WO2004006358A2 - Current collector systems for multipolar machines - Google Patents

Abstract

The invention concerns current collector systems for multipolar machines (figure 1C) with many brushes (33). The electrical connections to outside electrical power source can be releasable (54, 144, 148).

Description

CURRENT COLLECTOR SYSTEMS FOR MULTIPOLAR MACHINES Note changes on pp.6, 7, 8, 14, 17, 21 and 22. Also note that Figure 1 has been replaced.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] A related U.S. Patent Application is "A Novel Tubular Brush Holder", D. Kuhlmann- Wilsdorf, U.S. Utility Patent Application, Serial Number 10/134,686, Filed April 30, 2002.

Applicant claims priority for this application to the following: "Multipolar Machines - Optimized Homopolar Motor/Generators", D. Kuhlmann-Wilsdorf, Provisional Patent Application, filed July 9, 2002; Serial Number #60/394639.

"Multipolar Machines - Transformer Applications", D. Kuhlmann-Wilsdorf, Provisional Patent Application, filed July 30, 2002; Serial Number 60/399,546.

"Multipolar Machines - Optimized Homopolar Motor/Generators", D. Kuhlmann-Wilsdorf, Patent Application, in preparation

FIELD OF THE INVENTION

[0002] Electrical current collector systems for multipolar machines.

I. GENERAL DESCRIPTION OF THE INVENTION [0003] Multipolar machines are electrical machines that are capable of operating at will as motors, generators and or transformers. Their operation depends on the low-loss current conduction between adjoining axially oriented "zones" in a thin- walled cylindrical rotor that consists of a "set" of N_τ> 1 nested, concentric, mechanically joined but electrically insulated rotors. All rotors are "current channeling", meaning that they are electrically conductive in only one direction (normally parallel to the rotation axis) but are electrically insulating at right angles thereto.

[0004] Typically, (i) the zones are of uniform width, are uniformly distributed about the rotor circumference, and are penetrated by radial magnetic fields. Typically, also, (ii) the sense of the radial direction of said magnetic fields alternates between the zones and current flows to and fro along the zones such that the Lorentz force has the same sense for all zones. [0005] Whether in the motor, generator or transformer mode, the voltage difference between the two ends of a zone of length L and penetrated by radial magnetic flux density B, is V] = LV_R B where V_R is the circumferential speed. Herein the current in multipolar machines is conducted from one zone to the next by means of electrical brushes at opposite ends of the zones. Those brushes run on parallel slip rings, on each end of the zones, one for each of the Nj > 1 individual concentric rotors in the set. According to the outlined geometry, then, an Nj = 3 rotor set will have Nr = 3 slip rings at each end of the zones, and on each slip ring, there will be a plurality of essentially equipotential pairs of neighboring brushes, or "brush pairs" for short, that lead the current from one zone to the next with low electrical resistance. However, in the case of all similar zones, neighboring brush pairs on the same slip ring will be electrically separated by two zones and thus will have a potential difference of 2Vι. Moreover, if there are No zones distributed about the rotor circumference and if the brushes are connected sequentially from the last zone on rotor, say, n, to the first zone of rotor n+1, neighboring brushes on the same zone but on neighboring slip rings will be separated by N_D zones, and therefore will have a potential difference of N_DV_J . Depending on the value of N_D, the potential difference of N_D Vi can amount to hundreds are even thousands of Volts. Correspondingly, neighboring brush pairs on the same slip ring need to be electrically insulated from each other to withstand up to a few hundred Volts in large machines, while the electrical insulation between neighboring brush pairs on adjoining slip rings must be able to withstand up to thousands, perhaps even ten thousand volts.

[0006] In addition to the outlined electrical conditions, provision needs to be made to interchangeably connect brushes to the outside with potentially heavy currents, in large machines up to many thousands of amperes. In fact comparatively easy switching between brushes and external terminals or bus bars is a requirement not only to, say, connect and disconnect a multipolar motor to and from power terminals, but in sophisticated machines to perform various functions, e.g. to operate a multipolar machine as a generator with plural secondary circuits, or to temporarily act simultaneously as a machine, a generator and/or a transformer. [0007] The above requirements are in addition to the normal requirements of brush holders that include (i) reliably loading brushes mechanically with a steady predetermined force, (ii) to permit brushes to smoothly advance in the course of brush wear, and (iii) to lead currents to and from brushes. Especially for large multipolar machines, the outlined demands can be very severe on account of the already indicated high currents that require correspondingly stiff current leads even though the brush forces are typically modest, e.g. a pound of force or less, and also on account of the large numbers of brushes needed, namely 2NχNo typically amounting to hundreds and on occasion to thousands. Reliability and ready accessibility of brushes for installation, monitoring, maintenance and replacement is therefore mandatory, and simplicity as well as reasonable cost are at least highly desirable.

[0008] The present invention discloses designs and design features for current collector systems that are integrated into multipolar machines, in brief "current collectors for multipolar machines" comprising electrical brushes and brush holders, that fulfill the indicated varied requirements. While multipolar machines are a special type of homopolar machine, and for these "monolithic" brushes are generally found to be unsatisfactory on account of relatively high friction and joule heat losses, the machine voltage increase on account of No ranging from several to many, relaxes this constraint for multipolar machines. As a result all types of electrical brushes may be employed in multipolar machines, including metal fiber, metal foil, and monolithic brushes. Even so, generally metal fiber brushes are superior and will be used in most of the examples in this patent application.

II. BRIEF DESCRIPTION OF THE DRAWINGS [0009] A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein

Figure 1 A is a schematic cross section of one end of a multipolar machine showing among others its current collector system.

Figures IB and IB show possible modifications of the overall morphology of the current collector system of Figure 1A. Figure 2 is a schematic end-view of one end of a multipolar machine showing a current collector system composed of individual brush holders. Figure 3 is a schematic end view of part of a current collector system composed of brush holder sections. Figures 4 is a detail of Figure 3. Figure 5 shows schematic perspective views of different types of brush pairses that could be used in a current collector system such as shown in Figures 3 and 4. Figure 6 is a schematic perspective view of a brush pair including a wear indicator.

Figure 7 is a perspective view of a slanting cross section of a current collector system as in

Figures 3 and 4 including slanting metal fiber brushes and some refinements. Figure 8 is a top view of an end of a brush holder section as in Figure 3. Figure 9 is an end view of an end of a brush holder section as in Figure 3 that includes conductors for connection to the outside. Figure 10 clarifies a method of lifting brush loading springs off brushes for access to the brushes. Figure 11 is, like Figure 2, a schematic end-view of a current collector system composed of individual brush holders but including some refinements. Figure 12 is a top view of an arrangement as in Figure 11 for the case of a large rotor. Figure 13 shows a module for the construction of a system as in Figures 11 and 12. Figure 14 shows how a current collector system may be assembled from modules. Figure 15 shows different methods for making releasable low-resistance electrical contacts among modules as in Figure 14.

III. DESCRIPTION OF PREFERRED EMBODIMENTS

1) General Principles - Current Paths in Multipolar Machines [0010] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, the present invention will now be described.

[0011] Figure 1 is a schematic cross sectional view through one end of a multipolar machine.

Shown is a rotor set 2 that is composed of three concentric, electrically insulated but mechanically fused rotors, labeled 2(1), 2(2) and 2(3), rigidly rotating with axle 10. Rotor 2 is

"current channeling" as already explained in Section I above. It moves in the gap between two stationary, concentric "magnet tubes", 5 and 6, that establish in the rotor axially extended

"zones" that are penetrated by radial magnet fields whose sense of orientation alternates, again as already indicated in Section I. By means of brushes 27(1), 27(2) and 27(3) sliding on slip rings 34(1), 34(2) and 34(3) on rotor 2(1), 2(2) and 2(3), respectively, and mirror symmetrical brushes and slip rings on the other side of the machine, a current in the rotor is made to pass to and fro along the zones, such that the torque acting on the current has the same sense of rotation for all.

