The annual AHR Exposition is the HVAC/R industry’s largest trade show.  The purpose of the exposition is to present the latest tools and technologies that allow HVAC/R professionals to keep up with the state of the art.  AHR shows typically have at least 2,000 exhibitors, and over 60,000 visitors. That’s the population of a small city!

The exposition has something for everyone involved with HVAC:  from manufacturers and engineers, to contractors and facility operators, to professors and technical school instructors.  In addition to the 2,000-plus exhibitors, there will be 210 learning sessions, most of them free.  You can see the full itinerary here, or see more reasons to attend here.

The next Expo will be in Atlanta, from January 14-16, 2019, at the Georgia World Congress Center.  This will be the first AHR Expo in Atlanta since 2001.  Advanced registration is free until January 9th, and after that is $30.

While you’re there, be sure to stop by the AEGIS Shaft Grounding booth, #C5562.  We’ll be having a drawing to give away a $200 LL Bean gift card!  We’ll also have Bearing Protection Handbooks and other handouts, samples of motor bearings that were ruined by variable frequency drives, and live demos showing how AEGIS rings bypass that damage.  Hope to see you there!

Read the New White Paper

Summary:

The use of variable frequency drives (VFDs) to control AC motors has increased dramatically in recent years. In addition to their low operating cost and high performance, they save energy. Today, the challenge facing system designers and engineers is to minimize damage to AC motors from bearing current. From its first minute of operation, a VFD induces destructive voltages that build up on the motor shaft until they find discharge paths to the frame (and then to ground).

Micron-sized pits are formed by shaft voltage arcing through the bearing. Pits accumulate to form visible frosting, which may in turn produce fluting.

In most cases, the motor bearings present the path of least resistance. Once voltage is sufficient to overcome the resistance of the oil film layer in the bearing, shaft voltage discharges, causing electrical discharge machining (EDM) pits — fusion craters in the race wall and ball bearings. This phenomenon continues until the bearings become so severely pitted that fluting, excessive noise, and failure occur.

Over the years, researchers have proposed many solutions to minimize this damage and prevent premature failure. These range from blocking current flow with bearing insulation, to allowing current to flow without arcing by using conductive grease, to diverting the current by grounding the shaft. No one method is perfect for all motors, in all situations.

The shaft grounding ring is one of the newer and more effective methods. Like older carbon grounding brushes, they provide a low-resistance path from shaft to ground, so current flows through the brush, not the bearings. But shaft grounding rings have several advantages over grounding brushes and other methods of bearing protection.

To read the full white paper, click here.

Electro Static Technology has been added to the
NCEES CPC Registry

The National Council of Examiners for Engineering and Surveying (NCEES) is an American nonprofit group whose mission is to advance licensure for engineers and surveyors.  Among many other things, they provide a number of tools to help engineers become licensed, and to stay licensed.

NCEES logo and sloganOne of these tools is MyNCEES, a webservice that allows engineers to store all of the documents that they need for license applications and renewals.  One big part of this is continuing education, which they call CPC (Continuing Professional Competency).  NCEES maintains a registry of listed providers of CPC courses.  So when an EIT or PE takes a course taught by one of these listed providers, they can just log into MyNCEES, select the listed provider from the list, and log all of their CPC hours in the same place.

No need to print certificates of completion, no need to wonder where on your computer you saved those records:  MyNCEES logs and stores those records, and, when the time comes for license renewal, it can submit them to the appropriate state licensure boards.  MyNCEES takes a time-consuming process and makes it quicker and easier.

So we at Electro Static Technology, manufacturer of AEGIS® Shaft Grounding Rings, are excited to have been added to the NCEES CPC listed provider registry.  This means that when most engineers attend an AEGIS Lunch & Learn or take our webinar course, Electrical Bearing Protection Best Practices, they can use MyNCEES to log, store, and submit the course for CPC.

At the moment, the AEGIS training is not valid for continuing education credit in Florida, New Jersey, New York, or Maryland.  The licensure boards of these states require courses to be preapproved in order for engineers to get credit for them.  We are working on gaining this approval.  In the meantime, engineers licensed in the remaining states, and in DC, Guam, the Northern Mariana Islands, and Puerto Rico, can quickly and simply log their AEGIS training using MyNCEES.  Find out when our next live webinar is and give it a try!

Today, there are hundreds of types and blends of plastics, and they can be formed, molded, extruded, blown, and otherwise fashioned into a dizzying array of products. Processing equipment must be precisely controlled to ensure the quality, durability, and finish of final products at every stage of processing.  This goes for every operation, from the production of raw chemical ingredients; to their blending and polymerization to produce pellets, sheets, or blanks; to the forming of finished products.

