System and method for selectively activating and deactivating brushes used in electric motors for current density optimization

Abstract

A system and method for selectively activating and deactivating brushes used in an electric motor for current density optimization is disclosed. The method includes selectively activating and deactivating the brush during operation of the motor using an arrangement of switches electrically connected to the brush. This entails opening and closing a selective one of the switches for a predetermined period of time to adjust the average current density of the current flowing through the brush to within a predetermined current density range while the motor is operating.

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 No. _______ (Attorney Docket No.: 608597-US-1), entitled “SYSTEM AND METHOD FOR CONTROLLING CURRENT DISTRIBUTION TO ELECTRICALBRUSHES USED IN DYNAMOELECTRIC MACHINE,” 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 an arrangement of switches deployed in electrical communication with brushes held on the surface of slip rings placed on the rotating shaft of the motor, the brushes transferring current between an external source and the motor, and selectively activating and deactivating the brushes via the switches for predetermined time periods during operation of the motor to regulate an average current density of current flowing through the brushes within a predetermined current density range.

[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 and 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 to 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 within 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 to continuously remain on the surface of the collector ring when the collector ring rotates with the shaft. Current from an external source can be supplied to the slip rings via brushes. From the slip rings, the current passes 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] The brushes have an optimal current level to ensure proper film formation between the brushes and the slip rings (this is necessary to maintain brush life and minimize fluctuations in contact resistance). High variable contact resistance causes some brushes to have almost zero current, while other brushes will receive two to three times the average current value. This uneven distribution of current between the brushes (often referred to as selectivity) can cause brush overheating and exacerbate poor film formation between the brushes and the slip rings. These conditions can eventually lead to flashovers, which can cause significant arc damage and melted components, posing a safety risk to nearby operators. Power plants continue to increase downregulation, which requires power plants to operate over a wide range of field currents that are typically outside the range of current density requirements for the brushes. Therefore, there is a need to address this problem so that the brushes can operate within their optimal current density range requirements. Summary of the invention

[0007] 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.

[0008] The solution provided by various embodiments to eliminate the above-mentioned selectivity problem requires providing an arrangement of switches in the circuit of the brushes to activate or deactivate a single brush or a group of brushes at a time so as to adjust the average current density of the active brushes to a specific current density when the motor is in operation. In this way, by obtaining a specific current density through the arrangement of switches, various embodiments enable the formation of a film between the brushes and the slip rings, so that there is a better chance of evenly distributing the current between the brushes, although their inherent resistance fluctuations make this difficult. In addition to the use of an arrangement of switches, an embodiment may include an arrangement of balancing resistor devices that can be selectively connected to the switches and brushes to remove resistance fluctuations in the electrical path between these components, thereby ensuring an equal distribution of current flowing through certain brushes.

[0009] According to one embodiment, a system is provided. The system includes: a slip ring placed 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 switches electrically connected to the plurality of brushes, the arrangement of the plurality of switches being used to selectively activate and deactivate the plurality of brushes during operation of the motor, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to adjust an average current density of current flowing through the brushes to within a predetermined current density range when the motor is in operation.

[0010] According to another embodiment, a motor is provided. The 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 placed 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 switches, the arrangement of the plurality of switches being electrically connected to the plurality of brushes, the arrangement of the plurality of switches being used to selectively activate and deactivate the plurality of brushes during rotation of the rotor body, wherein selective switches of the plurality of switches are opened and closed for a predetermined period of time to adjust the average current density of the current flowing through the brushes to a predetermined current density range when the rotor body rotates.

[0011] According to yet another embodiment, a method for optimizing current density to a plurality of brushes held on a surface of a slip ring placed on a rotating shaft of a motor, the plurality of brushes transferring current between an external source and the motor, is provided. The method includes: arranging a plurality of switches electrically connected to the plurality of brushes; and selectively activating and deactivating the plurality of brushes via the plurality of switches during operation of the motor, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to adjust an average current density of current flowing through the brushes to within a predetermined current density range when the motor is in operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0013] FIG1 shows an isometric view of an electric motor such as a generator according to the prior art;

[0014] FIG2 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 FIG1 according to the prior art;

[0015] FIG3 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 FIG1 via brushes which are continuously held on the surface of a slip ring of a generator as depicted in FIG2 ;

[0016] Figure 4 shows a schematic representation of a circuit with a switch arrangement electrically connected to brushes, illustrating current transfer between an external source and a plurality of field windings from a coil of a generator, according to one embodiment of the present invention;

