WO2019197556A1

WO2019197556A1 - Emi filter incuding overvoltage protection devices

Info

Publication number: WO2019197556A1
Application number: PCT/EP2019/059312
Authority: WO
Inventors: Fabio DE MARCO; Marco SANTELLO
Original assignee: Sit S.P.A.
Priority date: 2018-04-12
Filing date: 2019-04-11
Publication date: 2019-10-17
Also published as: IT201800002353U1

Abstract

Protection device for protection against electromagnetic disturbances in electrical networks (200), the protection device (100) comprising an electromagnetic filter (1). The electromagnetic filter (1) comprises a first and a second input end (2, 3) which are suitable for being connected to a first electrical conductor (201) and a second electrical conductor (202) of an electrical network (200), respectively, a first and a second output end (4, 5) which are connected or suitable for being connected to an electrical circuit (310) of an electrical apparatus (300), and a first electrical path (6) which extends from the first input end (2) to the first output end (4) and a second electrical path (7) which extends from the second input end (3) to the second output end (5), the first and second electrical paths (6, 7) comprising a first inductor (8) and a second inductor (9), respectively.The protection device comprises a first voltage suppressor (11) and a second voltage suppressor (12), each of the voltage suppressors being a two- terminal network, wherein the terminals (13, 14) of the first voltage suppressor (11) are electrically connected to the first input end (2) and the first output end (4), respectively, and the terminals (15, 16) of the second voltage suppressor (12) are electrically connected to the second input end (3) and the second output end (5), respectively.

Description

EMI FILTER INCUDING OVERVOLTAGE PROTECTION DEVICES

Technical Field

The present invention relates to a protection device for protection against electromagnetic disturbances in electrical networks, in particular in single- phase electrical networks.

Background Art

The invention is used particularly though non-exclusively in the field of electromagnetic compatibility inherent to solutions for protection against electromagnetic disturbances which are produced by electrical or electronic apparatuses in electrical networks.

Nowadays, in fact, electrical and electronic products have to comply with a number of national and international directives in order to be able to freely circulate on different markets.

By way of example, the free circulation of the electrical and electronic apparatuses on the European market is regulated by the Directive 2014/30/EU (also referred to as the EMC directive, where EMC stands for "Electro Magnetic Compatibility") which has as an essential requirement ensuring that the devices are configured and produced in such a manner that:

• the electromagnetic disturbances generated do not exceed the limits above which the radio and telecommunication apparatuses or other apparatuses do not operate as intended and

• they have a level of immunity from electromagnetic disturbances which is provided for by the intended use thereof so that they can continue to operate without unacceptable damage in terms of what is provided for during the intended use thereof.

In order to make the products of an electrical/electronic type compliant with the standards on electromagnetic compatibility, with regard to the electromagnetic disturbances originating or introduced in the electrical supply network it is known to provide such products with so-called EMC line filters, that is to say, electromagnetic filters which are configured both to attenuate the influence of the disturbances originating from the electrical line on the operation of the device being tested and to limit the electromagnetic disturbances which are generated by the products themselves within a predetermined limit.

However, the Applicant has observed that such filters are subjected to some disadvantages. In particular, the EMC filters as a result of the inductive nature thereof may bring about problems of safety and/or integrity of the electrical /electronic apparatuses which are associated therewith when the electrical network to which the EMC filters are connected is in an impulse type excess voltage condition (surge impulse).

In fact, a discharge of a lightning bolt in the electric line may generate a surge impulse with possible formation of electric arcs between the components and the tracks of the electronic boards. This effect is usually increased by the EMC filter which in these cases behaves like a step-up transformer. This phenomenon may be found to be destructive (including explosive or incendiary) for the electrical/ electronic components of the apparatuses connected to these filters.

It is known to solve this problem by increasing the distance between the tracks of the electronic board of the apparatus or by reducing the inductive portion of the EMC filters.

