Methods for detecting an interruption of an active conductor in an ungrounded direct-voltage power supply system

Abstract

The invention relates to a method for detecting an interruption of an active conductor in an ungrounded direct-voltage power supply system. Five alternative methods are introduced, which are based on determining a current load current, a current total insulation resistance, a current displacement voltage, a current total capacitance or a current total impedance. Each of these methods minimizes the hazard related to accidental touching of two active conductors in an ungrounded direct-voltage power supply system.

Claims

1. A method for detecting an interruption of an active conductor (L+, L) in an ungrounded direct-voltage power supply system (2), comprising the method steps of: connecting an ohmic minimal load (14) to generate a minimal load current (Imin) on the active conductors (L+, L), determining a current load current (I), checking whether the current load current (I) falls short of the value of the minimal load current (Imin), and signaling a shortfall.

2. The method according to claim 1, characterized in that if the load current falls short of the minimal load-current value (Imin), the power supply system (2) is shut off by means of an undercurrent relay.

3. A method for detecting an interruption of an active conductor (L+, L) in an ungrounded direct-voltage power supply system (2), comprising the method steps of: connecting a high-resistance resistor (Riso1, Riso2) between each active conductor (L+, L) and ground, determining a current total insulation resistance (R) of the power supply system (2) by means of an insulation monitoring device (10), checking whether the current total insulation resistance (R) exceeds a limit value (Rlim), and signaling an exceedance.

4. The method according to claim 3, characterized in that the total insulation-resistance limit value (Rlim) is defined as a function of an insulation resistance value specific to the power supply system and as a function of the connected high-resistance resistors (Riso1, Riso2).

5. The method according to claim 3, characterized in that if the total insulation resistance exceeds the limit value (Rlim), the power supply system (2) is shut off.

6. A method for detecting an interruption of an active conductor (L+, L) in an ungrounded direct-voltage power supply system (2), comprising the method steps of: placing a high-resistance resistor between each active conductor (L+, L) and ground close to a load, determining a current displacement voltage (UV) between an interconnected point of all active conductors (L+, L) and ground, checking whether the current displacement voltage (UV) exceeds a limit value (UVmax), and signaling an exceedance.

7. The method according to claim 6, characterized in that the displacement-voltage limit value (UVmax) is defined as a function of an insulation resistance value specific to the power supply system and as a function of the connected high-resistance resistors and as a function of a nominal voltage (UN) of the power supply system (2).

8. The method according to claim 6, characterized in that the current displacement voltage (UV) is determined and the power supply system (2) is shut down in case of an exceedance of the displacement-voltage limit value (UVmax) by means of a voltage relay.

9. The method according to claim 6, characterized in that the current displacement voltage (UV) is determined by means of a voltage measuring function (30) integrated in an insulation monitoring device (10) and the power supply system (2) is shut off by means of a shut-off means in case of an exceedance of the displacement-voltage limit value (UVmax).

10. A method for detecting an interruption of an active conductor (L+, L) in an ungrounded direct-voltage power supply system (2), comprising the method steps of: connecting a capacitance (Ce1, Ce2) between each active conductor (L+, L) and ground, determining a current total capacitance (Ce) of the power supply system (2), checking whether the current total capacitance (Ce) falls short of a limit value (Cemin), and signaling a shortfall.

11. The method according to claim 10, characterized in that the total capacitance limit value (Cemin) is defined as a function of leakage capacitances specific to the power supply system and as a function of the connected capacitances (Ce1, Ce2).

12. The method according to claim 10, characterized in that the current total capacitance (Ce) is determined by means of a capacitance measuring device and/or by means of an insulation monitoring device having an integrated capacitance measuring function.

13. The method according to claim 10, characterized in that if the total capacitance falls short of the limit value (Cemin), the power supply system (2) is shut off.

14. A method for detecting an interruption of an active conductor (L+, L) in an ungrounded direct-voltage power supply system (2), comprising the method steps of: connecting a capacitance (Ce1, Ce2) between each active conductor (L+, L) and ground, determining a current total impedance (Ze) of the power supply system (2), checking whether the current total impedance (Ze) exceeds a limit value (Zlim), and signaling an exceedance.