[0012] For example with reference to Figure 1, a current arriving from the right at the left end of zone j in rotor 2(1) that is penetrated by a radially outward oriented magnetic flux B, is picked up by a brush labeled 27(1) sliding on slip ring 34(1) whose foot print is aligned with zone j. From there, via a low-resistance connection, the current is conducted to the neighboring brush on the same slip ring 34(1) but aligned with zone j+1 that is penetrated by a flux B pointing towards axle 10. In zone j+1, the current passes back to the right side, i.e. now traveling in opposite direction and intersected by a radial field of inverted sense so as to suffer a Lorentz force in the same sense of rotation, e.g. anti-clockwise, as in zone j. At the right end of zone j+1 the current is similarly picked up by a brush aligned with zone j+1 and sliding on the mirror symmetrical image of slip ring 34(1) of rotor 2(1) but on the right side. From here the current is passed on to a neighboring brush into zone j+2 that is penetrated by again inverted, i.e. outwards pointing, magnetic flux B, and thus is again subject to an anticlockwise Lorentz force. The pattern is repeated now again on the left side by the current passing from zone j+2 to zone j+3 via the next electrically connected pair of neighboring brushes on slip ring 34(1), and so on. Thus on the left side, current passes through pair-wise electrically connected neighboring brushes (from here on called "brush pairs") sliding on the same slip ring from zone j to j+1, from zone j+2 to zone j+3, and so on, while similarly on the right side the current passes through pair-wise electrically connected neighboring brushes, i.e. through brush pairs on a slip ring on the same rotor from zone j+1 to j+2, from j+3 to j+4 and so on. Thus the current is channeled to flow to and fro in the same rotor and is always subject to a Lorentz force of same sense of rotation, i.e. anti-clockwise in the present example. Inversion of the sense of current direction will correspondingly invert the sense of rotation, i.e. in the present example make it anti-clockwise.

[0013] After all zones in rotor 2(1) have been traversed in the indicated manner, the current is led to rotor 2(2) by means of a low-resistance connection between the last brush on slip ring 34(1) to the first brush on slip ring 34(2) to repeat the pattern until the current may exit the machine via the last brush on slip ring 34(3).

[0014] In fact it is not necessary that a current traverse all zones in a machine in the manner just discussed. Rather, on each current "turn", i.e. each passage along any one zone, a current suffers a Lorentz force and thus contributes an increment to the motor torque when in the machine mode, or contributes the same voltage increment in the generator mode. Therefore by connect-ing the brushes selectively to outside circuits, e.g. passing currents into or out of the machine when acting as a motor, optionally from different sources at different voltages, the torque can be regulated. Similarly the output voltage can be regulated when the multipolar machine is mechanically rotated and acts as a generator, to supply a single or plural outside electrical loads at optionally different voltages. Optionally, also, both actions may occur simultaneously. [0015] The outlined regular progression of currents in, say, a motor, from an outside current source connected to an arbitrarily selected first brush on slip ring 34(1), to a return terminal from any arbitrary brush on slip ring 34(n), and in the extreme case to the last brush on slip ring 34(3) in our example (or in general slip ring 34(Nχ) for a rotor set of Nj concentric rotors) is the most advantageous in most cases, but many other possibilities exist. However, for practical purposes the regular case will be a preferred embodiment and is preferentially considered below. In that case, and in line with the above explanation, firstly, there will be low-resistance pair-wise connections between neighboring brushes, i.e. there will be a succession of brush pairs on the same slip ring, plus similar low-resistance connections between the last brush on, say, slip ring 34(n) to the first brush in slip ring 34(n+l). Secondly, for flexibility of machine use, there should be opportunities for making releasable electrical connections to external current sources or, in the case of a generator, loads. For economy of expression, two neighboring brushes whose foot-prints are aligned with neighboring zones on the same slip ring and which are interconnected to lead current between those neighboring zones, are dubbed a "brush pair", as already introduced above.

2) Overall Morphology of Current Collector Systems and Attachment to Multipolar Machine

[0016] The required multitude of electrical brushes and releasable electrical connections as outlined above poses a problem in terms of current collector systems, especially also because in large machines, currents can range into the thousands of amperes, and may have to pass through many brushes in-series. On account of their potential for very high current densities as well as reliability, metal fiber brushes are the preferred choice and will be assumed to be used in the following, but other brushes, specifically monolithic (i.e. traditional graphitic) brushes as well as metal foil brushes may also be used where appropriate. Thus in Figure IB, the brushes are indicated as being monolithic, while they are shown as metal fiber brushes in Figures 1A and lC.

[0017] In Figure 1A, the brush holder, 33, is sketched as having a simple cylindrical ring shape. This is one among many different possibilities that are meant to be indicated semi- schematically in Figures IB and lC. In each case brush holder 33 (or brush holder sections if the brush holder ring is divided into a plurality of arc-shaped sections) is mechanically attached to the multipolar machine via some electrically insulating structure 25 and/or via electrically insulating structure 154 that is attached to the outer magnet tube 6. Magnet tube 6, in turn, is rigidly fastened, directly or indirectly, to the stationary machine surroundings, such as a base plate, a shell, a foundation (19), or a housing. Structure 154 is optional and brushes and brush holder sections, as indeed the whole current collector system, may be directly mechanically connected to magnet tube 6 or may be solely supported by structure 25. In any case, the goal is to keep brush holders in fixed positions aligned with the various zones of the rotor or rotor set while the multipolar machine is in operation. [0018] Except for the electrically conductive connections between brush pairs (or brush holder pairs to be discussed below), brushes need to be mutually electrically isolated, and even more so parallel slip rings. Therefore, structure 154 and similarly any mechanical attachment of brush holders or brush holder sections to structure 154 or its alternative mechanical connection(s), must be electrically insulating or at the least must be electrically insulated from the brushes. This means also that brush holder 33 as drawn in Figure 1 A must be made of insulating material and, as discussed above, so as not to provide an electrical connection between rotors 2(1), 2(2) and 2(3) outside of the deliberate interconnections between any two brushes on different rotors. Further, slip rings 34(1), 34(2) and 34(3) are optionally provided with electrically insulating separator walls 11(1), 11(2) and 11(3) that prevent accidental contact between brushes on neighboring slip rings as well as accidental electrical contact at the rotor end.

[0019] Figure IB shows a more realistic shape for brush holder 33 that takes into account the stepwise reduced radius of rotors 2(1) to 2(3), that with a simple cylindrically-shaped brush holder 33 would require correspondingly different brush lengths as shown in Figure 1 A. This would be undesirable because brush lengths should normally be determined in accordance with the guidance of brushes in the brush holders and the intended brush wear life. A further improvement in brush holder design is indicated in Figure 1C by means of insulating separator walls 146(1) and 146(2) between the now definitely electrically separated brush holders 33(1), 33(2) and 33(3). Separator wall 146(3) at the machine end is optional, as is separator wall 11(3).

