DE102014013417A1 - Method and device for determining the earth fault current - Google Patents

Abstract

The present invention relates to a method and apparatus 20 for determining the ground fault current in an electric power grid operated with alternating current at a fundamental frequency f, characterized in that the apparatus 20 is adapted to determine at least a harmonic content of the ground fault current and the fundamental components to suppress the earth fault current. This makes it possible to determine the ground fault current very precisely by measurements without having to accept the risk of double earth faults.

Description

The present invention relates to a method for determining the ground fault current according to the preamble of claim 1 and a device for determining the earth fault current according to the preamble of claim 11.

For every consumer in Germany, the power supply in 2011 fell on average for 15.31 minutes, as from the source http://www.bundesnetzagentur.de/cln_1911/DE/Sachgebiete/ElektrizitaetundGas/ Unternehmen_Institutionen / Security of supply / Power grids / Supply quality / Supply quality-node.html evident. Thus, the German electric power grids (hereinafter referred to as "grids") are the most reliable in Europe. Substantial contribution to the high security of supply in such a network 1 , which is operated for example as a medium-voltage network at 20 kV, thereby has the use of Erdschlusslöschspule 3 [Resonance Star Point Estimation (RESPE) cf. 1 ]. In medium and high voltage networks 1 causes the use of the earth leakage quench coil 3 at a ground fault 5 in that only a relatively small ground fault residual current flows across the fault location (the earth fault residual current is the earth fault current that occurs in the event of a fault when using a ground fault quench coil, while the earth fault current is the ground fault current that occurs in the event of a fault if the earth fault quench coil is disconnected). This allows the network 1 , despite the mistake 5 , continue to operate. Meanwhile, the error may be 5 be isolated and targeted shut down. The connected consumers (not shown) notice nothing of all this.

However, the use of earth leakage quenching coils is bound to compliance with limit values. These limits will be loud DINVDE 0228-2 reached when the residual leakage current in medium voltage networks is 60 A and in high voltage networks 132 A. In the course of the energy transition, the grid operators are urged to expand their grids, which also increases the leakage current in these grids. If the limit is exceeded, the network operators terminate the operation of the ground fault suppression coil and, for safety reasons, rebuild the affected network in such a way that a ground fault leads to the immediate shutdown of the faulty power supply unit. As a result, the connected consumers are also switched off.

The conversion of the star point treatment of RESPE to rigid or low-impedance star point earthing is very complicated and cost-intensive. In RESPE networks, the grounding systems of the operating elements are usually designed for the maximum permissible residual leakage current, but after conversion of the neutral point treatment, the ground fault current can amount to several thousand amperes. The grounding systems must be suitably upgraded to meet the increased ground fault current many times over. Also, the protection and positioning technology must be retrofitted.

In order to make the decision about this serious network rebuilding measure, the network operator must know exactly how large the ground fault residual current is. There are basically two different possibilities for this, namely the calculation and the measurement of the residual earth leakage current.

The first case of the calculation will be by using the 10% estimation formula DINVDE 0101-2 carried out. However, experience has shown that this often leads to values that are too high or too low for the ground fault residual current.

The second case of the measurement is associated with the risk of so-called double earth faults. Specifically, the measurement is artificially grounded 5 generated in which at least one outer conductor 7 with the grounding system 9 is short-circuited ("earth fault operation"). This is compared to the "normal operation", the phase-earth voltage of the two ungrounded outer conductor 11 . 13 raised to the height of the conductor-conductor voltage (see. 2a . 2 B , but in this case not the outer conductors 7 . 9 . 11 themselves are shown, but the outer conductor voltages in phasor representation). In the case shown a three-phase AC network 1 the voltage increase is 3 ^1/2 ≈ 1.73.

Although the conductor insulation of the nets is designed for this case, this voltage increase often leads to weak points for breakdown ("second fault location") and thus to double ground fault. Double Earth faults are of their kind two-pole short-circuits with earth contact and are immediately switched off by the mains protection.

If the second fault occurs in an outflow other than the earth fault test, then the network protection only shuts off one fault and a ground fault remains. This can lead to a new ground fault and thus to a cascade of double earth faults. The network operators want to avoid this scenario, so that most network operators carry out virtually no ground fault tests.

The exact magnitude of the earth fault residual current is not known, since on the one hand the harmonic components can not be calculated with sufficient accuracy and, on the other hand, the only way of determining this is rarely used because of risks.

The object of the present invention is to eliminate the above-mentioned disadvantages in the determination of the ground fault current.

