Shaft grounding system

Abstract

A shaft grounding system for rotating electrical machinery includes a collar attachable to the shaft and presenting a circumferential contact surface of a first metal. A stator securable to the machine housing carries at least one resiliently biased contact element of a second metal that wipes against the contact surface to conduct unwanted charge from the shaft to ground. In preferred embodiments the metals are dissimilar and at least one is a noble metal. The system may incorporate multiple contact surfaces, modular contact elements and an on-board monitoring subsystem that provides local and remote diagnostics.

Description

[0001] SHAFT GROUNDING SYSTEM

[0002] FIELD OF THE INVENTION

[0003] This invention relates generally to electric machinery, and more particularly, to systems for dissipating unwanted electric charge in rotating electric machinery.

[0004] BACKGROUND TO THE INVENTION

[0005] Rotating electrical machinery is essential to a broad spectrum of industrial applications. However, such equipment is prone to developing shaft voltages induced by variable frequency drive systems, electromagnetic interference, and static electricity. If left unmanaged, these voltages can lead to damaging discharges through motor bearings or other components, causing premature failure, unplanned downtime, and costly repairs.

[0006] Traditional solutions include brush-type, collar-type, and ring-type grounding devices. These typically rely on non-metallic conductive elements, such as carbon brushes or graphite fibre rings, to provide a conductive path from the rotating shaft to ground. Each of these known systems exhibits limitations. Carbon brushes, while effective for conducting high voltage (typically in excess of 400V), are poor conductors at high frequencies (typically in excess of 100 kHz). Conversely, fibre rings better handle high- frequency currents but are vulnerable to breakdown under high voltages, particularly in environments like wind turbines, where voltages may exceed 900 volts. Additionally, both brush and fibre-ring systems struggle in environments contaminated by oil or grease. Carbon brushes tend to absorb contaminants, reducing conductivity, while fibre rings can only brush aside limited amounts of contamination before performance deteriorates.

[0007] Another widespread drawback of conventional grounding systems is the inability to determine, in real time, whether grounding performance has been compromised. Wear, misalignment, corrosion, or contamination can all lead to failure of the grounding path without any visual or diagnostic cue.

[0008] Accordingly, there remains a need for a shaft-grounding solution that: (i) accommodates both high-frequency and high-voltage conditions; (ii) maintains reliable metal-to-metal contact even in contaminated environments; and (iii) provides real-time feedback on grounding integrity so that preventive maintenance can be scheduled.

[0009] OBJECT OF THE INVENTION

[0010] It is accordingly an object of this invention to provide a shaft grounding system that addresses at least partially addresses the abovementioned problems, and / or that is a useful alternative to conventional devices. SUMMARY OF THE INVENTION

[0011] According to the invention, there is provided a shaft grounding system for an electric apparatus having a housing and a shaft mounted for rotation within and extending from the housing, the system comprising:

[0012] - a collar attachable to the shaft for rotation therewith, the collar defining a circumferential contact surface that includes a first electrically-conductive metal; and

[0013] - a stator mountable to the housing and positioned radially outward of the collar, the stator including a conductive arrangement that includes at least one contact element configured to abut the contact surface during shaft rotation so as to conduct electric charge from the collar, the contact element including a second electrically-conductive metal.

[0014] The first and second metals are preferably dissimilar. At least one, and preferably both, of the first and second metals may be a noble or precious metal selected from gold, silver, platinum and an alloy thereof.

[0015] The contact surface may be integral with the collar or defined by a replaceable sleeve fitted around the collar periphery. The contact surface may be grooved (e.g., U or V- shaped) or raised relative to the surrounding surface to enhance wiping action. A plurality of axially spaced contact surfaces may be provided to increase conductive area and mechanical stability. The contact element may be a line, band, filament or strip oriented obliquely to the shaft axis. The contact element may be resiliently biased for maintaining a controlled contact force with the contact surface. The contact element may extend perpendicularly with respect to the shaft axis. In some embodiments, multiple contact elements may be arranged in parallel, at an obtuse angle to one another, grouped, or staggered to achieve a desired impedance and current handling capacity.

[0016] The conductive arrangement is preferably modular and removably secured to the stator so that it can be replaced as a unit during routine maintenance.

[0017] There is still further provided for the shaft grounding system to include a monitoring subsystem comprising:

[0018] - a voltmeter operatively coupled between the contact element and a remainder of the stator;

[0019] - a processor in communication with the voltmeter and configured to generate at least one status signal representative of a measured shaft-to-ground voltage; and

[0020] - an indicator in communication with the processor and configured to generate a visible or audible indication responsive to the status signal.

[0021] Optionally, the shaft grounding system includes a communication module for transmitting the status signal to a remote device via a wired or wireless network.

[0022] According to a second aspect, the invention provides a kit that includes the shaft grounding system and at least one additional conductive arrangement. These and other features of the invention are described in more detail below.

