The INST and ST would be set by looking up at the device that feeds it and adjusting accordingly. GF is adjusted in a similar manner. But also realize that 240.100 allows the cable to be protected at higher than ampacity, at which point you focus on the load and prevent overloading of the MV protective device by limiting the connected load. You still have to balance xfmr protection with cable overcurrent protection, but 240.100 gives some level of adjustability that's not available under 1000 Volts.
Yes. Ideally you know the fault current and can make that type of definitive assessment.
It's probably okay, however, transformer inrush is theoretically higher. SKM plots it out at 12X as the standard inrush. I haven't experienced that in the field, but that's the precaution given.
Yes to the inrush question. In fact, there's folks who swear that inrush is only minimized when a transformer is fully loaded. But I measured the cumulative inrush on multiple 13.8 kV circuits on a prison campus with 6-8 transformers getting energized at once, and didn't see more than 2X. So I think the 12X is high, but that's what ANSI C57.109 standard defines it as. I'll be happy to plot your primary and secondary devices for you if you want to give me the info.
Current is not drawn by the load until the magnetic field of the transformer has been established. It is common to analyze transformers using equivalent circuits with 'open secondaries' rather than include any conductor or load impedances.
Yes to the inrush question. In fact, there's folks who swear that inrush is only minimized when a transformer is fully loaded. But I measured the cumulative inrush on multiple 13.8 kV circuits on a prison campus with 6-8 transformers getting energized at once, and didn't see more than 2X. So I think the 12X is high, but that's what ANSI C57.109 standard defines it as. I'll be happy to plot your primary and secondary devices for you if you want to give me the info.
