Inductive rotary transformer and electric machine with an inductive rotary transformer

Abstract

Inductive rotary transformer (10, 25, 30, 40, 45, 50) for the inductive transmission of electrical energy and / or electrical signals between machine parts (12, 13) rotatable relative to each other, comprising a secondary winding (15) rotatably mounted relative to a primary winding (14) and inductively coupled to the primary winding (14), wherein a magnetic core is provided for inductive coupling, comprising at least one primary winding-side core part (16) and a secondary winding-side core part (18) separated from the primary winding-side core part (16) by an air gap (17) in order to form a magnetic circuit for guiding a magnetic flux between the primary winding (14) and the secondary winding (15),wherein a lubricant is introduced into the air gap (17) and an air gap limiting surface (19) of the primary winding-side core part (16) and an air gap limiting surface of the secondary winding-side core part (18) form mutually interacting sliding surfaces (20) of a sliding bearing; and an electric machine (11) with such an inductive rotary transformer.

Description

[0001] The invention relates to an inductive rotary transformer for the inductive transmission of electrical energy and / or electrical signals between machine parts that are rotatable relative to each other, such as a rotor and a stator of an electric machine. The invention further relates to an electric machine with an inductive rotary transformer.

[0002] Separately excited electrical machines, such as separately excited synchronous machines, have a rotor rotatably mounted in a stator. Electrical energy must be supplied to the rotor to generate a magnetic field. It is generally known to transfer this electrical energy to the rotor either via a slip ring transmission system or, alternatively, via a contactless inductive energy transfer system.

[0003] A slip ring transmission system can be operated in a dry or wet environment. In a dry system, the slip ring and brushes, such as carbon brushes, are located in a sealed compartment containing only air. This system requires a reliable seal, especially if an active area of ​​the electric machine (e.g., rotor surface and / or winding heads) is cooled by a coolant, as is common practice in the electric vehicle industry today. Over time, dust can accumulate in this sealed compartment due to wear on the slip ring and brushes.

[0004] A wet slip ring transmission system means that a fluid, usually oil, is present in the same space as the slip ring and brushes, as the oil also acts as a coolant for the electrical motor. The oil cools the slip ring contacts, reduces wear, and carries dust particles away from the slip ring transmission system. Furthermore, in most cases, sealing the active area of ​​the electrical motor is not required.

[0005] A slip ring transmission system inherently exhibits relatively high wear and therefore a relatively short service life. Due to the requirement that the materials for the slip rings and brushes must possess good electrical conductivity, these materials (usually copper or carbon alloys) have inferior mechanical properties because they are softer. Furthermore, an optimal spring force is required to press the carbon brushes against the slip rings and establish sufficient electrical contact. There is an optimum force required. If the carbon brush is pressed with insufficient force, a poor electrical connection with high contact resistance is created, leading to increased wear, temperature rise, and a shorter service life.If the carbon brush is pressed with too much force, the electrical contact resistance decreases, but high mechanical friction is created, which also leads to increased wear, temperature rise and shorter service life.

[0006] In contactless inductive power transmission, electrical energy is transferred to the rotor via two coils and alternating current (so-called "rotary transformer"). Due to the contactless transmission, there is no mechanical wear, resulting in a long service life. However, this advantage is offset by higher manufacturing costs. Furthermore, there is always an air gap in the magnetic circuit between the stator and the rotor, which creates a high magnetic resistance and consequently reduces the efficiency of the contactless inductive transmission system. Typical maximum achievable efficiencies are around 92%. Typical air gap thicknesses range from approximately 0.5 to 0.8 mm.

[0007] For example, DE 20 2011 107 803 U1 discloses such an inductive rotary transformer.

[0008] Against this background, the invention is based on the objective of providing an inductive rotary transformer and an electric machine that have high efficiency, low wear and a long service life or long operating time.

[0009] This problem is solved by an inductive rotary transformer with the features of claim 1 and by an electric machine with the features of claim 10. Further, particularly advantageous embodiments of the invention are disclosed in the respective dependent claims.

[0010] It should be noted that the features listed individually in the claims can be combined with one another in any technically meaningful way (even across category boundaries) and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0011] It should also be noted that the conjunction “and / or” used herein, which stands between two features and links them together, is always to be interpreted in such a way that in a first embodiment of the object according to the invention only the first feature may be present, in a second embodiment only the second feature may be present, and in a third embodiment both the first and the second feature may be present.

