NO20201199A1

NO20201199A1 - High-voltage transformer for a plasma-based gas-treatment apparatus

Info

Publication number: NO20201199A1
Application number: NO20201199A
Authority: NO
Inventors: Frode Vik; Bjarte Kvingedal
Original assignee: Seid As
Priority date: 2020-11-04
Filing date: 2020-11-04
Publication date: 2022-05-05
Also published as: WO2022098245A1

Description

HIGH-VOLTAGE TRANSFORMER FOR A PLASMA-BASED GAS-TREATMENT APPA-RATUS

FIELD OF THE INVENTION

The invention relates to a high-voltage transformer for generating an output voltage for a high voltage non-thermal plasma chamber electrode. The invention further relates to a high-voltage generation circuit for generating an output voltage for a high-voltage nonthermal plasma chamber electrode, wherein the generation circuit comprises such transformer.

BACKGROUND OF THE INVENTION

Systems and solutions for air pollution control are known and widely used to reduce odours, limit particle emission to the ambient and to reduce or remove the emission of chemical substances.

Air pollution control measures are taken in a wide range of industries. Some industries or polluters are limited by official regulations, other choose to deal with issues to maintain a good relationship with their surroundings. Large factories may have polluted air (gas) flows of several hundred thousand cubic meters of exhaust per hour, hence the required gas-treatment capacity is also large. A variety of gas-treatment systems are present in the market, some based on biological or chemical processes, others on adsorption and/or filtration technologies. Non-thermal plasma based solutions have been available for industrial applications for at least 25 years. Two different approaches; injection of ozone- and radical enriched gas into an exhaust airstream, or alternatively, treatment of the exhaust directly in a non-thermal plasma reaction chamber.

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The current technologies have various limiting factors in terms of capacity, size, operating costs and abatement efficiency.

Improved efficiency, lower energy costs and less environmental impact are factors playing an important role when deciding what solution to choose, especially when regulations are tightening up.

In view of the above there is a need to further develop gas-treatment systems, such that they get larger treatment capacities at lower financial and environmental costs, in particular non-thermal plasma-based gas treatment systems.

SUMMARY OF THE INVENTION

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. The inventor(s) identified the need for creating new technologies to solve this problem, not in the least to reduce the footprint and volume of such non-thermal plasma-based gas treatment systems.

The object is achieved through features which are specified in the description below and in the claims that follow.

The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect the invention relates to a high-voltage transformer for generating an output voltage for a high-voltage non-thermal plasma chamber electrode. The transformer comprises: i) at least one magnetic core defining an opening and having a winding portion at a side of the opening, and ii) a primary coil and a secondary coil that are magnetically coupled through the magnetic core. The primary coil and the secondary coil have a turns ratio lower than or equal to 1, wherein the primary coil has a number of primary windings, and wherein the secondary coil has a number of secondary windings larger than the number of primary windings. The primary coil, the secondary coil and the winding portion are placed concentrically when seen in a cross-sectional plane through the winding portion. The high-voltage transformer is characterized in that it further comprises:

i) a first insulation foil provided in between the primary windings and the secondary windings for insulating the secondary windings from the primary windings, wherein the first insulation foil is spaced apart from both the primary windings and the secondary windings,

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and

ii) a second insulation foil provided around the secondary windings with-in the opening for insulating the secondary windings from the magnetic core within the opening.

The effects of the features of the high-voltage transformer in accordance with the invention are as follows. Transformers for generating an output voltage for a high-voltage nonthermal plasma chamber electrode are known as such. Expressed differently, it is known to use a transformer coupled to a rectifier circuit (multiplier circuit) for generating high-output voltages.

However, a transformer in accordance with the first aspect of the invention is designed such that it tolerates much higher voltages on its secondary winding without spark-over. Conventionally, one of the terminals of the secondary winding in a high-voltage generation circuit is conventionally grounded, in a half-wave rectifier circuit this means one of the outer terminals of the secondary coil of the transformer, and in a full-wave rectifier circuit this conventionally is the middle terminal on the DC-line of the rectifier circuit (in such cases the secondary coil is a series connection of two secondary coils, such that the middle terminal can be formed and connected to). In any case, in a conventional transformer the voltages that are generated on the outer terminal(s) of the secondary coil are AC-voltages centred around ground level. This AC-voltage is generally an amplified AC-signal compared to the AC-voltage on the terminals of the primary coil, wherein the amplification factor is inversely proportional to the turns ratio of the transformer.

The inventor developed a novel and unconventional high-voltage generation circuit, wherein the output of the rectifier circuit (which is a multi-stage voltage multiplier circuit) is grounded, which cause the input of the rectifier circuit to generate high-DC voltages superimposed with an AC-voltage. This on itself is very counter-intuitive, because this puts severe requirements on the transformer, which is already a very costly component of the system. However, the inventor solved this challenge by designing a special transformer, that is very robust and tolerates high-voltages on the terminals of the secondary coil. This robustness is obtained by various features in combination. A first feature concerns the concentric placement of the winding portion of the magnetic core and the primary and secondary coil. This gives two main options. One option where the primary coil is on the outside (further away from the magnetic core) and the secondary coil on the inside (closest to the magnetic core), and another option where the secondary coil is on the outside, while the primary coil is on the inside. Either way, in the invention it is important that the primary

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coil and secondary coil are spaced apart from each other, i.e. that there is space in between them. The invention further provides a first insulation foil in between the primary windings and secondary windings. The magnetic core is generally closed, that is that the magnetic field lines are concentrated within the core material in operational use. Therefore the magnetic core defines an opening and has the winding portion (where the primary and secondary coil are placed). The secondary windings, which have to tolerate the highest voltages in the invention are further provided with an extra insulation foil in the space within the opening, in order to further insulate the secondary windings from the magnetic core, i.e. the secondary windings, within the space within the opening, have a double insulation foil (that is the first and the second insulation foil together) between the primary coil and the secondary coil, and, additionally, an insulation foil (that is the second insulation foil) between the secondary coil and the magnetic core. The resulting transformer is able to tolerate much higher voltages on the terminals of the secondary coil without getting problems with “spark-over” and low dielectric ruggedness.

In order to facilitate understanding of the invention one or more expressions are further defined hereinafter.

The wording “high-voltage” must be interpreted as voltages of at least 1000V for alternating current (AC) and at least 1500V for direct current. This definition complies with the standards set by the International Electrotechnical Commission and its national counterparts (IET, IEEE, VDE, etc.). The typical output voltages in the current invention will be well above these levels.

Throughout this specification the wording “non-thermal plasma” is to be interpreted as a plasma which is not in thermodynamic equilibrium, because the electron temperature is much hotter than the temperature of heavy species (ions and neutrals). Alternative words for non-thermal plasma are cold plasma or non-equilibrium plasma.

Throughout this specification the wording “magnetic core” must be interpreted as a core built from material that can be magnetized, thus soft-magnetic material.

