Electric circuit arrangement and a method for the functional testing of a monitoring device for an electric power supply system

Abstract

The invention relates to an electric circuit arrangement (20) for the functional testing of a monitoring device (4) for a power supply system (2), the electric circuit arrangement (20) having a test resistance (R.sub.f1, R.sub.f2) which is switched between an active conductor (L.sub.1, L.sub.2) of the power supply system (2) and ground (PE) and has a settable actual resistance value (R.sub.x). In this context, a bidirectional cascade (12) consisting of field-effect transistors as test resistances (R.sub.f1, R.sub.f2) and an analog control (10) for the continuous-value setting of the actual resistance value (R.sub.x) to a predefined target resistance value (R.sub.0) are provided. Furthermore, the invention relates to a modular circuit arrangement (60) consisting of several electric circuit arrangements (20) according to the invention, each of the electric circuit arrangements (20) being assigned a different active conductor (L.sub.1, L.sub.2) of the electric power supply system (2), and a central control unit (50) being implemented for controlling and monitoring the electric circuit arrangements (20).

Claims

1. An electric circuit arrangement (20) for the functional testing of a monitoring device (4) for a power supply system (2), the electric circuit arrangement (20) having a test resistance (R.sub.f1, R.sub.f2) which is switched between an active conductor (L.sub.1, L.sub.2) of the power supply system (2) and ground (PE) and has a settable actual resistance value (R.sub.x), characterized by a bidirectional cascade (12) consisting of field-effect transistors as test resistances (R.sub.f1, R.sub.f2) and by an analog control (10) for the continuous-value setting of the actual resistance value (R.sub.x) to a predeterminable target resistance value (R.sub.0).

2. The electric circuit arrangement (20) according to claim 1, characterized in that the control (10) comprises a transformation block (22) which transforms the predeterminable target resistance value (R.sub.0) to a target voltage (U.sub.0) as a reference variable by means of an actual current (I.sub.x); a current measurement (25) which detects a transistor current (I.sub.m) flowing through the transistor cascade (12) and supplies the transistor current (I.sub.m) to the transformation block in a scaled manner as the actual current (I.sub.x); a comparison element (24) which compares the target voltage (U.sub.0) to an actual voltage (U.sub.x) and forms a differential voltage (U.sub.d) as a control deviation; a voltage measurement (26) which detects a transistor voltage (U.sub.m) dropping via the transistor cascade (12) and supplies the transistor voltage (U.sub.m) to the comparison element (24) in a scaled manner as the actual voltage (U.sub.x); a controller (40) which generates an actuating variable (W) from the differential voltage (U.sub.d) for controlling a control path which is formed by the transistor cascade (12) having the resistance value as a control variable (R.sub.x); a controllable switch device (27) which switches the actual voltage (U.sub.x) to zero to shut down the control (10).

3. The electric circuit arrangement (20) according to claim 2, characterized by a microcontroller (30) for predetermining the target resistance value (R.sub.0) via a digital setting element (32) and for controlling the switch device (27) by means of a switch signal (S.sub.u).

4. The electric circuit arrangement (20) according to claim 3, characterized in that the microcontroller (30) is configured for specifying an amplitude-modulated resistance pattern from consecutive target resistance values (R.sub.0).

5. The electric circuit arrangement (20) according to claim 3, characterized in that the control (10) comprises an overtemperature detector (42) for detecting an overtemperature of the transistor cascade (12) and an overcurrent detector (43) for detecting an overload value of the actual current (I.sub.x), an overtemperature signal (S.sub.t) and an overcurrent signal (S.sub.i) being merged with an output signal (S.sub.a) of the microcontroller (30) via a digital circuit (44) for controlling the switch device (27).

6. The electric circuit arrangement (20) according to claim 5, characterized in that the digital circuit (44) is realized as a set-reset flipflop.

7. The electric circuit arrangement (20) according to claim 2, characterized in that the controller (40) is realized as a PI controller.

8. A modular circuit arrangement (60) consisting of several electric circuit arrangements (20) according to claim 1, characterized in that each of the electric circuit arrangements (20) is assigned a different active conductor (L.sub.1, L.sub.2) of the electric power supply system (2), and a central control unit (50) is implemented for controlling and monitoring the electric circuit arrangements (20).