[0020] An alternative to applying brush holders 33 or 33(1) to 33(3) to slip rings on the outer surface of rotor 2, is their application to the inside surface of rotor 2, i.e. of rotors 2(3), 2(2) and 2(1) with reverse order of stepping. However, that placement would make the brushes by far less assessable for visual monitoring, inspection, changes of electrical connections, installation and replacement and does not seem to offer any compensatory advantages. Also possible but less desirable for the same reason is fastening brush holders to a cover or shroud that may cylindrically extend over the machine. On the other hand, mechanical stability may be enhanced if brush holders are independently or additionally supported by some other structure that is rigidly attached to the stationary machine surroundings, e.g. a base plate, a shell or a housing, especially if that structure is made of lengthwise extended members and is configured to permit easy access to brushes for the already enumerated purposes. In preferred embodiments, therefore, the brush holders and brush holder sections, on both sides of the machine, are rigidly connected to the outer magnet tube or a lengthwise structure in extension thereof, and/or they are mechanically supported by means of a structure (25) that favorably may be at least partly composed of struts, rods or other elongated members to permit ready access to brushes and that is mechanically connected to any non-rotating part of the multipolar machine and/or any part of its stationary surroundings. In fact structure 25 may be a part of the housing or shell that supports outer magnet tube 6 as indicated in Figure 1A by broken lines. Also member 154 may be rigidly connected to structure 25 in a manner not shown in Figure 1 A, in lieu of a direct connection to outer magnet tube 6.

[0021] The means of attachment may be selected from a variety of choices, among them making member 154 in the form of a plate of insulating material, i.e. having a shape wherein one dimension is small compared to the other two and providing mechanical means of attachment such as nailing, screwing, riveting, gluing, soldering, dove tailing, making a bayonet closure or other. Alternatively, member 154 may be present only in the form of washers, or else it may be an adhesive tape, or an adhesive of suitable kind, e.g. an epoxy or glue. Or member 154 may be a combination of any of the above including Velcro®. However, in preferred embodiments, brush holders are replaceable and their fastening to the machine should preferably be releasable, e.g. in regard to member 154 consist of dovetailing or bayonet closures.

3) Modules for Constructing Current Collector Systems and Connections to External Circuits [0022] Figure 2 shows a semi-schematic front view of a current collector system attached to insulating member 154 in the form of eight individual "short-circuited brush holders" 31, that have been formed into four brush pairs by means of pair-wise low-resistance electrical connections 29 between them. Here the term "short-circuited brush holder" is used to identify an at least partly metallic brush holder that is designed to establish low-resistance electrical contact between the brush holder and the brush or brushes in it. With metal fiber brushes mounted on metal base plates, such short circuiting may be automatic if the interior of a brush holder is free of insulating surface films. That condition may be achieved, for example, with noble metal plating on the inside surface of the brush holder that is in mechanical contact with the brush in it, especially if also the surface of the metal fiber brush is similarly plated. For large currents such short circuiting may not be sufficient and may need to be enhanced or replaced by a low-friction, low resistance resilient multi-contact metal material of the kind disclosed in "A Novel Tubular Brush Holder", D. Kuhimann-Wilsdorf, U.S. Utility Patent Application, Serial Number 10/134,686, Filed April 30, 2002, Pub. No. 2003/0071536A1 , Pub. Date April 17, 2003. Such material, also referred to as metal "fur", is labeled 170 and is indicated in several of the following figures Except for the indicated low internal resistance between a brush holder and the brush in it, a short-circuited brush holder may be of conventional design, indeed commercial brush holders could perhaps be used. As in Figure 1, the brush holders slide on slip rings on the three rotors in our example of N_T = 3, but that number is just an arbitrary example. Anyway, implied in Figure 2 is a rigid, mutually insulating connection between brush holders 31(1), 31(2) and 31(3) aligned with any one zone, such as in Figure 1C, no matter what may be their particular construction, thereby to form a module for incorporation into a current collection system.

[0023] A more complex design is shown in Figure 3 wherein brush pairs are mechanically rigidly connected to increase the size of a module and concomitantly to decrease the number of modules and thus simplify the construction of a current collector system. Figure 3 may be better understood in conjunction with Figure 4 that shows two units in greater detail, as well as Figure 5 showing various forms of brush pairs that are formed by direct electrically conducting rigid mechanical connection between two brushes. In Figures 3 and on, the electrically conducting, rigid mechanical connection between the two members of a brush pair is labeled 28 and the part that slides on the slip ring is labeled 27. In the figures, 27 is mostly indicated as fibrous, as indeed will commonly be the case. However other types of brushes, in particular metal foil brushes and monolithic brushes could also be used, albeit less effectively.

[0024] Rotor set 2 with its components of rotors 2(1), 2(2) and 2(3) (again choosing the example of Nj = 3 for Figure 3, as is done throughout this patent application), is attached to axle 10 by means of structural part 61 whose particular form is immaterial to the present invention. Not shown in Figure 3 but implied is a rigid mechanical connection of the brush holders to a stationary part of the multipolar machine andVor its static surroundings as already discussed. This patent application places no restrictions on the form, material or particular points of connection of that mechanical connection. These may be adapted to any particular multipolar machine and intended uses. The relevant characteristic of the mechanical connection between a current collector system and a multipolar machine is that it maintains the brush holders in line with their correlated zones at a suitable distance (e.g. between 0.1 and 1") from the correlated slip rings.

[0025] The brushes in Figure 3 and in subsequent figures are depicted as mechanically loaded, i.e. pressed against their respective slip rings, by means of constant force springs 54. This is an optional choice and any other feasible brush loading devices, such as helical springs, will be included in the present disclosure. However, constant force springs are a preferred embodiment of springs 54 because they are proven to be reliable by a wealth of practical experience, are commercially available in a wide range of sizes and spring forces and, unlike helical springs, maintain the brush force constant independent of momentary brush length. [0026] In Figure 3 and subsequent figures, constant force springs 54 are assumed to be attached to lid 144 rotating about hinge 148 with a two position mechanism, i.e. open or closed. Again this is optional and many other possibilities exist. However, an open-closed two- position lid 144 has great advantages foremost among them that it will not move uncontrollably either in the course of any work done on the current collection system such as for installation, monitoring and replacement of brushes, or in response to inertial forces on the machine, e.g. in air craft, on ships depending on waves, and in land vehicles in response to rough terrain. Moreover, brushes are physically in all orientations so that gravity may pull them out of upside- down holders. For this reason, not only are they usefully contained by an open/closed lid but further springs 54 ought to be corrected for the brush weight in accordance with the brush orientation.

