This video shows everything you need to install AEGIS Shaft Grounding Rings with conductive epoxy.
The “Greening” of America’s Buildings: The growing “green” movement has led to a flood of new standards including the US Greens Building Councils Building Performance Initiative, the Green Building Initiative, and LEED — all aimed at increasing energy efficiency and sustainability. Challenged to reduce energy consumption and to document savings, America’s facilities managers are installing variable frequency drives (VFDs) in HVAC systems as one of the best ways of achieving such savings.
The Promise of VFDs: VFDs reduce energy consumption by allowing motors to run less than full speed. When used to control air conditioning, air handling,
or pump motors, VFDs can yield energy savings of 20 ~ 30% or more by allowing motors to run at reduced speeds to compensate for changes in load.
The Need for Shaft Grounding on VFD-Driven Motors: But, VFDs can damage the motors they control. They induce currents on motor shafts that discharge through the bearings, causing pitting, fluting, and catastrophic motor failure. Without bearing protection, any savings from the use of VFDs can be
quickly wiped out by the cost of replacing motors and by system downtime. To make HVAC systems sustainable as well as energy efficient, a reliable method of bearing protection is required.
Proven, Long-Term Bearing Protection: By diverting bearing currents safely to ground, AEGIS® SGR Shaft Grounding Rings ensure the reliable, long-term operation of VFD driven motor systems, locking in energy savings and making these systems truly sustainable and truly green.
AEGIS® Shaft Voltage Tester™ Digital Oscilloscope to Test VFD-Controlled Motors for Damaging Shaft Voltages
Industrial motors controlled by variable frequency drives (VFDs) are at risk of electrical bearing damage. The new AEGIS® Shaft Voltage Tester™ Digital Oscilloscope makes it easier than ever to check in-service motors for damaging VFD-induced shaft voltages and head off bearing damage and costly unplanned equipment downtime. Read the rest of the article…
In our October 2016 e-newsletter we mentioned that “…by limiting the amount of inrush current to motors, VFDs can also extend motor life.”
This inspired some conversation so to provide more information we looked at what Jerry Muehlbauer of Marathon Electric had to say on the subject. In a Q&A he address the subject as follows:
Q: Can a motor handle more starts/hour on VFD power?
A: Yes, provided that the VFD is properly tuned and its output frequency is steadily increased (or ‘ramped up’) from zero to the set point and the motor is not ‘line-started’, which causes extremely high (6-8 times rated) motor currents. When a motor is line-started the enormous heat generated in the motor windings limits the number of starts/hour (motor must cool down between starts). Line starting could be compared to starting your car while on jack stands: Put it in gear, start the engine, place a brick on the gas pedal, and then push it off the jack stands. This results in uncontrolled acceleration & huge mechanical stress on the transmission and engine. How many times can you do this before something breaks? Across the line (ACL) starting produces similar thermal and mechanical stresses in the motor and driven load. According to NEMA MG1, the life of a motor is basically determined by the number of ACL starts.
When the VFD ramps up the output frequency, inrush current is eliminated and mechanical stress is greatly reduced, permitting the motor to be repeatedly started without significantly shortening insulation life. Acceleration rates as short as 1/2 second (for small motors) or 1-2 seconds (for larger motors) are still long enough to avoid high inrush currents. In the automotive example, this is comparable to starting the engine, putting the transmission in gear, then driving away at the selected acceleration rate.
Excellent article on the many things which must be looked out for wen handling or installing bearings in electric motors. Published in the M+R (maintenance + Reliability) section of Maintenance Technology Magazine, the article, also available on line at http://www.maintenancetechnology.com/2016/09/handle-bearings-care/ lists 9 different conditions or practices and gives great advice on each. Of course, each section is a topic in and of its self and the one I would like to discuss in some more depth is on:
Electric Current Arcing:
Most pitting in a motor’s bearings comes from one of 2 sources: (1) Capacitive coupled voltage from the stator to rotor through parasitic capacitance on all motors operated by a variable frequency drive (VFD)from small 1 HP to the largest medium voltage motors and (2) high frequency circulating currents which can occur on motors over 100 HP. Separate mitigation is necessary to protect the bearings from these two sources of bearing currents.
The phenomenon for the creation of electrical discharges is similar for both. Essentially the voltage on the motor’s shaft creates a potential high enough to overcome the dielectric of the oil film in the motor’s bearings. When this happens an electrical arc shoots through from the inner race via the rolling element to the outer race which is connected to ground.
The energy in this arc is great enough to melt the hardened bearing steel and create an electrical discharge machining (EDM) pit in the bearing race. The steel surface melts and the metal hardens on the rim of the EDM pit. Then the rolling element can either deform the bearing race surface or break the metal particle and contaminate the bearing. Last but not least, the lubrication burns and deteriorates.
This process can occur MILLIONS of times per hour and after just a short while the bearing surface is pitted and a phenomenon known as “fluting” starts. This is a washboard type pattern along the bearing race creating vibration, heat and eventual bearing failure.
How do we stop this from happening?
First: Download the AEGIS Bearing Protection Handbook!
Low-Voltage Motors up to 100 HP: Install AEGIS® Shaft Grounding Rings for these motors usually on the drive side, either internally or externally.
Motors over 100 HP: Install one AEGIS® Shaft Grounding Ring on the drive end AND and insulated bearing on the non-drive end opposite the shaft grounding ring which prevents circulating currents that may be present in addition to capacitive induced shaft voltage.