Circuit arrangement with active measuring voltage for determining the insulation resistance relative to ground potential in ungrounded supply systems

Abstract

The invention relates to a circuit arrangement (20) having an active measuring voltage (U G ) for determining the insulation resistance (R F ) or the complex-valued insulation impedance (Z F ) of an ungrounded power supply system (12) relative to a ground potential (PE), the circuit arrangement (20) having a measuring path (24) which extends between the active conductors (L1, L2) of the power supply system (12) and the ground potential (PE) and which comprises a measuring voltage generator (V G ) for generating the measuring voltage (U G ), a measuring resistor (R M ) for capturing the measured voltage (U M ), and a coupling resistor (R A ), the circuit arrangement (20) comprising a signal evaluation circuit (26) which comprises a signal input for evaluating the measured voltage (U M ) and a ground connection (GND) which is connected to the ground potential (PE).

Description

Technical Field

[0001] The invention relates to a circuit arrangement with an active measuring voltage for determining the insulation resistance or the complex-valued insulation impedance of an ungrounded power supply system relative to a ground potential, the circuit arrangement having a measuring path which extends between an active conductor of the power supply system and the ground potential and comprises a measuring voltage generator for generating the measuring voltage, a measuring resistor for capturing the measured voltage, and a coupling resistor, the circuit arrangement comprising a signal evaluation circuit which comprises a signal input for evaluating the measured voltage and a ground connection. Background Art

[0002] When higher requirements for operational, fire and contact safety need to be met, network configurations of ungrounded power supply systems are applied, which are also called insulated networks or IT power supply systems (IT: isoléterre in French). For this type of power supply system, the active parts are separated from the ground potential (relative to "ground"). The advantage of these networks is that the functioning of the connected electrical consumers is not hindered in the event of an insulation fault (first fault), for example a ground fault of an active conductor of the power supply system, because the ideally infinite impedance values ​​between the active conductor of the network and the ground do not form a closed circuit. The network leakage capacitance - which in parallel connection with the insulation resistance forms the complex-valued insulation impedance of the power supply system - will be omitted from this discussion. The ungrounded power supply system discussed within the framework of the present invention can be an AC or DC system or a hybrid of both systems.

[0003] The resistance of an ungrounded supply system relative to ground potential (insulation resistance; in the event of a fault, also called insulation fault resistance or fault resistance) must also be monitored by a standard insulation monitoring device (IMD) in accordance with standard specifications, since a fault loop can be created by a further fault on a different active conductor (secondary fault), which can cause a flowing fault current to shut down the equipment together with the overcurrent protection device, resulting in a stoppage of operation.

[0004] In addition to passive insulation monitoring devices which utilize the network voltage of the power supply system as a driving source for the measuring current to detect insulation faults, active insulation monitoring devices are also common knowledge in the art. These active insulation monitoring devices have a measuring path which extends between one or more active conductors of the power supply system and the ground potential and comprises an internal measuring voltage generator. The measuring voltage generated by the measuring voltage generator actively drives the measuring voltage back to the measuring path via the active conductor and the insulation resistance, the measuring path having a measuring resistor connected in series to the measuring voltage generator for capturing the measuring voltage and a coupling resistor connected in series for coupling to the power supply system. The voltage drop obtained across the measuring resistor is supplied via a signal input to a signal evaluation circuit for evaluation in order to determine the insulation resistance.

[0005] In the simplest case, a monopole coupling with exactly one measuring path at only one active conductor is sufficient. In multi-pole non-grounded power supply systems, coupling to at least two measuring paths can be sensitive in order to also measure the network voltage or the displacement voltage and monitor the coupling.

[0006] In non-grounded power supply systems whose configuration is variable, such as in coupled non-grounded power supply systems on board ships, in which generators supplying different IT networks are connected or disconnected depending on the load conditions, the insulation monitoring devices must also be coupled to one another. In this case, it proves disadvantageous that this coupling of the insulation monitoring devices is established via electrically isolable paths, since the intersection points between the insulation monitoring devices are not directly grounded and signal loops can therefore occur.

