Method for the continuous insulation monitoring of an electrical conductor arrangement

Abstract

Method for the continuous insulation monitoring of an electrical conductor arrangement (12) with an active conductor (3) and a conductor structure (14) electrically insulated from the active conductor (3), wherein the quality of the conductor arrangement (12) as well as the arrangement of the active conductor (3) and the conductor structure (14) is such that almost identical propagation conditions for the active conductor (3) and the conductor structure (14) apply to a current flow against ground (E), wherein an insulation resistance measurement is being carried out, wherein an insulation monitoring unit (20) is connected between the conductor structure (14) and ground (E), which superimposes a measurement voltage onto the electrical conductor arrangement (12), which generates a measurement current proportionally to the insulation resistance of the conductor arrangement (12), which is acquired in the insulation resistance measurement unit (20) and evaluated.

Claims

1. A method for the continuous insulation monitoring of an electrical conductor arrangement (12) with an active conductor (3) and a conductor structure (14) electrically insulated from the active conductor (3), wherein the quality of the conductor arrangement (12) as well as the arrangement of the active conductor (3) and the conductor structure (14) is such that almost identical propagation conditions for the active conductor (3) and the conductor structure (14) apply to a current flow against ground (E), comprising the method steps: carrying out an insulation resistance measurement, wherein an insulation monitoring unit (20) is connected between the conductor structure (14) and ground (E), which superimposes a measurement voltage onto the electrical conductor arrangement (12), which generates a measurement current proportionally to the insulation resistance of the conductor arrangement (12) without integrating the active conductor (3) into a measurement circuit, the measurement current being acquired in the insulation resistance measurement unit (20) and evaluated.

2. The method according to claim 1, characterized in that one or a plurality of conductors (26), not carry operating current, of the conductor arrangement (12) is/are used as the conductor structure (14).

3. The method according to claim 1, characterized in that a shielding layer (36) is used as a conductor structure (14).

4. The method according to claim 1, characterized in that, in the case of a transformer (38) as a conductor arrangement (12), a capacitively earthed shielding winding (46) of the transformer (38) is used as a conductor structure (14).

5. An application of the method according to claim 1, for the continuous insulation monitoring of an electrical conductor arrangement (12) of an unearthed power supply system (2).

6. An application of the method according to claim 1 for the continuous insulation monitoring of an electrical conductor arrangement of an earthed power supply system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other favourable embodiment features result from the following description and the drawings, which explain a preferred embodiment of the invention as well as applications of the invention based on examples. The figures show:

(2) FIG. 1: schematically, a branched unearthed power supply system for illustrating the problem,

(3) FIG. 2: the progression of an overall insulation resistance

(4) FIG. 3: an application of the method according to the invention in connection with a circuit board,

(5) FIG. 4: an application of the method according to the invention in connection with an underwater power supply line and

(6) FIG. 5: an application of the method according to the invention in connection with a transformer

DETAILED DESCRIPTION

(7) In order to illustrate the problem, a power supply system 2 is shown in FIG. 1, which consists of a main system 4 and a subsystem 6 and is powered by a power source 10. The main system 4 represents a conductor arrangement 12, which comprises two active conductors 3. In the present example, the conductor arrangement 12 is designed as an underwater power supply line 28 (see FIG. 4).

(8) The main system 4 as well as the subsystem 6 are respectively characterized by the insulation resistances R.sub.iso1 to R.sub.iso4. According to the most recent background art, for insulation resistance measurement, an insulation monitoring unit 20 according to standard is connected between the active conductor 3 and the earth E. The insulation monitoring unit 20 superimposes a measurement voltage on to the power supply system 2, wherein the measurement current circuit is formed in an earthed manner via the active conductor 3 and the insulation resistances R.sub.iso1 to R.sub.iso4. The insulation resistance R.sub.umb of the main system 4 results from the parallel connection of the insulation resistance R.sub.iso1 and the insulation resistance R.sub.iso2; the insulation resistance R.sub.sub of the subsystem 6 results from the parallel connection of the insulation resistance R.sub.iso3 and the insulation resistance R.sub.iso4. In turn, the overall insulation resistance of the power supply system 2 results from the parallel connection of the insulation resistance R.sub.umb of the main system 4 and the insulation resistance R.sub.sub of the subsystem 6. Due to the parallel connection of the insulation resistances R.sub.iso1 to R.sub.iso4, the insulation level of the power supply system 2 decreases. Against the background of the special task of determining the insulation resistance of individual system parts of an unearthed power supply system, the isolation level of which is considerably higher—by powers of 10 higher—these system parts insulated against ground in a very high-impedance manner must be separated. In addition, in accordance with the most recent background art, circuit breakers 8 for switching off the subsystem 6 are provided. These circuit breakers are used to disconnect from the main system 4, which is insulated against ground in much higher-impedance manner with relation to the subsystem 6, which is insulated against ground in a much lower-impedance manner.

