Ground conductor monitoring

Description

[0001] The invention relates to an earth conductor monitoring device with the features of claim 1. The invention further relates to a computer program for carrying out a method for monitoring an earth conductor of an electrical device grounded by means of the earth conductor, which provides and / or is supplied with electrical energy by means of a first electrical potential that differs from the earth conductor potential and a second electrical potential that differs from the first potential and from the earth conductor potential.

[0002] When operating electrical machines and systems, the safety of persons and the safe operation of the electrical equipment are paramount. Fault and overcurrent protection devices are used for this purpose. A prerequisite for this is the connection of such machines and systems to an earth conductor, also known as a protective conductor, to achieve a low-resistance earth connection. The invention therefore relates to the field of connection technology for electrical devices that have an earth conductor connection (or protective conductor connection).

[0003] In automation technology, for example, a power supply unit is used in the control cabinet to generate a supply voltage for electrical devices installed within the cabinet. Such a power supply unit is typically connected to an earth conductor via an earth conductor connection. In these applications, the devices in the control cabinet are often mounted on a DIN rail. The DIN rail is frequently used as the earth conductor in this case.

[0004] To ensure ongoing safety during the operation of such systems, regular earth fault testing is required. This testing verifies whether an earth fault exists, i.e., a short circuit between one of the two supply potentials of the power supply and the earth conductor. The supply potentials of the power supply can be, for example, 0 volts and operating voltage, e.g., 24 volts DC. Currently, earth conductor disconnect clamps with a manually operated disconnector are used for these earth fault tests. The disconnector allows the normally existing connection between the 0-volt line and the earth conductor to be broken. With the connection broken, a measurement can then be taken to determine whether an earth fault is present.

[0005] A method and a system for monitoring electrical insulation are known from US patent 2017 / 0138995 A1. An insulation fault locator and a device for locating insulation faults in an ungrounded power supply network are known from EP patent 2 574 939 A1. An analysis device for analyzing a power network is known from EP patent 2 237 057 A1.

[0006] The invention is based on the objective of reducing the effort required for such earth fault tests.

[0007] This problem is solved by means of an earth conductor monitoring device according to claim 1 for monitoring an earth conductor in the sense of a protective conductor, via which an electrical device is earthed. The earth conductor monitoring device comprises the following: a) at least one earth conductor terminal configured for connecting an earth conductor potential, b) at least one first potential terminal configured for connecting a first electrical potential that differs from the earth conductor potential, c) at least one second potential terminal configured for connecting a second electrical potential that differs from the first potential and the earth conductor potential, d) at least one electrical switching device configured to selectively establish (connected state) or interrupt (interrupted state) an electrical connection between the first potential terminal and the earth conductor terminal depending on an electrical control signal, e) at least one control unit configured to automatically send control signals to the electrical switching device. characterized in that the evaluation of the electrical signals at the earth conductor connection takes place without measuring the current in the earth conductor.

[0008] The invention has the advantage that earth fault tests no longer need to be performed manually, but can be carried out at least partially automatically using the earth conductor monitoring device according to the invention. This significantly reduces the personnel effort required. Furthermore, safety is increased because the automatic earth fault test can be performed much more frequently than was previously possible with manual processes. With manual testing, the earth fault test was typically performed every three months. The earth conductor monitoring device according to the invention enables quasi-permanent earth fault testing.

[0009] A further advantage of the invention is that it can also detect slowly developing ground faults. The invention therefore enables predictive maintenance of electrical systems. In this way, problematic downtime of such systems can be avoided or at least reduced, since predictive maintenance can be carried out.

[0010] In an advantageous embodiment of the invention, this can be facilitated by detecting not only low-resistance short circuits of the earth conductor to the first or second electrical potential, but also somewhat higher-resistance connections, e.g., in the range of several kiloohms. Furthermore, due to the quasi-permanent monitoring provided by the invention, it is possible to detect intermittent earth faults.