Throughout this specification the wording “winding portion” must be interpreted as the leg of the magnetic core around which the windings are located.

Throughout this specification the wording “concentric” must be interpreted broadly. In fact this word is generally used for circles, which also implies that the centres of the circles match accurately and the distance between those circles is constant. In a transformer the

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magnetic coils are generally not circular and neither is the magnetic core circular. In the current invention the word “concentric” must be interpreted as covering also non-circular coils that are placed inside each other. In addition the word “concentric” does not exclude the situation that the distance between the primary coil and secondary coil is not constant, i.e. that the distance may be larger at one side than at another side. As long as one magnetic coil is placed inside the other coil it is considered “concentric”.

Throughout this specification the wording “within the opening” is to be interpreted as the space or volume defined by the opening of the magnetic core, that is the volume that is surrounded by the magnetic core. This opening may also be called the “winding window” in the technical field of the invention.

In an embodiment of the high-voltage transformer of the invention the secondary windings are located outside the first insulation foil, while the primary windings are located inside the first insulation foil. This embodiment is advantageous because the secondary coil carries the highest voltages (both DC and AC) and placing the secondary coil on the outside makes the insulation easier for the part of winding outside the opening. Only the inner side faces objects with high voltage difference, and the first insulation foil alone gives adequate insulation properties for this part of the winding. In an alternative embodiment the secondary coil may be placed on the inside and the primary coil on the outside, but this will lead to an inferior robustness. Then also the part of the secondary winding outside the magnetic core would need a further insulation foil, similar to the first insulation foil, which insulates the secondary coil from the magnetic core all around the winding portion.

An embodiment of the high-voltage transformer of the invention further comprises support structure for holding the first insulation foil. It is convenient to implement a support structure for holding the first insulation foil in place in between the primary coil and the secondary coil.

In an embodiment of the high-voltage transformer of the invention the support structure comprises four corner structure, wherein each corner structure extends away from the winding portion of the at least one magnetic core, each corner structure having a slot for guiding the first insulation foil. Using corner structures that extend away from the magnetic core opens up for a variety of interesting technical features as will be explained with reference to some other dependent claims.

In an embodiment of the high-voltage transformer of the invention each corner structure

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comprises a primary winding yoke and a secondary winding yoke. This embodiment provides a first advantageous feature of the corner structures, i.e. to form the yokes for the primary and secondary windings.

In an embodiment of the high-voltage transformer of the invention the secondary winding yoke defines recesses for receiving groups of secondary windings. This embodiment provides a further advantageous feature of the corner structures, i.e. to be shaped such that the secondary windings can be grouped, which improves the robustness of the transformer, i.e. makes it tolerate higher voltages.

An embodiment of the high-voltage transformer of the invention further comprising a further support structure configured for holding the magnetic core within the transformer. As various parts have to be placed at predefined distances from each other, this embodiment conveniently provides a support structure, which holds the magnetic core in place relative to the primary and secondary coils.

In an embodiment of the high-voltage transformer of the invention the further support structure is further configured for holding the support structure. In this embodiment the further support structure conveniently holds the earlier-mentioned support structure, which comprises the corner structures. To achieve this effect the further support structure and support structure are either connected to each other or they made be made as one piece.

In an embodiment of the high-voltage transformer of the invention each of said insulation foils selected from the group consisting of: Teflon, Kapton, Nomex or any other adequate insulation material. These materials are the most known insulation materials. However, the invention is not limited to any one of these materials. Further materials may be invented or chosen in the future.

In an embodiment of the high-voltage transformer of the invention the first insulation foil comprises a single foil wound around the winding portion of the magnetic core multiple times for forming multiple layers of insulation material. It is a clear advantage of the invention that the thickness of the first insulation foil may be designed by wrapping the foil a number of times around the inner coil (either the primary coil or the secondary coil).

In an embodiment of the high-voltage transformer of the invention the second insulation foil comprises a single foil wound around the winding portion of the magnetic core multiple times forming multiple layers of insulation material. It is a clear advantage of the invention that the thickness of the second insulation foil may be designed by wrapping the foil a

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number of times around the secondary windings.

In a second aspect the invention relates to a high-voltage generation circuit for generating an output voltage for a high-voltage non-thermal plasma chamber electrode, the generation circuit comprising:

- the transformer according to the first aspect of the invention, wherein the primary coil has input terminals for receiving an input voltage, wherein the secondary coil has a first terminal at a first end and a second terminal at an opposite end, the first and second terminals being configured for delivering an amplified output voltage;

- a multi-stage rectifier circuit having a first terminal coupled to the first terminal of the secondary coil and a second terminal coupled to the second terminal of the secondary coil, the rectifier circuit having at least one and a half multiplier stages connected in series and coupled to the first terminal and the second terminal, the rectifier circuit having a DC-output terminal coupled to the last stage in the series of multiplier stages;

- a ground terminal coupled to the rectifier circuit for providing a ground potential to the rectifier circuit, and

- an generator output being coupled to the rectifier circuit and being configured for supplying the amplified output voltage to the non-thermal plasma chamber electrode, wherein the ground terminal is coupled to the DC-output terminal of the rectifier circuit, and in that the generator output is coupled to one of the first and second terminals of the rectifier circuit.

The high-voltage generation circuit in accordance with the second aspect concerns a first application for the high-voltage transformer of the invention. However, it is likely that this transformer can be used in other applications as well, even those where the rectifier circuit that is connected to the transformer is a conventional one, with a grounded terminal on its input side.

In an embodiment of the high-voltage transformer of the invention the magnetic core is electrically connected to an intermediate DC-voltage in between ground level and the output voltage to be generated. This embodiment concerns a further improvement of the circuit, wherein the magnetic core is no longer connected to ground, but connected to a voltage in between ground and the DC-output voltage. This further increases the robustness of the transformer, because it minimizes the electric fields.

In a third aspect the invention relates to a high-voltage generation circuit for generating an output voltage for a high voltage non-thermal plasma chamber electrode. The generation

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circuit comprises: i) a transformer having a primary coil and a secondary coil that are magnetically coupled, wherein the primary coil and the secondary coil have a turns ratio lower than or equal to 1, wherein the primary coil has input terminals for receiving an input voltage, wherein the secondary coil has a first terminal at a first end and a second terminal at an opposite end, the first and second terminals being configured for delivering an amplified output voltage; ii) a multi-stage full-wave rectifier circuit having a first terminal coupled to the first terminal of the secondary coil and a second terminal coupled to the second terminal of the secondary coil, the rectifier circuit having at least one and a half full-wave multiplier stages connected in series and coupled to the first terminal and the second terminal, the rectifier circuit having a DC-output terminal coupled to the last stage in the series of multiplier stages; iii) a ground terminal coupled to the rectifier circuit for providing a ground potential to the rectifier circuit, and iv) a generator output being coupled to the rectifier circuit and being configured for supplying the amplified output voltage to the nonthermal plasma chamber electrode. Interestingly, in the invention, the ground terminal is coupled to the DC-output terminal of the rectifier circuit, and the generator output is coupled to one of the first and second terminals of the rectifier circuit.

