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EP-4575525-B1 - MEASURING ARRANGEMENT AND MEASURING METHOD FOR MEASURING A GROUNDING IMPEDANCE IN AN UNEARTHED POWER SUPPLY SYSTEM

EP4575525B1EP 4575525 B1EP4575525 B1EP 4575525B1EP-4575525-B1

Inventors

  • Reitz, Julian

Dates

Publication Date
20260513
Application Date
20241204

Claims (13)

  1. A measuring arrangement (M (M1, M2, K)) for measuring a loop impedance (Z s ) of a residual current loop (W) formed by an active conductor (L1, L2) and a protective conductor (PE) in an ungrounded power supply system (2), the measuring arrangement (M (M1, M2, K)) having a measuring device (6) connected to a consumer point (4) and serving to measure a conductor-to-ground voltage (U 0 , U 1 ) and to compute the loop impedance (Z s ), characterized in that a controlled grounding device (M1) is disposed between the active conductors (L1, L2) and the protective ground (PE) at a feeding point (3) of the ungrounded power supply system (2) and switches the grounding of one of the active conductors (L1, L2), and in that a unidirectional communication channel (K) is formed between an extended measuring device (M2) and the grounding device (M1), control information being transmitted from the extended measuring device (M2) to the grounding device (M1) via the communication channel (K) in order to control the grounding device (M1).
  2. The measuring arrangement (M) according to claim 1, characterized in that the communication channel (K) is formed by the residual current loop (W), a modulated residual current, which transmits the control information, flowing in the residual current loop (W).
  3. The measuring arrangement (M) according to claim 2, characterized in that during a setting time (T s ), the modulated residual current has the shape of a residual-current pulse sequence binary encoded via amplitude modulation, the active conductor to be grounded being encoded in the residual-current pulse sequence as the control information.
  4. The measuring arrangement (M) according to any one of the claims 1 to 3, characterized in that the extended measuring device (M2) has a coupling change-over switch (S2) for the controlled overriding of one of the active conductors (L1, L2), a load resistance (R 1 ), via which the conductor-to-ground voltage (U 0 , U 1 ) is registered, a make contact (S1) for the controlled overriding of the load resistance (R 1 ) and measuring and control electronics (20), the measuring and control electronics (20) being configured to measure the conductor-to-ground voltage (U 0 , U 1 ), to control the coupling change-over switch (S2) and the make contact (S1), to generate and transmit the control information to the grounding device (M1) via the communication channel (K) and to compute the loop impedance (Z s ).
  5. The measuring arrangement (M) according to claim 4, characterized in that the make contact (S1) is designed as a semiconductor switch.
  6. The measuring arrangement (M) according to any one of the claims 1 to 5, characterized in that the grounding device (M1) has a three-way switch (S3) for grounding one of the active conductors and measuring and evaluation electronics (10) for evaluating the modulated residual current using a measuring resistance (R m ) connected between the active conductors (L1, L2) and the protective conductor (PE) via coupling capacitors (C e1 , C e2 ).
  7. An insulation monitoring device (IMD) for determining the insulation resistance in an ungrounded power supply system (2) characterized by a grounding device (M1) according to any one of the claims 1 to 6.
  8. A measuring method for measuring a loop impedance (Z s ) of a residual current loop (W) formed by an active conductor (L1, L2) and a protective conductor in an ungrounded power supply system (2), the method comprising the following steps: measuring a conductor-to-ground voltage (U 0 , U 1 ) and computing the loop impedance (Z s ) by means of an extended measuring device (M2) connected to a consumer point (4), characterized in that the grounding of one of the active conductors (L1, L2) is switched by means of a controlled grounding device (M1) disposed at a feeding point (3) of the ungrounded power supply system between the active conductors and the protective conductor, and in that control information is transmitted to the grounding device (M1) from the extended measuring device (M2) by means of a unidirectional communication channel (K) formed between the extended measuring device (M2) and the grounding device (M1) in order to control the grounding device (M1).
  9. The measuring method according to claim 8, characterized in that the control information is transmitted by a modulated residual current which flows in the residual current loop (W) forming the communication channel (K).
  10. The measuring method according to claim 9, characterized in that the modulated residual current is transmitted as a binary-encoded residual-current pulse sequence during a setting time (T s ), the active conductor (L1, L2) to be grounded being encoded in the residual-current pulse sequence as control information.
  11. The measuring method according to any one of the claims 8 to 10, characterized by a controlled overriding of one of the active conductors (L1, L2) by means of a coupling change-over switch (S 2 ) of the extended measuring device (M2), a detection of the conductor-to-ground voltage (U 0 , U 1 ) via a load resistance (R 1 ) in the extended measuring device (M2), a controlled overriding of the load resistance (R 1 ) by means of a make contact (S 1 ) of the extended measuring device (M2), a measurement of the conductor-to-ground voltage (U 0 , U 1 ) by means of measuring and control electronics (20) of the extended measuring device (M2), a control of the coupling change-over switch (S 2 ) and the make contact (S1), a generation and transmission of the control information by means of the measuring and control electronics (20), and a computation of the loop impedance (Z s ) by means of the measuring and control electronics (20).
  12. The measuring method according to claim 11, characterized in that the load resistance (R 1 ) is overridden by means of a make contact (S1) designed as a semiconductor switch.
  13. The measuring method according to any one of the claims 8 to 12, characterized by a grounding of one of the active conductors (L1, L2) by means of a three-way switch (S3) of the grounding device (M1), an evaluation of the modulated residual current by means of measuring and evaluation electronics (10) using a measuring resistance (R m ) connected via coupling capacitors (C e1 , C e2 ).