[0011] In an automation application, the first electrical potential could be, for example, a 0-volt potential. The second electrical potential could be the operating voltage of the automation system's power supply, e.g., a low voltage, particularly a DC voltage. This second electrical potential could be, for example, a 12-volt, 24-volt, or 48-volt potential.

[0012] The electrical switching device can be implemented in a variety of ways. In one option, the existing manually operated disconnect switch of the earth conductor disconnect terminal can be reused and driven automatically by an electric actuator, such as an electric motor or an electromagnet. In a second option, the electrical switching device can be implemented using an electromechanical switch, such as a relay or a contactor. In a third option, the electrical switching device can be designed as a semiconductor switch, such as a transistor, thyristor, or a circuit arrangement of transistors and / or thyristors. This has the advantage that switching between the connected and disconnected states is virtually wear-free and noiseless. Furthermore, the electrical switching device can be implemented cost-effectively and with a very small footprint.

[0013] The electrical switching device has at least two switching states: a connected state and an open state. In the connected state, the first potential terminal is connected to the earth terminal via the electrical switching device; in the open state, the electrical connection between the first potential terminal and the earth terminal is interrupted by the electrical switching device. It is advantageous if, in the connected state, the electrical switching device connects the first potential terminal to the earth terminal with a relatively low resistance. The electrical switching device can have further switching states, for example, an intermediate state in which the electrical connection between the first potential terminal and the earth terminal has a higher resistance than in the connected state.

[0014] According to an advantageous embodiment of the invention, the control unit is configured to evaluate electrical signals at the earth conductor terminal, at least when the circuit is open. This makes it possible to perform earth fault tests comparable to those performed using the previous manual method with the earth conductor monitoring device according to the invention. The control unit can additionally be configured to evaluate electrical signals at the earth conductor terminal even when the circuit is connected.

[0015] According to an advantageous embodiment of the invention, the control unit is configured to automatically switch the electrical switching device between the connected and open states at predetermined regular and / or irregular intervals using the control signals generated by the control unit. In this way, the previously manual earth fault test can be performed fully automatically. The automatic execution can significantly increase the test frequency, for example, to several earth fault tests per minute. The control unit can generate and output, in particular, an on signal and an off signal as control signals to the electrical switching device. These on and off signals then combine to form a pulse-width modulated signal (PWM signal) with which the electrical switching device is controlled.

[0016] According to an advantageous embodiment of the invention, the connected state is activated more frequently on average than the open state. This has the advantage that only short test pulses are required for evaluating the electrical signals at the earth conductor connection, during which the open state is present. Otherwise, the desired connected state is always present. Furthermore, because the connected state occurs more frequently on average than the open state, proper tripping of the fuses can be ensured in the event of a fault, i.e., a ground fault. In this way, the relevant regulations can be met.

[0017] For example, the pulse-width modulated signal can be switched with a duty cycle of 95% on and 5% off. Accordingly, the connection state is active 95% of the time. Generally speaking, the duty cycle can range from 90% to 99% on. The off-time, i.e., the duration of the interrupted state, can be less than 500 ms, less than 100 ms, or less than 10 ms. The period of the pulse-width modulated signal can be, for example, 10 seconds. Generally, it is also possible to implement significantly shorter periods. To comply with the relevant regulations, it is advantageous if the on-time of the pulse-width modulated signal is at least five seconds.

[0018] According to the invention, the evaluation of the electrical signals at the earth conductor connection is performed without measuring the current in the earth conductor. This has the advantage that no complex components, such as a shunt, are required for earth fault testing. Furthermore, risks that can arise from an interruption in the earth conductor can be minimized.

[0019] According to an advantageous embodiment of the invention, the earth conductor monitoring device is configured to detect, based on the evaluated electrical signals at the earth conductor terminal, whether the earth conductor is connected to the first electrical potential and / or whether the earth conductor is connected to the second electrical potential. In this way, the earth conductor monitoring device according to the invention can detect at least the same fault conditions in the earth conductor as previous manual checks.

