Underwriters Laboratories (UL) has an approved set of procedures for installing AEGIS® shaft grounding rings inside explosion proof (XP) motors. XP motors with AEGIS® rings installed according to these procedures may be used in hazardous environments, Class I: Division 1.
The following diagrams are the approved installation locations inside the XP motor.
Note: In Class I: Division 2 designs. Because shaft grounding devices must be installed inside explosion proof enclosures (as per IEEE 303) for Class I: Division 2, they may not be installed internally or externally in/on a non-XP motor.
At this time, Marathon Electric is the only electric motor manufacturer marketing XP motors with AEGIS® shaft grounding protection installed inside. They range from 3 HP (182T Frame) to 50 HP (326T Frame) and Marathon Electric will install AEGIS Rings in larger models. For more information on Marathon Hazardous Duty motors with AEGIS® Inside. For catalog numbers and pricing, see the highlighted “-P” motors on the Hazardous Duty™ pages of the 2014 catalog.
To install AEGIS® rings in explosion proof motors in a hazardous environment, a motor repair shop must first be UL approved to work on all XP motors. They must then apply for certification for the addition of adding shaft grounding to their UL binder and then demonstrate adherence to the additional set of procedures required for installing shaft grounding inside of XP motors.
Motor repair shops with UL certification to work on XP motors and certification of their ability to add shaft grounding can “rework” any size explosion proof motor and then re-nameplate the motor as explosion proof. The drawing below was created by UL to show where the ring must be installed to comply.
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.
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.
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.