Description

The invention relates to a measuring arrangement and a measuring method for measuring a loop impedance of a fault current loop formed from an active conductor and a protective conductor in an ungrounded power supply system, with a measuring device connected at a consumption point for measuring a conductor-earth voltage and for calculating the loop impedance. Furthermore, the invention relates to an insulation monitoring device for determining the insulation resistance in an ungrounded power supply system. The loop impedance represents the total resistance of all impedances in the fault current loop and is used to determine the short-circuit current that can occur due to an insulation fault – for example, in the case of unintentional contact between a live conductor and the protective conductor in electrical equipment. For the short-circuit current to reach the tripping current of an overcurrent protective device, the loop impedance must be as low as possible. The measurement of loop impedance during initial and recurring inspections of electrical installations is not only required by DIN VDE 0100-600 (IEC 60364-6), but is also an important measure for reasons of electrical safety and fire protection. To perform these types of measurements on power supply systems, special measuring devices are available on the market. This measurement function is often also included in so-called installation testers, which cover other standard tests. Document EP0915347 discloses a method for measuring the loop resistance in circuit breaker-protected networks. The state of the art is based on the standard DIN EN 61557-3 (IEC 61557-3), which describes the requirements for measuring instruments for measuring loop impedance (loop impedance testers) that operate using the voltage drop method. In this method, the line-to-earth voltage is measured at the measuring point (point of consumption) under no-load conditions U <sub>0 </sub> (open-circuit voltage) and under resistive load conditions U<sub> 1 </sub>. Under load conditions, the line-to-earth voltage drops slightly due to the existing loop impedance Z <sub>s</sub> . Using the two voltage values U <sub>0 </sub> and U <sub>1 </sub>, and the known load resistance R<sub> 1 </sub>, the magnitude of the loop impedance Z<sub>s</sub> can be calculated (see also...). Fig. 1 ): Zs=R1U_0U_1−1 The voltage values U 0 , U 1 must be recorded in complex terms, i.e., in terms of magnitude and phase, in order to be able to calculate the loop impedance Zs correctly in terms of magnitude. All (complex) resistances in the fault loop, such as the resistance of the protective conductor PE, the terminals, the fuses, and the impedance of a transformer winding, are included in the loop impedance Zs. While loop measurements in grounded networks can be carried out directly at the point of consumption, for example a socket, without further circuit-related interventions, in ungrounded power supply systems - which are also referred to as IT networks (French: Isolé Terre - IT) - special technical measures are required for testing. In this type of power supply system, the active parts of the IT network are separated from earth potential – isolated from earth. The conductive housings of the devices connected to the IT network are individually or collectively connected to earth potential via the protective conductor, and thus grounded. The advantage of an ungrounded power supply system is that in the event of an insulation fault (first fault), such as a ground fault or a short circuit to earth, the function of the connected devices is not affected. This is because, due to the ideally infinitely high impedance value between an active conductor of the IT network and earth, a closed fault current loop cannot form. This inherent safety ensures a continuous power supply to the devices fed by the ungrounded power supply system, even if a first insulation fault occurs. This network configuration is therefore particularly common in medical facilities. To measure the loop impedance of a fault current loop formed by a live conductor and a protective conductor in the ungrounded power supply system, the grounding of a live conductor in the immediate vicinity of the mains voltage supply point must therefore first be checked. AC systems of the network transformer - are carried out in order to create a fault current loop in conjunction with a measuring device connected on the load side at the point of consumption. However, grounding the live conductor is often associated with additional organizational and technical effort, as the grounding connection must be made manually by a qualified electrician. Particularly in medical facilities such as hospitals, a more efficient technical solution would be desirable, one that reduces the number of recurring interventions in the electrical distribution board (distribution cabinet). The present invention is therefore based on the objective of designing a measuring arrangement and a meas