[0007] With the insulation monitoring devices known to date, the series connection of the measuring paths is configured so that the ground connection of the signal evaluation circuit is not connected to the ground potential. All intersection signals of the insulation monitoring device are therefore superimposed by a (common mode) measurement voltage relative to ground and must be transmitted in an electrically isolated manner when integrated in a non-grounded power supply system. There is no electrical connection between the insulation monitoring device or other grounded devices. However, these electrically isolated intersections generate significant costs because they must be implemented in each insulation monitoring device. Therefore, repeaters for forwarding alarm messages or data couplers for digital intersections are required for electrical isolation. Summary of the invention

[0008] The object of the invention is therefore to describe a circuit arrangement with an active measuring voltage for determining the insulation resistance or for determining the complex-valued insulation impedance and which, for use in ungrounded power supply systems, does not require complex electrical isolation between coupled insulation monitoring devices.

[0009] Together with the features of the preamble of claim 1 , this object is achieved in that the ground connection of the signal evaluation circuit is connected to ground potential.

[0010] The basic idea of ​​the invention is therefore to connect the ground connection of the signal evaluation circuit to ground potential. Since no potential gradients exist in this case, fault currents (signal loops) can be prevented. All analog and digital intersections then no longer need to be electrically isolated. By eliminating the electrical isolation of all intersections of the signal evaluation circuit (including its voltage supply relative to ground), insulation monitoring devices can be coupled without causing erroneous measurements via interfering loop currents.

[0011] Advantageously, the measuring path is configured such that the ground potential, the measuring voltage generator, the measuring resistor and the coupling resistor form a series connection in a first order.

[0012] In this embodiment, starting from ground potential, the elements of the measurement path, i.e. the measurement path elements (measurement voltage generator, measurement resistor and coupling resistor), are arranged in a first order starting with the measurement voltage generator, followed by the measurement resistor and ending with the coupling resistor.

[0013] In this first measuring arrangement, the connection of the measuring voltage generator together with the ground connection of the signal evaluation circuit is connected to ground potential.

[0014] In this case, the voltage measurement of only a few volts (in the range of ±2 volts) measured via the measuring resistor is superimposed on the larger (common-mode) measurement voltage (in the range of ±20 volts), so that the signal evaluation circuit must perform a high common-mode rejection of the measured voltage.

[0015] Furthermore, a multi-pole coupling in a non-grounded power supply system is provided, the non-grounded power supply system comprising at least two conductors, at least two of the active conductors being each connected to ground potential via a measurement path.

[0016] In an ungrounded power supply system comprising several active conductors, it therefore proves to be advantageous to install a measuring path for each of at least two active conductors.

[0017] The measurement paths can be completely separate, ie each have its own measurement voltage generator, measurement resistor and coupling resistor, or at least two measurement paths can comprise a common measurement voltage generator.

[0018] As an alternative to the first sequence, a second sequence of measuring paths is implemented such that the measuring paths, the measuring voltage generator and the coupling resistor form a series connection starting from the ground potential.

[0019] In this second measuring arrangement, the connection of the measuring resistor is connected to ground potential together with the ground connection of the signal evaluation circuit.

[0020] Here, the measured voltage is captured directly with respect to the ground potential via a measuring resistor; however, the (common mode) measuring voltage is detected differentially. In this case, no high requirements need to be met for the common mode rejection, since the differentially detected measuring voltage is significantly greater than the measured voltage applied via the measuring resistor.

[0021] The second sequence of configurations may be implemented in an ungrounded power supply system having at least two active conductors in such a way that at least two of the active conductors are each independently connected to ground potential via a measuring path.

[0022] In the same way as for the coupling of several active conductors in the first order, completely separate measuring paths can be used for the respective active conductors.

