System and method for controlling current distribution to a brush used in an electric motor

Abstract

A system and method for controlling current distribution to a brush used in an electric motor is disclosed. The method includes controlling distribution of current flow between an external source and the brushes using an arrangement of resistor devices electrically connected to the brushes. The arrangement of resistor devices is configured to control the flow of current distributed to a single brush and / or one or more sets of brushes during operation of the motor.

Description

[0001] Cross-references to related patent applications

[0002] This patent application is related to concurrently filed, co-pending and commonly assigned U.S. patent application Ser. No. 18 / 493,906 (Attorney Docket No. 608596-US-1), entitled “SYSTEM AND METHOD FOR SELECTIVE ACTIVATION AND DEACTIVATION OF ELECTRICAL BRUSHES USED IN DYNAMO ELECTRIC MACHINE FOR CURRENT DENSITY OPTIMIZATION,” the disclosure of which is incorporated herein by reference. Background Art Technical Field

[0003] Embodiments of the present disclosure relate generally to electric motors and, more particularly, to arrangements for deploying resistor devices electrically connected to brushes held on surfaces of slip rings disposed on a rotating shaft of the electric motor for controlling current distribution to individual brushes or groups of brushes.

[0004] Discussion of the field

[0005] An electric motor (such as, for example, a generator) includes a rotor body that may be made of a ferrous metal material, which is rotatably mounted on a shaft via a bearing assembly. A plurality of axially oriented slots extending radially outward from the center of the rotor body are circumferentially arranged around the middle section of the rotor body, and these slots hold a plurality of field windings of coils that may be made of copper or aluminum. These field windings of the coils may include a longitudinally oriented center winding fixed in the slot, and turns of end windings extending from the slot at the axial ends of the rotor body. The shaft of the generator may include a drive end having a coupling for a prime mover (such as, for example, a gas turbine or a steam turbine) that operates to rotate the shaft. The prime mover rotates the shaft to generate a rotating magnetic field in the machine. This induces a three-phase voltage group with the stator windings in the generator stator surrounding the rotor body. The opposite end of the shaft (which may be referred to as the non-drive end) includes a collector ring mounted on or attached to the shaft, which rotates with the shaft when the shaft rotates. The stationary brushes are usually spring loaded and are continuously held on the surface of the slip rings as they rotate with the shaft. Current from an external source can be supplied to the slip rings via the brushes. The current passes from the slip rings internally through the shaft to the field windings of the coils in the rotor body. In this way, the current flowing from the brushes to the slip rings to the field windings of the coils can maintain the rotating electromagnetic field at a fixed polarity.

[0006] In operation, the brushes can be configured to act as a manifold to distribute current from an external source to the slip rings. In such a manifold configuration, the typical number of brushes that can be used for each slip ring can be in the range of, for example, between 10 and 100. Any small difference in resistance in each individual brush path or branch from the external source to the slip ring compared to other branches will affect the distribution of current between all brushes. In general, the resistance in each branch includes multiple resistance components that contribute to the total resistance of the branch. Figure 1 shows these resistance components present between an external source 48, which supplies current to the slip ring 32 via multiple brushes 40 according to a conventional configuration. The main resistance in each branch is the sliding contact between the brush 40 and the slip ring 32, where the contact resistance is depicted as Rc in Figure 1. By its nature, the contact resistance Rc is a very variable resistance. The variability of the contact resistance Rc becomes worse when the brushes are operated at low or high current density and is becoming more common as power plants increase their turn-down capability to operate over a wider load range requiring operation over a larger field current range that is typically outside the current density requirements of the brushes.

[0007] Other resistance components in the electrical path from the external source 48 to each branch of the slip ring 32 that are inherently variable and can affect the current distribution include the resistance of the brush 40 itself and other miscellaneous resistances caused by the electrical connections and unintended electrical paths formed in the path from the external source 48 to the slip ring 32. The resistance of the brush 40 is depicted as Rb in Figure 1, while the miscellaneous resistances are depicted as Rm. The resistance of the brush Rb generally varies inversely with the temperature of the brush during operation and the length of the brush as it wears. The miscellaneous resistance Rm is generally caused by the electrical connections and unintended electrical paths that are formed by the need to mechanically support the brushes during operation of the generator.

[0008] All resistive components present in the branch between the external source 48 and the slip ring 32 can significantly affect the distribution or splitting of the current through the branch, so that some brushes will receive almost zero current while other brushes will receive two to three times the average current value that the brushes are optimized to handle. This uneven distribution of current between the brushes is generally referred to as selectivity, which can cause the brushes to overheat, thereby forming a poor quality film between the brushes and the slip ring (this film is critical to maintaining brush life and minimizing the variability of the contact resistance Rc). These conditions can eventually lead to flashovers, which can cause significant arc damage and melted components, thereby posing a safety risk to nearby operators. Summary of the invention

[0009] A simplified overview of the disclosed subject matter is presented below in order to provide a basic understanding of some aspects of the various embodiments described herein. This overview is not an extensive review of the various embodiments. It is not intended to exclusively identify the key features or essential features of the claimed subject matter set forth in the claims, nor is it intended to be used to help determine the scope of the claimed subject matter. Its sole purpose is to present some concepts of the disclosure in a simplified form for preface, with a more detailed description presented later.

[0010] The solution provided by various embodiments to eliminate the above-mentioned selectivity problem caused by the inherent variability of the resistance in a single brush path or branch from an external source to a collector ring includes providing an arrangement of a resistor device between the external source and the brush to remove the variable resistance between the external source and the brush. In this way, the resistor device can control the flow of current distributed from the external source to a single brush and / or one or more groups of brushes by balancing the resistance changes in each branch. This ensures that each brush can receive a specific current. In one embodiment, the resistor device can be used to control the flow of current from an external source so that each brush in the brush is driven to share an equal amount of current. In passive applications or active applications, the resistor device that can be deployed in any of the various embodiments can be selected from a group consisting of fixed resistors, variable resistors, resistors based on power electronics, and combinations thereof.