15. The method according to claim 14, characterized in that the total impedance limit value (Zlim) is defined as a function of an insulation resistance value specific to the power supply system and as a function of leakage capacitances specific to the power supply system and as a function of the connected capacitances (Ce1, Ce2).

16. The method according to claim 14, characterized in that the current total impedance (Ze) is determined by means of an impedance measuring device and/or by means of an insulation monitoring device (10) having an integrated impedance measuring function (50).

17. The method according to claim 14, characterized in that if the total impedance exceeds the limit value (Zlim), the power supply system (2) is shut off.

18. A method for determined an interruption of an active conductor (L+, L) in an underground direct-voltage power supply system (2), characterized in that at least two of the following methods A-E are executed for redundant detection of the interruption of the active conductor: A. connecting an ohmic minimal load (14) to generate a minimal load current (Imin) on the active conductors (L+, L), determining a current load current (I), checking whether the current load current (I) falls short of the value of the minimal load current (Imin), and signaling a shortfall; B. connecting a high-resistance resistor (Riso1, Riso2) between each active conductor (L+, L) and ground, determining a current total insulation resistance (R) of the power supply system (2) by means of an insulation monitoring device (10), checking whether the current total insulation resistance (R) exceeds a limit value (Rlim), and signaling an exceedance; C. connecting a high-resistance resistor between each active conductor (L+, L) and ground, determining a current displacement voltage (UV) between an interconnected point of all active conductors (L+, L) and ground, checking whether the current displacement voltage (UV) exceeds a limit value (UVmax), and signaling an exceedance; D. connecting a capacitance (Ce1, Ce2) between each active conductor (L+, L) and ground, determining a current total capacitance (Ce) of the power supply system (2), checking whether the current total capacitance (Ce) falls short of a limit value (Cemin), and signaling a shortfall; or E. connecting a capacitance (Ce1, Ce2) between each active conductor (L+, L) and ground, determining a current total impedance (Ze) of the power supply system (2), checking whether the current total impedance (Ze) exceeds a limit value (Zlim), and signaling an exceedance.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) Other advantageous embodiment features become apparent from the following description and from the drawings, which illustrate preferred applications of the invention with the aid of examples. In the drawings:

(2) FIG. 1: shows an ungrounded direct-voltage power supply system in which a current load current is determined,

(3) FIG. 2: shows an ungrounded direct-voltage power supply system in which a current total insulation resistance is determined,

(4) FIG. 3: shows an ungrounded direct-voltage power supply system in which a current displacement voltage is determined,

(5) FIG. 4: shows an ungrounded direct-voltage power supply system in which a current total capacitance is determined, and

(6) FIG. 5: shows an ungrounded direct-voltage power supply system in which a current total impedance is determined.

DETAILED DESCRIPTION

(7) In the embodiment illustrated in FIG. 1 to FIG. 5, each of the claimed alternative solutions is based on an ungrounded direct-voltage power supply system 2 (DC-IT power supply system) which has two active conductors L+, L which are subjected to a nominal voltage U.sub.N at a feeding point 4.

(8) At a load connection point 6, a load 8 (equipment) is connected to the active conductors L+, L. The DC-IT power supply system 2 is monitored as prescribed by an insulation monitoring device 10 which is connected between the active conductors L+, L and ground PE.

(9) The DC-IT power supply system 2 is shut off by a shut-off means 12. In FIG. 1 to FIG. 5, the shut-off means 12 is to be understood as a functional unit, which can be realized as an independent device or which can be integrated into other measuring and monitoring devices connected to the DC-IT power supply system 2.

(10) In FIG. 1, an ohmic minimal load 14 connected between the active conductors L+, L in conjunction with a determination of a current load current I is illustrated as the first alternative solution. The minimal load 14 is to be connected as close to the load as possible, but at least far enough away from the shut-off means 12 for a desired line section that is to be monitored and on which a potential line break 15 can occur to be located between the shut-off means 12 and the load connection point 6 of the minimal load 14.

