DE102020215671A1 - Bifilar winding and method of making a bifilar winding - Google Patents

Abstract

Proposed is a bifilar winding for limiting a short-circuit current in the event of a turn fault, comprising a first partial winding and a second partial winding, turns of the partial windings being wound into one another and the turns of the first partial winding being spaced apart from one another by the turns of the second partial winding, and the first Part winding and the second part winding have a conductive connection.

Description

field of invention

The invention relates to a bifilar winding for limiting a short-circuit current in the event of an interturn fault.

Furthermore, the invention relates to a method for producing a bifilar winding.

background

Electrical machines, in particular permanently excited synchronous machines for use in aircraft drives, have a high power and/or torque density. In permanently excited synchronous machines with toothed coil windings, the excitation field is generated by permanent magnets and therefore cannot be switched off. The teeth in the stator are wound individually. Safety aspects play a central role in flight applications in particular, so that fault case considerations are fundamental to machine design. The interturn short-circuit is to be regarded as a critical error case, since the short-circuit current, driven by the induced voltage of the rotating permanent magnets, is a multiple of the terminal short-circuit current and can destroy both the stator winding and structural parts in a very short time. In order to prevent damage, the machine must be stopped immediately in the event of an interturn fault.

There is therefore a need to design electrical machines with short-circuit protection.

To this end, it has already been proposed to dimension electrical machines in such a way that the high short-circuit currents cannot cause any damage. The probability of failure of the insulation can be minimized through the robust design of the conductor insulation and the highest quality standards in production.

However, this has the disadvantage that thicker insulation increases the thermal resistance of the conductor. This reduces the dissipated power loss. In addition, the required cross-section for the insulation is at the expense of the conductor cross-section. Both limit the performance of the machine.

It has also been proposed to actively short-circuit windings in which an interturn short has occurred. Active short-circuiting of the terminals distributes the short-circuit current evenly to all windings and thus reduces the power loss at the fault location. Here, however, there is the disadvantage that devices must be provided for the immediate detection of an interturn short.

The object of the invention is therefore to provide a winding for an electrical machine which at least alleviates these disadvantages.

Brief description of the invention

This object is solved by the invention specified in the independent claims. Advantageous configurations can be found in the dependent claims.

According to the invention, a winding of the type mentioned is created, comprising a first partial winding and a second partial winding, with turns of the partial windings being wound into one another and with the turns of the first partial winding being spaced apart from one another by the turns of the second partial winding, and with the first partial winding and the second partial winding have a conductive connection.

In the case of an interturn short, the insulation between two adjacent turns typically fails, so that a short-circuit current can flow between the turns. The path of the short-circuit current in this case corresponds to a single turn. However, in a permanently excited synchronous machine, the short-circuit current is limited by the inductance of the short-circuited path. The short-circuited path forms its own "coil" with its own inductance in which its own current is generated by the permanently excited rotor during operation of the machine, which in turn creates its own magnetic field, which is directed counter to the magnetic field of the rotor. This magnetic field is dependent on the inductance of the shorted path. Therefore, the short-circuit current is largely limited by the inductance of the short-circuited path. If this is high, an even stronger magnetic field can form, which counteracts the generator magnetic field and thus limits the short-circuit current induced in the defective winding. If a single turn in a winding with n turns is short-circuited, the short-circuit current corresponds to n times the terminal short-circuit current. The terminal short-circuit current corresponds to the current induced by an excitation field in the n-turn winding when the winding ends (terminals) are short-circuited.

