AT503598B1 - Earth fault distance locating method for earth fault-compensated, operated three-phase-electrical power network, involves calculating distance to earth fault based on phase voltage under consideration of earth impedance - Google Patents

Abstract

The method involves measuring and monitoring current and voltage constantly at a measuring point in a phase. Distance to an earth fault is calculated based on the measured phase voltage at the measuring point under consideration of earth impedance at the measuring point and at a fault location. The distance is calculated during exceeding of a given threshold value of a biasing voltage and during lowering of a minimum voltage of a phase conductor by the current and voltage measurements of a conductor resistance in the phase conductor up to the earth fault position.

Description

2 AT 503 598 B1

The invention relates to a method for the location of ground faults in ground-fault-compensated operated 3-phase electric power networks with at least one star point, which is connected via a inductive portion possessing Kompensationsimpedanz to ground, wherein at least one location in each phase constantly current and voltage be measured and monitored.

Ground faults occurring during operation are, apart from the associated possible interruptions in operation of a network section with all the consequences also of concern, because they represent high potential differences in the vicinity of the ground fault and thus a hazard to persons and animals.

In order to compensate earth currents as far as possible during an earth fault of a phase or to extinguish an arc resulting from an earth fault, it has become known to call the neutral point of a three-phase network via an inductance, also called "Petersen coil", according to its inventor. to connect with earth. Such a compensation is possible because the current is largely capacitive in an earth fault and this capacitive current through the compensation inductance is opposed by an equal inductive current. For example, WO 99/10959 describes a method for adjusting the compensation inductance to the ground fault capacitance in the sense of the presence of a resonance condition.

It has become known from GB 525,334 to temporarily switch an ohmic resistor parallel to the Petersen coil so as to reduce the compensation, to increase the current across the star point and thus to be able to more easily determine the conductor which is subject to earth leakage.

The document WO 02/15355 A2 describes the feeding of an additional voltage in parallel with the compensation impedance in order to compensate in this way for the residual voltage arising in the event of an earth fault. By evaluating the summation currents, a faulty line section can also be identified.

WO 99/10959 discloses a method in which an adjustable compensation impedance is adapted in operation to the earth impedance, starting from transients occurring during switching operations.

Ground faults can be recognized by the fact that the total current of the three phase conductors in an earth fault case generally deviates significantly from the current sum in earth fault-free operation. In compensated operated networks occurs in case of failure in addition to a significant increase in the displacement voltage.

The known methods for fault location in electrical power distribution networks operate on the principle of impedance measurement. l + k0l £ where: Z measured impedance from location to fault U measured phase voltage at location I measured phase current at location k0 length independent factor to take into account Zo ("earth impedance") ΙΣ total current at location 3 AT 503 598 B1

At the measuring point, the voltage and the current of the faulty phase and the total current of the own line are measured and used for the evaluation.

This principle works with earth short circuits (ground faults with currents greater than 1 kA) and is widely used in low-resistance grounded networks.

For about 15 years, modern, microprocessor-controlled devices, so-called "distance protection relays" have been used which detect an earth short circuit and possibly a forced release, i. cause disconnection of the faulty cable portion of the network, these devices, of course, treat short circuits between phase conductors, which are not the subject of the invention. In the case of deleted networks, however, a forced triggering in case of ground faults is intentionally suppressed in order to ensure, if possible, uninterrupted operation.

It is known for fault location in erased networks, e.g. after finding the faulty line by switching operations to exit the line and to search the fault location, but this requires a great deal of experience entrusted to people, a large staff and usually a very high amount of time.

Attempts have also been made to determine the location of the fault by evaluating transient transients during earth faults, but the transient processes are dependent on the network structure and the currently occurring network situation, so that no generally valid method based on the evaluation of transients during earth faults can be specified ,

An object of the invention is to provide a method that essentially allows already existing protection devices a simple and reliable removal location in case of ground faults in deleted networks and, if necessary, a shutdown of line sections.

This object is achieved on the basis of a method of the type mentioned in the present invention that when exceeding a predetermined limit of the displacement voltage and falls below a predetermined minimum voltage of a phase conductor by current and voltage measurement, the line impedance in this phase conductor up to the ground fault point and on the basis of the known Line impedance per unit length is calculated by an impedance calculation, based on the measured phase voltage at the measurement location, the measured phase current at the measurement location and the summation current at the measurement location, taking into account the Erdungsimpendanzen at the measurement location and the fault location, the distance up to the ground fault.

