DE10307668B3 - Determining parameters of Petersen-coil compensated network without de-tuning the coils, by feeding composite current into zero-phase system, and measuring voltages - Google Patents

Abstract

The method involves feeding a composite current into the zero-phase system of the network. The composite current comprises a current of a first amplitude and frequency, superimposed on a current of a second amplitude and frequency. The size and angle of two voltages are measured for the two frequencies, the angle being referenced to the associated feed current. Further calculations are preformed to determine the absolute de-tuning V 5 0Hz.

Description

The The present invention relates to a method for the determination of Parameter of a deleted one Net without detuning the Petersen coil, which is also very symmetrical Networks is suitable. These determined network parameters can be found under Compliance with specified parameters for readjustment of a Petersenspule be used.

The earth fault quenching greatly reduces the current across the fault location in the event of a single-ended ground fault. If the network of Figure 1 is described with the aid of the symmetrical components, the unbalance causes a coupling of the component systems, as shown in simplified form in Figure 2. The advantage of this representation is that Figure 2 is valid for both the healthy and the unipolar error case. Neglecting the longitudinal impedance of the cables and summarizing the earth capacitances gives Figure 3. In most cases the zero impedance of the transformer in Figure 3 is neglected. From Figure 3 it can be seen that the current across the fault location is minimal when the Petersen coil is adjusted so that the reactive components consisting of the series connection of the Petersen coil and the mostly neglected transformer impedance compensate for the conductor-earth capacitance. The network is tuned to resonance. The remaining current across the fault location is essentially limited by the equivalent resistance Rp. This equivalent resistor includes the total losses of the zero system ie the losses of the Petersen coil, the losses of the transformer in the zero system, the losses of the line impedances and the leakage losses to earth. Practice has shown that the losses of the Petersen coil account for only about 40% of total losses. Since the Petersen coil is used to compensate for the capacitive current through C _E , the Petersen coil is in practice not indicated in H but in A, using the strand nominal voltage U _{1 of} the network for the specification. This is in the case of a full earth fault on the Petersen coil. When describing the network with symmetrical components and the complex ^rotation operator a = e ^{j2π / 3} , U ₁ corresponds to the stress of the unloaded positive sequence system.

The Petersen coil can be connected directly to the neutral point of a transformer or via a grounding transformer. In practice, it has been shown that the active losses are reduced over the lines when the Petersen coil is placed in the vicinity of cable networks, the supply per km line length almost 50 times the capacitive current compared to overhead line. On the other hand, today extinguishing districts are very often merged, so that in today's networks in a fire-fighting district not only with a central Petersen coil, but with several and distributed throughout the extinguishing district Petersen coils must be expected. For the control usually only one coil is used and set the remaining coils fixed. An information transfer to the controller over the number and size of the distributed set and fixed Petersen coils usually does not exist. For this reason, the absolute compensation in A has already developed with the introduction of the controller EFC30 in 1991 as a new standard, as in this case no information about the distributed in the extinguishing district Petersen coils are required. However, the current across the fault location in the event of a full ground fault can be completely calculated, since this results from the geometric sum of the active current and the absolute detuning of the Petersen coil. I U = I rp + j (I CE - I LP ) (17)

The absolute detuning in A is thus too ν 50Hz = I LP - I CE (18)

With positive values when the current through the Petersen coil is greater than the capacitive current is.

This current is essential for the determination of the danger due to step voltage and contact voltage at the fault location. This current has always been determined using the scaling of the Petersen coil and neglecting the zero impedance of the transformer. However, due to the grid sizes used today, the transformer zero impedance already reaches values of 10% to 20% of the Impe danz the tuned Petersen coil and is therefore no longer negligible for determining the extinguishing current. Due to the series connection of the impedances, the actual extinguishing current is considerably smaller than that specified only with the aid of the scaling of the Petersen coil.

Out Picture 2 shows that for the detection of a switching action or to determine the vote a minimum imbalance of the network is needed. In today's Cable networks, this is very often no longer given, so a recognition a switching operation or a correct tuning of the Petersen coil difficult or impossible is. Furthermore aggravate the interference especially at small displacement voltages by load currents the correct detection of switching operations and the correct tuning by the Petersen coil, as already mentioned in the article "Control of Petersen Coils, ISTEE 2001 " becomes.

