Adjustable Frequency AC Drive Systems are nowadays a reality in industrial applications. Occurrence of failures in these systems can compromise plants production severely. Therefore, rising their reliability is highly desirable. With this in mind, grounding and protection systems have been developed over the time. Particularly, the situation of a PWM (Pulse Width Modulated) drive in a non-grounded system deserves closer examination. If it is driving a system with insulation failures to ground (e.g. induction motor), at first it will not be interrupted by existing protections, which is good for operation continuity. However, phase-to-ground overvoltages will arise and may lead to insulation failure, equipment breakdown and undesirable unscheduled production stop. This paper aims to characterize involved phenomena that can cause system failure, loss of drive equipment and the subsequent production stop or restriction. Based on this understanding, a circuit capable to ensure operation continuity while motor failures are not eliminated is designed and built, avoiding the risk of drive loss.
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