Combined monitoring device for insulation-resistance monitoring and protective-conductor-resistance monitoring of a power supply system

Abstract

A combined monitoring device for insulation-resistance monitoring and protective-conductor-resistance monitoring in a power supply system includes a grounded power supply system and an ungrounded power supply system, the combined monitoring device having a coupling circuit for being coupled to one or several active conductors of the grounded power supply system via coupling points, the combined monitoring device including an active monitoring device with a first operating mode for monitoring an insulation resistance in an ungrounded network state of the power supply system and a second operating mode for monitoring a protective-conductor resistance in a grounded network state of the power supply system, the combined monitoring device having an evaluation unit switchable between the first and second operating modes as a function of the ungrounded or grounded network state and configured for testing the insulation resistance in the first operating mode and the protective-conductor resistance in the second operating mode.

Claims

1. A combined monitoring device (20, 30, 40) for insulation-resistance monitoring and protective-conductor-resistance monitoring in a power supply system which comprises a grounded power supply system (6) and an ungrounded power supply system (2, 4), the combined monitoring device (20, 30, 40) comprising: a coupling circuit (21) for being coupled to one or several active conductors (L1, L2, L3, N) of the grounded power supply system (6) via coupling points (28), comprising an active monitoring device (22, 32, 42) which comprises a first operating mode for monitoring an insulation resistance (Rf) in an ungrounded network state of the power supply system (2, 4, 6) and a second operating mode for monitoring a protective-conductor resistance (Rpe) in a grounded network state of the power supply system (2, 4, 6), and comprising an evaluation unit (25) which is switchable between the first operating mode and the second operating mode as a function of the ungrounded or grounded network state and is configured for testing the insulation resistance (Rf) in the first operating mode and for testing the protective-conductor resistance (Rpe) in the second operating mode.

2. The combined monitoring device (20, 30, 40) according to claim 1, wherein the active monitoring device (22, 32, 42) comprises a switch-signal input (26) for switching between the first operating mode and the second operating mode by means of an external switch signal.

3. The combined monitoring device (20, 30, 40) according to claim 1, wherein the evaluation unit (25) is configured for testing in the first operating mode whether a settable insulation-resistance threshold (Rflim) has been undershot and for testing in the second operating mode whether a settable protective-conductor-resistance threshold (Rpelim) has been exceeded.

4. The combined monitoring device (20) according to claim 1, further including a switch device (29) which is connected upstream of the coupling points (28) for disconnecting the active conductors (L1, L2, L3, N) of the grounded power supply system (6) so as to prevent the grounded power supply system (6) from being operated in the event that an impermissibly low insulation resistance (Rf) is determined in the ungrounded power supply system (2, 4).

5. The combined monitoring device (30) according to claim 1, further including a first load relay (35) which is connected upstream of the coupling points (28) for disconnecting the active conductors (L1, L2, L3, N), and a second load relay (36) which is connected downstream of the coupling points (28) for disconnecting the active conductors (L1, L2, L3, N).

6. The combined monitoring device (30, 40) according to claim 5, further including a voltage-measuring device (34) for measuring one changeover voltage or several changeover voltages in the grounded power supply system (6) and for automatically switching the evaluation unit (25) to the second operating mode so as to monitor the protective-conductor resistance (Rpe) if the changeover voltage or a changeover voltage which has been derived from the combination of several changeover voltages exceeds a settable changeover-voltage threshold and switches back to the first operating mode for insulation monitoring when the changeover-voltage threshold is undershot.

7. The combined monitoring device (30, 40) according to claim 6, wherein the corresponding measured changeover voltage is a conductor-conductor voltage via measuring points between two arbitrary active conductors (L1, L2, L3, N) of the grounded power supply system (6) or a conductor-ground voltage via measuring points between an arbitrary active conductor (L1, L2, L3, N) and the protective conductor (PE) of the grounded power supply system (6).

