Came across an unusual case of voltage regulation for a CT Scanner site recently.
So, what’s going on?
My first guess was a slow, electro-mechanical voltage regulator (such as a motor driven Variac or Powerstat) and which shows up occasionally for medical imaging or other sensitive loads. However, that sort of regulator would not eliminate short utility sags or drop-outs, or affect the voltage harmonics or THD.
My next theory is that this site has a large UPS or static power conditioning device feeding an entire medical imaging department. The voltage drop and increased voltage distortion under load would be the result of voltage drops in distribution (impedance calculated to be roughly 60 mohms @ 480 VAC) – so perhaps the power conditioning device is located in the basement with normal distribution voltage drops (primarily wiring, perhaps a transformer) from there to the equipment.
No significant power issues found, just like to understand what I am seeing in the data!