According to the invention, the windings are bifilar. The conductors that form the winding consist of two independent partial conductors that are insulated from one another. Form the two sub-conductors two independent partial windings. The turns of the first partial winding are separated and spaced apart from one another by the turns of the second partial winding. Therefore, if the insulation fails, no direct short circuit can occur between two turns of a partial winding. A short circuit that occurs when the insulation fails is therefore a short circuit between adjacent turns of the first partial winding and the second partial winding. In order to lengthen the path of the short-circuit current as much as possible in this case, i.e. to create a "coil" with high inductance, the first partial winding and the second partial winding have a conductive connection. The increased inductance of the enlarged coil as a result of the conductive connection, which is formed by the path of the short-circuit current, also results in an increased magnetic field, which counteracts the magnetic field of the rotor and thus limits the short-circuit current. The power loss that occurs is therefore lower and can be thermally controlled with an appropriate design. Therefore, the invention enables the safe continued operation of a motor even if an interturn short occurs. Another advantage is that when a winding, in particular a tooth winding, is designed according to the invention, the conductor filling factor of the tooth winding is retained and the conductivity of an electrical machine in which the winding is used is therefore not reduced.

In one embodiment of the invention, the first partial winding is connected in series with the second partial winding by the conductive connection. In particular, there is a conductive connection between a first end of the second partial winding and a second end of the first partial winding.

Due to the series connection of the first and second partial windings, it follows that on the path of a short-circuit current between adjacent conductors of the first partial winding and the second partial winding, 50% of the turns of a single partial winding with a number of turns n must always be passed through. However, if the short-circuit current always has to pass through 50% of all turns, there are effectively two turns left, so that n has the value 2 in this case. The effective number of turns of the short-circuited "coil" is therefore n=2. Because it applies that when a single turn in a winding with n turns is short-circuited, the short-circuit current corresponds to n times the terminal short-circuit current, it also applies that, according to the invention, the short-circuit current is limited to twice the terminal short-circuit current of a partial winding. The following applies: I (short) = 2 I (clamp). Because the current is limited to twice the terminal short-circuit current, no active short-circuiting of the terminals is required in the event of a fault. As a result, complex devices for detecting an interturn fault can also be dispensed with.

In one embodiment of the invention, the bifilar winding is a single-tooth winding of a stator coil in a permanently excited synchronous machine, in particular in an electric drive. Since permanently excited synchronous machines are also used in aviation applications, and aviation applications require high power densities in connection with high fault tolerance, the invention is particularly suitable for use in such synchronous machines.

In one embodiment of the invention, the bifilar winding is a winding of a single-layer coil winding.

In one embodiment of the invention, the bifilar winding is a winding of a two-layer coil winding, the two-layer coil winding comprising a first layer and a second layer, the first layer comprising the first partial winding and the second partial winding and the second layer comprising a third and a fourth partial winding , wherein the first partial winding is connected in series with the second partial winding and the third partial winding is connected in series with the fourth partial winding and wherein the second partial winding is connected in series with the third partial winding. In addition to single-layer coils, the invention can also be applied to two-layer coils, in which case the first layer and the second layer must not have a layer jump area at the end of the coil, but must first be guided independently in parallel one above the other. Both layers initially include independent partial windings as described above. In order to increase the inductance in the event of an interturn short of adjacent coils, the first and second partial windings are connected in series in the first layer and the third and fourth partial windings are connected in series in the second layer. In addition, the two layers are connected in series with one another, in that the second and third partial windings are connected in series. In the event of a turn short between turns of the partial coils within one layer, the respective other layer remains fully functional. In the case of a turn-to-turn short between turns in different layers, half of all the turns in both layers are again traversed by a short-circuit current. Thus, the path of the short-circuit current can be lengthened and its inductance increased even in the case of a turn-to-turn short between turns of two layers. The series connections are given by conductive connections.

In one embodiment of the invention, the conductive connection includes a device for interrupting a current flow. In particular, a fuse can be provided in the conductive connection hen that breaks the path of the short-circuit current. The conductive connection is a section of conductor that is energized whenever there is a short circuit between adjacent turns. As a result, a single fuse can protect all initial faults (turn shorts) in insulation between two conductors, regardless of the number of turns in the coil sections. In the event of a fault, the current is switched off immediately by the fuse. As a result, an electrical machine that is not designed to absorb high currents, in particular the short-circuit currents I(short)=2 I(terminal), can continue to be operated if a short circuit has occurred. This makes the machine intrinsically safe.

