METHOD AND DEVICE FOR IMPEDANCE MONITORING FOR PROTECTION AGAINST ELECTRIC SHOCK

Abstract

A method and a device for impedance monitoring for a single-phase or multiphase, ungrounded power supply system. The method comprising the following steps: measuring a complex impedance against ground simultaneously for each active conductor using a measuring device; calculating a complex touch current for each active conductor; testing in the computing unit whether the corresponding complex touch current exceeds a settable body-current threshold value; generating a switch signal in the computing unit upon the body-current threshold value being exceeded; and controlling a switch element using the switch signal for shutting off or isolating the power source.

Claims

1-10. (canceled)

11. A method for impedance monitoring for a single-phase or multiphase, ungrounded power supply system having a power source, active conductors and a consumer, the method comprising: measuring a complex impedance against ground for each active conductor simultaneously using a measuring device; computing a complex touch current, which would flow upon a touching of another active conductor after a first insulation fault has arisen at one of the active conductors, for each active conductor using a computing unit as a quotient from a conductor-to-ground voltage of the corresponding conductor and the parallel connection of the complex impedances, a total-body impedance being added to the complex impedance of that conductor which is touched by the person; testing in the computing unit whether the corresponding complex touch current exceeds a settable body-current threshold value; generating a switch signal in the computing unit upon the body-current threshold value being exceeded; and controlling a switch element using the switch signal for shutting off or isolating the power source.

12. The method according to claim 11, further including deriving the body-current threshold value from an implemented current-time characteristic curve which represents a duration of the touch current over the level of the body current.

13. The method according to claim 12, further including using one of the shapes shown in FIG. 20 of standard IEC 60479-1 as the current-time characteristic curve.

14. The method according to claim 13, further including constituting the total-body impedance as the vectorial sum of a settable body inner impedance and a settable skin impedance.

15. An impedance monitoring device for a single-phase or multiphase, ungrounded power supply system having a power source, active conductors and a consumer, comprising: a measuring device for simultaneously measuring a complex impedance against ground for each active conductor; a computing unit configured for computing a complex touch current, which would flow upon a touching of another active conductor after a first insulation fault has arisen at one of the active conductors, for each active conductor as a quotient from a conductor-to-ground voltage of the corresponding conductor and the parallel connection of the complex impedances, a total-body impedance being added to the complex impedance of that conductor which is touched by the person, for testing whether the corresponding complex touch current exceeds a settable body-current threshold value and for generating a switch signal upon the body-current threshold value being exceeded; and a switch element which is controlled for shutting off or isolating the power source using the switch signal.

16. The impedance monitoring device according to claim 15, wherein the computing unit is configured for deriving the body-current threshold value of an implemented current-time characteristic curve which represents a duration of the body current over the level of the body current.

17. The impedance monitoring device according to claim 16, wherein the computing unit is configured to use a shape represented in FIG. 20 of standard IEC 60479-1 as the current-time characteristic curve.

18. The impedance monitoring device according to claim 17, further including a shut-off device as a switch element for preventively shutting off the power source.

19. The impedance monitoring device according to claim 17, further including an isolator as a switch element for standardized isolation of the power source.

20. The impedance monitoring device according to claim 19, wherein the computing unit is configured for implementing the total-body impedance which is formed as the vectorial sum of the body inner impedance and the skin impedance.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0056] The Figure shows an impedance monitoring device 10 for an ungrounded power supply system 2.

DETAILED DESCRIPTION

[0057] Shown in a functional block diagram is an impedance monitoring device 10 according to the invention for a three-phase, ungrounded power supply system 2 (IT system) in which a power source 4 feeds a consumer 6 via active conductors L1, L2, L3 secured via excess-current cutouts F1, F2, F3. Power supply system 2 is characterized by ohmic insulation resistances R1, R2, R3 and leakage capacitances C1, C2, C3 for corresponding active conductor L1, L2, L3, ohmic insulation resistances R1, R2, R3 and leakage capacitances C1, C2, C3 forming the real part and the imaginary part of the corresponding conductor-specific, complex impedance Z1, Z2, Z3.

[0058] Impedance monitoring device 10 has a measuring device 12 which comprises a coupling branch (shown in a simplified manner) between corresponding active conductor L1, L2, L3 and ground PE for each active conductor L1, L2, L3. The coupling branch in turn comprises a coupling resistance Ri, a measuring voltage generator G (which can also be configured together for all three coupling branches) and a measuring resistance Rm.

[0059] Via the voltage detected at measuring resistance Rm, corresponding complex impedance Z1, Z2, Z3 is first computed for each active conductor L1, L2, L3 in a computing unit 14.

[0060] To determine a complex touch current I1, I2, I3, a body current model 16 having a settable total-body impedance Zk is stored in computing unit 14. Computed complex impedance Z1 or Z2 or Z3 of that conductor with which the human body comes into contact is increased by the value of total-body impedance Zk (series connection of the impedances). By means of conductor-to-ground voltage UL1_E, UL2_E, UL3_E of corresponding conductor L1, L2, L3 and a complex total impedance Zges, corresponding complex touch current I1, I2, I3 can be computed according to Ohm's Law. In doing so, complex total impedance Zges is yielded from the parallel connection of complex impedances Z1, Z2, Z3, total-body impedance Zk being added to corresponding complex impedance Z1 or Z2 or Z3.

[0061] In the event of the touching of active conductor L3, the following applies to complex touch current I3:

I3=UL3_E/Zges

with Zges=Z1∥Z2∥(Z3+Zk).

[0062] Subsequently, corresponding complex touch current I1, I2, I3 is evaluated based on a current-time characteristic curve 18 stored in the computing unit. For this purpose, a test takes place for each complex touch current I1, I2, I3 to discover whether it exceeds a body-current threshold value.

[0063] When exceeding a settable body-current threshold value gathered from current-time characteristic curve 18 and posing a risk to persons, a switch signal 20 is generated as soon as an exceedance has been identified.

[0064] Switch signal 20 controls a switch element 22 which is configured as a shut-off device or an isolator and which causes power source 4 to be shut off or to be safely isolated according to standards VDE 0100-530 and IEC 60364-5-53.

[0065] Furthermore, shown in a simplified manner are case A where direct touching takes place, i.e., a direct contact between the human body and a live active conductor L1, L2, L3 comes to pass, and case B where indirect touching takes place, i.e., a risk arises of an insulation fault applying an electric voltage to parts of the electric installation, such as a motor casing, to which voltage is not applied under normal operating conditions (fault to frame).