DE2242529A1 - ELECTRIC CURRENT SUCTION DEVICE - Google Patents

Description

Patenicmwälie

Dr.-Ing. Wilhelm Reichel Dipl-Ing. Woliccng EeMeI

6 Frcmkmri a. M. 1
Park street 13

7181

GENERAL ELECTRIC COMPANY, Schenectady, N.Y., VStA

Electric current tapping device

The invention relates to an electrical current collection device with first and second electrically conductive parts, which can perform a relative movement to each other and are close to each other for power transmission.

The invention is further directed to an improved electrical current collection device which includes a body made of a metal oxide semiconductor material, in particular to a brush holder device in which the brush or the brush holder consists partially of such a metal oxide semiconductor material, which in the The current path lies between the brush and the commutator segment when the commutator segment is picked up by the brush, the directionally linear resistance properties of the metal-oxide semiconductor material considerably reducing the formation of sparks. . ■■ -

The brushes in rotating machines of the brush type and the like. Are generally made of carbon, which is a relatively is a poor electrical conductor and is reinforced by other materials. The brushes are

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construction position held by brush holders, which are generally in in the form of square or rectangular sleeves, which act as guides for all radial movements of the brush serve that result from vibrations or the eccentricity of the armature. The brush holder can be on an arm or Be attached bracket so that it assumes a fixed position and is spaced from the commutator surface. One Adjustable spring connected to the arm or bracket rests against the top of the brush, around the bottom or floor surface the brush with a desired contact pressure on the commutator segments.

The one in various rotating electrical machines of the brush type, e.g. a universal or all-current motor and DC motor as well as electrical current commutated in devices such as a controllable autotransformer has an inductive component and therefore tends to generate equalizing voltages between the commutator segment and the brush when the two separate, causing sparking to occur. The sparking causes heavy brush wear, a collector rod damage and radio interference among other further disadvantages and can at high Current values lead to flashovers or round fires, which all limit machine performance. It is known to take precautions in rotating machinery to avoid sparking between brush and commutator by using different types of brushes commutating poles and electronic commutator circuits as well as by increasing the number of collector bars or segments, but the sparking is still often too strong.

The invention is therefore based on the object of creating an improved electrical current collecting device as well to provide a brush holder device which is an exceptional causes strong spark suppression between the brushes and the commutator.

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There are some known materials that show nonlinear resistance properties and that are and stress values satisfy the following equation:

In this, V denotes the voltage between two points separated by a body of the material in question, I the current flowing between the two points, C a constant and «an exponent greater than 1. C and α are both functions of the geometry of the body made from the material and its composition, and C is primarily a function of the grain or texture size of the material, whereas et is predominantly a function of grain limitation. Materials such as silicon carbide have non-linear or exponential resistance properties and are used in commercially available silicon carbide semiconductors, but these non-metallic semiconductors typically have an alpha ( a ) exponent that is no more than 6. . >

A new family of semiconductor materials, their alpha values

- "3 2/2 / cm within the current density range of 10 to 10 A higher than 10, it has recently been made of metal oxides, 'with very few applications for this new metal oxide semiconductor material (MOV) were found ^Although: the area. in which the alpha of the MOV materials remains substantially constant through the current density range of 10 "to

2 2
10 A / cm, it is noted, however, that the α values ^{remain high 1} even at higher and lower current values, although a certain deviation from the maximum α values can occur. The MOV material is a polycrystalline ceramic material made from a special metal oxide to which small amounts of one or more other metal oxides are added. As an example, zinc oxide is mentioned as the predominant metal oxide, to which small amounts of bismuth oxide are added. As another

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Examples of additives come aluminum oxide, iron oxide, Magnesium oxide and calcium oxide in question. The predominant metal oxide is sintered with the additional oxide (s) to form a sintered ceramic metal oxide body. Because the MOV material is manufactured as a ceramic powder, it can come in many different forms, varying from one another Size to be pressed. The properties of the MOV material are, as it is polycrystalline, due to the grain (crystal) size, the grain composition, grain boundary composition and grain boundary thickness are predetermined, all of these Sizes in the ceramic manufacturing process can be controlled or influenced.