[0027] In Figure 3, three similar brush holders for one brush pair each, i.e. for altogether six brushes, are assembled a module in the form of a rigid arc-shaped "brush holder section" of mechanically fused but electrically insulated brush holder units. In addition the brush holder section module comprises one single brush in a short-circuited brush holder at each of its two ends. The ends of this brush holder, as the ends of brush holder sections in general, permit leading currents in other patterns than between neighbor brushes as brush pairs do. In particular they may be used for making electrical connections between the multipolar machine and outside electrical circuits such as power supplies or loads, as may be desired. Further, any two single brushes, whether at the ends of two different brush holder sections or in individual short- circuited brush holders, may be connected, preferably by means of a low-resistance current lead or bus bar, so as to pass current between those two brush holder sections or brushes. [0028] This flexibility of electrical connections among brushes and to external electrical circuits is possible, with the resulting corresponding flexibility in machine use, on account of the already indicated feature that each current "turn" (i.e. current passage through a zone) electrically acts like an independent circuit, i.e. in a motor adding its own torque increment and in a generator acting like an independent battery. As a result, each brush holder section or any single brush holder may accept electrical power from, or deliver electrical power to, a different external current circuit. Correspondingly, a sizeable multipolar machine with a multiplicity of brush holder sections and/or individual short-circuited brush holders, may alternatively or independently act as at least one motor, as at least one generator, and indeed also as at least one transformer, wherein the current from one or more primary power supplies rotates the machine in the motor mode, and electrical power is delivered to one or more external loads at secondary voltages. The machine will act as an electric heater in regard to any excess of external power input over the sum of power delivered to the outside in the form of motor, generator and transformer power. [0029] In accordance with the above explanation, the number of brush holder sections and of individual brush holders in a multipolar machine, and the selection of zones in them in terms of zone widths and radial magnetic flux density penetrating them, determine the number of external power sources and external loads to which a multipolar machine may be connected, and thus determine the alternative and/or simultaneous uses of a multipolar machine. These variables, i.e. the number of brush holders and their arrangement into modules, may thus be chosen at will, within a wide range of values, from an arbitrary number of single short-circuited brush holders, of insulated brush holders for a single brush pair, and of brush holder sections of arbitrary lengths with or without single short-circuited ends, up to a single brush holder section spanning the whole circumference of a particular slip ring. Note herein particular that the nature, geometry and distribution of the zones, once they have been selected, or perhaps have been willfully controlled by the use of electromagnets and/or superconducting magnets with adjustable current input, is the same for all N_T rotors in a rotor set, namely as determined by the magnets in the permanently stationary inner (5) and outer (6) magnet tubes. Note also that the angular rotation speed is necessarily the same for all rotors in the set. Even so, wide latitude exists for routing of currents in a multipolar machine by suitable connections among short- circuited brush holders on any slip ring wherein any one current route is largely independent of all other current routes and any one zone may participate in more than one current route. [0030] In view of the above, the availability of current leads to and from single brushes in short-circuited brush holder sections are of great importance, and in preferred embodiments of the invention, releasable electrical connections to these are favorably provided. Specifically, in preferred embodiments, single short-circuited brushes at the ends of brush holder sections may be provided with one or more receptacles suitable for making releasable electrical connection with one or more external electrical circuits, whether power sources, loads or other. Alternative or additionally, electrical conductors (or "bus bars", labeled 160, 163 and 165) suitable for connection to external circuits and extending to near or beyond the ends of the multipolar machine for easy access from the outside, may be provided, in lieu of or in additions to receptacles, at single brushes as well as at the ends of brush holder sections. Even while the term "bus bars" is used, in multipolar machines with small machine currents, "bus bars" may degenerate into any type of cable in lieu of solid metal pieces, down to floppy leads in machines with small machine currents. Preferably, bus bars (including their form of cables in case of small machine currents) each comprise at least one current connector to facilitate the making and breaking (i.e. the "switching") of releasable electrical connections between the multipolar machine and external electrical circuits. In Figure 3 bus bars or cables extending from short-circuited brush holders, labeled 160, 163 and 165, make electrical connection to slip rings 34(1), 34(2) and 34(3), respectively, as will be further discussed in connection with Figure 8 below. [0031] Additional to the possible variability in regard to brush holder placement and consolidation into modules such as brush holder sections, is the possibility that the magnets in magnet tubes 5 and 6 that generate the zones can be of different sizes and kinds, thereby giving rise to correspondingly zones of different width, and still further that the B values can be changed in the case of superconducting magnets and electromagnets by supplying them with adjustable currents, as already indicated above. Moreover, depending on the use of the machine, the current passing through the brushes in individual brush holders as well as in brush holder sections, can be of quite different amperages, again depending on the choice of magnets in the zones. This may require correspondingly different brushes and suitably adapted brush holders. However, throughout, the brush foot print dimension in sliding direction of brushes should preferably be adjusted to the widths of the correlated zones because any significant deflections from this rule will impair machine efficiency.

[0032] In the present disclosure all of the above forms of variability are recognized, even while for the sake of simplicity they are not included in the figures. Thus while the present application is meant to include all of the above variations and all of their possible combinations, and while the present application requests patent protection for all of them, the descriptions herein concentrate on the basic preferred embodiments wherein the number and distribution of single brushes and brush holder sections will be the same for all N_T rotors, and thus for all N_T slip rings of a multipolar machine, and wherein the width of the zones and thus the brush length in sliding direction, is the same everywhere. The further discussion, then, will concentrate on that choice, i.e. it will be assumed that all zones are similar to each other and also that all single brushes at the ends of brush holder sections will be similar to each other. Even so, the manifold wider choices discussed above are available. [0033] Within the enumerated restrictions on variability in preferred embodiments that are further considered below, then, the number of brushes in any one "brush holder module" may vary between a single brush in a single short-circuited brush holder, a to a brush pair in a separate brush holder, to a brush holder section of just one brush pair plus two short-circuited single brushes at its two ends, and up to more than one hundred brush pairs per brush holder section, as could be the case for a large machine with many brushes per rotor circumference. Also freely chosen may be the brush axis orientation relative to the slip rings. Specifically, brush pairs and single brushes in the brush holder sections of Figure 3 are depicted as sliding with the brush axes inclined against the slip ring normal. That angle may be selected at will, leading or tailing or nor-mal brush axis orientation relative to the slip ring, anywhere between, say, +45° and -45°. Again this angle need not be the same over a whole slip ring, nor indeed even within any one brush holder section since that choice may depend on the width of a zone and the magnetic flux density penetrating it. However, below that variability is also not further considered but is intended to be included and patent protection for it is sought by means of the present patent application.

4) Construction of Brush Pairs, Split Brushes and Short-Circuited Brush Holders

[0034] Figure 5 presents a variety of possible embodiments of brush pairs. Specifically Figure 5 A is a brush pair formed from a block of a monolithic brush material (175). Figure 5B is a brush pair consisting of two similar monolithic brushes made of a monolithic brush material 175, which two brushes are connected by means of a rigid, electrically conductive bar 28. This connection may be achieved by any suitable means, including but not limited to gluing with an electrically conductive adhesive, fastening by means of at least one embedded screw, soldering, brazing, friction welding or other.

[0035] Figure 5C is the same as Figure 5B except that the two monolithic brushes 175 are replaced by metal fiber brush material. The means of assembling such a brush pair may be the same as for the brush pair of Figure 5B, additionally the brush pair of Figure 5C may be formed in the manner indicated in Figure 5D, namely by spooling suitable metal fibers in the indicated pattern and embedding it in some mechanically rigid material to form part 28. Since in Fig.5D the current is conducted between the two brushes of the brush pair via embedded metal fiber sections 18, the embedment material of connector 28 does not have to be electrically conductive and thus could be Plexiglass or any other castable or moldable polymer. If the embedment material of part 28 in Figure 5D is a metal it may be formed by electro-deposition, infiltration in the molten state, vapor deposition or other. Specifically for small brushes connection 28 may favorably be made by electro-deposition and vapor deposition. Moreover, in all cases care must be taken to avoid wicking of the material of 28 into fibrous part 27 since that could interfere with proper metal fiber brush operation and lead to reduced brush wear life. Wicked material of part 28 may be removed from fibrous parts 27 through etching, chemical dissolution by means of solvents and/or electro dissolution.

[0036] The brush pairs depicted in Figures 5D and 5E comprise "metal fur", or more precisely, "low resistance resilient multi-contact metal material" (170) that was already introduced above and morphologically may be a metal velvet as indicated in Figures 5E and 5F, or is a metal fiber brush material wherein the fibers may be less directionally aligned than they are in a velvet or a metal fiber brush, up to random orientations similar to a felt or may be in the form of a textile, i.e. a cloth, a knit or a weave. When lightly pressed against a smooth highly conductive metal surface, e.g. in the interior of well-prepared short-circuited brush holders (31), low-resistance resilient multi-contact material 170 will at low potential differences conduct currents across the interface up to quite high current densities and at low contact resistance. Metal "fur", i.e. resilient multi-contact metal material (170) is a preferred means for establishing a short-circuit between brush pair and brush pair holder. The material is the same utilized in the already mentioned patent application "A Novel Tubular Brush Holder", except that herein it is mechanically fused with part 28 of the brush rather than the holder. "Fur" 170 may be used in the form of sheet to be applied to selected surfaces by means of an adhesive or adhesive tape, or it may protrude from a surface when the fibers are an integral part of the underlying material and have been exposed though etching, superficial melting, exposure to a laser, particle bombardment chemical dissolution e.g. by a solvent or selective chemical attack, or other.