Methods of tuning a ground fault quench coil to resonance or to a desired compensation value are currently known primarily for healthy nets. For this purpose, some methods which work according to the resonance method require a sufficient displacement voltage U _0, for example EZR 2 from Spezielektra or EFC30 from Trench. In today's cable networks is usually not given by the symmetrical structure of the cable or by the twisting of the conductor. In addition, an adjustment of the Petersen coil is required for a calculation cycle. Due to the necessary adjustment of the Petersen coil, this calculation cycle can take up to several minutes and requires constant network conditions during the calculation. As a triggering operation for the tuning attempt, which causes an adjustment of the Petersen coil is a change in the displacement voltage. If the cause of the change in the displacement voltage is not a change in the network size, then the Petersen coil leaves the matched state for a longer time during the search process. If a ground fault occurs during this search, the network is not optimally compensated.

The other methods, such as according to WO 86/03350 or US 5 559 439 work according to a reduced circuit diagram so that the tuning of the earth-fault quenching coil in the healthy grid is successful for small displacement voltages. In the method according to the patent US 5 559 439 the zero impedance of the network including the earth leakage quench coil is measured in healthy condition. This method has also been described by Leitloff, V Bergeal, J, [et al.] In the article "Measurement of the parameters of a compensated network by injection of a current into the neutral point" in Elektrizitätswirtschaft, vol. 93 (1994), issue 22. The measurement determines the deviation from the full compensation. To determine the parameters of the network, the actual size of the Petersen coil is additionally required. If additional Petersen coils are present in the same network, it is difficult to detect them and consider them for the calculation of the network parameters. Practice has shown that certain current quantities lead to settling times in the minute range. In addition, symmetrical networks lack an incentive criterion for checking the current vote. Furthermore, the calculation is very inaccurate in large moods. In addition, during the measuring cycle consisting of a period without power supply and a period with power supply a constant displacement voltage or unbalance of the network is required, which is not the case with many networks. As described in the article "Control of Petersen Coils, ISTEE 2001", a load-dependent cross-talk of the positive sequence system takes place on the zero system. For this reason, it is not possible to determine the current or necessary voting in some networks by averaging over a few minutes.

In the patent US 5 559 439 a constant set current is switched. However, switching operations in the network can greatly change the network parameters. The feeding current can thus lead to unacceptable unbalance voltages in the case of small networks or, in the case of large networks, results in too little change in the residual voltage.

In the EP 0 823 057 B1 Only one method is described, with a switching action in the network is recognizable in very symmetrical networks. This method itself can not be used to tune the Petersen coil and serves only as a supplement to other methods. Similarly, the feed with a deviating from 50 Hz frequency is used only to detect a switching operation but not to determine the network parameters or the necessary readjustment of the Petersen coil.

something similar applies to the method of patent WO 86/03350 in which it is assumed that will be the biggest displacement voltage is in the resonance point. The method requires a minimum displacement voltage and does not work with symmetric networks, as you usually do with cable networks are to be found.

In the patent DE 195 25 417 C2 is a combination of a stepped earth fault extinguishing coil in connection with an auxiliary transformer. By generating a "compensation current", this combination permits compensation of the reactive component as well as of the normally remaining resistive active current via the fault location. The "compensation current" is set using known methods for calculating the necessary parameters in the "healthy network". Only the possibility of perfect compensation at the fault location is described, but not how the "compensation current" is set from the available measurements in the substation in case of a ground fault. A necessary readjustment of the "compensation current" as a result of switching off power supplies during a ground fault is not described.

in the WO 02/15355 A2 is a method for determining the detuning used by feeding a frequency not equal to 50 Hz. It will assuming, however, that no distributed in the network Petersen coils available. The entire inductive reactive power becomes central and assumed to be known. The recalculation to 50 Hz delivers completely wrong values if this assumption does not apply. It is mentioned that the measurement is repeated at different frequencies, but only to find an average value in the sense of the best possible approximation. It is always calculated only with the known coil inductance. Likewise, no consideration the transformer zero impedance

The Control of a Petersen coil is a preventive measure in the case of a single-pole Ground fault. By a correct compensation the current over the Fault reduced. This will on the one hand to the destruction reduces the fault and on the other hand, the step and Berührspannungen greatly reduced in the area of the fault. By the increasing Cabling and expansion of the extinguishing districts reach the capacitive currents Values up to 1000A, so action to reduce the currents across the fault becoming more important.