The effects of the features of the high-voltage generation circuit in accordance with the invention are as follows. High-voltage generation circuits having a transformer coupled to a rectifier circuit (multiplier circuit) are known as such.

However, a first key feature of the invention in accordance with the third aspect is that, instead of using the DC-output of the rectifier circuit for suppling a high DC-voltage, a different output is used as generator output, namely an output which carries both a DC-component as well as an AC-component. The DC-output of the rectifier circuit, which is normally coupled to further components for supplying the high output voltage, is coupled to ground. A traditional High-voltage generation circuit using a transformer with a traditional multiplier circuit would produce a high DC-voltage on this output. But now that the output is grounded the multiplier circuit will create large signals on at least one of its inputs (that is coupled to the secondary coil of the transformer), which signal is a high DC-voltage (either positive or negative compared to ground) with an AC-component on the top. The ratio between DC and AC is, amongst other factors, dependent on the number of multiplier stages in the rectifier circuit. In case of a full-wave rectifier circuit, there are even two inputs that carry large signals, namely both inputs that are coupled to the extreme ends of the secondary coil of the transformer. As will be elaborated upon, the inventor realized that in this way one high-voltage generation circuit may be used to drive two high-voltage non-thermal plasma electrodes. This is an enormous gain, which will be elaborated upon later. In a

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rectifier circuit, none of the outer terminals of the secondary coil must be grounded, but should instead be coupled to the input terminals of the rectifier circuit. One of these input terminals, namely the one that carries both a DC-voltage as well as an AC-voltage (the other terminal on the DC-line carries a DC-voltage only in a half-wave rectifier), is further coupled with the generator output, i.e. the terminal of the secondary coil that is coupled with the input terminal of the multiplier/rectifier circuit is used as generator output. This is the second key feature of the invention, which makes the circuit very revolutionary. It must be stressed that the invention factually changes the function of the input and output of the rectifier circuit. Hence the input terminals of the rectifier circuit are called first terminal and second terminal, respectively, in the claims. As far as the inventor is aware of, such way of using a multiplier circuit has not been seen before in the prior art. In fact this is also counter-intuitive as this puts extra design constraints on the transformer, which has to be able to tolerate higher voltages on its secondary coil. This will be elaborated upon in the detailed description.

In an embodiment of the high-voltage generation circuit according to the invention the multi-stage rectifier circuit (MS) comprises full-wave rectifier stages. The use of full-wave rectifier stages opens up the possibility for a very advantageous embodiment, when combined with the double-output embodiment as discussed in the previous paragraph, namely the AC-components on said generator outputs (of the full-wave rectifier) are in anti-phase (in case of a load balance).

The wording “full-wave rectifier circuit” must be interpreted as a rectifier circuit, which rectifies both positive and negative cycles of alternating-current (AC) voltages on its input. In contrast, the wording “half-wave rectifier circuit” is a rectifier circuit, which on rectifies either the positive cycle or the negative cycle of alternating-current (AC) voltages.

An embodiment of the high-voltage generation circuit according to the invention further comprises a further generator output being coupled to the other one of the first and second terminals of the rectifier circuit (not being the terminal on the DC line). The earliermentioned embodiment of the high-voltage generation circuit having a full-wave rectifier circuit allows for making two generator outputs on a single rectifier circuit, because it comprises two input terminals of the rectifier circuit, which carry a DC-voltage as well as an AC-voltage. This enables controlling two non-thermal plasma chamber electrodes with a single circuit simultaneously. In addition driving two (similar) non-thermal plasma chamber electrodes will automatically balance the loading on the generator outputs.

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In an embodiment of the high-voltage generation circuit according to the invention the rectifier circuit comprises a series of Cockcroft-Walton multiplier stages. Cockcroft-Walton multiplier stages are well-known and very suitable for being used as rectifier. There are different names for the same circuit: Villard Cascade. A traditional Cockcroft-Walton multiplier, as colloquially known, is a charge pump used to turn high voltage into very high voltage. For this task transformers are not as suitable. Much like coupled inductors a Cockcroft-Walton multiplier ‘trades’ current for voltage, but unlike a transformer, a traditional Cockcroft-Walton multiplier outputs a DC voltage.

In an embodiment of the high-voltage generation circuit according to the invention each multiplier stage comprises rectifying components and energy storage. Rectifying components, such as diodes, and energy storage elements, such as capacitors, are common components of most conventional multiplier stages.

In an embodiment of the high-voltage generation circuit according to the invention all rectifying components in the series of multiplier stages are placed such that their forward bias direction is directed from the ground terminal to the secondary coil. In this embodiment the DC-component of the voltage on two generator outputs is positive, whereas the AC-components on said generator outputs (of the full-wave rectifier) are in anti-phase (in case of a load balance).

In an embodiment of the high-voltage generation circuit according to the invention all rectifying components in the series of multiplier stages are placed such that their forward bias direction is directed from the secondary coil to the ground terminal. In this embodiment the DC-component of the voltage on two generator outputs is negative, whereas the AC-components on said generator outputs (of the full-wave rectifier) are in anti-phase (in case of a load balance).

In an embodiment of the high-voltage generation circuit according to the invention the middle line of capacitors is left out. The inventor(s) realised that in case of enough balance in the loads (when both outputs are used in a full-wave rectifier) coupled to the generator outputs of the high-voltage generator, the AC-current through the middle line of capacitors is virtually zero and hence the capacitors of the middle line can be taken out. This saves both space and costs. Any oscillations in the loads may also require extra measures in the driver on the primary side of the transformer, which generates the signal to be amplified and rectified.

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In a fourth aspect the invention relates to a high-voltage non-thermal plasma system comprising the high-voltage generation circuit according to the invention, and further comprising at least one electrode pair of which one electrode is a high-voltage non-thermal plasma chamber electrode coupled to one generator output and of which the other electrode is coupled to ground. A high-voltage non-thermal plasma system typically comprises at least two electrodes, one of which coupled to ground and the other to a high voltage.

An embodiment of the high-voltage non-thermal plasma system according to the invention, comprises at least one electrode pair of which one electrode is a high-voltage nonthermal plasma chamber electrode coupled to one generator output and of which the other electrode is coupled to ground. This embodiment of the high-voltage non-thermal plasma system benefits from the fact that the high-voltage generator of the invention offers two generator outputs, with phase-shifted signals.

In a fifth aspect the invention relates to a non-thermal plasma-based gas-treatment system comprising the high-voltage non-thermal plasma system according to the second aspect of the invention. The non-thermal plasma-based gas-treatment system comprises a gas-treatment apparatus. The gas-treatment apparatus comprises an gas inlet, a plasma chamber in fluid communication with the gas inlet and a gas outlet in fluid communication with the plasma chamber. The plasma chamber comprises said high voltage non-thermal plasma chamber electrodes for creating a corona for treating gas that flows through the plasma chamber in operational use. Non-thermal plasma-based gas-treatment device, when based on high-density non-thermal plasma (corona discharge), can be easily designed with gas-treatment capacities between 40000-60000m3/hour per module as the inventors prototype showed.

