Improved low EMI transformer

Abstract

The present invention relates to a transformer (100e1) comprising: i) a magnetizable core (110) having a primary coil and a secondary coil, ii) a ground terminal (PE) for electrical connection to an external ground terminal (999) of a power grid (900), and iii) a physical electrical ground node (175) located at a location internal to the isolation transformer (100e1), the physical electrical ground node (175) being electrically connected to the ground terminal (PE, 199). The transformer (100e1) further comprises: iv) at least two conductive loops (CL1..CL6), each located at a distinct location within the transformer (100e1) where a magnetic field may build up during operational use, and v) a switching circuit (801) configured to sequentially, temporarily and selectively electrically couple a subset (SS) of the conductive loops (CL1..CL6) to the physical electrical ground node (175) according to a particular sequence and pattern. The present invention defines an isolation transformer that is much less susceptible to EMI without requiring any standards compliance, and furthermore, the transformer does not require any electromagnetic field adjustment or calibration.

Description

Detailed Description of the Invention

[0001] [Field of the Invention] The present invention relates to a transformer comprising a magnetisable core, at least one primary coil and at least one secondary coil arranged around the magnetisable core, a ground terminal for electrical connection to an external ground terminal of a power grid, and a physical electrical ground node located at a location internal to the transformer, the physical electrical ground node being electrically connected to the ground terminal. The present invention further relates to a power system comprising such a transformer. The present invention also relates to a method for improving the performance of an electrical or electronic device.

[0002] [Background of the invention] An isolation transformer prevents the transmission of the DC component of a signal from one circuit to another, but allows the AC component of the signal to pass. Transformers with a 1:1 primary to secondary winding ratio are often used to protect secondary circuits and individuals from electric shock between the energized conductor and ground. Properly designed isolation transformers block interference caused by ground loops. Isolation transformers with electrostatic shielding are used to power interference-sensitive equipment such as computers, medical equipment, or laboratory equipment.

[0003] Faraday cages are commonly used to block electric fields. An external electric field causes charges inside the conductive material (that makes up the cage) to distribute inside the cage in a way that cancels the effect of the electric field. This phenomenon is used to protect sensitive electronic devices inside the cage from external radio frequency interference (RFI). Faraday cages are also used to enclose devices that generate RFI themselves, such as radio transmitters. Thus, Faraday cages prevent radio waves from interfering with nearby devices outside the cage. If an electromagnetic field is changing, the faster it changes (i.e. the higher the frequency), the better the material is for the magnetic field to be impermeable. Shielding in this case also depends on the electrical conductivity and magnetic properties of the conductive material used in the cage, as well as its thickness.

[0004] The problem with the above-mentioned known isolation transformers is that they suffer from numerous electromagnetic interferences (EMI) even when used according to the international standards for the connection of isolation transformers. The noise levels can be an order of magnitude or more higher than the specified maximum permissible levels. Therefore, there is a clear need for further improvements in isolation transformers. The most relevant international standard is the "2011 NEC" which references UL, CSA and NEMA standards (NEMA ST-20).

[0005] The inventor of the present invention previously proposed a low EMI transformer in WO2019 / 013642, comprising: i) a Faraday cage with a magnetic core, at least one primary coil and at least one secondary coil; ii) an input terminal connected to at least one primary coil via an input wire; iii) an output terminal connected to at least one secondary coil via an output wire; iv) an input ground terminal for connecting to the Faraday cage; and an output ground terminal connected to the Faraday cage for further connection to another circuit connected to the isolation transformer. In WO2019 / 013642, the isolation transformer further comprises: v) a clean ground input terminal for receiving an external clean ground; vi) a clean ground output terminal for connecting to another clean ground input terminal of another circuit; and vii) a physical electrical node located inside the Faraday cage at a position where the magnetic flux and electric field are at a minimum, preferably close to zero. The clean ground input terminal transmits power to the isolation transformer and is connected to the physical electrical node via a first electrical connection. Additionally, the physical electrical node is further electrically connected to a clean ground output terminal via a second electrical connection.

[0006] An important feature of the transformer described in WO2019 / 013642 is that the transformer is provided with a separate (additional) input terminal for receiving a clean ground and a separate (additional) output terminal for supplying a clean ground to another circuit. Whereas in this previous prior art solution, all grounds are connected to each other, i.e. there is no separate low EMI ground. The (normal) input ground terminal is connected to a Faraday cage, which may be further connected to another Faraday cage of another circuit. This is also the case in previous prior art solutions. The clean ground input terminal is fed to a physical electrical node, which is further fed towards a clean ground output terminal. The inventors have found that the location of this physical electrical node is very important, i.e. the node must be located where the magnetic flux and electric field are at their lowest values. Furthermore, the ideal location of the physical electrical node is also determined by the load of the transformer, since the load determines the electric and magnetic fields generated inside. Furthermore, the clean ground output terminal is fed to another clean ground input of another circuit during operation. The first and second electrical connections are preferably arranged in such a way that they generate minimal EMI, for example by using shielded wires and running the wires in parallel with other signal carrying conductors. The first and second electrical connections should also have low impedance at high frequencies as well as at low frequencies. By taking these technical measures, the transformer described in WO2019 / 013642 defines a transformer in which EMI generated in another circuit is re-fed to the transformer via a low impedance clean ground connection, instead of via a high impedance ground connection which would cause a lot of noise in the supply voltage of the other circuit as well as in circuits and components connected to the other circuit. The result of the combination of the above mentioned features is an isolation transformer which is much less susceptible to EMI than isolation transformers known in the previous prior art.