By the disconnection of line segments becomes the one to be deleted line capacity changed. This will overflow the electricity the fault location changes in the event of a ground fault and can exceed specified limits. Usually, among other things, the extinction limit according to VDE 228 is exceeded.

The known methods recognize changes in the network only if one is sufficient high displacement voltage exists and when the displacement voltage while of the calculation cycle is reasonably constant. For the calculation is for a few minutes the Petersenspule adjusted from the last tuning point. Because a distinction between an actual switching action and a load-dependent crosstalk from the co-system only by measuring the displacement voltage not possible is, a calculation also takes place when the displacement voltage by load-dependent crosstalk changes from the co-system. Another reason for a change the displacement voltage without change the compensating conductor-earth capacitance are switching operations in parallel guided Systems that influence the zero voltage through capacitive couplings.

Out these reasons should be a change the line length, already before a pending ground fault, detected as soon as possible and the Petersen coil as quickly as possible be reconciled.

• a. Einspeisen eines zusammengesetzten Stromes in das Nullsystem des gelöschten Netzes,
• b. Wobei sich der Strom aus der Überlagerung des Stromes mit der Amplitude Î_f1 und der Frequenz f₁ und des zweiten Stromes mit der Amplitude Î_f2 und der Frequenz f₂ zusammensetzt.
• c. Messen der Spannungen U _{NE_f1} und U _{NE_f2} nach bekannten Verfahren nach Betrag und Winkel für die beiden Frequenzen. Der Winkel bezieht sich auf den zugehörigen Einspeisestrom.
• d. Ermitteln der Admittanz für beide Frequenzen:
  
• e. Mit Berücksichtigung der Trafo-Nullinduktivität kann mit Schritt k. fortgesetzt werden.
• f. Ohne Berücksichtigung der Trafo-Nullinduktivität ist die Nulladmittanz für die Frequenz f₁ bzw. f₂:
  
• g. Der Wirkanteil Rp der Ersatzschaltung ergibt sich unmittelbar aus dem Realteil der Nulladmittanz.
  
• h. Berechnung der Erdkapazität C_E des Netzes und die Gesamtinduktivität der Petersenspule L_P inklusive den vorhandenen Fixspulen aus den beiden Imaginärteilen durch Umformung
  
• i. Berechnung der absoluten Verstimmung ν_50Hz in A für 50 Hz unter Berücksichtigung der Spannung U₁ des Mitsystems
  
• j. Weiter mit Schritt p.
• k. Aufstellen der folgenden Relation durch die Messung der Verlagerungsspannung U _{0_fx} mit der Frequenz x an den Klemmen des Trafos für die Frequenz x:
  
• l. Die Nulladmittanz für die Frequenz x ergibt sich mit:
  
• m. Der Wirkanteil ist direkt aus dem Realteil der Nulladmittanz ablesbar:
  
• n. Durch Umformen erhält man analog zu Gleichung (5) aus den Imaginärteilen der Gleichung (10) für die Frequenzen f₁ und f₂ unter Berücksichtigung des Spannungsverhältnisses K _fx:
  
• o. Berechnung der absoluten Verstimmung ν_50Hz in A für 50 Hz unter Berücksichtigung der Spannung U₁ des Mitsystems:
  
• p. Anzeigen der ermittelten Netz-Parameter.

Wiederholen der Punkte a. bis p.According to the invention, the method for determining the parameters of a quenched net without detuning the Petersen coil, which is also suitable for very symmetrical grids, is characterized by the following steps

• a. Injecting a composite stream into the null system of the deleted network,
• b. Wherein the current from the superimposition of the current with the amplitude Î _f1 and the frequency f ₁ and the second current with the amplitude Î _f2 and the frequency f ₂ composed.
• c. Measuring the voltages U _{NE_f1} and U _{NE_f2} according to known methods by amount and angle for the two frequencies. The angle refers to the associated feed-in current.
• d. Determining the admittance for both frequencies:
  
• e. Taking into account the transformer zero inductance, step k. to be continued.
• f. Without consideration of the transformer zero inductance, the zero admittance for the frequency f ₁ or f _{2 is} :
  
• G. The effective component Rp of the equivalent circuit results directly from the real part of the zero admittance.
  