BRIEF INTRODUCTION OF THE FIGURES

In the following is described examples of embodiments illustrated in the accompanying figures, wherein:

Fig. 1a shows a perspective view of a non-thermal plasma-based gas-treatment system in accordance with an embodiment of the invention;

Fig. 1b shows a front-view of the non-thermal plasma-based gas-treatment system of Fig.1a;

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Fig. 2 shows a half-wave high-voltage generation circuit as known from the prior art;

Fig. 3 shows a modified half-wave high-voltage generation circuit in accordance with an embodiment of the invention;

Fig. 4 shows a modified full-wave high-voltage generation circuit in accordance with another embodiment of the invention;

Fig. 5 shows a further modified full-wave high-voltage generation circuit in accordance with another embodiment of the invention;

Fig. 6 shows the same full-wave high-voltage generation circuit as Fig.5, yet drawn differently;

Fig. 7 shows a yet further modified full-wave high-voltage generation circuit in accordance with another embodiment of the invention;

Fig. 8 shows a simplified full-wave high-voltage generation circuit in accordance with another embodiment of the invention;

Fig. 9 shows a high-voltage non-thermal plasma system using the high-voltage generation circuit of Fig.8 driving two high-voltage non-thermal plasma chamber electrodes;

Fig. 10 illustrates an important advantage of the high-voltage non-thermal plasma system of Fig.9;

Fig. 11 shows a front-view of a high-voltage transformer in accordance with an embodiment of the invention;

Fig. 12 shows a side-view of the high-voltage transformer of Fig.11;

Fig. 13 shows a top-view of the high-voltage transformer of Fig.11;

Fig. 14 shows a perspective view of the high-voltage transformer of Fig.11;

Fig. 15 shows an enlarged view of part of Fig.14;

Fig. 16 shows a different perspective view of the high-voltage transformer of Fig. 11;

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Fig. 17 shows an enlarged view of part of Fig.16, and

Fig. 18 shows a corner structure as part of the support structure in accordance with the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various illustrative embodiments of the present subject matter are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various systems, structures and devices are schematically depicted in the figures for purposes of explanation only and to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached figures are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

The invention will be discussed in more detail with reference to the figures. The figures will be mainly discussed in as far as they differ from previous figures.

Fig. 1a shows a perspective view of a non-thermal plasma-based gas-treatment system 1 in accordance with an embodiment of the invention. Fig.1b shows a front-view of the non-

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thermal plasma-based gas-treatment system 1 of Fig.1a. The gas-treatment system 1 comprises an gas-treatment apparatus 10 as illustrated on the right side of the drawing. The gas-treatment apparatus 10 comprises an inlet 12, a plasma chamber 15 in fluid communication with the inlet 12, and an outlet 18 in fluid communication with the plasma chamber 15. The plasma chamber 15 is fed with high-voltage through high-voltage supply cables 30-1, 30-2 as illustrated. A shielded interface cabinet may be provided to cover the supply cables, but this part is not shown in figure 1. The high-voltage supply cables 30-1, 30-2 are supplying high voltages to the plasma chamber 15, which voltages are generated by a high-voltage unit 20. The high-voltage unit 20 comprises a high-voltage generation circuit (not shown in Figs.1a and 1b). The system 1 in Figs.1a and 1b is operated as follows. During operation polluted gas 99d is sucked or pumped into inlet 12 as illustrated by the thick arrow at the bottom of the drawing. In order to achieve this gas flow a pump or a fan may be implemented either inside the system 1 or outside. Gas flow may be achieved with one or more fans creating pressure difference resulting in a gas flow through the plasma reaction chamber. The fans may be installed upstream or downstream of the plasma chamber. After entering the inlet 12 the polluted gas 99d flows to the plasma chamber 15, where it is treated with non-thermal plasma, i.e. corona discharge. During this plasma treatment the gas is cleaned, i.e. removed from pollution and smell, and thus turned into clean gas (or treated gas) 99c, which is then flowing to the outlet 18 and leaves the gas-treatment system 1 as illustrated by the large arrow at the top.

When it comes down to non-thermal plasma treatment of gas, it is important to note that there are different ways of doing so. The applicant developed a system, which is a corona radical shower (CRS) system, which generates a certain type of Non-Thermal Plasma (NTP). “Corona discharge” is a name of one discharge process that leads to NTP. The applicant developed a pulsed-plasma system, which is capable of generating high-density NTP.

In the following figures the high-voltage unit 20 will be elaborated upon in more detail, in particular the high-voltage generation circuit that forms part of it.

In order to properly understand the inventiveness of the current invention the discussion will start with a presentation of a known high-voltage generation circuit.

Fig. 2 shows such half-wave high-voltage generation circuit 100p as known from the prior art. This circuit 100p uses a so-called Cockcroft-Walton generator, which is well-known as such. Villard cascade is another name of the same circuit. The circuit 100p comprises a

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transformer Tp having a primary coil L1 that is magnetically coupled with a secondary coil L2 in accordance with a turns ratio (defined as the number of primary turns divided by the number of secondary turns). The consequence of the turns ratio of the transformer Tp is that an alternating input voltage Vti on terminals of the primary coil L1 results in an upscaled alternating output voltage Vto on the terminals of the secondary coil L2. When the turns ratio is smaller than 1 the amplitude of the output voltage Vto is equal to the amplitude of the input voltage Vti divided by the turns ratio.

As one of the terminals of the secondary coil L2 is coupled to a ground terminal GND as illustrated, it will be the other terminal of the secondary coil L2 that makes the full swing in accordance with the upscaled amplitude.

The transformer Tp is coupled to a multi-stage half-wave rectifier circuit HMSp (here a multi-stage Cockcroft-Walton (CW) multiplier). The output terminal To of the high-voltage generation circuit 100p is coupled to an output TM2 of the last stage of the multi-stage half-wave rectifier circuit HMSp.

The CW multiplier is a voltage multiplier that converts AC or pulsing DC electrical power from a low voltage level to a higher DC voltage level. It is made up of a voltage multiplier ladder network of capacitors and diodes to generate high voltages. Using only capacitors and diodes, these voltage multipliers can step up relatively low voltages to extremely high values, while at the same time being far lighter and cheaper than transformers. The biggest advantage of such circuits is that the voltage across each stage of the cascade is equal to only twice the peak input voltage. A great advantage of CW is that it requires relatively low-cost components which are easy to insulate.

The multi-stage half-wave rectifier circuit HMSp of Fig.2 comprises a ladder of capacitors C1..C4 and diodes D1..D4, which form a 2-stage CW multiplier as illustrated. The CW multiplier is operated as follows. The circuit HMSp is powered by the alternating voltage Vto with a peak value of that we define as equal to Vp, and initially the capacitors C1..C4 are uncharged. After the input voltage Vto is turned on, the following happens:

1) When the input voltage Vto reaches its negative peak −Vp, current flows through diode D1 to charge capacitor C1 to a voltage of Vp.

