GB2276993A

GB2276993A - Filter

Info

Publication number: GB2276993A
Application number: GB9406350A
Authority: GB
Inventors: Peter Aufleger
Original assignee: Siemens Matsushita Components GmbH and Co KG
Current assignee: TDK Electronics AG
Priority date: 1993-04-05
Filing date: 1994-03-30
Publication date: 1994-10-12
Anticipated expiration: 2014-03-30
Also published as: FR2703857B1; GB2276993B; CH689030A5; FR2703857A1; DE4311125A1; DE4311125B4; GB9406350D0

Description

2276993 FILTER The invention relates to filters, and in particular to

electromagnetic compatibility (EMC) filters for installations, systems and screened rooms, with a metallic housing in which chokes and capacitors are arranged.

In order to suppress electrical and electronic equipment and installations, as well as cables that lead into and out of screened rooms, filters are required with very high attenuation for both symmetrical and asymmetrical suppression and with low leakage current, through low phase-to-earth capacitance. Furthermore, such types of filters must exhibit a low voltage-drop across the electrical conductors and low power dissipation. Also, given the desired electrical requirements, the weight and size of the filter should be reduced to a minimum.

Known filters are commonly constructed with current-compensated chokes and rod-core chokes using wire-winding techniques. These chokes are responsible for symmetrical and asymmetrical interference suppression. For interference suppression in the higher frequency range, capacitors (single line or multiple line capacitors) are provided for example between the phase conductors and a common potential, as well as capacitors that are arranged between the phase conductors or between phase conductors and neutral conductors, respectively.

The connection by means of capacitors between phase conductors and protective earth conductors or a neutral conductor is known as an asymmetrical or star (Y) connection.

The terminals of the capacitors of the prior art are fitted with electrical leads and are connected to the respective electrical conductors by clamping, crimping, screwing, soldering or other bonding arrangements. The connecting leads may typically be very long because of the physical arrangement of the circuit into which the capacitor is connected. Consequently, the capacitors present a significant inductance which results in poorer attenuation in the higher frequency range. These long connecting leads also cause resonance effects in the lower frequency range.

According to the present invention there is provided an electric filter comprising a metallic housing in which chokes and capacitors are arranged, the filter having a plurality of feed- through electrical conductors, the chokes being designed as multiple line chokes having components for asymmetrical and symmetrical interference suppression.

Preferably, the component for asymmetrical interference suppression of the choke comprises at least one core through which electrical conductors pass. The component for symmetrical interference suppression may comprise at least one individual core placed on one of the electrical conductors.

Preferably, the conductors are suitably shaped between the components for symmetrical and asymmetrical interference suppression to enable application of the individual core to its respective electrical conductor.

Electrical conductors of the filter may comprise a neutral conductor and at least one phase conductor, and the capacitors may comprise capacitors for symmetrical interference suppression which are connected between the or each phase conductor and the neutral conductor. Preferably the capacitors for symmetrical interference suppression are designed as multiple line feed-through capacitors. Such multiple line feed-through capacitors are positioned around respective electrical conductors, and in each case one of their electrodes makes direct coaxial contact with the respective electrical conductor, and the other electrode is connected over a large surface area to a common potential.

The capacitors may further comprise a capacitor for asymmetrical interference suppression, one electrode of which is connected, over a large surface area, to earth. The capacitors for symmetrical and asymmetrical interference suppression and preferably designed as a common multiple line feed-through capacitor.

Preferably, an overvoltage protection device is arranged at the input and/or the output side of the filter.

The filter is preferably an electromagnetic compatibility filter.

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 shows a filter according to the invention; and Figure 2 shows a circuit diagram of the filter illustrated in Figure 1.

Figure 1 shows a filter that is built into a metallic filter housing 1.

The metallic housing is subdivided into three compartments by high-frequency suppressing partitions 2, the filter construction for the centre compartment only being shown in Figure 1. The right-hand and left hand compartments have the same construction.

The filter has a number, n, of phase conductors Ll- Ln and a neutral conductor N.

In the area 3 the electrical conductors preferably have screw connections with internal or external threads, so that they can be easily connected to the filter unit in the next compartment by screwing them together. The electrical conductors are designed in such a way that they form a current-compensated multiple line choke of compact construction inside each compartment, having components U for asymmetrical interference suppression and S for symmetrical 5 interference suppression.

The components U for asymmetrical interference suppression have at least one toroidal core 4, inside which run the electrical conductors. Following the components U for asymmetrical interference suppression the electrical conductors are separated from each other by suitable forming, e.g. bending, so that at least one toroidal core 5, which represents the component S for symmetrical interference suppression, can be fitted to at least one electrical conductor. 15 The electrical conductors can be in the form of flexible or solid conductors and they may be hollow. A plate 6 arranged between the components U and S is connected to the housing potential through a capacitor, not shown in Figure 1. 20 Capacitors 7 are also connected between this plate 6 and the individual electrical conductors. One electrode of each capacitor 7 is connected, over a large area, to the plate 6, the other electrode of each capacitor 7 being connected to a respective conductor.

These capacitors are used for symmetrical and asymmetrical interference suppression for high frequencies.