In one embodiment of the invention, the conductive connection includes a measuring point, in particular an ammeter or a measuring coil. The measuring point can be used in particular for diagnosis and - based on this - for initiating countermeasures such as active short-circuiting. In particular, the measuring point can be designed as a measuring coil.

In particular, the measuring coil is connected to measuring coils of other windings to form a measuring bridge.

In one embodiment of the invention, the conductive connection is integrated into the bifilar winding, in particular the conductive connection is provided by a layer jump, in particular by a layer jump of n-2 layers. The conductive connection can also be provided by a layer setback, in particular by a layer setback of n−2. The layers are formed by the turns. In this case, a second end of the first partial winding is brought together directly with a first end of the second partial winding, resulting in a recessed conductor loop. The conductor loop can be dimensioned in such a way that it jumps back exactly n-2 layers. The jump back results in exactly two partial windings with N/2 turns, i.e. the same number of turns, so that in the event of a short circuit, I(short) = 2 I (terminal) again applies. This configuration has the advantage that only a small amount of additional effort is required in the manufacture of the windings.

In one embodiment of the invention, the windings are dimensioned to absorb a thermal power loss in the event of a short circuit between turns. A dimensioning, in particular a thickness of the strands or wires that form the turns and a thickness of the insulation between the turns of the first and second partial windings, is advantageously designed such that short-circuit currents and therefore thermal power losses do not lead to damage. This further increases operational reliability.

In the aforementioned embodiments, the bifilar winding can be part of a coil. In this respect, a coil is also created according to the invention.

According to a second aspect of the invention, a method is created for producing a bifilar winding according to the first aspect, in particular a single-tooth winding for a permanently excited electrical synchronous machine, the method comprising: winding the first partial winding comprising N turns, returning a last turn of the first partial winding, forming, through the returned turn, a conductor loop, the conductor loop forming a first turn of the second partial winding and winding the second partial winding along the turns of the first partial winding.

As a result of the jump back, no additional connection or interconnection of the free ends of the first and second partial windings is required. Additional connecting elements can therefore be dispensed with. This reduces the manufacturing effort with the same advantageous electrical properties.

In one configuration of the method, the winding of the first partial winding includes winding with the final pitch, and the winding of the second partial winding includes threading the second partial winding through the conductor loop. The conductor loop forms the return and is at the same time a transition from the first partial winding to the second partial winding. Due to the return, the turns remaining after the return must be threaded through the conductor loop during winding.

In one configuration of the method, the last turn of the first partial winding is returned by N-2 turns. This creates two partial windings with the same number of turns and the following applies: I(short) = 2 I(terminal).

character list

• Die 1 eine beispielhafte Wicklung aus dem Stand der Technik in der ein Windungsschluss aufgetreten ist;
• Die 2 eine beispielhafte bifiliare Wicklung gemäß der Erfindung;
• Die 3 eine beispielhafte Ausgestaltung der bifiliaren Wicklung gemäß 2;
• Die 4 eine weitere beispielhafte Ausgestaltung der bifiliaren Wicklung gemäß 2; und
• Die 5a und 5b eine beispielhafte bifiliare Wicklung gemäß der Erfindung mit Lagensprung;
• Die 6 eine beispielhafte zweilagige bifiliare Wicklungen; und
• Die 7 beispielhafte bifiliare Wicklungen in einer zweilagigen Spule.

