CIRCUIT ARRANGEMENT FOR VOLTAGE TESTING AND PARTIAL DISCHARGE DETECTION

Description

[0001] The invention relates to a circuit arrangement for voltage testing and partial discharge detection in a single- or multi-phase medium- or high-voltage system according to the preamble of claim 1.

[0002] Single- or multi-phase medium- or high-voltage systems, especially in the form of so-called medium- or high-voltage switchgear, are known to contain a number of live electrical lines, referred to as conductors, corresponding to the number of phases. In common three-phase systems, this is therefore three conductors, usually abbreviated as L1, L2, or L3.

[0003] In such systems, the circuit arrangement in question serves, on the one hand, for threshold-based voltage testing, in particular in accordance with the IEC 61243-5 standard. It includes one or more conductor signal inputs, each of which is configured for coupling to a capacitive coupling electrode, which in turn is coupled to a conductor of the single- or multi-phase medium- or high-voltage system. A voltage detection unit is connected to the respective conductor signal input of the circuit arrangement on the input side, which is configured for threshold-based voltage state detection with respect to the assigned conductor.

[0004] On the other hand, the circuit arrangement in such systems serves to detect partial discharges on a respective conductor and for this purpose includes at least one partial discharge detector unit configured to detect partial discharges with respect to the associated conductor, which comprises a partial discharge detector circuit and a partial discharge display circuit coupled on the input side to a signal output of the partial discharge detector circuit.

[0005] The circuit arrangement also has a suitable power supply for the partial discharge detector unit, wherein the power supply for the partial discharge detector unit comprises a first power supply circuit configured to supply the partial discharge detector circuit with power from the one or more conductor signal inputs of the circuit arrangement, and / or a second power supply circuit configured to supply the partial discharge indicator circuit with power from the one or more conductor signal inputs of the circuit arrangement. The detection and display of partial discharges on a respective conductor of the medium- or high-voltage system is possible without auxiliary power for the partial discharge detector circuit when the first power supply circuit is present, and without auxiliary power for the partial discharge indicator circuit when the second power supply circuit is present.Auxiliary power refers to any electrical energy that is not drawn via the respective line signal input of the circuit arrangement, but is provided by another source, e.g., a battery or a mains voltage connection of a device containing the circuit arrangement. Compared to this type of auxiliary power, this offers the advantage that maintenance-intensive batteries are not required and that no interference signals need to be considered, which could be mistakenly interpreted as partial discharge signals and are often caused by switching power supplies used to connect such devices to mains voltage.

[0006] A circuit arrangement of this generic type mentioned above is disclosed in patent DE 10 2020 214 614 B3. In the circuit arrangement therein, the partial discharge detector circuit is coupled on the input side to the or one of the conductor signal inputs of the circuit arrangement and, via this, to the relevant capacitive coupling electrode in order to tap the partial discharge signal therefrom.

[0007] Similarly, in a circuit arrangement for voltage testing and partial discharge detection disclosed in published patent application US 2020 / 0003804 A1, the partial discharge detector circuit is coupled on the input side to the conductor signal input of the circuit arrangement and, via this input, to the relevant capacitive coupling electrode. In addition, a fail-safe circuit is provided between the partial discharge detector circuit and the voltage detection circuit to prevent false indications from the voltage detection circuit in the event of a fault in the partial discharge detector circuit, particularly due to conductor open-circuit faults or conductor short-circuit faults to ground.

[0008] Furthermore, various similar circuit arrangements are known which, however, use auxiliary power in the form of external electrical energy or energy provided in addition to the coupling to the respective conductor of the medium- or high-voltage system to power the partial discharge detector unit. A conventional design of this type is disclosed, for example, in published patent application DE 101 34 790 A1. For example, the partial discharge detector circuit often uses an amplifier unit which requires external power for power supply. And the partial discharge display circuit is also often designed in conventional designs to require auxiliary power. For example, patent application EP 0 428 601 B1 and published patent application WO 97 / 07411 A1 disclose circuit arrangements for partial discharge detection which require external auxiliary power for signal processing of the partial discharge detection and / or for displaying the acquired partial discharge information.

[0009] The published patent application WO 2017 / 144091 A1 discloses a circuit arrangement for detecting partial discharges on an electrical object such as a cable connection between two high-voltage cables, wherein a battery or a power supply unit or a magnetic coil can be used to supply energy to the circuit arrangement, with which electrical energy is inductively tapped from one of the two high-voltage cables.

[0010] For so-called voltage detection systems, which are circuit arrangements solely for threshold-based voltage state detection without partial charge detection, versions with and without auxiliary power are known and are described, for example, in the standards VDE0682T415 and IEC61243-5. Patent specification DE 103 04 396 B4 discloses such a voltage detection system that has user-operated power supply means for providing the system with user-activated auxiliary power.

[0011] Various voltage detection systems for voltage testing in medium- or high-voltage systems are already known, which additionally have means for detecting a conductor break on the test signal connecting line from the capacitive coupling electrode to the conductor signal input of the test circuit, as disclosed, for example, in utility model documents DE 203 20 394 U1, DE 297 24 824 U1, and DE 20 2004 012 798 U1. Utility model document DE 20 2013 002 563 U1 proposes installation monitoring means for this purpose, which are designed to detect a high-impedance fault in both the test signal connecting line and an earth connection.

[0012] The invention is based on the technical problem of providing a circuit arrangement of the type mentioned at the outset which offers advantages over the prior art explained above, in particular with regard to its partial charge detection capability.

[0013] The invention solves this problem by providing a circuit arrangement having the features of claim 1.

[0014] The circuit arrangement according to the invention comprises a partial discharge connection path which is designed to couple an input side of the partial discharge detector circuit to an earth side of a system capacitance which is electrically parallel to the capacitive coupling electrode. The term system capacitance here refers to electrical capacitances there, i.e. in the vicinity of the relevant capacitive coupling electrode of the medium- or high-voltage system, of any cables or lines located there, and of electrical capacitances of any terminations located there, in particular so-called plug-in terminations. This system capacitance can become significantly apparent in the present case, for example, when a high-voltage cable is connected to a switchgear panel of the medium- or high-voltage system and the capacitive coupling electrode is dimensioned with a relatively small capacitance.Specifically, capacitances resulting from field control coatings of high-voltage cable connectors and / or from the shielding sheaths of high-voltage cables contribute to the system capacitance. These capacitances are always present in a medium-voltage system as soon as the medium-voltage cable is connected to the system. This system capacitance can often be significantly greater than the coupling capacitance of the respective capacitive coupling electrode. It has been shown that, especially in such cases, the partial discharge detection by the partial discharge detector circuit via the partial discharge connection path offers advantages over other partial discharge detection methods, such as coupling the partial discharge detector circuit to the relevant capacitive coupling electrode or to the associated conductor signal input of the circuit arrangement coupled to this coupling electrode.