This object is achieved by the method according to the invention for determining the ground fault current as claimed in claim 1 and the device according to the invention for determining the ground fault current as claimed in claim 11. Advantageous further developments are specified in the dependent subclaims.

The inventor has recognized that the uncertainty in the ground fault current mainly results from the harmonic components of the ground fault current and that therefore the measurement of the harmonic components with the suppression of the fundamental components must be performed to determine the ground fault current. If only the harmonic components are measured and the fundamental components are suppressed, then there is no danger of double earth faults.

The fundamental component of the earth fault current can be calculated with sufficient accuracy, whereby the total ground fault current can then be determined by phytagorean addition of the harmonic and fundamental components. Usually this has the network operator the characteristics of its 50 Hz network available. So he knows where the line is. The data of the line then include, among other things, the specification of the capacitive ground fault current caused by it. In addition, the network operator knows how the ground fault quench coil is set. Often special regulators are also used to set the earth fault quenching coil, which automatically detect the residual capacitive residual current and the misregistration of the coil, whereby the earth fault residual current is given.

The inventive method for determining the Erdschlussfehlerstroms in an electric power supply network, which is operated with alternating current at a fundamental frequency f, thus characterized by the fact that at least one harmonic content of the ground fault current is determined and the fundamental components of the Erdschlussfehlerstroms be suppressed to prevent double earth faults.

In a further development, it is provided that a ground fault is generated between at least one phase of the electrical energy supply network and ground, wherein the ground fault is preferably generated by an error impedance, wherein it is provided in particular that the ground fault current is measured by the fault impedance and / or the voltage across the Error impedance is measured.

In an advantageous development, it is provided that the earth fault current is determined for at least two different fault impedances.

The resistances of coils and capacitors occurring in real arrangements reduce the ground fault current flowing through the generated ground fault, as well as an exact tuning to an impedance of 0 Ω for the frequency of the harmonic is very expensive. In order to take this influence into account, a two-point measurement is carried out at different fault impedances. Thereafter, it is possible to determine the current at an impedance of 0 ohms by means of a ratio equation. From this, the driving harmonic voltage and the fault impedance of the network can be determined.

In an advantageous embodiment, it is provided that the fault impedance is changed by connecting in series at least one of the elements ohmic resistance, capacitor and coil, wherein preferably a coil is used.

The calculation would then be appropriate 7 and 8th be made as follows:
Z _NW (fault impedance of the generated ground fault) and Z _Z (additional impedance) are known.

I ₁ and I ₂ are measured in two steps. Z _mains (mains impedance when the ground fault is generated), U _ES (voltage that drives the ground fault current) and I _satt (current that would flow during normal ground fault) are calculated, each for a frequency of the harmonic. For each additional frequency, this calculation would have to be repeated. In this regard, it should be noted that the measured currents I ₁ and I _{2 are} a frequency mixture. The individual frequency components can be extracted via the Fourier transformation. Then Z _network is obtained I ₁ (205 Hz) and I ₁ (350 Hz) and I ₂ (250 Hz) and I ₂ (350 Hz) from which it then (250 Hz) and Z _grid (350 Hz) is determined.

Alternatively or additionally, it is provided that at least one reverse voltage is applied between at least one phase and earth, wherein the back voltage is an alternating voltage, preferably such a back voltage is applied that the ground fault current is eliminated.

Then the two-point measurement is carried out with an additional voltage source. The voltage source can either have a fixed voltage and phase with the frequency of the examined harmonic or frequency, phase and amplitude are variable. In the first case, a ratio equation would be used again In the second case, the source will be controlled in magnitude and phase so that the ground fault current becomes zero. If this is done, the amount of additional voltage corresponds to the amount of the driving voltage and the phase position is shifted by 180 ° to this. With the determined voltage and the previously determined without additional voltage earth fault current then the impedance of the network can be calculated.

The calculation would then be appropriate 10 and 11 be made as follows:
Z _NW (fault impedance of the generated ground fault) and U _counter (reverse voltage) are known. I ₁ and I ₂ are measured in two steps. Z _mains (mains impedance when the ground fault is generated) and I _satt (current that would flow during normal ground fault) are calculated, each for a harmonic frequency, with the phase and amplitude adjusted to make the earth leakage residual current minimum or zero. However, an enlargement could also be made. It is only important in this connection that fundamentally a change of the residual earth leakage current takes place. For each additional frequency, this calculation would have to be repeated. For example, for two harmonics then the frequency of the counter-voltage would be adjusted first for one and then for the other harmonic. Alternatively, two countervoltage sources of different frequency could be used.