[0023] In order to advantageously use the embodiments of the circuit arrangement according to the invention, in which separate measuring paths are present in the first or second order for each exemplary embodiment, the measuring voltage generators arranged in the respective measuring paths generate different measuring voltages in order to test the functionality of the coupling.

[0024] This allows the connectivity to be monitored so that, for example, line breaks can be detected in the measuring path.

[0025] During operation of the power supply network, when the circuit arrangement is multi-pole, there is a low impedance connection between the measurement paths via the source impedance and the load impedance of the power supply system to be monitored. If the respective driven measurement voltages of the measurement paths are the same, the respective measurement currents in the coupling paths driven by the respective measurement voltages should also be the same. If the measurement voltages between the measurement paths are different, they generate a current via the source impedance and the load impedance if the coupling is intact. If this current does not match the expected current that can be detected from the current load constellation and the network characteristics, an interrupted connection of the measurement path can be identified by this process.

[0026] Advantageously, a circuit arrangement with multi-pole coupling can be used for simultaneously and actively measuring respective insulation resistances or complex-valued insulation impedances connected to ground potential in several ungrounded power supply systems via separate measurement paths, to which active conductors of different power supply systems are assigned.

[0027] In such a configuration, it is only possible to use a multi-pole circuit arrangement to determine the insulation resistance or insulation impedance for several independent power supply systems simultaneously.

[0028] Independent power supply systems are networks with network voltage sources and their own loads that are independent of each other.

[0029] Since active conductors from different supply systems are assigned to each measuring path, the corresponding insulation resistance can be determined for each individual network.

[0030] Advantageously, when a circuit arrangement with multi-pole coupling via separate measuring paths is used for several independent power supply systems, different measuring voltages are applied to the respective power supply systems for identifying low-impedance connections between the power supply systems.

[0031] This configuration allows the insulation resistance or insulation impedance between two independent power supply systems to be determined. By using different measurement voltages in the measurement paths, the current between the power supply systems is set via the measurement paths, thereby identifying an unexpected low-impedance connection (cross fault) of the power supply network and the element of this cross fault can be determined from the real and imaginary parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further advantageous embodiment features emerge from the following description and the drawings which describe preferred embodiments of the invention using examples.

[0033] FIG. 1 shows a circuit arrangement for determining an insulation resistance according to the prior art,

[0034] Figure 2 shows a circuit arrangement according to the invention with a first order of measuring path elements,

[0035] Figure 3a shows a measurement path with galvanic isolation in a differential amplifier,

[0036] Figure 3b shows a measuring path with electrical isolation in the signal processing of the measured voltage,

[0037] Figure 4 shows a circuit arrangement according to the invention with measuring path elements of a second order,

[0038] Figure 5a , 5b shows how the measured voltage is determined without its own signal processing,

[0039] Figure 6a , 6b A measuring voltage generator with a galvanically isolated power supply is shown in two embodiments; and

[0040] Figure 7 The use of the circuit arrangement according to the invention in an independent power supply system is shown. DETAILED DESCRIPTION

[0041] FIG1 shows the general arrangement of a circuit arrangement 10 for determining the insulation resistance of an ungrounded power supply system 12 (insulation monitoring device). N Through two active conductors L1, L2 for the load R L powered by.

[0042] The insulation monitoring device 10 is connected between the two active conductors L1, L2 and the ground (ground potential) PE. The insulation monitoring device 10 is coupled to each active conductor L1, L2 via a branch measurement path 14 so that the insulation monitoring device 10 can be connected via the active conductors L1, L2 and the insulation resistor R F A closed measuring current circuit is formed. The power supply system 12 is further provided with a leakage capacitor C E Description, the leakage capacitance C E With insulation resistance R F Modeled in the same way and together with the insulation resistance R F Together they form the complex insulation resistance Z F In the simplified diagram, the complex value Z FOnly the active conductor L2 is shown; however, the insulation impedance Z F Applied to each active conductor L1, L2.