8. The combined monitoring device (40) according to claim 1, further including a load relay (44) for disconnecting the active conductors (L1, L2, L3, N), and a changeover relay (45) which connects the active conductors (L1, L2, L3, N) to the coupling circuit (21) upstream of the load relay (44) via first coupling points (28a) so as to monitor the grounded power supply system (6) or connects the active conductors (L1, L2, L3, N) to the coupling circuit (21) downstream of the load relay (44) via second coupling points (28b) so as to monitor the ungrounded power supply system (2, 4).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further advantageous embodiment features are derived from the following description and the drawings which describe preferred embodiments of the invention using examples. In the following,

(2) FIG. 1 shows a monitoring system for insulation-resistance monitoring and protective-conductor-resistance monitoring according to the state of the art,

(3) FIG. 2 shows a combined monitoring device according to the invention as a first embodiment (basic configuration),

(4) FIG. 3 shows a second embodiment of a combined monitoring device according to the invention having voltage measuring and two load relays,

(5) FIG. 4 shows a third embodiment of a combined monitoring device according to the invention having voltage measuring, a load relay and a changeover relay, and

(6) FIG. 5 shows a use of the combined monitoring device according to the invention based on the state of the art.

DETAILED DESCRIPTION

(7) Using a functional block diagram, FIG. 1 shows a structure of a monitoring system known from the state of the art for insulation-resistance monitoring and protective-conductor-resistance monitoring.

(8) In the grounded network state, ungrounded power supply system 2 (ungrounded network) is connected as a battery network 4 to a grounded power supply network 6 (grounded network) via a connection cable 8. It is visible that battery network 4 having chargeable electric energy storage 10 (battery) is grounded by means of this connection via a central grounding point ZEP and is converted to a consumer of grounded power supply system 6. A casing resistance Rg of the consumer casing against ground (central grounding point ZEP) is typically to be considered as high-impedance.

(9) As an example, grounded power supply system 6 is configured as a supplying, three-phase network having active conductors L1, L2, L3 and N and a protective conductor PE (PE conductor). Protective conductor PE has a protective-conductor resistance Rpe. The continuity of protective conductor PE must be ensured, for which reason protective-conductor resistance Rpe must be of sufficiently low impedance.

(10) An additional signal contact 16, as prescribed in the field of electromobility by standard IEC 61851-1, for example, serves for protective-conductor monitoring during operation in the grounded network state. Via this signal contact 16, a defined signal 18 is sent to the supplied consumer (e.g., the electric vehicle) from the supplying infrastructure (e.g., a charging station of grounded power supply system 6) and returned via PE conductor PE. The presence of PE conductor PE is tested by means of the returned signal. In the example of electromobility, however, further data is exchanged via this signal contact and the PE conductor. What proves to be disadvantageous is that no conclusion can be made regarding the quality of the protective-conductor resistance Rpe as only the presence of protective conductor PE (“PE is present” or “PE is not present”) can be determined.

(11) Insulation resistance is monitored in the ungrounded network state during operation via a discretely disposed active insulation monitoring device 14 (IMD).

(12) Thus, according to the state of the art, two devices (one for monitoring the protective-conductor resistance and another for monitoring the insulation resistance) having the disadvantages arising therefrom concerning costs, energy consumption and installation space are required.

(13) The following FIGS. 2 to 4 show in functional block diagrams three embodiments of a combined monitoring device 20, 30, 40 according to the invention which can be connected together with grounded power supply system 6 and ungrounded power supply system 2, 4 according to FIG. 5.

(14) Combined monitoring devices 20, 30, 40 described above each comprise a coupling circuit 21 having coupling resistances Rc for being coupled to active conductors L1, L2, L3, N of grounded power supply system 6 via coupling points 28. Combined monitoring devices 20, 30, 40 each further comprise an active monitoring device 22, 32, 42, thus are based upon an active measuring method during which a measuring voltage is superimposed on ungrounded network 2 by means of a symbolically illustrated measuring-voltage source 23, and during which the resulting measuring current is detected via a voltage drop at a measuring resistance within active monitoring device 22, 32, 42 for determining insulation resistance Rf or, in an advanced function according to the invention, for determining protective-conductor resistance Rpe.

(15) Functionally illustrated coupling circuit 21 can also be a structural part of active monitoring device 22, 32, 42.

