Method and device for insulation monitoring and insulation fault location for unearthed power supply networks
A method and device for insulation monitoring and insulation fault location in an unearthed power supply network operate without a testing current generator by using an insulation monitoring device to generate a permanent measuring voltage between a mains conductor and earth and to feed a measuring current into the network. Measuring currents are detected using at least one current transformer arranged at each mains outgoing circuit, and total measuring current and proportional measuring currents in the mains outgoing circuits are determined and evaluated such that the measuring current used for insulation monitoring of the overall network is also used for insulation fault location in individual circuits. From a time variation of each circuit measuring current and the measuring voltage, an ohmic insulation resistance and a capacitive reactance (and/or impedance) are determined and analyzed for each mains outgoing circuit.
1 . A method for insulation monitoring and insulation fault location for unearthed power supply networks without a testing current generator, comprising
A) providing a permanent measuring voltage between the mains conductor ( 60 ) and earth ( 80 ) and feeding in a measuring current by means of an insulation monitoring device ( 61 ),
B) determining the measuring currents by means of at least one current transformer ( 64 ) arranged at each mains outgoing circuit ( 79 ),
characterised in that the method further comprises
C) determining the total measuring current and the proportional measuring currents in the mains outgoing circuits ( 79 ) by means of an insulation monitoring device ( 61 ),
D) evaluating the measuring currents detected, wherein
E) the measuring current of the insulation monitoring of the entire network is also used for insulation fault location in the individual circuits of the network, and
F) the ohmic insulation resistance ( 69 ) and the capacitive reactance ( 65 ) of each mains outgoing circuit ( 79 ) are determined and analysed from the variation over time of the measuring current of each current transformer ( 64 ) and the measuring voltage of the insulation monitoring device ( 61 ).
2 . The method according to claim 1 , further comprising one or more of the substeps
pre-magnetising the current transformer core,
reducing high-frequency interference on the measurement electronics,
using low-noise operational amplifiers in the measurement electronics,
providing a high-pass function to suppress low-frequency noise,
bandwidth reduction to reduce the influence of noise on the measuring current detection ( 10 ).
3 . The method according to claim 1 , wherein the insulation monitoring and the insulation fault location run simultaneously.
4 . The method according to claim 1 , wherein the insulation monitoring and the insulation fault location take place when the transformer ( 81 ) is switched on or switched off.
5 . The method according to claim 1 , wherein in the secondary circuit ( 2 ) of the current transformer ( 64 ) the copper resistance (R cu ) ( 91 ) of the secondary coil ( 1 ) is compensated by a negative resistance.
6 . The method according to claim 1 , wherein the measuring current detection ( 10 ) is performed by at least one correlation of the sampled values of the measuring current.
7 . The method according to claim 6 , wherein
the correlations of the sampled values of the measuring current are carried out by means of a sinusoidal oscillation whose frequency corresponds to the measuring voltage frequency f m of the insulation monitoring,
or
the measuring current detection ( 10 ) is carried out by at least two correlations of the sampled values of the measuring current, preferably with a cosine and a sine oscillation, wherein the two correlations of the sampled values of the measuring current can be synchronised, and a complex value of the measuring current is determined, the angle of which is related to the measuring voltage.
8 . The method according to claim 6 , wherein the ohmic insulation resistance ( 69 ) and the capacitive reactance ( 65 ) and/or the impedance ( 67 ) of each mains outgoing circuit ( 79 ) are calculated from the ratio of the individual measuring currents to the total measuring current using the current divider rule.
9 . The method according to claim 1 , wherein the insulation monitoring and insulation fault detection of insulation faults in the mains outgoing circuit ( 79 ) are carried out permanently in the switched-on and switched-off state of the transformer ( 81 ).
10 . The method according to claim 1 , wherein the differential inductance (L s ) of the secondary coil ( 1 ) of the current transformer ( 64 ) is increased by a premagnetisation.
11 . The method according to claim 1 , wherein the current transformer core of the secondary coil ( 1 ) of the current transformer ( 64 ) is demagnetised.
12 . The method according to claim 1 , wherein the differential inductance (L s ) of the secondary coil ( 1 ) of the current transformer ( 64 ) is determined by measuring the impedance ( 65 ) of the secondary circuit ( 2 ).
13 . The method according to claim 5 , wherein a zero-point adjustment of the secondary circuit ( 2 ) of the differential current transformer and the compensation of the copper resistance (R cu ) ( 91 ) of the secondary coil ( 1 ) is performed by the same proportional-integral controller ( 95 ).
14 . The method according to claim 1 , wherein the evaluation of the measuring currents is carried out at a central point and the values of the measuring currents are transmitted to the central point via suitable communication media.
15 . A device for insulation monitoring and insulation fault location for unearthed power supply networks without testing current generator, comprising
an insulation monitoring device ( 61 ) at a central point of the supply network, wherein the insulation monitoring device ( 61 ) is designed to generate a permanent measuring voltage between the mains conductor ( 60 ) and earth ( 80 ) and to feed in a measuring current,
characterised in that the device further comprises
at least one current transformer ( 64 ) arranged in each mains outgoing circuit ( 79 ) centrally at the infeed of the power supply network ( 63 ) between the insulation monitoring device ( 61 ) and the first mains outgoing circuit ( 79 ), which is designed for the temporal recording of the course of the fed-in measuring current of the insulation monitoring device ( 61 ) and the proportional measuring currents of the insulation monitoring device ( 61 ) at the mains outgoing circuits ( 79 ) when the transformer ( 81 ) is switched on or off,
at least one evaluation device for evaluating the measuring currents detected, wherein
the measuring current of the insulation monitoring of the overall network can also be used for insulation fault location in the individual circuits of the network, and
the measuring current of each current transformer ( 64 ) and the measuring voltage of the insulation monitoring device ( 61 ) can be used to determine and analyse the ohmic insulation resistance ( 69 ) and the capacitive reactance ( 65 ) of each mains outgoing circuit ( 79 ) over time.