Circuit arrangement for emergency shutdown of standard insulation monitoring of non-grounded power supply systems upon detection of a ground fault

Abstract

The invention relates to a circuit arrangement (2) for emergency shutdown of a standard insulation monitoring of an ungrounded power supply system (4) upon detection of a ground fault, having a standard insulation monitoring device (10) coupled to an active conductor (L1, L2, L3) of the power supply system (4) via each coupling branch (12) on the network side or to a neutral point (S) of the power supply system (4) via a coupling branch (12) and connected to a ground (PE) on the ground side via a ground branch (14). The circuit arrangement (2) comprises an AC / DC-sensitive measuring current transformer (20) for detecting a fault current at the active conductor (L1, L2, L3) in the coupling branch (12) or at the neutral point (S) in the coupling branch (12) on the network side or in the ground branch (14) of the insulation monitoring device (10) on the ground side, an evaluator (30) for evaluating whether the fault current exceeds a fault current threshold value, and a tripping device (40) for switching off the power supply system (4).

Description

TECHNICAL FIELD

[0001] The invention relates to a circuit arrangement for emergency shutdown of standard insulation monitoring of a non-grounded power supply system in case of detection of a ground fault, having a standard insulation monitoring device coupled on the network side via each coupling branch to an active conductor of the power supply system or to a neutral point of the power supply system via a coupling branch and connected to the ground on the ground side via a grounding branch. BACKGROUND

[0002] For the purpose of supplying electrical operating devices, network configurations with non-grounded power supply systems are used when there are higher requirements for operation, fire protection and touch safety. Such network configurations are also referred to as insulated networks, IT networks or IT power supply systems (French: isolé terre - IT).

[0003] The advantage of IT networks is that the functionality of electrical operating devices is not impaired when a first insulation fault, such as a ground fault or a frame fault, occurs, since in this first (insulation) fault the circuit cannot be completed due to the ideally infinite impedance value between the active conductors (outer conductor and neutral conductor) of the non-grounded power supply system and the ground.

[0004] Due to the intrinsic safety of IT power supply systems, even in the event of a first insulation fault, the continuous supply of operating devices connected to the IT power supply system, i.e. of users supplied by the IT power supply system, is ensured.

[0005] According to the standard IEC-61557-8, the resistance of the IT power supply system to ground (insulation resistance - insulation fault resistance or fault resistance in the event of a fault also referred to as insulation fault) is therefore continuously monitored by an insulation monitoring device (IMD) coupled between one or more active conductors and the ground or between the neutral point of the IT power supply system and the ground (functional ground), since a fault circuit can arise due to a further possible fault (second fault) at a different active conductor; the fault current flowing together with an overcurrent protection device leads to the device being shut down and completely stopped.

[0006] When applied to the low-voltage range using IT power supply systems, the aim according to the purpose of IT networks is generally to continue the unimpaired operation of the device in the event of a first ground fault.

[0007] When it comes to specific applications in the low-voltage range using IT power supply systems, in particular in the medium-voltage range, the requirement to shut down the electrical device or at least the affected fault device component as quickly as possible arises when a first insulation fault occurs, which leads to a displacement voltage that is considered critical in this case, while taking into account the applicable standards in the specific operating setting, which differ from the general application principle of IT power supply systems.

[0008] According to the state of the art, ground fault monitors or ground fault relays are used in most of these devices to fulfill the requirement of fast shutdown in case of a simple ground fault.

[0009] These devices have no product standard and different models are on the market, which function according to different methods.

[0010] However, all these ground fault monitors and ground fault relays have in common that they do not comply with the requirements of a standard insulation monitoring device according to standard IEC-61557-8 and thus, for example, cannot identify a slowly occurring symmetrical insulation fault.

[0011] In modern electrical devices in the low-voltage and medium-voltage range based on ungrounded network configurations, there is an increasing need to implement both monitoring functions in parallel, i.e. to implement the insulation monitoring function according to standard IEC-61557-8 and the ground fault monitoring function in parallel, which ensures an emergency shutdown of the device or device component when a critical operating state is identified, without the two monitoring tasks interfering with each other.

[0012] DE 10 2015 207 456 B3 discloses an insulation monitoring device and a method for standard monitoring of the insulation resistance of a non-grounded single-phase or multi-phase power supply system. The insulation monitoring device also comprises a voltage monitoring circuit in order to continuously detect a conductor voltage of at least one active conductor with respect to the ground potential. In this case, if a voltage rise is recorded on the active conductor, the voltage monitoring circuit generates a shutdown signal to shut down the power supply system.

