Recently, I have come across 3.3kV VFD output stepped up to 11kV supplying a 7MW motor. The step-up transformer is Y-D with floating neutral on star side. I am used to Dyn connected captive transformers with the star point high resistance earthed. But, that is without VFD.
Is Y-D with floating neutral a requirement from VFD designer? What could be the issues if we use Dyn with high resistance earthed neutral?
The pulse pattern generation in VFDs relies on cancellation of certain harmonics in the current due to having no ground connection on the load side. Usually the load is a motor a no one would consider to ground the neutral of a motor with a star-connected stator.
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