[0007] However, a possible drawback of the transformer described in WO2019 / 013642 is that it requires the application of international standards for the connection of isolation transformers, which may pose a barrier or at least delay the commercialization of this exciting product.

[0008] Another drawback of the transformer described in WO2019 / 013642 is that it requires some degree of electromagnetic field calibration and application dependent adjustment, and requires a great deal of electromagnetic knowledge.

[0009] Therefore, there is a need to further develop low EMI transformers to solve these problems. [Summary of the Invention] The present invention aims to ameliorate or reduce at least one of the disadvantages of the prior art, or at least to provide a useful alternative to the prior art.

[0010] This object is achieved by means of the features set out in the following description and the claims that follow. The invention is defined by the independent claims. The dependent claims define advantageous embodiments of the invention.

[0011] In a first aspect, the present invention relates to a transformer comprising: Magnetizable core and at least one primary coil and at least one secondary coil disposed around a magnetizable core; a ground terminal for electrical connection to an external ground terminal of the power grid; a physical electrical ground node located at a location internal to the transformer, the physical electrical ground node being electrically connected to the ground terminal.

[0012] The transformer further at least two conductive loops each disposed at a separate location within the transformer where a magnetic field may build up during operational use; and switching circuitry configured to sequentially, temporarily, and selectively electrically couple a subset of the conductive loops to a physical electrical ground node according to a particular order and pattern.

[0013] The effects of the transformer according to the present invention are as follows. It should be noted that an important feature of the present invention is that it does not require the application of international standards for the electrical connection of the transformer to the power grid and to the load. On the outside, the transformer has conventional input and output terminals, as well as a ground terminal. On the inside, however, the transformer has some special features, which are explained below.

[0014] The first feature involves providing at least two conductive loops, each located at a distinct location within the transformer where a magnetic field may build up during operational use. As the various embodiments show, there are different locations suitable for such placement, but what is important is that the conductive loops are purposefully placed where magnetic fields are expected to build up, and therefore where EMI is actually expected to build up. This is as opposed to the placement of physical electrical nodes in WO2019 / 013642, which are purposefully placed where the magnetic fields are determined or predicted to be lowest.

[0015] The second feature relates to providing a switching circuit configured to sequentially, temporarily, and selectively electrically couple a subset of the conductive loops to the physical electrical ground node according to a predetermined order and pattern. In the most basic form, where there are two conductive loops, this means that the loops are alternately electrically connected to the physical electrical ground node. The inventor has observed that by sequentially, temporarily, and selectively electrically coupling a subset of the conductive loops to the physical electrical ground node, EMI is effectively "captured" by the loops and then driven to the physical electrical ground node when each loop is subsequently coupled to the physical electrical ground node. In this way, EMI is prevented from building up and electrical performance is improved. In other words, the transformer does not get a chance to build up as many magnetic fields because they are captured by the conductive loops and any induced currents (EMI) are driven to the physical electrical ground node. The inventor has discovered that this is not only related to averaging out EMI, but also reduces heat, thereby improving the power factor of the transformer. So far, a high power factor of about 0.9 has been achieved, but without the present invention, this power factor has decreased to about 0.4. It is believed possible to achieve a total harmonic distortion (THD) of 8% or less, which is a requirement for isolation transformers recently published in the international standard IEC 61000.

[0016] Another major advantage of the present invention is that the location of the physical electrical nodes is no longer as important; they may be located in locations where there is some magnetic flux and electric field.

[0017] In addition to having a very high power factor, the transformer according to the present invention also has the great advantage that it no longer requires calibration or adjustment of the electromagnetic field. The transformer effectively self-calibrates regardless of the load, even if the load is not properly balanced. Moreover, the transformer does not have any moving parts for adjustment or calibration. This is a great advantage of the present invention, which is obtained by using a conductive loop to capture the EMI and drive it to a physical electrical node. Instead of minimizing the EMI by manipulating the location of a physical electrical ground node, as was done in WO2019 / 013642, the present invention simply allows the EMI to accumulate and drives it to this node so that it averages out / disappears gradually. This is a very innovative idea.

