A VFD-heavy manufacturing facility, medium-voltage service, and the first project in the program where power quality — not occupant life safety — is the dominant design constraint.
The project brief: a manufacturing facility with roughly 3,500 connected horsepower of process motor load, 60% of it on variable frequency drives, served by 13.8kV medium-voltage utility service stepped down through an on-site unit substation to 480V. At this connected load, taking service directly at 480V the way the school and hospital projects do stops making sense — and everything downstream of that decision, from grounding philosophy to harmonics to arc-flash risk, follows from operating at the MV/LV boundary.
This module walks the whole project the way a real industrial design engineer would: a fully worked unit substation transformer and protective device sizing calculation, why the 480V system is high-resistance grounded instead of solidly grounded, Motor Control Center design philosophy versus branch panelboards, a worked IEEE 519 harmonics calculation and mitigation strategy for the VFD fleet, a worked power factor correction calculation using a detuned filter bank, and why an arc-flash study has to be calculated individually at the MV/LV boundary and at every downstream MCC rather than assumed from voltage alone. The full worked numbers, complete bill of materials, and finished design reasoning are part of the unlocked module below.