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2) When Vto reverses polarity and reaches its positive peak Vp, it adds to the capacitor's voltage to produce a voltage of 2Vp on the righthand plate of capacitor C1. Since diode D1 is reverse-biased, current flows from capacitor C1 through diode D2, charging capacitor C2 to a voltage of 2Vp.

3) When Vto reverses polarity again, current from capacitor C2 flows through diode D3, charging capacitor C3 also to a voltage of 2Vp.

4) When Vto reverses polarity again, current from capacitor C3 flows through diode D4, charging capacitor C4 also to a voltage of 2Vp on the DC-output TM2 of the last stage.

With each change in input polarity, current flows up the "stack" of capacitors through the diodes, until they are all charged. All the capacitors C2..C4 are charged to a voltage of 2Vp, except for the first capacitor C1, which is charged to Vp. The key to the voltage multiplication is that while the capacitors C1..C4 are charged in parallel, they are coupled to the load in series. Since C2 and C4 are in series between the output and ground, the total output voltage (under no-load conditions) is 4Vp. The circuit HMSp can be extended to any number of stages. The no-load output voltage is twice the peak input voltage multiplied by the number of stages N or equivalently the peak-to-peak input voltage swing (Vpp) times the number of stages.

When considering the circuit of Fig.2, the inventor realized the following. The output terminal To of the high-voltage generation circuit 100p is coupled to the DC-line, defined by the series connection of capacitors C2 and C4, of the CW-circuit. The output terminal carries a DC-voltage. The other line of the high-voltage generation circuit 100p, defined by the series connection of capacitors C1 and C3, does not carry pure DC voltages, but rather a DC-voltage with an AC-voltage superimposed. The ratio of the DC-component and the AC-component of these voltages depends on the position in the ladder. Then the idea was born that these DC/AC voltages can be used to create a pulsed non-thermal plasma.

Fig. 3 shows a modified half-wave high-voltage generation circuit 100 in accordance with an embodiment of the invention. This figure will only be discussed in as far as it differs from Fig.2.

The first group of modifications of the modified half-wave high-voltage generation circuit 100 is concerns a modified transformer T. How this modified transformer T has been modified will be explained with reference to Figs.11 to 17. The second group of modifications

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concerns a modified half-wave multiplier circuit HMS. The inventor realized that, as a first technical modification, the DC-output TM2 of the multi-stage half-wave rectifier circuit HMS may be coupled to ground instead of connecting of the input terminals to ground as Fig. 2. shows. By doing so, the high-voltage generation circuit 100 will push (pump) the input potentials on the input terminals to large values, albeit negative voltages compared to ground, in the example of Fig.3. Then, as a second technical modification, the output terminal To1 of the high-voltage generation circuit 100 is coupled to an AC-input terminal of the rectifier circuit HMS. The output terminal To1 will then carry a high DC-voltage with an AC-component on top of it. Consequently, the requirements for the transformer T will be more severe in that the transformer needs to tolerate large voltages on its secondary coil terminals. The inventors came with inventive measures to solve this problem, which will be elaborated upon in the discussion of Figs.11-17.

Fig. 4 shows a modified full-wave high-voltage generation circuit 100-1 in accordance with another embodiment of the invention. Fig.4 extends the idea behind Fig.3 to full-wave multiplier circuits. This figure shows a full-wave Cockcroft-Walton multiplier having a ladder of capacitors C and diodes D as shown. The secondary coil L2 of the transformer differs from the one in Fig.3 in that it comprises three terminals, namely a first output terminal TL2A to be coupled with a first AC-line of the CW multiplier, a middle output terminal TL2M to be coupled with the DC-line of the CW multiplier, and a second output terminal TL2B to be coupled with a second AC-line of the CW multiplier. A great advantage of the illustrated full-wave multiplier 100-1 is that it offers the possibility of implementing two output terminals To1, To2 to both AC-input terminals of the rectifier circuit HMS as illustrated. The interesting thing is that both terminals carry a high DC-voltage (negative) with an AC-component on top of it. However, the respective AC-components are in antiphase (in case of balanced load). In this way one high-voltage generation circuit can be used to drive two high-voltage electrodes as will be explained later, which constitutes a very advantageous embodiment. A full-wave rectifier operates similar to two half-wave rectifier circuits, which are placed “back-to-back” sharing their DC-lines.

Fig. 5 shows a further modified full-wave high-voltage generation circuit 100-2 in accordance with another embodiment of the invention. Fig.6 shows the same full-wave high-voltage generation circuit as Fig.5, yet drawn differently. These figures will only be discussed in as far as they differs from Fig.4. The main difference is that an extra half stage has been added to the ladder at the left side of the multiplier, i.e. one capacitor C and two diodes D have been added. The operation of the circuit is exactly the same, apart from the fact that output voltage in the current example will be 3 times the amplitude on the inputs

P29707NO00 - description and claims, priority

of the ladder. It is important to note that in a two-and-a-half stage multiplier as shown in the figure, the peak voltage is three times the amplitude (peak-peak) on the input voltage. However, the voltage swing on the terminal TL2M connected to the middle line is two-anda-half times the amplitude (peak-peak) on the input voltage. Hence the fact that this circuit is referred to in this specification as a two-and-a-half-stage multiplier, because this complies with the traditional DC-view on multipliers, i.e. it is the DC-line which is generally of interest in multipliers.

Fig. 7 shows a yet further modified full-wave high-voltage generation circuit 100-3 in accordance with another embodiment of the invention. This figure will only be discussed in as far as it differs from Fig.6. The main difference is that the diodes D have been put in reverse, i.e. their forward bias direction is now from the ground terminal (GND) to the secondary coil (L2), instead of the opposite. The consequence of this is that the DC voltage on the output terminals To1, To2 is now positive. Both terminals still carry an AC-component on top of this DC-voltage. Furthermore, in Fig.7 the middle line ML (or DC-line) has now been highlighted with the dashed box. The capacitors CM of the DC-line are marked with reference sign CM.

Fig. 8 shows a simplified full-wave high-voltage generation circuit 100-4 in accordance with another embodiment of the invention. This figure will only be discussed in as far as it differs from Fig.7. The inventors realized that because of the presence of the two diodes of the half-stage in case of a properly balanced load on the outputs To1, To2 there is hardly any current running through the capacitors CM of the DC-line ML (Fig.7). In other words, these components CM can be left out, which saves both space and costs. This results in a simplified multi-stage full-wave rectifier circuit.