[0012] The term "approximately" here indicates a tolerance range that a person skilled in the art in this field would consider customary. In particular, the term "approximately" is to be understood as a tolerance range of the related quantity of up to a maximum of + / -20%, preferably up to a maximum of + / -10%.

[0013] The invention relates to an inductive rotary transformer (hereinafter also simply referred to as an inductive transformer) for the inductive transmission of electrical energy and / or electrical signals between machine parts rotatable relative to each other, such as a rotor and a stator of an electric machine, which has a secondary winding rotatably mounted relative to a primary winding and inductively coupled to the primary winding. For inductive coupling, a magnetic core is provided, which has at least one core part on the primary winding side, in particular a stationary core part, and a core part on the secondary winding side, rotatable relative to the core part on the primary winding side and separated from the core part on the primary winding side by an air gap, in order to form a magnetic circuit for guiding a magnetic flux between the primary winding and the secondary winding.The magnetic circuit thus represents a closed path of the guided magnetic flux. The invention further provides that a lubricant, e.g., oil, is introduced into the air gap and that an air gap boundary surface of the primary winding-side core part and an air gap boundary surface of the secondary winding-side core part form mutually interacting sliding surfaces of a sliding bearing.

[0014] The invention is based on a wet, contact-based inductive energy and / or signal transmission between the primary and secondary windings, which can be used, for example, to excite a rotor excitation winding of an electric machine. However, the invention is not necessarily limited to use in combination with electric machines. The primary-winding-side (stationary) core part of the magnetic core is slidably mounted on the secondary-winding-side (rotatable) core part of the magnetic core. This allows for a minimization of the air gap thickness, thereby significantly improving the efficiency of the energy / signal transmission to the secondary winding.In particular, the thickness of the air gap can be reduced to a range of about 25 µm to about 50 µm, which, compared to the typical air gap thicknesses mentioned at the beginning for conventional non-contact, dry inductive power transmission systems, represents a reduction by a factor of at least about 20, i.e. a reduction by at least one order of magnitude.

[0015] The air gap of the wet energy / signal transmission system according to the invention contains essentially no air, but rather the lubricant or a lubricant film with a thickness of, for example, 0.025 mm (25 micrometers). In other words, the thickness of the air gap is essentially determined by the thickness of the lubricant film that forms in the air gap during the operational use of the rotary transmitter, i.e., during the rotation of the secondary-winding-side core part relative to the primary-winding-side core part. The thickness of the lubricant film is influenced, among other things, by the viscosity of the lubricant. When using, for example, ordinary 0W-20 automotive engine oil as the lubricant, the oil film thickness is in the range of approximately 0.025 mm to 0.05 mm (25 to 50 µm).

[0016] In addition to providing good lubrication of the sliding bearing, which significantly reduces mechanical friction and wear between the sliding surfaces involved, the lubricant (e.g. oil) also provides effective cooling of the sliding bearing, vibration damping, sealing effect and corrosion protection.

[0017] Overall, the invention achieves efficiencies in energy transfer to the secondary winding of well over 90%, for example at least 93% or 94% or even 95% and above.

[0018] The inductive rotary transformer can be used both for the transmission of alternating current energy and for the transmission of data or signals between the primary and secondary windings.

[0019] It should be understood that the terms primary winding and secondary winding do not necessarily define a specific electrical and / or mechanical property of the respective windings, but are merely used here to conceptually distinguish one winding from the other. In this sense, these terms are interchangeable, so that, for example, the primary winding can be rotatably mounted relative to the secondary winding, and the secondary winding can be stationary.

[0020] In preferred embodiments, the sliding surfaces are pressed together by a spring-like force. This means that at least one stationary core part on the primary winding side and the core part on the secondary winding side, which is rotatable relative to it, are pressed together with a low contact force. Low contact forces, as defined in the invention, are understood to be, for example, approximately 0.5 N. By pressing the surfaces together, the air gap between them is further minimized, and the efficiency of the energy transfer is further increased.

[0021] Other advantageous embodiments provide that the sliding bearing is designed as a simply lubricated, hydrostatic or hydrodynamic sliding bearing.

