Reliability Features of Large Load Commutated Inverter Drives and Some Cautions in Their Application

The special features built into load commutated inverter (LCI) drives to satisfy the demand of the paper industry for extreme reliability in critical utility type drives are examined. Examples of special circuit arrangements, redundancy, derating, and diagnostics will be discussed. Special attention will be given to the features which help make these large ac inverter drives nearly "uninterruptible." In addition to reliability, two areas of concern in applying LCI drives- harmonics and shaft torque pulsations¿briefly addressed. The harmonic and torque pulsations are not considered to be problems, per se, but characteristics of the drives which must be recognized and dealt with. While LCI\´s do deliver the economic and functional benefits claimed by the suppliers, users are cautioned not to overlook these characteristics (harmonics and torque pulsations) in their enthusiasm to apply these new ac drive systems.