[0017] Figure 5 A schematic representation of a circuit with a switch arrangement illustrating current transfer between an external source and a plurality of field windings from a coil of a generator is shown, wherein some switches are placed in series with respective brushes and other switches are operatively coupled to a pair of brushes, according to an embodiment of the present invention;

[0018] Figure 6 shows a schematic representation of a circuit with a switch arrangement illustrating current transfer between an external source and a plurality of field windings from a coil of a generator, wherein some switches are placed in series with respective brushes and other switches are operably coupled to a set of brushes, according to one embodiment of the present invention;

[0019] Figure 7 A collector brush monitoring system for monitoring brushes according to an embodiment of the present invention is shown. Figure 4 A schematic representation of the circuit depicted in;

[0020] Figure 8 shows a schematic representation of a circuit according to one embodiment of the present invention, illustrating current transfer between an external source and a plurality of field windings from a coil of a generator, having a resistor device arrangement, which may include a fixed resistor operably coupled with a switch arrangement and brushes; and

[0021] Fig. 9 A schematic representation of a circuit having a resistor device arrangement according to one embodiment of the present invention is shown, illustrating current transfer between an external source and multiple field windings from a coil of a generator, the resistor device arrangement may include power electronics operably coupled to a switch arrangement and brushes. DETAILED DESCRIPTION

[0022] 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.

[0023] The present disclosure relates generally to electric motors, and more particularly to an arrangement of switches deployed in electrical communication with brushes held on the surface of slip rings placed on the rotating shaft of the motor, the brushes transferring current between an external source and the motor, and selectively activating and deactivating the brushes via the switches for predetermined time periods during operation of the motor to regulate an average current density of current flowing through the brushes within a predetermined current density range.

[0024] 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.

[0025] Turning now to the drawings, FIG1 shows an isometric view of a generator 10 according to the prior art. As shown in FIG1 , the generator 10 includes a rotor body 12, which may be made of a ferrous metal material, which is 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, which may be made of copper or aluminum. The plurality of field windings of the coils 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.

[0026] 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 to generate 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. 1) 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. 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.

[0027] FIG. 2 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. 1 according to the prior art. Although not shown in FIG. 2 , the collector ring 32 rotates with the shaft and rotor body of the generator. For clarity, FIG. 2 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. 2 shows that the brush holder rigging assembly 36 may include a pair of brushes 40 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.

[0028] 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.

[0029] FIG3 shows a schematic diagram of a circuit 46 according to the prior art, illustrating the transfer of current between an external source such as a generator excitation system 48 and a plurality of field windings 18 of coils from the rotor body 12 of the generator 10 shown in FIG1 via brushes 40, which are continuously maintained on the surface of the slip rings 32 of the generator as depicted in FIG2. As shown in FIG3, the generator excitation system 48 (which may be a power source such as, for example, a direct current (DC) source) supplies 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 generator excitation system 48, while the other ring 32 having the brush 40 is connected to the negative terminal of the generator excitation system 48. With this configuration, not only can current flow from the brushes 40 and slip rings 32 to the field winding 18 of the coil, but current can also flow from the field winding 18 of the coil to the generator magnetic system 48 via the slip rings 32 and brushes 40 .

[0030] The schematic diagram of FIG. 3 and the schematic diagrams of other figures disclosed herein only show four brushes 40 per 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 20 to 40 parallel brush paths.

[0031] In this configuration of FIG. 3 , there may be too many brushes 40 to maintain an optimal average current density. This results in poor film formation and may have a tendency to unevenly supply current to the slip ring 32. This results in the above-mentioned selectivity problem of some of the brushes 40. That is, those brushes will receive too much current, which results in an accelerated wear rate due to the excess current and the heat generated by the current. For example, when the brushes have a selectivity problem, some brushes may receive 100 amperes (A) while other brushes receive 2A.