The non-linear resistance ratio of the MOV material is such that the resistance is very high at very low current values in the microampere range (up to about 10,000 Mi2), while in a non-linear manner it drops to an extremely low value (tenths of an ohm) at high current values. falls off. The resistance is not linear even with increasing values of alpha. These non-linear resistance characteristics result in voltage-current characteristics in which the voltage is effectively limited, the voltage limitation or constriction being more pronounced at higher values of the α-exponent, as shown in FIG. The voltage-current characteristics of the MOV material are accordingly similar to those of the Zener diode with the additional property that it is symmetrically bidirectional and extends over more current decades. The "breakdown mechanism" of the MOV material is not yet fully understood, but it is very different from the "avalanche mechanism" of the Zener diodes. A possible theoretical explanation of its mode of operation is the space charge limited current. The "breakdown" voltage of a MOV device is determined by the particular composition of the MOV material and the thickness to which it is compressed in the manufacturing process. The MOV material is subject to conductivity changes at the grain boundaries which lead to the benefit of the "mass phenomenon" which is related to

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the construction one size for certain applications; > Flexibility made possible by simply having changed the dimensions of the body of the MÖV material. I.e. » the current is conducted through its one surface of the MOV body without closely spaced electrodes Dimensions. The mass phenomenon of MOV material leaves one too significantly higher energy consumption compared to contact devices to. Thus, since a MOV device can be made to have virtually any desired thickness, it can be made operate at much higher voltages than zener diode contactors, ranging from a few volts to to several, kilovolts. The stress changes in a silicon carbide semiconductor device are much larger than on a MOV device for a given change in current, and the silicon carbide semiconductor thus has a much smaller working voltage range, whereby its possible applications are limited. * The thermal conductivity of the MOV material is quite high (about half that of aluminum), which makes it suitable for is suitable for significantly higher loads than silicon carbide, and it also has a negligible switching time, in that its response time is in the sub-nanosecond range. Finally, the MQV material and the devices made from it can be precisely machined, soldered and used very low voltages can be operated. These are all properties that are found in silicon carbide with a larger grain structure not found. ,

¹ I.

Accordingly, a body made of a metal oxide semiconductor material should also be provided in the current path between the brush and the commutator segment of a rotating electrical machine in order, if these parts separate,! to achieve the increased spark suppression. ^!

At least part of the brush should be made of metal oxide semiconductor material be formed. ι

I I

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Furthermore, at least a part of the brush holder should be made of metal oxide semiconductor material getting produced,

The above object is achieved according to the invention with an electrical current collection device of the type specified at the outset by a body of metal oxide semiconductor material which is switched into the current path between the first and second parts is to improve the current transfer or commutation of the current.

The invention therefore provides an improved brush holder device created in which a body made of a metal oxide semiconductor material with an o-exponent of more than 10 is trapped in the current path between the brush and a segment of the commutator when they separate. The non-linear resistance characteristic of the metal oxide semiconductor material limits the build-up of stress in the area of the separating segment and the brush, thereby creating a superior one during the operation of the rotating machine Spark suppression. The body made of the metal oxide semiconductor material can be embedded in the brush, and although along their front and / or rear edges, as is the case with an exemplary embodiment of the invention is. Furthermore, this material can also be built into the brush holder, either in the entire holder or only in its lower part, which rests on the commutator segments, in order to thereby transfer the current between the brush and to favor the commutator segments with reduced spark formation.

The invention will now be described in detail with reference to the accompanying drawings, all of which are taken from the description and the details or features emerging from the figures can contribute to the solution of the problem within the meaning of the invention and were included in the application with the intention of being patented. Show it:

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Fig. 1 is a graph of the non-linear resistance and the stress limiting property of the MOV material at different values of the exponent ο in terms of volts and amperes recorded on a logarithmic scale;

Fig. 2 is a side view of a brush holder device according to the invention, partially in section, in which the Brush is provided with the MOV material along its front and rear edges;

Fig. 3 a. Side view of a brush holder device, partly in section, the body made of MOV material between the brush holder and the brush along the front and rear edges are j

Fig. 4 is a side view of an embodiment, partially in section, in which the entire brush holder is made of MOV material j

Fig. 5 is a partially sectioned side view of an embodiment in which the lower part of the brush holder is made from the MOV material and

Fig. 6 is a partially sectioned side view of a variant in which a body made of MOV material along the rear edge of the brush holder is attached.