However, this solution brings about an increase of the dimensions of the printed circuits of the electronic apparatus and a decrease of the filtering capacity with a resultant difficulty in developing the electrical or electronic apparatus for complying with the EMC directive.

Summary of Invention

An object of the present invention is to provide a protection device which is structurally and functionally conceived to overcome at least one of the limits set out above with reference to the known solutions.

This object is achieved by means of a protection device for protection against electromagnetic disturbances in electrical networks which is achieved according to the independent claim which is appended to the present description.

Preferred features of the invention are defined in the dependent claims.

Brief Description of Drawings

Features and advantages of the invention will be better appreciated from the following detailed description of a preferred embodiment thereof which is illustrated by way of non-limiting example with reference to the appended Figures, in which :

• Figure 1 is a schematic illustration of a protection device according to the present invention and

• Figure 2 is a schematic illustration of an electrical apparatus comprising a protection device according to the present invention. Description of Embodiments Initially with reference to Figure 1, there is generally designated 100 a protection device according to the invention for protection against electromagnetic disturbances in electrical networks 200. In particular, "electromagnetic disturbances in electrical networks 200" means electromagnetic disturbances which are propagated through the electrical networks 200.

The electrical network 200 comprises a first electrical conductor 201 and a second electrical conductor 202.

The electrical network 200 may be identified with a single-phase network which is supplied with alternating current; therefore the first electrical conductor and the second electrical conductor 201, 202 can be identified with a phase conductor and with a neutral conductor of this network, respectively.

Alternatively, the electrical network 200 may be identified with a three- phase network which is supplied with alternating current; therefore the first electrical conductor 201 can be identified with one of the phase conductors of the electrical network 200 whereas the second electrical conductor 202 can be identified with a neutral conductor of this network.

Alternatively, the electrical network 200 may be identified with a telecommunication network; therefore the first electrical conductor and the second electrical conductor 201, 202 can be identified with a first wire and a second wire for exchanging information, respectively.

Alternatively, the electrical network 200 may be identified with a network which is supplied with direct current; therefore the first electrical conductor and the second electrical conductor 201, 202 can be identified with respective electric current conductors of this network.

In particular, the network 200 can be identified with a low-voltage network which is supplied by means of alternating current voltages between 50 and 1000 V. The supply (alternating current) voltage between the first electrical conductor 201 and the second electrical conductor 202 may be 120 V or 230 V. Preferably, the supply voltage of the electrical network 200 has a frequency of 50 or 60 Hz.

According to a first aspect of the invention, the protection device 100 comprises an electromagnetic filter 1 comprising a first input end 2 and a second input end 3 which are suitable for being connected to the first electrical conductor 201 and the second electrical conductor 202 of the electrical network 200, respectively, and a first output end 4 and a second output end 5 which are connected or suitable for being connected to an electrical circuit 301 of an electrical apparatus 300.

In particular, the first input end 2 and the second input end 3 of the electromagnetic filter 1 are connected to the first electrical conductor 201 and the second electrical conductor 202, respectively.

In the context of the present invention, the term "electrical apparatus" is intended to be understood to signify both an "electrical apparatus" and an "electronic apparatus".

The electrical apparatus 300 may be provided with one or more electronic boards, therefore the electrical circuit 301 can be constructed as a printed circuit.

The electromagnetic filter 1 further comprises a first electrical path 6 which extends from the first input end 2 to the first output end 4 and a second electrical path 7 which extends from the second input end 3 to the second output end 5.

The first electrical path 6 comprises a first inductor 8, in particular a first coil, and the second electrical path 7 comprises a second inductor 9, in particular a second coil.

Preferably, the first inductor 8 and the second inductor 9 have an inductance which is greater than 100 pH.

According to an aspect of the invention, the first inductor 8 and the second inductor 9 are magnetically connected to each other.

According to an aspect of the invention, the first inductor 8 and the second inductor 9 are electrically insulated from each other.

According to an aspect of the invention, the electromagnetic filter 1 comprises a common mode choke 10 which includes the first inductor 8 and the second inductor 9.