• H. Calculation of the earth capacitance C _{E of} the network and the total inductance of the Petersen coil L _P including the existing fixed coils of the two imaginary parts by forming
  
• i. Calculation of the absolute detuning ν _50Hz in A for 50 Hz taking into account the voltage U _{1 of} the co-system
  
• j. Continue with step p.
• k. Establishing the following relation by measuring the displacement _voltage U _{0_fx} with the frequency x at the terminals of the transformer for the frequency x:
  
• l. The zero admittance for the frequency x is given by:
  
• m. The active component can be read directly from the real part of the zero admittance:
  
• n. By transformation, analogously to equation (5), we obtain from the imaginary parts of equation (10) for the frequencies f ₁ and f ₂ taking into account the stress ratio K _fx :
  
• o. Calculation of the absolute detuning ν _50Hz in A for 50 Hz taking into account the voltage U _{1 of} the positive sequence:
  
• p. Display of the determined network parameters.

Repeat the points a. to p.

The new method measures at a frequency different from 50 Hz. The 50 Hz components are filtered out and do not affect the determination of the parameters. By a parameterization maximum values for the change of the displacement voltage U ₀ caused by the current source or maximum current values for the current source can be specified.

By the simultaneous feeding of two streams with two different ones Frequencies and simultaneous evaluation of the measurement takes place Calculation very fast and at the same time. It does not have to successive measured values or network states are compared.

By monitoring the displacement voltage, the size of the injected currents is adjusted so that on the one hand, a sufficiently large displacement voltage at large moods arises or on the other hand, the limits for U _{0 is} not exceeded for very small networks.

When trigger criterion for one Calculation can be a change the 50Hz shift voltage be.

at symmetric networks must be a change the network does not necessarily change the displacement voltage to lead. In this case will be constantly fed a mixed stream and the monitoring of network parameters takes place constantly. A change the network parameter leads to a calculation cycle and if necessary to readjust the Petersen coil.

The Petersen coil is usually calibrated in amperes. In today's usual method of tuning Petersen coils, the zero inductance of the transformer is not taken into account. The result is a capacitive current displayed too large. By measuring the voltage U ₀ at the secondary terminals of the transformer and the displacement voltage U _NE also Nullinduktivität of the transformer can be determined and taken into account during operation. In the case of tapped transformers, the zero inductance is also dependent on the current tap position of the transformer.

The new measuring method also eliminates the disadvantages of measuring with the open triangle. Due to the summation of three large values, this measurement is not suitable for controllers with a search for a resonance maximum. The error vector of U ₀ can lead to a completely wrong control behavior. Due to the feed in the zero system, all three voltages on the converter have the same direction. Tolerances of the voltage transformers are therefore no longer so strong.

The infeed can be made via a power development winding of the Petersen coil or via an auxiliary transformer. The voltage U _NE can be done directly at the supply or via the voltage measurement winding of the Petersen coil. The measurement of the zero voltage U ₀ can be done with the known methods of open delta winding on the transformer or on the busbar. The zero currents can be measured either between the Petersen coil and the ground or at the transformer by means of a cable conversion transformer or by means of the Holmgreen circuit.

• Bild 1: Ein gelöschtes Drehstromnetz mit einem Abgang mit zwei Leitungssegmenten. Die natürliche kapazitive Unsymmetrie des Netzes ist vereinfacht als konzentriertes Element zwischen den beiden Leitungsabschnitten dargestellt.
• Bild 2: Darstellung des obigen Netzes mit Hilfe der Symmetrischen Komponenten.
• Bild 3: Reduktion des Bildes 2 auf die für die Bestimmung der Netzparameter und Regelung wesentlichen Komponenten

In the following the invention will be described by way of example with reference to the following diagrams:

• Fig. 1: One deleted three-phase system with one outlet with two line segments. The natural capacitive imbalance of the network is simplified as a concentrated element between the two line sections shown.
• Figure 2: Representation of the above network using the Symmetrical Components.
• Fig. 3: Reduction of Fig. 2 to the components essential for the determination of the network parameters and control

The controller evaluates the measurement of the neutral-to-ground voltage U _NE, the displacement voltage U ₀ at the terminals of the transformer, and the current of current source I _SQ. For additional evaluations, the zero current can be measured directly with a cable conversion transformer on the transformer, on the Petersen coil or via the Holmgreen circuit.

in the Figure 1 shows a three-phase system with one outlet. It was for the streams and tensions the older ones Term used to better delineate the symmetrical To obtain components. The supply of the network is done via a Transformer. The power is supplied via the star point of the supply transformer or with the help of a neutralizer. The coupling can alternatively via a Auxiliary transformer or over The performance development of the Petersen coil takes place.