[0020] According to an advantageous embodiment of the invention, the earth conductor monitoring device includes a light signaling device that automatically emits a light signal when the earth conductor monitoring device detects that the earth conductor is connected to the first potential and / or the earth conductor is connected to the second potential. The light signaling device can have one or more light sources. In this way, the presence of an earth fault can be visually indicated to the user. For example, a warning signal can be emitted via one or more light sources, such as light-emitting diodes (LEDs) or neon lamps.

[0021] According to an advantageous embodiment of the invention, the earth conductor monitoring device has an output interface through which a warning signal can be automatically sent when the earth conductor monitoring device detects that the earth conductor is connected to the first potential and / or the earth conductor is connected to the second potential. In this way, a connected device, e.g., a control computer (PLC) of the plant, can be controlled by means of the earth conductor monitoring device.

[0022] According to an advantageous embodiment of the invention, the output interface has a potential-free output terminal. This has the advantage that further components can be easily connected to the output terminal. The output terminal can, for example, be configured as an ISO-OK contact. Alternatively or additionally, the output terminal can also be a data bus terminal, so that the warning signal can be transmitted via a data bus.

[0023] According to an advantageous embodiment of the invention, the earth conductor monitoring device includes an evaluation circuit via which the electrical signals at the earth conductor connection can be evaluated by the control unit, at least in the interrupted state. This has the advantage that the monitoring is solved circuit-wise, so that rapid monitoring is possible with minimal effort and no software-related delays or other disadvantages can occur.

[0024] The remaining elements of the earth conductor monitoring device, in particular the control unit, can be designed entirely without a computer or other unit executing a computer program, e.g., in the form of a logic circuit. For generating the control signals, the control unit can, for example, include a hardware timer.

[0025] According to an advantageous embodiment of the invention, the evaluation circuit comprises at least one first voltage sensing device connected between the earth conductor terminal and the first potential terminal, and / or at least one second voltage sensing device connected between the earth conductor terminal and the second potential terminal. This allows for simple acquisition and evaluation of the electrical signals at the earth conductor terminal. The first voltage sensing device and / or the second voltage sensing device can, for example, have a trigger threshold, such that the voltage sensing device outputs a trigger signal when the voltage monitored by the voltage sensing device reaches, exceeds, or falls below the trigger threshold. This enables simple downstream signal processing of the trigger signals, which can be configured as binary signals.Further evaluation of the trigger signals can then be carried out, for example, by evaluation logic, e.g., by flip-flop memory.

[0026] The first voltage sensing device can be configured to detect the insulation resistance between the earth conductor terminal and the first potential terminal. The second voltage sensing device can be configured to detect the insulation resistance between the earth conductor terminal and the second potential terminal. For example, the aforementioned trigger signal can be generated when the insulation resistance falls below a predetermined resistance value, such as 1 kΩ.

[0027] According to an advantageous embodiment of the invention, the first and / or second voltage sensing device is designed as an optocoupler or incorporates an optocoupler. This allows for a simple, cost-effective, and durable implementation of the first and / or second voltage sensing device. The optocouplers can be configured such that the respective LED of the optocoupler is switched off when there is no ground fault. The LED only switches on in the event of a fault, i.e., a ground fault. In this way, the LEDs of the optocouplers are protected from wear.

[0028] According to an advantageous embodiment of the invention, the earth conductor monitoring device comprises a power supply unit configured to supply at least the control unit and the electrical switching device with the electrical energy required for operation. The power supply unit draws the electrical energy from the first and second potential connections and supplies it in a buffered state via a buffer circuit. The buffer circuit can be designed, in particular, to bridge periods during which the connection state exists, i.e., to ensure that the electrical switching device and the control unit continue to be supplied with electrical energy via the power supply unit even during the connection state. The buffer circuit can, in particular, include a buffer capacitor.This prevents the function of the earth conductor monitoring device from being disrupted if the earth conductor has a comparatively low-resistance short circuit to the second electrical potential connection.