In particular, the common mode choke 10 is a choke coil having at least two coils, more specifically having at least the first and second inductor 8, 9, which are wound on a single (ferromagnetic) core.

According to an aspect of the invention, the electromagnetic filter 1 is configured so as to provide a voltage between the first output end 4 and the second output end 5 which is substantially equal to that between the first input end 2 and the second input end 3 when the electromagnetic filter 1 is supplied by the supply voltage of the electrical network 200 in a normal operating condition thereof, that is to say, in the absence of excess voltages or other phenomena which bring about a change of the network voltage. According to an aspect of the invention, the protection device 100 comprises a first voltage suppressor and a second voltage suppressor 11, 12, each of the voltage suppressors being a two-terminal network.

In other words, the first voltage suppressor is a first two-terminal network whereas the second voltage suppressor is a second two-terminal network. The first voltage suppressor has two terminals designated by 13 and 14 in the figures. The second voltage suppressor has two terminals designated by 15 and 16 in the figures.

The terminals 13, 14 of the first voltage suppressor 11 are electrically connected to the first input end 2 and the first output end 4, respectively. In particular, the first voltage suppressor 11 is connected to the electromagnetic filter 1 in parallel with the first inductor 8.

The terminals 15, 16 of the second voltage suppressor 12 are electrically connected to the second input end 3 and the second output end 5, respectively.

In particular, the second voltage suppressor 12 is connected to the electromagnetic filter 1 in parallel with the second inductor 9.

According to an aspect of the invention, each voltage suppressor 11, 12 can be formed by an electrical component or by an electrical circuit comprising a plurality of electrical/electronic components, characterized by an electrical resistance between its terminals which varies in accordance with the difference in electrical potential present between such terminals.

In other words, each voltage suppressor has an electrical resistance which varies on the basis of the voltage at the terminals thereof.

The electrical resistance of each voltage suppressor 11, 12 is preferably in the order of tens of MW if the voltage at the terminals of the voltage suppressor 11, 12 is less than a predetermined threshold voltage and is preferably in the order of a few W if the voltage at the terminals of the voltage suppressor 11, 12 is greater than or equal to the above-mentioned threshold voltage.

Preferably, the electrical resistance of each voltage suppressor is between 10 MW and 1 OW if the voltage at the terminals of the voltage suppressor is less than a predetermined threshold voltage and is between 0 and 1 I<W, in particular between substantially 0 and 1 I<W, if the voltage at the terminals of the voltage suppressor is greater than or equal to the above-mentioned threshold voltage.

Preferably, each voltage suppressor 11, 12 substantially corresponds to an open circuit if the voltage at the terminals thereof is less than the threshold voltage.

Preferably, each voltage suppressors 11, 12 substantially corresponds to a closed circuit if the voltage at the terminals thereof is greater than or equal to the threshold voltage.

In other words, the voltage suppressors 11, 12 are characterized by a predetermined threshold voltage so that, if the voltage at the terminals thereof is less than the threshold voltage, the voltage suppressors 11, 12 have a relatively high resistance so as to act as an open circuit. Conversely, that is to say, if the voltage at the terminals of the voltage suppressors 11, 12 is greater than or equal to the threshold voltage, the electrical resistance provided by the voltage suppressors 11, 12 is abruptly decreased so as to act as a closed circuit.

Preferably, the threshold voltage is greater than the supply voltage of the network 200 and/or the supply voltage at the input ends of the electromagnetic filter 1 in a normal working condition.

Preferably, the threshold voltage is between a few volts and a few kV, more preferably it is between 5 V and 4 kV. In particular, the preferred range of the threshold voltage is from a few volt (5-10 V) up to a few kV (1-4 kV), in accordance with the application of the protection device 100.

In this manner, in a normal operating condition of the electrical network 200, the electric potential difference between the terminals of the voltage suppressors 11, 12 is less than the threshold voltage mentioned above and the electrical resistance supplied by those two-terminal networks is therefore preferably in the order of a few tens of MW.