[0011] In addition to arrangements using resistors, embodiments may include deploying switches to selectively activate and deactivate the brushes to control the current density of the flow of current provided to the brushes. For example, selective switches in the switch may be opened and closed within a predetermined time period to adjust the average current density of the current flowing through the brushes to within a predetermined current density range. In these embodiments where switches are deployed to adjust the average current density provided to the brushes, the resistor device may then be used to control the amount of current received at each of the brushes to a specific current amount.

[0012] According to one embodiment, a system is provided. The system includes: a slip ring disposed on a rotating shaft of a motor; a plurality of brushes held on a surface of the slip ring when the slip ring rotates with the rotating shaft, wherein the plurality of brushes are configured to transfer current between an external source and the motor via the slip ring; and an arrangement of a plurality of resistor devices electrically connected to the plurality of brushes to control the distribution of the current flowing between the external source and the plurality of brushes, wherein the arrangement of the plurality of resistor devices is configured to control the flow of current distributed to a single brush and / or one or more groups of brushes among the plurality of brushes when the motor is running.

[0013] According to another embodiment, an electric motor is provided. The electric motor includes: a rotatable shaft; a rotor body mounted on the rotatable shaft, the rotor body having a plurality of field windings of a coil, the plurality of field windings of the coil being fixed around the rotor body; at least one slip ring, the at least one slip ring being disposed on the end of the rotatable shaft; a plurality of brushes, the plurality of brushes being held on the surface of the at least one slip ring when the at least one slip ring rotates with the rotatable shaft, wherein the plurality of brushes are configured to pass current between an external source and the field windings of the coil fixed to the rotor body via the at least one slip ring; and an arrangement of a plurality of resistor devices, the arrangement of the plurality of resistor devices being electrically connected to the plurality of brushes to control the distribution of the flow of the current between the external source and the plurality of brushes, wherein the arrangement of the plurality of resistor devices is configured to control the flow of current distributed to a single brush and / or one or more groups of brushes among the plurality of brushes when the electric motor is running.

[0014] According to yet another embodiment, a method for controlling current distribution to a plurality of brushes is provided, the plurality of brushes being held on the surface of a slip ring disposed on a rotating shaft of an electric motor, the plurality of brushes transferring current between an external source and the electric motor. The method comprises: arranging a plurality of resistor devices electrically connected to the plurality of brushes and the external source; and controlling the distribution of the flow of the current between the external source and the plurality of brushes using the plurality of resistor devices, wherein the plurality of resistor devices are configured to control the flow of current distributed to a single brush and / or one or more groups of brushes among the plurality of brushes when the electric motor is running. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0016] FIG1 shows a schematic diagram of the total resistance existing between an external source that supplies current to a slip ring via a plurality of brushes according to the prior art;

[0017] FIG2 shows an isometric view of an electric motor such as a generator according to the prior art;

[0018] FIG3 shows a partial perspective view of a single brush holder rigging assembly mounted on a brush mount or a collector horseshoe mounted on a collector ring of a generator as depicted in FIG2 according to the prior art;

[0019] FIG4 shows a schematic representation of a circuit according to the prior art illustrating the transfer of current between an external source and a plurality of field windings of coils from a rotor body of a generator as depicted in FIG2 via brushes which are continuously held on the surface of a slip ring of a generator as depicted in FIG3 ;

[0020] Figure 5 shows a schematic representation of a circuit according to one embodiment of the invention, illustrating the transfer of current between an external source and a plurality of field windings from a coil of a generator, with an arrangement of resistor means in the form of fixed resistors connected between the external source and the brushes;

[0021] Figure 6 shows a schematic representation of a circuit according to one embodiment of the invention illustrating the transfer of current between an external source and a plurality of field windings from a coil of a generator, with an arrangement of resistor means in the form of a variable resistor connected between the external source and the brushes;

[0022] Figure 7 A schematic representation of a circuit illustrating current transfer between an external source and a plurality of field windings from a coil of a generator is shown having an arrangement of resistor means in the form of power electronics based resistors connected between the external source and the brushes according to an embodiment of the present invention;

[0023] Figure 8 shows a schematic representation of a circuit illustrating current transfer between an external source and a plurality of field windings from a coil of a generator having an arrangement of resistors in which each resistor is electrically connected to a set of brushes according to an embodiment of the present invention;

[0024] Fig. 9 A schematic representation of a circuit with an arrangement of resistors illustrating current transfer between an external source and a plurality of field windings from a coil of a generator is shown, wherein a first set of resistors is placed in a branch leading to the brushes and a second set of resistors is placed between the external source and each set of brushes, according to an embodiment of the present invention;

[0025] Fig.10 A monitoring system for monitoring current around a brush and resistor arrangement according to an embodiment of the present invention is shown. Figure 7 A schematic representation of the circuit depicted in;

[0026] Fig.11 shows a schematic representation of a circuit in which a switch arrangement is operatively coupled to an arrangement of resistor means in the form of fixed resistors placed between the external source and the brushes, illustrating the transfer of current between an external source and a plurality of field windings from a coil of a generator, according to an embodiment of the present invention; and

[0027] Fig.12A schematic representation of a circuit in which a switch arrangement is operably coupled to an arrangement of resistor means in the form of variable resistors placed between the external source and the brushes is shown, illustrating the transfer of current between an external source and a plurality of field windings from a coil of a generator according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Exemplary embodiments of the invention will be described more fully hereinafter with reference to the accompanying drawings, in which some but not all embodiments are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers may refer to like elements throughout.

[0029] The present disclosure relates generally to electric motors, and more particularly to arrangements for deploying a resistor device electrically connected to an external source that delivers current between brushes that are held on the surface of slip rings placed on a rotating shaft of the electric motor. In operation, the resistor device is configured to remove a variable resistance between the source and the brushes. In this regard, the resistor device can control the flow of current distributed to a single brush and / or one or more groups of brushes when the electric motor is running. This ensures that each brush can receive a specific current.

[0030] Although various embodiments are described with respect to generators, it should be understood that these embodiments can be applied to other types of electric motors that utilize slip rings and brushes that can ride on the slip rings during operation of the motor. Examples of other electric motors to which various embodiments can be applied include, but are not limited to, electric motors and alternators.