[0032] Various embodiments described herein provide a switch arrangement between the generator excitation system 48 and the brushes 40 that can be implemented in a brush holder rigging assembly (e.g., in a stationary support member or other component within the brush holder rigging assembly containing the wires) and is used to activate or deactivate one or more of a single brush, a pair of brushes, and a group of brushes for a predetermined period of time so as to adjust the average current density of the current flowing through the active brushes to within a predetermined current density range. This is different from the configuration shown in Figure 3, in which the brushes are hardwired with the generator excitation system 48 to always be in the circuit 46. Using the switch arrangement, various embodiments can ensure that, on average, each active brush is within a specific current density range that represents the optimal current density of the brush. As used herein, the optimal current density of the brush refers to the brush current density at, for example, 40A / in 2 Up to 65A / in 2 Operate within the range of

[0033] Due to this switch arrangement, each of the various embodiments can ensure that the brushes 40 can maintain an optimal average current density, which promotes good film formation and helps to evenly distribute current among all brushes when the generator is operating. As used herein, evenly distributing or supplying current among all brushes when the generator is operating means that the brushes share approximately the same current (e.g., all values ​​are within 10%) versus unequal sharing (e.g., where some brushes carry no current while other brushes carry up to twice the average or more current). In this regard, the selective activation and deactivation of the switch can prevent the brushes from getting too hot, and therefore prevent the brushes from getting more current and getting even hotter to the point where the increased current flow and heating causes accelerated wear of the brushes.

[0034] Figure 4 A schematic diagram of an electrical circuit 52 is shown illustrating the passage of current between the generator excitation system 48 and the plurality of field windings 18 of the coils, wherein an arrangement 54 of switches 56 is electrically connected to the brushes 40 and the excitation system, according to an embodiment of the present invention. Figure 4 In the illustrated embodiment, the arrangement 54 of switches 56 includes a switch electrically connected between each brush and the generator excitation system 48. With a switch 56 placed in each branch of the circuit 52 between the generator excitation system 48 and one of the brushes 40, the current supplied to each brush can be individually controlled by using the switch. In this regard, the brushes can be selectively activated and deactivated during generator operation. In one embodiment, the activation and deactivation of the brushes 40 requires opening and closing the switch for a predetermined period of time to adjust the average current density of the current flowing through the brushes to within a predetermined current density range.

[0035] The inventors of the present invention have determined that activation and deactivation of the brush 40 is not simply a matter of opening and closing the switch 56. When the switch 56 to the brush is open, as shown in the top two branches of the circuit 52 for the two rings 32, no current flows to the corresponding brush. When the brush has no current flowing to it, glaze can begin to form at its interface with the slip ring 32 and become a problem as it accumulates. For example, once its corresponding switch is moved from an open position to a closed position, as shown in the bottom two branches of the circuit 52 for the two rings 32, this accumulation of glaze can inhibit current from flowing through the brush 40. In effect, the accumulation of glaze creates a resistance to the flow of current, and therefore, current cannot flow to the brush even though its corresponding switch is closed.

[0036] The solution to this glazing provided by various embodiments includes selectively activating and deactivating the switch 56 between the open position and the closed position so that the accumulation of glazing does not occur. In one embodiment, the switch 56 can be selectively opened and closed for a predetermined time period. As used herein, the predetermined time period is the amount of time sufficient to prevent the accumulation of glaze on the brush interface. It will be understood by those skilled in the art that this amount of time for the switch to be opened and closed can depend on the known time that the glaze formation can take. Typically, the range of the predetermined time period can range from a few seconds or a few fractions of a second to a few hours or even a few days. In this regard, the selective switch in the switch 56 in the arrangement 54 can be periodically opened for the predetermined time and then closed. After closing the switch, another switch 56 can be opened for the predetermined time period and then closed. This short-term opening and closing of the switch 56 can be cycled through all switches in the arrangement. In this regard, the switch 56 in the arrangement 54 can be opened for a long enough time so that the accumulation of glazing does not occur on the interface of its corresponding brush 40. At the same time, the closed switch allows its corresponding brush 40 to maintain its operation at the optimal average current density level specified for the brush. In this way, on average, the brush never carries too much current or too little current. Therefore, a good film is formed and the current can be kept constant. Figure 4 The circuit 52 is evenly distributed among the brushes 40 .

[0037] Figure 5 A schematic diagram of a circuit 58 according to an embodiment of the present invention is shown having an arrangement 60 of switches 56, some of which are placed in series with respective brushes 40 and others of which are operably coupled to a pair of brushes, illustrating the passage of current between the generator excitation system 48 and the plurality of field windings 18 of the coils. Figure 5 In the depicted example, the circuit 58 shows that each slip ring 32 has at least one switch 56 configured to activate a pair of brushes 40 operatively coupled to those rings. Figure 5Each slip ring 32 is shown to include a number of switches 56 connected in series with corresponding brushes, but it should be understood that the circuit 58 represents only one configuration and is not meant to be limiting. Figure 5 Each of the switches 56 in may be operably coupled to a different pair of brushes.