The Method is used to determine the current through the fault location in case a single-pole low-impedance ground fault and thus for determination the necessary adjustment of the ground fault extinguishing coil as a preventive measure. The measurement can be repeated at any time.

in the Figure 2 is the result of the transformation of the network described above with the help of the "Symmetrical Components ". The transformation takes place according to the known rules and will not be here described. In the picture, the coupling of the systems through the concentrated imaginary asymmetry of the network dC already drawn. In the healthy Operation is the imbalance usually the capacitive unbalance of the conductors against earth of the network.

• – Die Impedanz der Last ist üblicherweise um mindestens den Faktor 10 höher als die Längsimpedanzen des Trafos und der Leitung, und kann in erster Näherung vernachlässigt werden.
• – Die Impedanz der kapazitiven Unsymmetrie dC ist wesentlich größer als die Impedanz Z _1Tr, Z _1A1, Z _2Tr, Z _2A2
• – Die Spannung U ₁ und die verbleibende Innenimpedanz bestehend aus Z _1Tr, Z _1A1, Z _2Tr, Z _2A2 und dC können durch die Hochohmigkeit der kapazitiven Unsymmetrie auch als Stromquelle mit einer Frequenz von 50 Hz betrachtet werden.
• – Im Nullsystem sind die Leitungsimpedanzen vernachlässigbar, sodass alle Kapazitäten zu einer Leiter-Erde Kapazität C_E zusammengefasst werden können.
• – Die ohmschen Verluste der Trafo-Nullimpedanz sind vernachlässigbar im Vergleich zur Null-Induktivität des Trafos
• – Sämtliche Verluste des Nullsystems werden im Widerstand R_P zusammengefasst.
• – Die Stromeinspeisung in das Nullsystem wird als einstellbare Stromquelle realisiert. Mit der Stromquelle können gleichzeitig Ströme mit unterschiedlicher Amplitude, Frequenz und Phasenlage erzeugt werden.

For the further considerations, the following simplifications are made for Figure 3

• - The impedance of the load is usually at least a factor of 10 higher than the longitudinal impedances of the transformer and the line, and can be neglected to a first approximation.
• The impedance of the capacitive asymmetry dC is substantially greater than the impedance Z _1Tr , Z _1A1 , Z _2Tr , Z _2A2
• - The voltage U ₁ and the remaining internal impedance consisting of Z _1Tr , Z _1A1 , Z _2Tr , Z _2A2 and dC can be considered by the high impedance capacitive unbalance as a power source with a frequency of 50 Hz.
• - In the zero system, the line impedances are negligible, so that all capacitances can be combined to a conductor-earth capacitance C _E.
• - The ohmic losses of the transformer zero impedance are negligible compared to the zero inductance of the transformer
• - All losses of the zero system are summarized in the resistor R _P.
• - The power supply to the zero system is realized as an adjustable current source. The current source can simultaneously generate currents with different amplitude, frequency and phase angle.

In the controller, the voltages U _Re , U _SE , U _TE and U _{NE are} measured against ground and the three phase currents I _R , I _S and I _T. From these, the symmetrical components U ₁ , U ₂ , U ₀ and I ₁ , I ₂ , and I ₀ can be calculated according to the known methods. The zero voltage U ₀ and the zero current I ₀ can alternatively also be measured directly with the aid of the known methods.