Particularly preferably, it is provided that a band-stop filter is used for the fundamental components and that a band-pass filter is used for the at least one harmonic component. As a result, the determination method according to the invention can be implemented in a particularly simple and effective manner.

In this context, it is advantageous if a, in particular passive, reactance circuit is used, for the fundamental oscillation, a pole in the impedance, preferably an impedance of greater than or equal to 1000 ohms, in particular greater than or equal to 5,000 ohms and a minimum in the impedance for the harmonic , preferably an impedance of less than or equal to 20 ohms, in particular of less than or equal to 1 ohm. In a passive reactance circuit, passive elements in the form of inductors and capacitors are used.

In a further development, it is provided that the pole point is provided by a parallel resonant circuit, which can be represented in a particularly simple manner.

In a further development, it is provided that the minimum is provided by a series resonant circuit, which can be represented particularly easily.

In this context, the so-called Forster basic circuits are used particularly advantageous, for example, in Gerhard Ulbricht; Network analysis, network systems theory and management theory; 1986 BG Teubner; Stuttgart are published.

Appropriately, it is provided that the electric power supply network has a Resonanzsternpunkterdung, which is preferably designed switchable. Then both residual earth leakage current and ground fault current can be determined.

In an advantageous development, a switch for disconnecting and connecting the earth fault to be generated is provided. As a result, the network can insert a ground fault for the harmonics at any desired times without installation effort.

Independent protection is claimed for the inventive device for determining the ground fault current in an electric power grid operated with alternating current at a fundamental frequency f characterized by the fact that the device is adapted to determine at least a harmonic content of the ground fault current and the fundamental parts of the earth fault current suppress to prevent double earth faults.

In an advantageous development, it is provided that the device is adapted to carry out the method according to the invention.

The characteristics and further advantages of the invention will become apparent in the context of the following description of preferred embodiments in conjunction with the figures. Here are purely schematic:

1 a diagram of a network with resonance earthing according to the prior art,

2a . 2 B Schematics for increasing the voltage in case of ground fault in the network 1 .

3 a diagram of the method according to the invention according to a first preferred embodiment,

4 the frequency response of the device according to the invention 3 .

5a - 5e various schemes for preferred embodiments of the device according to the invention,

6 a diagram of the method according to the invention according to a second preferred embodiment,

7 a scheme for two-point measurement according to the method according to 6 .

8th Formulas according to the scheme 7 .

9 a diagram of the method according to the invention according to a third preferred embodiment,

10 a scheme for two-point measurement according to the method according to 9 .

11 Formulas according to the scheme 10 and

12 a diagram of the method according to the invention according to a fourth preferred embodiment.

In a conventional ground fault test, a metallic connection between an outer conductor 7 and the grounding system 9 produced. The potential of the grounding system 9 corresponds to that of the grounded outer conductor 7 , so that the conductor-earth voltage of the ungrounded outer conductor 11 . 13 is equal to the phase-to-phase voltage, the height of the voltage boost is determined by the fundamental component of the outer conductor voltage. Depending on the magnitude of the harmonic voltages and the fault loop impedance, the fundamental and harmonic components of the earth fault residual current (cf. 1 and 2 ).

Since the fundamental oscillation component of the residual earth fault current can be calculated accurately enough, this measured value is less interesting in an earth fault test than the harmonic components.

In the 3 to 11 different schemes are shown to preferred embodiments of the inventive method and apparatus according to the invention purely schematically.

Since ground fault tests are only necessary in the area of the harmonics (especially the 5th and 7th harmonics), a bandpass is used as a ground fault connection, which only allows the current flow of the harmonics. The fundamental component of the ground fault current should be suppressed. For this purpose, the bandpass should be combined with a bandstop filter (cf. 3 ), so that a frequency response as in 4 arises.

It can be seen that the device according to the invention 20 as earth fault network (NW) 21 is formed, that between an outer conductor 7 and the grounding system 9 is arranged. The grounding network 21 has two parallel resonant circuits 23 . 25 on, each one a coil 27 . 29 and a capacitor connected in parallel with it 31 . 33 exhibit. In addition, one is to the resonant circuits 23 . 25 coil connected in series 35 intended. In doing so, generate the first parallel resonant circuit 23 a pole of impedance at the mains frequency of 50 Hz and the second parallel resonant circuit 25 one pole at 300 Hz. All elements 27 . 29 . 31 . 33 . 35 together produce a minimum at the 5th harmonic of 250 Hz and a minimum at the 7th harmonic of 350 Hz (cf. 4 ). The earth fault residual current is then with the current clamp 36 measured.