[0015] The circuit arrangement can be implemented in a single device, if required, enabling combined voltage testing and partial discharge detection, and is suitable for both single-phase and multi-phase, particularly three-phase, medium / high voltage systems.

[0016] The circuit arrangement also makes it possible to derive the electrical energy required for the operation of the partial discharge detector unit and in particular of its partial discharge detector circuit and / or its partial discharge display circuit, preferably entirely, or alternatively partly, from the measurement signal present at the associated conductor signal input of the circuit arrangement, in particular from its low-frequency signal component.

[0017] Furthermore, the circuit arrangement offers the advantage that active partial discharge detection, consisting of the evaluation of the pending input signal and the display of the evaluation result, can be limited to the only time periods of interest in which the measurement signal is effectively present at the relevant conductor signal input of the circuit arrangement, which means that the measurement signal is present at a signal size or signal strength sufficient for the voltage testing unit to carry out the voltage testing. During inactive time periods in which this active measurement signal, which reflects corresponding voltage carrying activity on the associated conductor of the medium or high voltage system, is not present, no partial discharge detection is required. By supplying the partial discharge detector circuit and / or the partial discharge display circuit with energy via the first orsecond energy supply circuit is / are supplied by the measurement signal present at the line signal input of the circuit arrangement, one or both of these components for partial discharge detection remain inactive due to insufficient energy supply as long as no active measurement signal is present at the line signal input.

[0018] By supplying the partial discharge detector unit with energy from the same measurement signal supplied to the voltage test unit, the energy supply for the detection and indication of partial discharges via the first or second power supply circuit can be maintained in an adjustable manner dependent on the magnitude or strength of the measurement signal for the voltage test, so that, for example, below a minimum threshold for the presence of the voltage detected by the voltage test unit, the detection and indication of partial discharges is automatically omitted. This also automatically protects against false partial discharge detection due to high-frequency interference signals or interference coupling into the conductor signal input of the circuit arrangement, whose frequency is significantly higher than the usual mains frequency of the normal, low-frequency measurement signal.In the absence of an active measurement signal, the partial discharge detector unit remains inactive due to a lack of sufficient power supply and is therefore insensitive to these interference signals. In other words, the power supply for the partial discharge detection from the measurement signal for the voltage test makes it possible to evaluate the partial discharge detection for partial discharge exclusively for signals coupled with a specific low-frequency mains frequency signal, whereas high-frequency interference couplings without a low-frequency signal component do not result in a partial discharge indication.

[0019] To keep the energy consumption for partial discharge detection low, the evaluation of the partial discharge detection can, in appropriate implementations, simply consist of specifying and determining a plurality of discrete, different partial discharge levels and correspondingly reporting or displaying which of these levels is currently present. In the simplest implementation, this can be a purely binary, two-stage reporting and display that simply indicates whether a partial discharge is present or not.

[0020] In a corresponding embodiment, the circuit arrangement is capable of carrying out the voltage test and the partial discharge detection as part of a combined multi-phase test and display system. In particular, the circuit arrangement can have an assigned voltage test unit for each of several conductors of the medium-voltage or high-voltage system to be monitored, or only for some of all the conductors of this system. Analogously, as required, the circuit arrangement can have an assigned partial discharge detector unit for each of several conductors of the medium-voltage or high-voltage system, or only for one conductor or only some of all the conductors of the system. Using the partial discharge detector unit on only one of several phases of a multi-phase system minimizes the circuit complexity and the energy consumption. Using the partial discharge detector unit on several orall phases increases the circuit complexity, but can, if necessary, improve the reporting or display selectivity with regard to partial discharges.

[0021] When dimensioning the circuit arrangement, it is useful if the energy-consuming components of the partial discharge detector unit, i.e., the partial discharge detector circuit and the partial discharge indicator circuit, are designed with sufficiently high impedance so that their presence leaves the response behavior of the voltage detection unit largely unchanged. Furthermore, such a high-impedance design of the partial discharge detector unit contributes to its minimal energy consumption, which can easily be covered by the measurement signal at the relevant conductor signal input via the first and / or second power supply circuit.

[0022] In a further development of the invention, the circuit arrangement includes a selector switch for switchably connecting the input side of the partial discharge detector circuit either to the partial discharge connection path or to the or one of the conductor signal inputs of the circuit arrangement, via which the associated voltage test unit is coupled to the capacitive coupling electrode. This advantageously enables selective partial charge detection via the partial discharge connection path and the grounding side of the system capacitance, particularly in situations with a higher system capacitance or a relatively small coupling electrode capacitance compared to the capacitance of the coupling electrode, or via the relevant conductor signal input of the circuit arrangement and the capacitive coupling electrode, particularly in cases with a relatively high capacitance of the coupling electrode or a sufficiently high partial discharge signal level at the coupling electrode.Alternatively, it may be provided that partial charge detection is carried out exclusively via the partial discharge connection path.

[0023] In a further development of the invention, the circuit arrangement includes a coaxial cable with an inner conductor, which forms at least part of a connecting line from the respective conductor signal input to the associated capacitive coupling electrode, and an outer conductor surrounding the inner conductor, which forms at least part of the partial discharge connection path. This advantageously enables the combination of a shielded coupling of the respective conductor signal input and thus the voltage test by the voltage test unit via the inner conductor to the capacitive coupling electrode with the use of the outer conductor to couple the partial discharge detector unit to the ground side of the system capacitance. Alternatively, the connection from the conductor signal input to the capacitive coupling electrode can be realized by a non-coaxial cable.Furthermore, the partial discharge connection path can alternatively include a separate connection path line instead of using the outer conductor of the coaxial line.

[0024] In a further development of the invention, the grounding side of the system capacitor and the partial discharge connection path coupled to it are connected to a ground potential via a high-frequency blocking element. The high-frequency blocking element can help keep the partial discharge signal sufficiently high on the grounding side of the system capacitor by preventing it from being dissipated via the ground potential. Alternatively, the high-frequency blocking element can be omitted in certain applications or replaced by a correspondingly long length of an associated connection cable.

[0025] In one embodiment of the invention, the first power supply circuit can be coupled to the same conductor signal input of the circuit arrangement as the partial discharge detector unit or to another of several conductor signal inputs of the circuit arrangement. The first alternative is provided for single-phase systems and can also be provided for multi-phase systems if access by the power supply circuit for the partial discharge detector unit to a conductor signal input other than the one possibly used by the partial discharge detector unit is not desired. The other alternative can be advantageous in multi-phase systems, for example, to distribute the energy consumption by the circuit arrangement as evenly as possible across several conductors of the medium / high-voltage system.