[0022] In a simply lubricated plain bearing, the lubricant is drawn into and drawn out of the air gap by the secondary winding-side core part, which moves or rotates relative to the primary winding-side (stationary) core part, due to adhesion. This results in a uniform lubricant film forming in the air gap. The air gap is not sealed off from the surrounding environment but is open, meaning that during operation of the rotary transmission (e.g., during the operation of an electric machine with such a rotary transmission), there is a continuous flow of lubricant into and out of the air gap.

[0023] In hydrostatic sliding bearings, the lubricant is continuously pressurized and forced into the air gap (e.g., by a pump) during operation of the rotary transmission and then discharged from it. Accordingly, the air gap is also open. The lubricant can be supplied to and removed from the air gap via the core section on the primary winding side. For this purpose, the core section on the primary winding side can provide corresponding lubricant channels.

[0024] In hydrodynamic sliding bearings, the air gap is hermetically sealed from the external environment. The lubricant can be introduced into the air gap once before sealing. During operation of the rotary transmission, essentially no lubricant exchange takes place in the air gap. Advantageously, for example, a pump for pressurizing the lubricant in the air gap can be omitted.

[0025] In a further preferred embodiment, the respective sliding surfaces, i.e., the sliding surfaces of the primary-winding-side and secondary-winding-side core parts, are formed from a hardened metal material. Due to the reciprocal contact, the sliding surfaces are subject to wear. The surfaces of the opposing sliding surfaces of the respective core parts, which define the air gap, can be hardened by various known processes, such as electron beam hardening, thereby creating a metal component that is mechanically hard for low wear and simultaneously highly magnetically conductive with high relative permeability.

[0026] In further advantageous embodiments, the sliding surfaces, i.e., the sliding surfaces of the primary-winding-side and secondary-winding-side core parts that interact with each other in the sliding bearing, are each formed by a first core segment on the air gap side of the primary-winding-side and secondary-winding-side core parts, which differs from a second core segment located away from the air gap in at least one material property. In other words, the first and second core segments can be formed from different components that exhibit different material properties, such as different mechanical hardness, different relative permeability (magnetic conductivity), different electrical conductivity, different density, and the like.The various core segments can be separate components that can be bonded together to form the respective core part. Other joining techniques, such as welding, screwing, clamping, etc., are also conceivable.

[0027] The first core segments, due to the provision of the respective sliding surfaces involved in the sliding bearing, are subject to wear and may be made of a hardened metal material (e.g., by electron beam hardening). Accordingly, in this case, the sliding surfaces provided by the first core segments are also made of a hardened metal material, which in this way can be both mechanically hard for low wear and magnetically conductive with high relative permeability.

[0028] For the second core segments located away from the air gap in the magnetic circuit, which are not directly involved in the sliding bearing and therefore do not provide wear-prone sliding surfaces, there is no requirement for high mechanical hardness. When selecting the material properties for these second core segments, high relative permeability (magnetic conductivity) and low iron losses are paramount. For example, the second core segments can be made of laminated electrical steel sheets, soft magnetic composites (SMC), or ferrites. Accordingly, in preferred further embodiments, the second core segments are made of a metallic material, a ferrite, or a soft magnetic composite.

[0029] In embodiments where the sliding surfaces or the first and / or second core segments are formed from a metallic material, the metallic material may, in further embodiments, comprise laminated electrical steel sheets to reduce iron losses in the metallic material. Preferably, the sliding surfaces are formed by the end faces of the laminated electrical steel sheets joined to form a stack, wherein the end faces are the respective narrow sides of the electrical steel sheets.

[0030] In yet another advantageous embodiment, several primary-winding-side core sections are provided, arranged at equidistant intervals around the secondary-winding-side core section. These form magnetically parallel primary-winding-side core sections with respect to the magnetic circuit, allowing the total amount of energy to be transferred to the secondary winding to be distributed among them. This means that the individual primary-winding-side core sections can be designed more compactly for lower magnetic power output.

[0031] Advantageously, in a further embodiment, each core section on the primary winding side has a separate primary winding. Since the total amount of energy to be transferred to the secondary winding is distributed across the multiple primary windings of the core sections on the primary winding side, the primary windings can be designed for lower electrical power and, accordingly, be built in a space-saving and compact manner.

