ELECTRIC MEASURING ARRANGEMENT AND MEASURING METHOD FOR A GROUND CONNECTION MONITORING SYSTEM FOR AN INSULATION MONITORING DEVICE AND INSULATION MONITORING DEVICE

Abstract

The invention relates an electric measuring arrangement (10) and to a measuring method both for monitoring a ground connection for an insulation monitoring device (4), which is connected to at least one active conductor (L1, L2) of an ungrounded power supply system (2) and a ground terminal (PE) of an electric installation (3), with an active loop measurement device (20), which is connectable between a ground-connection clamp (E) of the insulation monitoring device (4) and the ground terminal (PE) and has an independent excitation voltage source (U.sub.gEKE) for quantitatively determining a ground resistance (R.sub.EKE) of the ground connection (6) between the insulation monitoring device (4) and the ground terminal (PE).

Furthermore, the invention relates to an insulation monitoring device (30) having an electric measuring arrangement (10) according to the invention.

Claims

1. An electric measurement arrangement (10) for a ground connection monitoring system for an insulation monitoring device (4), which is connected to at least one active conductor (L1, L2) of an ungrounded power supply system (2) and to a ground terminal (PE) of an electric installation (3), characterized by an active loop measurement device (20), which is connectable between a ground-connection clamp (E) of the insulation monitoring device (4) and the ground terminal (PE) and has an independent excitation voltage source (U.sub.gEKE) for quantitatively determining a ground resistance (R.sub.EKE) of the ground connection (6) between the insulation monitoring device (4) and the ground terminal (PE).

2. The electric measurement arrangement (10) according to claim 1, characterized in that the loop measurement device (20) has a series connection comprising the excitation voltage source (U.sub.gEKE) for superimposing an excitation voltage (U.sub.gEKE), a loop measuring resistance (R.sub.mEKE), a loop coupling resistance (R.sub.aEKE), a test and filter circuit (12) which detects a loop measuring voltage (U.sub.mEKE) between the loop measuring resistance (R.sub.mEKE) and the loop coupling resistance (R.sub.aEKE), a microcontroller (14) which evaluates the loop measuring voltage (U.sub.mEKE) for computing the ground resistance (R.sub.EKE), and a control-ground connection clamp (KE) for connecting the loop couple resistance (R.sub.aEKE) to the ground terminal (PE).

3. The electric measurement arrangement (10) according to claim 2, characterized in that the excitation voltage (U.sub.gEKE) is a bipolar square wave voltage having a base frequency ranging from 0.1 Hz to 10 Hz and a voltage change less than 10 V.

4. The electric measurement arrangement (10) according to claim 2, characterized in that a TVS diode (16) is switched between the ground-connection clamp (E) of the insulation monitoring device (4) and the control-ground connection clamp (KE) of the loop measuring device.

5. An insulation monitoring device (30) which is connectable to at least one active conductor (L1, L2) of the ungrounded power supply system (2) and to a ground terminal (PE) of an electric installation (3) in order to monitor an insulation resistance of an ungrounded power supply system (2), characterized by an electric measuring arrangement (10) according to claim 1.

6. A measuring method for monitoring a ground connection for an insulation monitoring device (4), which is connected to at least one active conductor (L1, L2) of an ungrounded power supply system (2) and a ground terminal (PE) of an electric installation (3), characterized by quantitatively determining a ground resistance (R.sub.EKE) of the ground connection (6) between the insulation monitoring device (4) and the ground terminal (PE) by means of an active loop measuring device (20), which is connectable between a ground-connection clamp (E) of the insulation monitoring device (4) and the ground terminal (PE) and has an independent excitation voltage source (U.sub.gEKE).

7. A measuring method according to claim 6, wherein the ground resistance (R.sub.EKE) is quantitatively determined in the loop measuring device (20), which has a series connection comprising the excitation voltage source (U.sub.gEKE), which is connectable to the ground-connection clamp (E) of the insulation monitoring device (4), a loop measuring resistance (R.sub.mEKE), a loop coupling resistance (R.sub.aEKE), a test and filter circuit (12) having a voltage tap between the loop measuring resistance (R.sub.mEKE) and the loop coupling resistance (R.sub.aEKE), a microcontroller (14), and a control-ground connection clamp (KE) for connecting the loop coupling resistance (R.sub.aEKE) to the ground terminal (PE), characterized by superposing an excitation voltage (U.sub.gEKE) by means of the excitation voltage source (U.sub.gEKE), detecting and filtering a loop measuring voltage (U.sub.mEKE) by means of the test and filter circuit (12), evaluating the loop measuring voltage (U.sub.mEKE) and computing the ground resistance (R.sub.EKE) by means of the microcontroller (14).