[0029] According to an advantageous embodiment of the invention, the earth conductor monitoring device is designed as a terminal block or arranged in or on a terminal block. The earth conductor monitoring device can, for example, be structurally integrated into the housing of a terminal block. A terminal block is an object used in electrical installation technology, designed for mounting on a DIN rail and able to be arranged side-by-side with other terminal blocks on the DIN rail. A terminal block has multiple conductor connections, e.g., in the form of spring-loaded clamping connections, so that several electrical conductors can be connected to the terminal block.

[0030] The aforementioned problem is also solved by a method for monitoring an earth conductor in the sense of a protective conductor of an electrical device grounded by means of the earth conductor, which provides and / or is supplied with electrical energy by means of a first electrical potential that differs from the earth conductor potential of the earth conductor and a second electrical potential that differs from the first potential and from the earth conductor potential, with the following characteristics: a) By means of at least one electrical switching device, the switching state is automatically changed between the connected state and the open state at predetermined regular and / or irregular time intervals, wherein in the connected state an electrical connection between the first electrical potential and the earth conductor is established by means of the electrical switching device and in the open state the electrical connection between the first electrical potential and the earth conductor is interrupted by means of the electrical switching device, b) at least in the open state electrical signals are detected and evaluated at the earth conductor, c) based on the evaluated electrical signals at the earth conductor it is determined whether the earth conductor is connected to the first electrical potential and / or whether the earth conductor is connected to the second electrical potential, characterized in that the evaluation of the electrical signals at the earth conductor connection (13) is carried out without measuring the current in the earth conductor.

[0031] This also allows the previously explained advantages to be realized.

[0032] According to an advantageous embodiment of the method, a warning signal is emitted when it is detected that the earth conductor is connected to the first potential and / or when the earth conductor is connected to the second potential. In this way, the presence of an earth fault can be signaled to the user. For example, a warning signal can be output via one or more light sources, such as light-emitting diodes (LEDs) or neon lamps, or via the output interface.

[0033] According to an advantageous embodiment, the method is carried out by means of an earth conductor monitoring device of the type described above.

[0034] The aforementioned task can also be solved by a computer program using program code tools, configured to execute a procedure of the type described above, when the computer program is run on a computer. The advantages described above can also be realized in this way.

[0035] For the purposes of the present invention, the indefinite term "a" is not to be understood as a numeral. Therefore, when, for example, a component is mentioned, this is to be interpreted as "at least one component." Where angles are specified in degrees, these refer to a circle of 360 degrees (360°). Where a computer is mentioned, it may be configured to execute a computer program, e.g., in the sense of software. The computer may be a commercially available computer, e.g., a PC, laptop, notebook, tablet, or smartphone, or a microprocessor, microcontroller, or FPGA, or a combination of such elements.

[0036] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings. The drawings show: Figure 1 - a terminal block with an earth conductor monitoring device, Figure 2 - an earth conductor monitoring device in schematic representation, and Figure 3 - an evaluation circuit of an earth conductor monitoring device.

[0037] The Figure 1 Figure 1 shows a terminal block 1 designed for mounting on a DIN rail 5. For this purpose, the terminal block 1 has DIN rail mounting elements 4 on one side of its housing that faces the DIN rail 5. The terminal block 1 can, for example, be snapped onto the DIN rail 5 using these mounting elements 4. The DIN rail 5 can carry the earth conductor potential PE.

[0038] The terminal block 1 has several conductor entry openings 2, which lead to respective conductor terminals 3. The conductor terminals 3 can advantageously be designed as spring-loaded clamping terminals. Electrical conductors inserted into the conductor entry openings 2 can be electrically connected to the terminal block 1 via the conductor terminals 3.

[0039] The terminal block 1 also features an earth conductor monitoring device 7. A light signal unit 6, which is part of the earth conductor monitoring device 7, is located on one side of the housing facing away from the mounting rail fasteners 4. The light signal unit 6 can, for example, visually indicate an earth fault detected by the earth conductor monitoring device 7.