[0038] Rather than having the switch 56 operably coupled to different pairs of brushes 40 , the switch may be electrically connected to different sets of brushes for the slip rings. Figure 6 A circuit 62 is shown having an arrangement 64 of switches 56, some of which are placed in series with respective brushes 40 and others of which are operably coupled to a set of brushes. Figure 6 In the depicted example, the circuit 62 shows that each slip ring 32 has at least one switch 56 configured to activate a set of brushes 40 (e.g., three brushes) operably coupled to the rings. It should be understood that a set of brushes may include more than Figure 6 In the example depicted in Figure 1, there are three brushes. In addition, Figure 6 Each slip ring 32 is shown to include at least one switch 56 connected in series with a corresponding brush. Figure 6 The embodiment depicted in represents only one configuration and is not meant to be limiting. For example, one switch 56 may be used with each slip ring 32 to activate and deactivate all brushes operably coupled to each ring. In another variation, there may be at least one switch for activating or deactivating a set of brushes 40 for at least one ring, and at least one switch 56 for activating or deactivating a pair of brushes. Furthermore, it should be understood that these variations may also include a switch 56 configured to operate with one brush.

[0039] The arrangement of switches depicted in conjunction with the various embodiments described herein that can be used to adjust the average current density of the brushes to within a predetermined current density range specified for the brushes has utility in a variety of situations. For example, when the generator is used during a period of low power demand, the switch can be selectively activated and deactivated for a predetermined period of time to ensure that the brushes receive a current supply within a predetermined average current density range that represents the optimal current density range for the brushes. For example, consider a situation in which there are 100 brushes operating with slip rings, but only 90 brushes are required to obtain the optimal average current density. The switches of the various embodiments can be used to selectively activate and deactivate 90 brushes to ensure that the average current density of these brushes is correct. Presumably, if the average current density of these brushes is correct, the current should be shared more equally between the brushes, which will eliminate the occurrence of selectivity issues.

[0040] The predetermined time period during which the electrical switch is selectively closed and opened may determine the speed at which the brushes are activated and deactivated. Other factors that may play a role in this time period and how the switch is opened and closed may include the amount of current supplied by the generator excitation system, the optimal current density of the brushes, the number of brushes connected to the slip rings, and the number of brushes that need to be activated in order to handle the current supplied by the excitation system. In any case, the switch may cause the current to be distributed among all the brushes so that glazing is avoided at the interface of the brushes and the slip rings. Once the generator begins to operate in a period of high power demand, the switch may remain in the closed position.

[0041] Furthermore, it should be understood that various embodiments may be implemented in one of a variety of different situations.In one embodiment, the switch may be turned on and off depending on the level of the driver current supplied.

[0042] In another embodiment, the use of a switch arrangement to selectively activate and deactivate brushes may be used as part of a collector brush monitoring system. For example, a collector brush 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 actively manage the operation of the switches to selectively supply current to the brushes. For example, if a problem is noted for any particular brush, the switch controlling the power to that brush may be opened so that it is turned off. In summary, implementing various embodiments with a brush monitoring system may be used to create a more robust monitoring system because it may perform additional functions including ensuring that the current from the generator excitation system is evenly distributed between the brushes.

[0043] Figure 7 A schematic diagram of one of the switch arrangements disclosed herein having a collector brush monitoring system 66 for monitoring the brushes is shown. In particular, Figure 7 Shown with Figure 4 The circuit depicted in corresponds to the schematic representation of circuit 68, but Figure 7 The circuit 68 includes a collector brush monitoring system 66. In operation, the collector brush monitoring system 66 can monitor the wear and temperature of the brush 40, the amount of current supplied to the brush via current sensors (e.g., current transformers) disposed around the switch 56 and the brush 40. For clarity, Figure 7 The current sensor is not shown, however, those skilled in the art will appreciate that the sensor may be located in a variety of locations including before and / or after the switch 56. In addition, it should be understood that the use of the collector brush monitoring system 66 to monitor the brushes is not meant to be limited to this configuration. The collector brush monitoring system 66 is suitable for Figures 4 to 6 Any switch arrangement depicted in and any alternative switch arrangement that may be configured. In addition, the collector brush monitoring system 66 is suitable for use with Figure 8 and Fig. 9 , which employs resistor devices in each branch between the generator excitation system 48 and the brushes 40.