[0026] In one embodiment of the invention, the second power supply circuit can be coupled to the same conductor signal input of the circuit arrangement as the partial discharge detector unit or to another of several conductor signal inputs of the circuit arrangement. Here, too, this measure can be advantageous for the second power supply circuit in one or the other alternative, depending on the application, as explained above for the first power supply circuit.

[0027] Specifically, in a corresponding implementation, the partial discharge detector unit, the first power supply circuit, and the second power supply circuit can be coupled to three different conductor signal inputs of the circuit arrangement. This design can be particularly advantageous for a three-phase system, where it evens out the energy consumption from the various conductors and places a very even load on the voltage detection units, which are preferably provided for all three conductors, across all three conductors or phases. This contributes to the ability to specify an approximately uniform response threshold for the voltage test across all three phases or conductors without additional effort.

[0028] In a further development of the invention, the circuit arrangement has a variable capacitor at the respective conductor signal input to form a capacitive voltage divider with the associated capacitive coupling electrode. Using this variable capacitor, i.e. a capacitor with variably adjustable capacitance, the response threshold for the voltage test by the voltage testing unit and the sensitivity for partial discharge detection by the partial discharge detector unit can be variably set, i.e. adjusted, as required. With a larger capacitance of the variable capacitor, partial discharge detection becomes less sensitive; as this capacitance is reduced, it becomes more sensitive. Since the response thresholds for the voltage test according to the IEC61243-5 standard for non-response orthe response of the voltage indicator has a relatively high tolerance, namely 10% to 45%, the capacitance of the variable capacitor can be varied within a correspondingly large range to change the sensitivity of the partial discharge detection without violating the response thresholds of the voltage indicator according to this standard.

[0029] In a further development of the invention, the partial discharge detector unit is designed with adjustable sensitivity. The adjustability of the sensitivity of the partial discharge detector unit can advantageously be used, for example, to set a response level for partial discharge detection sufficiently high, depending on the given system, in order to avoid false indications that can arise from background noise caused by high-frequency external interference that often occurs in practice. For sensitivity adjustment, the partial discharge detector unit comprises a circuit component coupled to the signal output of the partial discharge detector circuit, which has a variable capacitor or a potentiometer or an adjustable resistor network, i.e., a network of ohmic resistors with a variably adjustable total ohmic resistance.In addition to or as an alternative to the aforementioned arrangement of a variable capacitor at the conductor signal input, this represents an advantageous implementation option for adjusting the sensitivity with regard to partial discharge detection. The voltage testing unit remains unaffected by this variant of the sensitivity adjustment of the partial discharge detection, so that with this variant, the sensitivity of the partial discharge detection can be adjusted, if necessary, beyond the range which, with a corresponding adjustment of the capacitance of the variable capacitor at the conductor signal input, does not yet lead to a violation of the standard response thresholds for the voltage display of the voltage test.

[0030] In a further development of the invention, the partial discharge detector unit has a deactivation element that allows it to be deactivated independently of the voltage detection unit connected to the same conductor signal input of the circuit arrangement. This deactivation element allows the partial discharge detector unit to be deactivated as needed, while the voltage detection unit can remain active. This allows voltage tests to be performed by the voltage detection unit during periods in which the partial discharge detector unit is deactivated, so that the voltage test can be kept completely unaffected by the partial discharge detector unit.

[0031] In a further development of the invention, the partial discharge indicator circuit comprises a display unit and a controllable switch connected between the display unit and the second power supply circuit, which is coupled via a control input to the signal output of the partial discharge detector circuit. This represents an advantageous circuit implementation for the partial discharge indicator circuit in terms of energy consumption and required display functionality, requiring only minimal circuit complexity.

[0032] In a further development of the invention, the circuit arrangement includes a detection information connection for transmitting detection information from the partial discharge detector unit to the outside, and a controllable switch connected to the detection information connection, with a control input of the controllable switch being connected to the signal output of the partial discharge detector circuit. Information regarding a detected partial discharge can be transmitted to the outside via the detection information connection. Alternatively, the switch's output signal can, of course, also be used within the device to connect a remote transmission circuit, e.g., via a radio transmitter, so that the partial discharge signal is reported wirelessly to a remote control system.

[0033] In a further development of the invention, the circuit arrangement includes a diagnostic connection connected to the signal output of the partial discharge detector circuit. If a partial discharge is detected, the corresponding partial discharge signal present at the signal output of the partial discharge detector circuit can be tapped via the diagnostic connection, e.g., for external examination using an oscilloscope to diagnose the cause of the partial discharge.

[0034] In a further development of the invention, the respective voltage testing unit comprises a voltage testing circuit coupled on the input side to the associated conductor signal input of the circuit arrangement, and a voltage state display circuit coupled on the input side to a signal output of the voltage testing circuit. The partial discharge display circuit of the partial discharge detector unit and the voltage state display circuit of the voltage testing unit coupled to the same conductor signal input of the circuit arrangement have a common display unit. Thus, the voltage testing unit and the partial discharge detector unit advantageously share a common display unit, which contributes to keeping the circuit complexity and power consumption of the circuit arrangement low.

[0035] In one embodiment of the invention, the circuit arrangement comprises a connecting line monitoring circuit that can be coupled to a second end of the outer conductor, remote from the coupling electrode, and is configured to detect a potential deviation on the outer conductor. The connecting line monitoring circuit implements an installation monitoring means with which a high-impedance fault in the outer conductor can be detected, which can be caused in particular by a conductor break in the coaxial line and is typically also accompanied by a high-impedance fault in the inner conductor and thus in the connecting line. The term "high-impedance fault" is understood here to mean a fault that significantly increases the electrical resistance of the connecting line compared to its normal, fault-free operating state, which particularly includes the case where the connecting line is completely interrupted.

[0036] In a further embodiment of the invention, the circuit arrangement includes a common connector plug for the simultaneous, detachable coupling of the connecting line monitoring circuit to the second end of the outer conductor and the conductor signal input to an end of the inner conductor facing away from the coupling electrode. This can prevent, for example, the error scenario where the conductor signal input was connected to the inner conductor, but it was forgotten to also connect the outer conductor to the connecting line monitoring circuit.

[0037] In a further embodiment of the invention, the connecting line monitoring circuit is connected to a ground potential via a ground connection and is configured to detect a potential deviation on the ground connection. In this implementation, the connecting line monitoring circuit can thus also detect a high-impedance fault in its ground connection. The term "high-impedance fault" is understood here to mean a fault that significantly increases the electrical resistance of the ground connection compared to its normal, fault-free operating state, which particularly includes the case where the ground connection is completely interrupted.

