Ieee White Paper Capacitor Application Issues

Páginas: 48 (11942 palabras) Publicado: 21 de enero de 2013
Thomas M. Blooming, P.E.
Senior Member, IEEE Eaton Corporation 7000 Highlands Parkway SE Smyrna, GA 30082

Daniel J. Carnovale, P.E.
Senior Member, IEEE Eaton Corporation 1000 Cherrington Pkwy Moon Township, PA 15108
the former case, one would use the power factor and the peak kW or kVA during the demand intervalto do the required kvar calculation. In the latter, one would use the accumulated kWh and kvarh to first calculate the required kvarh of correction needed over the month, and then divide out the hours in the month to get the required capacitor bank size. In most real-world cases, power factor correction calculations based on peak kW/kVA and power factor in a short demand interval will require alarger capacitor bank to correct the power factor than the accumulated kWh and kvarh over a month method. This is because the kvar calculation is done at peak load, even if the power factor during that interval may not be as low as at periods of lighter load. The reason that a power factor correction calculation based on accumulated kWh and kvarh generally results in a lower required capacitor sizefor correction is that you do not need to meet the target power factor at any particular point in time or during any particular demand interval. It is okay, for instance, if you do not meet the target power factor during the middle of the day, when loads are typically highest, as long as you exceed the target power factor at other times, typically at night when loads are lower. In the extremecase, one can meet the target power factor by running a leading power factor at times (sending vars back the utility), in effect turning the kvarh meter backwards. Some utilities allow this. It is more common for utilities using this type of contract (accumulated kWh and kvarh) to not give credit for leading power factor. A utility may state in its rate that the power factor shall be determined bythe kWh and lagging kvarh accumulated over the month—note the exclusion of leading kvarh. One utility explicitly states, “A device will be installed on each kilovar meter to prevent reverse operation of the meter.” Regardless of whether leading kvarh are credited, with power factor calculated by accumulating kWh and kvarh over the month one can make up for being below the target power factor atsome times by being above the target power factor at other times. This may allow one to choose a smaller fixed capacitor, as opposed to a larger, switched capacitor bank. It is not practical to cover all the possible variations on how power factor might be calculated; there is an exception to every rule. The point is that engineers should be aware that the way power factor is calculated affectsthe required kvar calculation. Engineers should read the electric utility’s published rate to determine how power factor is calculated and take this into account. B. Month-by-Month Calculations versus Averaging Another source of error when calculating the required kvar needed to correct poor power factor is relying too much on

Abstract - Capacitors provide well-known benefits to electric powersystems. These benefits include power factor correction, voltage support, release of system capacity, and reduced system losses. As with any piece of electrical equipment, there are a number of application issues that engineers need to be aware of. These issues range from the very basic to the very complex. Most of these application issues can be, and have been, the subject of their own detailedtechnical papers. This paper does not get into rigorous detail but rather discusses these issues with the goal of making the reader aware of many of the traps one can fall into when applying capacitors. The application issues are addressed based on the authors’ experiences working in various capacities (performing power system measurements and studies, performing engineering service failure...
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