[0040] The Figure 2Figure 1 shows the structure of the earth conductor monitoring device 7. The earth conductor monitoring device 7 has an earth conductor terminal 13 to which an earth conductor potential PE can be connected. The earth conductor monitoring device 7 has a first potential terminal 12 to which a first potential 0 V can be connected. The earth conductor monitoring device 7 has a second potential terminal 11 to which a second electrical potential U b can be connected.

[0041] The earth conductor monitoring device 7 further comprises an electrical switching device 14, an evaluation circuit with a first voltage detection device 17 and a second voltage detection device 16, a control unit 8 with a timer 9, the light signaling unit 6, an output interface 20, and a power supply unit 10. The power supply unit 10 serves to supply the electrically powered elements of the earth conductor monitoring device 7 with electrical energy. The electrical energy required for the supply is obtained from the voltage difference between the first potential terminal 12 and the second potential terminal 11.

[0042] The control unit 8 is connected, in this case via its timer 9, to a control input of the electrical switching device 14 via a signal line 15. The timer 9 can send electrical control signals to the electrical switching device 14 via the signal line 15, thereby controlling it in such a way that an electrical connection between the first potential terminal 12 and the earth conductor terminal 13 is established or broken.

[0043] The first voltage detection device 17 is connected to the first potential terminal 12 and the earth conductor terminal 13. The first voltage detection device 17 can thus evaluate the voltage between these terminals. Upon detecting a specific voltage between these terminals, indicating a breach of a certain insulation resistance, the first voltage detection device 17 sends a signal via a signal line 19 to the control unit 8. This signal then indicates a ground fault at the second potential terminal 11.

[0044] The second voltage detection device 16 is connected to the second potential terminal 11 and the earth conductor terminal 13. The second voltage detection device 16 can thus evaluate the voltage between these terminals. Upon detecting a specific voltage between these terminals, indicating a breach of a certain insulation resistance, the second voltage detection device 16 sends a signal via a signal line 18 to the control unit 8. This signal then indicates a ground fault at the first potential terminal 12.

[0045] In the control unit 8, the signals received via signal lines 18 and 19 are evaluated, and in the event of a ground fault, the light signaling device 6 is activated. Alternatively or additionally, a warning signal can be output via output interface 20 to an output terminal 21. This can be used, for example, to control a PLC.

[0046] The Figure 3 Figure 1 shows an advantageous embodiment of the first voltage sensing device 17 and the second voltage sensing device 16. The first voltage sensing device 17 comprises a series circuit consisting of a Zener diode 33, a resistor 34, and the light-emitting diode of an optocoupler 35. The optocoupler 35 has an output terminal that is connected to the signal line 19, so that when the light-emitting diode of the optocoupler 35 is switched on, the corresponding signal can be output to the control unit 8.

[0047] The second voltage sensing device 16 comprises a series circuit consisting of a Zener diode 30, a resistor 31, and the LED of an optocoupler 32. The optocoupler 32 has an output terminal that is connected to the signal line 18, so that when the LED of the optocoupler 32 is switched on, the corresponding signal can be output to the control unit 8.

Claims

1. Earth conductor monitoring device (7) for monitoring an earth conductor in the sense of a protective conductor via which an electrical appliance is earthed: a) at least one earth conductor connection (13), which is set up for connecting an earth conductor potential (PE) of the earth conductor, b) at least one first potential connection (12), which is set up for connecting a first electrical potential (0 V) that is different from the earth conductor potential (PE), c) at least one second potential connection (11), which is set up for connecting a second electrical potential (Ub ) that differs from the first potential (0 V) and the earth conductor potential (PE), d) at least one electrical switching device (14) which is set up to selectively establish (connection state) or interrupt (interruption state) an electrical connection between the first potential connection (12) and the earth conductor connection (13) as a function of an electrical control signal, e) at least one control device (8), which is set up to automatically emit control signals to the electrical switching device (14), characterized in that the electrical signals at the earth conductor connection (13) are evaluated without measuring the current in the earth conductor.