[0031] Referring to the drawings, FIG2 shows an isometric view of a generator 10 according to the prior art. As shown in FIG2 , the generator 10 includes a rotor body 12, which may be made of a ferrous metal material, rotatably mounted on a shaft 14 via a bearing assembly (not shown). A plurality of axially oriented slots 16 extending radially outward from the center of the rotor body are arranged circumferentially around a middle section of the rotor body 12. The slots are used to hold a plurality of field windings 18 of coils that may be made of copper or aluminum. These plurality of field windings of the coil may include a longitudinally oriented center winding 20 fixed within the slot 16, and turns 22 of end windings extending from the slot 16 at an axial end 24 of the rotor body 12.

[0032] The shaft 14 of the generator 10 may include a drive end 26 having a coupling 28 for a prime mover such as a gas turbine or a steam turbine, which operates to rotate the shaft. The prime mover rotates the shaft and generates a rotating magnetic field in the machine. This induces a three-phase voltage group with the stator winding in the stator of the generator 10 surrounding the rotor body 12. For clarity, neither the stator nor the stator winding is shown. The opposite end of the shaft 14 (which may be referred to as the non-drive end 30) includes a collector ring 32 such as, for example, a slip ring (which rotates with the shaft when the shaft rotates), and a coupling 34, which can be used to connect the generator excitation system in one embodiment or can be used to connect the gear reduction unit in another embodiment. The stationary brush (not shown in FIG. 2) that can be spring-loaded is continuously maintained on the surface of the collector ring 32 when the collector ring 32 rotates with the shaft 14. Current from an external source such as a generator excitation system can be supplied to the collector ring 32 via the brush. The current from the slip rings 32 flows internally through the shaft 14 to the field windings 18 in the rotor body 12. In this way, the current flowing from the brushes to the slip rings 32 to the field windings 18 can maintain the rotating electromagnetic field at a fixed polarity.

[0033] FIG. 3 shows a partial perspective view of a single brush holder rigging assembly 36 mounted on a brush mount or a collector horseshoe 38 mounted on a collector ring 32 of a generator as depicted in FIG. 2 according to the prior art. Although not shown in FIG. 3 , the collector ring 32 rotates with the shaft and rotor body of the generator. For clarity, FIG. 3 shows only one brush holder rigging assembly 36 , but it should be understood that more rigging assemblies may be mounted on the collector horseshoe 38 and distributed at least partially around the collector ring 32 . Each brush holder rigging assembly 36 may include one or more brushes 40 and a corresponding brush holder 42 for the brushes and a stationary support member 44 . For example, FIG. 3 shows that the brush holder rigging assembly 36 may include a pair of brushes 40 located in a brush holder 42 . The brush 40 is typically a piece of graphite-like carbon compound that is able to freely conduct electricity and generally has very low friction so that it does not wear the collector ring 32 . The brush holder 42 holds the brushes contained therein at least in the axial and circumferential directions. In one embodiment, the brush holder 42 may use a brush spring that radially biases the brush in a downward direction to maintain contact with the surface of the slip ring 32. The stationary support member 44 is configured for electrical connection to the current collecting horseshoe 38. In this regard, the stationary support member 44 may be made of or include an electrically conductive material, and have wires for carrying current to or from the brushes. The brush holder rigging assembly 36 may be bolted or threaded to the current collecting horseshoe 38, however it should be understood that other methods of fastening, attachment, etc. may be used. The details of the brush holder rigging assembly 36 are well known and disclosed, for example, in U.S. Patent No. 10,158,206, the disclosure of which is incorporated herein by reference.

[0034] It should be understood that the foregoing description of the brush holder rigging assembly 36 represents only one configuration that may be used to continuously hold the brushes on the surface of the slip ring 32 while operating to cause current to flow between the field winding 18 in the rotor body 12 of the generator 10 and the generator excitation system as the slip ring 32 rotates with the shaft 14, and is not meant to limit the scope of the various embodiments. Those skilled in the art will appreciate that the embodiments described herein may be implemented with other types of brush holder rigging assemblies.

[0035] FIG4 shows a schematic diagram of a circuit 46 according to the prior art, illustrating the transfer of current between an external source 48, such as a generator excitation system, and a plurality of field windings 18 of coils from the rotor body 12 of the generator 10 shown in FIG2 via brushes 40, which are continuously maintained on the surface of a slip ring 32 of the generator as depicted in FIG3. As shown in FIG4, an external source 48, which may be a power source, such as, for example, a direct current (DC) source, may supply DC power to the brushes in the form of current via wires 50. The brushes 40 transfer the current to the slip rings 32, which supply the current to the field windings 18 of the coils. As shown in the figure, one ring 32 having the brush 40 operatively coupled thereto is connected to the positive terminal of the external source 48, while the other ring 32 having the brush 40 is connected to the negative terminal of the external source 48. With this configuration, current can not only be transferred from the brushes 40 and slip rings 32 to the coil's field winding 18 , but current can also be transferred from the coil's field winding 18 to an external source 48 via the slip rings 32 and brushes 40 .

[0036] The schematic diagram of FIG. 4 and the schematic diagrams of other figures disclosed herein only show four brushes 40 for each slip ring 32, which are configured to supply current to the rings via corresponding parallel paths. However, it should be understood that there may be significantly more brushes operatively coupled to the slip rings. For example, each slip ring 32 may have 10 to 100 parallel brush paths.