By designing this grounding network 21 ensures that the outer conductor 7 by the high impedance at 50 Hz for the network nominal frequency continues to be isolated to ground, so that the increase of the conductor-earth voltage of the unaffected outer conductor 11 . 13 is much lower and determined only by the harmonic voltages (a few hundred volts in medium voltage networks). The impedance of the grounding network 21 for 250 Hz and 350 Hz, on the other hand, it is close to zero, so that the corresponding harmonic ground fault currents can flow and be measured unhindered.

The reactance network 21 can be designed by adding or omitting dummy elements so that it represents a band pass for only one or any number of harmonics. The grounding network 21 to 3 represents therefore only one possibility dar. Other possibilities are in the 5a to 5e shown, the so-called Forster basic circuits show.

The show 5a and 5b Erdschlussnetzwerke 37 . 39 of parallel resonant circuits 23 . 25 for fixing poles at 50 Hz and 300 Hz, while the minima at 250 Hz and at 350 Hz by the interaction of all elements 27 . 29 . 31 . 33 . 35 . 41 be generated.

Both 5c to 5e on the other hand are for the earth fault networks 43 . 45 . 47 Series resonant circuits 49 . 51 to define minimums at 250 Hz and 350 Hz, while both series resonant circuits 49 . 51 in conjunction with the dummy elements 53 . 55 generate the poles at 50 Hz and at 300 Hz, so that here too the poles and minima accordingly 4 available.

In addition to the resonant circuits shown 23 . 25 . 49 . 51 can one or more additional corresponding resonant circuits (indicated by the puncture) are provided to take into account further frequencies or sharper to define poles or minima.

With regard to the exact dimensioning of the dummy elements of the devices 21 . 37 . 39 . 43 . 45 . 47 The expert will interpret this in the usual way so that after 4 desired effects are caused.

In 6 a second preferred embodiment of the method according to the invention is shown purely schematically, wherein the earth fault network used 60 additionally at least one of the reactive elements ohmic resistance 61 , Kitchen sink 63 and capacitor 65 that's over the switch 67 is switchable. The coil is preferred 63 used because it only generates reactive power.

With this earth fault network 60 a two-point measurement is performed, where once the earth fault residual current through the current clamp 69 without dummy element 61 . 63 . 65 is measured and once, for example, the coil 65 is connected as a blind element. This coil 65 has only a very low inductance of a few, in particular 1 to 2 mH, which leads to an impedance increase of the ground fault network 60 leads. This can cause deviations of the ground fault network 60 from the exact minimum layers of the frequency response 4 of 250 Hz and 350 Hz, using the in 7 and 8th The values shown here are Z _mains (mains impedance with earth fault generated), U _ES (voltage which drives the ground fault current) and I _satt (current which is generated during normal ground fault).

In 9 a third preferred embodiment of the method according to the invention is shown purely schematically, wherein the earth fault network used 80 in addition to the ground fault network 21 another source of reverse voltage 81 having.

With this earth fault network 80 a two-point measurement is performed, where once the earth fault residual current through the current clamp 83 is measured without reverse voltage and once the counter voltage is adjusted so in relation to the frequency of a harmonic, for example, 250 Hz, in phase and amplitude, that with the current clamp 83 measured residual earth current is zero or minimal. However, an enlargement could also be made. It is only important in this connection that fundamentally a change of the residual earth leakage current takes place. Then with the help of in 10 and 11 the procedure shown, the values Z _network (line impedance with earth fault generated) and I _satt (current that would flow in normal ground fault) are calculated.

In 12 Finally, a fourth preferred embodiment of the method according to the invention is shown purely schematically, wherein the earth fault network used 100 in addition to the ground fault network 21 another switch 101 to connect to the existing network 1 having. This allows the ground fault network 100 At any time without installation effort insert a ground fault for the harmonics and the residual earth current with the current clamp 103 be measured. Alternatively, three different switches (not shown) could be provided to not only between outer conductors 7 and grounding system 9 , but also between one of the outer conductors 11 . 13 and the grounding system 9 cause a desired ground fault, which may therefore be appropriate, because experience has shown that the impedances of the network 1 concerning the different outer conductors 7 . 11 . 13 may vary.

From the above description it has become clear that with the present invention, the ground fault current can be determined very accurately by measurements without having to accept the risk of Doppelerdschlüssen in purchasing.

