Consulting-Specifying Engineer - March 2008 - (Page 18)

M/E Roundtable several other VFD options available that will mitigate harmonics right out of the starting gate: 12- or 18-pulse rectifier front-end VFD. This VFD has either 12 or 18 rectifiers in its front end, which eliminates the lowercurrent harmonics, such as the fifth and seventh, allowing only the 11th for the 12pulse, or 17th for the 18-pulse. Active switch rectifier VFD: An active front-end VFD uses insulated-gate bipolar transistors (IGBTs) or other semiconductor switches and pulsewidth modulation techniques to shape the input current waveform sinusoidally with less than 5% THID, and control input power factor to any desired value between 0.8 leading to 0.8 lagging. An added benefit is that it can also convert mechanical energy into electrical, and return it to the ac input lines or power mains. KEN LOVORN: The two key methods of harmonic mitigation in VFDs are input line filters and higher pulse count. However, it should be noted that in the instance where the distribution system is large in comparison to the size of the VFDs, only minor current harmonics will be generated. The pervasive and damaging portion of the harmonics are the voltage harmonics, which are mitigated when the distribution has a large available fault duty and the VFDs are small in relation to the system size. CSE : For existing facilities that have a problem with harmonics caused by drives, what can consulting engineers do to help facilities assess electrical loads in a building to solve harmonic problems? CARR: Generate a list of questions, such as: When did the problem occur? Did anything change in the facility recently that coincided with the problem showing up? Does the problem go away when a particular drive is shut down? Does the problem appear to be related more to the power input to the VFD or to its output? Is the problem more severe when the VFD/motor load is loaded versus unloaded? PEERAN: First, the situation would be assessed by field measurements and by a harmonic analysis. If it is found necessary to mitigate the harmonics, several options such as replacing the older drives with 18-pulse drives or installing harmonic filters would be evaluated. LOVORN: The expensive answer is to have a harmonic study performed at the main electrical service, each motor control center, and each distribution panel. However, a quick and dirty method is to Clean & Fiber-free er-free The black insulation for green solutions Rely on Armaﬂex: The IAQ Insulation™ Th Mold-resistant Armaﬂex insulates mechanical Armaﬂe systems, chilled lines and air ducts without lin Mold Resistant & Low VOC ant V ﬁbers or emissio Cost-effective for ﬁbers emissions. ASHRAE 90.1 an IECC. Made with and Microban® antimicrobial product protection. antim Save time! Ask for our free new !A Product Maste Spec CD. Master nergy Savin ng n Durable & Energy Saving Armacell LLC 1 800 866-5638 • www.armacell.com/us • info.us@armacell.com www.armace MICROBAN is a registered trademark of Microban Products Company. 1249_Armacell_ConSpec_HalfPg_final.indd 1 Input #211 at csemag.com/quickResponse 2/23/08 11:04:36 AM 18 Consulting-Specifying Engineer • MARCH 2008 http://www.armacell.com/us http://www.armacell.com/us http://csemag.com/quickResponse

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Consulting-Specifying Engineer - March 2008 Contents Viewpoint Letters News M/E Roundtable Grade A HVAC When UPS and Gensets Have Issues Ignite Opportunities To Mentor Fire Protection Engineers Cooling People, Not Buildings Codes & Standards Case Study New Products Equipment Lifecycles Advertiser Index Green Space Pure Power Supplement Edison Institute Honors Recovery Efforts Canada Launches Clean Energy Software Climate Change Drives Increased Investment Critical Power for R&D Heating Calculations for Electrical Duct Bank Submetering for Energy Profiling New Products

Consulting-Specifying Engineer - March 2008

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