[0032] In further advantageous embodiments, the sliding surface of the secondary-winding-side core part is annular, wherein the sliding surface of the primary-winding-side core part either completely surrounds the sliding surface of the secondary-winding-side core part or only partially surrounds it. Completely surrounding means that the sliding surface of the primary-winding-side core part encloses the (annular) sliding surface of the secondary-winding-side core part in an annular manner and can accordingly also be designed as a closed ring. This allows for both hydrostatic and hydrodynamic bearing configurations (hermetically sealed air gap). The lubricant can be supplied to or removed from the air gap at a point on the annular primary-winding-side sliding surface.

[0033] In the case of multiple primary winding-side core sections with individual sliding surfaces, the lubricant supply and return lines can be connected in parallel to lubricate these surfaces. This simplifies lubrication of the air gap and allows for greater design flexibility in the lubricant supply. The partially formed sliding surface of at least one primary winding-side core section enables a more compact design when using only one or a few (e.g., two or three) primary winding-side core sections.

[0034] The invention further relates to an electric machine with a rotor rotatably mounted on a stator, which carries at least one electrical rotor excitation winding, and with an inductive rotary transformer for the inductive electrical supply of the rotor excitation winding, wherein the inductive rotary transformer is designed according to one of the embodiments disclosed herein. Its secondary winding is attached to the rotor and electrically coupled to the rotor excitation winding. Its primary winding is arranged in a stationary position relative to the rotor, for example, held on the stator.

[0035] Excitation windings (e.g., rotor and stator windings) are coils (i.e., field windings formed from wire windings) in an electrical machine that generate the magnetic field for energy conversion between electrical / magnetic energy and mechanical energy when an electric current (excitation current) flows through them. In contrast, the inductive rotary transformer does not serve to generate or transmit mechanical forces resulting from the magnetic field generated between the primary and secondary windings.

[0036] The inductive rotary transformer can be used both for the transmission of alternating current energy and for the transmission of data or signals between the primary and secondary windings.

[0037] It is understood that definitions relating to the claimed electrical machine, as well as the effects and advantages of features of the claimed electrical machine, can be fully derived from the disclosure of analogous definitions, effects, and advantages of the rotary transmitter, and vice versa. A repetition of explanations of analogous features, their effects, and advantages can therefore be omitted in favor of a more concise description, without such omissions being interpreted as a limitation of either of the disclosed inventions.

[0038] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are not to be understood as limiting and are explained in more detail below with reference to the drawing. This drawing schematically shows: Fig. 1 a perspective view of a rotary transmitter and of a part of an electric machine, each according to an embodiment of the invention; Fig. 2 a perspective view of a rotary transmitter according to a further embodiment of the invention; Fig. 3 a perspective view of a rotary transmitter according to a further embodiment of the invention; Fig. 4 a perspective view of a primary-side core part of the rotary transmitter made of Fig. 5; Fig. 5 a top view of the core part made of Fig. 6; Fig. 6 a perspective view of a rotary transmitter according to a further embodiment of the invention; Fig. 7 a perspective view of a rotary transmitter according to a further embodiment of the invention; Fig. 8 a perspective view of a rotary transmitter according to a further embodiment of the invention; Fig. 9 a rotary transmitter according to a further embodiment of the invention; Fig. 10 a rotary transmitter according to a further embodiment of the invention; and

[0039] The specific examples described below are purely illustrative in nature and serve to clarify the basic structures and processes.

[0040] Fig. Figure 1 shows a perspective view of a rotary transmitter 10 and of a part of an indicated electrical machine 11, each according to an embodiment of the invention.

[0041] The inductive rotary transformer 10 serves for the inductive transmission of electrical energy and / or electrical signals between machine parts that are rotatable relative to each other. In the example shown, these are a stator 12 and a rotor 13 of the electric machine 11, which is rotatably mounted on the stator. The rotor 13 carries at least one electrical rotor excitation winding (not shown), which is inductively supplied with electrical energy via the rotary transformer 10.

[0042] The rotary transformer 10 has a secondary winding 15 that is rotatably mounted relative to a primary winding 14 and inductively coupled to the primary winding 14. The secondary winding 15 of the rotary transformer 10 is fixed to the rotor 13 and electrically coupled to the rotor excitation winding. The primary winding 14 of the rotary transformer 10 is stationary relative to the rotor 13, for example, held against the stator 12.