[0043] Starting from ground potential PE, the measurement path 14 comprises a measurement voltage generator V G , measure the resistance R M and coupling resistor R A (V G , R M , R A and S A Here and below, all corresponding measuring path elements V that operate in the same way are described. Gi , R Mi , R Ai and S Ai Optionally, a switch S is provided in each measurement path 14. A , used to disconnect the insulation monitoring device 10 from the ungrounded power supply system 12.

[0044] Measuring voltage generator V G Generates the measuring voltage U G , measure voltage U G Driven via insulation resistance R F The current in the closed measuring circuit causes the measuring resistor R M Measurable voltage drop U M (Measured voltage). The measured voltage U G and the measured voltage U M is supplied to the signal evaluation circuit 16 to determine the insulation resistance R F For digital processing of the input signal, the signal evaluation device 16 comprises an analog-to-digital converter ADC and a microcontroller μC, as well as a junction 18 , for example for outputting an alarm signal.

[0045] Figure 2 A circuit arrangement 20 according to the invention is shown; starting from the ground potential PE, a measuring voltage generator V G , measure the resistance R M and coupling resistor R A The series connection is made up in a first order in the branched measuring path 24. According to the invention, the ground connection GND of the signal evaluation circuit 26 is connected via the electrical connection 22 to the ground potential PE.

[0046] In using the measurement voltage generator V G Provide AC signal (measurement voltage U G ), the complex insulation impedance Z can be calculated in the signal evaluation circuit 26 via a digital signal processing algorithm such as a discrete Fourier transform (DFT). F , complex insulation resistance ZF With component R F (real part) and C E (imaginary part).

[0047] In the multi-pole coupling shown, the two measuring paths 24 are arranged on a common measuring voltage generator V G Alternatively, each measurement path 24 may include its own measurement current generator V G .

[0048] In this first order configuration, due to the (low) measured voltage U M With (high) common mode measurement voltage U G superposition, and therefore is required to determine the measured voltage U M With high common-mode rejection, the measured voltage U M Detected via differential amplifier 25 (ie instrumentation amplifier). Faced with the current voltage conditions - measured voltage U M Relative to the measured voltage U G is within the range of ±2 volts, while the measured voltage U G In the range of ±20 volts, an instrumentation amplifier with a common-mode rejection of at least 120 dB will be required to correctly determine the measured voltage U M .

[0049] As an alternative to such a high-quality instrumentation amplifier 25, the required high common-mode rejection is achieved via galvanic isolation in the signal processing path and is therefore ideally suited for the measured voltage U M .

[0050] Figure 3a and 3b Two options are shown for this. Thus, the electrical isolation 32 can be used, for example, for a differential amplifier circuit 34 ( Figure 3a ) or the measured voltage U M The signal processing circuit 36 ​​( Figure 3b )Inside.

[0051] Figure 4 The method for determining the insulation resistance R in an ungrounded power supply system 12 with multi-pole coupling according to the present invention is shown. F The circuit arrangement 40. Figure 2 In contrast to the first sequence shown, the measurement path elements are arranged in the measurement path 44 in a second sequence starting from the ground potential PE, starting with the measurement resistor R M , followed by measuring the voltage generator V G and terminated with a coupling resistor R A The measured voltage U M Via the corresponding measuring resistor R directly to PE Mis detected as a voltage drop and together with the measured voltage U detected differentially via the differential amplifier 45 G are supplied together to a signal evaluation unit 46 .

[0052] According to the invention, the signal evaluation unit 46 is connected via the electrical connection 42 to the ground potential PE.

[0053] For measuring voltage U G The common-mode suppression in the signal processing path has fewer requirements to meet, since the measuring voltage U G Than the measured voltage U M Much bigger.

[0054] exist Figure 5a and 5b The method for determining the measured voltage U G In principle, the insulation resistance R F The voltage U needs to be measured G However, the measured voltage U G does not have to be known; measured via reference R F =0hms, measured voltage U G This reference measurement value can be used as a reference. G does not have to be detected in a synchronous and continuous manner to capture the measured voltage U M Therefore, by closing the voltage generator V G and measuring resistance R M The series connection consists of switches S arranged in parallel G , the measured voltage U can be obtained by means of the signal evaluation circuits 26 , 46 M Determine the measured voltage U G ,like Figure 5a shown.

