WO1991009451A1

WO1991009451A1 - Filter arrangement

Info

Publication number: WO1991009451A1
Application number: PCT/AT1990/000118
Authority: WO
Inventors: Gerhard Titscher; Günter Moraw; Walter Richter
Original assignee: Elin Energieversorgung Gesellschaft M.B.H.
Priority date: 1989-12-07
Filing date: 1990-12-07
Publication date: 1991-06-27
Also published as: FI922617A; HU9201884D0; EP0502929A1; BR9007897A; HUT61140A; CA2074260A1; FI922617A0; JPH05502364A; CS611090A3

Abstract

A filter arrangement is useful for filtering and damping harmonics and for shifting resonance points in electric networks. To this end, a first energy-absorbing damping element (Rp21) is connected in parallel with a series arrangement consisting of a first inductance (Lp2), a first capacitance (Cp21) and a fourth capacitance (Cp22). This parallel arrangement is connected in series with a parallel path consisting of a second inductance (Lp3) and a second capacitance (Cp3), as well as with a third capacitance (C1). In addition, a second energy-absorbing damping element (Rp41) is connected in parallel with the series arrangement consisting of the fourth capacitance (Cp22) and the second capacitance (Cp3). The use of this filter arrangement in the case of two tuning frequencies permits strong damping of harmonic currents with frequencies close to one of the two tuning frequencies, without significant losses due to currents with the operating frequency.

Description

FILTER ARRANGEMENT

The invention relates to a filter arrangement for filtering and damping harmonics or higher-frequency vibration packets and for shifting resonance points in electrical networks. In electrical networks, low-frequency harmonics, which arise, for example, from load shedding due to transformer saturation, in connection with resonance points can lead to significant overvoltages and voltage distortions that are sensitive to normal network operation.

The nature of the AC system plays only a minor role with regard to the occurrence of these faults. This means that the interference cannot be prevented by a special structure of the AC system.

DE-OS 35 39 950 deals with a high-pass filter arrangement for a connected to converters

Three-phase network. A capacitor and a

Choke connected in series to a parallel circuit of ohmic, inductive and capacitive circuit elements which are grounded at high voltage and free at medium voltage. The two resonance frequencies and qualities of the double high-pass filter are adjusted so that only a small one in the critical harmonic range

Resonance increase can occur.

The disadvantage of this circuit is that the losses caused by the operating currents in it

Arrangement are comparatively high if the resistors To achieve rapid damping of low-frequency harmonics can be chosen accordingly low.

EP-A-0 318 790 proposes a high pass filter arrangement for a line connected to converters. A C-link with an L-link and a parallel path is connected in series, an L-link of a series connection consisting of an R-link and a C-link being arranged in parallel in the parallel path. A further R element is arranged in parallel with the series connection part of the L element and the parallel path. With this circuit, it is also not possible to strongly attenuate harmonics without the losses caused by operating frequency currents remaining small. The problem of filtering harmonics is also discussed in Chapter 200-15 under the title "Characterization and control of harmonic overvoltages at HVDC stations" by E.V. Larsen and R.A. Walling, on the occasion of the

"Cigre" symposium, held in September 1987 in Boston, USA, dealt with the published conference book (section 2, pages 1 to 6).

Here, in a first circuit arrangement, a first and a second series-connected C-element are connected in series with a parallel path consisting of a surge arrester and an L-element, and an R-element is connected in parallel to the series circuit part of the second C-element and the L-element arranged. The disadvantage of this circuit is that only the harmonic currents of only one tuning frequency can be sucked out of the network and attenuated in the process. In a second circuit in the same conference book, a first C-element is connected in series with a parallel path, which consists of a series circuit consisting of a second C-element and a first L-element and a series circuit consisting of a voltage-dependent resistor and an R-element is constructed; the series connection part of the two C-elements is a

Surge arrester arranged in parallel. The disadvantage of this circuit is also in the

Limitation of the suction and damping effect given only one tuning frequency.

The object of the invention is to provide a filter arrangement with which sufficient damping for two tuning frequencies can be achieved and with which the losses due to operating frequency currents are limited to a minimum. The object is achieved by the invention. This is characterized in that a first inductance and a first capacitance are arranged in a series circuit, and in that this series circuit is connected with a first damping element to a first parallel path, and in that the first parallel path with one of a second inductance and a second Capacity existing second parallel path and a third capacitance is connected in series. With the invention it is possible for the first time to attenuate harmonic currents with frequencies in the vicinity of one of these tuning frequencies very strongly at two tuning frequencies and to prevent significant losses due to operating frequency currents.