Unless otherwise indicated, all features of the present invention may be freely combined with each other. The features described in the description of the figures can, unless stated otherwise, be freely combined with the other features as features of the invention. Objective features can also be used as process features and process features as representational features.

LIST OF REFERENCE NUMBERS

1

Electric power supply network, network

3

Arc Suppression

5

Ground fault, error

7

outer conductor

9

grounding system

11, 13

outer conductor

20

inventive device

21

Ground fault network, reactance network

23, 25

Parallel resonant circuits

27, 29

Kitchen sink

31, 33

capacitor

35

Kitchen sink

36

current Probe

37, 39

Erdschlussnetzwerke

35, 41

blind elements

43, 45, 47

Erdschlussnetzwerke

49, 51

Series resonant circuits

53, 55

blind elements

60

Erdschlussnetzwerk

61

ohmic resistance

63

Kitchen sink

65

capacitor

67

switch

69

current Probe

80

Erdschlussnetzwerk

81

To voltage source

83

current Probe

100

Erdschlussnetzwerk

101

switch

103

current Probe

I, I ₁ , I ₂

ground-fault current

U _ES

Voltage that drives the ground fault current

U _counter

against stress

Z _network

Line impedance

Z _NW

Impedance of the reactance network

Z _Z

additional impedance

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• http://www.bundesnetzagentur.de/cln_1911/DE/Sachgebiete/ElektrizitaetundGas/ Unternehmen_Institutionen / Security of Supply / Electricity Networks / Quality of Supply / Supply Quality-node.html [0002]
• DIN VDE 0228-2 [0003]
• DINVDE 0101-2 [0006]
• Gerhard Ulbricht; Network analysis, network systems theory and management theory; 1986 BG Teubner; Stuttgart [0029]

Claims (12)

Method for determining the earth fault current (I) in an electrical energy supply network ( 1 ) operated with alternating current at a fundamental frequency f, characterized in that at least one harmonic content of the ground fault current (I) is determined and the fundamental portions of the ground fault current (I) are suppressed to prevent double earth faults. Method according to claim 1, characterized in that between at least one phase ( 7 ) of the electrical energy supply network ( 1 ) and earth ( 9 ) a ground fault is generated, wherein the ground fault is preferably due to an error impedance ( 21 , Z _NW ; 60 ; 80 ) is provided, wherein it is provided in particular that the ground fault current (I) through the fault impedance ( 21 , Z _NW ; 60 ; 80 ) and / or the voltage across the fault impedance ( 21 , Z _NW ; 60 ; 80 ) is measured. Method according to one of the preceding claims, characterized in that the ground fault current (I) for at least two different fault impedances ( 60 , Z _NW , Z _Z , 61 . 63 . 65 ) is determined. A method according to claim 3, characterized in that the fault impedance by connecting in series at least one of the elements ohmic resistance ( 61 ), Capacitor ( 65 ) and coil ( 63 ), preferably a coil ( 63 ) is used. Method according to one of the preceding claims, characterized in that at least one countervoltage ( 81 , U _Gegen ) between at least one phase ( 7 ) and earth ( 9 ) is applied, the counter tension ( 81 , U _counter ) is an AC voltage, preferably such a reverse voltage is applied that the ground fault current (I) is eliminated. Method according to one of the preceding claims, characterized in that a band-stop filter is used for the fundamental components and a band-pass filter is used for the at least one harmonic component. Method according to one of the preceding claims, characterized in that a, in particular passive, reactance circuit ( 21 ; 60 ; 80 ), which has a pole in the impedance for the fundamental, preferably an impedance of greater than or equal to 1,000 ohms, in particular greater than or equal to 5,000 ohms, and a minimum in impedance for the harmonic, preferably an impedance of less than or equal to 20 ohms, in particular of less than or equal to 1 ohm, ready. A method according to claim 7, characterized in that the pole point by a parallel resonant circuit ( 23 . 25 ) provided. A method according to claim 7 or 8, characterized in that the minimum by a series resonant circuit ( 49 . 51 ) provided. Method according to one of the preceding claims, characterized in that the electrical energy supply network ( 1 ) has a Resonanzsternpunkterdung, which is preferably formed switchable. Contraption ( 20 ) for the determination of the ground fault current (I) in an electrical energy supply network ( 1 ) operated with alternating current at a fundamental frequency f, characterized in that the device ( 20 ) is adapted to determine at least a harmonic content of the ground fault current (I) and to suppress the fundamental parts of the ground fault current (I) to prevent double earth faults. Contraption ( 20 ) according to claim 11, characterized in that the device is adapted to carry out the method according to one of claims 1 to 10.

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