ABSORPTION FILTER AND METHOD FOR MANUFACTURING SUCH A

Description

[0001] The invention relates to a filter arrangement which is an absorption filter for absorbing high-frequency differential currents in phase conductors of a supply line of an electric motor, and to a method for its production.

[0002] A filter assembly that can be pushed onto a cable is known from US Pat. No. 5,200,730 A. The filter assembly comprises a single toroidal core encapsulated in a housing. To form a filter assembly with multiple toroidal cores, it is proposed to plug individual housings, each with a single toroidal core, together to then obtain the filter assembly with multiple toroidal cores.

[0003] JP 6 643 596 B2 concerns a similar filter assembly that comprises only a single toroidal core. The toroidal core is inserted into a mold and then encapsulated with potting compound.

[0004] US 2006 / 0283006 A1 relates to a method for producing magnetic induction devices.

[0005] JP H03 102 808 A relates to a filter assembly comprising a housing with at least one toroidal core that is electromagnetically coupled to at least one phase conductor. The at least one toroidal core is encapsulated together with the at least one phase conductor in the housing using a potting compound. Consequently, the housing, toroidal core, and phase conductor form a single unit. Replacing the phase conductors or using the filter assembly with different phase conductors is not provided for.

[0006] US Pat. No. 6,218,913 B1 relates to a filter assembly comprising a housing with at least one toroidal core. Phase conductors are routed through the at least one toroidal core. The phase conductors are mechanically connected to each other, thus preventing any relative movement to the toroidal cores. The toroidal cores and the phase conductors are encapsulated in the housing with a potting compound. The phase conductors are thus fixed in the housing.

[0007] DT 27 04 337 A1 relates to an overcurrent protection device for an AC motor with at least one current transformer, the iron core of which encloses at least part of a connecting cable connecting the motor to an AC power source. The overcurrent protection device comprises a housing having three spaced-apart holes or windows extending between the side walls. The holes are formed by tubes extending between corresponding openings and in the side walls and passing through the circular openings of the toroidal cores of the current transformers.

[0008] US 2015 / 0244339 A1 relates to a filter assembly comprising a housing with at least one toroidal core electromagnetically coupled to electrical conductors. The electrical conductors have ends connected to terminals of the housing.

[0009] DT 25 43 977 A1 relates to a method for producing channels in castings, particularly cooling channels for resin-impregnated and resin-cast normal and superconducting coils with a winding core and coil windings wound thereon, which are surrounded by a resin compound. This method involves attaching fabric pieces adapted to the shape of the cooling channels to the designated locations on the coil prior to casting. The fabric pieces are then cast in the casting process. After the resin compound has dried, the fabric pieces are subjected to tensile stress such that they detach from the resin compound, and the fabric pieces are then removed from their layers.

[0010] Absorption filters of the aforementioned type are offered by the applicant, for example, under the designation "AF-DSR" and are described, for example, in the brochure "EPA Absorption Filters," available at www.epa.de.

[0011] Due to a constantly increasing integration density of components in control cabinets - combined with the corresponding wiring - increasingly high parasitic capacitances against reference potential, such as control cabinet housing, PE and / or reference earth, arise.

[0012] By using electronic drive controllers with a DC link, high voltage gradients, i.e. duJdt values, also called common mode voltage, are created by the output stages switching with short rise times.

[0013] In combination with the parasitic capacitances, the voltage gradients create high-frequency voltages against the reference potential, generating high-frequency differential currents (common mode currents) in the kilohertz to megahertz range. The effective values ​​of these currents can be in the double-digit ampere range, depending on the design of the control cabinet and the wiring of the machines.

[0014] For the most part, differential currents do not flow between the live lines, but rather on all phase lines simultaneously, galvanically on possibly shielded lines or via the motor bearings. The current then flows back to the source of the interference via the reference potential, such as the housing, earth, PE, and PA (potential equalization) connections. This is particularly true for three-phase motors with higher power and spindle motors, as these have higher capacitance values ​​between the stator and rotor due to their design.

[0015] By using absorption filters, these unwanted currents can be reduced and the operational reliability of machines and systems can be increased.

[0016] According to the current state of the art, absorption filters are connected between the frequency converter and the motor. Connection terminals are provided on an outer wall of the absorption filter housing, to which the electric motor cables and the frequency converter cables are connected.

[0017] Inside the housing of the absorption filter, there is at least one closed toroidal core with electrical conductors that are internally connected to the terminals. The electrical conductors must be stripped, soldered, or provided with a cable lug to allow the necessary wiring and connection of the electrical conductors to the terminals, which involves increased assembly and manufacturing effort.