[0037] The purpose of incorporating the metal fur into the brush instead of the holder as in "is "A Novel Tubular Brush Holder" (U.S. Utility Patent Application, Serial Number 10/134,686, Filed April 30, 2002) to reduce matting and/or wearing down the resilient multi-contact material through repeated use in a brush holder, whereas by the present design, any one material 170 will only be used once, namely through the life-time of any particular brush pair.

[0038] While the examples in Figure 5 all pertain to either monolithic or fiber brushes, the use of metal foil brushes is not excluded and these may prove to be superior in some applications. [0039] A further refinement of brush-pair design is illustrated in Figure 6, namely a brush wear indicator, or "tab", (150) that is firmly attached to part 28 of a brush pair so as to project out of the brush holder to be readily visible in course of brush wear monitoring, thereby permitting timely brush replacement when the projecting length of tab 150 has decreased to some predetermined limiting value. For further enhancement of that function, the tab may be colored in two distinctly different vivid colors, e.g. red and yellow as indicated in Figure 6. In that case it will be time to replace the brush when the yellow vanishes from sight. Again, while Figure 6 illustrates a fiber brush this is but an example and monolithic brushes as well as metal foil brushes could be similarly used.

[0040] As in Figures 3 and 4, so also in Figure 6 the brush is depicted as being slanted relative to the slip ring normal. Practical experience with metal fiber brushes suggests that this will be a preferred embodiment with a mild slant in trailing direction, i.e. in the orientation that the friction forces will tend to automatically induce. Albeit, normal orientation may be advantageous especially for multipolar machines that operate reversibly. In case "scarfing", i.e. slanting of the brush axis in the plane normal to sliding direction, may be advantageous. [0041] Figure 7 clarifies some additional features of brush holders and/or brush holder sections. In particular it introduces "split brushes" or "split brush pairs", consisting of a plurality of parallel brushes that are loaded and wear independently of each other but by virtue of being electrically parallel to each other are a safety feature. Namely, if one of a plurality of parallel brushes comprising a split brush or split brush pair should fail, its current share will automatically shift to the one or more remaining components of the split brush or split brush pair. [0042] In the example of Figure 7, the depicted split brush slides on slip ring 34(1) and has two similar components, both labeled 27(1) and 28(1) for their fibrous and low-resistance connecting parts, respectively. They are loaded by similar springs 54 assumed to project from the same two-position lid 144 that is not shown. The two components of the split brush pair of Figure 7 are depicted as each making electrical contact with a smooth low-resistance metal surface 171 via metal furs 170 on opposite sides of the drawing. For brush pairs this is an optional feature that is designed to help transfer the current to a surviving brush in case one of the brushes should fail, but is it a potentially important feature for short-circuited end brushes of brush holder sections as well as for single brushes in short-circuited single brush holders as further discussed below.

5) Current Collector System with Modules of Insulated Brush Holders Except for "End Brushes"

[0043] The two components in Figure 7 are guided in what amounts to one common brush holder, namely insulating brush holder 33(1), but they are mechanically separated from each other by an optional low-friction separator wall 149. Wall 149 may be conductive or insulating, whatever may seem to be more favorable from case to case, since in the normal course of events the two components of the split brush pair are at the same electric potential and in case one of the two component brush should fail, the current will favorably be shared to whatever extent may be possible. Optional separating wall 149 is intended to assist in the smooth independent sliding in the course of wear of the two components.

[0044] On the right side of Figure 7, the split brush pair abuts the wall of insulating brush holder 33(1) that is attached to component 154 by means of which it is fastened by any suitable means to outer magnet tube 6 (not shown in Figure 7) or an element of the multipolar machine that may be in line with magnet tube 6 such as a cooling ring. Alternatively, in lieu of part 154, brush holder wall 33(1) may be mechanically connected to structure 25 or any other non- rotating part of the multipolar machine or its surroundings, in line with the previous discussion.

[0045] On their left, the two parts of the split brush of Figure 7 are electrically insulated from the neighboring brushes sliding on slip ring 34(2) (barely indicated in Figure 7) by insulating separator wall 146(1) that is rigidly attached to the brush holders. Similarly on their side slip rings 34(1) and 34(2) are separated by separator wall 11(1) that projects out from the joint between those slip rings as indicated. Together separator walls 11(1) and 146(1) extending radially in opposite directions and leaving only a modest gap between them, effectively seal off brushes 27(1) from brushes 27(2) with their potentially large voltage difference.

[0046] Figure 8 is a top view of part of a brush holder section with split brushes of the kind shown in Figure 7, including the end of the brush holder section. Figure 8 further clarifies the construction of brush holder sections, and in particular clarifies the construction of their short- circuited ends with optionally attached bus bars or cables that physically extend at least to near the end of the multipolar machine for the purpose of making releasable electrical connections to at least one external current circuit or at least one electrical power source. In Figure 8 the bus bar for connection to the outside is labeled 160 because it is specifically connected to slip ring 34(1), whereas similar conductors, whether rigid bus bars or cables, that are connected to slip rings 34(2) and 34(3) are labeled 163 and 165, respectively, as in the example of Figure 3.

[0047] In Figure 8, the top left brush box is shown with lid 144 closed, whereas lids 144 are assumed to be in open position in the other three brush holders and therefore are not shown, i.e. at the brush holder for a split brush pair at left bottom, and for two split single end brushes in the other two holders at right. Lid 144 is envisaged to be smaller than the opening that guides the two split brushes mainly in order to provide space for tab 150 (compare Figure 6). In order to avoid complications of radially changing perspectives in Figure 8, the cross sections of brush parts 28, like those of all of the other brushes in the drawing, are shown as if they were oriented normal to the clip rings or were situated at the very top of the holders.

[0048] With closed lid 144, in the top left brush holder, springs 54 that are attached to the lid are shown in outline, but they are not shown in the other brush holders whose lids are assumed to be in the open position as already stated. Further, wear indicator tabs 150 are seen to extend through the gap between the wall of the brush holder cavity and lid 144. Also, optional metal "fur", i.e. resilient multi-contact metal material, and metallic lining are not assumed to be present in the brush holders for brush pairs, but they are included for the split single brushes at the short-circuited brush holder section end at right in order to make electric connection with bus bar 160. End brushes are single and therefore have less than half the length of brush pairs in sliding direction because brush pairs include space for the gap between the two brushes on either side, as seen in Figure 5.

[0049] In order to make electrical connections to the outside, the single brush holders at the brush holder section ends are made of metal and are short-circuited in the already defined sense, but those sliding on different slip rings are electrically insulated from each other by means of insulating separator walls 146. In order to clearly delineate the insulating brush holders of brush pairs at left, from the short-circuited brush holders for single brushes at brush holder section ends, non-conducting material is shown by means of a simple diagonal shading at left and the metal is shown by cross hatching in Figure 8 at right. The boundary between these two materials is indicated as a broken line labeled 168. Conveniently the non-conducting material may be joined to the metal by means of an adhesive, by soldering or brazing, or by any suitable mechanical means.

