A recent white paper from The Green Grid examines data center power system harmonics and provides an overview of this phenomenon's effects on data center efficiency and reliability. "Harmonic currents can be a major factor in power quality and efficiency issues within a data center and can be a complex subject to understand," states the paper. "Power quality issues associated with alternating current (AC) power line harmonics...can distort the voltage that is being consumed by information technology (IT) equipment, thereby disrupting the operation of the equipment."
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The paper notes that "ironically, these harmonic currents are usually caused by the power supply units (PSUs) within the IT equipment itself, but there can be other causes as well, such as variable frequency drives in cooling and ventilation equipment. [Further], some devices meant to improve power quality, such as uninterruptible power supply (UPS) systems, can actually create harmonic currents that could interfere with equipment further upstream...Causes of harmonic currents can come from any number of nonlinear loads in the data center, including older IT server PSUs, non-server IT equipment, external power supplies for laptop computers, electronic ballasts, variable frequency drives, UPS's in eco or bypass mode, and electronic and magnetic ballasted lighting."
The paper's executive summary notes that "less appreciated is the effect of harmonic currents on the overall efficiency of a data center. Harmonic currents are wasted energy that appears as heat. Not only can the heat have a detrimental effect on the performance and life expectancy of various pieces of equipment, but the harmonic currents also reduce the overall efficiency of the entire data center by increasing the amount of heat that must be removed."
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"The expectation is that without careful study and planning, harmonics in the data center will continue to increase as the number and types of devices that generate harmonics are more widely adopted," concludes Green Grid. "Mitigation techniques for harmonics are available, but without proper analysis and planning, they may come at a cost to efficiency. Similarly, harmonics may increase as data centers strive to make improvements in efficiency; careful study and analysis must be made to find the optimal balance of harmonic currents and efficiency in the data center."
The white paper's editorship includes representatives from Emerson Network Power, ABB Inc., Eaton, Schneider Electric, IBM and Dell, among other data center power experts.
View/Download the white paper.