Today, VFDs are used to provide precise control of a wide range of processes and process variables in manufacturing applications.
By allowing motors to run at less than full speed, VFDs can save energy — often 30% or more. But they also offer other benefits. They can improve equipment and machinery uptime, reduce switchgear and cabling costs, and enable more precise process control. As a result, they can improve productivity, quality, and profitability. But VFDs can cause unplanned motor bearing failures — often in as little as three months.
VFDs Improve Process Control...
When used to control conveyors — belts or overhead lines — VFDs allow line balancing for optimized production and minimal idle time. With their rapid acceleration and deceleration capability, VFDs can also minimize transfer times between production cells. And by providing non-emergency stop and start control, VFDs can also be used to gently slow the speed of inclined conveyors.
For processes that could run at full uncontrolled speed (such as extrusion), VFDs offer greater control by eliminating variations in line voltage or frequency that could cause unwanted variations in the product itself.
VFDs also improve the efficiency of machines that control process variables in industrial production processes such as the speed of heating blowers and cooling fans, air compressors, assembly lines, quench lines, filling equipment, wire drawing equipment, etc.
Rather than throttling or braking fixed-speed motors, VFDs control motor speed by controlling the amount of power to the motor itself. And by varying the amount of power to the motor according to precise time curves, VFDs can provide soft starting and stopping — smooth ramp ups and slow downs of machines to reduce wear-and-tear and extend machine life.
And by limiting the amount of inrush current to motors, VFDs can also extend motor life.
And yet, the most impressive benefit from the use of VFDs may well be the energy savings they produce. According to a U.S. Department of Energy study, approximately 25% of industrial motor system energy usage was for pumps, and another 14% was for fans. Rather than diverting, redirecting, or throttling the output of motors that power these devices, VFDs provide a way of precisely matching motor output to load. And the benefits of VFDs extend beyond manufacturing systems to plant/facility systems such as HVAC and air handling systems.
But VFDs Damage Motor Bearings
But despite all the control and energy saving benefits they offer, VFDs can damage the motors they control. VFDs produce voltages on the shafts of the motors they control — voltages that can discharge through motor bearings, causing electrical discharge machining (EDM) pitting, frosting, and fluting failure.
AEGIS® Rings Protect Motor Bearings from VFD Damage
To protect process and facility system motors and prevent crippling, costly downtime, VFD-driven motors need proven long-term bearing protection from damaging VFD-induced shaft voltages.
Proven in millions of installations worldwide, AEGIS® Shaft Grounding Rings channel damaging shaft currents away from bearings and safely to ground.
AEGIS® SGR Rings are available in solid- or split-ring versions, and also as uKITs with mounting brackets that simplify installation on motors with shaft shoulders or end bell protrusions.
For medium-voltage motors and large low-voltage motors with shafts to 30” in diameter, AEGIS® PRO Series Rings also come in solid- and split-ring versions, and may also be mounted on universal mounting brackets.
AEGIS® solid rings are designed for installation on new motors before they are put into service, and split rings are ideal for field installation on in-service motors because they eliminate the need to decouple motors from attached equipment.
In addition, a large and growing number of motor manufacturers now offer motors with AEGIS® Rings factory installed.
For more information on the types of bearing damage VFDs can cause, click here.
For an application story on how AEGIS® Rings solved the ongoing problem of bearing damage to a 1000 HP transfer motor at a pulp and paper plant, click here.
For a list of manufacturers that offer motors with AEGIS® Rings factory-installed, click here.