The voltage and voltage shown in Fig. 1 of the drawings Amperage values illustrate the nonlinear, or exponential, resistive property that the MOV material exhibits, in particular the increasing non-linearity and the amplified Voltage limitation that occurs with increased values of the exponent alpha (α) is reached. The volt abscissa relates to the voltage drop between the brush and the commutator segment, and the current ordinate refers to the current or current density. The application of straight-line scales in the diagram would

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- 8 - ■ ..:. ■■

sloping slopes (decreasing resistance values) show increasing currents, but these curves can easily be changed by selecting the appropriate scales, and for this reason logarithmic hate rods have been chosen, to accommodate a family of lines, each of which is substantially rectilinear within the indicated current range runs. It can be seen from the recordings of FIG. 1 that the resistance provided by the MOV material is at low current values is quite high and increases with increasing current values in a non-linear exponential course becomes smaller, and that this unlinearity fit with larger Values of the exponent α becomes larger. An extension of the records for lower and higher current values would become obvious show correspondingly much higher and lower resistances, and such Masdiinen can easily temporarily reach such values during operation. The "leakage or creep" current through the MOV material is compared negligible to the normal machine working current during normal operating conditions.

Reference is now made to FIG. This shows an improved brush holder device which is designed in accordance with the invention and in which the MOV material is installed at selected locations on the brush. The brush, which is indicated as a whole by the reference number 10, can consist of a conventional carbon brush, the front and rear edge parts of which, however, are made of the MOV material described above. As shown, the MOV parts 11, 12 may have a rectangular shape. This is just one example of the many possible shapes for such MOV parts. The MOV parts or bodies 11 and 12 are bonded or glued to the main body of the brush 10 in a suitable manner such that the entire brush body takes on the usual generally rectangular shape of such brushes. The connection can be effected, for example, by soldering at low temperature or by pressing, in both cases a metallized surface being provided on the MOV material. the

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_ 9 -

metallized surface can be achieved, for example, by melting a thin glass layer and silver particles on the MOV surface can be achieved. In general, an ohmic contact is made. turns to take advantage of the bulk phenomenon operation of the MOV material. The lower pages or Bottom surfaces of the MOV bodies 11 and 12 are slightly curved and align with the bottom surface of the brush 10, which is in contact with the surfaces of the electrically conductive segments 13 of the commutator.

The brush 10 is in contact with the surface by spring force of the commutator (i.e., it runs on its surface), the spring force being generated by a brush spring 14 which rests on the top of the brush 10. The brush 10 is in its desired position relatively ζμ dem Commutator held by means of a brush holder 15, which in turn is held in a fixed position by an arm 16 at a distance from the surface of the commutator. The brush holder 15 is made of a conventional one Construction comprising a rectangular sleeve made of a high tensile strength metal and used as a guide for all radial movements of the brush 10 is used, the vibrations or the eccentricity of the armature or commutator originate. For the sake of simplicity, the flexible copper cable is commonly called brush bridging or compensating piece and is often used to transfer the current from the brush to the brush holder, not shown, but it can be provided if desired. ::

The MOV material is preferably 10 to 30% by volume the brush 10, although it is found that, depending on the special applications, smaller and larger amounts of this MOV material are also used in the context of the invention can be. The special choice of the percentage of MOV-f Material depends on the optimal selection of the number of collector bars or segments, which is based on the result of the invention and the corresponding need for a larger one

^v 30 8813/0268

Energy consumption in the MOV material can be reduced « In the event that the machine only moves in one direction circulates, it may be sufficient to provide the MOV material only along the rear edge of the brush 10. The MOV footage that is arranged at least at the rear edge of the brush, is therefore in the current path of the brush when it is Separate the brush and the commutator segment first when rotating the commutator. The high thermal conductivity of the MOV material also allows the brushes to run cooler.

The main advantage of the invention is superior suppression the arcs and sparks that are specifically located between the rear edges of the brushes and the commutator segments want to train, or alternatively to enable the construction of a machine which less commutator or collector segments, has a correspondingly higher speed and lower manufacturing costs. These superior suppression is mainly due to the following achieved three extraordinary properties of the MOV material:

1) The resistance characteristics are largely non-linear over a wide range of currents (α > 10) and therefore lead to a high degree of voltage limitation,

2) The response time is negligible and

3) The high thermal conductivity enables rapid dissipation of the heat generated by the commutator brush sparking is caused.