9. The modular circuit arrangement (60) according to claim 8, characterized by a communication connection (52) between the central control unit (50) and the monitoring device (4).

10. A method for the functional testing of a monitoring device (4) for an electric power supply system (2), the method comprising the following steps: switching a test resistance (R.sub.f1, R.sub.f2) having a settable actual resistance value (R.sub.x) between an active conductor (L.sub.1, L.sub.2) of the power supply system (2) and ground (PE), characterized in that the test resistance (R.sub.f1, R.sub.f2) is a bidirectional cascade (12) consisting of field-effect transistors and in that the setting of the actual resistance value (R.sub.x) to a predeterminable target resistance value (R.sub.0) takes place in a continuous-value manner by means of an analog control (10).

11. The method according to claim 10, characterized in that via the control (10) the predeterminable target resistance value (R.sub.0) is transformed to a target voltage (U.sub.0) in a transformation block (22) as a reference variable by means of an actual current (I.sub.x); a current measurement device (25) detects a transistor current (I.sub.m) flowing through the transistor cascade (12) and supplies the transistor current (I.sub.m) to the transformation block (22) in a scaled manner as the actual current (I.sub.x); the target voltage (U.sub.0) is compared to an actual voltage (U.sub.x) in a comparison element (24) and a differential voltage (U.sub.d) is formed as a control deviation; a voltage measurement device (26) detects a transistor voltage (U.sub.m) dropping via the transistor cascade (12) and supplies the transistor voltage (U.sub.m) to the comparison element (24) in a scaled manner as the actual voltage (U.sub.x); an actuating variable (W) is generated from the differential voltage (U.sub.d) by means of a controller (40) in order to control a control path, which is formed by the transistor cascade (12) having the actual resistance value (R.sub.x) as a control variable; and a controllable switch device (27) switches the actual voltage (U.sub.x) to zero using to shut down the control (10).

12. The method according to claim 11, characterized in that a microcontroller (30) specifies the target resistance value (R.sub.0) via a digital setting element (32) and controls the switch device (27) by means of a switch signal.

13. The method according to claim 12, characterized in that the microcontroller (30) specifies an amplitude-modulated resistance pattern from consecutive target resistance values (R.sub.0).

14. The method according to claim 12, characterized by detecting an overtemperature of the transistor cascade in the control (10) by means of an overtemperature detector; detecting an overload value of the actual current (I.sub.x) by means of an overcurrent detector (43), an overtemperature signal (S.sub.t) and an overcurrent signal (S.sub.i) being merged with an output signal (S.sub.a) of the microcontroller (30) via a digital circuit (44) for controlling the switch device (27).

15. The method according to claim 14, characterized in that the digital circuit (44) is implemented as a set-reset flipflop.

16. The method according to claim 11, characterized in that the controller (40) performs a PI control.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) Further advantageous embodiment features are derived from the following description and the drawing which describe a preferred embodiment of the invention using examples.

(2) FIG. 1 shows a test arrangement having changeable test resistances according to the state of the art for the functional testing of an insulation monitoring device;

(3) FIG. 2 shows a set of characteristic curves of a bidirectional MOSFET transistor cascade;

(4) FIG. 3 shows an electric circuit arrangement according to the invention having a transistor cascade and analog control; and

(5) FIG. 4 shows a modular circuit arrangement having two circuit arrangements according to the invention.

DETAILED DESCRIPTION

(6) FIG. 1 shows a test arrangement according to the state of the art having changeable test resistances for the functional testing of an insulation monitoring device 4 installed in an ungrounded power supply system 2.

(7) Power supply system 2 comprises two active conductors L1, L2 to which a consumer R.sub.L is switched. Insulation monitoring device 4 is connected to active conductors L1, L2 and ground (ground potential) PE for measuring an insulation resistance (measuring the fault resistance in power supply system 2).

(8) For generating a defined fault resistance, changeable test resistances R.sub.f1, R.sub.f2 are disposed between active conductor L1, L2, respectively, and ground PE, the corresponding conductor-to-ground voltage U.sub.L1-PE, U.sub.L2-PE dropping across the test resistances R.sub.f1, R.sub.f2. For the functional testing of insulation monitoring device 4, a closed measuring circuit is formed via each active conductor L1, L2, test resistance R.sub.f1, R.sub.f2 and ground PE back to insulation monitoring device 4, a fault current (measuring current), which can be evaluated in insulation monitoring device 4, flowing in the closed measuring circuit.