[0038] An advantageous embodiment of the invention is shown in the drawing. This and other advantageous embodiments of the invention are explained in more detail below. Herein: Fig. 1 a schematic diagram of a circuit arrangement for voltage testing and partial discharge detection in a single- or multi-phase medium- or high-voltage system.

[0039] The only Figure 1 The circuit arrangement shown in an exemplary embodiment is designed for voltage testing and partial discharge detection in a single- or multi-phase medium- or high-voltage system. For this purpose, it has one or more conductor signal inputs, each of which is configured for coupling to a capacitive coupling electrode, which is coupled to a conductor of the single- or multi-phase medium- or high-voltage system. The circuit arrangement is shown in Fig. 1shown coupled to three conductors L1, L2, L3 of a three-phase medium- or high-voltage system, each with a coupled capacitive coupling electrode 2 1 , 2 2 , 2 3. Here, the circuit arrangement is coupled with one conductor signal input 1 1 , 1 2 , 1 3 to the respective coupling electrode 2 1 , 2 2 , 2 3 of the respective conductor L1, L2, L3.

[0040] The circuit arrangement shown includes a voltage detection unit 3, each coupled on the input side to the associated conductor signal input 11, 12, 13, which is configured for threshold-based voltage state detection of the associated conductor L1, L2, L3. For this purpose, the voltage detection unit 3 preferably has a circuit design known per se for such voltage detection units operating according to the IEC61243-5 standard, which therefore requires no further explanation here.

[0041] Furthermore, the circuit arrangement shown has at least one partial discharge detector unit 4 configured for partial discharge detection with respect to the associated conductor L1, L2 and / or L3, which comprises a partial discharge detector circuit 5 and a partial discharge display circuit 7 coupled on the input side to a signal output 6 of the partial discharge detector circuit 5.

[0042] In addition, the circuit arrangement shown includes a power supply for the partial discharge detector unit 4, this power supply comprising a first power supply circuit 8 and / or a second power supply circuit 9. The first power supply circuit 8 is configured to supply the partial discharge detector circuit 5 with power from the or one of the conductor signal inputs 1 1 , 1 2 , 1 3 of the circuit arrangement, and the second power supply circuit 9 is configured to supply the partial discharge indicator circuit 7 with power from the or one of the conductor signal inputs 1 1 , 1 2 , 1 3 of the circuit arrangement. In advantageous embodiments, this power supply comprises both the first and the second power supply circuits 8, 9, as in the example shown; in alternative embodiments, only one of these two power supply circuits 8, 9 is provided.The first and second power supply circuits 8, 9 have a circuit design that provides the functionality required by each of them. Suitable circuit implementations in this regard are known per se to the person skilled in the art, given knowledge of the functionality specified here, and therefore require no further explanation here.

[0043] In Figure 1 The circuit arrangement is shown in more detail with its components coupled to the conductor L1. Similarly, the circuit arrangement may comprise circuit components coupled to the conductor L2 or to the conductor L3, e.g., a further voltage detection unit 3, as in Fig. 1indicated. Since these additional circuit components can be designed identically to the circuit components shown, which are coupled to conductor L1, the following description of the circuit components shown is sufficient. In particular, in corresponding embodiments, it is possible to provide the voltage detection unit 3 for all three phases, i.e., three-phase, and the partial discharge detector unit 4 for only one phase, i.e., single-phase.

[0044] In corresponding designs, as in the example shown, the voltage testing unit 3 has a voltage testing circuit 16, e.g., in the form of a suitable conventional threshold detector, coupled on the input side to the associated conductor signal input 11, 12, 13, and a voltage state display circuit 18, e.g., in the form of a liquid crystal display (LCD) known per se, coupled on the input side to a signal output 17 of the voltage testing circuit 16. Furthermore, the measurement signal supplied on the input side via the conductor signal input 11, 12, 13 can be routed in parallel to an external measurement point 19 of the voltage testing unit 3, as shown.

[0045] The circuit arrangement further comprises a partial discharge connection path 37, which is configured to couple an input side 5a of the partial discharge detector circuit 5 to a ground side 39 of a system capacitance C S1 , C S2 , C S3 that is electrically parallel to the respective capacitive coupling electrode 2 1 , 2 2 , 2 3 . This enables the detection of partial discharges by means of the partial discharge detector unit 4 at the system capacitance C S1 , C S2 , C S3 that is electrically parallel to the capacitive coupling electrode 2 1 , 2 2 , 2 3 via the partial discharge connection path 37.The respective system capacitance C S1 , C S2 , C S3 is made up in particular of electrical capacitances of cables, lines and terminations, in particular plug-in terminations in the vicinity of the relevant capacitive coupling electrode 2 1 , 2 2 , 2 3 of the medium-voltage or high-voltage system and is particularly noticeable when a high-voltage cable is connected to a switchgear panel of the medium-voltage or high-voltage system and the capacitive coupling electrode 2 1 , 2 2 , 2 3 is dimensioned with a rather small capacitance, so that the system capacitance is greater than the capacitance of the coupling electrode 2 1 , 2 2 , 2 3. In particular, capacitances which result from field control coatings of high-voltage cable plugs and / or from shielding sheaths of high-voltage cables and which are always present in a medium-voltage system as soon as the medium-voltage cable is connected to the system.It turns out that, especially in such cases, partial discharge detection via the earthing side 39 of this system capacitance C S1 , C S2 , C S3 can be superior to partial discharge detection via the capacitive coupling electrode 2 1 , 2 2 , 2 3 .

[0046] In advantageous embodiments, the circuit arrangement has a changeover switch 25 for the switchable connection of the input side 5a of the partial discharge detector circuit 5 either to the partial discharge connection path 37 or to the or one of the conductor signal inputs 1 1 , 1 2 , 1 3 . This allows the user to switch, if desired, between the partial discharge detection at the respective system capacitance C S1 , C S2 , C S3 via the partial discharge connection path 37 and a partial discharge detection at the relevant capacitive coupling electrode 2 1 , 2 2 , 2 3 via the associated conductor signal input 1 1 , 1 2 , 1 3 and thus to optimally adjust each time depending on the situation and / or system.