With conventional commutation, when the commutator segment and the brush are initially disconnected, the current cannot separate instantly change, and the inductive voltage

e sLw must increase in order to continue the same

Causing the flow of current, which creates the spark and the possible arcing is caused. However, the use of the body of MOV material limits the stress build-up on the separating one

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Segment and the brush and creates a relatively low resistance current path, the current then decreasing at a rate determined mainly by the LR time constant, the Machine is determined, or until a zero " Electricity is achieved. The resistance of the MOV body increases;. < considerably, while the voltage and mainly the ν current decrease. That is, the body made of MOV material remains in the Current path after the brush and the commutator segment have separated for the first time, due to the arrangement and geometry of that MOV body, and since the current path grows as the segment moves away from under the brush, the voltage drop between the brush and the segment slowly increases and quickly consumes the stored inductive energy, until, as soon as the segment has left the MOV body, the energy has reached the value zero. The amount of MOV material in the brush and in particular the ratio of the bottom area of the MOV material to the bottom area of the entire brush are chosen so that at maximum engine speed no current at the time of separation of the body of MOV material flows from the segment. The commutator-brush sparking is thus essentially eliminated, or at least quite considerably when comparing the brush according to the invention with conventional known brushes.

Fig. 3 shows an embodiment of the invention in which two plates of MOV material 20 and 21 are inserted into the brush holder. These plates are held therein between the inner end faces of the brush holder and the outer front and rear end faces of a conventional carbon brush 10. The MOV bodies 20 and 21 are loaded by a spring 22, independently of the spring loading of the brush 10, which is caused by a spring 14, which rests on the surface of the brush. The bodies 20 and 21 may each assume a substantially rectangular shape, and it may be sufficient, as already mentioned in connection with the embodiment of Fig. 2 has been mentioned, even a single such a body along the rear edge of the citizens

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Steer to be provided when it comes to machines that only rotate in one direction. The advantage of the embodiment according to Fig. 3 is that the separate spring loading of the MOV body and the brush compensate for the differences in the comparative extent of the MOV material and brush material as well as with regard to the thermal expansion and contraction of these materials.

A third embodiment of the invention is shown in FIG. 4 shown in which the entire brush holder 15 is made of the MOV material and a spring 17 is the bottom surface or holding the underside of the brush holder 15 in contact with the rotating commutator with the desired pressure. The brush consists in this special execution example of a conventional design.

Fig. 5 shows a fourth embodiment of the invention, which is very similar to the embodiment shown in Fig. 4, except that the MOV material 15a is only along the bottom portion of the brush holder 15 is arranged, as this is the optimal position for this material to the Improve commutation. The brush holder 15 is also in contact with the rotating commutator, as in Embodiment of Fig. 4 is the case, although it can be seen that only its MOV part 15a in contact with the Commutator stands. The MOV part 15a of the brush holder is secured by any convenient means, for example by gluing, rigidly attached to the main body 15 of the brush holder.

A fifth embodiment of the invention is shown in Fig. 6 in which a conventional carbon brush 10 is used and a body made of the MOV material is attached along the rear end of a conventional brush holder 15 and itself extends beyond its bottom, pool or underside. A generally rectangular body of MOV material 15b can thus be rigidly attached to the inner or outer side of the rear End of the brush holder to be attached, or alternatively a

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form the rear end of the same by removing the neighboring spanned two side walls of the brush holder in a suitable manner. The body made of MOV material can only be along the bottom Be arranged parts of the rear end of the brush holder, and if it forms the rear end of the same, he can also only be provided along the lower part of the brush holder, the upper end part being remote from the commutator is made from conventional brush holder material that forms the other three sides. In the event of a reversible machine, the MOV bodies 15b are arranged along both front and rear edges of the brush holder. The spring 1? causes the bottom of the MOV body 15b, but not the rest of the underside of the brush holder, is placed against the commutator, and the body 15b is thereby spring-loaded independently of the brush 10. In all of the above use cases, the MOV body is for a normal Operating voltage is selected that is just slightly above the expected commutator segment to segment (or brush) voltage drop lies.

From the above description of the five exemplary embodiments of the improved brush holder device it can be seen that that the bodies made of MOV material can take any shape, as required by the special applications, and that they can also be positioned somewhat differently, as shown in the drawings. The criterion is that this body or bodies of MOV material lie in the current path between the brush and a commutator segment occurs when these parts separate. Although only one brush is shown in all of FIGS. 2 to 6, it should be understood it turns out that also a conventional parallel series; separate brushes in a brush holder, especially at Large construction machines, can be accommodated. The brush

and / or, the brush holder and the geometry of these devices may take forms other than those shown, such as those commonly found in smaller electrical Machines, e.g. vacuum cleaners, mixers, and hand tools and the like.