8. The measuring method according to claim 7, characterized in that an a bipolar square wave voltage having a base frequency ranging from 0.1 Hz to 10 Hz and a voltage change less than 10 V is superimposed as excitation voltage (U.sub.gEKE).

9. The measuring method according to claim 8, characterized in that the voltage change of the excitation voltage (U.sub.gEKE) and the loop measuring voltage (U.sub.mEKE) in the test and filter circuit (12) and the microcontroller (14) is used to compute the ground resistance (R.sub.EKE).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further advantageous embodiment features are derived from the following description and the drawings, which describe a preferred embodiment of the invention by means of examples.

[0033] FIG. 1: shows a ground connection monitoring system according to the state of the art.

[0034] FIG. 2: shows a ground connection monitoring system with an insulation monitoring device and an electric measuring arrangement according to the invention.

DETAILED DESCRIPTION

[0035] FIG. 1 shows a ground connection monitoring system according to the state of the art with an insulation monitoring device 4, which is connected to the active conductors L1, L2 of an ungrounded power supply system 2 and to a ground terminal PE of an electric installation 3 via a ground connection 6.

[0036] FIG. 2 shows a ground connection monitoring system with an insulation monitoring device 4 connected to the ungrounded power supply system 2 and an electric measuring arrangement 10 according to the invention.

[0037] The insulation monitoring device 4 is coupled to the active conductors L1, L2 of the ungrounded power supply system 2 via coupling resistances R.sub.aIMD and comprises a measuring voltage generator U.sub.gIMD for supplying a measuring voltage U.sub.gIMD and a measuring resistance R.sub.mIMD for measuring a measuring current I.sub.m corresponding to the insulation resistance. The ground-connection clamp E is used to connect the insulation monitoring device 4 having the reference potential GND to the ground terminal PE in order to establish the ground connection 6.

[0038] The electric measuring arrangement 10 according to the invention is disposed between the ground-connection clamp E of the insulation monitoring device 4 and a control-ground connection clamp KE. The electric measuring arrangement 10 is designed as an active loop measurement device 20 in the form of a series connection. The series connection comprises an excitation voltage source U.sub.gEKE, which generates an excitation voltage U.sub.gEKE. The excitation voltage U.sub.gEKE drives a current in a current loop via the ground-connection clamp E and the control-ground connection clamp KE having the contact resistances R.sub.E and R.sub.KE.

[0039] As a result, voltage drop is caused at a loop measurement resistance R.sub.mEKE, which is detected as loop measuring voltage U.sub.mEKE and used to measure the ground resistance R.sub.EKE.

[0040] The measuring point M of the loop measuring voltage U.sub.mEKE is connected to the control-ground connection clamp KE via a loop coupling resistance R.sub.aEKE.

[0041] The ground resistance R.sub.EKE composed of the transition resistances R.sub.E, R.sub.KE in the current loop formed via the ground-connection clamp E, the ground terminal PE and the control-ground connection clamp KE can be computed using the current/voltage relationships applicable to linear networks (mesh and node point rule and Ohm's law) as follows

[00001]$R_{EKE}=R_E+R_{KE}=\frac{R_{mEKE}}{\left(\frac{U_{gEKE}}{U_{mEKE}}-1\right)}-R_{aEKE}.$

[0042] To make the method more resistant to interference, the voltage change A of the excitation voltage U.sub.gEKE and the voltage change A of the loop measuring voltage U.sub.mEKE are included in the computation instead of the absolute values.

[0043] To record the loop measuring voltage U.sub.mEKE at the measuring point M, an electronic test and filter circuit 12 with low-pass effect and any stages for level adjustment is provided.

[0044] The test and filter circuit 12 forwards the measurement result to a microcontroller 14, which evaluates the loop measuring voltage U.sub.mEKE to compute the ground resistance R.sub.EKE according to the equation above.

[0045] The microcontroller 14 has an evaluation algorithm which quantifies the ground resistance R.sub.EKE as the resistance value of the loop in the range R.sub.EKE=0 . . . 2 k. Threshold value R.sub.EKEth can be set by software for this purpose. Moreover, the microcontroller 14 can also perform tasks other than loop measurement, e.g., the measurement technology for insulation monitoring in the insulation monitoring device 4 or HMI control.

[0046] In FIG. 2, a TVS diode 16 is optionally inserted in a line branch between the ground-connection clamp E of the insulation monitoring device 4 and the control-ground connection clamp KE in order to provide a redundant ground connection.