[0044] The ability of various embodiments to evenly distribute current to the brushes can be further enhanced by using an arrangement of balancing resistor devices operably coupled to the switches and brushes to control the flow of current to each brush, brush pair, or brush group operably coupled to the slip ring. For example, in one embodiment, selective activation and deactivation of the switches can be used to control the average current density of a target number of brushes, while the balancing resistor device can be used to ensure that each brush receives a specified current flow. In one embodiment, the balancing resistor device can be used to drive an equal sharing of current between the brushes, aiming to handle the average current density. In one embodiment, the balancing resistor device can be used to control the current to each brush so that each brush receives a specified amount of current.

[0045] Figure 8 A schematic diagram of a circuit 70 according to an embodiment of the present invention is shown, the circuit having an arrangement 72 of fixed resistors 74 operatively coupled to an arrangement 76 of switches 56 and brushes 40. In one embodiment, the resistors 74 are configured to remove the variable resistance between the generator excitation system 48 and the brushes 40, thereby ensuring that each brush receives a specified current flow. When the arrangement 76 of switches 56 is selectively activated and deactivated as described above for a predetermined period of time to adjust the average current density of the current flowing through the brushes 40 to a predetermined current density range, each brush has a tendency to act in its own way due to the inherent fluctuations present in each branch that electrically connects the brushes to the generator excitation system 48 and the fluctuations present at the interface between the brushes and the slip rings 32. Adding a fixed resistor 74 in each branch between the switch 56 and the brush 40 helps overcome this fluctuation. As long as the resistor 74 has a resistance greater than the resistance at the interface between the brush 40 and the slip ring 32, the resistor can drive how much current to flow to each brush. In one embodiment, if the resistance of resistor 74 is significantly greater than the resistance at the interface between brush 40 and slip ring 32, the resistor can ensure that each brush receives an equal amount of current supplied from generator excitation system 48. In one embodiment, the resistance of resistor 74 can be specified to have an amount that can drive a specified current through each brush 40. Setting the resistance of each resistor 74 to a specified amount to drive a specific current through brush 40 is deemed to be within the scope of those skilled in the art.

[0046] Not like Figure 8 Instead of using fixed resistors as depicted in FIG, variable resistors may be used in their place or in an arrangement including combinations with fixed resistors. For example, Fig. 9A schematic diagram of a circuit 78 having an arrangement 80 of variable resistor devices 82 operatively coupled to an arrangement 84 of switches 56 and brushes 40 is shown in accordance with an embodiment of the present invention. Figure 8 The arrangement 72 of the fixed resistor 74 depicted in FIG. Fig. 9 The arrangement 80 of the variable resistor devices 82 in the generator excitation system 48 can be used to remove the variable resistance between the brushes 40 and the generator excitation system, thereby ensuring that each brush receives a specified current flow. In one embodiment, each variable resistor device 82 can be adjusted in a manner to ensure that each brush receives an equal amount of current supplied from the generator excitation system 48. In one embodiment, each variable resistor device 82 can be adjusted to drive a specific current through each brush 40. The variable resistor may include any of a variety of different types of variable resistors. A non-exhaustive list of possible variable resistors suitable for use with various embodiments includes any type of power electronic resistance device such as a thyristor, for example, an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), and a silicon controlled rectifier (SCR).

[0047] It should be understood that Figure 8 The arrangement 72 of the fixed resistor device 74 depicted in Fig. 9 The arrangement 80 of variable resistors 82 depicted in FIG. 4 is merely representative of a pair of configurations for using resistor devices to remove fluctuations in the branch between the generator excitation system 48 and the brushes 40 so that a specified current can be supplied to each of the brushes. For example, instead of having individual resistor devices (e.g., fixed resistors, variable resistors) connected to different brushes, the resistor devices can be coupled to groups of brushes. Also, instead of having one resistor device electrically connected to a group of brushes, a subgroup of resistor devices can operate with a main resistor device operably coupled to the generator excitation system 48 to facilitate supplying a specified current to each brush in the group.