[0018] It is not necessary to keep the loops constantly connected to a physical electrical ground node to achieve the desired effect. There may be several, indeed long, intervals of time during which no loop is connected to a physical electrical ground node. Many variations of each sequence and pattern are possible. The inventors have performed many experiments to discover the best practical embodiment.

[0019] To facilitate understanding of the present invention, one or more expressions used throughout this specification are further defined below. Whenever the term "coil" is used, it is to be understood as at least one winding of a conductor configured to create inductance.

[0020] Whenever the term "conductive loop" is used, it is to be understood as at least one winding of a conductor configured to create an inductance. Whenever the term "Faraday cage" is used, it is to be interpreted as an enclosure used to block electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material or, in the case of the Faraday cage, by a mesh of such material. The Faraday cage is named after the British scientist Michael Faraday, who invented it in 1836.

[0021] In some embodiments of the transformer according to the present invention, the at least two conductive loops comprise at least three conductive loops, the more loops that are arranged, the better the EMI averaging will be, as well as the more switching between loops can be performed to further reduce EMI build-up.

[0022] In one embodiment of the transformer of the present invention, the at least two conductive loops comprise at least six conductive loops. The more loops that are deployed, the better the EMI averaging, but also the more switching between loops can be performed to further reduce EMI buildup. This embodiment is explained in more detail in the detailed description.

[0023] In some embodiments of the transformer according to the present invention, the smallest conductive loops are located in the spaces between the coils. Whereas in WO2019 / 013642 it was important to place the physical electrical ground node in a position where there is no or little magnetic or electric field, this is literally not an issue in the present invention as far as the placement of the conductive loops is concerned. It has been found that the spaces between the coils can be conveniently used for the placement of the conductive loops. These spaces in transformers are traditionally minimized for compactness, but are very useful in the present invention. If the transformer is a three-phase transformer with three legs and respective openings in the core between them, each leg having its own primary and secondary coils, the spaces between the coils in these openings can be conveniently used. This will be further explained with reference to the drawings.

[0024] In one embodiment of the transformer according to the invention, at least two conductive loops are integrated in a plate or plates that are thinly coated with a material that is permeable to magnetic fields and electrically insulating. Since the loops are conductive like the coils, it is advantageous to implement these loops in a plate or plates that are thinly coated with a material that is permeable to magnetic fields and electrically insulating. Examples of this material that can be chosen include carbon, Teflon, rubber, plastic, fiberglass, etc.

[0025] In some embodiments of a transformer according to the present invention, a subset of the conductive loops constitute pairs of conductive loops, for example, if there are six conductive loops, the first loop may be paired with the fourth loop, the second loop with the fifth loop, the third loop with the sixth loop, and so on.

[0026] In some embodiments of transformers according to the present invention, the particular sequence and pattern extends to substantially all of the conductive loops, and while it is not necessary to use all of the loops, this provides the best averaging effect and the most efficient use of resources.

[0027] In some embodiments of the transformer of the present invention, the particular sequence and pattern constitutes a predetermined order for selecting a subset of conductive loops, which may be selected based on the position of each loop in the transformer, i.e., the order that provides the best averaging.

[0028] In certain embodiments of the transformer of the present invention, the particular sequence and pattern constitutes a random order for selecting a subset of conductive loops, which may constitute a convenient solution for certain applications.

[0029] In one embodiment of the transformer according to the invention, the magnetizable core is floating and electrically isolated from all externally accessible parts of the transformer. The inventors have discovered that the performance of the transformer is significantly improved when the magnetizable core is floating and electrically isolated from all externally accessible parts of the transformer. Tests have shown that the performance of the transformer is significantly improved when the magnetizable core is kept electrically floating, disconnected from the ground terminal. This can be explained by the fact that the impedance of the ground network can be set more appropriately when the core is floating.

[0030] An embodiment of the transformer of the present invention includes three sets of coils, each set including at least one primary coil and at least one secondary coil, to form a three-phase transformer. This group of embodiments may have the widest scope of application in the art. However, the present invention is not limited to three-phase transformers.

[0031] In one embodiment of the isolation transformer according to the present invention, the magnetizable core comprises at least three legs, at least one leg for each pair of primary and secondary coils.

[0032] An embodiment of the isolation transformer of the present invention further comprises a Faraday cage in which the magnetizable core, the respective coils and the at least two conductive loops are disposed, the Faraday cage being electrically connected to a physical electrical ground node.

[0033] In a second aspect, the present invention relates to an electric power system, the electric power system comprising: a terminal for coupling to a power grid; A dedicated earth to form an external ground terminal; a power supply network with all necessary cables, electrical contacts and plugs; A transformer according to any one of the preceding claims, The input terminals of the transformer are electrically connected to the power supply network and the ground terminal of the transformer is electrically connected to a dedicated earth.

[0034] The inventor has realized that the technical effect of the present invention can be further improved if a dedicated earth is used for electrical connection with the earth terminal of the transformer instead of using the earth provided by the power grid, thus providing a situation where the transformer starts from a clean earth, avoiding feeding EMI and other noise on the power grid terminal into the transformer.