(16) Active monitoring devices 22, 32, 42 each comprise an evaluation unit 25 which is configured so as to be switchable between a first operating mode for identifying whether an insulation-resistance threshold Rflim is being undershot by detected insulation resistance Rf and a second operating mode for identifying whether protective-conductor-resistance threshold Rpelim is being exceeded by detected protective-conductor resistance Rpe.

(17) The difference between the two operating modes can be summed up by means of the following characteristics: insulation monitoring mode (for an ungrounded network): high resistance value (of the detected insulation resistance)>good state low resistance value (of the detected insulation resistance)>bad state alarm>when undershooting insulation-resistance threshold Rflim PE monitoring mode (for a grounded network): high resistance value (of the detected protective-conductor resistance)>bad state low resistance value (of the detected protective-conductor resistance)>good state alarm signal>when exceeding protective-conductor-resistance threshold Rpelim,
the threshold between high and low resistance values being specified by corresponding threshold Rflim, Rpelim according to the specifications of each installation.

(18) For switching the operating mode, it is therefore required to merely “reverse” the decision-making logic of evaluation unit 25 and to adjust the thresholds as a function of the network configuration and the monitoring task resulting therefrom.

(19) With all three embodiments of combined monitoring device 20, 30, 40, the operating modes can be switched via a switch-signal input 26 of active monitoring device 22, 32, 42 by means of an external switch signal; moreover, with embodiments 30, 40, as illustrated in FIGS. 3 and 4, the operating modes can be switched automatically via a voltage measuring device 34.

(20) For sending the alarm signal, evaluation unit 25 comprises at least one alarm-signal output 27. Alarm-signal output 27 can, for example, switch an external relay in order to disconnect battery network 4 galvanically from connected grounded power supply system 6. Several alarm-signal outputs 27 pose a further possibility which can be configured as analog and digital and represent different alarm levels (pre-alarm, main alarm), for example.

(21) In FIG. 2, combined monitoring device 20 is schematically illustrated in a first embodiment. The all-pole coupling in this instance (coupling to all active conductors L1, L2, L3, N) via coupling resistances Rc is meant as an example. Generally, a one-pole coupling is also sufficient as it is for the other embodiments of combined monitoring device 30, 40 in FIGS. 3 and 4. It is then irrelevant for measuring the protective-conductor resistance whether the one-pole coupling is on an outer conductor L1, L2, L3 or the neutral conductor N. For voltage measurement and the accompanied automatic switch, however, it must be ensured that the combined monitoring device 20 is coupled to an outer conductor L1, L2, L3.

(22) In this first embodiment, the operating mode is switched exclusively by an external switch signal via switch-signal input 26.

(23) For disconnecting active conductors L1, L2, L3, N of grounded power supply system 6, a switch device 29 is connected upstream of coupling points 28 so as to prevent grounded power supply system 6 from being operated in the event that an impermissibly low insulation resistance Rf is detected in ungrounded power supply system 2, 4.

(24) FIG. 3 shows combined monitoring device 30 according to the invention in a second embodiment having a symbolically illustrated voltage measuring device 34, a first load relay 35 and a second load relay 36.

(25) First load relay 35 is connected upstream of coupling points 28 for disconnecting the active conductors of grounded power supply system 6 with respect to the direction determined by the inputs and outputs of combined monitoring device 30. Second load relay 36 is connected downstream of coupling points 28 for disconnecting the active conductors of grounded power supply system 6.

(26) The operating mode is switched automatically by measuring voltage by means of voltage measuring device 34, but can also be triggered by the external switch signal as in the first embodiment.

(27) If a voltage which exceeds a settable switch-voltage threshold is measured between two arbitrary conductors L1, L2, L3, N when the switching is caused by voltage measuring, second load relay 36 opens up and first load relay 35 closes. As a consequence, ungrounded network 2 is disconnected from active monitoring device 32 and active monitoring device 32 is coupled to grounded power supply system 6 via coupling circuit 21 for protective-conductor monitoring. Evaluation unit 25 works in the PE monitoring mode and detects protective-conductor resistance Rpe. If protective-conductor resistance Rpe undershoots a previously defined protective-conductor-resistance threshold and if insulation resistance Rf previously detected before opening second load relay 36 exceeds a defined insulation-resistance threshold Rflim, second load relay 36 closes again and ungrounded power supply system 2, 4 connected to connections OUT_x is thus grounded.