The method according to the invention can be carried out with the aid of existing distance protection devices; only the starting and release parameters or algorithms need to be adapted to the method.

In an expedient variant of the invention, it is provided that, before the current and voltage measurement in the earth-faulty phase conductors, an additional impedance is connected in parallel with the compensation impedance of the neutral point and the current and voltage measurement for distance determination via the line impedance is carried out with an earth current increased by the parallel circuit and then the additional impedance is switched off again.

In this way it is ensured that a sufficiently high measuring current is available, which is not necessarily the case with compensated networks in the case of a ground fault, since theoretically the compensation does not allow any fault current. In this way, a very accurate determination of the fault location is possible in any case. 4 AT 503 598 B1

It is expedient if the connection of the additional impedance and the taking place with this current and voltage measurement is delayed by at least one grid period, since in this way so-called "ground fault wiper" and transient processes are not included in the measurement.

In practice, it has been proven that, as an additional impedance, an ohmic resistance is connected in parallel to the compensation impedance of the star point.

It is further expedient if the phase voltage UUe, the phase current lLi and the sum current ΙΣ determined at the measuring location and from this the impedance Z1 are calculated up to the ground fault point, resulting in Z1 = - u

L1E

Ili + Ις '^ O = z; -i with Z1 = impedance related to a unit of length giving the distance I up to the ground fault point.

An often significant improvement of the fault localization can result if a consideration of the fault impedance Zfw by Z1 = -

L1E

'FW

FW

In + Ις 'kI = Zrl, where Ifw is the current at the fault location.

An additional increase in accuracy can be achieved in many cases, if the capacitive currents are taken into account by Ifw = + Uap.

Another influence affecting the accuracy can be eliminated if the capacitive currents according to

1 FW Σ + Uap u ü o measurement can be evaluated by the ratio of the displacement voltage U ° mess to the rated voltage Unenn.

It is also advisable to provide that in the presence of non-plausible measurement results an additional impedance is switched again and also temporarily parallel to the compensation impedance of the star point and the current and voltage measurements for the calculation of the ground fault distance are repeated.

Advantageously, it can be provided that, after fault location calculation, the faulty line is switched off on one or both sides, namely when quality and / or quantity of the ground fault seem necessary.

In practice, if the current and voltage measurement is carried out with the fundamental frequency of the network, it is also possible to take into account harmonics and / or interharmonics of current and voltage during the measurement in order to increase the accuracy. 5 AT 503 598 B1

Since the method is extremely flexible with regard to the choice of the measuring location, it can also be provided that the measurement takes place at at least two, spaced measuring locations of a line which has a plurality of line sections which can be separated by switching devices, and a faulty line section on the basis of these measurements is selectively separated. In this way, extensive failures of a network can be effectively avoided.

The invention together with further advantages is explained in more detail below with reference to exemplary embodiments, which are illustrated in the drawing. In this show

1 is a schematic representation of part of an electric power network with a compensation impedance at a transformer neutral point,

2 shows in phasor diagrams the formation of the displacement voltage when a ground fault occurs,

3 shows the arrangement of several measuring locations and switching points in a sectioned network,

4a and 4b with reference to equivalent circuit diagrams a measurement using a switchable additional impedance with or without consideration of an error impedance,

5 shows a simplified section of FIG. 1 with an error impedance and

Fig. 6 in a simplified circuit diagram of a network section the conclusion of a capacitive total current.

1 shows a schematic diagram of a 3-phase electric power network in which a network section NAB is fed via a transformer TRA with primary windings PWI and secondary windings SEW. Inductances LR, Ls, LT, capacitances CR1, CSi, CT1, CR2, CS2, CT2 as well as resistors Rr, Rs, Rt adhere to this section in the equivalent circuit diagram. With the aid of a so-called distance protection device DSG, the line section NAB following the transformer TRA is monitored for errors. In particular, current and voltage are measured and monitored by means of a set STW or SPW of current and voltage transformers in each phase.

The transformer star point STP is in a known manner via a compensation impedance KIP, usually Petersenspule called "connected to ground, with a controlled switch SWI the impedance KIP an additional impedance ZIP, here an ohmic resistance can be connected in parallel.