(9) In FIG. 2, a set of characteristic curves of the bidirectional MOSFET transistor cascade is illustrated.

(10) Preferably, the transistors used are MOSFETs. As a function of control voltage U.sub.GS a certain current I.sub.DD flowing via the cascade is set when voltage U.sub.DD is applied across the transistor cascade.

(11) Bidirectional transistor cascade 12 consists of a series connection having two inversely disposed MOSFET transistors, meaning operating areas of transistor cascade 12 are derived in the first and third quadrant of the set of characteristic curves. Analog control 10 (FIG. 3) forces transistor cascade 12 into an ohmic behavior.

(12) FIG. 3 shows electric circuit arrangement 20 according to the invention having bidirectional cascade 12 and control 10.

(13) Initially, desired target resistance value R.sub.0 is specified as the input parameter of control 10, target resistance value R.sub.0 being transformed to target voltage U.sub.0 via transformation block 22. The transformation takes place via current measurement device 25 which detects transistor current I.sub.m (corresponds to I.sub.DD in FIG. 2) flowing via transistor cascade 12 and supplies it to transformation block 22 in a scaled manner (k.sub.2) as actual current I.sub.x.

(14) In comparison element 24, a residual voltage U.sub.d is formed from target voltage U.sub.0 and actual voltage U.sub.x, which is won via voltage measurement device 26 from transistor voltage U.sub.m dropping across transistor cascade 12 and is scaled (k.sub.1). Residual current U.sub.d is supplied to controller 40—preferably a PI controller—which forms an actuating variable W therefrom for controlling transistor cascade 12.

(15) Besides a real transistor path 14, transistor cascade 12 comprises a driver circuit 16 for controlling transistor path 14.

(16) Control 10 effectuates setting actual resistance value R.sub.x of transistor path 14 of transistor cascade 12 to prespecified target resistance value R.sub.0.

(17) In order to be able to switch control 10 on and off, with particular emphasis on a soft switching-off and on, a switch device 27, which draws actual voltage U.sub.x to zero (mass potential), is provided between voltage measurement device 26 and comparison element 24.

(18) Switch device 27 can be controlled directly by means of a switch signal S.sub.u by microcontroller 30 or via digital circuit 44.

(19) Digital circuit 44 realized as a set-reset flipflop is to be provided if an actual temperature T.sub.x of transistor cascade 12 is detected by means of an overtemperature detector 42 and/or if an inadmissibly high value of actual current I.sub.x is determined by means of overcurrent detector 43 and an overtemperature signal S.sub.t and/or an overcurrent signal S.sub.i is output at the output of overtemperature detector 42 and/or of overcurrent detector 43. Overtemperature signal S.sub.t and overcurrent signal S.sub.i are merged with an output signal S.sub.a of microcontroller 30 to form switch signal S.sub.u, which controls switch device 27, via set-reset flipflop 44.

(20) Microcontroller 30 specifies target resistance value R.sub.0 as the reference variable via digital setting element 32.

(21) For the superordinate control, microcontroller 30 can be connected to a control device 34, such as a PC, laptop, smartphone or a stored program control (SPS).

(22) FIG. 4 shows a modular circuit arrangement 60 having two circuit arrangements 20 according to the invention.

(23) In this context, circuit arrangement 20 according to the invention is understood to be a module which simultaneously imprints different fault resistances R.sub.f1, R.sub.f2 at different positions, e.g., at different active conductors L1, L2 of power supply system 2.

(24) Presently, first electric circuit arrangement 20 according to the invention is connected to active conductor L1 and second electric circuit arrangement 20 according to the invention is connected to conductor L2 and both are switched to ground. Both electric circuit arrangements 20 are controlled by a central control unit 50.

(25) Central control unit 50 is connected to insulation monitoring device 4 to be tested via a communication connection 52. Via communication connection 52, all data, in particular data for signaling between modular circuit arrangement 60 and insulation monitoring device 4, can be exchanged.

(26) Communication connection 52 itself can be wired or wireless and be integrated in a shared data network with control device 34.