Variable Frequency Drives or VFDs offer a number of factual benefits to any facilities for energy savings and complete process control. They can however generate problems like static buildups and issues for the electric and equipment bearings. Varying frequency may result in electrical discharge and this can cause for the occurrence of an electrical discharge machining (EDM), which may eventually result to premature system and bearing malfunction.
To prevent such problems from happening, use and installation of shaft grounding rings to the electric motors is highly recommended.
Shaft grounding rings are maintenance free and can effectively go up against contamination. Additionally, these rings are particularly apt to be used with high-frequency voltages and currents, because they tolerate current-conduction based on electric field emission too.
Increased demand for Shaft Grounding Rings
As VFD utilization rises, the demand for shaft bearing protection rings also increases. Nevertheless, variable frequency drives are recognized to produce massive amounts of electric current that result to bearing damages. These damaging currents are known as shaft-voltage, which in turn occurs in electric motors and generators due to three major causes; leakage, induction and capacitive coupling.
Stimulated electric motor currents will constantly discover a course that has the slightest resistance for it to ground. Usually, these electric motor currents are discovered in ball bearings that ultimately lead to damage to bearings and motor malfunction. Destructive currents go throughout the dialectic film of oil amid the rolling elements and bearing race and this situation is known as EDM effect, which is responsible for the generation of stern pitting, bearing fluting, as well as fusion craters.
Shaft grounding rings are innovative tools that utilize innovative approach that employs the use of the ring to effectively redirect the shaft current and to supply reliable and steady low impedance course from the shaft to the frame. This is an effective way to completely bypass the motor bearings. The electron transport technology of the ring utilizes ionization principles to increase the rate of electron-transfer and to promote highly efficient high frequency shaft current discharge.
By grounding the motor shaft, lower impedance course is possible to pass through the motor frame than the bearings. Most grounding rings are used externally and may require additional space as well as special mechanical designs for brush mounting.
The electric motors bearings driven by variable frequency drives are at risk of electrical damage due to the inherent nature of parasitic capacitive coupling between the rotor and the stator. The electrical damage is larger than the damage that AC sinusoidal motors had ever displayed before. This electrical damage of the bearings must be lessened to guarantee long service existence of a motor driven by VFD. The bearing current dilemma is regarded as the last outstanding consistency issue that requires to be conquered on VFDs and the conductive microfiber shaft grounding ring development is the best practical solution for bearing current mitigation. It offers far better benefits than previous solutions and techniques.
All images courtesy of Electro-Static Technology.