[0037] As discussed above with respect to FIG. 1 , each of the individual brush paths or branches in the circuit 46 from the external source 48 through the brushes 40 to the contact surfaces between the brushes and the slip rings 32 will have an inherent resistance that may affect the current distribution from the external source to the brushes. For example, each branch will have a contact resistance Rc between the brush 40 and the slip ring 32, a resistance Rb of the brush itself, and miscellaneous resistances Rm generated by electrical connections and unintended electrical paths, all of which together contribute to the total resistance in each branch. If there is a high level of resistance in a branch, the brush 40 in that branch will receive a small amount of current from the external source 48 compared to a brush with a lower level of resistance in the branch. Similarly, if there is a low level of resistance in a branch, the brush 40 in that branch will receive a large amount of current from the external source 48 compared to a brush with a higher level of resistance in the branch. This imbalance in the current received by the brushes 40 due to the inherent resistance in each branch can result in some brushes receiving nearly zero current while other brushes may receive two to three times the average current value that the brushes are optimized to handle. This uneven distribution or selectivity of current between the brushes can cause the brushes to overheat because they receive too much current. In addition, this uneven distribution of current between the brushes can cause a poor quality film to form between the brushes and the slip rings, which is essential for maintaining brush life and resisting significant variability in contact resistance Rc. These effects of selectivity in the brushes 40 that may occur in the configuration depicted in Figure 4 can result in flashovers, which can pose safety and operating risks (e.g., significant arc damage, melting of components, putting nearby operators in danger).

[0038] The various embodiments described herein address the variability of the inherent resistance that occurs in the brush paths or branches from the external source 48 through the brushes 40 to the contact surface between the brushes and the slip rings 32 by deploying an arrangement of resistor devices (such as, for example, balancing resistor devices) that are capable of controlling the resistance in each branch to balance the distribution of current. In this way, the arrangement of the resistors enables the various embodiments to drive a more equal sharing of the current between the brushes 40. Therefore, the arrangement of the resistor devices allows the various embodiments to control the amount of current distributed to a single brush and / or one or more groups of brushes so that the brushes can receive a specific amount of current.

[0039] These arrangements of resistor devices may be implemented in any of a number of different locations. These locations include, but are not limited to, brush holders and brush holder rigging assemblies (e.g., in fixed support members or other components within the brush holder rigging assembly, including wires in the rigging assembly, including pigtails).

[0040] Figure 5A schematic diagram of a circuit 52 having an arrangement 54 of resistor devices 56 connected between the external source and the brushes illustrating current transfer between an external source 48 and a plurality of field windings 18 of a coil is shown according to an embodiment of the present invention. Figure 5 As shown, the resistor device 56 may include a fixed resistor. In one embodiment, the fixed resistor is selected to have a resistance greater than the contact resistance Rc between the brush 40 and the collector ring 32. Making the resistance of the fixed resistor in each branch greater than the contact resistance Rc allows the branch resistance in the branch to be controlled to a resistance value that will overcome the variability of the inherent resistance of each branch. In this regard, the resistor device 56 can drive a more equal sharing of the current supply from the external source 48. Specifically, making the resistance of the fixed resistor in each branch greater than the contact resistance Rc drives a more equal sharing of the current between the brushes 40. As used herein, more equal sharing of current means that the brushes share approximately the same current (e.g., all values ​​are within 10%) compared to unequal sharing (e.g., some of the brushes carry no current, while other brushes carry up to twice the average value or more). It should be understood that there will still be some variation in the branch resistance in the branch, but making the resistance of the fixed resistor greater than the contact resistance Rc is sufficient to drive a more equal sharing of the current between the brushes 40.

[0041] The selection of the resistance of the fixed resistor is understood to be within the scope of those skilled in the art and will depend on factors that may include, but are not limited to, contact resistance Rc, brush resistance Rb, and miscellaneous resistance Rm in the branch, as well as the current supplied by the external source 48. In one embodiment, the resistance of the fixed resistors in each branch may all have the same resistance value. As long as the size of this same resistance value of the fixed resistor is large enough so that any variation in resistance from other sources in the branch (e.g., Rc, Rb, and Rm) is a small percentage, the variation in resistance can be overcome so that the current will be shared more equally.

[0042] Since using fixed resistors with the same resistance value requires using values ​​large enough to overcome resistance variations from other sources in the branch, it is possible to introduce Figure 5 The losses of the slip ring 32 in the circuit 52 of FIG. 5A can be reduced by reducing the slip ring. To avoid introducing slip rings, other types of balancing resistor device configurations can be used. For example, instead of using fixed resistors, variable resistor devices can be deployed.

[0043] Figure 6 A schematic representation of a circuit 58 is shown, illustrating the current transfer between an external source 48 and a plurality of field windings 18 of a coil, with an arrangement 60 of resistor means 62 connected between the external source and the brushes 40 in the form of a variable resistor. In the case of using a variable resistor, Figure 6 The resistance value of the resistor means 62 in the brushes 40 can be adjusted as needed to ensure a more equal sharing of the current between the brushes 40. In one embodiment, the variable resistors can be adjusted to obtain substantially equal resistance values ​​in each branch. As used herein, "substantially equal resistance" refers to resistance values ​​that are within 10% of each other. By having the ability to adjust the variable resistors to obtain substantially equal resistance, Figure 6 The circuit 58 can drive a more consistent current to each individual brush 40.

[0044] In one embodiment, the adjustable Figure 6 The variable resistors in the circuit 58 of FIG. 5A are provided with different resistance values ​​in order to drive a specific amount of current from the external source 48 to each of the brushes 40. Note that the width of the pointer used to depict the variable resistor is associated with the resistance value of the resistor. In general, Figure 6 A variable resistor depicted in FIG. 1 having a pointer covering a larger resistor width indicates a low resistance value, while a smaller resistor width indicates a high resistance value. For example, a variable resistor having a pointer covering substantially the entire width of the resistor indicates zero resistance.

[0045] It should be understood that, in addition to Figure 6 In addition to the variable resistors depicted in , other types of devices can also be used to adjust the resistance in each branch so that the current is shared more equally between the brushes 40. For example, a power electronics-based resistor device can be connected between the external source 48 and the brushes 40 and used to adjust the resistance in each branch to drive the current in the branch, which flows to the corresponding brush to have a specific amount of current. In one embodiment, the power electronics-based resistor device can drive the current sharing so that the current in each brush is substantially equal. In another embodiment, the power electronics-based resistor device can drive a specific amount of current to each brush in the brushes 40. As used herein, a "power electronics-based resistor device" refers to a power electronics device that can act as a solid-state switch that specifies the resistance value in the brush path branch. An illustrative but non-exhaustive list of resistor devices based on power electronic devices includes power diodes, metal oxide semiconductor field effect transistors (MOSFETs), bipolar junction transistors (BJTs), insulated gate bipolar transistors (IGBTs), and thyristors (e.g., silicon controlled rectifiers (SCRs), gate turn-off (GTO) thyristors, and MOS controlled thyristors).