Exemplary embodiments of the invention are described in more detail below with reference to the accompanying drawings. It shows:

• the 1 an exemplary prior art winding in which a shorted turn has occurred;
• the 2 an exemplary bifilar winding according to the invention;
• the 3 an exemplary embodiment of the bifilar winding according to FIG 2 ;
• the 4 a further exemplary embodiment of the bifilar winding according to FIG 2 ; and
• the 5a and 5b an exemplary bifilar winding according to the invention with layer jump;
• the 6 an example two-layer bifilar windings; and
• the 7 exemplary bifilar windings in a two-layer coil.

character description

1 Figure 12 shows an exemplary prior art winding in which a shorted turn has occurred. The winding is formed by a simple coiled conductor and has a fault (dashed circle) where an interturn short has occurred. As a result of excitation by a rotor (not shown) which continues to turn, a short-circuit current I(short) flows between two adjacent turns of the winding. A path of the short-circuit current (dashed line) leads through two windings, so that the short-circuit means that current effectively only flows through one winding. For a winding with n turns, the short-circuit current I(short) is therefore I(short) = n I(terminal).

2 shows a bifilar winding 1. The bifilar winding 1 comprises a first partial winding 2 and a second partial winding 3. Both the first partial winding 2 and the second partial winding 3 are formed by conductive wires and are provided with insulation (not shown). The first partial winding has a first end 4 and a second end 5 . Likewise, the second partial winding has a first end 6 and a second end 7 . The first partial winding 2 and the second partial winding 3 are wound into one another, so that the turns of one partial winding are spatially separated from one another by the turns of the other partial winding. Therefore, there are never two turns of the same partial winding 2.3 next to each other and no short circuit can occur between turns of the same partial winding. The two partial windings 2.3 are conductively connected to one another by a connecting element 8, for example a wire or other conductor. The bifilar winding is therefore formed by two partial windings that are insulated from one another and has a fault point 9 (dashed circle) in which an interturn short has occurred. The turn short occurs here between one turn of the first partial winding 2 and one turn of the second partial winding 3 . A short-circuit current I(short) flows as a result of excitation by a rotor which continues to turn (not shown). However, a path of the short-circuit current I(short) (dashed line) does not only lead through the two adjacent windings, but always through 50% of all windings. The path of the short-circuit current is lengthened by the conductive connecting element 8 . In the event of a short-circuit, the short-circuit current I(short) always flows through the remaining intact windings of a partial winding, viewed in the direction of the current, as well as all preceding turns of the other partial winding. As a result, in the event of a short circuit, 50% of the conductors in a stator tooth are traversed. This results in an effective number of turns of 2 in the event of a short circuit. This limits the short-circuit current to twice the terminal short-circuit current I(terminal).

3 shows an exemplary configuration of the bifilar winding 1 according to FIG 2 , wherein the connecting element 8 comprises a fuse 10 . The fuse 10 interrupts the circuit that is formed by connecting the first and the second partial windings 2.3 in the event of a turn short.

4 shows an exemplary configuration of the bifilar winding 1 according to FIG 2 or 3 , wherein the connecting element 8 comprises a measuring point 11 . Measuring point 11 is an ammeter A.

5 shows an exemplary bifilar winding 1 according to the invention with layer jump 12. The in 5a shown ends of the first partial winding 5 and the second partial winding 6 are according to 5b connected with each other. The connection according to 5b However, does not consist of a separate element 8, but the two ends 5.6 are designed as an overarching conductor loop. The first partial winding 2 merges into the second partial winding 3 along this conductor loop. The conductor loop returns the turns of the first partial winding 2 and forms a layer jump 12.

6 12 shows an exemplary two-layer bifilar winding 1 according to the invention. The two-layer bifilar winding 1 comprises a first, lower layer 13 and a second, upper layer 14. In the left part of the 6 the lower layer 13 and the second layer 14 at the lower end have a layer jump of between 8 and 9 turns. Therefore, in this arrangement, the turns 8 and 9 of the first partial winding 2 are together one above the other and there is a risk of a turn short circuit since there is no spatial separation. In the right part of 6 the first layer 13 and the second layer 14 have no layer jump, but are two initially independent bifilar windings 1 and are applied as layers one above the other. The second layer 14 includes a third partial winding 15 and a fourth partial winding 16. There are always turns of the first and the fourth part windings 2,16 and turns of the second and third partial windings 3, 15 opposite, so that turns of the same partial winding can never come into contact with one another here.