Conversely, that is to say, in the case of an excess voltage in the electrical network 200, the electric potential difference between the terminals of the voltage suppressors 11, 12 is greater than or equal to the threshold voltage and the electrical resistance supplied by those two-terminal networks is therefore preferably in the order of a few W.

Those characteristics advantageously allow protection of the electrical apparatus 300 which is associated with the protection device 100, in particular the electrical circuit 301 of the apparatus 300, from excess voltages which are amplified by the electromagnetic filter 1.

In fact, the response of the electromagnetic filter 1 to a voltage peak at the input (for example, as a result of a bolt of lightning discharged into the electrical network 200) is an output voltage having a magnitude which is increased with respect to the input voltage as a result of the presence of the first and the second inductors 8, 9, the output voltage therefore being able to be destructive for the electrical circuit 301 of the electrical apparatus 300 which is associated with the protection device 100.

However, if an excess voltage is identified at the input to the protection device 100, that is to say, during an excess voltage between the first and the second input ends 2, 3 of the electromagnetic filter 1, the first voltage suppressor 11 and the second voltage suppressor 12 change from a first operating condition, in which they have a relatively high resistance, to a second operating condition in which they have relatively low resistance, thereby forcing a voltage between the first and the second output ends 4, 5 of the electromagnetic filter 1 having a magnitude which substantially corresponds to that of the voltage between the first and the second input ends 2, 3.

The excess voltages amplified by the electromagnetic filter 1 are therefore suppressed by means of the presence of the two voltage suppressors 11, 12, ensuring the integrity of the electrical/electronic components of the electrical circuit 310 which is connected to the protection device 100.

According to an aspect of the invention, the first voltage suppressor 11 comprises a varistor. Alternatively or additionally, the first voltage suppressor 11 comprises a transil (transient voltage suppression diode). According to an aspect of the invention, the second voltage suppressor 12 comprises a varistor. Alternatively or additionally, the second voltage suppressor 12 comprises a transil (transient voltage suppression diode). According to an aspect of the invention, the electromagnetic filter 1 is an EMC filter.

With reference to Figure 2, the electrical apparatus 300 may comprise the electrical circuit 301 and the protection device 100 which is connected to the electrical circuit 301. The protection device 100 and the electrical circuit 301 can be constructed in the same electronic board.

In an embodiment of the invention which is not illustrated in the Figures, the electromagnetic filter of the protection device may comprise a third input end and a fourth input end which are suitable for being connected to respective electrical conductors of the electrical network and a third output end and a fourth output end which are connected or suitable for being connected to an electrical circuit of an electrical apparatus. In particular, the third input end and the fourth input end are connected to respective electrical conductors of the electrical network.

This protection device is found to be particularly suitable for being used in three-phase electrical networks in which the first, second and third input ends are intended to be connected to respective phase conductors of this network while the fourth input end is intended to be connected to the neutral conductor.

In this embodiment of the invention, the electromagnetic filter comprises a third electrical path which extends from the third input end to the third output end and a fourth electrical path which extends from the fourth input end to the fourth output end.

Preferably, the third and fourth electrical paths have the same characteristics as the first and second electrical paths described above. As a result, each electrical path comprises a respective inductor. The inductors are preferably magnetically connected to each other. According to an aspect of the invention, the inductors are insulated from each other. In this embodiment of the invention, the electromagnetic filter also preferably comprises a common mode choke comprising the above- mentioned inductors.

According to an aspect of the invention, the protection device comprises a third voltage suppressor and a fourth voltage suppressor in addition to the above-mentioned first and second voltage suppressors, each of the voltage suppressors being a two-terminal network. The terminals of the third voltage suppressor are electrically connected to the third input end and the third output end of the electromagnetic filter, respectively, whereas the terminals of the fourth voltage suppressor are electrically connected to the fourth input end and the fourth output end, respectively. The third voltage suppressor and the fourth voltage suppressor have the same characteristics as the first and second voltage suppressors described above. Preferably, the third voltage suppressor and the fourth voltage suppressor comprise a respective varistor and/or transil.