2. Earth conductor monitoring device according to claim 1, characterized in that the control device (8) is set up to evaluate electrical signals at the earth conductor connection (13) at least in the interrupted state.

3. Earth conductor monitoring device according to one of the preceding claims, characterized in that the control device (8) is set up to automatically switch the electrical switching device (14) between the switching states connection state and interruption state at predetermined regular and / or irregular intervals by means of the actuation signals generated by the control device (8).

4. Earth conductor monitoring device according to one of the preceding claims, characterized in that the connection state is activated more often on average over time than the disconnection state.

5. Earth conductor monitoring device according to one of the preceding claims, characterized in that the earth conductor monitoring device (7) is set up to detect whether the earth conductor is connected to the first electrical potential (0 V) and / or whether the earth conductor is connected to the second electrical potential (Ub) on the basis of the evaluated electrical signals at the earth conductor connection (13).

6. Earth conductor monitoring device according to one of the preceding claims, characterized in that the electrical switching device (14) is designed as a semiconductor switch.

7. Earth conductor monitoring device according to one of the preceding claims, characterized in that the earth conductor monitoring device (7) has a light signal device (6) via which a light signal can be emitted automatically if the earth conductor monitoring device (7) detects that the earth conductor is connected to the first potential (0 V) and / or the earth conductor is connected to the second potential (Ub).

8. Earth conductor monitoring device according to one of the preceding claims, characterized in that the earth conductor monitoring device (7) has an output interface (20) via which a warning signal can be automatically emitted if it is detected by the earth conductor monitoring device (7) that the earth conductor is connected to the first potential (0 V) and / or the earth conductor is connected to the second potential (Ub).

9. Earth conductor monitoring device according to claim 8, characterized in that the output interface (20) has a potential-free output connection.

10. Earth conductor monitoring device according to claim 2, characterized in that the earth conductor monitoring device (7) has an evaluation circuit via which the electrical signals at the earth conductor connection (13) can be evaluated by means of the control device (8) at least in the interrupted state.

11. Earth conductor monitoring device according to claim 10, characterized in that the evaluation circuit has at least one first voltage detection device (17) connected between the earth conductor connection (13) and the first potential connection (12) and / or at least one second voltage detection device (16) connected between the earth conductor connection (13) and the second potential connection (11).

12. Earth conductor monitoring device according to claim 11, characterized in that the first and / or the second voltage detection device (16, 17) is designed as an optocoupler (32, 35) or has an optocoupler (32, 35).

13. Earth conductor monitoring device according to one of the preceding claims, characterized in that the earth conductor monitoring device (7) has a power supply device (10) which is set up to supply at least the control unit (8) and the electrical switching device (14) with the electrical energy required for operation, the power supply device (10) taking the electrical energy from the first and the second potential connection (11, 12) and outputting it in a buffered manner by means of a buffer circuit.

14. Earth conductor monitoring device according to one of the preceding claims, characterized in that the earth conductor monitoring device (7) is designed as a terminal block (1) or is arranged in or on a terminal block (1).

15. Computer program comprising program code means adapted to perform the following method for monitoring a ground conductor in the sense of a protective conductor of an electrical device grounded by means of the ground conductor, which provides and / or is supplied with electrical energy by means of a first electrical potential (0 V) different from the earth conductor potential (PE) of the earth conductor and a second electrical potential (Ub) different from the first potential (0 V) and the earth conductor potential (PE), when the computer program is executed on a computer: a) an electrical connection between the first electrical potential (0 V) and the earth conductor is established by means of the electrical switching device (14) in the connection state and the electrical connection between the first electrical potential (0 V) and the earth conductor is interrupted by means of the electrical switching device (14) in the interruption state, b) electrical signals on the earth conductor are detected and evaluated at least in the interrupted state, c) the evaluated electrical signals on the earth conductor are used to detect whether the earth conductor is connected to the first electrical potential (0 V) and / or whether the earth conductor is connected to the second electrical potential (Ub ), characterized in that the electrical signals at the earth conductor connection (13) are evaluated without measuring the current in the earth conductor.