A further development of the invention is that the first inductance with the first capacitance and one fourth capacitance is arranged in a series circuit such that the first capacitance is arranged between the first inductance and the fourth capacitance, and that this series circuit is connected to an expanded first parallel path with the first damping element, and that this first expanded parallel path with the second parallel path and is connected in series with the third capacitance in such a way that the third capacitance is connected on the one hand to a line pole and on the other hand to the connecting line from the first damping element to the first inductor, and the second parallel path on the one hand to the connecting line from the first damping element to the fourth capacitance and on the other hand is connected to a grounding pole and that a second damping element is connected to the connecting line from the first capacitance to the fourth capacitance on the one hand and to ground potential directly or via current transformers on the other.

This further development results in an increased damping effect of the filter arrangement.

One embodiment of the invention provides that the first inductance is arranged between the first capacitance and the fourth capacitance, and that the third

Capacity is connected on the one hand to the line pole and on the other hand to a connecting line from the first damping element to the first capacity. With this circuit variant, which interchanges the first inductance and the first capacitance, the possibility advantageously arises of being able to arrange the first and the third capacitance in the same framework, if necessary.

Further advantageous refinements and developments of the invention result from further subclaims. This makes it possible to take special properties of network systems into account.

The invention will be explained in more detail on the basis of exemplary embodiments. 1 shows the simplest form of a filter arrangement according to the invention, FIG. 2 shows a filter arrangement with increased damping. FIG. 3 shows a filter arrangement with a special characteristic curve, while the circuit shown in FIG. 4 ensures optimization of all important characteristic values.

In connection with the use of static compensators in electrical networks, there is a need to dampen the free vibrations of the system, which are superimposed on the fundamental frequency of these networks and which are excited with each compensation operation, so quickly that at the time when the individual voltage values of all of them Overlay waveforms in the same direction at the time of their maximum value

Amplitudes of these free vibrations are already greatly reduced.

The same applies to the magnetization currents of transformers, which are driven into the saturation range of their magnetization characteristic in the event of larger overvoltages or switching operations. In the case of asymmetrical saturation, the second and third harmonics are pronounced in these currents and also lead to significant overvoltages in the case of existing network resonants in the vicinity of twice and three times the basic frequency of the network. An extraction and simultaneous damping of these currents causes the accelerated

Return of the working area of the transformers to the normal working area.

For both of the above-mentioned processes, the use of filters that have a suction effect at two frequencies is therefore necessary and on the other hand have a strong damping effect. The property of such filters to have very low losses for the operating frequency fundamental oscillation is of great technical and economic importance.

1 shows the simplest basic form of a filter arrangement according to the invention. An ohmic resistor (R _p21 ) is arranged in parallel with a series circuit consisting of a first inductance (L _p2 ) and a first capacitance (C _p21 ) as the first damping element. This parallel connection is connected in series with a parallel _path consisting of a second inductance (L _p3 ) and a second capacitance (C _p3 ) and with a third capacitance (C ₁ ).

This basic form already has all the characteristic properties of the invention. It is thus possible to attenuate harmonic currents with frequencies in the vicinity of one of these tuning frequencies very strongly at two tuning frequencies without significant losses from operating frequency currents occurring in this arrangement. FIG. 2 shows an expansion of the circuit according to FIG. 1. As can be seen from FIG. 2, the series circuit consisting of a first inductance (L _p2 ) and a first capacitance (C _p21 ) is a fourth capacitance (C _p21 ) the first capacitance (C _p21 ) then connected in series. In addition, a second ohmic resistor (R _p41 ) of the series circuit of the fourth capacitance (C _p22 ) and the second capacitance (C _p3 ) is connected in parallel. This simple circuit expansion by means of the capacitance (R _p22 ) and the resistance (R _p41 ) makes the

Attenuation of the filter arrangement increased significantly. FIG. 3 shows a further development of the circuit shown in FIG. 2. The first ohmic resistor (R _p21 ) is expanded with a first varistor (V _p2 ) to form a series connection, and this series connection is made up of a first inductance (L _p2 ), a first capacitance (C _p21 ) and a fourth capacitance ( C _p22 ) existing series connection connected in parallel. In addition, the second ohmic resistor (R _p41 ) is expanded with a second varistor (V _p4 ) to form a series connection. This series circuit is connected in parallel with the fourth capacitance (C _p22 ) and the second capacitance (C _p3 ).

The filter arrangement shown in FIG. 3 has a very steep impedance characteristic with an impedance minimum with two tuning resonances. The greatest possible damping occurs with a higher harmonic content.

. The circuit as a further development of Figure 3 - - In the circuit of Figure 4. Consisting of a first ohmic resistance (R _p21) and a first varistor (V _p2) existing series connection of a third ohmic resistor connected in parallel (R _p21). Furthermore, the series circuit consisting of a second ohmic resistor (R _p41 ) and a second varistor (V _{p 4} ) is arranged in parallel with a fourth ohmic resistor (R _p42 ).

