Pardon the pun, but why were the transformers connected WYE-WYE? Everything I have ever used was either Delta-WYE, or Delta-Delta. There are too many problems WYE-WYE which is why it is almost never used.
Sometimes, those high power gen-sets need to have a neutral grounding resistor installed to prevent that very problem. Most of my experience is with solid-state inverter units but the principals are still the same.
Harmonic currents make me think of rectifier-capacitor style power supplies - these generate a large current pulse just before the voltage crest as the filter capacitor charges. I suspect this is where the load-side 3rd harmonic current was actually coming from.
Today, we would install power factor corrected power supplies that force current to be in proportion to the voltage, and make the load (field winding power) appear almost purely resistive. A smaller field transformer would have worked quite well in that situation as there would have been little or no neutral current, even at full load.
Before PFC power supplies were common, oversized transformers or harmonic filters were just about the only way to deal with harmonic currents.
Transfers the control of a large number of motion axes from one numerical control kernel to another within a CNC system, using multiple NCKs, and enables implement control schemes for virtually any type of machine tool.
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