[0050] As shown, conductor 160 projects out from the single, short-circuited end brush holder whose brush is sliding on slip ring 34(1) in accordance with Figure 7. The coπesponding conductors 163 and 165 are not shown in order not to unnecessarily confuse the drawing. A possible aπangement is shown in the end-view of a brush holder section end in Figure 9. Herein, for simplicity it is assumed that the brush holder sections are shaped as simple cylindrical arcs as in Figure 1A, rather than being stepped in order to follow the contour of the slip rings as in Figures IB and 1C

[0051] A holder for a brush pair wherein the brush loading spring or springs 54 extend from a lid 144, as in Figures 3, 4 and 8, poses the problem that on opening lid 144 for access to the brush pair, the spring(s) will extend to full length. That will awkwardly obstruct working space and makes spring(s) 54 vulnerable to accidental damage, besides the difficulty of getting spring(s) 54 back into position for resumption of brush operation. According to the present invention, this problem is solved by means of a "lifter" 176 in the form of a slender rod that, depending on the size of spring 56, resembles a knitting or sewing needle and that at its upper end carries a simple handle which in Figure 10 is oval-shaped. At its lower end, lifter 176 is supplied with a loop or hook that can be attached to spring 56 so that spring 56 can be coiled up by pulling on the loop or hook in the direction towards the handle of the lifter.

[0052] Further, near its opposite end at spring 54, a short, small "catch" 177 is hinged to lifter 176 that flares away from the stem of lifter 176 by spring-loading or elastic force, as indicated in Figure 10. On first installation or an installation of a fresh brush, the lower end of lifter 176 with catch 177 and loop for connecting to spring 54 will be threaded through a hole 178 in lid 144 and the loop or hook is attached to the coil of the spring that will be in its highest position near lid 144 but still such that catch 177 is inside of the brush holder box. [0053] In operation, with closed lid 144, lifter 176 and catch 177 do not interfere with brush loading and brush operation, except for the (typically negligible) weight of the lifter being added to or subtracted from the brush force, in the 12 o'clock and 6 o'clock positions, respectively. When the brush has worn down or shall be removed for any other reason, lifter 177 will be pulled up through hole 178 until catch 177 has passed through hole 178, whereupon is will flare out and thereby lock lifter 176 in its upper position with spring 54 fully coiled. This then permits opening of lid 144 and if desired to replace the brush. In order to re-activate springs 54, catch 177 will be threaded back through hole 178 while compressing it by means of mild finger pressure.

6) Cuπent Collector System with Individual Short-Circuited Brush Holders

[0054] Current collectors with mechanically fused brush pairs in brush holders that are adapted to brush pairs as in Figures 3, 4, 7 and 8, differ from current collectors utilizing individual brushes in individual short-circuited brush holders. The principle is clarified in Figure 11 that is an elaboration of Figure 2. Herein the unspecified electrical connections 29 of Figure 2 are replaced by rigid metallic connections 28 as indicated in Figure 11. These play the same role for neighboring brush holders as connections 28 play for individual brushes in Figure 5. Thus two neighboring short-circuited brush holders 31 connected by rigid metal members 28 are "brush holder pairs" that operate like ordinary brush pairs in their own right. The safety feature of split brushes is also adaptable to them, namely as parallel brushes sliding in each brush holder much as already explained in connection with Figure 7 for the case of insulating brush holders. This similarity is particularly close, if brush "furs" 170 and conductive surfaces 171 are used as envisaged in Figure 7, but other embodiments are also possible, e.g. as in Figures 5E and 5F with an almost unlimited range of obvious modifications, for all of which the present application seeks present protection.

[0055] One advantage of using individual short-circuited brush holders and forming them into brush holder pairs by means of electrical connections as desired, rather than using insulated brush holders for brush pairs as discussed before, is that every short-circuited individual holder can be used like an end brush in a brush holder section for brush pairs and thus is capable of connection to outside cuπent sources or loads. This will provide great additional flexibility in machine use. Another advantage of the use of individual short-circuited brush holders is that commercially developed brush holder designs may be employed that are already well proven and rugged. Additionally, the individual brush holders permit ready adaptation to another safety feature, namely the in-series connection of adjoining pseudo-brush pairs via dielectrics that are programmed for electric break down whenever some specified voltage across them is exceeded (180). If such dielectric layers 180 are interposed between adjoining brush pairs, they will cause the current to short-circuit about possibly malfunctioning brushes on the other side of the machine that will cause a voltage difference in excess of the expected 2Vj. discussed in section I. A suitable dielectric would be an anodizing film between adjoining aluminum blocks. More reliable may well be electronic devices although for large currents, as used in large machines, these might be too bulky to fit the available space between the brush holders. Layers of suitable granulated dielectrics to serve the intended purpose might also be identified. Anyway, independent of what dielectric or device may eventually be used for this safety device, in Figure 11 the dielectrics between brush pairs are indicated as radially oriented strips labeled 180 (1), 180(2) and 180(3), depending on whether they are exposed to voltages on slip ring 34(1), 34(2) or 34(3). [0056] In Figure 11, the mechanical attachment of brush holders 31 to member 154 is visualized as being done by means of dove tails 181, but any other means of attachment that have already been enumerated above, are intended to be covered also. These include also the use of a structure composed of slender members such as rods and struts to permit ready access to brushes and brush holders, and the mechanical connection of such a structure to any non- rotating part of the multipolar machine and/or its surroundings.

[0057] Figure 12, comparable to Figure 8 further clarifies the assembly of current collector systems for multipolar machines with individual brush holders by means of a plan view in the style of Figure 8, wherein the mild reduction of slip ring circumference from 34(1) to 34(3), and in general from 34(1) to 34(Nτ), and the resulting changes of perspective from brush to brush are neglected, i.e. the drawing assumes a large rotor with many zones. Herein note dovetails 181 for attaching modules of, in this case, three rigidly connected but mutually electrically insulated brush holders 31 as shown in Figure 13, to member 154. Again here, too, all possible modes of attachment are intended to be covered and patent protection for these is sought. [0058] In Figures 12 and 13 it is assumed that the electrical joining between neighboring short-circuited brush holders with electrically conductive members 29 occurs through metal "fur" 170, and that low contact resistance between brush holders and dielectrics 180 sandwiched between metal is similarly achieved. The particular arrangement drawn in Figure 12 would be impractical, however, because it does not provide mechanical support for the weight of conductors 29 and of the metal/dielectric/metal sandwiches (180). If this such support takes the form of additional dovetails, for example, or of rods 185 as indicated in the middle of Figure 12, any even minor misalignments could lead to highly unwanted significant contact resistances in spite of the elastic resiliency of multi-contact metal material 170 between the modules. Figure 14 offers the solution that, in alternating order, short-circuited brush holders 31 be integrated with the equivalent of members 29, and dielectric layer sandwiches 180. Thereby one half of the interfaces is eliminated and the mechamcal support of all parts is possible by no more mechanical attachments to member 154, e.g. dovetails 181, and/or member 25 than would be needed for all units of the type in Figure 13.

[0058] Figure 14 also indicates possible sites for attachment for bus bars 160, 163 and 163 for connection to outside cuπent sources, in fact to each of the short-circuited brush holders which in many cases may be more than needed or desired but would provide unique flexibility of multipolar machine operation. Should these bus bars cause the weight of the current collector system to become too large for safe support by member 154 alone, support via structure 25 may become mandatory. In any case, care must be taken to control mechanical vibrations as much as possible because these will lead to extra electrical brush resistance and wear. However, with the rotor being the only moving part, and this never moving very fast on account of the maximum sliding velocity of electrical brushes, and the rotor typically having low weight relative to the rest of the machine and being very well balanced, multipolar machines are expected to be exceptionally quiet, acoustically, mechanically and electrically.