[0013] By upgrading the insulation monitoring device by such a voltage monitoring circuit, it thus becomes a dedicated insulation monitoring device, which can fulfill the requirements of a standard insulation monitoring combined with a ground fault monitoring function.

[0014] EP 2 848 949 A1 discloses a method and a device in which an insulation monitoring function is combined with a ground fault monitoring function. Due to the special feature of synchronization with the network frequency of the monitored IT system, the application of this method is limited to pure AC IT systems with a relatively small permissible network leakage capacity.

[0015] The disadvantage of the known method and device is that the ground fault monitoring function cannot be retrofitted in accordance with the standard IEC-61557-8 in combination with any standard insulation monitoring device that can already be installed in the device. The (measuring) channels and signal processing paths for the respective implementation of the insulation monitoring on the one hand and the ground fault monitoring function on the other hand are not independent of one another, since the known method and device represent a custom solution for a specific application case. The ground fault monitoring function based on the measurement of the voltage to ground of the active conductor in the shared device also leads to higher requirements for the insulation coordination in the combined device, in particular for power supply systems with higher nominal voltages, for example for the monitored medium voltage system. SUMMARY

[0016] It is therefore the object of the present invention to combine standard insulation monitoring with ground fault identification in such a way that both safety measures are effective independently of one another without negatively interfering with their functions, which means that retrofitting standard insulation monitoring with ground fault identification is possible in a simple manner in terms of circuitry.

[0017] This object is achieved in conjunction with the features of the preamble of claim 1 in that the circuit arrangement comprises an AC / DC-sensitive measuring current transformer that detects a fault current in the coupling branch at the active conductor or at the neutral point in the coupling branch on the network side or in the grounding branch of the insulation monitoring device on the ground side, an evaluator for evaluating whether the fault current exceeds a fault current threshold value, and a tripping device for switching off the power supply system.

[0018] The starting point for the observation is the product standard IEC-61557-8 that applies to insulation monitoring devices and stipulates that the internal resistance Ri and the alternating current internal impedance Zi of the insulation monitoring device must be at least 30 Ohm / V of the network nominal voltage.

[0019] As a result of this requirement, the current on the active conductor of the monitored IT power supply system is limited to below 33 mA, independent of the frequency and nominal voltage in the coupling branch / grounding branch of the insulation monitoring device, when a low-impedance ground fault occurs. The coupling branch together with the grounding branch forms a measuring branch, through which the fault current of the standard limit is detected by a measuring current transformer in series with the insulation monitoring device.

[0020] According to the invention, the current limit stipulated by the standard is used to implement a small and inexpensive AC / DC-sensitive measuring current transformer as a current sensor for detecting a ground fault and thus as an elementary component of the ground fault monitoring function. The measuring current transformer allows a current-isolated and fully autonomous detection of the ground fault state via AC / DC-sensitive detection of the fault current in the coupling branch or the grounding branch of the insulation monitoring device.

[0021] In configuring the insulation monitoring device, starting from the specifications related to the electrical circuit, there are different options for installing the measuring current transducer in series with the insulation monitoring device in the measuring branch. The measuring branch consists of the coupling branch and the grounding branch. The specifications related to the electrical circuit are determined by the current type (alternating current (AC), direct current (DC)), the type and number of conductors (single-phase or multi-phase power supply system, with or without a carried neutral conductor) and the structural environment (control cabinet).

[0022] According to the invention, the measuring current transducer is usually arranged on the network side in such a way that the entire fault current flowing through all coupling branches is detected. This applies to ungrounded AC power supply systems and ungrounded DC power supply systems.

[0023] Alternatively, in a three-phase AC power supply system with an accessible neutral point, the measuring current transducer is arranged in the coupling branch leading to the neutral point.

[0024] In another embodiment, the measuring current transducer for ungrounded AC power supply systems and ungrounded DC power supply systems is arranged in the grounding branch of the insulation monitoring device on the ground side.

[0025] In all star constellations, the measuring current transducer detects the entire fault current, which is dissipated via the active conductors of the power supply system to ground.

[0026] The circuit arrangement further comprises an evaluator for evaluating whether the fault current exceeds a fault current threshold value and a tripping device for switching off the power supply system.

[0027] The ground fault monitoring based on the AC / DC-sensitive measuring current transducer interacts with a suitable evaluator and tripping device in order to urgently switch off the monitored power supply system when the fault current threshold value is exceeded.

[0028] Preferably, the evaluator and the tripping device are designed in such a way that the requirements regarding the switching-off time for the automatic shutdown of the power supply system as a fault protection are met, as required in the standard IEC-60364-4-41 for establishing low-voltage devices in the section 4:41, Protection for preventing electric shock (Section 411). This is the case, for example, by using a residual current monitoring module (MRCD) according to the standard IEC-60947-2.