[0043] For inductive coupling, a magnetic core is provided which has at least one primary winding-side core part 16, which in this case comprises two core segments 16.1 and 16.2, and a secondary winding-side core part 18, which in this case also comprises two core segments 18.1 and 18.2, separated from the primary winding-side core part 16 by an air gap 17, in order to form a magnetic circuit for guiding a magnetic flux between the primary winding 14 and the secondary winding 15.

[0044] A lubricant, e.g. oil, is introduced into the air gap 17. An air gap boundary surface 19 (see figure) Fig. 6) of the primary winding-side core part 16 and one shown in the representation of the Fig. The air gap limiting surface of the secondary winding-side core part 18, which is concealed by the core part 16, forms interacting sliding surfaces 20 (see also Fig. 6) a sliding bearing.

[0045] At the in Fig. In the rotary transmitter 10 shown, the sliding surfaces 20 are pressed together by means of spring elements 21 in a spring-elastic manner, but this is not necessarily the only possible application.

[0046] The respective sliding surfaces 20 of the primary and secondary winding-side core parts 16 and 18 can be made of a hardened metal material.

[0047] In the exemplary embodiment shown here, the Fig. 1 the sliding surfaces 20 are each formed by the air-gap-side first core segment 16.1 or 18.1 of the primary-winding-side and secondary-winding-side core parts 16, 18, which differs from the air-gap-remote second core segment 16.2 or 18.2 of the primary-winding-side and secondary-winding-side core parts 16, 18 in at least one material property.

[0048] For example, the second core segments 16.2 and / or 18.2 can be made of a metallic material, a ferrite or a soft magnetic composite material, and the first core segments 16.1 and / or 18.1 can be made of a hardened metallic material.

[0049] The sliding surface 20 of the secondary winding-side core part 18 of the rotary transformer 10 made of Fig. 1 is ring-shaped. The sliding surface 20 of the primary winding-side core part 16 surrounds the sliding surface 20 of the secondary winding-side core part 18 only in sections. This design allows for a simply lubricated sliding bearing.

[0050] All further embodiments of rotary joints described below can be constructed similarly to the one in Fig. 1 The rotary transmitter 10 shown can be used in combination with an electric machine similar to the electric machine 11, but is not necessarily limited to use with electric machines.

[0051] All embodiments of rotary transformers described herein can be used both for the transmission of alternating current energy and for the transmission of data or signals between the primary and secondary windings.

[0052] Fig. Figure 2 shows a perspective view of a rotary transmitter 25 according to a further embodiment of the invention. In contrast to the rotary transmitter 10 made of Fig. The sliding surface 20 of the primary winding-side core part 16 or core segment 16.1 is formed to completely surround the sliding surface 20 of the secondary winding-side core part 18 or core segment 18.1. The sliding surface 20 of the secondary winding-side core part 18 or 18.1 is annular. This design enables a hydrodynamic sliding bearing.

[0053] Fig. Figure 3 shows a perspective view of a rotary transmitter 30 according to a further embodiment of the invention. It can be seen that the lubricant is introduced into the air gap 17 under pressure via lubricant channels 31. This design enables a hydrostatic sliding bearing.

[0054] Fig. Figure 4 shows a perspective view of the primary-side core part 16 of the rotary transmitter 30. Fig. 5 dar, Fig. 5 a top view of this.

[0055] Fig. Figure 6 shows a perspective view of a rotary transformer 40 according to a further embodiment of the invention. In this embodiment, the rotary transformer 40 has two primary-winding-side core parts 16, which are arranged at equidistant intervals around the secondary-winding-side core part 18. The two primary-winding-side core parts 16 utilize a common first core segment 16.1, which completely surrounds the secondary-winding-side first core segment 18.1. Each primary-winding-side core part 16 has a separate primary winding 14.

[0056] Fig. Figure 7 shows a perspective view of a rotary transformer 45 according to a further embodiment of the invention. The rotary transformer 45 has three primary winding-side core parts 16, each with first and second core segments 16.1 and 16.2, respectively. The three core parts 16 are arranged at equidistant intervals around the secondary winding-side core part 18.