[0059] A weakness of the design of Figure 14 is the envisaged conduction of the machine cuπent across the interfaces between the members of the brush pairs, i.e. across adjoining parts of low resistance connections 29. In prefeπed embodiments, the mechanical stability of these interfaces is enhanced through the provision of matching surface profiling as illustrated in Figures 15 A, B and C. The contact resistance of such profiled interfaces is liable to be lower than of planar interfaces as envisaged in Figure 14, and it may be reduced by means noble metal plating, as well as "fur" 170, as in Figure 15C. Alternatively or additionally it may be further reduced through applied mechanical pressure, e.g. by means of elastic spring pressure, e.g. a spring clip as in Figure 15 A, or by applied mechanical force, e.g. by means of a screw bolt as in Figure 15C.

[0060] The advantage of using individual short-circuited brush holders as in Figure 15, in lieu of brush holders made for brush pairs or insulated brush holder sections with short-circuited ends, is the opportunity to use each holder for switching to outside circuits as may be desired and changed over time. For example, the same short-circuited brush holders may be used pair- wise as in Figure 15 A to C, or may be used singly for switching by replacing one of the holders in the pair by a bus bar (e.g. 160 in case of connection to slip ring 34(1)) Albeit, the designs of Figures 15 A, B and C would need appropriate modifications for accommodating bus bars for N_T > 1. Modules with sandwiched break-down dielectrics 180 may be similarly incorporated into cuπent collector modules as shown in Figure 15D.

7) Current Collector System Integrating All Approaches [0061] On balance, the lower expected cost and simplicity of insulated brush holders for brush pairs in combination with single short-circuited brush holders where connections to exterior circuits are planned, is liable to overbalance the possible advantage of short-circuited single brush holders everywhere. Also, although electrical break down dielectrics (180) have been prominently included in the present discussion, practical experience is expected to prove them to be an unnecessary complication.

[0062] In summary:

Three current collector systems have been disclosed in accordance with the present invention, i.e. disregarding for the moment dielectrics with programmed electric breakdown voltages 1) Cuπent collector systems composed of insulated brush holder sections with short-circuited end brushes for making electrical connection to external circuits (Figures 3, 5 and 8),

2) Cuπent collector systems composed of all single-brush/split brush short-circuited brush holders for combination into brush holder pairs or connection to external circuits as desired (Figures 2 and 11 to 15), 3) Cuπent collector systems that combine, as considered to be optimal, (i) individual insulated brush holders for brush pairs, (ii) brush holder sections with or without short-circuited end- brushes, and (iii) single short-circuited brush holders.

All three of these options have advantages and drawbacks. All appear to be functional, readily producible at reasonable cost (with short-circuited brush holders presumably the most expensive per brush), easily assembled, reliable, and to offer easy access to brushes for installation, monitoring and replacement. Further all are expected to be easily installed especially if dovetailing is employed. Albeit, dovetails will need safety catches to protect brush holders from loosening through machine vibrations, external accelerations, e.g. through waves or shock, and simply under the influence of gravity.

Claims

WHAT IS CLAIMED AS NEW AND DESIRED TO BE SECURED BY LETTERS PATENT OF THE UNITED STATES IS:

1. A cuπent collector system for a multipolar machine comprising: a multiplicity of electrical brushes; a multiplicity of electrical brush holders; and a rigid, mechanical connection between at least one of said electrical brush holders and said multipolar machine.

2. A cuπent collector system according to claim 1 one wherein said mechanical connection between at least one of said electrical brush holders and said multipolar machine is releasable.

3. A cuπent collector system according to claims 1 and 2 wherein said mechanical connection is to an outer magnet tube of said multipolar machine.

4. A cuπent collector system according to claims 1 and 2 wherein said mechanical connection is to an element of said multipolar machine that is in line with an outer magnet tube , such as a "cooling ring".

5. A cuπent collector system according to claims 1 and 2 wherein said mechanical connection is to at least one part of the stationary suπoundings of said multipolar machine such as a base plate, a shell or a housing.

6. A cuπent collector system according to claims 1 and 2 wherein said mechanical connection comprises elongated members such as struts and rods configured to permit easy access to said brush holders.

7. A cuπent collector system according to claim 6 wherein said structure comprising elongated members such as struts and rods is mechanically connected to at least one non- rotating part of a multipolar machine.

8. A cuπent collector system according to claim 6 wherein said structure comprising elongated members such as struts and rods is mechanically connected to at least one part of the stationary suπoundings of said multipolar machine such as a base plate, a shell or a housing.

9. A cuπent collector system according to claim 6 wherein said mechanical connection comprising elongated members such as struts and rods is mechanically connected to both, at least one part of the stationary suπoundings of said multipolar machine such as a base plate, a shell or a housing, and to at least one non-rotating part of a multipolar machine.

10. A cuπent collector system according to claim 1 wherein at least two of said multiplicity of electrical brushes are joined into a brush pair by means of a low-resistance connection between said two electrical brushes.

11. A cuπent collector system according to claim 1 wherein at least one of said brush holders is configured for at least one brush pair.

12. A cuπent collector system according to claims 1 and 2 wherein at least one of said electrical brushes is a metal fiber brush.

13. A cuπent collector system according to claims 1 and 2 wherein at least one of said electrical brushes is a metal foil brush.

14. A cuπent collector system according to claims 1 and 2 wherein at least one of said electrical brushes is a monolithic brush.

15. A cuπent collector system according to claims 1 and 2 wherein said rigid mechanical connection comprises at least one electrical insulator in the form of a plate having one dimension that is small compared to the other two.

16. A cuπent collector system according to claims 1 and 2 wherein said rigid mechanical connection comprises at least one electrically insulating washer.

17. A cuπent collector system according to claim 1 further comprising means of attachment between said at least one brush holder and said rigid mechanical connection selected from gluing, application of an adhesive, an adhesive tape, soldering, screwing, dove tailing, fitting into a slot, a bayonet closure, a magnetic closure, spring action, an elastic clip and Velcro

18. A cuπent collector system according to claim 2 further comprising means of attachment between said at least one brush holder and said rigid mechanical connection selected from screwing, dove tailing, fitting into a slot, a bayonet closure, a magnetic closure, spring action, an elastic clip and Velcro.

19. A cuπent collector system according to claim 1 wherein at least two of said brush holders are separated by at least one insulating separator wall.

20. A cuπent collector system according to claims 1, 10 and 11 wherein a least one of said brush holders is short-circuited by means of a low-resistance electrical contact between said at least one brush holder and at least one brush in it.

21. A cuπent collector system according to claim 1 wherein a plurality of said multiplicity of brush holders is configured into at least one brush holder section.

22. A cuπent collector system according to claim 21 wherein said at least one brush holder section comprises a brush holder for a single brush at each end.

23. A cuπent collector system according to claim 1 wherein at least one of said brush holders is configured for making an electrical connection to at least one electrical circuit outside of said multipolar machine.

24. A current collector system according to claim 20 wherein said electrical connection to at least one electric circuit outside of said multipolar machine is releasable.

25. A cuπent collector system according to claims 22 and 23 wherein at least one of said brush holders for a single brush at each end of a brush holder section comprises means for making at least one releasable electrical connection to at least one electrical circuit or power source outside of said multipolar machine.

26. A cuπent collector system according to claim 25 wherein said means for making at least one releasable electrical connection is at least one bus bar or cable that physically extends at least to near the end of said multipolar machine.

27. A cuπent collector system according to claim 10 wherein said at least one brush holder for at least one brush pair comprises at least one hinged lid.

28. A cuπent collector system according to claim 27 wherein said at least one hinged lid has only two stable positions, for example open and shut.