• – Die Messung kann jederzeit wiederholt und auf Plausibilität überprüft werden.
• – Durch Einspeisung von Strömen und Auswertung der Ströme und Spannungen mit einer von 50 Hz unterschiedlichen Frequenz wird der "Störeinfluss" der Unsymmetrie beseitigt.
• – Die Messung der Spannungen für die von 50 Hz abweichenden Frequenzen über das offene Dreieck ist wesentlich genauer, da eine Summenbildung von drei großen Werten, wie es beim 50Hz Drehstromsystem erfolgt, nicht statt findet.
• – Die Messung kann kontinuierlich erfolgen.
• – Der Messzyklus ist im wesentlichen nur vom verwendeten Filteralgorithmus abhängig.
• – Die Messung kann auch auf Anforderung, z.B. nach Änderung der 50 Hz Verlagerungsspannung oder in zyklischen Zeitabständen z.B. 1h erfolgen.
• – Die Messung liefert die Netzparameter auch für vollkommen symmetrische Netze.
• – Schalthandlungen werden mit diesem Messverfahren auch in symmetrischen Netzen erkannt.
• – Lastabhängiges Übersprechen aus dem 50 Hz Drehstromsystem auf das Nullsystem werden unterdrückt.
• – Die Messung erfasst alle im gelöschten Netz installierten Petersen-Spulen, eine komplizierte Berücksichtigung von verteilten Petersen-Spulen ist nicht notwendig.
• – Durch Auswertung der 50 Hz Komponenten kann auch die Aufteilung der Unsymmetrie zu den einzelnen Leitern erfolgen.
• – Durch die einstellbare Stromamplitude können geforderte Grenzwerte in Be zug auf maximale Änderung der Verlagerungsspannung eingehalten werden.
• – Durch die einstellbare Stromamplitude können benötigte Spannungsamplituden für eine ausreichend genaue Messung der Admittanzen auch bei stark verstimmten Netzen erreicht werden.
• – Es können auch über mehrere Messungen statistische Mittelwerte durchgeführt werden.
• – Für die Berechnung der tatsächlichen Leiter-Erde Kapazität kann die Null-Induktivität, die üblicherweise unbekannt ist, durch eine zusätzliche Messung der Nullspannung U ₀ an den Trafo-Klemmen oder an der Sammelschiene berücksichtigt werden.
• – Die Messung erfolgt, ohne einer Verstellung der Petersen-Spule, wodurch die mechanische Beanspruchung der Petersen-Spule stark reduziert wird. Diese kann vor allem in Netzen mit Übersprechen des Laststromes auf das Nullsystem sehr groß sein, da bei jeder Laständerung ein Suchlauf gestartet wird.
• – Während der Messung wird die Petersen-Spule nicht verstellt, sodass die geforderte Kompensation bei den meisten Messaufgaben beibehalten wird. Zum Vergleich wird beim Resonanzverfahren bei symmetrischen Netzen der gesamte Verstellbereich der Petersen-Spule mehrfach nach einem Resonanzmaximum abgesucht.
• – Die Frequenzen können bei großer Verstimmung so gewählt werden, dass in der Nähe der Eigenfrequenz des Netzes gemessen wird. Dadurch wird auch für stark verstimmte Netze eine genaue Messung erreicht.
• – Durch die schnelle Erfassung der Änderung der Abstimmung des Netzes kann eine schnelle und zielgerichtete Abstimmung der Petersen-Spule erfolgen.
• – Bei der Bestimmung der Kapazität C_E nach Gleichung (15) wirken sich die Fehler der Holmgreenschaltung nicht so stark aus, da nicht die Summe von drei großen Strömen gebildet und bewertet werden muss.

The advantages of the method are:

• - The measurement can be repeated at any time and checked for plausibility.
• - By feeding in currents and evaluating the currents and voltages with a frequency different from 50 Hz, the "disturbing influence" of the asymmetry is eliminated.
• - The measurement of the voltages for the frequencies deviating from 50 Hz across the open triangle is much more accurate, since there is no summation of three large values, as is the case with the 50Hz three-phase system.
• - The measurement can be done continuously.
• - The measuring cycle essentially depends only on the filter algorithm used.
• - The measurement can also be made on request, for example, after changing the 50 Hz shift voltage or in cyclic intervals eg 1h.
• - The measurement provides the network parameters even for perfectly balanced networks.
• - Switching operations are also detected in symmetrical networks with this measuring method.
• - Load-dependent crosstalk from the 50 Hz three-phase system to the zero system is suppressed.
• - The measurement covers all Petersen coils installed in the quenched network, a complicated consideration of distributed Petersen coils is not necessary.
• - By evaluating the 50 Hz components, the distribution of the asymmetry to the individual conductors can also be made.
• - Due to the adjustable current amplitude required limit values can be maintained in relation to Be the maximum change in the displacement voltage.
• - Due to the adjustable current amplitude required voltage amplitudes for a sufficiently accurate measurement of the admittances can be achieved even with heavily detuned networks.
• - It is also possible to carry out statistical averages over several measurements.
• - For the calculation of the actual phase-earth capacitance, the zero inductance, which is usually unknown, can be taken into account by an additional measurement of the zero voltage U ₀ at the transformer terminals or at the busbar.
• - The measurement is done without an adjustment of the Petersen coil, which greatly reduces the mechanical stress on the Petersen coil. This can be very large, especially in networks with crosstalk of the load current to the zero system, since a search is started with each load change.
• - During the measurement, the Petersen coil is not adjusted so that the required compensation is maintained for most measurement tasks. For comparison, in the resonance method in symmetrical networks, the entire adjustment range of the Petersen coil is searched several times for a resonance maximum.
• - The frequencies can be selected in a large detuning that is measured in the vicinity of the natural frequency of the network. As a result, an accurate measurement is achieved even for heavily detuned networks.
• - By quickly detecting the change in the tuning of the network can be done quickly and targeted tuning of the Petersen coil.
• - When determining the capacitance C _E according to equation (15), the errors of the Holmgreenschaltung not so strong, since not the sum of three large currents must be formed and evaluated.