[0047] Thus, in high-voltage installations, there are typically switchgear panels in the form of so-called reserve panels, which are operated at least temporarily without high-voltage cables. In these panels, the capacitance of the relevant coupling electrode 2 1 , 2 2 , 2 3 acts primarily to couple out the partial discharge signal, via which corresponding signals from the other conductors can also be coupled in. In this case, therefore, the coupling of the partial discharge detector circuit 5 to the relevant conductor signal input 1 1 , 1 2 , 1 3 is generally expedient. In general, this switching of the partial discharge detection to the relevant conductor signal input 1 1 , 1 2 , 1 3 , e.g.the conductor signal input 1 1 , is displayed when it can be assumed that the partial discharge is coupled so well across all conductors L1, L2, L3 due to sufficiently large capacitances of the coupling electrodes 2 1 , 2 2 , 2 3 that a sufficiently large partial discharge signal level arrives via the associated conductor signal input, such as the conductor signal input 1 1 , and its connection to the corresponding coupling electrode, such as the coupling electrode 2 1 , regardless of which of the conductors L1, L2, L3 the partial discharge originally originates from. If, on the other hand, it can be assumed that the capacitances of the coupling electrodes 2 1 , 2 2 , 2 3 are not sufficiently large for this type of partial discharge signal coupling, the partial discharge detection can be switched to the respective system capacitance C S1 , C S2 , C S3 via the partial discharge connection path 37. This can be done, for example,This can be the case when a high-voltage cable is connected to the switchgear panel, resulting in additional cable capacitance or termination capacitance that dampens or absorbs the high-frequency partial discharge signal. This effect is particularly noticeable when the capacitance of the coupling electrodes 2 1 , 2 2 , 2 3 is relatively low.

[0048] In advantageous embodiments, the circuit arrangement for one, two or, as in the example shown, for all three phases, has a coaxial line 31 with an inner conductor 32, which forms at least part of a connecting line 30 from the respective conductor signal input 1 1 , 1 2 , 1 3 to the associated capacitive coupling electrode 2 1 , 2 2 , 2 3 , and an outer conductor 33 surrounding the inner conductor 32, which forms at least part of the partial discharge connection path 37. As a result, the outer conductor 33 can function as a coupling or connecting line, via which the partial discharge detector circuit 5 can be coupled to the ground side 39 of the system capacitance C S1 , C S2 , C S3 . In an alternative embodiment, the partial discharge connection path 37 includes a Fig. 1A separate coupling line 51, indicated by dotted lines, is used to connect the partial discharge detector circuit 5 to the grounding side 39 of the system capacitance C S1 , C S2 , C S3 , instead of using the outer conductor 33 for this purpose. This design is therefore also possible if the coaxial line 31 is not provided. On the other hand, the use of the coaxial line 31 can improve the sensitivity of the partial discharge detection on the relevant phase if the partial discharge detector circuit 5 is connected to the associated conductor signal input 1 1 , 1 2 , 1 3 and thus to the inner conductor 32.

[0049] In the example shown, the outer conductor 33 is grounded at a first end 33a facing the coupling electrode together with the grounding side 39 of the respective system capacitance C S1 , C S2 , C S3 , i.e. together with an earth line of the respective system capacitance C S1 , C S2 , C S3 , i.e. connected to an earth potential 36. In addition, an end 32a of the inner conductor 32 facing the coupling electrode is connected to the earth potential 36 together with the associated coupling electrode 2 1 , 2 2 , 2 3 via a voltage-limiting predetermined breaking point 35. In advantageous three-phase implementations, the earthing sides 39 of all three system capacitances C S1 , C S2 , C S3 are connected to one another and to the earth potential 36 via a common earth line 52, as in the example shown. Alternatively, they can be connected individually to the earth potential 36, separately from one another.

[0050] In corresponding embodiments, as in the example shown, the grounding side 39 of the respective system capacitance C S1 , C S2 , C S3 and the partial discharge connection path 37 coupled thereto are connected to the ground potential 36 via a high-frequency blocking element 40. The high-frequency blocking element 40 can be an inductor or another conventional electrical component that prevents high-frequency signals, and in particular the partial discharge signal, from being diverted via the ground potential 36, whereby this function can possibly also be achieved solely by an appropriately designed connection line. This can contribute to improved detection of the partial discharge signal by the coupled partial discharge detector circuit 5.In the example shown, the high-frequency blocking element 40 is looped in between the common earth line 52 and the earth potential 36 for the three earthing sides 39 of the system capacitances C S1 , C S2 , C S3; in alternative embodiments without the common earth line 52, a high-frequency blocking element 40 is located between the earthing side 39 of the respective system capacitance C S1 , C S2 , C S3 and the earth potential 36.

[0051] In the embodiment shown, the first power supply circuit 8 is coupled to the same conductor signal input 1 1 , 1 2 , 1 3 of the circuit arrangement as the partial discharge detector unit 4, specifically to the conductor signal input 1 1 leading to the conductor L1. In alternative embodiments of the circuit arrangement (not shown), the first power supply circuit 8 is coupled to another of the plurality of conductor signal inputs 1 1 , 1 2 , 1 3 of the circuit arrangement, such as the associated partial discharge detector unit 4, whose partial discharge detector circuit 5 is fed by the first power supply circuit 8.

[0052] Likewise, in the illustrated embodiment, the second power supply circuit 9 is coupled to the same conductor signal input, for example, the conductor signal input 11, of the circuit arrangement as the associated partial discharge detector unit 4, whose partial discharge display circuit 5 is supplied by the second power supply circuit 9. In alternative embodiments, the second power supply circuit 9 is coupled to a different one of the plurality of conductor signal inputs 11, 12, 13 of the circuit arrangement than the respective partial discharge detector unit 4.

[0053] For example, in an advantageous implementation, the partial discharge detector unit 4 can be connected to the first conductor L1, the first power supply circuit 8 to the second conductor L2, and the second power supply circuit 9 to the third conductor L3 of the three-phase medium / high-voltage system, particularly if only a single partial discharge detector unit 4 is used for this three-phase system. The voltage detection unit 3 is preferably present in triplicate, once for each of the three conductors L1, L2, L3.

[0054] In advantageous embodiments, the circuit arrangement, as in the example shown, includes a variable capacitor 10 for forming a capacitive voltage divider with the associated capacitive coupling electrode 2 1 , 2 2 , 2 3 . The associated conductor signal input 1 1 , 1 2 , 1 3 then forms the center tap of this capacitive voltage divider. The capacitive voltage divider divides the signal of the respective phase or conductor L1, L2, L3 down to the measurement signal at extra-low voltage level. The variable capacitor 10 can be used to set the response threshold for the capacitive voltage indication provided by the voltage testing unit 3 and, at the same time, to variably adjust the sensitivity of the partial discharge detection by the partial discharge detector unit 4, preferably while adhering to the response thresholds for the voltage indication specified in the IEC61243-5 standard.By increasing the capacitance of the variable capacitor 10, the partial discharge detection can be made less sensitive, or by reducing this capacitance, it can be made more sensitive.