[0018] Based on this, the present invention is based on the object of developing an absorption filter and a method for producing an absorption filter of the type mentioned above in such a way that, on the one hand, the production and, on the other hand, the assembly or installation of the absorption filter are simplified. In particular, the absorption filter should be easy to retrofit, e.g., in a control cabinet, without significant time and expense.

[0019] The object is achieved according to the invention, inter alia, by the features of claim 1.

[0020] The filter arrangement has at least one feedthrough in the form of a channel formed free of potting compound, wherein the at least one feedthrough passes through the at least one toroidal core and the housing in such a way that the at least one phase conductor can be passed through, in particular pushed through.

[0021] According to the invention, it is provided that the at least one toroidal core is cast in the housing by means of a casting compound to form at least one feedthrough in the form of a channel which is free of casting compound, wherein the at least one feedthrough passes through the at least one toroidal core and the housing in such a way that the at least one phase conductor can be passed through, in particular pushed through.

[0022] The at least one toroidal core comprises several toroidal cores arranged along a longitudinal axis of the housing or adjacent to one another within the housing. The phase conductor can pass through all of the toroidal cores arranged in a row, or only through individual ones.

[0023] The individual toroidal cores are secured within the housing by means of a framework structure, spaced apart from each other and from the housing walls. This ensures that the toroidal cores can be fully encapsulated to achieve optimal heat transfer to the housing walls. Full encapsulation also ensures that no dangerous contact voltages, leakage currents, or fault currents occur in the housing, which is preferably made of plastic.

[0024] Compared to the state of the art, the absorption filter no longer has connection terminals. The motor phase conductors can be routed through the bushings or plugged in and connected directly to the frequency converter. This allows for easy retrofitting of the filter without significant time and expense. There is no connection between the housing or toroidal core and the phase conductor. This eliminates the otherwise necessary separation of the phase conductors, stripping the sheath, attaching / crimping wire end ferrules, and connecting to connection terminals. The absorption filter is maintenance-free because it has no connection terminals. Furthermore, the elimination of connection terminals reduces the manufacturing costs of the absorption filter and also significantly reduces the housing dimensions.The selection of the appropriate absorption filter therefore does not depend on the size of the terminals and / or the motor's operating current, but rather on the diameter of the bushings. The bushings have a diameter larger than the diameter of the phase conductors so that they can be inserted or pushed through. The phase conductors can be pulled through the filter when it is installed.

[0025] Preferably, the at least one feedthrough is defined by the potting compound or by at least one pipe section, wherein the at least one pipe section extends longitudinally through the at least one toroidal core and the housing. In the first variant, the feedthrough is defined by the potting compound, so that no additional materials are required. The phase conductors can also be easily passed through. The second variant, in which the feedthrough is formed by a pipe section, can preferably be used for large diameters.

[0026] The at least one leadthrough or the at least one pipe section preferably opens into opposite walls of the housing, so that the phase conductors can be inserted through the leadthrough in the longitudinal direction.

[0027] Depending on the application, the at least one bushing can be designed as a single bushing or as multiple bushings. Individual bushings have the advantage that the phase conductors can be routed, inserted, or removed through the toroidal cores in a defined manner.

[0028] The toroidal cores are preferably closed toroidal cores made of nanocrystalline material.

[0029] The potting compound is preferably selected from the group of polyurethanes and / or can preferably form the housing itself.

[0030] Furthermore, the invention relates to a method for producing a filter arrangement according to claim 7, wherein at least one toroidal core is arranged in a housing so that it can be electrically coupled to the at least one phase conductor of the supply line of the electric motor, wherein the housing with the at least one toroidal core arranged therein is cast by means of a casting compound, wherein at least one feedthrough in the form of a channel which is free of casting compound is formed in the housing and the casting compound, wherein the at least one feedthrough passes through the at least one toroidal core and the housing in such a way that the at least one phase conductor can be passed through, such as pushed through.

[0031] It is provided that several toroidal cores are arranged along a longitudinal axis of the housing or also next to one another in the housing, wherein individual toroidal cores are fixed in the housing by means of a framework construction at a distance from one another and at a distance from the housing walls of the housing and wherein the absorption filter is used to absorb high-frequency differential currents in phase conductors of a supply line of an electric motor.

[0032] The process according to the invention enables simple and cost-effective production. The housings are compact, and the bonding of the potting compound to the housing improves heat dissipation of the toroidal cores' heat loss to the environment.

[0033] The toroidal cores and the diameters of the at least one bushing are preferably configured such that they are independent of the current flowing through the individual phase conductors. Consequently, only a limited number of variants need to be maintained. The absorption filters are designed for both small- and large-cross-section supply lines. The current and voltage ratings of the connecting terminals do not need to be considered.