[0055] exist Figure 5a In the circuit expansion, according to Figure 5b Can disconnect (separate) switch S A , with the help of switch S G The resistor R is added in series G , the measured voltage U M Adjust to the measured voltage U M The permissible range of the measuring voltage U G .

[0056] Figure 6a and Figure 6b shows a measurement voltage generator V with a galvanically isolated power supply G To avoid bypassing the measuring resistor R M Via the measurement voltage generator V GThe cross current with respect to ground GND is measured by the voltage generator V G A galvanically isolated power supply and a high impedance input for control must be included. If the measurement voltage generator V is to be controlled via an analog signal G , and if the measured voltage U G is bipolar, such as Figure 6a As shown, the measurement voltage source V G It has a voltage V CC or V DD Bipolar supply differential amplifier. In this case, the supply voltage U GS Powering the internal and electrically isolated voltage source 62. Control voltage U GE Control bipolar measuring voltage U G .

[0057] By using a differential amplifier 66 with differential outputs, the complexity of the internal and electrically isolated voltage source 62 can be reduced. Figure 6b As shown, this amplifier type produces a bipolar measuring voltage U even when the supply is unipolar. G .

[0058] Figure 7 The circuit arrangement 40 according to the invention is shown in two independent power supply systems 12 according to Figure 4 The second order is used.

[0059] An active conductor L1 from two independent power supply systems 12 is assigned to each of the two measuring paths 44, so that the respective insulation resistances R of the power supply systems 12 can be determined independently of one another in the signal evaluation unit 46. F Thus, this circuit configuration makes it possible to simultaneously determine the respective insulation resistances R of several independent power supply systems 12 using only one circuit arrangement 40 of the invention. F , although more than two power supply systems 12 shown in an exemplary manner can be monitored simultaneously in any case. Furthermore, with this configuration, multi-pole coupling to the respective power supply systems 12 also becomes possible.

[0060] Furthermore, it is possible to detect in the measurement path 44 when the measurement voltage U G The currents occur when there are different amplitudes and when there is a low impedance connection 72 (cross fault) between the power supply systems 12. Cross faults occurring between the power supply systems 12, even complex faults, are thereby identified.

Claims

1. A use of a circuit arrangement (20) having an active measurement voltage (U G ) for determining the insulation resistance (R F ) or the complex-valued insulation impedance (Z F ) of an ungrounded power supply system (12) with respect to the ground potential (PE), the circuit arrangement having a measurement path (24) that extends between the active conductors (L1, L2) of the power supply system (12) and the ground potential (PE) and includes a measurement voltage generator (V G ) for generating the measurement voltage (U G ), a measurement resistor (R M ) for capturing the measured voltage (U M ), and a coupling resistor (R A ), the circuit arrangement including a signal evaluation circuit (26) that includes a signal input for evaluating the measured voltage (U M ) and a ground connection (GND) that is connected to the ground potential (PE), The ground potential (PE), the measurement voltage generator (V G ), the measuring resistance (R M ) and the coupling resistor (R A ) are connected in series in a first order in the measuring path (24), Utilizing multi-pole coupling in an ungrounded power supply system (12) having at least two active conductors (L1, L2), at least two of the active conductors (L1, L2) being each connected to the ground potential (PE) via a measuring path (24), and the measuring paths (24) being realized individually, It is characterized in that The corresponding measuring voltage generator (V G ) produces different measurement voltages (U G ) to test the functionality of the coupling.