[0023] BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

[0024] Embodiments of the invention are described below, by way of non-limiting examples only, and with reference to the accompanying Figures in which:

[0025] Figure 1 is a schematic perspective view of a shaft grounding system in accordance with a first embodiment of the invention, showing a collar attached to a shaft and a stator mounted to a housing;

[0026] Figure 2 is a plan view of the shaft grounding system shown in Figure 1 ;

[0027] Figure 3 is a transparent perspective view of a stator portion of the shaft grounding system shown in Figure 1 to reveal internal features including band-type contact elements;

[0028] Figure 4 is a schematic diagram of an exemplary electronic hardware platform for a monitoring system; and

[0029] Figure 5 is a transparent perspective view of a stator portion of a shaft grounding system in accordance with a second embodiment of the invention to reveal internal features including grouped line-type contact elements. DETAILED DESCRIPTION OF THE INVENTION

[0030] Referring to the Figures, wherein like features are indicated by like numerals, a shaft grounding system according to a first embodiment of the invention is generally indicated by reference numeral 10 in Figures 1 -3, and a shaft grounding system according to a second embodiment of the invention is generally indicated by reference numeral 10A in Figure 5.

[0031] Referring to Figure 1 , the system 10 is shown in operative association with a rotatable shaft 102 that extends from a machine housing 104 of an electric apparatus 100. The electric apparatus 100 could comprise an electric motor, generator, alternator, or similar rotating equipment.

[0032] The system 10 broadly comprises a collar 12 fixed to the shaft 102 and a stator 14 secured to the housing 104 adjacent the collar 12 so that the stator 14 remains stationary while the collar 12 rotates. The stator 14 is positioned radially outward of the collar 12.

[0033] The collar 12 serves as the primary interface for facilitating the transfer of electric charge from the shaft 102, thereby preventing harmful charge accumulation that could compromise equipment performance and reliability. The collar 12 features a pair of axially spaced, circumferential contact surfaces 16. In the illustrated embodiment, each surface 16 is formed on a sleeve 18 that is interference fit to a collar body 19. The sleeves 18 are coated with, or manufactured from, a first electrically-conductive metal, preferably a noble metal or precious metal for their superior conductivity and corrosion resistance. The contact surfaces 16 serve as a contact point for efficient charge dissipation. In an alternative embodiment, the contact surfaces 16 may be machined directly into the collar 12.

[0034] To further enhance conductivity and maximize surface area contact, the contact surfaces 16 are configured in the form of grooves, such as a U-shaped groove as depicted in Figure 3. Alternatively, and although not shown, it is envisaged that the grooves could also be in the form of V-shaped grooves. Further alternatively, the contact surfaces 16 could stand proud of a remaining radially outer periphery of the collar 12.

[0035] Referring specifically to Figure 3, which shows a casing of the stator 14 as transparent to reveal otherwise hidden internal components, the stator 14 houses a conductive arrangement 20 having a plurality of elongated contact elements 22. Each element 22 is mounted to extend transversely with respect to an axis A of the shaft 102 (when viewed from above), and at an acute angle to the collar tangent and is urged radially inward against the contact surfaces 16.

[0036] There are four strip-like elements 22 which are arranged in two opposed pairs 24.1 and 24.2 so that current paths are duplicated for redundancy. The contacts 22 of each pair 24.1 , 24.2 extend parallel to each other and are spaced axially from each other, and the contacts 22 of the first pair 24.1 extend at an obtuse angle relative to those of the second pair 24.2 near their contact with the surfaces 16. The contact elements 22 are resiliently biased abutting laterally against the collar 12 for maintaining a controlled contact force with the contact surfaces 16. Each element 22 includes a second electrically-conductive metal, preferably also a noble or precious metal. Preferably, the first and second metals are dissimilar, but it is foreseen that they may also be similar in some embodiments of the invention. The contacts 22 could be coated with the second metal or manufactured from the second metal.

[0037] The noble or precious metals are selected from gold, silver, platinum and alloys thereof.

[0038] The conductive arrangement 20 is removably secured to a remainder of the stator and may be removed as a single module for replacement.

[0039] Turning to Figure 4, an exemplary configuration of several electronic components of the stator 14 is shown for illustrative purposes only, which include an on-board monitoring sub-system 26 designed to provide real-time feedback on the system’s 10 performance and operational status. In some embodiments, certain components may be arranged differently or absent. Additional components may also be present. It would be appreciated that the monitoring system 26 is housed underneath the cover of the stator 14.

[0040] The monitoring system 26 includes at least one system bus 28, whereby the other electronic components can communicate with each other. The contacts 22 are connected to the system bus 28 and form part of the monitoring system 26. Also connected to the system bus 28 are a central processing unit 30 and one or more storage 32 and memory modules 34. A voltmeter 36 is further connected to the bus 28 for measuring the potential difference between the contact element 22 and a remainder of the stator (such as a stator frame) 14 to offer valuable insights into the effectiveness of charge dissipation by the system 10. Also connected to the system bus 28 are an indicator 38 for providing a human perceptible visual and / or audible indication to a user which is dependent upon the measured voltage, and a communication module 40 for facilitating communication over a network with a remote device.