[0029] Since the insulation of the potential of the monitored IT power supply system is determined by the solid insulation of the monitored active conductors and the distance of the monitored active conductors to the AC / DC-sensitive measuring current transducer, the ground fault monitoring can be retrofitted by the AC / DC-sensitive measuring current transducer, independently of the nominal voltage level using constructive measures, and also independently of the type of insulation monitoring device used.

[0030] The circuit arrangement according to the invention, which comprises a standard insulation monitoring device for insulation monitoring and an AC / DC-sensitive measuring current transformer for ground fault detection, via an evaluator and a tripping device as its main components, emergency shutdown, results in the following advantageous technical effects, namely:

[0031] • the insulation monitoring and the additional ground fault monitoring do not interfere with each other in their respective functions;

[0032] • any insulation monitoring device available on the market can take over the function of insulation monitoring as intended and can be easily retrofitted with the AC / DC-sensitive ground fault monitoring function with emergency shutdown function;

[0033] • the ground fault monitoring function provides higher reliability and higher flexibility in the design of the ground fault monitoring function, as it has independent different channels;

[0034] • the ground fault monitoring is AC / DC-sensitive, i.e. it can be used in direct current power supply systems (DC) and alternating current power supply systems (AC);

[0035] • the ground fault monitoring can be configured with different sensitivities for DC and different AC frequency ranges;

[0036] • the ground fault monitoring function does not lead to higher requirements for the insulation coordination of the insulation monitoring device, even for medium voltage systems;

[0037] • the ground fault monitoring function does not lead to higher requirements for the insulation coordination of the AC / DC-sensitive measuring current transformer, even for medium voltage systems;

[0038] • if necessary, the ground fault monitoring function can be designed to be very fast so that, in the event of a ground fault, the power supply can be automatically switched off preventively within a shutdown time of less than 5 seconds, as for example required by IEC-60364-4-41 Section 411 for automatic power supply switching off as a fault protection;

[0039] • in addition to providing additional protection for the monitored IT power supply system, additional protection of the insulation monitoring device and / or the coupling device can be achieved in the event that these components are operated beyond their specifications.

[0040] In another advantageous embodiment, the measuring current transformer detects the fault current in the ground branch of the insulation monitoring device, or, in the case of a coupling device that is coupled to an active conductor in the coupling branch or to the neutral point in the coupling branch and is connected to the insulation monitoring device via a connection line, the fault current in the connection line.

[0041] In IT power supply systems with a nominal voltage above the insulation coordination of the used insulation monitoring device, i.e. in the medium voltage range, a coupling device is used to ensure that the requirements specified by the standard IEC-61557-8 are adhered to, which means that the internal resistance Ri of the insulation monitoring device must be at least 30 Ohm / V of the nominal voltage and also the alternating current internal impedance Zi of the insulation monitoring device must be at least 30 Ohm / V of the nominal voltage.

[0042] In order to detect the entire fault current which is dissipated via the active conductor of the power supply system and via the coupling device to ground, a measuring current transformer is arranged on the connecting line between the IMD and the coupling device or on the ground coupling branch.

[0043] The ground fault monitoring which can be retrofitted according to the invention and which has an AC / DC-sensitive measuring current transformer can additionally be used to ensure that the current-limiting function of the coupling device can be achieved even at high network nominal voltages and to ensure that the power supply is automatically switched off when the critical current which can lead to an insulation breakdown of the insulation monitoring device is exceeded.

[0044] Preferably, when a coupling device with a coupling device ground connection (functional ground) is used, the measuring current transformer additionally detects the coupling device fault current which flows through the coupling device ground connection when a fault current in the ground branch of the insulation monitoring device is detected.

[0045] In addition to the current limitation and its own coupling device ground connection for this purpose, some coupling devices also perform a voltage limitation via an internal resistance or internal impedance.

[0046] When a coupling device ground connection is present, the fault current which is caused by a ground fault and which passes through the coupling device is distributed to both functional ground connections of the insulation monitoring device and the coupling device. In order to correctly detect the entire fault current which flows through the coupling device when measurements are being taken, the invention aims to monitor the ground coupling branch of the insulation monitoring device and the coupling device ground connection via a measuring current transformer in an AC / DC-sensitive manner.

[0047] This is advantageous because in this case the voltage level is at the same level as the ground potential, so that there are no special requirements for the insulation coordination of the AC / DC-sensitive measuring current transformer. BRIEF DESCRIPTION OF DRAWINGS

[0048] Further advantageous embodiment features result from the following description and the figures, which explain preferred embodiments of the invention by way of example.

