Medium Voltage Adjustable Speed Drives: Power Factor and Motor Control – A Beautiful Combination

Abstract

There has been a significant evolution in power semiconductor devices from small, low power devices to very high capacity devices. As a result, multi-megawatt range adjustable speed drive (ASD) systems are increasingly being used not only in the global cement industry but others such as oil & gas, mining, water/wastewater, and power generation. In a modern cement plant, Medium Voltage (MV) ASDs are used on ID fans, kilns, separators, finish mill, ball/sag mills, conveyors, & pumps. A new generation of regenerative medium voltage adjustable speed drives are being applied that not only deliver motor control but also can inject reactive power back to the connected bus. This topology of drives helps in improving power factor and providing voltage support thereby reducing or eliminating nuisance trips due to power instability, optimize the size of backup generators, release capacity tied up in lagging loads thereby enabling plant expansion. The focus of the paper is to show how this novel topology of drives works, application considerations, procurement guidance, and correct sizing of the ASD to meet overall VAR compensation objectives of a facility. Finally, a case study is presented where the end user applied an ASD for VAR compensation and discuss the results.