(9) In practice, this circuit breakers 8 stand for a multitude of circuit breakers that make a separation from a multitude of subsystems 6 possible. In an unfavourable way, the effort for a disconnection operation is remarkably high since this disconnection must take place at depths of several thousands of metres in the sea using robots.

(10) If, for example, the conductor arrangement 12 is designed as an underwater power supply line 28 (FIG. 4), it is therefore attempted to increase the overall insulation level by selectively switching off system parts at a range of the overall insulation resistance above 100 MOhm.

(11) FIG. 2 shows in a diagram the ratio of the overall insulation resistance R.sub.iso of the power supply system 2 to the insulation resistance R.sub.sub of the subsystem 6 depending on the insulation resistance R.sub.umb of the main system 4.

(12) The expected low level of change of the overall insulation resistance value R.sub.iso determined by the insulation monitoring unit 20 in the case of a parallel connection of the subsystem 6 with an insulation level of approx. one MOhm and an insulation resistance R.sub.umb of the main system 4 designed as an underwater power supply cable 28, which varies between 10 MOhm and 1 GOhm, can be clearly recognized.

(13) Based on the measured overall insulation resistance R.sub.iso, in this example, a statement concerning the state of the insulation of the main system 4 (conductor arrangement 12 in the form of the underwater power supply line 28) can hardly be made.

(14) FIG. 3 shows the application of the method according to the invention on a conductor arrangement 12 designed as a circuit board 18. The conductor arrangement 12 comprises conductor tracks 13 as active conductors 3 and other conductor tracks 16 as a conductor structure 14. Deviating from the most recent background art, the insulation monitoring unit 20 is not coupled to the active conductor tracks 13 but to the other conductor tracks 16, which are embedded into a common insulating varnish layer 15, thereby being insulated from the active conductors 3, 13. According to the preamble of Claim 1, the requirement also applies here that the insulating varnish layer 15 exerts the same influence on both the active conductors 3, 13 as well as the other conductor tracks 16 with regard to the determination of an insulation resistance. The other conductor tracks 16 are thereby exposed to the same influencing factors, which influence the quality of the insulation. The measurement of the overall insulation resistance R.sub.iso on the conductor structure 14 thereby allows for an assessment of the insulation state of the common insulating varnish layer 15 to be made without having to apply a voltage to the active conductors 3, 13.

(15) Since the active conductors 3, 13 are not integrated into the measurement current circuit, there is also no need to interrupt the operation of the conductor arrangement 12 in order to carry out an insulation resistance measurement.

(16) FIG. 4 shows an application of the method according to the invention from the oil and gas supply sector where the conductor arrangement 12 is designed as an underwater power supply line 28. The underwater power supply line 28 here encloses four active conductors 3 as well as four unused conductors 26, which do not carry operating current, as a conductor structure 14. The insulation monitoring unit 20 is coupled to this conductor structure 14 consisting of the unused conductors 26. Since the conductor structure 14 is also exposed to the same environmental influences here as the active conductor 3, here, an approximate estimation of the insulation state of the conductor arrangement 12 can be made.

(17) In addition or as an alternative to coupling the insulation monitoring unit 20 to the unused conductors 26, which do not carry operating current, a conducting or a semi-conducting shielding layer 36 of the conductor arrangement 12 designed as an underwater power supply line 28 can be used as a conductor structure 14.

(18) FIG. 5 shows an application of the method according to the invention in connection with a conductor arrangement 12, which is designed as a transformer 38.

(19) In addition to the active transformer windings 33, the transformer 38 comprises a conductor structure 14 designed as a shielding winding 46. The insulation monitoring unit 20 is coupled to this shielding winding 46. Here as well, the measurement current, which flows within the measurement circuit formed via the shielding winding 46, provides an indication concerning the insulation state of the transformer 38.

(20) If, for example, the insulation state should deteriorate due to an excess formation of moisture in the transformer 38 and, thereby, the insulation state declines, this would be determined by an increase of the measurement current in the insulation monitoring unit 20.