[0057] Fig. Figure 8 shows a perspective view of a rotary transformer 50 according to a further embodiment of the invention. The rotary transformer 50 has four primary winding-side core parts 16, which are arranged at equidistant intervals around the secondary winding-side core part 18 and use a common first core segment 16.1.

[0058] The in the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 to Fig. The embodiments described in section 8 each relate to radial arrangements of the primary and secondary winding-side core parts 16 and 18 to each other.

[0059] Fig. Figure 9 shows a view of a rotary transformer according to a further embodiment of the invention. In particular, this rotary transformer, unlike the embodiments described above, has an axial or coaxial arrangement of the core parts on the primary and secondary winding sides relative to each other. The arrangement consists of a primary core 1 made of ferrite, a primary coil 2, a secondary core 3 made of ferrite, a secondary coil 4, ring pairs made of electrical steel 5 with a wear element and slip ring, and a spring 6.

[0060] Fig.Figure 10 shows a view of a rotary transformer according to a further embodiment of the invention. In particular, this rotary transformer, unlike the embodiments described above, has two primary winding-side core parts that clamp around the secondary winding-side core part. The arrangement consists of primary cores 1a and 1b made of ferrite, primary coil 2, secondary core 3 made of ferrite, secondary coil 4, ring pairs made of electrical steel 5 with a wear element and slip ring. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 20 2011 107 803 U1

[0007]

Claims

[1] Inductive rotary transformer (10, 25, 30, 40, 45, 50) for the inductive transmission of electrical energy and / or electrical signals between machine parts (12, 13) rotatable relative to each other, comprising a secondary winding (15) rotatably mounted relative to a primary winding (14) and inductively coupled to the primary winding (14), wherein a magnetic core is provided for inductive coupling, comprising at least one primary winding-side core part (16) and a secondary winding-side core part (18) separated from the primary winding-side core part (16) by an air gap (17) in order to form a magnetic circuit for guiding a magnetic flux between the primary winding (14) and the secondary winding (15),wherein a lubricant is introduced into the air gap (17) and an air gap limiting surface (19) of the primary winding-side core part (16) and an air gap limiting surface of the secondary winding-side core part (18) form mutually interacting sliding surfaces (20) of a sliding bearing. [2] Rotary transmitter according to claim 1, in which the sliding surfaces (20) are pressed together in a spring-elastic manner. [3] Rotary transmitter according to claim 1 or 2, wherein the sliding bearing is designed as a simply lubricated, hydrostatic or hydrodynamic sliding bearing. [4] Rotary transmitter according to one of the preceding claims, wherein the respective sliding surfaces (20) are formed from a hardened metal material. [5] Rotary transformer according to one of the preceding claims, in which the sliding surfaces (20) are each formed by an air-gap-side first core segment (16.1, 18.1) of the primary-winding-side and secondary-winding-side core parts (16, 18), which differs from an air-gap-remote second core segment (16.2, 18.2) of the primary-winding-side and secondary-winding-side core parts (16, 18) in at least one material property. [6] Rotary transmitter according to claim 5, wherein the second core segments (16.2, 18.2) are formed from a metallic material, a ferrite or a soft magnetic composite material. [7] Rotary transformer according to one of the preceding claims, in which several primary winding-side core parts (16) are provided which are arranged at equidistant intervals circumferentially around the secondary winding-side core part (18). [8] Rotary transformer according to claim 7, wherein each primary winding-side core part (16) has a separate primary winding (14). [9] Rotary transformer according to one of the preceding claims, in which the sliding surface (20) of the secondary winding-side core part (18) is formed in an annular shape and the sliding surface (20) of the primary winding-side core part (16) is formed to completely surround the sliding surface (20) of the secondary winding-side core part (18) or to only partially surround it. [10] Electric machine (11) with a rotor (13) rotatably mounted on a stator (12) which carries at least one electrical rotor excitation winding, and with an inductive rotary transformer (10, 25, 30, 40, 45, 50) for inductive electrical supply of the rotor excitation winding, wherein the inductive rotary transformer is designed according to one of the preceding claims and the secondary winding (15) of the rotary transformer is attached to the rotor (13) and electrically coupled to the rotor excitation winding and the primary winding (14) of the rotary transformer is arranged stationary relative to the rotor (13), in particular held on the stator (12).

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