[0035] In a third aspect, the present invention relates to a method for improving the performance of an electrical or electronic device, the method comprising: positioning at least two conductive loops within the device at distinct locations where a magnetic field may build up during operational use of the device; Sequentially, temporarily, and selectively electrically coupling a subset of the conductive loops to a physical electrical ground node according to a particular order and pattern.

[0036] The present invention has a much broader scope of application than (isolation) transformers. EMI is a general problem that can occur in virtually any electrical device or equipment. The method according to claim 15 covers all these applications. It goes without saying that all embodiments of transformers relating to the number, arrangement and sequential, temporary and selective electrical connection of conductive loops with physical electrical ground nodes according to certain sequences and patterns have equivalent embodiments of the method of the present invention.

[0037] In the following, examples of embodiments are described which are illustrated in the accompanying drawings. [Brief description of the drawings]

[0038] [Figure 1] 1 shows various types of prior art transformers and illustrates where field free areas are feasible as previously presented in the prior art. [Diagram 2]1 shows various types of prior art transformers and illustrates where field free areas are feasible as previously presented in the prior art. [Diagram 3] 1 shows various types of prior art transformers and illustrates where field free areas are feasible as previously presented in the prior art. [Figure 4] 1 shows various types of prior art transformers and illustrates where field free areas are feasible as previously presented in the prior art. [Diagram 5] 1 shows a prior art low EMI transformer that still suffers from drawbacks. [Figure 6] 1 shows a first embodiment of an improved low EMI transformer according to the present invention. [Figure 7] 7 illustrates another embodiment of the low EMI transformer of FIG. 6. [Figure 8] 7 illustrates yet another embodiment of the low EMI transformer of FIG. 6. [Figure 9] A second embodiment of the low EMI transformer of the present invention is shown, along with several other aspects of the present invention. [Figure 10] 3 illustrates a third embodiment of an improved low EMI transformer according to the present invention. [Figure 11] 1 illustrates how the low EMI transformer of the present invention is preferably connected to a power grid. [Figure 12] 4 illustrates another aspect related to the present invention that relates to the connection of loops. [Figure 13] This shows the very wide range of applications of the invention, which also relates to the method according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Detailed Description of the Embodiments Various exemplary embodiments of the subject matter of the present invention are described below. For the sake of clarity, not all features of actual implementations are described herein. It will of course be appreciated that the development of any such actual implementation will require many implementation-specific decisions to be made in order to achieve the developer's specific goals, such as adhering to system-related and business-related constraints that vary from implementation to implementation. It will further be appreciated that such a development effort may be complex and time-consuming. However, it will be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0040] The subject matter of the present invention will now be described with reference to the attached drawings. In each drawing, various systems, structures, and devices are depicted in schematic form for illustrative purposes only, and with details well known to those skilled in the art, so as not to obscure the present disclosure. However, the attached drawings are included to describe and explain examples of the present disclosure. The words and phrases used in this specification should be understood and interpreted to have a meaning consistent with the understanding of the words and phrases by those skilled in the relevant art. There is no special definition of a word or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, that is intended to be implied by the consistent use of the word or phrase in this specification. To the extent that a word or phrase is intended to have a special meaning, i.e., a meaning other than that understood by those skilled in the art, such special definition is set forth herein as a reference to the definition that directly and clearly gives the special definition to the word or phrase.

[0041] When transformer requirements are higher, isolation transformers are usually used. Isolation transformers block the transmission of the DC component of the signal flowing from one circuit to the other, but allow the AC component of the signal to pass. Transformers with a 1:1 ratio of primary to secondary windings are often used to protect secondary circuits and individuals from electric shock between the live conductor and ground. A well-known approach to combating noise caused by EMI is to build expensive and complex filters that actively suppress the noise.

[0042] In WO2019 / 013642 it was found that the way isolation transformers are constructed and used actually makes the problem worse. It was found that the problem is often caused by simply connecting all the ground terminals together without realizing that such a connection exacerbates the amount of ground loops induced in the system. In other words, grounding in the way traditional isolation transformers are constructed and used is largely ineffective - it creates more problems than it solves.

[0043] The first improvement in WO2019 / 013642 concerns the design of the isolation transformer. As a first step, the isolation transformer of the present invention is provided with a separate electrical ground node at a location inside the Faraday cage where the magnetic flux and electric field are nearly zero. The main idea with this separate ground node is not only to keep the node as clean as possible, but also to keep the impedance to this separate ground node as low as possible. If it were to be placed in a place where there is a strong magnetic field and / or electric field, the separate electrical ground node would again pick up (act as an antenna) unwanted signals.