2. A device with active voltage measurement (U G ) is used to determine the insulation resistance (R) of an ungrounded supply system (12) relative to earth potential (PE). F ) or complex insulation resistance (Z F ) having a measuring path (44) extending between active conductors (L1, L2) of a power supply system (12) and a ground potential (PE) and comprising a circuit for generating a measuring voltage (U G ) of the measurement voltage generator (V G ), used to capture the measured voltage (U M ) of the measured resistance (R M ), and coupling resistance (R A ), the circuit arrangement (40) comprises a signal evaluation circuit (46) comprising a circuit for evaluating the measured voltage (U M ) and a ground connection (GND), the ground connection (GND) being connected to a ground potential (PE); The ground potential (PE), the measuring resistance (R M ), the measurement voltage generator (V G ) and the coupling resistor (R A ) are connected in series in a second order in the measurement path (44); By means of a multi-pole coupling in an ungrounded power supply system (12) having at least two active conductors (L1, L2), at least two of the active conductors (L1, L2) being each individually connected to the ground potential (PE) via a measuring path (44), It is characterized in that The corresponding measuring voltage generator (V G ) produces different measurement voltages (U G ) to test the functionality of the coupling.

3. A method for simultaneously actively measuring the insulation resistance (R) of a plurality of ungrounded power supply systems (12) relative to the ground potential (PE) F ) or complex insulation resistance (Z F ), active conductors (L1, L2) of different power supply systems (12) are assigned to the measuring paths (24), With active measurement voltage (U G ) is used to determine the insulation resistance (R) of an ungrounded supply system (12) relative to earth potential (PE). F ) or complex insulation resistance (Z F ) having a measuring path (24) which extends between active conductors (L1, L2) of a power supply system (12) and a ground potential (PE) and comprises a circuit for generating a measuring voltage (U G ) of the measurement voltage generator (V G ), used to capture the measured voltage (U M ) of the measured resistance (R M ), and coupling resistance (R A ), the circuit arrangement comprises a signal evaluation circuit (26) comprising a circuit for evaluating the measured voltage (U M ) of the signal input and a ground connection (GND), the ground connection (GND) being connected to the ground potential (PE), The ground potential (PE), the measurement voltage generator (V G ), the measuring resistance (R M ) and the coupling resistor (R A ) are connected in series in a first order in the measuring path (24), Utilizing multi-pole coupling in an ungrounded power supply system (12) having at least two active conductors (L1, L2), at least two of the active conductors (L1, L2) being each connected to the ground potential (PE) via a measuring path (24), and the measuring paths (24) being realized individually, It is characterized in that Different measurement voltages (U G ) is applied to the corresponding power supply systems (12) for identifying a low impedance connection between the power supply systems (12).

4. A device for simultaneously actively measuring the insulation resistance (R) of a plurality of ungrounded power supply systems (12) relative to the ground potential (PE) F ) or complex insulation resistance (Z F ), active conductors (L1, L2) of different power supply systems (12) are assigned to the measuring paths (44), With active measurement voltage (U G ) is used to determine the insulation resistance (R) of an ungrounded supply system (12) relative to earth potential (PE). F ) or complex insulation resistance (Z F ) having a measuring path (44) extending between active conductors (L1, L2) of a power supply system (12) and a ground potential (PE) and comprising a circuit for generating a measuring voltage (U G ) of the measurement voltage generator (V G ), used to capture the measured voltage (U M ) of the measured resistance (R M ), and coupling resistance (R A ), the circuit arrangement comprises a signal evaluation circuit (46) comprising a circuit for evaluating the measured voltage (U M ) of the signal input and a ground connection (GND), the ground connection (GND) being connected to the ground potential (PE), The ground potential (PE), the measuring resistance (R M ), the measurement voltage generator (V G ) and the coupling resistor (R A ) are connected in series in a second order in the measurement path (44); By means of a multi-pole coupling in an ungrounded power supply system (12) having at least two active conductors (L1, L2), at least two of the active conductors (L1, L2) being each individually connected to the ground potential (PE) via a measuring path (44), It is characterized in that Different measurement voltages (U G ) is applied to the corresponding power supply systems (12) for identifying a low impedance connection between the power supply systems (12).

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