[0048] A system and method for controlling current distribution of brushes used in an electric motor (ATTORNEY DOCKET NO. 608597-US-1) is provided as reference in U.S. Patent Application No. _______, entitled "SYSTEM AND METHOD FOR CONTROLLING CURRENT DISTRIBUTION TO ELECTRICAL BRUSHES USED INDYNAMO ELECTRIC MACHINE" (ATTORNEY DOCKET NO. 608597-US-1). Figure 8 and Fig. 9 The disclosure of this US patent application is incorporated herein by reference for further details discussing the use of an arrangement of resistor devices to remove resistance fluctuations between the generator excitation system 48 and the brushes 40 that may affect how current is distributed between the brushes.

[0049] From the description of the exemplary embodiments presented herein, it should be apparent that the present disclosure sets forth an effective solution for evenly distributing current to brushes that are operably coupled to collector rings placed on an electric motor such as a generator, thereby improving the performance of the electric motor. In addition, operating the switches to selectively activate and deactivate the brushes during operation of the generator in a manner that maintains the average current flowing through the brushes within a predetermined optimal average current density set for the brushes allows the embodiments to avoid glazing of the brushes. This capability helps to reduce selectivity problems that may occur as the power plant continues to increase downregulation, which continues to increase downregulation so that the power plant must operate over a wide range of field currents that are typically outside the range required by the current density of the brushes. Various embodiments not only provide the ability to optimize the brushes over any field current range, but also embodiments can improve the reliability of the collector system of the generator by reducing selectivity by shutting off poorly operating brushes or brush groups.

[0050] 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.

[0051] 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.

[0052] 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..."

[0053] 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.

[0054] 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.

[0055] Further aspects of the invention are provided by the subject matter of the following clauses:

[0056] A system comprises: a slip ring placed on a rotating shaft of an electric motor; a plurality of brushes held on the 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 switches electrically connected to the plurality of brushes, the arrangement of the plurality of switches being used to selectively activate and deactivate the plurality of brushes during operation of the electric motor, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to adjust an average current density of the current flowing through the brushes to within a predetermined current density range when the electric motor is operating.

[0057] The system of the preceding clause, wherein the plurality of switches are configured to divide current evenly between all of the plurality of brushes.

[0058] A system according to any of the preceding clauses, wherein each of the plurality of switches is electrically connected to a different one of the plurality of brushes.

[0059] A system according to any of the preceding clauses, wherein some of the plurality of switches are electrically connected to different pairs of brushes of the plurality of brushes.

[0060] A system according to any of the preceding clauses, wherein some of the plurality of switches are electrically connected to different sets of brushes of the plurality of brushes.

[0061] A system according to any of the preceding clauses, wherein the plurality of switches are configured to selectively activate and deactivate the plurality of brushes when the electric motor is operating at low power.

[0062] A system according to any of the preceding clauses, wherein the plurality of switches remain in a closed position when the motor is operating at high power.

[0063] A system according to any of the preceding clauses, wherein the selective activation and deactivation of the plurality of brushes by the plurality of switches is based on the amount of current flowing between the external source and the motor, the optimal average current density requirement of the brushes, and the number of the plurality of brushes that must be activated to handle the current supplied by the external source.

[0064] The system according to any of the preceding clauses further includes an arrangement of multiple resistor devices, which are operably connected to the arrangement of the multiple switches and the multiple brushes, wherein the multiple resistor devices are configured to remove the variable resistance between the external source and the brushes, thereby ensuring that each brush receives a specified current flow.

[0065] A system according to any of the preceding clauses, wherein each of the plurality of resistor devices is operably coupled to a different one of the plurality of brushes.

[0066] The system of any of the preceding clauses, wherein the plurality of resistor devices comprises one or more of fixed resistors and variable resistors.

[0067] 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 switches electrically connected to the plurality of brushes for selectively activating and deactivating the plurality of brushes during rotation of the rotor body, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to adjust an average current density of the current flowing through the brushes to within a predetermined current density range when the rotor body rotates.

[0068] An electric motor as described in the preceding clause, wherein the plurality of switches are configured to divide current evenly between all brushes in the plurality of brushes.

[0069] An electric motor according to any of the preceding clauses, wherein each of the plurality of switches is electrically connected to a different one of the plurality of brushes.

[0070] An electric motor according to any of the preceding clauses, wherein some of the plurality of switches are electrically connected to different pairs of brushes of the plurality of brushes.

[0071] An electric motor according to any of the preceding clauses, wherein some of the plurality of switches are electrically connected to different sets of brushes of the plurality of brushes.

