GROUNDED SOCKET AND METHOD FOR INSULATION FAULT LOCATION IN AN UNGROUNDED POWER SUPPLY SYSTEM INCLUDING INSULATION MONITORING

Abstract

A grounded socket and a method for insulation fault location in an ungrounded power supply system including insulation monitoring by a standard insulation monitoring device superimposing a measuring voltage on the ungrounded power supply system for determining an insulation resistance of the ungrounded power supply system. The grounded socket includes a housing having electrical contacts, a signaling device for signaling an insulation state, and a current measuring device for detecting and evaluating a differential current, the current measuring device having a measuring current transformer and evaluating electronics, and the current measuring device being configured for high-resolution detection and evaluation of a measuring current driven by the measuring voltage as a differential measuring current.

Claims

1. A grounded socket (10) for insulation fault location in an ungrounded power supply system (2) including insulation monitoring by a standard insulation monitoring device (4) superimposing a measuring voltage (U.sub.m) on the ungrounded power supply system (2) for determining an insulation resistance (R.sub.f) of the ungrounded power supply system (2), the grounded socket (10) comprising: a housing (16) having electrical contacts (17), a signaling device (14) for signaling an insulation state, and a current measuring device (12) for detecting and evaluating a differential current (I.sub.d, I.sub.dm, I.sub.df), the current measuring device (12) having a measuring current transformer (20) and evaluating electronics (22), characterized in that the current measuring device (12) is configured for high-resolution detection and evaluation of a measuring current (I.sub.m) driven by the measuring voltage (U.sub.m) as a differential measuring current (I.sub.d, I.sub.dm).

2. The grounded socket (10) for insulation fault location according to claim 1, wherein the current measuring device (12) is configured to detect and evaluate a fault current (I.sub.f) flowing at a network frequency of the ungrounded power supply system (2) as a differential fault current (I.sub.d, I.sub.df).

3. The grounded socket (10) for insulation fault location according to claim 1 wherein the current measuring device (12) is AC/DC-sensitive.

4. The grounded socket (10) for insulation fault location according to claim 1, wherein the current measuring device (12) has a test loop (15) routed through the measuring current transformer (20) for generating a test current (I.sub.t).

5. The grounded socket (10) for insulation fault location according to claim 1, wherein the evaluating electronics (22) are configured to assess the differential measuring current curve (I.sub.dm) in order to establish synchronous insulation fault signaling between the insulation monitoring device (4) and the device for insulation fault location (10).

6. The grounded socket (10) for insulation fault location according to claim 1, realized as a permanently installed socket (32), as an adapter plug (34) or as a mobile line coupler (36).

7. A method for insulation fault location in an ungrounded power supply system (2) including insulation monitoring by a standard insulation monitoring device (4) superimposing a measuring voltage (U.sub.m) on the ungrounded power supply system (2) for determining an insulation resistance (R.sub.f) of the ungrounded power supply system (2), the method comprising the method steps to be executed in a grounded socket according to claim 1, including detecting and evaluating a differential current (I.sub.d, I.sub.dm, I.sub.df) by means of a current measuring device (12) having a measuring current transformer (20) and evaluating electronics (22), signaling an insulation state by means of a signaling device (14), wherein a measuring current (Im) driven by the measuring voltage (U.sub.m) is detected and evaluated as a differential measuring current (I.sub.d, I.sub.dm) in high resolution by means of the current measuring device (12).

8. The method for insulation fault location according to claim 7, wherein a fault current (I.sub.f) flowing at a network frequency of the ungrounded power supply system (2) is detected and evaluated as a differential fault current (I.sub.d, I.sub.df) by means of the current measuring device (12).

9. The method for insulation fault location according to claim 7 wherein the detection and evaluation by means of the current measuring device (12) is AC/DC-sensitive.

10. The method for insulation fault location according claim 7, further including the step of generating a test current (I.sub.t) which is routed through the measuring current transformer (20) of the current measuring device (12) by means of a test loop (15).

11. The method for insulation fault location according to claim 7, further including the step of assessing the differential measuring current curve (I.sub.dm) by means of the evaluating electronics in order to synchronize insulation fault signaling between the insulation monitoring device (4) and the device for insulation fault location (10).

12. The method for insulation fault location according to claim 11, wherein the differential measuring current curve (I.sub.dm) is assessed by detecting a change in amplitude of the differential measuring current (I.sub.dm).

13. The method for insulation fault location according to claim 11 wherein the differential measuring current curve (I.sub.dm) is assessed by detecting a change in pattern (M.sub.1, M.sub.2) of the differential measuring current (I.sub.dm).

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0042] Other advantageous configuration features are apparent from the following description and from the drawings, which illustrate preferred embodiments of the invention based on examples.

[0043] FIG. 1 shows a functional block diagram of a grounded socket according to the invention for insulation fault location;

[0044] FIG. 2 shows a grounded socket according to the invention as a permanently installed socket;

[0045] FIG. 3 shows a grounded socket according to the invention as an adapter plug;

[0046] FIG. 4 shows a grounded socket according to the invention as a mobile line coupler;

[0047] FIG. 5 shows a grounded socket according to the invention having an omega symbol as an optical display;

[0048] FIG. 6 shows a differential measuring current curve exhibiting a change in amplitude;

[0049] FIG. 7 shows a differential measuring current curve exhibiting a change in pattern; and

[0050] FIG. 8 shows a flow chart for synchronous insulation fault synchronization.