Claims (14)

Method for determining the parameters of a deleted network without detuning the Petersen coil characterized by the following steps: a. Injecting a composite stream into the null system of the deleted net b. Wherein the current from the superimposition of the current with the amplitude Î _f1 and the frequency f ₁ and the second current with the amplitude Î _f2 and the frequency f ₂ composed. c. Measuring the voltages U _{NE_f1} and U _{NE_f2} according to magnitude and angle for the two frequencies. The angle refers to the associated feed-in current. d. Determining the admittance for both frequencies:

e. Taking into account the transformer zero inductance, step k. to be continued. f. Without consideration of the transformer zero inductance, the zero admittance for the frequency f ₁ or f _{2 is} :

G. The effective component Rp of the equivalent circuit results directly from the real part of the zero admittance.

H. Calculation of the earth capacitance C _{E of} the network and the total inductance of the Petersen coil L _P including the existing fixed coils of the two imaginary parts by forming

i. Calculation of the absolute detuning ν _50Hz in A for 50 Hz taking into account the voltage U _{1 of} the co-system

j. Continue with step pk Establish the following relation by measuring the displacement _voltage U _{0_fx} with the frequency x at the terminals of the transformer for the frequency x:

l. The zero admittance for the frequency x is given by:

m. The active component can be read directly from the real part of the zero admittance:

n. By transformation, analogously to equation (5), we obtain from the imaginary parts of equation (10) for the frequencies f ₁ and f ₂ taking into account the stress ratio K _fx :

o. Calculation of the absolute detuning ν _50Hz in A for 50 Hz taking into account the voltage U _{1 of} the positive sequence:

p. Display of the determined network parameters. - repeating the points a. to p. A method according to claim 1, characterized in that the power supply in the star point of Feed transformer takes place. Method according to claim 1, characterized in that that the current feed in the neutral point of a zero point generator he follows. Method according to one of the preceding claims, characterized characterized in that the coupling of the power supply via a Auxiliary transformer or over A performance development of the Petersen coil takes place Method according to one of the preceding claims, characterized characterized in that the results of the determination of the parameters of the deleted one Net for the tuning of the Petersen coil can be used. Method according to one of the preceding claims, characterized characterized in that in symmetrical networks, the measurement permanently he follows. Method according to one of the preceding claims, characterized characterized in that a change of 50 Hz displacement voltage one or more measuring cycles for determination the parameter of the deleted Trigger network. Method according to one of the preceding claims, characterized characterized in that by an external signal one or more Measuring cycles for determining the parameters of the deleted network are triggered. Method according to one of the preceding claims, characterized characterized in that the frequencies are chosen so that they are in the Near the Resonance frequency of the network are. Method according to one of the preceding claims, characterized characterized in that by consideration The 50 Hz measurements also show a breakdown of the unbalance to the individual ladders takes place. Method according to one of the preceding claims, characterized characterized in that by specifying a maximum change the displacement voltage of the feed current up to an associated maximum Value is regulated. Method according to one of the preceding claims, characterized characterized in that by specifying a minimum voltage change the supply current is regulated to a maximum predetermined value. Method according to one of the preceding claims, characterized characterized in that in noisy networks averaging over several Measurements are made Method according to one of the preceding claims, characterized in that the calculation of the conductor-earth capacitance is carried out directly from the measurement of the displacement voltage U ₀ and the current I ₀ at the frequency x: