AEGIS Bearing Protection Ring™ Outside Study - L&S Electric Paper.pdf · electrical discharge...

31 Winterbrook RoadMechanic Falls, ME 04256-5724 Toll free: 1-866-738-1857 Ph: 207-998-5140 Fax: 207-998-5143 [email protected] www.est-aegis.com

Test Report International Paper AEGIS Bearing Protection Ring™ Outside Study

Test Period: Feb 2008 to July 2008 Purpose: To protect VFD driven motors from

electrical bearing damage. Application: Inverter driven motor application Location: International Paper-Loveland, OH Product Development Center Motor: Siemens motor type: RGZEESD 143T NEMA Premium Efficiency Shaft diameter 0.875” inches

AEGIS SGR installed at Electro Static Technology-ITW and shipped to IP for testing Motor 1 Motor 2

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Test Set-Up:

• 2 Siemens motors (Type: RGZEESD), NEMA Premium Efficiency Motors 143T, shaft diameter 0.875”. • Motor #1 had a ground lead to monitor current. Motor #2 was grounded through end bracket via standard

mounting hardware. • ETE Sleeve was fitted over the motor shaft and secured with set screws. The OD of the sleeve was

coated with Ted Pella Fast Drying Silver Paint PN 16040-30. • AEGIS SGR was mounted to a NEMA mounting kit. The assembly was mounted over the ETE Sleeve

(sleeve OD 1.955”). Fibers were in direct contact with the silver paint, 360˚ around the shaft. • Motors ran concurrently for approximately 6 months on a PWM invertor. • Motors were disassembled and bearings cut. Half of the cut bearings for each motor were shipped to EST

for evaluation. Motor#1 was also sent back to EST. DE and NDE bearings were sent to the University of New Hampshire SEM Lab for independent observation.

• Bearings were analyzed using an AMRAY 3300 FE scanning electron microscope (SEM). Microscope parameters: 7kV, 30mm=Z, C1= -20, tilt=0˚

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Reference Images Bearing Race Comparison

New bearing race: Viewed under a scanning electron microscope, a new bearing race wall is a relatively smooth surface. As the motor runs, a track eventually forms where the bearing ball contacts the wall. With no electrical discharge damage, this type of mechanical wear would be the only cause of degradation.

Pitting and Frosting: During virtually every VFD cycle, induced currents discharge from the motor shaft to the frame via the bearings, leaving small fusion craters in ball bearings and the bearing race wall. These discharges are so frequent that before long the entire bearings race becomes riddled with pits known as frosting. The damage eventually leads to fluting, noisy bearings and bearing failure. Since many of today’s AC motors have sealed bearings to keep out dirt and other contaminants, electrical damage has become the most common cause of bearing failure in AC motors with VFD’s.

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Motor # 1: Drive End Bearing Observation: 14.5x magnification No frosting or fluting

Motor #1: Drive End Bearing Observation: 1000x magnification No frosting or fluting Note: Vertical lines are grinding lines which are made during the manufacturing process of the bearing.

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Motor #1: Non-Drive End Bearing Observation: 14.5x magnification No frosting or fluting

Motor #1: Non-Drive End Bearing Observation: 1000x magnification No frosting or fluting Note: Vertical lines are grinding lines which are made during the manufacturing process of the bearing.

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Motor #2: Drive End Bearing Observation: 14.5x magnification No frosting or fluting

Motor #2: Drive End Bearing Observation: 1000x magnification No frosting or fluting Note: Vertical lines are grinding lines which are made during the manufacturing process of the bearing.

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Motor #2: Non-Drive End Bearing Observation: 14.5x magnification No frosting or fluting

Motor #2: Non-Drive End Bearing Observation: 1000x magnification No frosting or fluting Note: Vertical lines are grinding lines which are made during the manufacturing process of the bearing.

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Background: Electrical voltages are induced onto the shaft of the inverter driven motors by the pulse width modulation (PWM) variable frequency drives (VFD) through parasitic capacitive coupling. The high frequency voltage changes (dv/dt) of the VFD switching pulses induce high frequency bearing currents while the drive is operating. Damaging currents arc through the dielectric oil film between the rolling elements and the bearing race. This is known as electrical discharge machining (EDM) effect. EDM causes pitting, frosting and fluting in the bearing race and ball which results in shortened bearing life and premature motor failure.

Typical oscilloscope image of shaft voltage.

Objective: • Increase motor/bearing life and reliability when PWM inverter technology is used.

• Protect motor from VFD induced shaft voltages and bearing currents.

• Divert destructive bearing currents to ground through a conductive micro fiber Bearing Protection Ring™.

• Improve system reliability and life.

Motor Protection Methodology: • Divert current away from the bearing by using conductive micro fiber AEGIS Bearing Protection Ring.

• Conductive micro fiber should be in 360˚ contact with shaft.

• Establish voltage discharge path to ground through conductive microfibers.

Test results: • Motor #1 & 2: No EDM present in bearing. No evidence of electrical discharges during the 6 month

test period.

• Note: A very small number of pits were visible in 1000x SEM images.

Conclusions:

1. Motor bearings had no evidence of frosting or fluting damage. 2. AEGIS Bearing Protection Ring eliminates the risk of EDM and the possibility of premature motor failure

due to discharge currents in these applications. Recommendations:

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VFD controlled Motors up to 100 HP (75 kW) Install one AEGIS SGR Bearing Protection Ring on either the drive end or the non-drive end of the motor. The simplest installation is to slide the AEGIS SGR over the drive end and fasten it to the motor end bell with the easy to install mounting hardware included with each AEGIS SGR.

VFD controlled Motors 100 HP to 1000 HP (75 kW to 750 kW) Large motors above 100 hp will have VFD induced EDM currents as well as high frequency circulating currents when they are controlled by VFDs. To protect the bearings, insulate the bearing on one end and install AEGIS SGR on the other end. If insulating one bearing is not possible, install an AEGIS SGR Bearing Protection Ring on each end of the motor..

John Shepherd Electro Static Technology-ITW 11765 Woodwind Drive Loveland, OH 45140 Cell: 513-417-1161 [email protected]

For more information please contact: Adam Willwerth Electro Static Technology-ITW 31 Winterbrook Road Mechanic Falls, ME 04256 Ph: 207-998-5140 Fx: 207-998-5143 [email protected] www.est-aegis.com

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http://www.est-aegis.com/

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AEGIS Bearing Protection Ring™ Outside Study - L&S Electric Paper.pdf · electrical discharge...

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