Inflater flanked by control panel

Variable frequency drives (VFDs) can provide the precise control of motor speed and torque required for a broad range of plastics processing applications, whether the motors drive pumps, conveyors, compressors, blowers, or any other equipment.

But VFDs can damage the motors they control. They induce voltage on motor shafts that causes electrical arcing through the bearings.  This arcing causes pitting in the bearing, leading to fluting and catastrophic bearing failure.  Bearing failure in turn causes unplanned downtime, and the colossal costs of lost production can quickly wipe out any benefits from the use of VFDs.  The bearings must be protected to minimize the risk of downtime due to bearing failure.

Plastics production processes typically involve very large runs, and machine failures can shut down production, resulting in costly repairs and huge revenue losses. So when the 300 HP motor for an injection molding machine at a North Carolina plastics plant experienced premature bearing failure, plant engineers wanted to know why. Testing showed that shaft voltage discharge through the bearings was the cause of the failure.

After doing some research, plant engineers learned about AEGIS® Shaft Grounding Rings.  Shaft grounding rings give electric charge on the shaft a low-resistance path to ground. So rather than arcing destructively through the bearings, voltage bleeds off harmlessly through the grounding ring. The engineers decided to try an AEGIS Ring.

Shaft voltage readings on an injection molder’s motor before and after installation of an AEGIS Ring

Before they installed the ring, the motor showed shaft voltage up to 25-30 volts (peak to peak). After installation, the shaft voltage was decimated, weighing in at just a couple of volts at most. The ring was obviously working: The shaft voltage had decreased to levels too low to discharge through the bearings.

So AEGIS Shaft Grounding Rings perform as advertised. And unlike any other form of electrical bearing protection, these rings are backed up with a two year manufacturer’s warranty.  For details, see the AEGIS warranty page.

ABB’s new Variant Code for IEC Low Voltage Motors (VC588) uses AEGIS® Shaft Grounding Rings installed inside the motors to mitigate the effects of bearing currents.  In various publications, ABB has described the phenomenon of bearing current as follows.

Bearing currents can be divided into four different categories:

This bearing has been exposed to bearing current. Note the EDM damage to the race track and bearing elements. Photo courtesy of SKF.

  • Electrostatic discharge currents (EDM)
  • Capacitive bearing currents
  • Circulating currents
  • Rotor ground currents

In detail, the three partial mitigation techniques for bearing currents are:

  • Incorporating an insulated bearing at the non-drive end
  • Using a common mode filter in conjunction with a VSD
  • Earthing and cabling of transformer, VSD, motor, and load-train

How to deal with persistent bearing current issues

The two new enhanced approaches to solve the persistent bearing current problems are:

Cutaway image of an ABB motor, showing the AEGIS ring installed inside.

An AEGIS Shaft Grounding Ring is used to solve bearing current problems. Image courtesy of ABB.

  • AEGIS Shaft Grounding Rings installed internally
    An important new solution for motors in IEC frame sizes 132 to 250is to install an AEGIS Shaft Grounding Ring that directs the current to ground via the ring, rather than through the bearing. This protects the motor itself and the complete installation. The ring can be pre-installed on new motors by specifying the variant code VC588. Or it can be retrofitted on-site.
    Note: AEGIS Shaft Grounding Rings can be installed on all sizes of motors.
  • Insulated bearings at both the drive and non-drive ends

How can you measure bearing currents?

In most cases it is difficult for operators to measure any bearing current that might be present on a standard motor.  But if bearing currents are suspected they can be detected using special equipment operated by experienced personnel.  ABB has developed vast experience in carrying out these measurements on motor and drive installations in a variety of different applications worldwide.  You also can use the AEGIS Shaft Voltage Tester, an oscilloscope, to measure shaft voltage and clearly detect the EDM discharge pattern.

Shaft voltage discharge and fluted bearing

Shaft voltage reading showing bearing current and fluted bearing race, from a motor not protected with an AEGIS Shaft Grounding Ring

Low shaft voltage and undamaged bearing

No bearing current indicated in shaft voltage, and undamaged bearing race, of a motor protected by an AEGIS ring.

Summary:  Bearing currents can be avoided

When bearing current is present, there is no “one size fits all” solution.  It is vital for the user and motor and drive supplier to work together to identify the most appropriate solution for the specific application.  Ensuring the correct use of grounding and connection cables according to best practice will always be an important first step.  New solutions in the form of AEGIS Shaft Grounding Rings in combination with insulated or hybrid bearings are now showing significant promise as a cost-effective way of eliminating the potentially harmful effects of bearing currents.

31 Winterbrook Road Mechanic Falls, ME 04256
Phone: 207-998-5140  Fax: 207-998-5143

Email: [email protected]

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