[0072] An electric motor according to any of the preceding clauses, wherein the plurality of switches are configured to selectively activate and deactivate the plurality of brushes when operating at low power, and wherein the plurality of switches are maintained in a closed position when operating at high power.

[0073] An electric motor according to any of the preceding clauses further comprises an arrangement of a plurality of resistor devices operably connected to the arrangement of the plurality of switches and the plurality of brushes, wherein the plurality of resistor devices are configured to remove a variable resistance between the external source and the brushes, thereby ensuring that each brush receives a specified current flow.

[0074] A method for optimizing current density to a plurality of brushes, the plurality of brushes being held on the surface of slip rings which are placed 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 switches electrically connected to the plurality of brushes; and selectively activating and deactivating the plurality of brushes via the plurality of switches during operation of the electric motor, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to adjust an average current density of the current flowing through the brushes to within a predetermined current density range when the electric motor is operating.

Claims

1. A system comprising: A slip ring, which is placed on the rotating shaft of the motor; a plurality of brushes retained 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 and the motor via the slip ring; and an arrangement of a plurality of switches electrically connected to the plurality of brushes, the arrangement of the plurality of switches being used to selectively activate and deactivate the plurality of brushes during operation of the motor, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to regulate an average current density of the current flowing through the brushes to within a predetermined current density range when the motor is in operation. 2 . The system of claim 1 , wherein the plurality of switches are configured to divide current evenly between all of the plurality of brushes. 3 . The system of claim 1 , wherein each of the plurality of switches is electrically connected to a different one of the plurality of brushes. 4 . The system of claim 1 , wherein some of the plurality of switches are electrically connected to different pairs of brushes of the plurality of brushes.

5. The system of claim 1, wherein some of the plurality of switches are electrically connected to different sets of brushes of the plurality of brushes.

6. The system of claim 1 , wherein selective activation and deactivation of the plurality of brushes by the plurality of switches is based on an amount of the current flowing between the external source and the motor, an optimal average current density requirement for the brushes, and a number of the plurality of brushes that must be activated to handle the current supplied by the external source.

7. The system of claim 1 further comprising an arrangement of a plurality of resistor devices operably coupled to the arrangement of the plurality of switches and the plurality of brushes, wherein the plurality of resistor devices are configured to remove a variable resistance between the external source and the brushes, thereby ensuring that each brush receives a specified current flow.

8. The system of claim 7, wherein each of the plurality of resistor devices is operably coupled to a different one of the plurality of brushes.

9. The system of claim 7, wherein the plurality of resistor devices include one or more of fixed resistors and variable resistors.

10. An electric motor, comprising: A rotatable shaft; a rotor body mounted on the rotatable shaft, the rotor body having a plurality of field windings of coils fixed around the rotor body; at least one slip ring disposed on an end of the rotatable shaft; a plurality of brushes 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 and a field winding of the coil fixed to the rotor body via the at least one slip ring; and an arrangement of a plurality of switches electrically connected to the plurality of brushes for selectively activating and deactivating the plurality of brushes during rotation of the rotor body, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to regulate an average current density of the current flowing through the brushes to within a predetermined current density range as the rotor body rotates.

11. The electric motor of claim 10, wherein the plurality of switches are configured to divide the current evenly between all of the plurality of brushes.

12. The electric motor of claim 10, wherein some of the plurality of switches are electrically connected to different sets of brushes of the plurality of brushes.

13. The electric motor of claim 10 further comprising an arrangement of a plurality of resistor devices operably coupled to the arrangement of the plurality of switches and the plurality of brushes, wherein the plurality of resistor devices are configured to remove a variable resistance between the external source and the brushes, thereby ensuring that each brush receives a specified current flow.

14. A method for optimizing current density to a plurality of brushes, the plurality of brushes being held on a surface of a slip ring, the slip ring being placed 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: disposing a plurality of switches electrically connected to the plurality of brushes; as well as The plurality of brushes are selectively activated and deactivated via the plurality of switches during operation of the motor, wherein selective switches among the plurality of switches are opened and closed for a predetermined period of time to adjust an average current density of the current flowing through the brushes to within a predetermined current density range when the motor is operating.

15. The method of claim 14, further comprising arranging a plurality of resistor devices for operatively coupling with the plurality of switches and the plurality of brushes, wherein the plurality of resistor devices are configured to remove a variable resistance between the external source and the brushes, thereby ensuring that each brush receives a specified current flow.

Images