Solving premature bearing failures with Shaft Grounding techniques is a Mechanical Solution to an Electrical Issue.
Grounding Rings do not get rid of the destructive currents. They simply and effectively provide a path to motor casing. If the electric motor casing is not properly grounded, that stray current can and will go into other parts of the system…back to VFD, to the load, etc. To date this process is the most common and effective as long as the grounding ring is properly maintained and Grounded. “Properly Maintained” is an important key component of this equation. Over time these mechanical grounding rings are susceptible to external contamination which results in little to no effectiveness for shaft current grounding.
Industrial Electrical has recently been researching and experimenting with Inductive Absorber technology. Inductive absorption is an Electrical Solution whereas inductive components are placed over the drive cables to absorb the transient voltage and common mode currents.
Quick review on how that works …..
Shaft Grounding Rings
- Installation is not an exact science. In order for the grounding ring to work sufficiently, it must be properly aligned with fibers touching all sides, at all times.
- Shaft must be completely free of contaminants, and in some cases a coating must be applied to the shaft, which adds cost.
- They have to be replaced every time anything is done inside the motor, i.e. new bearings are installed.
- Literally hundreds of products to fit hundreds of different motor shafts or motor sizes.
- On systems above 75HP, a hybrid or coated bearing/raceway is needed on non-load side of motor.
- Shaft must remain clean from contaminants. Any material, oil/grease/corrosion/other, will cause the fibers to loose contact, and lose their ability to properly shunt the currents to ground.
- One product per motor. For example, a simple wall of fans driven by one drive, requires all motors to have grounding ring installed.
- Grounding rings do not get rid of the destructive currents. They provide a path to motor casing.
Inductive Absorbers / Common Mode Choke
Inductive Absorbers absorb the noise on the power cables generated from the VFD before it gets to the motor. The cores act as a common mode choke (CMC) in this given configuration, and dissipates into thermal. No motor modifications, no shaft preparation, very easy installation. Can be added to systems with very minimal downtime.
Lasts the lifetime of system
- Installation can be done in a matter of minutes, on site.
- Shaft contaminants are not an issue since the currents are absorbed well before the motor.
- No extra parts because of motor keyways or wash-down applications. Cores are installed between motor drive and motor, even in harsh conditions.
- Last a lifetime of the system. Since it is not mechanical, they only need to be installed once.
- No hybrid or ceramic coated bearings needed, no matter the size.
- Common mode chokes are designed to absorb common mode currents BEFORE they get to the motor.
Industrial Electrical Company is now stocking CoolBlue Inductive absorbers and has trained technicians available to you, on-site, to perform system diagnostics, Furnish and installation of CoolBlue Absorbers, and conduct Post testing with reporting on shaft current mitigation. If you would like to minimize your reoccurring costs of purchasing Electric Motors with added Mechanical Shaft Grounding, Costly Downtime derived from neglected Grounding Devices or poorly grounded equipment. Consider asking us about CoolBlue and how we can help extend your uptime and reduce your cost of ownership.