[0041] The processing unit 30 is configured to receive a measured voltage from the voltmeter 36 and to generate at least one signal which is dependent upon the measured voltage. In the example embodiment, the signal comprises a first signal containing data relating to the measured voltage, which is transmitted to the indicator 38, in the form of a display, for displaying the measured voltage in real-time. It is envisaged that the signal could also comprise a second signal which is generated if the measured voltage is below a predetermined threshold, and / or a third signal which is generated if the measured voltage equals or exceeds a predetermined threshold. It is envisaged that in addition to or as an alternative to the display, the indicator 38 could comprise a speaker or light, wherein upon receipt of the second or third signal the indicator 38 will provide an indication to the user of whether the measured voltage is below, equals or exceeds a predetermined safe threshold.

[0042] The communication module 40 receives and on-transmits the first, second or third signal, as the case may be, via a network, for reception at a remote location. The communication module 40 could be configured to communicate via a wired or wireless network protocol, preferably, Ethernet, Bluetooth®, Wi-Fi, or the like. Turning to Figure 5, the grounding system 10A is similar to the grounding system as set out hereinabove, save that the contacts 22A of the grounding system 10A comprise lines which are arranged in groups, with each pair 24.1 , 24.2 including a pair of groups.

[0043] The invention further provides a grounding kit (not shown) comprising the shaft grounding system 10 or 10A described herein and multiple conductive arrangements 20, allowing for easy replacement and maintenance of the system.

[0044] It is envisaged that the system 10 enables the seamless transfer of electrical signals or power, allowing the rotating equipment to operate without interruption. The system’s intuitive monitoring and feedback system 26 empowers users to proactively monitor motor health, detect potential issues, and take corrective action as needed, thereby safeguarding motor integrity and optimising operational efficiency and prevent potential damage to motor systems. Some of the benefits of the grounding system 10 compared to conventional grounding system include:

[0045] 1 . Metal to metal contact that maintains a low, stable impedance path over a wide frequency and voltage range.

[0046] 2. Resilient contact elements that shed oil or grease contamination and do not absorb contaminants.

[0047] 3. A modular conductive arrangement that can be replaced rapidly in the field.

[0048] 4. An integrated monitoring subsystem that delivers real time diagnostic information locally and remotely It will be appreciated by those skilled in the art that the invention is not limited to the precise details as described herein and that many variations are possible without departing from the scope of the appended claims.

Claims

CLAIMS1 . A shaft grounding system for an electric apparatus having a housing and a shaft mounted for rotation within and extending from the housing, the system comprising: a collar attachable to the shaft for rotation with the shaft, the collar defining a circumferential contact surface that includes a first electrically conductive metal; and a stator mountable to the housing and positioned radially outward of the collar, the stator including a conductive arrangement that includes at least one contact element configured to abut the contact surface during shaft rotation to conduct electric charge from the collar, the contact element including a second electrically-conductive metal.

2. The shaft grounding system of claim 1 , wherein the first and second metals are dissimilar.

3. The shaft grounding system of claim 1 , wherein the first and second metals are the same.

4. The shaft grounding system of claim 1 , wherein one or both of first and second metals comprise at least one noble or precious metal selected from the group consisting of gold, silver, platinum, and alloys thereof.

5. The shaft grounding system of claim 1 , wherein the contact surface is defined by a conductive sleeve affixed to a periphery of the collar.

6. The shaft grounding system of claim 1 , wherein the contact surface is grooved or raised relative to an adjacent surface of the collar.

7. The shaft grounding system of claim 1 , wherein the collar comprises a plurality of axially spaced contact surfaces.

8. The shaft grounding system of claim 1 , wherein the contact element comprises at least one line, band, or filament.

9. The shaft grounding system of claim 1 , wherein the contact element is elongated and oriented transversely with respect to an axis of rotation of the shaft.

10. The shaft grounding system of claim 1 , wherein the contact element is resiliently biased to maintain engagement with the contact area during rotation of the shaft.1 1 . The shaft grounding system of claim 1 , wherein the conductive arrangement comprises a plurality of contact elements wherein at least some of the plurality of contact elements are configured to extend in parallel with each other or at an obtuse angle relative to each other.

12. The shaft grounding system of claim 1 , wherein the conductive arrangement is removably secured to a remainder of the stator.

13. The shaft grounding system of claim 1 , further comprising a monitoring system including: a voltmeter operatively coupled between the contact element and a remainder of the stator; - a processor in communication with the voltmeter and configured to generate at least one status signal representative of a measured shaft-to-ground voltage; and an indicator in communication with the processor and configured to generate a visible or audible indication responsive to the status signal.

14. The shaft grounding system of claim 13, further comprising a communication module configured to transmit the status signal to a remote device via a communication network.

15. A grounding kit comprising the shaft grounding system according to any one of the preceding claims and at least one additional conductive arrangement.

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