(11) The minimal load 14 generates a minimal load current I.sub.min, which runs through the active conductors L+, L from and to the feeding point 4 even in case of a deactivated load 8 and thus serves to detect a functioning line.

(12) Together with a load current I.sub.load running via the load 8, the minimal load current I.sub.min forms a current load current I. Said current load current I is detected by a current measuring means 16 on one of the active conductors L+, L and checked as to whether it falls short of the value of the minimal load current I.sub.min. In case of a line break 15 on at least one active conductor L+, L, the current load current I recedes to a magnitude close to zero and thus falls short of the value of the minimal load current I.sub.min. This is detected and signaled by a current measuring means 16, said signaling comprising the generation of a shut-off signal 17 for triggering the shut-off means 12.

(13) FIG. 2 shows a high-resistance resistor R.sub.iso1, R.sub.iso2 connected between each active conductor L+, L and ground PE in conjunction with a determination of a current total insulation resistance R.sub.iso of the power supply system 2 by means of an insulation monitoring device 10 as the second alternative solution.

(14) If a line break 15 occurs upstream of the connection point of the introduced high-resistance resistors R.sub.iso1, R.sub.iso2 (viewed from the feeding point 4), the current total insulation resistance R of the power supply system 2 increases as a consequence of the disconnection of at last one of the current paths running via the introduced resistors R.sub.iso1, R.sub.iso2. The exceedance of a predefined total-insulation-resistance limit value R.sub.lim by the current total insulation resistance R is detected by the insulation monitoring device 10 and is signaled to the shut-off means 12 in the form of the shut-off signal 17.

(15) In FIG. 3, a high-resistance resistor R.sub.iso1, R.sub.iso2 connected between each active conductor L+, L and ground PE in conjunction with a determination of a current displacement voltage U.sub.V between an interconnected point S of all active conductors L+, L and ground PE is illustrated as the third alternative solution.

(16) As in the second alternative solution, the high-resistance resistors R.sub.iso1, R.sub.iso2 are connected between the active conductors L+, L and ground PE close to the load.

(17) At the feeding side, the current displacement voltage U.sub.V is determined between an interconnected point S of all active conductors L+, L and ground PE by means of a device having a voltage measuring function 30. An interruption 15 of at least one active conductor L+, L leads to a raised value of the displacement voltage U.sub.V, allowing a hazardous state to be signaled and transmitted to the shut-off means 12 in the form of a shut-off signal 17 if the displacement-voltage limit value U.sub.Vmax is exceeded.

(18) FIG. 4 shows a capacitance C.sub.e1, C.sub.e2 connected between each active conductor L+, L and ground PE in conjunction with a determination of a current total capacitance C.sub.e of the power supply system 2.

(19) The introduction of the capacitances C.sub.e1, C.sub.e2 close to the load causes an increase of the current total capacitance C.sub.e of the power supply system 2 during normal operation. Consequently, a disconnection of the introduced capacitances C.sub.e1, C.sub.e2 can be detected as a drop of the current total capacitance C.sub.e by a device having a capacitance measuring function 40. In the illustrated embodiment example, the capacitance measuring function 40 is integrated into the insulation monitoring device 10.

(20) If the current total capacitance C.sub.e falls short of a total-capacitance limit value C.sub.emin, this is detected and signaled by means of a shut-off signal 17.

(21) The fifth alternative solution, shown in FIG. 5, differs from the fourth alternative merely in that a current total impedance Z.sub.e is evaluated instead of the current total capacitance C.sub.e. The comparison of the determined current total impedance Z.sub.e with a total-impedance limit value Z.sub.emin can advantageously be performed in an insulation monitoring device 10 having an integrated impedance measuring function 50. The total impedance against ground can be monitored at a network frequency of 50 Hz, for example. If an impedance increase due to a line break 15 is detected, the current total impedance Z.sub.e exceeding the total-impedance limit value Z.sub.lim, the insulation monitoring device 10 sends a shut-off signal 17 to the shut-off means 12.