[0046] Figure 7A schematic representation of a circuit 64 with an arrangement of resistor devices 66 in the form of power electronics based resistors 68 connected between the external source and the brushes 40 is shown, illustrating current transfer between an external source 48 and a plurality of field windings 18 of the coil. Figure 6 , the power electronics based resistors 68 are able to fine tune the resistance in each branch to drive equal sharing of current between the brushes and / or drive a specific amount of current to each of the brushes 40. The arrangement 66 of power electronics based resistors 68 has the advantage of reduced losses like variable resistors, but because of their smaller size, they take up less space in a specific implementation.

[0047] Although relative to Figures 5 to 7 The described embodiment relates to an arrangement of resistor means wherein the resistor means in each branch are connected in series with the external source 48 and the brush 40, but it will be appreciated that other arrangements of the resistor means relative to the external source, branches and brushes are possible. For example, Figure 8 A schematic representation of a circuit 70 is shown that illustrates current transfer between an external source 48 and a plurality of field windings 18 of a coil having an arrangement 72 of resistors 56, each of which is electrically connected to a set of brushes 40. Figure 8 As shown, the resistor 56 can be a fixed resistor. In this embodiment, each of the fixed resistors 56 in the arrangement 72 is coupled to a group of brushes 40. Specifically, each of the fixed resistors 56 for a particular group of brushes 40 is connected in series with the external source 48 and the parallel path of the branch leading to the corresponding brush in the group. With this configuration, assuming that the resistance value of the fixed resistor 56 is greater than the value of the contact resistance Rc of each brush in the brush 40 in the corresponding group of brushes, the fixed resistor 56 can control the current flowing from the external source 48 to the brushes in each group. In this regard, the fixed resistor 56 can drive the current from the external source 48 in a manner that promotes equal sharing of the current between the brushes 40 in each group.

[0048] To provide more control over the current supplied to each of the brushes 40 in each set of brushes, other arrangements of fixed resistors 56 connected to the brushes 40 for multiple sets of brushes may be provided in each branch. For example, Fig. 9 A schematic representation of a circuit 74 is shown illustrating the transfer of current between an external source 48 and a plurality of field windings 18 from the coils of a generator, with an additional arrangement 76 of fixed resistors 56 placed in each branch of a brush 40 in a particular set of brushes. In essence, Fig. 9The embodiment depicted in is a stepped approach whereby an arrangement of resistors 72 drives the current from the external source 48 to be shared between the groups of brushes 40, while an additional arrangement of fixed resistors 56 76 is used to control the distribution of the current shared by the multiple groups of brushes 40 to manage how much of the shared current flows to each brush in each group. In this way, the arrangement of resistors 72 provides a primary form of control to drive an equal share of the current flowing to each group, while the additional arrangement of fixed resistors 56 76 provides a secondary, more refined form of control to drive an equal share of the current received by each group between each of the brushes 40 in each group.

[0049] Figure 8 and Fig. 9 The arrangement 72 of fixed resistors 56 connected to multiple groups of brushes 40 including four brushes are shown, however, this configuration represents only one approach and is not intended to be limiting. For example, the arrangement 72 of fixed resistors 56 can be connected to multiple groups of brushes 40 including more or less than four brushes. In addition, instead of connecting the arrangement 72 of fixed resistors 56 to multiple groups of brushes 40, these resistors can be connected to pairs of brushes.

[0050] In addition, it should be noted that Figure 8 and Fig. 9 The arrangement of the resistor means used in these embodiments is shown as a fixed resistor, however, those skilled in the art will appreciate that other types of resistor means may be deployed. For example, Figure 8 and Fig. 9 The fixed resistor 56 in may be replaced with any of the other types of resistors described above, such as, for example but not including, variable resistors and power electronics based resistors.

[0051] Although relative to Figures 5 to 9 The described embodiments relate to arrangements of resistor devices in which all resistor devices in each of these embodiments include resistor devices of the same type, but it should be understood that other arrangements of resistor devices may include combinations of any of the aforementioned resistor devices. That is, the embodiments may have arrangements of different resistor devices, wherein the resistor devices are selected from the group consisting of fixed resistors, variable resistors, power electronics based resistors, and combinations thereof.

[0052] In addition, as mentioned above, each slip ring can have 10 to 100 parallel brush paths. Therefore, it should be understood that Figures 5 to 9 The depiction of the smaller number of paths depicted in the diagram does not represent all the various resistor devices that can be deployed in a typical configuration. In addition, the representation of various pairing levels of resistor devices and resistor devices connected to a single brush or multiple groups of brushes represents only a few possible options and is not intended to be limiting to various embodiments.

[0053] In another embodiment, the use of an arrangement of various resistor devices to control current sharing between brushes may be used as part of a brush collector monitoring system. For example, a brush collector monitoring system having the ability to monitor the wear and temperature of the brushes and the amount of current supplied to the brushes may be configured to monitor the current around the various resistor devices so that the resistance of the resistor devices may be adjusted in a manner that drives current sharing between brushes and / or facilitates a specific amount of current supplied to a single brush.

[0054] Fig.10 A schematic representation of a circuit 78 having a monitoring system 80 is shown that monitors the current around each of the various resistor devices in the circuit based on current measurements obtained from a current sensing device 82. In this embodiment, the current sensing device 82 measures the current around each of the resistor devices, which in one embodiment may include a power electronics-based resistor 68. The current sensing device 82 is preferably located between the external source 48 and the power electronics-based resistor 68, which may include, but is not limited to, a current transformer and a current sensor. In an alternative embodiment, the current sensing device 82 may be located between the power electronics-based resistor 68 and the brush 40. In another embodiment, the current sensing device 82 may be located between the external source 48 and the resistor device and between the resistor and the brush.