[0055] The partial discharge detector circuit 5 has a circuit design known per se for the desired functionality, which requires no further explanation here, for example, using a high-pass or band-pass circuit. If the partial discharge detector circuit 5 detects an existing partial discharge, e.g., by reaching a predetermined partial discharge level, the partial discharge detector circuit 5 outputs a detection signal at its signal output 6, which activates the partial discharge display circuit 7 to generate corresponding display information.

[0056] In advantageous implementations, the partial discharge display circuit 7 comprises, as in the example shown, a display unit 13 and a controllable switch 14, such as a semiconductor switch designed as a field-effect transistor, which is looped between the display unit 13 and the second power supply circuit 9, wherein this controllable switch 14 is coupled by a control input 15 to the signal output 6 of the partial discharge detector circuit 5.

[0057] In advantageous implementations of the circuit arrangement, the partial discharge detector unit 4 is designed with adjustable sensitivity. For this purpose, the partial discharge detector unit 4 in the example shown comprises a circuit component 11 coupled to the signal output 6 of the partial discharge detector circuit 5, which in the case shown comprises a potentiometer or, alternatively, a variable capacitor. This circuit component 11 enables a separate adjustment or adjustment of the sensitivity of the partial discharge detector unit 4, i.e., a variable adjustment of its response threshold, independent of the setting of the response thresholds for the voltage test unit 3 by means of the variable capacitor 10.

[0058] In advantageous embodiments, the partial discharge detector unit 4, as in the example shown, has a deactivation element 12, by which it can be deactivated without also deactivating the voltage detection unit 3 coupled to the same conductor signal input 11, 12, 13 of the circuit arrangement. In the example shown, a user-operable switch, which is looped between the signal output 6 of the partial discharge detector circuit 5 and a ground connection 20, serves as the deactivation element 12. During active operation of the partial discharge detector unit 4, the switch is open, and to deactivate the partial discharge detector unit 4, it can be closed by the user.

[0059] In corresponding implementations of the circuit arrangement, the partial discharge detector unit 4 alternatively or as shown in addition to the controllable switch 14 has a controllable switch 21, e.g. again a semiconductor switch. The switch 21 is connected on the one hand to the ground connection 20 and on the other hand, as shown, directly or alternatively indirectly via a coupling relay to a terminal 22, which, for example, enables connection to a telecontrol substation of a conventional type in order to transmit the partial discharge detection information via remote transmission, and in this way functions as a detection information terminal. A control input of this switch 21 is supplied with the output signal of the partial discharge detector circuit 5. Alternatively, the output signal of the switch 21 can also be used within the circuit arrangement or the device forming it for connecting a remote transmission circuit, e.g.can be used by means of a radio transmitter to report the partial discharge signal from the device to a remote control system via radio.

[0060] In the illustrated embodiment, the display unit 13 for displaying the information about the partial discharge detection and the voltage state display circuit 18 are designed as separate display units, preferably both in the form of suitable LCD display units. In alternative embodiments, the partial discharge display circuit 7 and the voltage state display circuit 18 have a common display unit, again preferably an LCD display unit.

[0061] Depending on the requirements and application, the partial discharge detector circuit 5 contains a single threshold detector with a predetermined threshold or several threshold detectors arranged in parallel with different thresholds. In the latter case, not only a binary indication of the presence or absence of a partial discharge is possible, but also the detection or evaluation with regard to partial discharge thresholds of varying heights. By appropriately adapting the design of the partial discharge indicator circuit 7, a separate indication of the respective partial discharge threshold or partial discharge level can then be provided, i.e., a partial discharge indication in more than two stages.

[0062] The circuit arrangement according to the invention enables the combined partial discharge detection and voltage testing by means of a single test device, for which purpose the circuit arrangement can be accommodated, for example, in a common housing 23, as in Fig. 1illustrated schematically. The circuit arrangement dispenses with a strict separation of the high-frequency and low-frequency components of the measurement signal on the respective conductor signal input 1 1 , 1 2 , 1 3 , which makes it easier to extract the energy required for evaluating the high-frequency signal component for the purpose of partial discharge detection and the energy required to display the detected information from the low-frequency signal component. In the case that the partial discharge detector circuit 5 is coupled to the respective conductor signal input 1 1 , 1 2 , 1 3, it is helpful here to dimension the partial discharge detector circuit 5 with a sufficiently high impedance, which also contributes to the response behavior of the voltage testing unit 3 not being significantly changed by the presence of the partial discharge detector unit 4.

[0063] In advantageous embodiments, the circuit arrangement, as in the example shown, has a diagnostic connection 24 which is connected to the signal output of the partial discharge detector circuit 5, wherein this connection is preferably implemented directly, i.e. without any other circuit components in between. Via the diagnostic connection 24, which, like the detection information connection 22, is located on the housing 23 and is preferably accessible from the outside and, like the latter, can be designed, for example, as a connection socket, the associated partial discharge signal present at the signal output 6 of the partial discharge detector circuit 5 can be tapped when a partial discharge is detected, e.g. in order to be able to examine it externally using an oscilloscope or the like for the purpose of diagnosing the cause of the partial discharge. In this case, the signal behind the, for example,The partial discharge detector circuit 5, designed as a high-pass filter, can be tapped and correlated with 50 Hz oscillations at the external measuring point 19 of the voltage test unit 3. This makes it possible to determine in which phase the partial discharge is generated. In alternative designs, the diagnostic connection 24 is omitted; in this case, the detection information connection 22 can be used to tap corresponding partial discharge information for external analysis if necessary. In further alternative designs, the detection information connection 22 is omitted, and the diagnostic connection 24 takes over its aforementioned functions.

[0064] In advantageous embodiments, the circuit arrangement in this case has a connecting line monitoring circuit 38 for at least one of the three phases or in association with at least one of the coaxial lines 31, which can be coupled to a second end 33b of the outer conductor 33 facing away from the coupling electrode and is configured to detect a potential deviation on the outer conductor 33 and thus monitor the fault-free connection state. To connect the outer conductor(s) 33, also referred to as shields, a common shield connection point 28 can be used on the device side or a corresponding separate shield connection point for each phase. If no connecting line monitoring circuit 38 is coupled to the outer conductor 33 of the respective coaxial line 31 for a phase, the outer conductor 33 can be grounded with its end 33b facing away from the coupling electrode, e.g. by being led to a ground potential 50.The shield connection point 28 can also be used, as in the example shown, as an input connection of the circuit arrangement for coupling the partial discharge detector circuit 5 to the partial discharge connection path 37 leading to the earth side 39 of the relevant system capacitance C S1 , C S2 , C S3 .