[0049] Figures 1a to 1f A retrofitable arrangement of the measuring current transformer in 3 AC and AC power supply systems is shown;

[0050] Figures 2a to 2f A retrofittable arrangement of a measuring current transformer in a 3AC and AC powered system with a coupling device is shown;

[0051] Figures 3a to 3c A retrofittable arrangement of a measuring current transformer in a 3AC and AC powered system with a voltage limited coupling device is shown;

[0052] Figures 4a to 4e A retrofittable arrangement of a measuring current transformer in a DC powered system is shown;

[0053] Fig. 5 shows a retrofittable arrangement of a measuring current transformer in an AC powered system with a frequency converter; and

[0054] Figure 6 A circuit arrangement 2 according to the present application is shown, which consists of a standard insulation monitoring device 10, an AC / DC sensitive measuring current transformer 20, an evaluator 30 and a tripping device 40. DETAILED DESCRIPTION

[0055] Using the example of a three-phase AC powered system 4, Figure 6 A circuit arrangement 2 according to the present application is shown, which consists of a standard insulation monitoring device 10, an AC / DC sensitive measuring current transformer 20, an evaluator 30 and a tripping device 40.

[0056] The insulation monitoring device 10 is coupled to each active conductor LI, L2, L3 of the powered system 4 via a coupling branch 12 and to the ground PE via a grounding branch 14.

[0057] The measuring current transformer 20 is preferably designed as a current sensor with a toroidal coil, which surrounds all coupling branches 12 in order to surround the entire fault current dissipated by the powered system 4 to the ground PE.

[0058] The measurement of the measuring current transformer 20 is provided to the evaluator 30, which controls the tripping device 40 upon exceeding a fault current threshold, which switches off the monitored powered system 4.

[0059] Figs. 1 to 5 show different retrofittable arrangement options of the measuring current transformer 20 in different powered systems specified by the type of current (AC, DC) and the type and number of conductors. For simplification of the figures, the evaluator 30 and the tripping device 40 are not shown in Figs. 1 to 5; in fact, as shown in Figure 6 the circuit arrangement 2 always comprises these components.

[0060] Figures 1a to 1f Mainly possible retrofittable arrangements of the measuring current transformer 20 in an AC powered system 4 are shown.

[0061] Figure 1a and 1b It is shown that in a three-phase AC power supply system 4 with an accessible neutral point S, the measuring current transformer 20 is either arranged in the coupling branch 12 Figure 1a ) or in the grounding branch 14 Figure 1b ) of the insulation monitoring device 10.

[0062] Alternatively, for example when the neutral point S is not accessible and thus the insulation monitoring device 10 has to be connected directly to each active conductor L1, L2, L3 of the power supply system 4 via the coupling branch 12, respectively, the measuring current transformer 20 is arranged in the grounding branch 14 Figure 1c ) or in all three coupling branches 12 Figure 1d ) by looping around said coupling branches 12.

[0063] Similarly, in a single-phase AC power supply system 4, it is possible to arrange the measuring current transformer 20 in two coupling branches 12 (Fig. le) or in the grounding branch 14 Figure 1f ).

[0064] Fig. 2 shows a retrofittable arrangement of the measuring current transformer 20 in a 3AC and AC power supply system 4, wherein the coupling device 18 is connected to the active conductor L1, L2, L3 or L1, N, respectively, "before" the insulation monitoring device 10.

[0065] When the neutral point S is accessible, the measuring current transformer 20 is arranged in the connecting line 16 Figure 2a ) between the coupling device 18 and the insulation monitoring device 10 in a three-phase AC power supply system 4 or in the grounding branch 14 Figure 2b ). When the neutral point S is not accessible and the coupling device 18 is connected directly to the active conductor L1, L2, L3 or L1, N, respectively, the measuring current transformer 20 is either arranged in the grounding branch 14 Figure 2c ) or in the connecting line 16 Figure 2d ).

[0066] The same applies to a single-phase AC power supply system 4, wherein the measuring current transformer 20 is in the connecting line 16 Figure 1e ) or in the grounding branch 14 Figure 2f ).

[0067] Fig. 3 shows a retrofittable arrangement of the measuring current transformer 20 in a 3AC and AC supply system 4 with a voltage limited coupling device 18. In this case, the coupling device 18 comprises its own coupling device ground connection 19. The fault current flowing through the coupling device ground connection 19 is detected by the measuring current transformer 20 in the same way as the fault current flowing in the ground branch 14 of the insulation monitoring device 10, i.e. by leading the coupling device ground connection 19 of the coupling device 18 through the toroidal coil of the measuring current transformer 20.