[0044] 1-4 show various types of prior art transformers and illustrate where field free zones are feasible as previously presented in the prior art. The transformer in Fig. 1 is a single-phase (generally referred to as single-phase, but actually two-phase) transformer 100a having an O-core 110a. The O-core 110a is for inducing a magnetic flux Φ from a primary coil 120 to a secondary coil 130, or in the reverse direction, as shown. The primary coil 120 and the secondary coil 130 are each disposed around a respective leg of the O-core 110a. The potential difference between the two input phases is called the input voltage Va, and the potential difference between the two output phases is called the output voltage Vb.

[0045] 2 shows another single-phase transformer 100b having a so-called three-limbed core 110b. Both the primary coil 120 and the secondary coil 130 are mounted around the central leg of the core 110b as shown.

[0046] 3 shows a so-called three-phase transformer 100c. In this type of transformer, each phase has a primary coil 120-1, 120-2, 120-3, respectively, and a secondary coil 130-1, 130-2, 130-3, respectively, as shown. Such coils may be connected in star or delta configurations as commonly known in the prior art. The figure also shows that the magnetizable core 110c has five legs (or limbs), three of which are provided with respective coils 120-1...120-3, 130-1...130-3.

[0047] 1-3 show possible no-field zones (or low-field zones) NFZ as proposed in WO2019 / 013642. In each embodiment, the no-field zones (or low-field zones) NFZ are formed between the two electrostatic shields 140-1, 140-2 (meaning that there is almost no electric field) and outside the respective magnetic cores 110a, 110b, 110c (meaning that there is almost no magnetic field).

[0048] Fig. 4 shows a different embodiment of a transformer 100d. Instead of providing an additional electrical ground node between the coils, here an additional Faraday cage 170 is implemented, which is manufactured inside the Faraday cage 150 of the insulating transformer 100d. As shown, the Faraday cage 150 comprises a separate primary coil 120 and a secondary coil 130, the primary coil 120 being supplied with an input voltage Va and the secondary coil 130 providing an output voltage Vb. By implementing this additional Faraday cage 170, a so-called field-free zone NFZ (or low field zone) can be established, even if the transformer itself generates some electric and magnetic fields. Instead of creating a completely closed Faraday cage, it is sufficient to implement a Faraday shield 171 inside the Faraday cage 150, which effectively defines the additional Faraday cage 170. Inside the field-free zone NFZ, the above-mentioned additional electrical ground node can be implemented.

[0049] The invention presented herein relating to an improved low EMI transformer may be applied using any type of transformer or core design, including those illustrated in FIGS. 1-4.

[0050] Fig. 5 shows a prior art low EMI transformer 100e that still suffers from the drawbacks. The transformer 100e is a three-phase isolation transformer (the three phases are conventionally called L1, L2, L3) with three input terminals Ti1, Ti2, Ti3. The input terminals Ti1, Ti2, Ti3 are fed via input wires i1, i2, i3 through a first isolation junction box 180 to respective primary coils 120-1, 120-2, 120-3, which are connected in a star network in this embodiment. The secondary coils 130-1, 130-2, 130-3 are connected via output wires o1, o2, o3 through a second isolation junction box 181 to respective output terminals To1, To2, To3. The secondary coils 130-1, 130-2, 130-3 are also connected in a star network in this embodiment. However, it should be noted that other types of networks, such as delta networks, may also be used, either on the input side, the output side, or both, of the transformer, all depending on the type of grid the transformer is coupled to and the type of grid it needs to generate electricity from.

[0051] Additionally, as shown, there is the aforementioned Faraday cage 150, which is connected to the input ground terminal GT1 (and thus to ground PE). The Faraday cage 150 is also connected to the electrostatic shields 140-1, 140-2, which in turn are connected to the ground output terminal GT2 for connection to another circuit. Up to this point, all the components described in Figure 7 are conventional for an isolation transformer.

[0052] What makes the isolation transformer 100e of FIG. 5 special is that a physical electrical node 175 is provided inside a further Faraday cage 170 (defining the no-field (or low-field) zone NFZ described above) inside a Faraday cage 150 defined as shown by a Faraday shield 171. The physical electrical node 175 is connected to a clean ground input terminal 179 via a first electrical connection 185 (e.g. a double-insulated cable typically used before a ground fault circuit interrupter in a home electrical system). The physical electrical node 175 is further connected to a clean ground output terminal 199 via a second electrical connection 195. The second electrical connection 195 in this embodiment is a twisted-pair shielded cable with two wires 196 intertwined as shown. Each of the wires 196 is connected to the physical electrical node 175 as shown and fed to the clean ground output terminal 199. 5, the second electrical connection 195 is shown routed between the electrostatic shields 140-1, 140-2 in a parallel relationship, but this is not required, and in fact the second electrical connection 195 may alternatively be routed to the outside of the isolation transformer 100e, for example parallel to the output wires o1, o2, o3.