29. A cuπent collector system according to claim 27 wherein at least one brush loading spring extends from said hinged lid.

30. A hinged lid according to claim 29 further comprising at least one lifter for the purpose of retracting a brush loading spring.

31. A cuπent collector according to claim 1 wherein the axis direction of said multiplicity of brushes make angles between +45° and -45° with the normal of the slip ring.

32. A cuπent collector system according to claim 20 wherein at least two of said short-circuited brush holders are formed into a brush holder pair by means of a low- resistance connection between said two short-circuited brush holders.

33. A cuπent collector system according to claim 20 wherein said at least one short- circuited brush holder comprises means for making at least one releasable electrical connection to at least one electrical circuit or power source outside of said multipolar machine.

34. A cuπent collector system according to claim 20 wherein said at least one short- circuited brush holder comprises means for making at least one releasable electrical connection to at least one electrical circuit or power source outside of said multipolar machine.

35. A cuπent collector system according to claim 34 wherein said means for making at least one releasable electrical connection is at least one bus bar or cable that physically extends at least to near the end of said multipolar machine.

36. A cuπent collector system according to claim 1 wherein at least one of said brushes comprises a brush wear indicator tab that projects out of a brush box for monitoring remaining brush life expectancy.

37. A brush wear indicator according to claim 36 that comprises contrasting colors to facilitate monitoring remaining brush life time expectancy.

38. A cuπent collector system according to claim 1 wherein at least one of said brushes comprises a low resistance resilient multi-contact metal material for making a short- circuit between said brush and its brush holder.

39. A current collector system according to claims 1 and 10 wherein at least one of said brush pairs comprises a low-resistance resilient multi-contact metal material for making a short-circuit between said brush pair and its brush holder.

40. A cuπent collector system according to claim 1 wherein at least one of said brushes is a split brush comprising a plurality of similar, parallel, independently loaded brushes.

41. A cuπent collector system according to claim 1 wherein at least one of said brush holders is configured for at least one split brush comprising a plurality of similar, parallel, independently loaded brushes.

42. A cuπent collector system according to claim 1 comprising at least one brush holder configured for at least one split brush and said brush holder further comprising a low- resistance, resilient multi-contact metal material for making a short circuit between said at least one split brush and said at least one brush holder configured for at least one split brush.

43. A cuπent collector system according to claim 1 wherein at least one of said brushes is a split brush pair comprising a plurality of similar, parallel, independently loaded brush pairs.

44. A cuπent collector system according to claim 1 wherein at least one of said brush holders is configured for at least one split brush pair comprising a plurality of similar, parallel, independently loaded brush pairs.

45. A cuπent collector system according to claim 1 comprising at least one brush holder configured for at least one split brush pair and said at least one brush holder further comprising a low-resistance, resilient multi-contact metal material for making a short circuit between said at least one split brush pair and said at least one brush holder configured for at least one split brush pair.

46. A brush holder according to claims 41 and 42 further comprising at least one low- friction wall between at least two components of said at least one split brush.

47. A brush holder according to claims 43 and 44 further comprising at least one low- friction wall between at least two components of said at least one split brush pair.

48. A brush pair according to claim 10 comprising two metal fiber brushes.

49. A brush pair according to claim 10 comprising two metal fiber brushes and a rigid electrically conducting joint between said two metal fiber brushes.

50. A brush pair according to claims 10 wherein said low-resistance connection is through the continuity of the same metal fibers in said two metal fiber brushes.

51. A brush pair according to claim 10 and 50 comprising two metal fiber brushes whose said same metal fibers extend through the space between said two metal fiber brushes

52. A brush pair according to claim 50 and 51 that has been at least partly made by means of spooling at least one long fiber into an elongated ring and cutting said ring into two.

53. A brush pair according to claims 50, 51 and 52 further comprising a rigid joint between said two metal fiber brushes.

54. A brush pair according to 49 and 53 wherein said same fibers in said two metal fiber brushes protrude from said rigid joint between said two metal fiber brushes.

55. A brush pair according to claims 49 and 53 wherein said rigid joint is composed of a matrix material in which a least one continuous fiber extending between said two metal fiber brushes is embedded.

56. A brush pair according to claims 49, 53 and 55 wherein said rigid joint is composed of a metal in which a least one continuous fiber extending between said two metal fiber brushes is embedded

57. A brush pair according to claims 49, 53 and 55 wherein said rigid joint is composed of a non-metal in which a least one continuous fiber extending between said two metal fiber brushes is embedded

58. A brush pair according to claims 49, 53 and 55 wherein said rigid joint is composed of a polymer in which a least one continuous fiber extending between said two metal fiber brushes is embedded

59. A cuπent collector system comprising at least one device, such as a dielectric sandwiched between metals, that is programmed for electric breakdown when a specified voltage across it is exceeded.

60. A cuπent collector system comprising a selection of the following components: a short-circuited brush holder for a single brush, a short-circuited brush holder for a split brush, an insulated brush holder for a brush pair, a brush holder section comprising at least one insulated brush holder for a brush pair and two short-circuited end-brushes and a device programmed for electrical breakdown according to claim 59.

61. A cuπent collector system according to claim 60 wherein at least two of the components are provided with matching surface profiling for the reduction of interfacial electrical resistance between said at least two components.

62. A cuπent collector system according to claim 60 wherein at least two of the components are provided with noble metal plating for the reduction of interfacial electrical resistance between said at least two components.

63. A cuπent collector system according to claim 60 wherein a resilient multi-contact metal material is provided at at least one interface between two components for the reduction of interfacial electrical resistance between said two components.

64. A cuπent collector system according to claim 63 wherein said resilient multi- contact metal material is in the form of sheet.

65. A cuπent collector system according to claim 63 wherein the contacting elements protrude from a surface after removal of some material from said surface.

66. A cuπent collector system according to claim 60 wherein elastic spring pressure such as by means of a metal clip is applied to at least part of the interface between at least two of the components for the reduction of interfacial electrical resistance between the said at least two components.

67. A cuπent collector system according to claim 60 wherein mechanical force such as by means of a screw bolt is applied to at least part of the interface between at least two of the components for the reduction of interfacial electrical resistance between the said at least two components.

68. A current collector system according to claim 60 making a rigid mechanical connection to a multipolar machine by at least one of the following means: gluing, application of an adhesive, an adhesive tape, brazing, soldering, screwing, dove tailing, fitting into a slot, a bayonet closure, a magnetic closure, spring action, an elastic clip and Velcro.

69. A cuπent collector system according to claim 60 wherein at least one of the components comprises at least one bus bar or cable that physically extends at least to near the end of said multipolar machine.

70. A cuπent collector system according to claim 60 wherein at least one of the components comprises at least one electric receptacle for making connection to an external electrical circuit such as a power supply or an electrical load.

71. A cuπent collector system according to claim 60 wherein at least one of the components comprises at least one bus bar or cable that physically extends at least to near the end of said multipolar machine and further comprising at least one electric receptacle for making connection to an external cuπent circuit such as a power supply or an electrical load, wherein said electrical receptacle is attached to said at least one bus bar or electrical cable.

72. A cuπent collector system according to claim 60 wherein at least one of the components is short-circuited by means of resilient multi-contact metal material.

73. A cuπent collector system according to claim 60 wherein at least one of the components is short-circuited by means of resilient multi-contact metal material in the form of sheet.

74. A cuπent collector system according to claim 60 wherein at least one of the components is short-circuited by means of resilient multi-contact metal material that protrudes from a surface.

75. A cuπent collector system according to claim 1 wherein the brush force applied to at least one of said multiplicity of electrical brushes is compensated for the weight of said at least one brush.