[0034] The at least one feedthrough can be formed by inserting at least one rod-shaped element into a channel defined by the at least one toroidal core prior to pouring the potting compound into the housing, wherein the at least one rod-shaped element preferably extends through opposite housing walls of the housing. The housing can then be filled with the potting compound. The rod-shaped element is preferably made of a material, such as Teflon or silicone, that does not bond to the potting compound, so that the rod-shaped element can be withdrawn from the potting compound after the potting compound has been poured and hardened without damaging it.

[0035] The at least one feedthrough can also be created by drilling or milling after the potting compound has been poured into the housing.

[0036] The casting compound used is preferably one from the polyurethane group, which has good thermal conductivity.

[0037] The potting compound itself can also form the housing.

[0038] Further details, advantages, and features of the invention will become apparent from the following description of a preferred embodiment. The invention is defined in the claims.

[0039] They show: Fig. 1 a perspective view of an absorption filter, Fig. 2 a side view of the absorption filter with potting compound in section, Fig. 3 a perspective view of a toroidal core package and Fig. 4 a perspective view of a framework structure supporting the toroidal cores.

[0040] Fig. 1 shows a perspective view of a filter arrangement 10, in particular an absorption filter for absorbing high-frequency differential currents (common mode current) in phase lines of an electric motor.

[0041] The filter assembly 10 comprises a housing 12, preferably made of plastic, which in the illustrated embodiment is designed as a standardized installation box with a substantially cuboid-shaped housing base 14. The base housing 14 comprises lateral fastening tabs 16, 18 with receptacles 20, 22 for fastening elements, by means of which the housing 12 can be mounted, for example, in a control cabinet. Furthermore, a cover 24 is provided, by means of which the housing base 14 can be closed.

[0042] A plurality of ring-shaped, closed, one-piece toroidal cores 26-34 are arranged in the housing 12. The toroidal cores 26-34 are arranged along a longitudinal axis 36 of the housing 12 and form a channel 38 with feedthroughs 40, 42, 44 for receiving phase lines of a connecting cable of the electric motor.

[0043] In the illustrated embodiment, a separate bushing 40, 42, 44 is provided for each phase line, each of which opens into preferably opposite housing walls 46, 48.

[0044] According to the invention, it is provided that the toroidal cores 26 - 34 in the housing 12, with the exception of the feedthroughs 40, 42, 44 leading through the toroidal cores 26 - 34, are cast by means of a casting compound 50, wherein the casting compound 50 substantially completely fills a cavity formed between the toroidal cores 26 - 34 and the housing 12, so that the toroidal cores 26 - 34, with the exception of the feedthroughs 40, 42, 44, are completely cast.

[0045] The potting compound 50 has good thermal conductivity, so that particularly good heat dissipation of the heat loss from the toroidal cores 26 - 34 to the housing surface is achieved.

[0046] Fig. 2 shows a perspective side view of the filter assembly 10, partially in section. A cavity 52 formed between the toroidal cores 26-34 and the housing wall is completely filled with the potting compound 50, so that the toroidal cores are fully embedded in the potting compound 50.

[0047] Fig. 3 shows a perspective view of the toroidal cores 26 - 34 in the form of a toroidal core package 54. The toroidal cores 26 - 34 are fixed at a distance from one another by means of a framework arrangement 56 in order to ensure that the potting compound 50 completely encloses the toroidal cores 26 - 34.

[0048] The scaffolding arrangement 56 is shown in perspective in Fig. 4 and comprises flat separating elements 58 - 68 running transversely to the longitudinal axis 36 and longitudinal struts 70, 72, 74 running in the longitudinal direction and fixing the separating elements 58 - 68 at an equidistant distance. The individual separating elements 58 - 68 are arranged at a distance from one another which is greater than the width of an individual toroidal core 26 - 34. Openings 76, 78, 80 are provided in the separating elements 58 - 68, which are aligned with one another and define the position of the feedthroughs 40, 42, 44.

[0049] The inventive method for producing the filter assembly 10 is characterized in that the filter cores 26-34 are first fixed by means of the framework assembly 56 and assembled to form the toroidal core package 54. The toroidal core package 54 is then inserted into the housing 12 so that the openings 76, 78, 80 of the separating elements 58-68 are aligned with the end openings of the housing walls 46, 48. Subsequently, rod-shaped elements, which do not bond to the potting compound, are passed through the openings 76, 78, 80, with the rods completely penetrating the housing 12 and the toroidal cores 26-34. The cover 24 is then placed on top, and the housing 12 is closed.

[0050] The potting compound 50 is then introduced into the housing interior via an opening in a housing wall until the toroidal cores 26 - 34 are completely enclosed or filled with potting compound 50.

[0051] After the potting compound 50 has hardened, the rods that do not bond with the potting compound 50 can be pulled out of the potting compound 50, so that the bushings 40, 42, 44 are formed in the form of channels for the individual phase lines of the motor cable.

