure 6 An ungrounded DC power supply system 2 is shown according to the invention, which activates the current return channel 20 in a fault event (ground fault brushing event 1).

[0045] In the event of a ground fault brushing event 1 occurring at line outlet 14, a fault circuit is formed via electronic circuit 22, which acts as a current return channel 20, and the fault current I... f A device 4 large enough to trigger the residual current flowing in the faulty circuit.

Claims

1. A current return path (20) for use in an ungrounded DC power supply system (2) having an active conductor (DC+, DC-) for a residual current device (4) having a differential current sensor (8), the current return path (20) comprising: Electronic circuit (22), which is coupled via two terminals between one of the active conductors (DC+, DC-) and ground (PE), and is configured to be temporarily and automatically activated when a low-resistance insulation fault (1) occurs momentarily and intermittently to generate a current-limiting fault current (If). f The fault circuit flows, and the current-limiting fault current triggers the residual current device (4).

2. The current return channel (20) according to claim 1. Its features are, The electronic circuit (22) has a coupling branch (24) extending between the corresponding active conductors (DC+, DC-) and ground. The coupling branch has a limiting resistor (26) and a switching transistor (28) switched in series with the limiting resistor. The switching transistor (28) is controlled by interlocking logic (34) via a trigger signal (36). The interlocking logic (34) receives a detection signal (32) from an adaptive filter (30), which detects and evaluates the displacement voltage (U) from each active conductor (DC+, DC-) to ground. DC+, PE U DC-, PE ).

3. A method for using a residual current device (4) with a differential current sensor (8) in an ungrounded DC power supply system (2) having active conductors (DC+, DC-), the method comprising the steps of: When a low-resistance insulation fault (1) occurs intermittently, the current return channel (20) is temporarily and automatically activated to form a current-limiting fault current (If). f The fault circuit of the current limit fault current triggers the residual current device (4), and the current return channel includes electronic circuitry (22), which is coupled to ground via two terminals in one of the active conductors (DC+, DC-).

4. The method according to claim 3, Its features are, The displacement voltage (U) to ground (PE) at each of the active conductors (DC+, DC-) is detected and evaluated using an adaptive filter (30). DC+, PE U DC-, PE ), The detection signal (32) from the adaptive filter (30) is forwarded to the interlock logic (34). A trigger signal (36) is used to control a switching transistor (28), which is connected in series with a limiting resistor (26) in a coupling branch (24) that extends between the corresponding active conductors (DC+, DC-) and ground. The corresponding complementary switching transistor (28) is interlocked via the interlocking logic (34).

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