[0055] With any of these implementations, the current sensing device 82 can provide electrical measurements around the power electronics-based resistor 68 to the monitoring system 80. The monitoring system 80, which can include a control unit, can monitor the current measurements and automatically adjust the resistance of the power electronics-based resistor 68 based on the measurements to drive current sharing between the brushes 40 and / or to facilitate a specific amount of current being delivered to each of the brushes. In this regard, the control unit of the monitoring system 80 can fine-tune the resistance using each power electronics-based resistor 68 in each branch to obtain a specific brush current at the brush.

[0056] although Fig.10 The embodiments described in the are described with respect to using power electronics based resistors, but it should be understood that other types of adjustable resistor devices may be deployed with the monitoring system to facilitate resistance adjustment of the resistor device. For example, in a comparable monitoring system, a variable adjustable resistor may be used in place of a power electronics based resistor.

[0057] Furthermore, it should be appreciated that the monitoring system 80 may perform additional functions in addition to monitoring current measurements from the current sensing device 82 and adjusting the resistance of the adjustable resistor device to drive and regulate the current received by the brush 40. For example, the control unit of the monitoring system 80 may perform functions including, but not limited to: controlling the supply of current from the external source 48; setting and monitoring protection limits for excessive current measurements using trip devices, alarms, etc.; and monitoring the wear of the brush 40.

[0058] exist Figures 5 to 10 The various embodiments depicted in the drawings are described with respect to using at least one arrangement of resistor devices to drive equal sharing of current between brushes 40 and / or drive a specific amount of current to a single brush or multiple groups of brushes, however, other electrical components may also be used to control the current supplied to the brushes from the external source 48. For example, an arrangement of switches may be electrically connected between the external source 48 and the resistor device. In one embodiment, an arrangement of switches may be used to ensure that an optimal average current density is supplied to the brushes 48. In one case, the switch may be turned on and off to activate or deactivate one or more of a single brush, a pair of brushes, and a group of brushes within a predetermined time period so as to adjust the average current density of the current passing through the activated brushes to within a predetermined current density range. Thus, turning the switch on and off to activate or deactivate the selective brushes ensures that all active brushes will operate at their optimal average current density. This can prevent the brushes 40 from becoming too hot, thereby preventing the brushes from getting more current or even getting hotter so that the increased current and heat cause accelerated wear of the brushes.

[0059] In the case of providing an optimal average current density to the brushes, the arrangement of resistors described herein can complement this aspect by providing further control over the amount of current received at each of the brushes 40. Specifically, the arrangement of resistors can ensure that a specific amount of current is provided to the brushes after the switch is used to ensure that the optimal average current density is supplied to the brushes. That is, the arrangement of the resistor device can drive equal sharing of current between the brushes and / or drive a specific amount of current to a single brush or multiple groups of brushes.

[0060] Fig.11A schematic diagram of a circuit 84 is shown in accordance with one embodiment of the present invention, wherein an arrangement 54 of fixed resistors 56 is operably coupled to an arrangement 86 of switches 88 and brushes 40. In one embodiment, the switches 88 are configured to switch on and off to activate or deactivate the selective brushes, thereby ensuring that all active brushes operate at their optimal average current density. As described above, the arrangement 54 of resistors 56 is configured to remove the variable resistance between the external source 48 and the brushes 40. In this way, the arrangement 54 of resistors 56 can ensure that a specific amount of current is provided to the brushes 40. That is, the arrangement 54 of resistor devices 56 can drive equal sharing of current between the brushes and / or drive a specific amount of current to a single brush or multiple groups of brushes.

[0061] Instead of using Fig.11 Instead of the fixed resistors shown, a variable resistor arrangement can be used. For example, Fig.12 A schematic representation of a circuit 90 is shown in which an arrangement 60 of variable resistor devices 62 is operatively coupled with an arrangement 86 of switches 86 and the brush 40 . Fig.12 The arrangement of switches and resistors depicted in FIG. 1 can be similar to that described with respect to FIG. Fig.11 The described embodiment operates in the same manner.

[0062] Further details of using a switching arrangement to control the supply of current from an external source 48 to the brush 40 are provided in U.S. patent application Ser. No. 18 / 493,906, entitled “SYSTEM AND METHOD FOR SELECTIVE ACTIVATION AND DEACTIVATION OF ELECTRICAL BRUSH USED IN DYNAMO ELECTRIC MACHINE FOR CURRENT DENSITY OPTIMIZATION” (Attorney Docket No. 608596-US-1), the disclosure of which is incorporated herein by reference.

[0063] From the description of the exemplary embodiments presented herein, it is apparent that the present disclosure sets forth an effective solution for evenly distributing drive current to brushes that are operably coupled to slip rings disposed on an electric motor, such as a generator, thereby improving the performance of the electric motor. By evenly distributing drive current to the brushes, various embodiments can eliminate or minimize selectivity issues that may cause overheating of the brushes, formation of a poor quality film between the brushes and the slip rings (which is essential for maintaining brush life and minimizing the variability of the contact resistance Rc). In the case where selectivity issues are avoided, flashovers that may create safety and operational risks (e.g., significant arc damage, melting of components, putting nearby operators at risk) can be avoided.

[0064] The above description of the exemplary embodiments of the present disclosure, including the contents described in the abstract of the specification, is not intended to be exhaustive or to limit the disclosed embodiments to the precise form disclosed. Although specific embodiments and examples are described herein for the purpose of illustration, it can be appreciated by those skilled in the relevant art that various modifications are possible within the scope of these embodiments and examples. For example, parts, components, steps, and aspects from different embodiments may be combined or applied to other embodiments, even if not described in the present disclosure or depicted in the accompanying drawings. Therefore, since certain changes may be made in the above invention without departing from the spirit and scope of the present invention involved herein, it is intended that all the subjects described above shown in the accompanying drawings should be interpreted only as examples illustrating the inventive concept of this article, and should not be understood as limiting the present invention.

[0065] In this regard, although the disclosed subject matter has been described in conjunction with various embodiments and corresponding drawings, it should be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiments to perform the same, similar, alternative or alternative functions of the disclosed subject matter without departing from the disclosed subject matter. Therefore, the disclosed subject matter should not be limited to any single embodiment described herein, but should be interpreted in accordance with the breadth and scope of the appended claims. For example, reference to "one embodiment" of the present invention is not intended to be interpreted as excluding the existence of other embodiments that also include the listed features.

