System and equipment problems associated with variable frequency drives in the pulp and paper industry

Energy savings, better control of process and cost reduction in solid state technology have resulted in a substantial growth of variable frequency drives (VFDs) in the pulp and paper industry. With new incentives from utility (power) companies, the rate of growth will further increase, and some estimates suggest that by the next decade, 50% of all AC motors will be VFDs. Problems associated with nonlinear loads such as rectifiers, DC drives, etc. are well established and documented. Problems associated with application of VFDs are much greater and include: higher harmonic generation from PWM drives; harmonic resonance; overheating of power equipment and conductors; application of power factor correction capacitors; system grounding; and motor insulation failure from overvoltages. This paper describes these problems, their impact on power system and equipment, and suggests guidelines to circumvent them. >