[0052] Alternatively, the feedthroughs 40, 42, 44 can be produced in the form of channels, e.g., by individual holes and / or millings, after the potting compound 50 has hardened.

[0053] As an alternative to individual feedthroughs 40, 42, 44, a single channel can also be formed. It is also possible to assign individual toroidal cores to each feedthrough.

[0054] The filter arrangement 10 according to the invention offers the advantage over the prior art that the individual phase cables of the motor can be loosely routed through the bushings 40, 42, 44, plugged in or pulled out, and then directly connected to the frequency converter. Since the filter arrangement 10 according to the invention no longer has any connection terminals, very simple installation is possible, especially retrofitting the filter without significant time and expense.

[0055] The manufacture of the filter arrangement itself is also considerably simplified, as there is no need for internal wiring of electrical lines between input and output terminals.

[0056] The embedding in a potting compound 50 also has the advantage that heat generated in the toroidal cores 26 - 34 can be dissipated to the housing 12 and thus the efficiency of the toroidal cores 26 - 34 is improved.

Claims

1. A filter arrangement (10), wherein the filter arrangement (10) is an absorption filter for absorbing high-frequency differential currents in phase conductors of a supply cable of an electric motor, comprising a housing (12) with several toroidal cores (26 - 34) electromagnetically couplable to at least one of the phase conductors, wherein the toroidal cores (26 - 34) are sealed inside the housing (12) by means of a filling compound (50); wherein the filter arrangement (10) has at least one leadthrough (40, 42, 44) in the form of a duct formed free of filling compound; wherein the at least one leadthrough (40, 42, 44) passes through the toroidal cores (26 - 34) and the housing (12) such that the at least one phase conductor can be passed through; wherein the toroidal cores (26 - 34) are arranged along a longitudinal axis (36) of the housing (12) or also adjacent to one another inside the housing (12); and wherein individual toroidal cores (26 - 34) are fixed inside the housing (12) at a distance to one another and at a distance to housing walls of the housing (12) by means of a frame structure (56).

2. The filter arrangement according to claim 1, wherein the at least one leadthrough (40, 42, 44) is limited by the filling compound (50) or by at least one pipe section, and wherein the at least one pipe section passes through the toroidal cores (26 - 34) and the housing (12) in the longitudinal direction.

3. The filter arrangement according to claim 1 or 2, wherein the at least one leadthrough (40, 42, 44) or the at least one pipe section leads into preferably opposite walls (46, 48) of the housing (12).

4. The filter arrangement according to at least one of the preceding claims, wherein the at least one leadthrough (40, 42, 44) comprises a single leadthrough or several leadthroughs (40, 42, 44), and wherein the at least one leadthrough (40, 42, 44) has a diameter greater than a diameter of the at least one phase conductor.

5. The filter arrangement according to at least one of the preceding claims, wherein the toroidal cores (26 - 34) are closed and / or wherein the toroidal cores (26 - 34) are of nanocrystalline material.

6. The filter arrangement according to at least one of the preceding claims, wherein the filling compound is selected preferably from the group of polyurethanes.

7. A method for manufacturing a filter arrangement (10) wherein the filter arrangement (10) is an absorption filter for absorbing high-frequency differential currents in phase conductors of a supply cable of an electric motor; wherein several toroidal cores (26 - 34) are arranged inside a housing (12) such that they are electrically couplable to the at least one phase conductor of the supply cable of the electric motor; wherein the housing (12) with the toroidal cores (26 - 34) arranged therein is filled by means of a filling compound (50); wherein at least one leadthrough (40, 42, 44) in the form of a duct free of filling compound is formed inside the housing (12) and the filling compound (50; wherein the at least one leadthrough (40, 42, 44) passes through the toroidal cores (26 - 34) and the housing (12) such that the at least one phase conductor can be passed through; wherein the toroidal cores (26 - 34) are arranged along a longitudinal axis (36) of the housing (12) or adjacent to one another inside the housing (12); and wherein individual toroidal cores (26 - 34) are fixed inside the housing (12) at a distance to one another and at a distance to housing walls of the housing (12) by means of a frame structure (56).

8. The method according to claim 7, wherein the at least one leadthrough (40, 42, 44) is formed in that at least one bar-like element which does not enter into any bonding with the filling compound is inserted into a duct (38) created by the toroidal cores prior to the pouring of the filling compound (50) into the housing (12), wherein the at least one bar-like element passes through opposite housing walls (46, 48) of the housing (12); and wherein the housing (12) is then filled by means of the filling compound (50) and the at least one bar-like element is extracted from the filling compound after setting of the filling compound.

9. The method according to claim 7, wherein the at least one leadthrough (40, 42, 44) is manufactured by drilling or milling into the housing (12) after filling of the latter with filling compound (50) and subsequent setting of the filling compound (50).