Variable speed drives (VSDs) can provide a host of advantages, claim vendors. They cite substantially improved energy efficiency, better performance and reliability, reduced maintenance costs, enhanced operating flexibility and lower emissions — to name but a few benefits.
But are these claims backed up in reality?
Yes, for the most part, says Kurt Bieniek of the technical materials management group of BASF, Ludwigshafen, Germany. "In many applications the above statements are true, for example, with extruders, large reciprocating or displacement pumps, large agitators, and high-inertia systems."
While BASF doesn't have specific figures on the benefits of using VSDs, they form an important part of an overall strategy aimed at improving the energy efficiency of its production processes by 25% by 2020.
The company finds the greatest benefits when VSD use is oriented toward a specific service or mode of operation (Figure 1).
"For some applications VSDs are predetermined solutions, such as for extruders and for larger reciprocating pumps (»1 kW). However, in other applications the use of VSDs is considered and analyzed. If the machines are frequently operated in partial load the savings potential rises. In individual cases the application of a frequency converter can reduce the energy costs by 40%," Bieniek adds.
BASF is working closely with original equipment manufacturers to develop solutions that will improve both its own device-testing capabilities and extend VSD applicability around the plant.
"In most cases, reliability and plant availability slightly deteriorate and maintenance costs slightly increase when using VSDs. But these effects have to be assessed in connection with the improvements caused by VSDs, especially in energy consumption and in production performance," notes Bieniek.
Reduced energy consumption and improved production performance, of course, appeal to all processors. However, plastics manufacturing is one sector in which such gains are especially crucial because companies are really struggling to maintain plant profitability in the face of rising energy costs, says Scott Barlow, vice president of Integrated Control Technologies, Carrollton, Tex., a distributor and authorized service provider for Yaskawa Industrial Drives, Waukegan, Ill.
"For most plastic extrusion manufacturing facilities, approximately 30% of the energy consumed can be attributed to extruder motors. If the line is more than five years old, it is more than likely that a direct current (DC) motor is being used as the extruder motor. Today, the majority of extruder machinery manufacturers are installing alternating current (AC) vector motors and drives on their extruders instead of DC systems. There are multiple reasons that they are making this change, but the biggest reasons are lower costs and better performance of the AC alternative," he explains.