With the help of this further development, it is possible to take small harmonics into account and the characteristic to a greater extent with regard to the damping at low

To influence harmonic content. There is also a further reduction in losses.

Claims

PATENT CLAIMS

1. Filter arrangement for filtering and damping

Harmonics or higher frequency vibration packets and for shifting resonance points in electrical networks, characterized in that a first inductance (L _p2 ) and a first

Capacitance (C _p21 ) are arranged to a series circuit, and that this series circuit is connected to a first parallel path with a first damping element (R _p21 ), and that the first parallel path with one of a second inductance (L _p3 ) and a second capacitance ( C _p3 ) existing second parallel _path and a third capacitance (C ₁ ) is connected in series.

(Fig. 1)

2. Filter arrangement according to claim 1, characterized in that the first inductance (L _p2 ) with the first capacitance (C _p21 ) and a fourth capacitance (C _p21 ) is arranged in such a way that the first capacitance (C _p21 ) between the first inductor (L _P2), and the fourth capacitance (C _p22), and that this series circuit is connected to the first damping element (R _p21) ^to an expanded first parallel path, and in that said first extended parallel path with the second parallel path, as well as with the third capacitance (C ₁ ) is connected in series in such a way that the third capacitance (C ₁ ) is connected on the one hand to a line pole (1) and on the other hand to the connecting line from the first damping element (R _p21 ) ^{to the} first inductance (L _{p 2} ) , and being the second

Parallel _path on the one hand to the connecting line from the first damping element (R _p21 ) to the fourth capacitance (C _p22 ) and on the other hand to a grounding _pole (2) is connected, and that a second damping _element (R _p41 ) on the one hand is connected to the connecting line from the first capacitance (R _p21 ) to the fourth capacitance (C _p22 ) and on the other hand directly or via current transformers to ground potential.

(Fig. 2)

3. _{Filter arrangement} according to claim 2, characterized in that the first inductance (L _p2 ) between the first capacitance (R _p21 ) and the fourth capacitance (C _p22 ) is arranged, and in that the third

Capacitance (C ₁ ) on the one hand to the line pole (1) and on the other hand to a connecting line from the first damping element (V _p2 ) to the first capacitance

(C _p21 ) is connected.

4. _{Filter arrangement} according to claim 1, 2 or 3, characterized in that a varistor is used as the first damping element (R _p21 ) and / or as the second damping _element (R _p41 ).

5. Filter arrangement according to claim 1 or 2, characterized

characterized in that as the first damping element (R _p21 ) and / or as the second damping element

(R _p41 ) A series or parallel connection of an ohmic resistor with a varistor (V _p2 , V _{p 4} ) is used.

6. Filter arrangement according to claim 5, characterized in that the first damping element (R _p21 ), a third ohmic resistor (R _p22 ) is connected in parallel.

7. Filter arrangement according to claim 5, characterized in that the second damping _element (R _p41 ), a fourth ohmic resistor (R _p42 ) is connected in parallel.

8. Filter arrangement according to claim 1 to 7, characterized in that as the first damping element (R _p21 ) and / or as a second damping element

(R _p41 ) a silicon carbide surge arrester is used without a spark gap.

9. Filter arrangement according to claim 1 to 7, characterized

(R _p41 ) a silicon carbide surge arrester with spark gap is used.

10. Filter arrangement according to claim 1 to 7, characterized

(R _p41 ) a series or parallel connection of an ohmic resistor with a silicon carbide _{surge arrester} without spark gap is used.

11. Filter arrangement according to claim 1 to 7, characterized

(R _p41 ) a series or parallel connection of an ohmic resistor with a silicon carbide surge arrester with spark gap is used.

12. _{Filter arrangement} according to one of claims 4 to 11, characterized in that the first and / or the second varistor (V _p2 , V _p4 ) is replaced by antiparallel connected thyristor _arrangements .

13. _{Filter arrangement} according to one of claims 4 to 12, characterized in that the first and / or the second varistor (V _p2 , V _p4 ) each have a response _{spark gap} connected in series.

14. _{Filter arrangement} according to at least one of claims 1 to 13, characterized in that at least one of the ohmic resistors used in the first damping element (V _p2 ) and in the second damping _element (R _p41 ) are connected in series with anti-parallel connected thyristor _arrangements .

15. _{Filter arrangement} according to at least one of claims 1 to 14, characterized in that at least one of the first damping element (V _p2 ) and in the second damping _element (R _p41 ) used

Varistors is replaced by a parallel connection of several varistors.