An alternative to the use of capacitors 7 is to construct the capacitors for symmetrical and asymmetrical interference suppression as a multiple line feed-through capacitor. In such a capacitor, a single capacitor 8 encloses all electrical conductors, the conductors being arranged as a concentric assembly, surrounded by the single capacitor 8. This single capacitor 8 operates as an asymmetrical capacitor. Also, individual capacitors 9, which operate as symmetrical capacitors, enclose respective ones of the electrical conductors. There may be one or more individual capacitors 9. In such an assembly, the asymmetrical capacitor 8 is fitted in such a way that a large area of one of its electrodes is connected to a housing potential and a large area of its other electrode is connected to the neutral potential. In the case of the symmetrical capacitors, a large area of one electrode of each is likewise connected to the neutral potential, whilst the other electrode of each individual capacitor is connected coaxially to a respective electrical conductor.

An overvoltage protector CS is provided at the input and/or output side of the filter. Furthermore, the filter has a high-frequency suppressing connection 10.

The circuit diagram of the filter in Figure 1 is shown with three compartments in Figure 2. It can be seen from the circuit diagram that the capacitors for symmetrical and asymmetrical interference suppression may be arranged as single capacitors (denoted 7 in Figure 1) between the components U for asymmetrical interference suppression, and the components S for symmetrical interference suppression of the multiple line chokes. Alternatively, as also shown in Figure 2, there may be provided a multiple line feed-through capacitor (shown in Figure 1 as 8, 9) at the end of the components S for symmetrical interference suppression of the multiple line chokes. These possible interference suppression capacitor arrangements represent alternatives, although the use of multiple line feed-through capacitors 8, 9 is preferred.

The use of current-compensated multiple line chokes and one or more feedthrough capacitors with suitable placement and, where applicable, wiring of the capacitors, produces a filter which can be manufactured in one or more stages with very high attenuation in both the lower and the upper frequency range. The arrangement of the capacitors, as multiple line feedthrough capacitors 8, 9, avoids the need for inductive 5 supply leads.

For example, the asymmetrical capacitor 8 is connected over a large surface area to earth which reduce, inductance in the connection, and does not require leads for its connection into the circuit.

In the filter arrangement shown, the d.c.

resistance is lower than in filters previously manufactured for the same attenuation requirements and identical load current. This results from the short lead run and from an increase in conductor cross- sections. Consequently, an increase in the inductance of one filter branch (which can be varied by the arrangement of several toroidal cores in the components for asymmetrical U and symmetrical S interference suppression) does not cause an appreciable increase in the d.c. resistance.

The arrangement of capacitors as described and the resulting low inductance loading of the leads of the capacitors gives rise to the advantage that the filters can be fitted with smaller, namely lower capacitance, capacitors, which leads to a reduced leakage current characteristic and to a lower reactive current.

Furthermore, in the filter shown the power dissipation is reduced by the low d.c. resistance and further, as a result of the low d.c. resistance, a lower voltage-drop is obtained across one or all conductors of the filter. These advantages enable a smaller overall size and a lower weight to be obtained in comparison to conventional filters, such as EMC filters. 35 Depending on the desired application, the filters can be fitted with one or more high frequency suppressing partitions.

The filter may, however, be designed without the partitions and feedthrough capacitors described above, and such a filter will have applications with lowerspecification attenuation requirements, for example in uninteruptible power Systems or converters.

1

Claims

1. A filter comprising a metallic housing in which chokes and capacitors are arranged, the filter having a plurality of feed-through electrical conductors, the chokes being designed as multiple line chokes having components for asymmetrical and symmetrical interference suppression.

2. A filter as claimed in to Claim 1, in which the component for asymmetrical interference suppression of the choke comprises at least one core through which the electrical conductors pass.

3. A filter as claimed in Claim 1 or 2, in which the component for symmetrical interference suppression comprises at least one individual core placed on one of the electrical conductors.

4. A filter as claimed in Claim 3, when appendant to Claim 2, in which the electrical conductors between the components for asymmetrical interference suppression and symmetrical interference suppression are suitably shaped to enable application of the individual core.

5. A filter as claimed in any preceding claim, in which the electrical conductors comprise a neutral conductor and at least one phase conductor, and in which the capacitors comprise capacitors for symmetrical interference suppression which are connected between the or each phase conductor and the neutral conductor.

6. A filter as claimed in Claim 5, in which the capacitors for symmetrical interference suppression are designed as multiple line feed-through capacitors.

7. A filter as claimed in Claim 6, in which the capacitors for symmetrical interference suppression are positioned around respective electrical conductors, and in each case one of their electrodes makes direct coaxial contact with the respective electrical 1 - conductor, and the other electrode is connected over a large surface area to a common potential.

8. A filter as claimed in any preceding claim, in which the capacitors further comprise a capacitor for asymmetrical interference suppression, one electrode of which is connected, over a large surface area, to earth.

9. A filter as claimed in Claim 8 when appendant to Claim 7, in which the capacitors acting symmetrically and asymmetrically are designed as a common multiple line feed-through capacitor.

10. A filter as claimed in any preceding claim, further comprising overvoltage protection components, arranged at the input or the output side of the filter.

11. A filter as claimed in any preceding claim, in which the metallic housing is subdivided into different compartments by at least one high-frequency suppressing partition.

12. A filter as claimed in any preceding claim, in which the input and output side of the filter are fitted with a connection fixture to enable flangemounting of suitable screening components.

13. A filter as claimed in any preceding claim, in which the filter is an electromagnetic compatibility filter.

14. A filter substantially as described herein, with reference to and as shown in, the accompanying drawings.