[0066] In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Further, in the following claims, terms such as "first," "second," "third," "upper," "lower," "bottom," "top," and the like, if used, are merely labels and are not intended to impose numerical or positional requirements on their objects. The terms "substantially," "typically," and "approximately" represent conditions within reasonably achievable manufacturing and assembly tolerances relative to ideal desired conditions suitable for achieving the functional purpose of a component or assembly. Further, the limitations in the following claims are not written in a mean-plus-function format and are not intended to be interpreted as such limitations unless and until such claim limitations are explicitly followed by the description of the void function of other structures using the phrase "in a manner of..."

[0067] The above-described content includes examples of systems and methods for illustrating the disclosed subject matter. Of course, it is impossible to describe every combination of parts or modes here. It can be recognized by those of ordinary skill in the art that many other combinations and arrangements of the claimed subject matter are possible. In addition, with respect to the term "including" or "comprising" adopted in the specific embodiments or claims, it is intended to be inclusive in a manner similar to the term "comprising", as "comprising" is translated when used as a transitional word in the claims. That is, unless explicitly stated to the contrary, the embodiment of "including", "comprising" or "having" an element or multiple elements with a specific attribute may include other such elements that do not have the attribute. In addition, the articles "one" and "a kind of" used in this specification and the accompanying drawings should generally be interpreted as meaning "one or more", unless otherwise indicated or clear from the context for the singular form. In addition, the phrase "one or more" used after listing multiple possible options or narrations is intended to represent any natural inclusive sequence. For example, "one or more of A and B" is satisfied by only A, only B, or both A and B.

[0068] This written description uses examples to disclose several embodiments of the invention, including the best mode, and also enables a person of ordinary skill in the art to practice the embodiments of the invention, including making and using any device or system and performing any combined methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to a person of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims.

[0069] Further aspects of the invention are provided by the subject matter of the following clauses:

[0070] A system comprises: a slip ring disposed on a rotating shaft of an electric motor; a plurality of brushes held on a surface of the slip ring when the slip ring rotates with the rotating shaft, wherein the plurality of brushes are configured to transfer current between an external source and the electric motor via the slip ring; and an arrangement of a plurality of resistor devices electrically connected to the plurality of brushes to control the distribution of the flow of the current between the external source and the plurality of brushes, wherein the arrangement of the plurality of resistor devices is configured to control the flow of current distributed to a single brush and / or one or more groups of brushes among the plurality of brushes when the electric motor is running.

[0071] The system of the preceding clause, wherein the arrangement of the plurality of resistor devices is configured to drive an equal share of the flow of the current between each of the plurality of brushes.

[0072] A system according to any of the preceding clauses, wherein each resistor arrangement of the plurality of resistor arrangements is electrically connected to a different brush of the plurality of brushes.

[0073] A system according to any of the preceding clauses, wherein some of the plurality of resistor arrangements are electrically connected to a different set of brushes.

[0074] A system according to any of the preceding clauses, wherein other resistor arrangements of the plurality of resistor arrangements are provided in brush path branches in each different group of brushes leading to one of the brushes in the group.

[0075] The system of any of the preceding clauses, wherein the plurality of resistor devices are selected from the group consisting of fixed resistors, variable resistors, power electronics based resistors, and combinations thereof.

[0076] The system of any of the preceding clauses, further comprising a monitoring system having a control unit operatively coupled to the plurality of resistor arrangements to control the resistance of the resistor arrangements.

[0077] The system according to any of the preceding clauses, further comprising a plurality of current sensing devices to measure the amount of current distributed to the plurality of brushes, wherein each of the plurality of current sensing devices is located near one of the plurality of resistor devices to measure the amount of current around these resistor devices.

[0078] A system according to any of the preceding clauses, wherein the control unit of the monitoring system is configured to receive current measurement results from each of the plurality of current sensing devices and to adjust the resistance of each of the plurality of resistor devices according to the amount of current measured by the corresponding current sensing device.

[0079] The system according to any of the preceding clauses further comprises an arrangement of a plurality of switches electrically connected to the external source and the arrangement of the plurality of resistor devices, wherein the plurality of switches are configured to selectively activate and deactivate the plurality of brushes when the motor is operating to control an average current density of the flow of the current supplied to the brushes.

[0080] A system according to any of the preceding clauses, wherein selective switches among the plurality of switches are opened and closed within a predetermined time period to adjust the average current density of the current flowing through the brush to within a predetermined current density range, and wherein the plurality of resistor devices are configured to control the amount of current received at each of the brushes to a specific current amount.

[0081] An electric motor comprises: a rotatable shaft; a rotor body mounted on the rotatable shaft, the rotor body having a plurality of field windings of a coil, the plurality of field windings of the coil being fixed around the rotor body; at least one slip ring, the at least one slip ring being placed on the end of the rotatable shaft; a plurality of brushes, the plurality of brushes being retained on the surface of the at least one slip ring when the at least one slip ring rotates together with the rotatable shaft, wherein the plurality of brushes are configured to transfer current between an external source and the field windings of the coil fixed to the rotor body via the at least one slip ring; and an arrangement of a plurality of resistor devices, the arrangement of the plurality of resistor devices being electrically connected to the plurality of brushes to control the distribution of the flow of the current between the external source and the plurality of brushes, wherein the arrangement of the plurality of resistor devices is configured to control the flow of current distributed to a single brush and / or one or more groups of brushes among the plurality of brushes when the electric motor is running.

[0082] An electric motor according to the preceding clause, wherein the arrangement of the plurality of resistor means is configured to drive an equal sharing of the flow of the current between each individual one of the plurality of brushes and / or the one or more groups of brushes.

[0083] An electric motor according to any of the preceding clauses, wherein each resistor arrangement of the plurality of resistor arrangements is electrically connected to a different brush of the plurality of brushes.

[0084] An electric motor according to any of the preceding clauses, wherein some of the plurality of resistor arrangements are electrically connected to a different set of brushes.

