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DHi's Metal Fiber Brush Shaft Grounding System Will Be Used Within A South African Electric Power Generation Facility To Prevent Damage To Turbine Bearings
MANASSAS PARK, Va., Oct 13, 2011 (BUSINESS WIRE) -- Defense Holdings, Inc.(R) (DHi(R)) has announced that it has received an initial contract from Machine Assessment and Reliability Technology Pty (MARTEC), its exclusive distributor in South Africa, for long-life, low-maintenance metal fiber brush shaft grounding system. This initial system will be installed within an Eskom coal-fired electric power generation facility. The shaft grounding systems will be used as bearing isolators to control and eliminate errant electrical current from damaging bearings and other internal components within the facility.
Shaft Grounding Electric Brushes for Protecting Motor Bearings in a Variable Frequency Drive (VFD)
High speed rotating components such as turbines and generators develop static charges on their shafts. As the static charge seeks ground, the resulting current transmitted through the bearings results in rapid damage to the bearing surfaces. The phenomenon is particularly acute in Variable Frequency Drive (VFD) motors. The VFD carrier pulse frequency is typically 1-20 kHz. The capacitance between the motor stator and the rotor induces a stray voltage on the VFD rotor shaft. If this voltage reaches a level greater than can be withstood by the bearing grease, it can discharge to ground through the motor shaft bearings. Each time it builds up and discharges, the bearing undergoes an electrical discharge machining (EDM) effect, initially pitting the bearing's rolling elements and raceways and, over time, grooving the bearing race and leading to bearing failure.
Shaft Grounding Electric Brushes are electromechanical devices that offer a low-resistance path around the bearings to prevent VFD stray electrical currents from damaging motor bearings and other internal components. Shaft grounding systems are very important as bearing isolators in a VFD. Traditionally, shaft grounding systems have used carbon brushes (a high resistance, monolithic brush made from graphite, which sometimes has added silver or copper). These electric brushes abrade over time, creating harmful and conductive carbon dust particles, wearing or gouging the surfaces they run on and requiring frequent maintenance.
Metal Fiber Electric Brushes as Bearing Isolators
To solve this problem, Defense Holdings, Inc (DHi) originally developed Metal Fiber Brushes for use on submarines under the Small Business Independent Research (SBIR) program working with HiPerCon, LLC, the U.S. Navy, and the University of Virginia. Metal Fiber Brushes, which gain their name from the fact that they are electric brushes constructed of thousands of hair-fine silver alloy fibers running on their tips, offer significant improvement over carbon brushes in contact resistance. DHi's metal fiber brush resistance contact drop across the sliding surface is < 1 milliohm ensuring the path of least resistance is through the brushes and not through the bearings. DHi's metal fiber brushes also far exceed carbon brushes in both data and current transfer, offering extended brush and slip ring service life of at least twice the service life of carbon brushes, high current capacity of 250 amps/inch2, and significant decreases in service acoustic and electrical noise at sliding speeds up to 70 m/second. These brushes produce 80% less wear debris than solid brushes reducing the need for expensive maintenance and reducing the potential for short and grounds. Metal Fiber Brushes, with their low spring force, are far less likely to damage shaft running surfaces than carbon brushes or carbon-metallic brushes. Metal Fiber Brushes' silver alloy fiber offers significantly better service life and higher sliding speeds over other competing shaft grounding technologies.
HiPerCon, LLC is the worldwide exclusive licensee for this technology. DHi is HiPerCon's sole distributor for Metal Fiber Brush and slip ring products including HiPerCon's line of shaft grounding brushes.
Rich Martin, DHi's President and CEO, States...
Rich Martin, DHi's President and CEO, states, "We are really excited to be working with MARTEC. We strongly believe that our shaft grounding system using HiPerCon's amazing Metal Fiber Brush (MFB) technology provide a one-of-a-kind shaft grounding solution offering low maintenance, long life and high reliability. Our shaft grounding systems build on lessons learned from our successes in the application of slip rings featuring Metal Fiber Brushes in nuclear submarines, fixed and rotary wing aircraft, and wind turbines. It is clear that the ability of HiPerCon brand brushes to overcome the limitations of carbon brushes and carbon-metallic brushes is a game-changer for those who require long shaft grounding system life, high reliability and minimal conductive wear debris."
Mario Kuisis, General Manager of MARTEC states, "We are very pleased to have entered into the agreement with DHI since we see a great future for the innovative technology to solve some difficult current collection problems and enhance reliability and performance of a range of industrial and utility power plant. We are excited to have placed our first order for DHI shaft grounding systems for use on large generators where the special properties of MFB's will be fully exploited."
Founded in 1994 and originally operated as Noesis, Inc., DHi is a privately-held, service-disabled, veteran-owned, minority-owned, small business. DHi has been ISO 9001 registered since 2003 and has received awards from the federal government for outstanding technical innovation and performance. DHi is based in Manassas Park, VA with other facilities in Charlottesville, VA and Trenton, NC. DHi works with customers worldwide to overcome the limitations of conventional carbon and carbon-metallic brushes and slip ring systems in a wide variety of applications. DHi has been ISO 9001 registered since 2003 and has received awards from the local, state, and federal government for outstanding technical innovation and performance.
Machine Assessment and Reliability Technology Pty (MARTEC) is located in Ferndale, Randburg, South Africa. MARTEC represents DHi exclusively in South Africa for the sales of DHi's shaft grounding technology products. Although MARTEC is a small company, its experts in reliability enhancement technologies are a highly skilled team with a wealth of hard-earned industry experience, each of whom is passionate about integrity, quality and reliability of service. Because it is small, MARTEC believes it can better offer personalized attention to our customers. MARTEC represents 12 manufacturers from around the world, each of whom is a global leader in his specialist field.
| Product Model | Inside Diameter | Outside Diameter | Thickness |
| 766/752 KOYO | 88.9 | 161.925 | 48.26 |
| 864R/854 KOYO | 95.25 | 190.5 | 57.531 |