(28) If a voltage below the switch-voltage threshold is measured, first load relay 35 is opened and the insulation monitoring mode is reactivated since it can be assumed that the connection to grounded power supply system 6 has been interrupted. In the insulation monitoring mode, an alarm signal is given via alarm-signal output 27 when insulation-resistance threshold Rflim is undershot in order to cause battery 10 (FIG. 5) to be switched off, for example.

(29) The switch-voltage threshold can generally be set to any threshold which corresponds to the safety objective and is specific to the installation and can have a safety extra-low voltage of 50 V, for example, with regard to the protective measure.

(30) In the PE monitoring mode, first load relay 35 is also opened in addition to the alarm signal being sent out. By opening first load relay 35, an ungrounded network 4 is now available again. In comparison to the first embodiment, the second embodiment thus brings the advantage that in the event of a fault—when exceeding protective-conductor-resistance threshold (Rpelim)—, the power electronics following in the consumer is galvanically disconnected from power supply network 6.

(31) Starting from evaluation unit 25, first/second load relay 35/36 is controlled by active monitoring device 32 by means of a first/second control-signal line 37/38.

(32) FIG. 4 shows combined monitoring device 40 according to the invention in a third embodiment.

(33) In this embodiment, combined monitoring device 40 works according to the same principles as the second embodiment, except that second load relay 36 (FIG. 3) is not required and network 2, 4 (ungrounded) or 6 (grounded) to be tested is alternatingly operated by a (central) load relay 44 in conjunction with a changeover relay 45.

(34) According to the corresponding operating mode, coupling resistances Rc of coupling circuit 21 are coupled upstream of load relay 44, illustrated on the left-hand side of load relay 44 via first coupling points (28a), for PE monitoring or downstream of load relay 44, illustrated on the right-hand side of load relay 44 via second coupling points (28b), for insulation monitoring. The indication of an alarm signal is given in the same manner as in the second embodiment.

(35) The advantage received by leaving out second load relay 36 (FIG. 3) regarding installation space, power loss and costs becomes even more apparent when active monitoring device 42 is coupled with one pole.

(36) Starting from evaluation unit 25, load relay 44/changeover relay 45 is controlled by active monitoring device 32 by means of control-signal line 47/alternating-signal line 48.

(37) In FIG. 5, a use of combined monitoring device 20, 30, 40 is shown using the example of a consumer which is not galvanically disconnected and has an integrated, chargeable electric energy storage 10, the combined monitoring device 20, 30, 40 being available in one of the three embodiments 20, 30, 40 for shared insulation-resistance and loop-resistance monitoring and being able to be connected to active conductors L1, L2, L3, N via connections IN_L1, IN_L2, IN_L3; IN_N on the input side and via connections OUT_L1, OUT_L2, OUT_L3, OUT_N on the output side.

(38) While being operated in the ungrounded network state—for example while driving the electric vehicle—, insulation resistance Rf of ungrounded battery network 4 formed by individual insulation resistances Rf+ and Rf− is monitored with respect to a conductive casing of the consumer, e.g., the vehicle body.

(39) In the grounded network state—for example, while charging the electric vehicle—, however, ungrounded battery network 4 turns into a consumer of typically grounded power supply network 6 via the connection not galvanically disconnected so that a complete grounded network is yielded. This is an operating means of protective class 1 according to IEC 60140. This means that the protection against electric shocks must be ensured by the connection of PE conductor PE (i.e., in this case the conductive casing of the consumer) to the grounded protective electrical potential of grounded power supply network 6. In this instance, the state of protective conductor PE (i.e., its low impedance) is critical to the effectiveness of the protective measure.

(40) Owing to the combined monitoring device according to the invention, the low-impedance connection to the ground potential (central grounding point ZEP) can be determined without an additional auxiliary conductor, and furthermore the actual resistance value of protective-conductor resistance Rpe can be determined—for example, in comparison to electric mobility—by measuring the loop resistance of L1, L2, L3 and N (depending on the type and number of active conductors L1, L2, L3, N of supplying grounded power supply system 6 and the type of coupling) in the grounded operation via protective-conductor resistance Rpe back to the vehicle.