Variable Speed Drive

Variable Speed Drives (http://www.vsdrive.com ) Induce Shaft Currents in AC Motors. Due in large part to an increased focus on energy savings, the use of pulse-width-modulated (PWM) variable speed drives to control AC motors has grown dramatically over the last few years. While they offer low operating costs and high performance, variable speed drives are not without their problems. Shaft currents induced by variable speed drives can lead to motor failures. Without some form of mitigation, shaft currents travel to ground through bearings, causing pitting, fusion craters, fluting, excessive bearing noise, eventual bearing failure, and subsequent motor failure. Types of Variable Speed Drives Mechanical Variable Speed Drives Variable pitch drives Traction drives Hydraulic Variable Speed Drives Hydrostatic drives Hydrodynamic drives Hydroviscous drives Continuously Variable Transmission (CVT) Electric Variable speed drives DC motor drives Eddy current drives AC motor drives Slip controlled drives Why Use variable frequency drives Saving energy Process control Smoother operation Acceleration/deceleration control Different operating speed for each process mode Compensate for changing process variables Allow slow operation for setup purposes Adjust rate of process parameters Allow accurate positioning Control torque or tension Assumes the need for Variable speed Variable output Steady state condition Reduced capital expenditure Solid state electronic power conversion devices Reduced maintenance