[0065] The connecting line monitoring circuit 38 is capable of detecting a high-impedance fault in the outer conductor 33, which can be caused in particular by a conductor break in the coaxial line 31 and which is typically also accompanied by a high-impedance fault in the inner conductor 32 and thus in the connecting line 30. The connecting line monitoring circuit 38 can preferably be housed in the common housing 23 together with the other mentioned components of the circuit arrangement, as in the example shown.

[0066] In corresponding implementations, a Fig. 1A schematically indicated common connector plug 34 is provided for the simultaneous, detachable coupling of the connecting line monitoring circuit 38 to the second end 33b of the outer conductor 33 and of the conductor signal input 1 to an end 32b of the inner conductor 32 facing away from the coupling electrode. This advantageously and simply avoids an incorrect indication that could result from the fact that the respective conductor signal input 11, 12, 13 was connected to the inner conductor 32, but the connecting line monitoring circuit 38 was inadvertently not connected to the outer conductor 33.

[0067] In corresponding implementations, the connecting line monitoring circuit 38 is connected to the ground potential 50 via a ground connection 49, as in the example shown, and is configured to detect a potential deviation on the ground connection 49. This also enables the connecting line monitoring circuit 38 to detect a high-impedance fault in its ground connection 49.

[0068] In advantageous implementations, the connecting line monitoring circuit 38, as in the example shown, comprises a display element 41 and two switching transistors T1, T2, which are connected in parallel with their respective switching paths between the display element 41 and a ground point 42, which represents a circuit-side ground potential. The monitoring circuit 38 is powered by a user-activated auxiliary voltage supply 43, which can be, for example, a piezo element or another element that converts mechanical energy into electrical energy, in a manner known per se. Activation of this auxiliary voltage supply 43 by a user triggers a corresponding monitoring test process.

[0069] A control terminal 44 of the first switching transistor T1 is coupled to the end 33b of the outer conductor 33 of the coaxial line 31 facing away from the coupling electrode, preferably via an optional coupling circuit with an inductance 29, as in the example shown. A control terminal 47 of the second switching transistor T2 is coupled to the ground connection 49. The circuit-side ground point 42 is connected to the control terminal 44, 47 of the first and second switching transistors T1, T2 via a resistor R1, R2, respectively.

[0070] The monitoring circuit 38 thus constructed, together with the outer conductor 33 of the coaxial line 31, forms an installation monitoring means by which both a high-impedance fault in the connection between the respective conductor L1, L2, L3 and the voltage testing unit 3 and the partial discharge detector unit 4, as well as a high-impedance fault in the grounding of the monitoring circuit 38, can be detected. In a fault-free situation, the outer conductor 33 and thus also the control electrode 44 of the first switching transistor T1 are permanently connected to ground potential 36. Likewise, the circuit-side ground point 42 is permanently connected to ground potential 36 or 50 via the ground connection 49 of the monitoring circuit 38. The first switching transistor T1 thereby assumes its blocking state. The same applies to the second switching transistor T2. When a monitoring test process is triggered by activating the auxiliary voltage supply 43, the display element 41 therefore remains deactivated.

[0071] If, however, a line break in the coaxial line 31 or another high-impedance disturbance occurs on the outer conductor 33, the grounding for the control electrode 44 of the first switching transistor T1 is lost, causing the first switching transistor T1 to become conductive. This closes a current path between the monitoring indicator element 41 and the ground point 42, with the result that the monitoring indicator element 41 is activated when a monitoring test process is triggered. The activated monitoring indicator element 41 can be used to detect that an installation error has occurred. The same error indication occurs if the plug connection via the connector plug 34 is not properly established. In this case, too, the control electrode 44 of the first switching transistor T1 is not permanently connected to ground potential and remains floating, so that the first switching transistor T1 is switched on.In other words, the monitoring circuit 38 detects the interruption of the outer conductor 33 by a potential difference between the earthing points or earth potentials 36 and 50.

[0072] A further installation error that can be detected via the second switching transistor T2 is the case where the monitoring circuit 38, with its ground connection 49, is not connected or not properly connected to ground potential 50. In this case, the fixed connection of the control electrode 47 of the second switching transistor T2 to ground potential is lost, causing the second switching transistor T2 to be switched into its conducting state, which now provides a display current path between the monitoring display element 41 and the ground point 12.

[0073] The two switching transistors T1, T2 operate independently of each other, which means that the monitoring circuit 38 is capable of detecting the described installation errors relating to the test signal connection line 30 on the one hand and the grounding of the monitoring circuit 38 on the other hand, both individually and in combination, and displaying them via the display element 41. This concerns an incomplete installation due to a connection not being established via the connector 34, an incomplete installation due to a missing or insufficient ground connection of the monitoring circuit 38, and a wire break or high-impedance fault in the coaxial line 31. The first transistor switch T1, with its associated peripheral circuit section, functions as the test signal connection line monitoring circuit section, while the second transistor switch T2, with its associated peripheral circuit section, functions as the ground connection monitoring circuit section.The outer conductor 33 functions as a monitoring line running along the inner conductor and thus the test signal connecting line 30. The monitoring line is connected to ground potential 36 at its end 32a facing the coupling electrode and is coupled to the connecting line monitoring circuit 38 at its other end 32b via the optional connector 34 and the optional coupling circuit with the inductor 29. The inductor 29 functions as a high-frequency filter to prevent a short circuit of the high-frequency partial discharge signal toward the monitoring circuit 38.

[0074] Although not explicitly mentioned above, it is understood that the voltage detection system shown can be designed in the usual way for voltage detection of three-phase high voltage, and the described monitoring and voltage detection can be provided for each of the three phases. In this case, it is advantageous to provide a common connection point for all three phases and the respective monitored coaxial cable shield or outer conductor 33 using an appropriately designed plug connection. The installation monitoring measure first determines whether an installation error exists. If no installation error exists, the voltage detection unit 3 can perform the normal voltage test for the high-voltage line to be monitored.

[0075] When monitoring circuit 38 detects a wire break, it can generally be assumed that a wire break in a three-phase voltage detection system is critical if all three test signal connecting lines 30 of a three-phase system are interrupted, since in this state, a wire break would be indistinguishable from the "voltage-free" state. However, if a single connecting line were to break, the other connecting lines would still carry a signal and indicate the "voltage present" state. A three-phase system is only considered "voltage-free" if all three phases are detected as being voltage-free. For this reason, monitoring just one coaxial connecting line is generally sufficient for wire break detection.