Some further aspects have been illustrated in Fig.8, which also apply to Figs.3 to 7. For instance, the turns ratio N between the primary coil and the secondary coil is illustrated. In other words the output voltage Vo on the terminals TL2A, TL2B of the secondary coil L2 will be the input voltage Vi on input terminals TL1A, TL1B divided by the turn ratio N. Also, Fig. 8 shows what is meant in the claims with first end e1 and opposite second e2. This also applies consistently for all figures 3 to 7. The input terminals TM1A, TM1B of the multi-stage full-wave rectifier MS, as for the other embodiments are connected to the terminals TL2A, TL2B of the secondary coil L2, and effectively function as a “outputs” of the high-voltage generation circuit 100-4.

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Fig. 8 also illustrates how multiplier stages are defined and connected within the multistage full-wave rectifier circuit 100-4. This also applies to Fig.5 to 7. The first multiplier stage SA on the left is a half-stage. This first multiplier SA comprises of two diodes D1, and in embodiments having a DC-line it comprises one capacitors CM in addition. However, the two extra diodes D added by this stage also lead to earlier-mentioned possibility of simplifying the multiplier circuit removing the DC-line. The second multiplier stage SB is a full-stage comprising four diodes D and two capacitors C. The third multiplier stage SC is also a full-stage comprising four diodes D and two capacitors C.

Fig. 9 shows a high-voltage non-thermal plasma system 200 using the high-voltage generation circuit 100-4 of Fig.8 driving two high-voltage non-thermal plasma chamber electrodes EL1A, EL2A. This figure will only be discussed in as far as it differs from Fig.7. The non-thermal plasma system 200 comprises the earlier discussed high-voltage generation circuit 100-4. In a pulsed non-thermal plasma gas-treatment system the plasma chamber (not shown) typically comprises electrode pairs, each having one high-voltage non-thermal plasma chamber electrode El1A, EL2A (connected to the respective output terminals To1, To2 of the high-voltage generation circuit 100-4 as illustrated) and one ground electrode EL1B, EL2B (connected to the ground terminal GND as illustrated).

Fig. 10 illustrates an important advantage of the high-voltage non-thermal plasma system 200 of Fig.9. In this figure many components (i.e. the diodes) have been left out in order to illustrate this advantage. Each output terminal of the high-voltage generation circuit is loaded with a so-called parasitic capacitance CP between each pair of electrodes, that is between the high-voltage non-thermal plasma electrode EL1A, EL2A and ground electrode EL1B, EL2B as illustrated.

It has already been mentioned that the AC-signals on the respective outputs are in antiphase. It is exactly because of these feature that, when the loads on the outputs of the high-voltage generation circuit are balanced, the load current Io (charging- and discharging current) that runs between said parasitic capacitances main runs through the secondary coil L2 and not through the capacitance network defined by the capacitors C. This is a huge gain as it relaxes the requirements for the high-voltage generation circuit. Another convenient property is that an uneven power distribution between the two loads will not create a DC-magnetic field in the transformer, as is the case without the half-stage of the multiplier.

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On the input side of the high-voltage generation circuits as shown in Figs.2-10 there must be put a rectangular-wave form. This has not been discussed in detail so far. A driver circuit (not shown) is required which drives the primary coil L1 of the transformer T. This driver circuit typically generates the required square-wave form.

Moving the transformer to the high-voltage side of the multiplying network introduces several important advantages, but also creates a need for the transformer to support the total output voltage between primary and secondary. In addition, when the load sparks in one of the load banks, it causes the secondary coil seeing full output voltage between the secondary coil terminals.

In addition to immersing the transformer in oil and paying attention to insulation and creepage distances, several measures were taken to make a transformer that is rugged enough to tolerate those voltages. Some of these measure are quite innovative:

Measure 1. Making the secondary winding out of Teflon-insulated wire. Teflon/PTFE has very high electric field breakdown and it is mineral oil resistant. Alternatives for Teflon are Kapton, Nomex or the like. These alternative materials apply for any part mentioned in this description that is made of Teflon.

Measure 2. Design and use a secondary winding bobbin strictly organising the winding in defined portions.

Measure 3. Use a primary winding bobbin giving insulation distance to the core.

Measure 4. Bias the magnetic core to a voltage level between GND and output, typically the DC-voltage of one of the intermediate nodes (see DC1, DC2 in Fig.10) on the middle line.

Measure 5. Introduce two perpendicular foils (rolls) of insulation sheet, one separating the secondary windings from the magnetic cores and primary winding, and one separating the secondary windings from the primary windings.

Measure 4, as simple as it may seem, is something which has not been reported before, the reason obviously being that there never has been a need to do so. In practise all what is required is to electrically connect the magnetic cores to this intermediate potential, which may be conveniently taken from the intermediate nodes of the multiplier circuit.

Measures 2, 3 and 5 will be discussed with reference to Figs.11-17.

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Fig. 11 shows a front-view of a high-voltage transformer T in accordance with an embodiment of the invention. The high-voltage transformer T comprises two magnetic cores T10 (but it could also be only one core or more than two) around which primary windings T5 of the primary coil and secondary windings T15 of the secondary coil are concentrically winded (the secondary windings on the outside), yet with a distance between the core T15 and the primary windings T5 and a distance between the primary windings T5 and the secondary windings T15 as illustrated. Fig.11 shows a first support structure T20 inside the coils as illustrated, which is for housing the magnetic cores T10 and for supporting a second support structure T22. The second support structure T22 comprises four corners parts T22a, T22b, T22c, T22d that are interconnected or kept in place by the first support structure T20 (not clearly visible in Fig.11). There is one corner structure at each corner of the windings, wherein the corner structures T22a-T22d each extend away from a respective corner of the magnetic core T10. The corner structures T22a-T22d of the second support structure T22 each have the function of the earlier mention bobbin for the primary windings T5 (measure 3), the bobbin for the second windings T15 (measure 2), but also for guiding and holding the first insulation foil T30 and keeping it in the right place (measure 5). Fig.11 shows that the first insulation foil T30 is positioned in between the primary windings T5 and the secondary windings T15 on the outside. The first insulation foil T30 may comprise materials from the group consisting of: Teflon, Kapton, Nomex or other adequate insulation foil. Also the first insulation foil T30 may be wound multiple times such that it forms multiple layers. Fig.11 also illustrates how a second insulation foil T32 is provided (wound one or more times) around the secondary windings T32. The second insulation foil T32 may comprise materials from the group consisting of: Teflon, Kapton, Nomex or other adequate insulation foil. In one embodiment the primary coil may comprise two primary windings T5 comprising copper foil with insulation material (i.e. Nomex) on one side, preferably facing towards the magnetic core T10. In an embodiment the secondary coil may comprise between 30 and 60 turns/secondary windings T15 of Teflon insulated copper wire. The primary coil may comprise a different number of windings/turns, but typically comprises between 1 and 4 turns.

On the input of the primary coil the input voltage is typically a rectangular wave form. The resulting output voltage on the secondary coil is then typically a sinusoidal pulse-like signal.

