The ARC Earthring is a shaft earthing ring designed to protect electric motor bearings from bearing fluting generated by modern-day variable speed drive systems.
“Damaging voltages are induced on the shafts of AC and DC motors controlled by variable frequency drives (VFD),” says Sixth Element Australia. “The extremely high on/off switching speeds of the pulse width modulation (PWM), generated by the insulated gate bipolar transistors (IGBT), induce damaging voltages onto the motor shaft through parasitic capacitive coupling between the stator and rotor. This common mode shaft voltage seeks a path to ground, usually through the motor’s bearings.
“Damaging currents arc through the di-electric oil film between the rolling elements and the bearing race. This is known as electrical discharge machining (EDM) effect. EDM causes fusion craters, severe pitting, and eventually bearing fluting (a washboard-like pattern in the bearing race) which results in premature bearing failure.”
Sixth Element says the ARC Earthrings protect electric motor bearings by diverting damaging discharge voltages to the motor frame and not via the motor bearings. Using highly conductive microfibres, including gold fibre clusters, the ARC Earthrings are designed to provide optimal electric motor bearing protection in harsh and arduous environments.
Earthrings are available for both low- (under 400kW and 600V) and high-voltage applications in solid and split configurations. Sizing is available to suit shaft sizes from 20mm through to 400mm in 20mm increments. The ARC range are fully adjustable, while a standard range of non-adjustable units are also available in solid and split designs to suit both IEC and NEMA type motor frames.
“Fitted to the motor housing via supplied brackets, the Earthrings are easily installed either onsite via maintenance personnel or via repair facilities during maintenance schedules,” says Sixth Element. “Protecting motor bearings from electrical discharge prevents unscheduled costly motor failures resulting in unnecessary downtime and un-budgeted costs.”
Sixth Element says the ARC Earthrings are suited to all AC motor drive systems, including applications such as HVAC fans and pumps, as well as conveyor drives, SAG mills, ball mills, crushers and wash plants. They also feature a contaminant dispersion design allowing the product to be used in difficult applications.
ARC Earthrings are available through Sixth Element Australia. For more information, click here.