The network or line section NAB can be separated from the rest of the network on both sides by switching devices SEA, SEB. These switching devices can be switched off starting from the evaluation of the measurement, which is indicated by leading from the distance protection device to the switching devices lines. In some cases, however, there will be a central data processing center that will evaluate the measurement results and decide on the basis of additional criteria whether and which sections of the route should be switched off.

If an earth fault, for example in phase T, occurs at a fault point indicated by a lightning symbol ERD, a displacement voltage Vo results at the measuring point which is less than the displacement voltage at the fault location. The phase voltages VSE and VRE increase up to the chained voltage. This is shown in the two diagrams a and b of FIG. 2.

Now, the invention provides that when a predefinable limit of this shift voltage V0 and falls below a predetermined minimum voltage of a phase conductor, here VTE of the phase conductor T by current and voltage measurement, the line impedance in this phase conductor up to the ground fault point and on the basis of the known line impedance depending Length unit is calculated by an impedance calculation, based on the phase voltage measured at the measuring location, the measured phase current at the measuring location and the total current at the measuring location by means of suitable evaluation factors, the distance up to the ground fault.

In view of the fact that the current in the grounded faulty phase conductor, here conductor T is often only small because of the compensation of the ground fault, it may be expedient to ensure sufficient measurement signals if, prior to the current and voltage measurement in the faulty phase conductor temporarily, the additional impedance ZIP is connected in parallel to the compensation impedance KIP of the star point STP and the current and voltage measurement is carried out for determination of the distance via the line impedance with an earth current increased by the parallel connection and then the additional impedance ZIP is switched off again.

The illustration according to FIG. 3 is intended to show that a line which is fed to the left by a transformer TRA, wherein a neutral point STP is connected to earth via a compensation impedance (Peter-senspule) and an activatable impedance ZIP, has several line sections NAB, NAB '. etc. may have. The sections can be separated by switching devices SEA, SEB, etc., and earth fault measurements in the sense of the inventions can be carried out at arbitrary locations of the line with the aid of distance protection devices DSG, here three are drawn. Via a data link DAB, all essential devices can communicate with each other, if necessary, of course, bidirectionally. This means that the evaluation results of the individual distance protection devices DSG can be transmitted to the other distance protection devices DSG, which then selectively sends switching signals to the switching devices SEA, SEB or also to the controlled switch SWI for switching on the impedance ZIP. Of course, depending on the conditions of the network switching commands can also be sent directly from a distance protection device DSG to a switching device or the controlled switch SWI.

With reference to the equivalent circuit diagrams of the symmetrical components according to FIG. 4, an example of a distance measurement is described. If a ground fault occurs, the fault current on the faulty line increases due to the parallel connected additional impedance ZIP. The additional impedance ZIP is usually designed as an ohmic resistance and, e.g. for 200 ms, the Petersen coil KIP is connected in parallel, the resistance being so dimensioned that an additional current of 10 to 300 amperes can be fed in.

One can represent the error case by the conversion into symmetrical components.

The following calculation shows that despite the load current, a distance measurement with the parameter Z1 = ZT-I with I ... length can be performed.

Up + Up + U ° = 0

U

measuring 0 -10 -Z ° = 0

With follows:

U mess + u 2 mess + Umes ° s = (l1 + l2) -Z1 + l ° z ° meas

With 7 AT 503 598 B1

Umess + U mess + U mess "UL1E follows:

With r n I1 + | 2 + | ° = | L1 and k0 = Z ° z1 -1 J follows: L; E = iu * 3i ° k0 Z1

With 3 l ° = ΙΣ follows:

U

L1E z1 -lLi + ΙΣ -k0 z1 = u

L1E I L1 + ll 'k0 = zri ^ DSG _ 2 ^ z ° Zi' L / 1 Ü2 ^ messi '·' i w w n

Ulie Ili ko Ις I Impedance displayed on a distance protection device up to the fault point zero impedance up to the fault location on an impedance related unit measured voltage of the faulty conductor at the measurement location in symmetrical components measured phase voltage at the measurement location measured phase current at the measurement location length independent factor for the consideration of Z0 summation current at the installation location of the Measuring instrument voltage at the fault location in symmetrical components distance up to the fault location

It has proven useful if the connection of the additional impedance and the current and voltage measurement taking place with it are delayed by at least one grid period, often by two or three grid periods, so that ground-fault wipers, ie transient short-term earth faults or transients do not distort the measurement.

