Protection of VSD transformers

Variable Speed Drives (VSD) protect themselves as well as the driven motors. In contrast, the isolation input transformer typically requires its dedicated protection. Unlike distribution and power transformers, the protection of VSD duty transformers need to consider several additional aspects, such as non-sinusoidal current with harmonic content, multi-winding design, phase-shifted converter windings etc. This paper aims to explain the challenges related to protection of VSD transformers. A guideline for reliable transformer protection based on good design practice is proposed. Finally the possibility to integrate the transformer protection into VSD protection scheme is being explored.