[0076] As the illustrated embodiments and the other embodiments explained above make clear, the invention provides a circuit arrangement that very advantageously fulfills the known monitoring tasks of partial discharge detection and voltage testing on medium- and high-voltage systems. It can be implemented with relatively little circuitry effort in a single device combining these functions. If desired, it can operate without any auxiliary power for both the voltage testing and the partial discharge detection. Partial discharge detection can be automatically limited to the periods of interest during which an active measurement signal for the voltage test is present. During other periods, partial discharge detection can be kept inactive due to a lack of power supply due to the absence of the measurement signal.To perform partial discharge detection, the associated partial discharge detector unit can be connected to the ground side of one or more of the system capacitances parallel to the capacitive coupling electrodes, and preferably also switchably to at least one of the capacitive coupling electrodes. Optionally, a conductor break detection function can also be provided as an integral component of the circuit arrangement. The circuit arrangement can be implemented in a common device or device housing.

Claims

1. A circuit arrangement for voltage testing and for detecting partial discharges in a single-phase or polyphase medium-voltage or high-voltage installation, comprising - one or more conductor signal inputs (11, 12, 13), each of which is set up for coupling to a capacitive coupling electrode (21, 22, 23) which is coupled to a conductor (L1, L2, L3) of the single-phase or polyphase medium-voltage or high-voltage system, at least one voltage testing unit (3) coupled on the input side to the or an associated one of the conductor signal inputs (11, 12, 13) of the circuit arrangement, which is set up for threshold-based detection of the voltage state with respect to the associated conductor, at least one partial discharge detector unit (4) set up to detect partial discharges with respect to the or an associated one of the conductors (L1, L2, L3), which comprises a partial discharge detector circuit (5) and a partial discharge display circuit (7) coupled on the input side to a signal output (6) of the partial discharge detector circuit (5), and - a power supply for the partial discharge detector unit (4) having a first power supply circuit (8) which is arranged to supply the partial discharge detector circuit (5) with power from the or one of the conductor signal inputs (11, 12, 13) of the circuit arrangement, and / or with a second power supply circuit (9) which is arranged to supply energy from the or one of the conductor signal inputs (11, 12, 13) of the circuit arrangement to the partial discharge display circuit (7), a partial discharge terminal path (37) which is set up to couple an input side (5a) of the partial discharge detector circuit (5) to an earth side (39) of a system capacity (CS1, CS2, Css) electrically parallel to the capacitive coupling electrode (21, 22, 23).

2. The circuit arrangement according to claim 1, characterized by a changeover switch (25) for switchable connection of the input side (5a) of the partial discharge detector circuit (5) either to the partial discharge connection path (37) or to the or one of the conductor signal inputs (11, 12, 13).

3. The circuit arrangement according to claim 1 or 2, further characterized by a coaxial line (31) having an inner conductor (32) which forms at least part of a connecting line (30) from the respective conductor signal input (11, 12, 13 ) to the associated capacitive coupling electrode (21, 22, 23), and an outer conductor (33) surrounding the inner conductor (32) and forming at least part of the partial discharge terminal path (37).

4. The circuit arrangement according to one of the claims 1 to 3, characterized in that the earth side (39) of the system capacitance (CS1, CS2, CS3) and the partial discharge terminal path (37) coupled thereto are connected to an earth potential (36) via a highfrequency blocking element (40).

5. The circuit arrangement according to one of the claims 2 to 4, characterized in that - the first power supply circuit (8) can be coupled to the same conductor signal input (11, 12, 13) of the circuit arrangement as the partial discharge detector unit (4) or to another of a plurality of conductor signal inputs (11, 12, 13) of the circuit arrangement, and / or - the second power supply circuit (9) can be coupled to the same conductor signal input (11, 12, 13) of the circuit arrangement as the partial discharge detector unit (4) or to another of a plurality of conductor signal inputs (11, 12, 13) of the circuit arrangement.

6. The circuit arrangement according to one of the claims 1 to 5, characterized by a variable capacitor (10) at the respective conductor signal input (11, 12, 13) for forming a capacitive voltage divider with the associated capacitive coupling electrode (21, 22, 23).

7. The circuit arrangement according to one of claims 1 to 6, further characterized in that - the partial discharge detector unit (4) for sensitivity adjustment comprises a circuit component (11) coupled to the signal output of the partial discharge detector circuit (5), which has a variable capacitor or a potentiometer or an adjustable resistor network, and / or - the partial discharge detection unit (4) has a deactivating element (12) by means of which it can be deactivated independently of the voltage testing unit (3).

8. The circuit arrangement according to one of claims 1 to 7, further characterized in that the partial discharge indicating circuit (7) comprises an indicating unit (13) and a semiconductor switch (14) which is looped in between the indicating unit (13) and the second power supply circuit (9) and having a control input (15) coupled to the signal output (6) of the partial discharge detector circuit (5).

9. The circuit arrangement according to one of claims 1 to 8, further characterized by - a detection information connection (22) for transmitting detection information from the partial discharge detector unit (4) to the outside and - a controllable switch (21) which is connected to the detection information connection (22), a control input of the controllable switch (21) being connected to the signal output (6) of the partial discharge detector circuit (5).

10. The circuit arrangement according to one of claims 1 to 9, characterized by a diagnosis connection (24) which is connected to the signal output (6) of the partial discharge detector circuit (5).

11. The circuit arrangement according to one of claims 1 to 10, characterized by the respective voltage testing unit (3) comprises a voltage testing circuit (16), which is coupled on the input side to the associated conductor signal input (11, 12, 13) of the circuit arrangement, and a voltage state indicating circuit (18), which is coupled on the input side to a signal output (17) of the voltage testing circuit, and - the partial discharge indicating circuit (7) of the partial discharge detector unit (4) and the voltage state indicating circuit (18) of the voltage testing unit (3) have a common indicating unit.

12. The circuit arrangement according to one of claims 3 to 11, characterized by a connecting line monitoring circuit (38) which can be coupled to a second end (33b) of the external conductor (33) facing away from the coupling electrode and is set up to detect a potential deviation on the external conductor (33).

13. The circuit arrangement according to claim 12, characterized by a common connector (34) for simultaneously and detachably coupling both the connecting line monitoring circuit (38) to the second end (33 b) of the external conductor (33) and of the respective conductor signal input (11, 12, 13) to an end (32b) of the internal conductor (32) facing away from the coupling electrode.

14. The circuit arrangement according to claim 12 or 13, further characterized in that the connecting line monitoring circuit (38) is connected to an earth potential (50) via an earth connection (49) and is set up to detect a potential deviation on the earth connection (49).