can be used, and "the invention can also be used for non-

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rotating machines can be used, e.g. with a device for changing the tapping point or brush displacement devices with controllable autotransformers. In this latter case, a brush touches a flat one lower side flattened areas of a conductor or several conductors that are wound on a magnetic body, and the brush is moved on an arc of a circle. The invention is thus directed in the broadest sense to an improved electrical current collection device in which two electrical conductive parts move relative to one another and are close to one another, with an electrical Bring power transmission. A body made of the metal oxide semiconductor material is placed in the current path between switched on the two parts and brings an improvement in terms of current transmission and / or an improved commutation of the stream. The invention is also applicable to the general field of electrical power collection, such as they are used, for example, in various types of slip rings, busbar collectors and roller wire pantograph current collectors is used. The invention therefore brings a new freedom in terms of the construction of 'machines Brush design, which facilitates the normal voltage limitation when commutating from rail to rail or rod to rod what enables the realization of machine constructions, the higher operating speeds, an improved Charge current management, a simplified construction and maintenance as well as a greater economic efficiency.

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Claims (12)

Claims Electrical power-take-off device having first and nits electrically conductive parts which are movable relative to one another and densely located, to allow power transmission, characterized by a body · (11, 12; 20, 21; 15 _t 15a; 15b) next to each other from Metal oxide calble conductor material inserted in the current path between the first and second parts (10, 13) to improve the current transmission or commutation of the current. 2. Apparatus according to claim 1 with a spark suppressing brush holder device for rotating electrical machines the Bürstetibaiart and the like., The one spring-loaded A brush and a brush holder which holds the brush in a generally fixed position relative to a rotating one Holds commutator, against which the brush is held with a desired contact pressure, which is due to its spring loading is determined characterized in that the body (11, 12; 20, 21; 15; 15a; 15b) is made of metal oxide semiconductor material is switched on in the current path between the brush (10) and the segment (13) of the commutator when the brush and the commutator segment separate as the commutator rotates. 3. Device according to claim 2,
characterized in that the body of metal oxide semiconductor material forms part of the brush along its rear edge which is in contact with the commutator. 4. Apparatus according to claim 2,
characterized in that the body of metal oxide semiconductor material consists of a first body (12) which forms part of the brush (10) along its rear edge, and a second body (11), 309813/0 268 which forms part of the brush along its front edge which is in contact with the commutator (13). 5. Apparatus according to claim 2,
characterized in that the body of metal oxide semiconductor material has a first body (21) which is spring-loaded independently of the spring loading of the brush (10) and is held between the rear end face of the brush and an adjacent inner end face of the brush holder (15). 6. Apparatus according to claim 5,
characterized in that a second body (20) made of metal oxide semiconductor material is spring-loaded independently of the spring loading of the brush (10) and is held between the front end face of the brush and an adjacent inner end face of the brush holder (15). 7. Apparatus according to claim 2,
characterized in that the brush holder (15) is made from the body of metal oxide semiconductor material and the spring means (17) holds the bottom surface of the brush holder on the commutator with a desired contact pressure. 8. Apparatus according to claim 2,
characterized in that a bottom part (15a) of the brush holder (15) is made of the body of metal oxide semiconductor material and the spring means (17) holds the bottom surface of the brush holder on the commutator with a desired contact pressure. 309813/0268 9. Apparatus according to claim 2,
characterized in that a bottom part (15b) of the brush holder is formed along its rear end from the body of metal oxide semiconductor material and extends beyond the bottom surface of the remaining part of the brush holder (15), and in that the spring means (17) cover the bottom surface of the body (15b) made of metal oxide semiconductor material with a desired contact pressure on the commutator. 10. Apparatus according to claim 2,
characterized in that the body of metal oxide semiconductor material is fixedly attached to an end face of the brush holder along its rear edge and extends beyond the bottom surface of the brush holder and the spring means the bottom surface of the body of metal oxide semiconductor material with a desired contact pressure on the commutator holds. 11. The device according to claim 2,
characterized in that the body of metal oxide semiconductor material bridges the two side walls of the brush holder to form its rear end, that the body of metal oxide semiconductor material extends beyond the bottom surface of the brush holder and the spring means the bottom surface of the body of metal oxide semiconductor material with a desired contact pressure on the commutator. 12. Device according to one or more of the preceding claims, characterized in that that the body of metal oxide semiconductor material has an alpha exponent greater than 10. 309813/0268 Blank page