Overhead cranes play a significant role in shipping and manufacturing, handling massive loads with precision. However, their motors face a persistent challenge. Stray shaft current can lead to electrical bearing damage. Without proper protection, crane motor bearings fail, requiring repair or replacement, and costly unplanned downtime, especially for large motors.
Why Shaft Grounding is Necessary for Crane Motors
Variable frequency drives (VFDs) have become standard for motors in many industries. They enable precise control of speed and torque, essential in crane applications. However, they also create shaft voltage that discharges through motor bearings. Over time, this electrical discharge causes pitting and fluting damage to bearing surfaces. Eventually, this results in bearing failure.
For container port cranes or other overhead crane systems, motor failure creates massive downtime and productivity losses. Repairing or replacing a large damaged motor often takes 16 hours or more. The operational ripple effects can disrupt entire facilities.
Some attempts to address this issue use insulated bearings or grounding brushes. Insulated bearings usually work well, but are quite expensive. Grounding brushes require regular maintenance and may fail in dirty environments where grease and debris are common. These solutions often fall short of solving the problem entirely.
AEGIS® Shaft Grounding Rings: A Reliable Solution
The AEGIS Shaft Grounding Ring was developed to get around shaft grounding brushes’ shortcomings. For large and medium voltage motors, AEGIS® PRO Rings solve these challenges for motors in demanding applications like overhead cranes. These rings safely channel harmful stray current away from motor bearings. Their six circumferential rows of conductive microfibers provide millions of discharge points to eliminate stray voltages effectively.
AEGIS rings are available both as solid rings and in a split-ring design that makes installation straightforward for in-service motors. The mating halves of the ring can be opened and then closed around the shaft without decoupling the motor from its driven equipment.
AEGIS Shaft Grounding Rings have been proven effective in the real world, in millions of installations. A detailed case study shows how AEGIS® rings resolved chronic motor failures at Pacific Container Terminal.
Case Study: Stopping Chronic Crane Motor Failures
At Pacific Container Terminal, port cranes were experiencing constant bearing damage in their 650-horsepower DC motors. Bearings would fail within one to two months due to shaft voltage arcing through them. Each repair required up to 18 hours of downtime per motor, which resulted in substantial costs.
Initial solutions included insulated bearings and carbon grounding brushes. Neither option fully resolved the problem. Reed Electric eventually installed AEGIS® PRO Rings on the inboard ends of the motors while using insulated bearings on the non-drive ends to block circulating currents.
The results were immediate and impressive. After the installation of AEGIS® rings, the first motor ran without issues for over three months, which was far better than before. Reed Electric overhauled five more motors with the same setup. None showed further damage to their bearings. Encouraged by this success, plans were made to retrofit all remaining crane motors at the terminal with AEGIS® rings.
Long-Term Benefits for Overhead Cranes
Overhead cranes must perform reliably in demanding conditions, in ports and elsewhere, where even brief downtime can disrupt operations. AEGIS® PRO Shaft Grounding Rings offer a proven solution to reduce risk of motor failure and help keep maintenance costs in check.
These rings are trusted worldwide to handle the challenges of crane shaft grounding. To explore how AEGIS® solutions can benefit your equipment, contact us for more information.
AEGIS Rings also come with a 2-year extended warranty against bearing fluting damage. No other form of protection against VFD-caused bearing damage offers a warranty like this.
To learn more about AEGIS shaft grounding and best practices for electrical bearing protection, sign up for a training. We offer monthly live training webinars, and - pandemic restrictions permitting - we can also visit your facility to review your exact application.