[0053] Figure 5 further illustrates a sensor and control circuit 190 (CPU). The control circuit 190 is configured to measure noise at the inputs and outputs shown by the arrows, and ultimately reduces / minimizes the noise by controlling the position of the physical electrical node 175 to minimize the electric and magnetic fields experienced by this node. In the embodiment of Figure 5, the position of the physical electrical node 175 is controllable as shown by the arrows.

[0054] By inspecting the transformer 100e in FIG. 5, it is easy to see that it is not a conventional transformer, since it has two different types of ground terminals on the outside, namely conventional ground terminals GT1, GT2, which are connected to the conventional ground potential Pe, and special clean ground terminals 179, 199, which serve to connect to a separate ground potential, also called ISPE in WO2019 / 013642. In other words, the low EMI transformer does not comply with the standards for the connection of isolated transformers, and requires new standards, as precisely explained in the same document. So, this is not a problem, but it may hinder the rapid commercialization of the transformer. As a result, the need for further improvements of low EMI transformers, as explained with reference to FIGS. 6 to 13, is recognized.

[0055] FIG. 6 shows a first embodiment of an improved low-EMI transformer 100e1 according to the present invention. This figure shows only some parts of the transformer in a schematic manner. Each of the primary and secondary coils 120-1..120-3, 130-1..130-3 forms a star network. A first plate 800-1 is provided between the coils of the primary and secondary phases. Similarly, a second plate 800-2 is provided between the coils of the secondary and tertiary phases. These plates 800-1, 800-2 act as so-called EMI collectors, as will be explained below. The plates are made of a material that is permeable to magnetic fields and at the same time electrically insulating. Examples of materials include carbon, Teflon, rubber, etc. Both plates each include a conductive loop (not visible in FIG. 6) that is electrically connected to a switching circuit 801 as shown. Switching circuitry 801 is configured to sequentially, temporarily, and selectively electrically couple a subset of the conductive loops to physical electrical ground node 175 as shown. What this means will be explained hereinafter with reference to the other figures. Physical electrical ground node 175 is in turn electrically connected to ground output terminal 199. In the remaining figures, physical electrical ground node 175 and ground output terminal 199 carry the same electrical potential, so these two electrical nodes are depicted (for simplicity) as one entity.

[0056] It must be emphasized that plates 800-1, 800-2 serve primarily to hold the loops in place. There can be any number of plates, and each plate can have any number of loops, but in the present description, the principles of the invention are explained using two plates, each implementing three loops. This is further explained in FIG. 7.

[0057] Figure 7 shows some other aspects of the low EMI transformer 100e1 of Figure 6. This figure illustrates the conductive loops CL1..CL6 mentioned above. In this embodiment, the first plate 800-1 comprises three loops CL1, CL2, CL3, and the second plate 800-2 also comprises three loops CL4, CL5, CL6. Every loop originally has two terminals, and both terminals are fed to the switching circuit 801 as shown.

[0058] FIG. 8 illustrates yet another embodiment of the low EMI transformer 100e1 of FIG. 6. This diagram illustrates how plates 800-1, 800-2 can be positioned between each phase of the transformer 100e1. To facilitate understanding of the diagram, the magnetizable core is not shown in this diagram. It should be noted that more plates could be added. For example, plates could be added to all sides of each phase, including the front, back, left and right sides of the diagram.

[0059] FIG. 9 shows a second embodiment of the low EMI transformer 100e2 of the present invention together with some other aspects of the present invention. This embodiment differs from the previous embodiments in that the primary side of the transformer 100e2 is connected as a delta network. In certain countries, including Norway, many areas still provide a 230V delta network power grid. This embodiment successfully transforms this network into a 230V star network, effectively providing a voltage of 400V between the secondary phase outputs I1, I2, I3. In this embodiment, the secondary star point n is not connected. FIG. 9 further shows a schematic of the magnetizable core 110, which in this embodiment is kept floating.

[0060] When transformer 100e2 is in operation and use, physical electrical ground node 175 is connected to an external ground terminal 999, which is typically connected to earth (e.g., connected to an earth rod or ground spear).

[0061] FIG. 10 shows a third embodiment of an improved low-EMI transformer 100e3 according to the present invention. This embodiment differs from the previous ones in that the star point n of the star network on the secondary side of the transformer 100e3 is also connected to the physical electrical ground node 175. It should be noted that in a perfectly balanced state, the star point n carries no signal and any conductor connected to this star point n does not carry any current. However, this can happen if the balance is disturbed. The present invention provides an additional technical effect of better load balancing by strongly reducing EMI in the transformer. Due to this effect, the present invention allows the star point n to be connected to the physical electrical ground node 175. Alternatively, the neutral point may be left unconnected or may be controlled by adjusting the impedance of the ground PE, as shown in the box. This aspect of the neutral terminal n on the secondary side of the transformer 100e2 applies to all the embodiments shown in FIGS. 9-11.