7 shows a schematic structure of an interconnection of partial windings of two bifilar windings 1 in a two-layer coil. The partial windings 2.3 of the first layer 13 are like too 2 described connected. Likewise, the partial windings 15,16 of the second layer 14 as to 2 described interconnected. In addition, the second partial winding 3 of the first layer 13 and the third partial winding 15 of the second layer 14 are connected in series with one another.

Reference List

1

bifilar winding

2

first partial winding

3

second partial winding

4

first end of the first partial winding

5

second end first partial winding

6

first end of the second partial winding

7

second end of the second partial winding

8th

fastener

9

point of failure

10

fuse

11

measuring point

12

layer jump

13

first layer

14

second layer

15

third partial winding

16

fourth partial winding

A

ammeter

I(short)

short-circuit current

Claims (14)

Bifilar winding (1) for limiting a short-circuit current in the event of an interturn short, comprising: a first partial winding (2); and a second partial winding (3); wherein turns of the partial windings (2,3) are wound into one another and wherein the turns of the first partial winding (2) are spaced apart from one another by the turns of the second partial winding (3), and wherein the first partial winding (2) and the second partial winding (3) have a conductive connection (8). Bifilar winding (1) after claim 1 , wherein the first partial winding (2) is connected in series with the second partial winding (3) by the conductive connection (8), in particular wherein the conductive connection (8) between a first end (6) of the second partial winding (3) and a second end (5) of the first partial winding (2). Bifilar winding (1) after claim 1 or 2 , wherein the bifilar winding (1) is a single-tooth winding of a stator coil in a permanently excited synchronous machine, in particular in an electric drive. Bifilar winding (1) according to one of the preceding claims, wherein the bifilar winding (1) is a winding of a single-layer coil winding. Bifilar winding (1) according to one of Claims 1 - 3 , wherein the bifilar winding (1) is a winding of a two-layer coil winding, the two-layer coil winding comprising a first layer (13) and a second layer (14), the first layer (13) having the first partial winding (2) and the second partial winding (3) and the second layer (14) comprises a third (15) and a fourth partial winding (16), the first partial winding (2) being connected in series with the second partial winding (3) via the conductive connection and the third The partial winding (15) is connected in series with the fourth partial winding (16) and the second partial winding (3) is connected in series with the third partial winding (15). Bifilar winding (1) according to one of the preceding claims, wherein the conductive connection (8) comprises a device for interrupting a current flow (10). Bifilar winding (1) according to one of the preceding claims, wherein the conductive connection (8) comprises a measuring point (11), in particular an ammeter (A) or a measuring coil. Bifilar winding (1) after claim 6 , the measuring coil being connected to measuring coils of other windings to form a measuring bridge. Bifilar winding (1) according to one of the preceding claims, in which the conductive connection (8) is integrated into the bifilar winding (1), in particular in which the conductive connection (8) is provided by a layer jump (12), in particular a layer jump by n- 2 layers, given. Bifilar winding (1) according to any one of the preceding claims, wherein the windings are dimensioned to absorb thermal power loss in the event of a short circuit between turns. Coil with at least one bifilar winding (1) according to one of the preceding claims. Method for producing a bifilar winding (1). claim 9 , In particular a single-tooth winding for a permanently excited electrical synchronous machine, the method comprising: winding the first partial winding (2) comprising N turns; returning a last turn of the first partial winding (2); Forming, through the returned turn, a conductor loop, the conductor loop forming a first turn of the second partial winding (3); and winding the second partial winding (3) along the turns of the first partial winding (2). procedure after claim 11 , wherein the winding of the first partial winding comprises the winding with the final pitch, and wherein the winding of the second partial winding (2) comprises a threading of the second partial winding through the conductor loop. procedure after claim 11 or 12 , wherein returning comprises returning the last turn of the first partial winding N-2 turns.

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