In particular, the third voltage suppressor and the fourth voltage suppressor are connected to the electromagnetic filter in parallel with the third inductor and the fourth inductor, respectively.

The invention thereby achieves the predetermined objects, achieving the advantages mentioned above with respect to the known solutions.

Claims

1. A protection device for protection against electromagnetic disturbances in electrical networks (200), the protection device (100) comprising :

• an electromagnetic filter (1) comprising :

• a first and a second input end (2, 3) which are suitable for being connected to a first electrical conductor (201) and a second electrical conductor (202) of an electrical network (200), respectively,

• a first and a second output end (4, 5) which are connected or suitable for being connected to an electrical circuit (310) of an electrical apparatus (300),

• a first electrical path (6) which extends from the first input end (2) to the first output end (4) and a second electrical path (7) which extends from the second input end (3) to the second output end (5), the first electrical path (6) and the second electrical path (7) comprising a first inductor (8) and a second inductor (9), respectively,

characterized in that it comprises a first voltage suppressor (11) and a second voltage suppressor (12), each of the voltage suppressors being a two-terminal network, wherein the terminals (13, 14) of the first voltage suppressor (11) are electrically connected to the first input end (2) and the first output end (4), respectively, and the terminals (15, 16) of the second voltage suppressor (12) are electrically connected to the second input end (3) and the second output end (5), respectively.

2. A protection device according to claim 1, wherein the protection device (100) further comprises:

• a third electrical path which extends from a third input end to a third output end of the electromagnetic filter (1) and a fourth electrical path which extends from a fourth input end to a fourth output end of the electromagnetic filter (1), each electrical path comprising a respective inductor, and

• a third voltage suppressor and a fourth voltage suppressor, each of the voltage suppressors being a two-terminal network, in which the terminals of the third voltage suppressor are electrically connected to the third input end and the third output end, respectively, and the terminals of the fourth voltage suppressor are electrically connected to the fourth input end and the fourth output end, respectively.

3. A protection device according to any one of the preceding claims, wherein the electromagnetic filter (1) is an EMC filter.

4. A protection device according to any one of the preceding claims, wherein the electromagnetic filter (1) comprises a common mode choke (10) which includes the inductors.

5. A protection device according to any one of the preceding claims, wherein each of the voltage suppressors (11, 12) is connected to a respective electrical path (6, 7) of the electromagnetic filter (1) in parallel with the inductor (8, 9) present in the electrical path (6, 7).

6. A protection device according to any one of the preceding claims, wherein each of the voltage suppressors (11, 12) has an electrical resistance which varies on the basis of the voltage at the terminals (13, 14; 15, 16) thereof.

7. A protection device according to claim 6, wherein the electrical resistance of each voltage suppressor (11, 12) is between 10 MW and 1 GQ if the voltage at the terminals of the voltage suppressor (11, 12) is less than a predetermined threshold voltage and is between 0 and 1 kQ if the voltage at the terminals of the voltage suppressor (11, 12) is greater than or equal to the threshold voltage.

8. A protection device according to claim 7, wherein the threshold voltage is greater than the supply voltage of the network (200) and/or the supply voltage at the input ends of the electromagnetic filter (1) in a normal working condition.

9. A protection device according to claim 7 or 8, wherein the threshold voltage is between 5 V and 4 kV.

10. A protection device according to any one of the preceding claims, wherein at least one of the voltage suppressors (11, 12) comprises a varistor and/or a transil.

11. A protection device according to any one of the preceding claims, wherein the inductors (8,9) are magnetically connected to each other.

12. A protection device according to any one of the preceding claims, wherein the inductors (8,9) are insulated from each other.

13. An electrical apparatus (300) comprising an electrical circuit (310) and a protection device (100) according to any one of claims 1 to 12 connected to the electrical circuit (310).