[0062] FIG. 11 shows how the low EMI transformer 100e3 of the present invention is preferably connected to the power grid. In this figure, the third embodiment is taken as an example. The same principle applies equally to the other embodiments. The transformer 100e3 is coupled to the power grid 900, which provides three phases L1, L2, L3, a neutral point N, and a ground terminal PE. The neutral point N and the ground terminal PE are preferably not used in the transformer 100e3. Instead, the transformer 100e3 of the present invention effectively defines its own clean ground by using a dedicated earth 999 as shown. Such an earth may be formed by locally implementing an earth rod or earth spear 999, thereby defining a new ground reference. Such an earth rod or earth spear 999 may be shared between adjacent buildings. The inventor has realized that to obtain the maximum effect of the present invention, the transformer should be provided with a dedicated earth 999. By doing this, the ground potential PE is kept the cleanest (i.e., least noise and EMI).

[0063] Figure 12 illustrates another aspect of the loop connection that leads to the present invention. It shows a switching circuit 801, which is a very important element of the present invention. As already mentioned above, the present invention requires at least two conductive loops, which are placed inside the transformer in a position where a magnetic field can build up during operational use. It has also been mentioned that a suitable position would be the space between the phases (the legs of the transformer). The embodiment shown in Figure 12 comprises six loops, each with its own loop terminal pair. FIG. 12 shows the first loop terminal pair T1a, T1b belonging to the first conductive loop CL1 (FIG. 7), the second loop terminal pair T2a, T2b belonging to the second conductive loop CL2 (FIG. 7), the third loop terminal pair T3a, T3b belonging to the third conductive loop CL3 (FIG. 7), the fourth loop terminal pair T4a, T4b belonging to the fourth conductive loop CL4 (FIG. 7), the fifth loop terminal pair T5a, T5b belonging to the second conductive loop CL5 (FIG. 7), and the sixth loop terminal pair T6a, T6b belonging to the second conductive loop CL6 (FIG. 7).

[0064] The switching circuitry 801 of the present invention is configured to sequentially electrically couple a subset SS of loops to a respective physical electrical ground node 175. Such a subset may comprise only one loop, but it is also possible to simultaneously couple two or more loops to the physical electrical ground node 175. Coupling a particular loop to the ground node 175 means electrically closing the loop by connecting both terminals of the loop to the same node. Any built-up EMI is thus effectively driven out via the ground node 175.

[0065] In the embodiment of FIG. 12, a selection is made to couple two loops simultaneously (loops 3 and 6 are connected simultaneously in the situation of FIG. 12) to the physical electrical ground node 175. This selection is then repeated through the available loops. However, the inventors have discovered that it is not necessary to keep multiple loops continuously coupled to the ground node 175. There may be significant interruptions between periods when multiple loops are coupled. The selection of a subset of loops, and the order and pattern in which they are connected to the ground node 175, can be tested to find the optimal solution, i.e., the best performance of the transformer. One way to determine this performance is to determine the power factor, and another is to determine the temperature of the transformer. A higher power factor indicates better performance (lower losses). Also, a lower operating temperature indicates lower losses.

[0066] It should be noted that, using the physical configuration of plates 800-1, 800-2 and loops as shown in FIG. 8, the inventors have found the following sequence to provide very good performance (high power factor and lowest temperature):

[0067] First, the first loop CL1 and the fourth loop CL4 are both connected to the ground node 175 for 5 seconds. -Then take a break for 20 minutes.

[0068] -Then, the second loop CL2 and the fifth loop CL5 are both connected to the ground node 175 for 5 seconds. -Then take a break for another 20 minutes.

[0069] -Then connect both the third loop CL3 and the sixth loop CL6 to the ground node 175 for 5 seconds. -Then take a break for another 20 minutes. -Then, the sequence is started all over again, as also indicated by the arrows in Figure 12.

[0070] It must be emphasized that there are many ways to create the switching circuit 801 as shown in Figure 12. Although the inventors have created this circuit as a time-controlled relay, this is just one possible example.

[0071] It should also be emphasized that the present invention is in no way limited to the sequences described above. Undoubtedly, other sequences and patterns (timing schemes) may emerge with more testing. Moreover, the optimal sequence and pattern also depends heavily on the physical design of the transformer and thus on many design parameters.

[0072] The inventor has constructed a prototype of an embodiment of the transformer according to the invention, implementing the above sequence. The transformer was constructed, for example, from a 250 kVA IEC 60076-11 transformer available from Trafox. The transformer is a three-phase transformer with a three-legged core, each leg being provided with its own primary and secondary coil, which are arranged concentrically (secondary on the outside). The minimum distance between each of the outer coils is 1.5 cm. The height of the coil (measured in the direction of the legs of the magnetizable core) is about 80 cm. Between the coils is placed a plate with a height of 80 cm, a depth of 30 cm and a thickness of about 1 cm. Both plates are provided with three conductive loops arranged side by side and distributed over the height of the plates. The minimum distance between the outer loops and the top and bottom edges of the plates is 11 cm. The minimum distance between the first and second loops is around 11 cm. The minimum distance between the third loops is 11 cm. The closed area of ​​each loop is approximately 60 cm. 2The plate is covered with carbon. The conductive loops are made of copper wire. It must be emphasized that the prototype described above is only one practical embodiment. Many modifications, optimizations and adjustments are possible in the course of further development of the product.

