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This Web Exclusive article is contributed by Electro Static Technology, maker of AEGIS shaft grounding products. Increasing Sustainability Of Motors In Manhattan’s Time & Life Building A preventive maintenance plan that reduced the total life cycle cost of operations in a prominent building at the heart of New York City serves as an example of how the push for more sustainable building management has led to a growing awareness of a chronic, widespread problem with HVAC motors — electrical bearing damage. The problem is all too common in AC motors controlled by variable frequency drives (VFDs), which are also known as inverters, adjustable speed drives, etc. These drives are widely used because they can save energy, especially in applications with varying loads. Because many centrifugal fans and pumps run continuously, their motors will use less power if the input is modulated by VFDs. For example, a 20% reduction in fan speed can reduce energy consumption by nearly 50%. With rising energy costs, the use of throttling mechanisms to restrict the work of a motor running at full speed would be wasteful. However, efficiency alone is not enough if equipment keeps breaking down. That is what had been happening for two decades at the 48-story Time & Life Building, one of 19 buildings in the Manhattan business and entertainment complex built and partially owned by the Rockefeller Group and known as Rockefeller Center. The building’s HVAC system can be powered by either natural gas or electricity, enabling management to switch back and forth to take advantage of whichever source costs less at the time. More than 100 VFDs control the speeds of the 240 motors that run the building’s HVAC fans and pumps. Unfortunately, a large portion of the savings from these systems had been wiped out by maintenance costs because, in addition to their intended function, VFDs induce powerful, unwanted currents which cause electrical bearing discharges and, ultimately, premature motor failure. The Role Of Shaft Grounding Proper tuning of a drive’s frequency output range and proper grounding of a VFD-controlled motor’s frame are paramount. Only in recent years has it become clear that without an effective shaft grounding device as well, stray currents can wreak havoc with bearings, causing premature motor failure. Ironically, some products designed to protect bearings, such as conventional metal grounding brushes, require extensive maintenance themselves. Others, such as insulation, can shift damage to connected equipment. One of the newest and most promising bearing damage mitigation devices uses patented advanced electron transport technology to safely bleed off… …Read More…
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