Fig. 12 shows a side-view of the high-voltage transformer T of Fig.11. In this side view the bobbin function of the corner structure T22a, T22b of the second support structure T22 is clearly illustrated, including how its form having a plurality of recess T23 facilitates

P29707NO00 - description and claims, priority

the grouping of the secondary windings T15. Also visible in the figure is how the first insulation foil T30 extends beyond the width of the secondary windings T15 such that it properly insulates the secondary windings T15 from the primary windings T5. The primary windings T5 are not visible in this view, because they are underneath the first insulation foil T30.

Fig. 13 shows a top-view of the high-voltage transformer T of Fig.11. In this view it is more clearly illustrated how the second insulation foil T32 insulates the secondary windings from the core T10. Also, this view illustrates how the corner structure T22b, T22c of the second support structure T22 are provided with elongated slots T25, which allow the first insulation foil T30 to be led through and to be wound around the primary windings T5 yet spaced apart from them. The figure further illustrates the shape of the magnetic core T10 and how it defines an opening T12. In addition, the figure shows what is meant with “winding portion” T11 of the magnetic core T10, namely that “leg” of the magnetic core T10 around which the respective windings T5, T15 and first insulation foil T30 are provided. The figure further serves to illustrate how the second insulation foil T32 is provided within the opening T12 such that it insulates the secondary windings T15 from the magnetic core T10.

Fig. 14 shows a perspective view of the high-voltage transformer T of Fig.11. Fig.15 shows an enlarged view of part of Fig.14. In these figures the placement of the first insulation foils T30 is more clearly illustrated. It is clearly visible that the first insulation foil T30 goes around the structure through the respective elongated slots T25 of the second support structure T22. Also the first support structure T20 inside the windings is more clearly visible. The first support structure T20 holds the second support structure in the right position, but also the magnetic cores T10, and the primary winding T5. It is clearly seen how the first insulation foil T30 effectively adds to the insulation of the primary winding. Like the previous figure, these figures illustrates the shape of the magnetic core T10 and how it defines the opening T12. In addition, these figures show what is meant with the winding portion T11. These figures also further serve to illustrate more clearly how the second insulation foil T32 is provided within the opening T12 such that it insulates the secondary windings T15 from the magnetic core T10.

Fig. 16 shows a different perspective view of the high-voltage transformer T of Fig.11. Fig. 17 shows an enlarged view of part of Fig.16. These figures serves to illustrate how the second insulating foil T32 is wound around the secondary windings T15, and also how in the volume within the magnetic cores T10 the second insulating foil T32 effectively adds

P29707NO00 - description and claims, priority

to the insulation of the first insulating foil T30, when it comes down to the insulation of the secondary windings T15 from the core T10, for the secondary winding portion located in the opening T12. Like Figs.14 and 15, these figures also further serve to illustrate more clearly how the second insulation foil T32 is provided within the opening T12 such that it insulates the secondary windings T15 from the magnetic core T10.

Fig. 18 shows a corner structure T22a-T22d as part of the support structure T22 in accordance with the invention. This figure clearly illustrates how the support structure T22 provides multiple technical features simultaneously. First of all, there is the primary winding yoke T22p and the secondary winding yoke T22s as illustrated. In between these two parts there is the elongated slot T25 for receiving and holding the first insulation foil T30 (Fig.17). The placement of this elongated slot T25 (determining the distance between the primary insulation foil T30 and the respective coils) is not critical, but chosen based on practical considerations when designing the transformer. Finally, there are the earlier discussed recesses T23 for grouping the secondary windings T15 (Fig.17). As the earlier figures show, there is one corner structure T22a-T22d on extending away from each corner of the winding portion T11 of the magnetic cores (here there are two magnetic cores, but this could alternatively have been only one larger core).

Some aspects of the invention are defined by the following items.

Item 1. High-voltage generation circuit (100) for generating an output voltage (Vo) for a high-voltage non-thermal plasma chamber electrode (EL1A, EL2A), the generation circuit (100) comprising:

- a transformer (T) having a primary coil (L1) and a secondary coil (L2) that are magnetically coupled, wherein the primary coil (L1) and the secondary coil (L2) have a turns ratio (N) lower than or equal to 1, wherein the primary coil (L1) has input terminals (TL1A,TL1B) for receiving an input voltage (Vi), wherein the secondary coil (L2) has a first terminal (TL2A) at a first end (e1) and a second terminal (TL2B) at an opposite end (e2), the first and second terminals (TL2A,TL2B) being configured for delivering an amplified output voltage (Vo);

- a multi-stage rectifier circuit (MS) having a first terminal (TM1A) coupled to the first terminal (TL2A) of the secondary coil (L2) and a second terminal (TM1B) coupled to the second terminal (TL2B) of the secondary coil (L2), the rectifier circuit (MS) having at least one and a half multiplier stages (SA, SB, SC) connected in series and coupled to the first terminal (TL2A) and the second terminal (TL2B), the rectifier circuit (MS) having a

P29707NO00 - description and claims, priority

DC-output terminal (TM2) coupled to the last stage (SA) in the series of multiplier stages (SA, SB, SC);

- a ground terminal (GND) coupled to the rectifier circuit (MS) for providing a ground potential to the rectifier circuit (MS), and

- a generator output (To1) being coupled to the rectifier circuit (MS) and being configured for supplying the amplified output voltage (Vo) to the non-thermal plasma chamber electrode (),

c h a r a c t e r i s e d i n that the ground terminal (GND) is coupled to the DC-output terminal (TM2) of the rectifier circuit (MS), and in that the generator output (To1) is coupled to one (TM1A) of the first and second terminals (TM1A, TM1B) of the rectifier circuit (MS).

Item 2. The high-voltage generation circuit (100) according to item 1, wherein the multistage rectifier circuit (MS) comprises full-wave rectifier stages.

Item 3. The high-voltage generation circuit (100) according to item 2, further comprising a further generator output (To2) being coupled to the other one (TM1B) of the first and second terminals (TM1A, TM1B) of the rectifier circuit (MS).

Item 4. The high-voltage generation circuit (100) according to any one of the preceding items, wherein the rectifier circuit (MS) comprises a series of Cockcroft-Walton multiplier stages (SA, SB, SC).

Item 5. The high-voltage generation circuit (100) according to any one of the preceding items, wherein each multiplier stage (SA, SB, SC) comprises rectifying components (D) and energy storage elements (C, CM).

Item 6. The high-voltage generation circuit (100) according to item 5, wherein all rectifying components (D) in the series of multiplier stages (SA, SB, SC) are placed such that their forward bias direction is directed from the ground terminal (GND) to the secondary coil (L2).

Item 7. The high-voltage generation circuit (100) according to item 5 or 6, wherein all rectifying components (D) in the series of multiplier stages (SA, SB, SC) are placed such that their forward bias direction is directed from the secondary coil (L2) to the ground terminal (GND).

P29707NO00 - description and claims, priority

Item 8. The high-voltage generation circuit (100) according to any one of items 5 to 7 in as far as directly or indirectly dependent on item 2, wherein the middle line (ML) of capacitors (CM) is left out.