[0073] Fig. 13 shows a very wide range of applications of the invention, which also concerns the method according to the invention. The inventors have realized that the concept of trapping EMI in conductive loops CL1..CL3 and expelling it towards the ground node 175 can be applied more broadly. The figure serves to illustrate this more general method of improving the performance of an electric or electronic device 1. EMI is a problem that becomes more serious every year. EMI can originate from an external source, i.e. from outside the device, but also from the device itself. In other words, the scope of application of the method steps according to claim 15 is broadly applicable outside the technical field of transformers. The applicant is entitled to protection for such applications of the method according to the invention. It goes without saying that this protection also extends to any such electric or electronic device incorporating such features.

[0074] All the embodiments disclosed in the figures and described so far focus on a time-driven loop selection. As an alternative embodiment, it is possible to perform a voltage-driven selection, i.e. to select the loop or loops that actually carry the maximum induced voltage, and connect that loop or loops to a physical electrical ground node to eliminate EMI.

[0075] As another embodiment, it is possible to perform a temperature driven selection, i.e., select the loop or loops having the highest temperature and connect that loop or loops to a physical electrical ground node to eliminate EMI.

[0076] 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, the method steps described above may be performed in a different order. Further, no limitations are intended to the details of construction or design shown herein, except as described in the claims below. It is therefore apparent that the particular embodiments disclosed above may be modified or varied and all such variations are considered within the scope of the present invention. Accordingly, the protection sought herein is as set forth in the claims below.

[0077] It should be noted that the above-described embodiments illustrate rather than limit the invention, and that a person skilled in the art can 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 claims. 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" 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. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware.

Claims

1. A transformer, a magnetizable core; at least one primary coil and at least one secondary coil disposed around the magnetizable core; a ground terminal for electrically connecting to an external ground terminal; a physical electrical ground node located at a location internal to the transformer, the physical electrical ground node being electrically connected to the ground terminal; The transformer further comprises: at least two conductive loops positioned within the transformer at separate locations where a magnetic field may build up during operational use; and switching circuitry configured to sequentially, temporarily, and selectively electrically couple a subset of the conductive loops to the physical electrical ground node according to a particular order and pattern.

2. The transformer of claim 1 , wherein the at least two conductive loops comprise at least three conductive loops.

3. The transformer of claim 2 , wherein the at least two conductive loops comprise at least six conductive loops.

4. 4. The transformer according to claim 1, wherein a minimum of two conductive loops are disposed in a space between the at least one primary coil and the at least one secondary coil.

5. 4. The transformer according to claim 1, wherein the at least two conductive loops are integrated into one or more flat plates that are thinly coated with a material that is permeable to magnetic fields and exhibits electrical insulation.

6. 4. The transformer of claim 1, wherein the subset of conductive loops constitutes pairs of conductive loops.

7. The transformer of any one of claims 1 to 3, wherein the particular order and pattern extends to substantially all conductive loops.

8. 4. The transformer of claim 1, wherein the particular order and pattern constitute a predetermined order for selecting a subset of conductive loops.

9. 4. The transformer of claim 1, wherein the particular order and pattern constitute a random order for selecting a subset of conductive loops.

10. Transformer according to any one of claims 1 to 3, wherein the magnetisable core is floating and electrically isolated from all externally accessible parts of the transformer.

11. 4. The transformer of claim 1, wherein the transformer comprises three sets of coils, each set comprising at least one primary coil and at least one secondary coil, to form a three-phase transformer.

12. 12. The transformer of claim 11, wherein the magnetizable core comprises at least three legs, at least one leg for each pair of primary and secondary coils.

13. 4. The transformer of claim 1, further comprising a Faraday cage in which the magnetizable core, the respective coils, and the at least two conductive loops are disposed, the Faraday cage being electrically connected to the physical electrical ground node.

14. 1. An electric power system comprising: a terminal for coupling to a power grid; A dedicated earth to form an external ground terminal; a power supply network with all necessary cables, electrical contacts and plugs; The transformer according to any one of claims 1 to 3, an input terminal of the transformer electrically connected to the power supply network and the ground terminal of the transformer electrically connected to the dedicated earth.

15. 1. A method for improving the performance of an electrical or electronic device, comprising: positioning at least two conductive loops within the electrical or electronic device at different locations where a magnetic field may build up during operational use of the electrical or electronic device; and sequentially, temporarily, and selectively electrically coupling a subset of the conductive loops to physical electrical ground nodes according to a particular order and pattern.

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