In practice, sometimes a larger contact resistance occurs at the fault, which must not be neglected.

Such an error impedance Zfw is shown in FIG. 5 and it has been shown that an improved error localization can result if an adapted algorithm is used when the additional impedance is switched on.

The corrected formula that is the starting point for the calculation is: 71 _ U | _1E ~ ^ FW ~ ^ FW _ 7 '| > L1 + lZ'k0 " 1'

The derivation by means of symmetrical components is as follows:

Up + Up + u £ = UFW

U 1 -I 1 -Z 1 + U 2 -l 2 -Z 2 + U 0 -10 -Z 0 = I Z

umess 1 umess 1 ^ u mess 1 'FW FW

With Z1 = Z2 follows:

Ujs + Umess + U mes ° s = (| 1 + l2) 'Z1 + l ° · Ζ ° + IFW -Z FW

U mess + U mess + U mess " U L1E

UliE ~ ^ FW '^ FW _ ^ | 1 + | 2 ^ + | 0.Z_ UL1E " ΥΖ * = | 1+ | 2+ | 0. | 0 +, 0 | |! -71 7 'L1 r + l2 + l ° = l

Ul1E '^ FW' ^ FW _ | 0 + | 0 Z z1 = L1 'z1 -l ° +, ° ~ =, ° Z1 Ή = l ° k0 3

Ul1E " 'fW Zpw _ 0. Z1 - = IL1 + ΟΊ 'K 0

3 · l ° = U

= lu + lj; kQ

Ul1E ~ * FW 'Z PW Z1 ^ 1 _ Ul1e' IfW Zpw, z = lL1 * ls * o 'where: 9 AT 503 598 B1 Z1 measured impedance up to the fault Z ° measured zero impedance up to the fault

Zi on a kilometer related impedance

Umess measured voltage at the installation site of the meter

Ulie measured phase voltage at the installation site of the meter lu measured phase current at the installation of the meter

Ko Length-independent factor to take account of Z0 ΙΣ total current at the installation site of the measuring instrument UF voltage at the fault location I distance to the fault location

Zfw fault impedance

Upw voltage dropping at the fault impedance

Ifw power at the fault location

In practice, it has also been shown that the fault impedance represents an almost purely ohmic resistance whose estimation can be made as follows:

Since, as mentioned above, the fault impedance can be regarded as purely resistive, only the real part is taken from this.

UL1E ZFW = real (- ^) 'ς

If contact resistances of approx. 20-30 ohms are detected, it is recommended to use this adaptation.

The derivation of this formula is easily understood from Fig. 5, which shows a simplified section of Fig. 1, in which the capacity of the faulty line has been neglected and in which an impedance is now located at the fault location.

Since typical impedance values of line lengths amount to approx. 10-15 ohms for one line section, it can be seen that the error resistance dominates the loop above approx. 20 ohms and therefore it can be deduced from this with a very good approximation.

The fault current can be estimated according to the following formula.

Ifw = Ις + Ikap lkap is the capacitive current that is caused only by the faulty line section. The size of this stream can already be determined in advance by tables, measurements, etc., since the capacitive contribution is known per unit of length. As shown in Fig. 6, each line part provides some contribution. FIG. 6 shows that the capacitive currents present at each distance protection device DSG of a line part occur summed up at the control point. The coil KIP is dimensioned so that the coil current must be equal to the sum of all capacitive currents.

1 UL1E

Then the well-known formula: Z = ----- is extended by the term: -Ipv / Zpw, where the lLi + l £ k0 capacitive currents must be evaluated with the ratio of the displacement voltage to the rated voltage, since the displacement voltage also changes associated

Claims (14)