[0068] Fig. 4 shows a retrofittable arrangement of the measuring current transformer in a DC supply system 4.

[0069] In this case, the measuring current transformer 20 is either arranged in the ground branch 14 of the insulation monitoring device 10 (Fig. 4a) or in the coupling branch 12 (Fig. 4b). Figure 4b

[0070] Figure 4c The respective arrangements with a coupling device 18 switched to upstream with a measuring current transformer 20 in the connecting line 16 between the coupling device 18 and the insulation monitoring device 10 are shown in Fig. 3 and in Fig. 4a and Fig. 4b. Figure 4d

[0071] When the voltage of the coupling device 18 is limited, its coupling device ground connection 19 is also led through the toroidal coil of the measuring current transformer 20 (Fig. 5) in order to detect the coupling device fault current in addition to the fault current flowing through the insulation monitoring device 10. Figure 4e

[0072] Fig. 5 shows a retrofittable arrangement of the measuring current transformer 20 in an AC supply system 4 with a frequency converter 50.

[0073] The retrofittable variants of the electrically isolated, AC / DC sensitive measuring current transformer 20 for additional and independent ground fault monitoring in non-grounded supply systems 4 with insulation monitoring functions according to the standard IEC-61557-8 shown in Figs. 1 to 6 can also be used in the same way in combined non-grounded AC / DC supply systems 4, i.e. in IT networks with a frequency converter 50.

[0074] Depending on whether the insulation monitoring device 10 is coupled to an AC feed, a DC intermediate circuit or to the AC output of the frequency converter 50, one of the variants shown before for arranging the measuring current transformer 20 can be chosen.

[0075] ​​​When using the ground fault monitoring according to the application in addition to the insulation monitoring in an IT power supply system 4 with a frequency converter 50, in addition to the function of preventive, automatic emergency shutdown of the power supply in states identified as critical for the monitored IT power supply system, a function is added which identifies states which are not critical for the monitored IT power supply system but are critical for the implementation of the insulation monitoring function via the insulation monitoring device 10. Examples in this regard are:

[0076] • high current amplitudes in frequency ranges for which the insulation monitoring device 10 used is not suitable;

[0077] • high current amplitudes in the switching frequency range of the frequency converter 50, which can lead to damage to the insulation monitoring device 10;

[0078] • current amplitudes in the DC range or in a low impedance range which is outside the specifications, which can lead to a saturation effect when coupled to the inductive coupling device.

[0079] The function of additional detection of critical states outside the specifications of the insulation monitoring device 10 and / or the coupling device 18 and the corresponding derived measures, such as the issuance of a warning notification and / or a preventive automatic shutdown of the power supply, allow the erroneous application or misuse of components for insulation monitoring to be handled in a safe and risk-minimized manner. In the case of applications with increased requirements for functional safety, the circuit arrangement 2 according to the application can be used to advantage.

Claims

1. Circuit arrangement (2) for emergency shutdown of a standard insulation monitoring of a non-grounded power supply system (4) upon detection of a ground fault, having a standard insulation monitoring device (10) according to product standard IEC-61557-8 of an active conductor (L1, L2, L3) coupled to a power supply system (4) on the network side via a coupling branch (12) or of a neutral point (S) coupled to the power supply system (4) via a coupling branch (12) and connected to a ground (PE) on the ground side via a ground branch (14), characterized in that an AC / DC-sensitive measuring current transformer (20) detects a fault current in the active conductor (L1, L2, L3) in the coupling branch (12) or in the neutral point (S) in the coupling branch (12) on the network side or in the ground branch (14) of the standard insulation monitoring device (10) according to product standard IEC-61557-8 on the ground side; an evaluator (30) for evaluating whether the fault current exceeds a fault current threshold value; and a tripping device (40) for shutting down the power supply system (4).

2. Circuit arrangement (2) according to claim 1, characterized in that the measuring current transformer (20) detects a fault current in the ground branch (14) of the standard insulation monitoring device (10) according to product standard IEC-61557-8 or, when using a coupling device (18) coupled to an active conductor (L1, L2, L3) in the coupling branch (12) or to a neutral point (S) in the coupling branch (12) and connected to the standard insulation monitoring device (10) according to product standard IEC-61557-8 via a connection line (16), a fault current in the connection line (16).

3. Circuit arrangement (2) according to claim 2, characterized in that when using a coupling device (18) with a coupling device ground connection (19), the measuring current transformer (20) additionally detects a coupling device fault current flowing through the coupling device ground connection (19) when detecting a fault current in the ground branch (14) of the standard insulation monitoring device (10) according to product standard IEC-61557-8. ​

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