[0085] An electric motor according to any of the preceding clauses, wherein the plurality of resistor devices are selected from the group consisting of fixed resistors, variable resistors, power electronics resistors and combinations thereof.

[0086] The electric motor according to any of the preceding clauses further comprises: a plurality of current sensing devices for measuring the amount of current distributed to the plurality of brushes; and a monitoring system having a control unit for controlling the resistance of the resistor device according to the amount of current measured by the plurality of current sensing devices.

[0087] An electric motor according to any of the preceding clauses, further comprising an arrangement of multiple switches electrically connected to the external source and the arrangement of multiple resistor devices, wherein the multiple switches are configured to selectively activate and deactivate the multiple brushes during rotation of the rotor body to control the flow of the current supplied to the brushes.

[0088] An electric motor according to any of the preceding clauses, wherein selective switches among the plurality of switches are opened and closed within a predetermined time period to adjust the average current density of the current flowing through the brushes when the rotor body rotates to within a predetermined current density range, and wherein the plurality of resistor devices are configured to control the amount of current received at each of the brushes to a specific current amount.

[0089] A method for controlling current distribution to a plurality of brushes, wherein the plurality of brushes are held on the surface of a slip ring, the slip ring being disposed on a rotating shaft of an electric motor, the plurality of brushes transferring current between an external source and the electric motor, the method comprising: arranging a plurality of resistor devices electrically connected to the plurality of brushes and the external source; and controlling the distribution of the flow of the current between the external source and the plurality of brushes using the plurality of resistor devices, wherein the plurality of resistor devices are configured to control the flow of current distributed to a single brush and / or one or more groups of brushes among the plurality of brushes when the electric motor is running.

Claims

1. A system comprising: A collector ring (32) is placed on a rotating shaft (14) of the motor (10); a plurality of brushes (40) held on a surface of the slip ring as the slip ring rotates with the rotating shaft, wherein the plurality of brushes are configured to transfer current between an external source (48) and the motor via the slip ring; as well as An arrangement of multiple resistor devices (54, 60, 66, 72, 76) electrically connected to the multiple brushes to control the distribution of the flow of current between the external source and the multiple brushes, wherein the arrangement of multiple resistor devices is configured to control the flow of current distributed to individual brushes and / or one or more groups of brushes among the multiple brushes when the motor is operating.

2. The system of claim 1, wherein the arrangement (54, 60, 66, 72, 76) are configured to drive an equal share of the flow of the current between each of the plurality of brushes (40).

3. The system of claim 1, wherein each resistor device of the plurality of resistor devices is electrically connected to a different brush of the plurality of brushes (40).

4. The system of claim 1, wherein some of the plurality of resistor devices are electrically connected to a different set of brushes (40).

5. The system of claim 4, wherein other resistor devices of the plurality of resistor devices are disposed in brush path branches in each different group of brushes (40) leading to one of the brushes in the group.

6. The system of claim 1, wherein the plurality of resistor devices are selected from the group consisting of fixed resistors (56), variable resistors (62), power electronics based resistors (68), and combinations thereof.

7. The system of claim 1, further comprising a monitoring system (80) having a control unit operably coupled to the plurality of resistor devices to control the resistance of the resistor devices.

8. The system of claim 7, further comprising a plurality of current sensing devices (82) to measure the amount of current distributed to the plurality of brushes (40), wherein each of the plurality of current sensing devices is located near one of the plurality of resistor devices to measure the amount of current around the resistor devices.

9. The system of claim 8, wherein the control unit of the monitoring system (80) is configured to receive current measurements from each of the plurality of current sensing devices (82) and to adjust the resistance of each of the plurality of resistor devices based on the amount of current measured by the corresponding current sensing device.

10. The system of claim 1 further comprising an arrangement (86) of a plurality of switches (88) electrically connected to the external source (48) and the arrangement (54, 60, 66, 72, 76) of the plurality of resistor devices, wherein the plurality of switches are configured to selectively activate and deactivate the plurality of brushes (40) when the motor (10) is operating to control an average current density of the flow of the current provided to the brushes.

11. The system of claim 10, wherein selective switches among the plurality of switches (88) open and close within a predetermined time period to adjust the average current density of the current flowing through the brush (40) to within a predetermined current density range, and wherein the plurality of resistor devices are configured to control the amount of current received at each of the brushes to a specific current amount.

12. An electric motor (10), comprising: A rotatable shaft (14); a rotor body (12) mounted on the rotatable shaft, the rotor body having a plurality of field windings (18) of coils fixed around the rotor body; at least one slip ring (32), the at least one slip ring being disposed on an end of the rotatable shaft; a plurality of brushes (40) retained on a surface of the at least one slip ring as the at least one slip ring rotates with the rotatable shaft, wherein the plurality of brushes are configured to transfer current between an external source (48) and a field winding of the coil fixed to the rotor body via the at least one slip ring; as well as An arrangement of multiple resistor devices (54, 60, 66, 72, 76) electrically connected to the multiple brushes to control the distribution of the flow of current between the external source and the multiple brushes, wherein the arrangement of multiple resistor devices is configured to control the flow of current distributed to individual brushes and / or one or more groups of brushes among the multiple brushes when the motor is operating.

13. The electric motor (10) of claim 12, wherein the arrangement (54, 60, 66, 72, 76) of the plurality of resistor devices is configured to drive an equal sharing of the flow of the current between each individual brush (40) of the plurality of brushes and / or between the one or more groups of brushes.

14. The electric motor (10) of claim 12, wherein each resistor device of the plurality of resistor devices is electrically connected to a different brush of the plurality of brushes (40).

15. A method for controlling current distribution to a plurality of brushes (40) held on a surface of a slip ring (32) disposed on a rotating shaft (14) of an electric motor (10), the plurality of brushes transferring current between an external source (48) and the electric motor, the method comprising: disposing a plurality of resistor devices electrically connected to the plurality of brushes and the external source; as well as The distribution of the flow of the current between the external source and the plurality of brushes is controlled using the plurality of resistor devices, wherein the plurality of resistor devices are configured to control the flow of current distributed to a single brush and / or one or more groups of brushes among the plurality of brushes when the motor is operating.

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