DETAILED DESCRIPTION

[0051] FIG. 1 shows a grounded socket 10 according to the invention for insulation fault location in an ungrounded power supply system 2 (IT network) to which a load 6 is connected via active conductors L.sub.1, L.sub.2.

[0052] A standard insulation monitoring device 4 superimposing a measuring voltage U.sub.m on the IT network is connected between active conductors L.sub.1, L.sub.2 and ground PE for determining an insulation resistance R.sub.f (insulation fault). A measuring circuit with a measuring current I.sub.m driven by measuring voltage U.sub.m forms via active conductors L.sub.1, L.sub.2, insulation resistance R.sub.f and the protective conductor (protective conductor connection to ground PE) back to insulation monitoring device 4. Measuring current I.sub.m is measured in insulation monitoring device 4 and allows an assessment of the magnitude of insulation resistance R.sub.f.

[0053] As essential components, grounded socket 10 according to the invention comprises a current measuring device 12, a signaling device 14 and a housing 16 having contacts 17. Contacts 17 are realized as plug contacts for connecting a plug of a supply line of load 6.

[0054] Current measuring device 12 has a measuring current transformer 20, a toroidal core of which surrounds active conductors L.sub.1 and L.sub.2 as a primary “winding”, and evaluating electronics 22.

[0055] Measuring current transformer 20 detects measuring current I.sub.m, which flows in the measuring circuit and continues as a differential measuring current I.sub.dm in active conductors L.sub.1 and L.sub.2, and transmits a differential current measurement result to evaluating electronics 22 via a secondary winding 24.

[0056] Evaluating electronics 22 are fed by a network voltage U.sub.n of ungrounded power supply system 2.

[0057] Furthermore, current measuring device 12 comprises a test loop 15, by means of which a test current I.sub.t is routed through measuring current transformer 20 to test the latter.

[0058] When an asymmetrical insulation fault R.sub.f occurs, measuring current transformer 20 additionally detects a fault current If as a differential fault current I.sub.df, which flows across always present leakage capacitances C.sub.e of ungrounded power supply system 2.

[0059] Following FIGS. 2 to 5 show different embodiments of grounded socket 10 according to the invention. The outer dimensions of the respective embodiments correspond to the dimensions of a standard, grounding-compatible conventional socket.

[0060] In FIG. 2, grounded socket 10 according to the invention is realized as a permanently installed socket 32 in a wall outlet (wall socket) or for a cable duct installation, for example. At hand, signaling device 14 is realized as an optical display 40 in the form of a lit LED ring. For example, the LED ring can light up green when no insulation fault has been located, and changes to yellow once an insulation fault has been located.

[0061] FIG. 3 shows the configuration of grounded socket 10 according to the invention as an adapter plug 34 for a commercially available socket. This allows simple retrofitting of existing load connections with grounded socket 10 according to the invention for insulation fault location.

[0062] In another embodiment according to FIG. 4, grounded socket 10 according to the invention is realized as a mobile line coupler 36 (multiple socket). This embodiment permits an insulation fault location individual to the load since insulation fault location is integrated for one or more of the slots of the multiple socket 36.

[0063] As an example of the grounded socket 10 according to the invention realized as a permanently installed socket 32, FIG. 5 shows a configuration of the signaling device 14 as an optical display 40 in the form of an omega symbol 42 for marking said socket as a grounded socket 10, 32 according to the invention including insulation fault location and therefor distinguishing it from conventional sockets without insulation fault location.

[0064] FIGS. 6 to 8 illustrate how the differential current measurement result is evaluated in evaluating electronics 22 by assessing differential measuring current curve I.sub.dm to synchronize insulation fault signaling between insulation monitoring device 4 and grounded socket 10 according to the invention.

[0065] Measuring current I.sub.m driven by measuring voltage Um continues at the location of measuring current transformer 20, i.e., in the socket, as differential measuring current I.sub.dm and is constantly measured there in a phase T.sub.1. Evaluating electronics 22 test whether differential measuring current I.sub.dm exceeds a differential current threshold I.sub.dm1 (peak-peak amplitude) applying to the fault-free case. If differential current threshold I.sub.dm1 is not exceeded in said first phase T.sub.1, optical display 40 lights up green (FIG. 8).

[0066] If detected differential measuring current I.sub.dm exceeds differential current threshold I.sub.dm1, optical display 40 changes to a yellow-flashing display as a pre-warning (FIG. 8) in phase T.sub.2.

[0067] Once insulation monitoring device 4 detects an insulation fault in ungrounded power supply system 2—based on its longer evaluation time—, insulation monitoring device 4, which is to be programmed accordingly, reduces its internal resistance by an admissible value and thereby increases measuring current I.sub.m. As detected differential measuring current I.sub.dm, measuring current I.sub.m thus exceeds a second differential current threshold I.sub.dm2. This increase (amplitude modulation of the measuring currents) in phase T.sub.3 is considered a criterion for an insulation fault report of insulation monitoring device 4, and yellow-flashing optical display 40 changes to a steady yellow display (FIG. 8).

[0068] Alternatively or additionally to the change in amplitude of measuring current I.sub.m, a detected change in pattern of measuring current I.sub.m (coding of the measuring current) can also cause the transition from second phase T.sub.2 to third phase T.sub.3. Evaluating electronics 22 test whether the pattern of differential measuring current curve I.sub.dm has changed from a pattern M.sub.1 to a pattern M.sub.2 by correlation calculation. If a change in pattern is detected, optical display 40 changes to a steady yellow display in phase T.sub.3 (FIG. 8).