10 AT 503 598 B1 change capacitive currents: 'FW = |. All required measurements can be made with a conventional protective device, generally a distance protection device, which forms the hardware basis for the method according to the invention. It should be clear to those skilled in the art from the above that measurement errors due to grounding impedances can be compensated at the measuring station and ground fault location. By measuring at different locations and by signal comparison method, preferably direction comparison method, even more accurate fault location and, if desired, a selective shutdown is possible. It should again be summarized that for the purposes of the present invention, a particular criterion for the decision as to whether a measurement is carried out and further consequences are drawn is to be the magnitude of the displacement voltage. Furthermore, the monitored network element, e.g. a line is switched off when fault location, but only an impedance measured, which leads to the calculation and output of the error removal. The corresponding message can be transmitted by suitable means and also evaluated centrally. The shutdown of network sections can then be released individually, depending on the mode of operation, routing or other peculiarities. Although it is preferable to measure with the fundamental frequency of the network, it should be noted that an increase in accuracy is possible if harmonics and / or interharmonics of current and voltage are taken into account in the measurement. If a ground fault remain, which can be determined by the displacement voltage, and after a short connection of the additional impedance no clear measurement had been carried out, one could by renewed, e.g. also manually started short connection of the additional impedance perform a new measurement. In principle, a new measurement, even without additional impedance, take place, if the first measurement has not brought plausible results. For example, this would be important if a dual earth fault would form. The first ground fault point was e.g. recognized correctly by the method, but it is switched off automatically due to the double ground fault. However, there is still a new ground fault point and this can be found and measured by retraining especially with the renewed connection of the additional impedance. In principle, however, the measurement can also take place without switching on the additional impedance. 1. A method for the distance detection of ground faults in 3-phase electric power networks operated with earth-fault compensated with at least one neutral point (STP), which is connected via a, inductive share Kompensationsimpedanz (KIP) to earth, wherein at least one measuring location in each phase Constant current and voltage measured and monitored are characterized in that when exceeding a predetermined limit of the displacement voltage (V0) and falls below a predetermined minimum voltage of a phase conductor by current and voltage measurement of the line resistance (Z1) in this phase conductor up to the Erd 1 1 AT 503 598 B1 connection point and on the basis of the known line resistance per unit length by an impedance calculation, starting from the measured phase voltage (UUe) at the measuring location taking into account the grounding impedances at the measuring location and at the fault location, the distance is calculated up to the ground fault. 2. The method according to claim 1, characterized in that before the current and voltage measurement in the earth-faulty phase conductors temporarily an additional impedance (ZIP) connected in parallel to the compensation impedance (KIP) of the neutral point (STP) and the current and voltage measurement for determining the distance over the line impedance with an increased by the parallel circuit ground current (ΙΣ) and then the additional impedance (ZIP) is switched off again. 3. The method of claim 1 or 2, characterized in that the connection of the additional impedance and taking place with this current and voltage measurement is delayed by at least one grid period. 4. The method according to any one of claims 1 to 3, characterized in that as additional impedance (ZIP) an ohmic resistance (R) is connected in parallel to the compensation impedance (KIP) of the neutral point. 5. The method according to any one of claims 1 to 4, characterized in that as an additional impedance, an inductance is connected in parallel to the compensation impedance of the neutral point. 6. The method according to any one of claims 1 to 5, characterized in that the phase voltage (Uue), the phase current (lLi) and the sum current (ΙΣ) determined at the measuring location and from the impedance (Z1) are calculated to the ground fault point, thereby according to Z1 = to a unit of length related impedance results in the distance (I) to the ground fault point. 7. The method according to any one of claims 1 to 5, characterized in that a consideration of the error impedance (Zfw) by., 1 _Uue -Ifw '^ fw, L ~ + | k = ^ 1 1L1 + ΙΣ K0, where Ifw is the current at the fault location. 8. The method according to claim 7, characterized in that a consideration of the capacitive currents by Ifw = Ις + Ikap takes place. 9. The method according to claim 8, characterized in that the capacitive currents according to 1 2 AT 503 598 B1 'FW kap u ü o measuring measured by the ratio of the displacement voltage (U ° mess) are rated to the rated voltage (Unenn). 10. The method according to any one of claims 1 to 9, characterized in that in the presence of non-plausible measurement results again and also temporarily an additional impedance is connected in parallel to the compensation impedance of the neutral point and the current and voltage measurements for the calculation of the ground fault distance are repeated. 11. The method according to any one of claims 1 to 10, characterized in that after fault location calculation, the faulty line is switched on or both sides off. 12. The method according to any one of claims 1 to 11, characterized in that the current and voltage measurement is performed at the fundamental frequency of the network. 13. The method according to claim 12, characterized in that harmonics and / or interharmonics of current and voltage are taken into account in the measurement. 14. The method according to any one of claims 1 to 13, characterized in that the measurement is carried out at least two, spaced apart measuring locations of a line having a plurality of separable by switching means line sections, and based on these measurements, a faulty line section is selectively separated , For this purpose 3 sheets of drawings