Item 9. High-voltage non-thermal plasma system (200) comprising the high-voltage generation circuit (100) according to any one of the preceding items, and further comprising at least one electrode pair (EL1A, EL1B) of which one electrode (EL1A) is a high-voltage non-thermal plasma chamber electrode coupled to one generator output (To1) and of which the other electrode (El1B) is coupled to ground.

Item 10. The high-voltage non-thermal plasma system (200) according to item 9, the system (200) comprising at least two electrode pairs (EL1A, EL1B, EL2A, EL2B) of which one electrode (EL1A, EL2A) is a high-voltage non-thermal plasma chamber electrode coupled to one generator output (To1, To2) and of which the other electrode (El1B, EL2B) is coupled to ground.

Item 11. Non-thermal plasma-based gas-treatment system (1) comprising the high-voltage non-thermal plasma system (200) according to item 9 or 10, the non-thermal plasmabased air-treatment system (1) comprising an gas-treatment apparatus (10), the gas-treatment apparatus (10) comprising an gas inlet (12), a plasma chamber (15) in fluid communication with the gas inlet (12) and an gas outlet (18) in fluid communication with the plasma chamber (15), the plasma chamber (15) comprising said high voltage non-thermal plasma chamber electrodes (EL1A, EL2A) for creating a corona for treating gas (99c, 99d) that flows through the plasma chamber (15) in operational use.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, instead of using Cockcroft-Walton multipliers, also other multiplier circuits may be used.

Furthermore, the number of multiplier stages in the multiplier circuit may be varied. All examples given show 2 or 2,5 stages. The invention applies for any number of stages larger than or equal to one and a half.

The person skilled in the art may find alternative solutions for the circuits presented here. The invention covers all these variants as long as they are covered by the independent claims. No limitations are intended to the details of construction or design herein shown,

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other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claims enumerating several means, several of these means may be embodied by one and the same item of hardware.

P29707NO00 - description and claims, priority

Claims

C l a i m s

1. High-voltage transformer (T) for generating an output voltage (V) for a high-voltage non-thermal plasma chamber electrode (EL1, EL2), the transformer (T) comprising: - at least one magnetic core (T10) defining an opening (T12) and having a winding portion (T11) at a side of the opening (T12), and

- a primary coil (L1) and a secondary coil (L2) that are magnetically coupled through the magnetic core (T10), wherein the primary coil (L1) and the secondary coil (L2) have a turns ratio (N) lower than or equal to 1, wherein the primary coil (L1) has a number of primary windings (T5), and wherein the secondary coil (L2) has a number of secondary windings (T15) larger than the number of primary windings (T5), the primary coil (L1), the secondary coil (L2) and the winding portion (T11) being placed concentrically when seen in a cross-sectional plane through the winding portion (T11);

- characterized in that the high-voltage transformer (T) further comprises:

i) a first insulation foil (T30) provided in between the primary windings (T5) and the secondary windings (T15) for insulating the secondary windings (T15) from the primary windings (T5), wherein the first insulation foil (T30) is spaced apart from both the primary windings (T5) and the secondary windings (T15), and

ii) a second insulation foil (T32) provided around the secondary windings (T15) within the opening (T12) for insulating the secondary windings (T15) from the magnetic core (T10) within the opening (T12).

2. The high-voltage transformer (T) according to claim 1, wherein the secondary windings (T15) are located outside the first insulation foil (T30), while the primary windings (T5) are located inside the first insulation foil (T30).

3. The high-voltage transformer (T) according to claim 1 or 2, further comprising a support structure (T22) for holding the first insulation foil (T30).

4 The high-voltage transformer (T) according to claim 3, wherein the support structure (T22) comprises four corner structures (T22a, T22b, T22c, T22d), wherein each corner structure (T22a, T22b, T22c, T22d) extends away from the winding portion (T11) of the at least one magnetic core (T10), each corner structure (T22a, T22b, T22c, T22d) having a slot (T25) for guiding the first insulation foil (T30).

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5 The high-voltage transformer (T) according to claim 4, wherein each corner structure (T22a, T22b, T22c, T22d) comprises a primary winding yoke (T22p) and a secondary winding yoke (T22s).

6 The high-voltage transformer (T) according to claim 5, wherein the secondary winding yoke (T22s) defines recesses (T23) for receiving groups of secondary windings (T15).

7. The high-voltage transformer (T) according to any one of the preceding claims, further comprising a further support structure (T20) configured for holding the magnetic core (T10) within the transformer (T).

8. The high-voltage transformer (T) according to claim 7, wherein the further support structure (T20) is further configured for holding the support structure (T22).

9. The high-voltage transformer (T) according to any one of the preceding claims, wherein each of said insulation foils (T30, T32) selected from the group consisting of: Teflon, Kapton, Nomex or any other adequate insulation material.

10. The high-voltage transformer (T) according to any one of the preceding claims, wherein the first insulation foil (T30) comprises a single foil wound around the magnetic core (T10) multiple times for forming multiple layers of insulation material.

11. The high-voltage transformer (T) according to any one of the preceding claims, wherein the second insulation foil (T32) comprises a single foil wound around the secondary windings (T15) multiple times forming multiple layers of insulation material.

12. High-voltage generation circuit (100) for generating an output voltage (Vo) for a high-voltage non-thermal plasma chamber electrode (EL1, EL2), the generation circuit (100) comprising:

- the transformer (T) according to any one of the preceding claims, wherein the primary coil (L1) has input terminals (TL1A,TL1B) for receiving an input voltage (Vi), wherein the secondary coil (L2) has a first terminal (TL2A) at a first end (e1) and a second terminal (TL2B) at an opposite end (e2), the first and second terminals (TL2A,TL2B) being configured for delivering an amplified output voltage (Vo);

- a multi-stage rectifier circuit (MS) having a first terminal (TM1A) coupled to the

P29707NO00 - description and claims, priority

first terminal (TL2A) of the secondary coil (L2) and a second terminal (TM1B) coupled to the second terminal (TL2B) of the secondary coil (L2), the rectifier circuit (MS) having at least one and a half multiplier stages (SA, SB, SC) connected in series and coupled to the first terminal (TL2A) and the second terminal (TL2B), the rectifier circuit (MS) having a DC-output terminal (TM2) coupled to the last stage (SA) in the series of multiplier stages (SA, SB, SC);

- an generator output (To1, To2) being coupled to the rectifier circuit (MS) and being configured for supplying the amplified output voltage (Vo) to the non-thermal plasma chamber electrode (EL1A, EL2A),

wherein the ground terminal (GND) is coupled to the DC-output terminal (TM2) of the rectifier circuit (MS), and in that the generator output (To1) is coupled to one (TM1A) of the first and second terminals (TM1A, TM1B) of the rectifier circuit (MS).

13. The high-voltage generation circuit (100) according to claim 12, wherein the magnetic core (T10) is electrically connected to an intermediate DC-voltage in between ground level and the output voltage (Vo) to be generated.

P29707NO00 - description and claims, priority